CN117936771B

CN117936771B - Positive electrode material, preparation method thereof and lithium ion battery

Info

Publication number: CN117936771B
Application number: CN202311803462.2A
Authority: CN
Inventors: 姜荪; 陈帅; 宋雄; 吴小珍; 杨顺毅; 黄友元; 张金龙
Original assignee: Better Jiangsu New Material Technology Co ltd
Current assignee: Better Jiangsu New Material Technology Co ltd
Priority date: 2023-12-25
Filing date: 2023-12-25
Publication date: 2025-05-02
Anticipated expiration: 2043-12-25
Also published as: WO2025123885A1; CN117936771A

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a positive electrode material and a preparation method thereof, and a lithium ion battery, wherein the positive electrode material is a nickel-cobalt lithium composite oxide, a particle size distribution curve of the positive electrode material is provided with a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A ₁, the peak area of the second characteristic peak is A ₂,P＝A₂/A₁, the stability coefficient of free lithium of the positive electrode material is L, L= (L ₁-L₂)/L₁,L₁ and L ₂) is tested by taking 5g of positive electrode material to disperse in 100ml of deionized water, magnetically stirring for t min, and carrying out suction filtration to obtain filtrate, so as to measure the content of free lithium, when t=60, the mass content of the free lithium in the positive electrode material is measured to be L ₁, when t=10, the mass content of the free lithium in the positive electrode material is measured to be L ₂, and the positive electrode material satisfies the following relation formula that 10 is less than or equal to P.

Description

Positive electrode material, preparation method thereof and lithium ion battery

Technical Field

The application relates to the technical field of lithium ion batteries, in particular to a positive electrode material, a preparation method thereof and a lithium ion battery.

Background

With the increasingly serious global energy crisis, environmental pollution and other problems, countries are continually called upon to reduce carbon emissions and develop sustainable clean energy to replace traditional fossil energy. Compared with the traditional energy battery, the lithium ion battery has the characteristics of high energy density, long cycle life, wide application range and the like, and in recent years, the lithium ion battery is rapidly developed under the stimulation of the strong patch of government and the new energy market demand. The positive electrode material is used as a core part of the lithium ion battery, determines the overall performance of the lithium ion battery, and development of the positive electrode material with excellent performance is always a research hot spot.

The high-nickel anode material has the advantages of high voltage platform, high specific capacity and the like, and is most hopeful to become the anode material for large-scale application in the power battery market. However, as the proportion of nickel is continuously increased, negative conditions such as cation mixing and discharging, residual alkali and the like of the positive electrode material are aggravated, electrochemical properties such as the circulation stability and the like of the positive electrode material are affected, and the safety problem of the battery is caused, so that the application of the high-nickel positive electrode material in the power battery market is limited. Therefore, the high-nickel cathode material is modified by doping and coating processes to improve the electrochemical performance, wherein the doping process generally improves the cycling stability and other electrochemical performances of the high-nickel cathode material by doping one or more elements into the structure of the high-nickel cathode material, and the coating process is to coat one or more elements on the surface of the high-nickel cathode material, and remove the residual lithium on the surface of the high-nickel cathode material by water washing or chemical reaction to form a coating layer on the surface of the high-nickel material, which is beneficial to ion transmission, thereby effectively relieving the side reaction of the electrode/electrolyte interface and improving the cycling performance of the material. However, in the modification process of the existing doping and coating process, at least the following problems are existed, namely (1) the compatibility problem of the doping agent and the main structure, (2) the problem that the doping agent has great influence on the conductivity and the reactivity of the high-nickel positive electrode material, and (3) the washing treatment in the existing coating process can cause the increase of the impedance of the positive electrode material in the circulating process, so that the lithium ion deintercalation is difficult, even the coating process which damages the structural stability is complicated, and the cost is increased.

Therefore, the conventional doping and coating process modification is difficult to greatly improve the electrochemical properties such as the cycle performance and the like of the high-nickel positive electrode material, the ideal target requirement cannot be met, and the problem of high cost exists.

Content of the application

The application provides a positive electrode material, a preparation method thereof and a lithium ion battery, which can improve the cycle performance of a lithium nickel cobalt oxide positive electrode material.

In a first aspect, the present application provides a positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide;

the particle size distribution curve of the positive electrode material is provided with a first characteristic peak and a second characteristic peak, wherein the peak area of the first characteristic peak is A ₁, and the peak area of the second characteristic peak is A ₂,P＝A₂/A₁;

The method for testing the stability coefficient of free lithium of the positive electrode material is L, wherein L= (L ₁-L₂)/L₁,L₁ and L ₂) is that 5g of positive electrode material is dispersed in 100ml of deionized water, magnetic stirring is carried out for t min, and filtrate is obtained after suction filtration for measuring the content of free lithium, wherein when t=60, the mass content of the free lithium in the positive electrode material is measured to be L ₁, and when t=10, the mass content of the free lithium in the positive electrode material is measured to be L ₂;

The positive electrode material satisfies the following relation that P is more than or equal to 10 and L is less than or equal to 25.

In some embodiments, the positive electrode material has a chemical formula of LiNi _aCo_bMn_cM_dN_eO₂, wherein 0.8< a <0.98, b <0.2, c <0.2, a+b+c+d+e=1, and the M comprises at least one of Sr, ti, al, zr, W, ba, mg, nb, and the N comprises at least one of W, B, mo, F, S, V, P and Cl.

In some embodiments, the positive electrode material includes a base material and a coating layer on at least a portion of a surface of the base material, the base material is a composite oxide including Ni, co, mn, and M elements including at least one of Sr, ti, al, zr, W, ba, mg, nb.

In some embodiments, the coating comprises a lithium salt having the formula Li _xN_yO_z, wherein x, y, z >0, and the N comprises at least one of W, B, mo, F, S, V, P and Cl.

In some embodiments, 0.25.ltoreq.L.ltoreq.0.85 in the positive electrode material.

In some embodiments, 0.15% to less than or equal to L ₁% to less than or equal to 0.45% of the positive electrode material.

In some embodiments, 0.02% to less than or equal to L ₂ to less than or equal to 0.16% of the positive electrode material.

In some embodiments, 8.ltoreq.P.ltoreq.50 in the positive electrode material.

In some embodiments, in the positive electrode material, 4.ltoreq.A ₁.ltoreq.25.

In some embodiments, 150.ltoreq.A ₂.ltoreq.250 in the positive electrode material.

In some embodiments, the positive electrode material has a conductivity of 0.025S/cm to 0.080S/cm.

In some embodiments, the positive electrode material has a compacted density of 3.10g/cm ³～3.65g/cm³.

In some embodiments, the specific surface area of the positive electrode material is 0.4m ²/g～0.8m²/g.

In a second aspect, the present application also provides a method for preparing a positive electrode material, including the steps of:

Adding a free lithium ion conversion agent into an aqueous solution of a matrix material for modification treatment, wherein the addition amount of the free lithium ion conversion agent is 0.6wt% -1.2wt% based on the mass of the matrix material, and a precursor is obtained through solid-liquid separation, wherein the matrix material is a lithium nickel cobalt oxide composite oxide, the particle size distribution curve of the matrix material has a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A ₁, the peak area of the second characteristic peak is A ₂,P＝A₂/A₁, and P is more than or equal to 8 and less than or equal to 50;

and sintering the precursor to obtain the anode material.

In some embodiments, the mass of deionized water in the aqueous solution of the matrix material is 15% -30% of the mass of the matrix material.

In some embodiments, the matrix material is a composite oxide including Li, ni, co, and Mn elements.

In some embodiments, the preparing of the matrix material includes preparing a mixture including a ternary precursor and a lithium source, and sintering the mixture under an oxygen atmosphere to obtain the matrix material.

In some embodiments, the oxygen flow of the oxygen atmosphere is 200m ³/h～450m³/h.

In some embodiments, in the step of preparing the base material, the sintering furnace pressure is 3pa to 25pa.

In some embodiments, in the step of preparing the matrix material, the sintering includes a constant temperature stage having a sintering temperature of 600-800 ℃.

In some embodiments, the sintering time of the constant temperature stage is 8h to 15h.

In some embodiments, in the preparation step of the matrix material, the sintering further includes a temperature raising stage, and a temperature raising rate of the temperature raising stage is 2 ℃ per minute to 5 ℃ per minute.

In some embodiments, the matrix material is a composite oxide comprising Li, ni, co, mn and an element M, the element M comprising at least one of Sr, ti, al, zr, W, ba, mg, nb.

In some embodiments, the mixture includes an M dopant.

In some embodiments, the ternary precursor has a chemical formula of Ni _aCo_bMn_c(OH)₂, 0.8.ltoreq.a.ltoreq. 0.98,0.01.ltoreq.b.ltoreq.0.2, 0.01.ltoreq.c.ltoreq.0.2.

In some embodiments, the M dopant comprises at least one of Sr(OH)₂、SrO、TiO₂、Al₂O₃、Al(OH)₃、ZrO₂、Zr(OH)₄、Ba(OH)₂、BaO、MgO、Mg(OH)₂、Nb₂O₅、Nb₂O₃、WO₃ and CaWO ₄.

In some embodiments, the mass of the M dopant is 0.1% -0.55% of the mass of the ternary precursor.

In some embodiments, the mass of the M dopant is 0.2% -0.4% of the mass of the ternary precursor.

In some embodiments, the ternary precursor includes first and second particles of different sizes, the first particles having a particle size D50 of 12 μm to 18 μm.

In some embodiments, the ternary precursor includes first and second particles of different particle sizes, the second particles having a particle size D50 of 2 μm to 5 μm.

In some embodiments, the ternary precursor comprises first particles and second particles with different particle sizes, and the mass ratio of the first particles to the second particles is 1 (1-5).

In some embodiments, the lithium source comprises at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, and lithium oxalate.

In some embodiments, the molar ratio of the Li element in the lithium source to the ternary precursor is 0.95-1.25.

In some embodiments, the mass of the free lithium ion transforming agent is 0.6% to 1.2% of the mass of the matrix material.

In some embodiments, the free lithium ion transforming agent contains N, which includes at least one of W, B, mo, F, S, V, P and Cl.

In some embodiments, the free lithium ion transforming agent comprises at least one of KAl(SO₄)₂、NH₄HSO₄、MgCl2、NH₄Cl、CaF2、NH₄HF₂、NaVO₃、NH₄VO₃、(NH4)₃PO₄、(NH₄)₂HPO₄、Ca(H₂PO₄)₂.

In some embodiments, the modification treatment is performed in an ultrasonic environment.

In some embodiments, the ultrasonic wave has a frequency of 20khz to 50khz.

In some embodiments, the ultrasound has an ultrasound time of 20min to 40min.

In some embodiments, the preparation method of the aqueous solution of the matrix material comprises the steps of mixing and uniformly stirring the matrix material with deionized water, wherein the stirring speed is 20 Hz-50 Hz.

In some embodiments, the stirring time is 20 min-40 min.

In some embodiments, during the sintering process of the precursor, the sintering temperature is 250 ℃ to 500 ℃.

In some embodiments, during the sintering process of the precursor, the sintering time is 6h to 12h.

In some embodiments, the solid-liquid separation comprises subjecting the modified blend to a pressure filtration treatment, wherein the pressure filtration has an extrusion pressure of 0.2MPa to 0.5MPa.

In some embodiments, the press time is from 10 minutes to 30 minutes.

In some embodiments, the solid-liquid separation further comprises subjecting the filter-pressed product to a drying process after the filter-pressing process.

In some embodiments, the drying temperature of the drying process is 80 ℃ to 170 ℃.

In some embodiments, the drying time of the drying process is 1h to 3h.

In some embodiments, the stability coefficient of free lithium of the positive electrode material is L, and P is more than or equal to 10 and less than or equal to L is less than or equal to 25, wherein L= (L ₁-L₂)/L₁,L₁ and L ₂ are tested by dispersing 5g of positive electrode material in 100ml of deionized water, magnetically stirring for t min, and performing suction filtration to obtain filtrate for measuring the content of free lithium, wherein when t=60, the mass content of the free lithium in the positive electrode material is measured to be L ₁%, and when t=10, the mass content of the free lithium in the positive electrode material is measured to be L ₂%.

In some embodiments, 0.25.ltoreq.L ₁-L₂)/L₁.ltoreq.0.85.

In some embodiments, 0.15% L ₁% 0.45%.

In some embodiments, 0.02% L ₂% 0.16%.

In some embodiments, 4.ltoreq.A ₁.ltoreq.25.

In some embodiments, 150.ltoreq.A ₂.ltoreq.250.

In a third aspect, the application also provides a lithium ion battery, which comprises the positive electrode material or the positive electrode material prepared by the preparation method.

Compared with the prior art, the technical scheme has at least the following technical effects:

The positive electrode material of the application comprises high nickel positive electrode materials, namely lithium nickel cobalt oxide positive electrode materials which satisfy the relation of 10-25P and have the characteristic of excellent cycle performance, and solves the problem that the application of the lithium nickel cobalt oxide positive electrode materials is limited due to poor cycle performance in the prior art. In the research process, the applicant finds through reasoning and verification that in the positive electrode material (specifically referred to as a lithium nickel cobalt oxide positive electrode material, the following description is the same), the particle size of particles and the matching proportion of the particles are important parameters affecting the cycle performance of the positive electrode material; in order to bring a plurality of parameters affecting the cycle performance of the positive electrode material into the range of the cycle performance of the positive electrode material to realize the accurate evaluation of the cycle performance of the positive electrode material, the application relates to the change of different parameters by introducing the value of the peak area ratio P, solves the problem that the cycle performance is difficult to accurately evaluate due to the complex influence factors, and the introduction of the peak area ratio P can be more intuitively reflected under the influence of each parameter, so that the cycle performance test result of the positive electrode material has more reference value, in addition, the applicant also finds that the free lithium stability coefficient L and the peak area ratio P have a certain association relation, the change of the peak area A ₂ or A ₁ means the change of the crystal boundary at the microscopic level, the change of the contact area is the change from the macroscopic angle, the conversion efficiency of the free lithium on the surface of the positive electrode material is changed due to the change of the residual alkali generated by the reaction of carbon dioxide and water in the air, the structural stability of the positive electrode material is influenced, the cycle performance of the positive electrode material is influenced by the dynamic change of the cycle performance of the positive electrode material, the positive electrode material is calculated by the fact that the free lithium stability coefficient is influenced by the cycle performance of the positive electrode material is calculated by the fact that the free lithium stability coefficient is calculated by the correlation coefficient of the positive electrode material and the cycle performance of the positive electrode material has a certain association coefficient between the free lithium stability coefficient and the positive electrode material is calculated by the fact that has a certain product of the cycle stability coefficient is calculated with the cycle performance of the positive coefficient of the application, when θ=p=l is 10-25, the positive electrode material has excellent cycle performance, and can meet application requirements. according to the application, the parameters influencing the cycle performance of the positive electrode material are summarized into the calculation formula of the cycle performance measurement parameter theta of the positive electrode material, and the cycle performance measurement parameter theta of the positive electrode material is in the range by regulating and optimizing the correlation coefficient in the calculation formula, so that the cycle performance of the positive electrode material is improved. In the technical scheme of the application, the circulation performance measurement parameter theta of the positive electrode material can be calculated according to the formula, and the circulation performance of the positive electrode material can be judged through the value of theta, and because the parameters A ₁、A₂、L₁ and L ₂ related in the calculation formula can be rapidly measured, compared with the conventional method for testing the circulation performance of the positive electrode material, the method can greatly shorten the testing period and the testing cost by evaluating the circulation performance of the positive electrode material through the tests A ₁、A₂、L₁ and L ₂.

In the preparation method of the application, the ratio of the peak area A ₁ of the first characteristic peak to the peak area A ₂ of the second characteristic peak in the particle size distribution curve of the matrix material is regulated and the matrix material is modified by adding a proper amount of free lithium ion conversion agent, so that the electrochemical properties such as capacity, conductivity and cycle performance of the matrix material are comprehensively improved, namely the capacity, the capacity and the cycle performance of the modified anode material, the electrochemical performance such as conductivity and cycle performance is excellent, and the application requirement can be met. In the research process, the applicant finds that in the lithium nickel cobalt oxide positive electrode material, the particle size of particles and the collocation proportion of the particles are important parameters influencing the cycle performance of the positive electrode material, the application realizes accurate evaluation of the cycle performance of the positive electrode material by bringing a plurality of parameters influencing the cycle performance of the positive electrode material into the consideration range of the cycle performance of the positive electrode material, but a plurality of influencing factors can also lead to the evaluation difficulty of the performance of the positive electrode material, in order to solve the problem, the application creatively introduces the parameter of peak area ratio P to be related with a plurality of factors influencing the cycle performance of the positive electrode material, in the positive electrode material, the effect of large particles is mainly reflected on improving the capacity of the positive electrode material, but the large particles also easily cause cracks and pores to appear in the cycle of the positive electrode material, thereby influencing the cycle performance of the positive electrode material, the small particles have better physical stability, the structure of the positive electrode material can be stabilized, the positive electrode material can be prevented from being broken in the cycle process, the proper size particles have the proper proportion for improving the cycle performance of the positive electrode material, proper particle size distribution and proper particle size distribution are very good for the positive electrode material solid interface and solid material are better in the solid interface transmission speed, and the solid material is better in the solid interface is better than solid material is good the matching form of the small particles can increase the compaction density of the positive electrode material, improve the mass of active substances in the positive electrode material in unit volume, and is beneficial to releasing the electrochemical performance of the positive electrode material. In addition, in the modification treatment of the matrix material, the added free lithium ion conversion agent can absorb residual lithium in the matrix material so as to realize the regulation and control of the free lithium in the matrix material, and the free lithium can react with the free lithium to generate a lithium salt coating layer coated on the surface of the matrix material, the structure of the lithium salt coating layer is stable, the surface structure of the positive electrode material can be optimized, the effective improvement of the circulation performance of the positive electrode material is realized, and the conversion rate of the free lithium in the positive electrode material is too high to damage the structural stability of the positive electrode material, so that the internal lattice lithium loss of the layered structure of the positive electrode material is caused, and the circulation performance of the positive electrode material is influenced.

In summary, in the preparation method of the application, the cycle performance of the positive electrode material is greatly improved by comprehensively regulating and controlling the ratio of the peak area A1 of the first characteristic peak to the peak area A2 of the second characteristic peak in the particle size distribution curve of the matrix material and the addition amount of the free lithium conversion agent.

Drawings

The application will be further described with reference to the drawings and examples.

FIG. 1 is a process flow diagram of a method for preparing a positive electrode material of the present application;

FIGS. 2 to 20 are particle size distribution diagrams of examples 1 to 11 and comparative examples 1 to 8, respectively;

FIG. 21 is XRD patterns of example 1 and example 5;

fig. 22-25 are SEM images of example 1.

Detailed Description

For a better understanding of the technical solution of the present application, the following detailed description of the embodiments of the present application refers to the accompanying drawings.

It should be understood that the described embodiments are merely some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be understood that the term "and/or" as used in the present application is merely an association relation describing the associated object, and means that three kinds of relations may exist, for example, a and/or B, and that three kinds of cases where a exists alone, while a and B exist alone, exist alone. In the present application, the character "/" generally indicates that the front and rear related objects are an or relationship.

In a first aspect. The application provides a positive electrode material which is a lithium nickel cobalt oxide composite oxide, wherein a particle size distribution curve of the positive electrode material comprises a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A ₁, the peak area of the second characteristic peak is A ₂,P＝A₂/A₁, the stability coefficient of free lithium of the positive electrode material is L, L= (L ₁-L₂)/L₁,L₁ and L ₂) the testing method comprises the steps of dispersing 5g of positive electrode material in 100ml of deionized water, magnetically stirring for t min, carrying out suction filtration to obtain filtrate, measuring the content of free lithium in the positive electrode material when t=60, measuring the content of the free lithium in the positive electrode material to be L ₁ when t=10, and measuring the content of the free lithium in the positive electrode material to be L ₂ when t=10, wherein the positive electrode material satisfies the following relational expression that θ=p is less than or equal to 10 and L is less than or equal to 25.

In some embodiments, the positive electrode material has a chemical formula of LiNi _aCo_bMn_cM_dN_eO₂, wherein 0.8< a <0.98, b <0.2, c <0.2, a+b+c+d+e=1, and M comprises at least one of Sr, ti, al, zr, W, ba, mg, nb, and N comprises at least one of W, B, mo, F, S, V, P and Cl.

In some embodiments, the positive electrode material comprises a matrix material and a coating layer positioned on at least part of the surface of the matrix material, wherein the matrix material is a composite oxide comprising Ni, co, mn and M elements, M comprises at least one of Sr, ti, al, zr, W, ba, mg, nb, and the doping of the M element can construct an ion conductor transmission layer in the matrix material, so that the conductivity of the positive electrode material is improved.

In some embodiments, the coating layer comprises a lithium salt, the chemical formula of the lithium salt is Li _xN_yO_z, wherein x, y and z are more than 0, N comprises at least one of W, B, mo, F, S, V, P and Cl element, and the Li _xN_yO_z coating layer has a stable structure and can effectively improve the cycle performance and the safety performance of the positive electrode material.

In some embodiments, L is more than or equal to 0.25 and less than or equal to 0.85, L is the stability coefficient of free lithium of the positive electrode material and is used for measuring the stability of the free lithium on the surface of the positive electrode material, L is too high, the content of the free lithium on the surface of the positive electrode material is higher, and lithium ions in an unstable state possibly exist in the positive electrode material and are easy to dissolve out, the stability of a structural functional layer on the surface of the positive electrode material is poor, L is too low, which indicates that lattice lithium in the positive electrode material is lost to a certain extent, and part of stable Li is dissolved out, so that different testing conditions are caused, the measured content of the free lithium is not changed greatly, and in this case, the capacity cycle retention rate of the positive electrode material is easy to influence. By limiting L to the above range, the structural stability of the positive electrode material is favorably improved, and the cycle performance of the positive electrode material is favorably improved greatly.

In some embodiments, L ₁ is 0.15% -0.45%, specifically 0.15%, 0.25%, 0.35%, 0.45% or any value therebetween.

In some embodiments, L ₂ is 0.02% -0.16%, specifically 0.02%, 0.08%, 0.12%, 0.16% or any value therebetween.

In some embodiments, P is more than or equal to 8 and less than or equal to 50, P is the ratio of the peak area of the volume density occupied by large particles to the peak area of the volume density occupied by small particles in the positive electrode material, the effect of the large particles is mainly reflected on improving the capacity of the positive electrode material, but the large particles easily cause cracks and pores of the positive electrode material in circulation, so that the circulation performance of the positive electrode material is influenced, the small particles have better physical stability, the structure of the positive electrode material can be stabilized, the positive electrode material is prevented from being broken in the circulation process, the circulation stability of the positive electrode material is improved, the proper particle size distribution and particle collocation are critical for improving the performance of the positive electrode material, the proper particle size distribution and particle collocation are favorable for enabling active substances and electrolytes of the positive electrode material to have better solid/solid interfaces, so that the transmission speed of lithium ions is improved, and the collocation form of the large particles and the small particles can increase the compaction density of the positive electrode material, the quality of active substances per unit volume in the positive electrode material is improved, and the electrochemical performance of the positive electrode material is favorable to release. When the P value is in the range, the particle size and the mixing ratio of the large and small particles of the positive electrode material are proper, so that the comprehensive improvement of the electrochemical performances such as capacity, conductivity, cycle performance and the like is facilitated.

In some embodiments, A ₁ is 4 to 25, in particular 4, 8, 12, 16, 20, 25 or any value in between.

In some embodiments, a ₂ is 150 to 250, and may specifically be 150, 200, 250 or any value therebetween.

In some embodiments, the positive electrode material has a conductivity of 0.025S/cm to 0.080S/cm, specifically 0.025S/cm, 0.040S/cm, 0.060S/cm, 0.080S/cm, or any value therebetween.

In some embodiments, the positive electrode material has a compacted density of 3.10g/cm ³～3.65g/cm³, which may specifically be 3.10g/cm³、3.20g/cm³、3.30g/cm³、3.40g/cm³、3.50g/cm³、3.65g/cm³ or any value therebetween.

In some embodiments, the specific surface area of the positive electrode material is 0.4m ²/g～0.8m²/g, specifically may be 0.4m ²/g、0.5m²/g、0.6m²/g、0.7m²/g、0.8m²/g or any value in between.

In a second aspect, the application also provides a preparation method of the positive electrode material.

Referring to fig. 1, in an embodiment of the application, the preparation method of the positive electrode material includes the following steps:

s1, adding a free lithium ion conversion agent into an aqueous solution of a matrix material to carry out modification treatment to obtain a modified mixed material, and carrying out solid-liquid separation on the modified mixed material to obtain a precursor, wherein the matrix material is a lithium nickel cobaltate composite oxide, a particle size distribution curve of the matrix material has a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A ₁, the peak area of the second characteristic peak is A ₂,P＝A₂/A₁, and P is more than or equal to 8 and less than or equal to 50;

S2, sintering the precursor to obtain the anode material.

In the above step, the amount of the free lithium ion transforming agent added is 0.6wt% to 1.2wt%, specifically may be 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt% or any value therebetween, based on 100wt% of the mass of the base material.

It is understood that in embodiments of the present application, the free lithium ion converting agent is an agent capable of converting free lithium ions in the positive electrode material into a lithium salt, and a specific type of the free lithium ion converting agent may be selected as desired by those skilled in the art.

In summary, in the preparation method of the application, the cycle performance of the positive electrode material is greatly improved by comprehensively regulating and controlling the ratio of the peak area A ₁ of the first characteristic peak to the peak area A ₂ of the second characteristic peak and the addition amount of the free lithium conversion agent in the particle size distribution curve of the matrix material.

The preparation method of the application is specifically described below with reference to examples:

In some embodiments, the free lithium ion transforming agent contains N, which includes at least one of W, B, mo, F, S, V, P and Cl elements.

In some embodiments, the free lithium ion transforming agent comprises at least one of KAl(SO₄)₂、NH₄HSO₄、MgCl2、NH₄Cl、CaF2、NH₄HWO₄、NH₄MoO₄、NH₄HBO₃、NH₄HF₂、NaVO₃、NH₄VO₃、(NH4)₃PO₄、(NH₄)₂HPO₄、Ca(H₂PO₄)₂. In this embodiment, after the free lithium ion transforming agent is added to the aqueous solution of the matrix material, the cation or the cation group and the anion or the anion group are hydrolyzed, wherein the anion or the anion group can be combined with lithium ions in residual lithium (lithium hydroxide and lithium carbonate) on the surface of the matrix material, and a lithium salt (Li _xN_yO_z) molecular layer, such as Li₂WO₄、Li₃BO₃、LiMoO₄、LiVO₃、Li₂SO₄、Li₃PO₄ molecular layer, is formed on the surface of the matrix material in situ, and such Li _xN_yO_z compound is generally stable in structure and can effectively improve the cycle performance of the positive electrode material, and the cation or the cation group can undergo oxidation-reduction reaction with OH-and CO ₃ ^2- in the residual lithium to generate H20 and CO2 to be discharged or be transferred from the surface of the matrix material to deionized water. In the embodiment, the free lithium ion conversion agent reduces free lithium on the surface of the positive electrode material, and simultaneously reduces the problems of structural damage and the like caused by water washing, thereby improving the cycle performance of the positive electrode material.

The conversion rate of the Li ₂SO₄ protective layer is lower than that of the Li ₃PO₄ protective layer, the theta value is 13.44 when calculated by substituting the formula, and the Li ₃PO₄ protective layer can effectively reduce the structural damage and side reaction in the circulation process.

In some embodiments, during the sintering process of the precursor, the sintering temperature is 250 ℃ to 500 ℃, specifically may be 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃ or any value therebetween.

In some embodiments, during the sintering treatment of the precursor, the sintering time is 6h to 12h, specifically may be 6h, 8h, 10h, 12h, or any value therebetween.

In some embodiments, the mass of deionized water in the aqueous solution of the matrix material is 15% -30% of the mass of the matrix material, and may specifically be 15%, 20%, 25%, 30% or any value therebetween.

In some embodiments, the step of preparing the aqueous solution of the matrix material includes mixing and stirring the matrix material with deionized water. In the preparation process of the aqueous solution of the matrix material, the deionized water can wash away part of residual lithium on the surface of the matrix material, and the activity of the residual lithium on the surface of the matrix material can be enhanced by uniformly dispersing the matrix material in the deionized water, so that the modification treatment of the matrix material by the free lithium ion conversion agent in the later stage is facilitated.

In some embodiments, the stirring speed is 20Hz to 50Hz, and may specifically be 20Hz, 30Hz, 40Hz, 50Hz or any value therebetween. The stirring rotating speed is controlled in the range, so that the P value is controlled in a proper range, and the stirring rotating speed is too high, so that loss of small particles is easy to cause, the stability of the material is damaged, and the P value is higher.

In some embodiments, the stirring time is 20 min-40 min, and may specifically be 20min, 30min, 40min or any value therebetween. The stirring time is controlled within the range, so that the P value is controlled within a proper range, and the stirring time is too long, so that loss of small particles is easy to cause, the stability of the material is damaged, and the P value is higher.

In some embodiments, in the preparation step of the matrix material, the oxygen flow rate of the oxygen atmosphere is 200m ³/h～450m³/h, in particular 200m ³/h、250m³/h、300m³/h、350m³/h、400m³/h、450m³/h or any value in between. By controlling the oxygen flow rate of the oxygen atmosphere within the above range, it is advantageous to control the P value within an appropriate range.

In some embodiments, in the step of preparing the base material, the firing furnace pressure is 3Pa to 25Pa, specifically may be 3Pa, 6Pa, 9Pa, 12Pa, 15Pa, 18Pa, 21Pa, 23Pa, 25Pa, or any value therebetween. By controlling the sintering furnace pressure within the above range, it is advantageous to control the P value within an appropriate range.

In some embodiments, in the step of preparing the matrix material, the sintering comprises a constant temperature stage, the sintering temperature of which is 600 ℃ to 800 ℃, in particular may be 600 ℃, 700 ℃, 800 ℃ or any value therebetween. By controlling the sintering temperature in the constant temperature stage within the above range, it is advantageous to control the P value within a suitable range.

In some embodiments, the sintering time in the constant temperature stage is 8h to 15h, and may specifically be 8h, 10h, 12h, 15h or any value therebetween. By controlling the sintering time of the constant temperature stage within the above range, it is advantageous to control the P value within a suitable range.

In some embodiments, in the preparation step of the matrix material, the sintering further comprises a heating stage, wherein the heating rate of the heating stage is 2 ℃ per minute to 5 ℃ per minute, specifically can be 2 ℃ per minute, 3 ℃ per minute, 4 ℃ per minute, 5 ℃ per minute or any value between them, and in the sintering process, the sintering temperature is heated to 600 ℃ to 800 ℃ at the heating rate of 2 ℃ per minute to 5 ℃ and then constant-temperature sintering is carried out in a constant-temperature stage.

In some embodiments, the ternary precursor has the chemical formula Ni _aCo_bMn_c(OH)₂, 0.8.ltoreq.a.ltoreq. 0.98,0.01.ltoreq.b.ltoreq.0.2, 0.01.ltoreq.c.ltoreq.0.2.

In some embodiments, the ternary precursor includes first particles (large particles) and second particles (small particles) of different particle sizes, the chemical expressions of the first particles and the second particles may be the same or different, and the particle size D50 of the first particles may be 12 μm to 18 μm, and specifically may be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any value therebetween. The particle size of the first particles influences the specific surface area of the positive electrode material, the smaller the particle size is, the larger the specific surface area is, the positive electrode material is more susceptible to reaction with water and carbon dioxide in the air, and residual lithium is increased, and the particle size D50 of the first particles is controlled within the range, so that the amount of the residual lithium on the surface of the positive electrode material is controlled within a preferred range.

In some embodiments, the second particles have a particle size D50 of 2 μm to 5 μm, which may specifically be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any value in between. Similarly, the particle size of the second particles affects the specific surface area of the positive electrode material, the smaller the particle size is, the larger the specific surface area is, the positive electrode material is more reactive with water and carbon dioxide in the air, and residual lithium is increased, and the particle size D50 of the second particles is controlled within the range, so that the amount of residual lithium on the surface of the positive electrode material is controlled within a preferred range.

In some embodiments, the first particles have a particle size D50 of 12 μm to 18 μm and the second particles have a particle size D50 of 2 μm to 5 μm. The particle sizes of the first particles and the second particles are controlled in the range, so that the adaptation degree of the first particles and the second particles is improved, the compaction density and the structural stability of the positive electrode material are improved, and the conductivity and the cycle performance of the positive electrode material are further improved.

In some embodiments, the mass ratio of the first particles to the second particles is 1 (1-5), specifically may be 1:1, 1:2, 1:3, 1:4, 1:5, or any value therebetween. By controlling the mass ratio of the first particles and the second particles within the above range, it is advantageous to further improve the cycle performance of the positive electrode material.

In some embodiments, the molar ratio of the Li element in the lithium source to the ternary precursor is 0.95-1.25, and specifically may be 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, or any value therebetween. The molar ratio of the Li element in the lithium source to the ternary precursor is controlled within the range, so that the bonding force of the Li element and the precursor is improved, the crystal structure is stabilized, and the release capacity and the cycle performance are improved.

In some embodiments, the matrix material is doped with an M element, the M element including at least one of Sr, ti, al, zr, W, ba, mg, nb.

In some embodiments, the mixed material further comprises an M doping agent, and in the preparation process of the matrix material, an ion conductor transmission layer is constructed by the M element in the M doping agent and other metal elements in the ternary precursor, so that the conductivity of the positive electrode material is improved.

In some embodiments, the mass of the M dopant is 0.1% -0.55% of the mass of the ternary precursor, specifically may be 0.1%, 0.2%, 0.3%, 0.4%, 0.55% or any value therebetween, preferably, the mass of the M dopant is 0.2% -0.4% of the mass of the ternary precursor, specifically may be 0.2%, 0.3%, 0.4% or any value therebetween. The addition amount of the M dopant is controlled within a proper range, so that the conductivity of the positive electrode material is improved on the basis of considering the capacity, the cycle performance and other performances of the positive electrode material.

In some embodiments, the modification treatment is performed in an ultrasonic environment. Simultaneously, the aggregation of molecules is induced by ultrasonic cavitation, the diffusion of reactants and the formation of a coating layer are accelerated, the uniform mixing among reaction materials is realized, under the induction of ultrasound, the distribution uniformity of elements is obviously improved, and a structural protection layer is directionally constructed on the surface of the positive electrode material by a lithium salt compound generated by the reaction, so that the main structure of the positive electrode material is protected from being lost, and the effective improvement of the cycle performance of the positive electrode material is realized.

In some embodiments, the frequency of the ultrasonic wave is 20kHz to 50kHz, and may specifically be 20kHz, 30kHz, 40kHz, 50kHz or any value therebetween. The frequency of the ultrasonic wave can influence the conversion rate of residual lithium on the surface of the positive electrode material and the structural stability of the surface coating layer of the positive electrode material, thereby influencing the cycle performance of the positive electrode material. The frequency of the ultrasonic wave is controlled within the range, so that the P value and the content of free lithium in the positive electrode material are controlled within a proper range, and the cycle performance of the positive electrode material is improved.

In some embodiments, the ultrasound time is 20min-40min, and may specifically be 20min, 30min, 40min, or any value therebetween. Similarly, the ultrasonic time of ultrasonic waves also affects the conversion rate of residual lithium on the surface of the positive electrode material and the structural stability of the surface coating layer of the positive electrode material, thereby affecting the cycle performance of the positive electrode material. The ultrasonic time of the ultrasonic wave is controlled within a proper range, so that the P value and the content of free lithium in the positive electrode material are controlled within a proper range, and the improvement of the cycle performance of the positive electrode material is facilitated.

In some embodiments, the solid-liquid separation comprises subjecting the modified blend to a pressure filtration treatment at an extrusion pressure of 0.2MPa to 0.5MPa, which may specifically be 0.2MPa, 0.3MPa, 0.4MPa, 0.5MPa or any value therebetween.

In some embodiments, the press time is 10min to 30min, and may specifically be 10min, 20min, 30min, or any value therebetween.

In some embodiments, after the filter pressing treatment, the solid-liquid separation further includes drying the modified mixed material sequentially, wherein the drying temperature is 80-170 ℃, and specifically may be 80 ℃, 100 ℃, 120, 140 ℃, 160 ℃, 170 ℃ or any value therebetween.

In some embodiments, the drying time is 1h to 3h, and may specifically be 1h, 2h, 3h, or any value therebetween.

The positive electrode material prepared by the preparation method has a free lithium stability coefficient of L, L= (L ₁-L₂)/L₁,L₁ and L ₂) and is prepared by dispersing 5g of positive electrode material in 100ml of deionized water, magnetically stirring for t min, and carrying out suction filtration to obtain filtrate, wherein the content of free lithium in the positive electrode material is measured to be L ₁% when t=60, and the content of free lithium in the positive electrode material is measured to be L ₂% when t=10.

In some embodiments of the present application, in some embodiments, and P is less than or equal to 10 and L is less than or equal to 25. The applicant also finds that in the research process, a certain association exists between the free lithium stability coefficient L and the peak area ratio P, the change of the peak area A ₂ or A ₁ means the change of a crystal boundary in a microscopic level, and the change of the contact area from a macroscopic angle means the change of the contact area, which can lead to the change of the residual alkali generated by the reaction of the positive electrode material with carbon dioxide and water in the air, so that the conversion efficiency of free lithium on the surface of the positive electrode material is changed, the structural stability of the positive electrode material is further influenced, and the structural stability of the positive electrode material is a key factor influencing the cycle performance of the positive electrode material. Therefore, in the embodiment, the free lithium stability coefficient L is included in the calculation formula of the cycle performance of the positive electrode material, and when θ=p×l is 10×25 or less, the positive electrode material has excellent cycle performance, and can meet the application requirement. Because parameters A ₁、A₂、L₁ and L ₂ related to the calculation formula of theta can be rapidly measured, in the evaluation of the cycle performance of the positive electrode material, the cycle performance measurement parameter theta can be calculated by testing the values A ₁、A₂、L₁ and L ₂ of the positive electrode material, so that the rapid evaluation of the cycle performance of the positive electrode material can be realized, and the test period and the test cost can be greatly shortened.

In some embodiments, L= (L ₁-L₂)/L₁ is less than or equal to 0.85.L is the free lithium stability coefficient of the positive electrode material, and is used for measuring the stability of free lithium on the surface of the positive electrode material, L is too high, the free lithium content on the surface of the positive electrode material is higher, and lithium ions in an unstable state possibly exist in the positive electrode material, are easily dissolved out, the stability of a structural functional layer on the surface of the positive electrode material is poor, L is too low, which means that lattice lithium in the positive electrode material is lost to a certain extent, so that part of stable Li is dissolved out, and different test conditions are caused, and the measured free lithium content is not changed greatly.

In a third aspect, the present application also provides a lithium ion battery, which comprises the positive electrode material or the positive electrode material prepared by the preparation method.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the application.

The following examples are provided to further illustrate embodiments of the application. The embodiments of the present application are not limited to the following specific embodiments, and can be modified and implemented appropriately within the scope of the main claim.

Example 1

(1) Taking a large-particle precursor Ni _aCo_bMn_c(OH)₂ (namely first particles), wherein the molar ratio of Ni to Co to Mn is 88.5:9.0:2.5, and the granularity D50 is 16 mu m, taking a small-particle precursor NiaCobMnc (OH) ₂ (namely second particles), wherein the molar ratio of Ni to Co to Mn is 88.5:9.0:2.5, and the granularity D50 is 3 mu m, and mixing the large-particle precursor and the small-particle precursor according to the weight ratio of 1:4 to obtain a mixed precursor Ni _88.5Co₉Mn_2.5(OH)₂.

(2) Mixing the obtained precursor Ni _88.5Co₉Mn_2.5(OH)₂ and LiOH with doping agents Al (OH) 3, tiO ₂ and Sr (OH) ₂, grinding and crushing, wherein the molar ratio of Ni _88.5Co₉Mn_2.5(OH)₂ to LiOH is 1.02, the mass of the precursor Ni _88.5Co₉Mn_2.5(OH)₂ is 100wt%, the content of Al (OH) ₃ is 0.2wt%, the content of TiO ₂ is 0.1wt% and the content of Sr (OH) ₂ is 0.2wt%, heating the mixed material to 750 ℃ at a speed of 2 ℃ per minute under oxygen atmosphere, then sintering for 10 hours at constant temperature, cooling, screening and crushing to obtain the matrix material.

(3) 200G of the obtained matrix material is weighed and put into a reaction kettle, deionized water with the content of 25wt% of the matrix material is added, the stirring rotation speed is set to be 30Hz, the stirring is carried out for 30min, after the stirring is finished, the reaction kettle is put into an ultrasonic vibrator, the frequency of a transducer is set to be 35kHz, and (NH ₄)₂HPO₄ and ultrasonic vibration for 30 min) with the content of 0.8wt% of the matrix material are added.

(4) And (3) putting the material obtained in the step (3) into a filter press for filter pressing, wherein the pressing pressure is 0.4MPa, the pressing is carried out for 20min, the material is put into an oven for drying after the filter pressing is finished, the drying temperature is 150 ℃ and 120min, and then the obtained material is further sintered, the sintering temperature is 400 ℃ and the sintering time is 8h, so that the anode material is obtained.

Referring to fig. 2, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 1, and calculated values of L, P and θ are shown in table 1.

Example 2

The difference from example 1 is that:

The D50 of the large particle precursor was changed to 12 μm and the D50 of the small particle precursor was changed to 2.5 μm.

Referring to fig. 3, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 2, and calculated values of L, P and θ are shown in table 1.

Example 3

The difference from example 1 is that:

the D50 of the large particle precursor was changed to 18 μm and the D50 of the small particle precursor was changed to 2.5 μm.

Referring to fig. 4, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 3, and calculated values of L, P and θ are shown in table 1.

Example 4

The difference from example 3 is that:

And (3) adjusting the constant sintering temperature in the step (2) to 700 ℃.

Referring to fig. 5, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 4, and calculated values of L, P and θ are shown in table 1.

Example 5

The difference from example 3 is that:

the dopant was replaced with 0.4wt% Al (OH) ₃, 0.2wt% TiO ₂, 0.2wt% Sr (OH) ₂, and 0.3wt% Ba (OH) ₂.

Referring to fig. 6, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 5, and calculated values of L, P and θ are shown in table 1.

Example 6

The difference from example 5 is that:

(NH ₄)₃PO₄) was added in the step (3) at a base material content of 1.2 wt%.

Referring to fig. 7, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 6, and calculated values of L, P and θ are shown in table 1.

Example 7

The difference from example 6 is that:

The free lithium ion converting agent is changed to NH ₄HSO₄.

Referring to fig. 8, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 7, and calculated values of L, P and θ are shown in table 1.

Example 8

The difference from example 5 is that:

The free lithium ion conversion agent was changed to 0.4wt% (NH ₄)₂HPO₄ and 0.4wt% NH ₄HSO₄).

Referring to fig. 9, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 8, and calculated values of L, P and θ are shown in table 1.

Example 9

The difference from example 1 is that:

(NH ₄)₂HPO₄) was added in the step (3) at a base material content of 0.6 wt%.

Referring to fig. 10, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 9, and calculated values of L, P and θ are shown in table 1.

Example 10

The difference from example 6 is that:

in step (3), the frequency of the transducer is 5kHZ.

Referring to fig. 11, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 10, and calculated values of L, P and θ are shown in table 1.

Example 11

The difference from example 6 is that:

the stirring time in the step (3) is 40min.

Referring to fig. 12, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in example 11, and calculated values of L, P and θ are shown in table 1.

Comparative example 1

The difference from example 5 is that:

the free lithium ion conversion agent was changed to 0.4wt% (NH ₄)₂HPO₄).

Referring to fig. 13, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 1, and calculated values of L, P and θ are shown in table 1.

Comparative example 2

The difference from example 5 is that:

the free lithium ion conversion agent was changed to 1.3wt% (NH ₄)₂HPO₄.

Referring to fig. 14, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 2, and calculated values of L, P and θ are shown in table 1.

Comparative example 3

The difference from example 1 is that:

and changing the mixing mass ratio of the large particle precursor and the small particle precursor to 3:2.

Referring to fig. 15, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 3, and calculated values of L, P and θ are shown in table 1.

Comparative example 4

The difference from example 1 is that:

And changing the mixing mass ratio of the large particle precursor and the small particle precursor to 1:6.

Referring to fig. 16, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 4, and calculated values of L, P and θ are shown in table 1.

Comparative example 5

The difference from example 1 is that:

The precursor D50 of the large particles was changed to 22. Mu.m.

Referring to fig. 17, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 5, and calculated values of L, P and θ are shown in table 1.

Comparative example 6

The difference from example 1 is that:

the precursor D50 of the large particles was changed to 8. Mu.m.

Referring to fig. 18, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 6, and calculated values of L, P and θ are shown in table 1.

Comparative example 7

The difference from example 1 is that:

the precursor D50 of the small particles was changed to 8. Mu.m.

Referring to fig. 19, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 7, and calculated values of L, P and θ are shown in table 1.

Comparative example 8

The difference from example 1 is that:

the precursor D50 of the small particles was changed to 1. Mu.m.

Referring to fig. 20, specific test results of the first characteristic peak area a ₁, the second characteristic peak area a ₂, the free lithium content L ₁ and the free lithium content L ₂ of the positive electrode material prepared in comparative example 8, and calculated values of L, P and θ are shown in table 1.

The samples prepared in examples 1 to 11 and comparative examples 1 to 8 were subjected to performance test as follows:

1. peak areas of the first characteristic peak and the second characteristic peak are calculated:

The raw data obtained by the particle size distribution test are imported into an origin drawing image, the starting point x ₁ and the end point x ₂ of the first characteristic peak are selected through an integration command, the peak area A ₁ taking y=0 as a substrate is obtained, and the peak area A ₂ of the second characteristic peak is obtained by the same method.

2. Residual alkali test:

Dispersing 5g of positive electrode material in 100ml of deionized water, magnetically stirring for a certain time to dissolve residual carbonate and hydroxyl, filtering to obtain filtrate, adding hydrochloric acid solution on an automatic potentiometric titrator, titrating in an equivalent drip mode, calculating the content of carbonate and hydroxyl of the positive electrode material according to the condition of the point of jump and the consumption degree of the hydrochloric acid solution, measuring the mass content of free lithium in a sample to be L ₁ when the stirring time is 60min, and measuring the mass content of free lithium in the sample to be L ₂ when the stirring time is 10 min.

3. Particle size testing:

The particle size distribution of the positive electrode material particles was obtained using a laser particle size analyzer model 3000, malvern Mastersizer, uk, using the light intensity distribution of laser diffraction.

4. Topography testing

The surface appearance of the material is characterized by adopting a Japanese Hitachi Regulus8100 field emission scanning electron microscope, and the accelerating voltage is 1Kv.

5. And (3) testing the buckling performance:

And (3) putting 0.8g of positive electrode material, 0.1g of conductive carbon black and 0.1g of polyvinylidene fluoride into a ball milling tank, adding 15ml of N-methyl pyrrolidone, ball milling to form uniform slurry, uniformly coating the uniform slurry on aluminum foil, and carrying out vacuum drying at 110 ℃ for 12 hours to obtain the positive electrode plate. Cutting the dried pole piece into a wafer with the working level of 15mm, assembling and sealing the wafer in a glove box according to a positive electrode shell, the pole piece, electrolyte (EC/DMC/EMC volume ratio is 1:1, liPF6 concentration is 1 mol/L), a diaphragm (CELGARD PP/PE/PP three-layer composite film), a lithium piece, electrolyte, foam nickel and a negative electrode shell to obtain a button cell, and standing for 24 hours. And then placing the obtained battery into an incubator for testing, discharging the battery to 2.0V under the current density of 1C, standing for 2min, and then charging to 4.2V under the current density cross current constant voltage of 1C, and repeating the steps for 50 weeks to obtain the cycle retention rate. The battery was charged to 4.2V for 1h, then the battery was adjusted to 100% SOC using 1C current density, left standing for 30min, the voltage V0 at this time was recorded, the discharge current t s of 1C was used, the voltage V1 of t s was recorded, and the dc resistance at week 50 was calculated from (V0-V1)/It.

And (3) performing discharge capacity (0.1C/0.5C/1C) and first-cycle charge-discharge efficiency performance tests at 25 ℃ and 3.0V-4.3V by adopting a LAND battery test system, wherein the reference capacity is set to be 200mA/g, and the corresponding current density of 1C is set to be 200mA/g.

6. Conductivity test:

A resistivity tester (Suzhou lattice electron ST-2255A) was used to take 5g of powder samples, and the powder samples were kept constant pressure to 5000 kg.+ -. 2kg with an electron press for 15-25s. Placing the sample between the electrodes of the tester, measuring the height h (cm) of the sample, the voltage U at two ends, the current I and the area S=3.14 cm ² after powder pressing, and calculating according to the formula sigma=h/(S×R)/1000 to obtain the electronic conductivity of the powder.

7. Compaction test:

The positive electrode material compaction performance was tested using a compaction densitometer model No. michaux 4350. After 1g of the positive electrode material was treated and compacted for 30 seconds under a pressure of 3t, compaction data of the material was obtained. The compaction density is >3g/cm ³.

8. Specific surface area test:

the specific surface area of the material was calculated using a specific surface area and pore analyzer of the U.S. TRISTARII model, using nitrogen adsorption material specific surface area and using BET method.

9. XRD test:

The crystal structure of the positive electrode active material can be measured by an X-ray powder diffractometer, for example, a Brucker D8A_A25 type X-ray diffractometer of Brucker AxS Germany is used, cuK alpha rays are used as a radiation source, the range of 2 theta angle of ray wavelength scanning is 10-90 degrees, and the scanning speed is 4 degrees/min.

The results of the physicochemical parameter tests of the samples prepared in examples 1 to 11 and comparative examples 1 to 8 are shown in Table 1 below:

the results of the electrical property tests of the samples prepared in examples 1 to 11 and comparative examples 1 to 8 are shown in Table 2 below:

The results of the electrical conductivity, compacted density and specific surface area tests obtained in examples 1 to 11 and comparative examples 1 to 8 are shown in the following Table 3:

Sample of	Conductivity (S/cm)	Compaction Density (g/cm ³)	Specific surface area (m ²/g)
				Example 1	0.058	3.51	0.62
Example 2	0.037	3.28	0.51
				Example 3	0.052	3.39	0.59
Example 4	0.041	2.36	0.52
				Example 5	0.068	3.55	0.65
Example 6	0.075	3.62	0.72
				Example 7	0.050	3.40	0.55
Example 8	0.046	3.38	0.54
				Example 9	0.052	3.40	0.52
Example 10	0.059	3.42	0.61
				Example 11	0.061	3.42	0.63
Comparative example 1	0.022	2.95	0.41
				Comparative example 2	0.023	3.11	0.39
Comparative example 3	0.036	2.18	0.35
				Comparative example 4	0.018	3.15	0.42
Comparative example 5	0.041	2.15	0.35
				Comparative example 6	0.037	2.07	0.37
Comparative example 7	0.025	3.12	0.43
				Comparative example 8	0.023	3.56	0.46

Analysis of tables 1,2 and 3 above:

As can be seen from examples 1 to 11, when the positive electrode material satisfies the relation of 10.ltoreq.θ=P.ltoreq.L.ltoreq.25, it has superior cycle performance and conductivity, and when θ is in the range of 10 to 20, the larger the value of θ, the higher the cycle retention and conductivity of the positive electrode material, wherein when θ is in the range of 18 to 20, the compaction density and specific surface area of the positive electrode material have significant advantages, and when θ is in the range of 20 to 25, the larger the value of θ, the smaller the cycle retention and conductivity of the positive electrode material, and when θ is not in the range, the cycle performance and conductivity of the positive electrode material are relatively poor, and the application is greatly restricted.

It can be seen from comparing comparative examples 1-2 with example 5 that too high and too low contents of the free lithium ion transforming agent are both unfavorable for forming a stable protective layer on the surface of the positive electrode material, too high results in uneven coating layer formed on the surface of the positive electrode material, too low results in no effective blocking of side reactions, and both of them result in decrease of conductivity and cycle performance of the material.

By comparing the example 1 with the comparative examples 3 to 8, it can be analyzed that the effect of large particles in the positive electrode material is mainly reflected on improving the capacity of the material, but cracks and pores are easily generated in circulation to influence the circulation performance, small particles have better physical stability, can stabilize the material structure, prevent the positive electrode material from crushing particles in the circulation process, improve the circulation stability and the safety performance, and the proper particle size proportion in the positive electrode material is critical for the improvement of the performance, namely proper particle size distribution and particle collocation, can enable better solid/solid interface between the active material and the electrolyte, and further accelerate the transmission speed of lithium ions. Meanwhile, due to the proper matching mode of large and small particles, the compaction density of the material can be increased, the quality of active substances in unit volume of the material can be improved, and the release of the electrochemical performance of the material is facilitated. In detail:

As can be seen from comparison of comparative examples 3, 5 and 6 with example 1, in the positive electrode material, the large particle precursor has a larger specific gravity or a larger D50, which results in the decrease of stability and safety of the positive electrode material, the decrease of the compacted density and capacity of the positive electrode material, and the significant decrease of the compacted density of the material due to too many large particles, and the decrease of the lithium ion transmission rate and the decrease of the conductivity and capacity of the material due to smaller D50 of the large particle precursor.

By comparing comparative examples 4, 7 and 8 with example 1, it can be seen that in the positive electrode material, the small particle precursor has a larger specific gravity or a larger D50, and is easy to agglomerate, so that the reduction of the compaction density and the specific surface of the material can lead to the reduction of the capacity of the material, and the structural stability of the material can be influenced, thereby leading to the reduction of the circulation of the positive electrode material, and the small particle precursor has a smaller specific gravity D50, so that the finished product of the positive electrode material is easy to generate micro powder, the electrochemical performance is influenced, and the micro powder also can influence the uniformity of the coating layer, thereby leading to the reduction of the conductivity of the material.

In addition, through detailed analysis of examples 1-11, it can be obtained that in the preparation process of the positive electrode material, the A ₁ value, A ₂ value, L ₁ value and L ₂ value of the positive electrode material finished product can be adjusted by adjusting and controlling the particle size of the precursor, the matching proportion of particles, sintering temperature, dopant type, type and content of free lithium ion conversion agent, ultrasonic strength, water washing stirring time and other conditions, so that the peak area ratio P value and the value of the free lithium stability coefficient L of the prepared positive electrode material finished product are in proper ranges.

In detail, in comparative example 1, the particle sizes D50 of the large and small particle precursors of example 2 were all reduced, the peak area of a ₁ was reduced, and the peak area of a ₂ was reduced, that is, the large and small particle precursors were all reduced, resulting in an increase in the specific surface, leading to a more reactive material with water and carbon dioxide in the air, and thus to an increase in the residual lithium on the surface of the material. Therefore, the positive electrode material finished product in example 2 was calculated to have a θ value of 21.18, a ₁ thereof was out of the prescribed range, and the cycle performance thereof was reduced as compared with example 1.

In comparative example 1, A ₁ of example 3 was reduced, A ₂ was increased, and the overall A ₂/A₁ was increased, because of the reduced particle size of the small particles and the increased particle size of the large particles, under which conditions the particle size suitability of the large particles and the small particles was better, the smaller small particles reduced the volume expansion of the material during charge and discharge, so that the structure of the material was more stable, and the appropriate increase in the particle size of the large particles also reduced the number of grain boundaries that hindered the diffusion of lithium ions, the transmission of Li ⁺ was more rapid, the conductivity was increased, and the θ value was increased to 16.16, with the similar stability coefficient of free lithium maintained, and the material cycle performance was improved.

Comparative example 3, example 4, the constant sintering temperature was lowered, L ₁ was increased, and the cycle performance was deteriorated. This is because the temperature conditions for the grain growth required for large and small particles are different, and an appropriate sintering temperature needs to be determined, and compared with experimental example 3, example 4 has the problems that the grain size growth rate of the material is slower, the grain size is smaller, the lithium ion transmission path is reduced, and the sintering temperature required for lithium to enter the crystal lattice is insufficient due to the reduction of the sintering temperature. Therefore, the range of L ₁ in example 4 was not satisfied to be 0.15% or less and L ₁ or less than 0.45% or less, and the cycle performance of the positive electrode material finished product was deteriorated, as compared with example 3.

In comparative example 3, in example 5, four metal ions Al/Ti/Sr/Ba are adopted for co-doping, so that the crystal structure of the material can be effectively stabilized, the chemical stability of TM-O-Li is improved, the Li/Ni mixed discharge condition is improved, and the conductivity and the cycle stability of the finished positive electrode material are improved.

In comparative example 5, examples 6 and 9, the content of the free lithium ion transforming agent is adjusted, and the content of the free lithium ion transforming agent is properly increased, which is favorable for further improving the cycle stability of the cathode material, because the increase of the content of the free lithium ion transforming agent further improves the transformation efficiency of free lithium in the cathode material, and excessive residual alkali on the surface of the material fully reacts with the free lithium transforming agent, so that the material obtains more effective coating layers, that is, the stability of the coating layer formed on the surface of the material is improved, the generation of pores and cracks can be reduced, and the side reaction of active substances and electrolyte can be effectively reduced.

In comparative example 1, the free lithium ion converting agent in example 7 was changed to NH ₄HSO₄, and the cycle performance of the positive electrode material finished product was lowered. According to the test results, the conversion of NH ₄HSO₄ to residual alkali is worse, a stable structural protective layer is more difficult to form, the conversion rate of the Li ₂SO₄ coating layer is lower than that of the Li ₃PO₄ coating layer, and the Li ₃PO₄ coating layer can more effectively reduce the structural damage and side reaction in the circulation process.

Comparative example 5, example 8 used free lithium ion converting agents (NH ₄)₂HPO₄ and NH ₄HSO₄) in combination, the cycle performance of the final positive electrode material was lowered because the Li ₂SO₄ coating layer and the Li ₃ PO4 coating layer were not uniformly formed, thereby affecting the structural stability of the surface coating layer of the final positive electrode material.

In comparative example 6, in example 10, the ultrasonic intensity was increased to 50kHZ, and the cycle performance of the positive electrode material finished product was lowered. The reason is that the ultrasonic energy is too high, which can cause the coating to be unstable and in a metastable state, and is unfavorable for improving the structural stability of the coating.

In comparative example 5, in example 11, the pre-washing stirring time in the reaction kettle was increased to 40min, and the cycle performance of the positive electrode material finished product was reduced. The reason is that the too high rotating speed is easy to cause the loss of small particles, thereby causing the A ₂/A₁ to be higher, damaging the stability of the material and reducing the cycle performance of the finished positive electrode material.

Claims

1. A positive electrode material, characterized in that the positive electrode material is a nickel-cobalt-lithium oxide composite oxide;

The particle size distribution curve of the positive electrode material has a first characteristic peak and a second characteristic peak, the peak area of the first characteristic peak is A ₁ , the peak area of the second characteristic peak is A ₂ , P= A ₂ /A ₁ , P is the ratio of the peak area of the volume density occupied by large particles to the peak area of the volume density occupied by small particles in the particle size distribution curve of the positive electrode material;

The free lithium stability coefficient of the positive electrode material is L, L=(L ₁ -L ₂ )/L ₁ , and the test method of L ₁ and L ₂ is: take 5g of positive electrode material and disperse it in 100ml of deionized water, stir it with magnetic force for t min, and filter the filtrate to measure the free lithium content; when t=60, the mass content of free lithium in the positive electrode material is measured to be L ₁ , and when t=10, the mass content of free lithium in the positive electrode material is measured to be L ₂ ;

The positive electrode material satisfies the following relationship: , where 0.25≤L≤0.85.

2. The positive electrode material according to claim 1, characterized in that it satisfies at least one of the following characteristics:

(1) The general chemical formula of the positive electrode material is: LiNi _a Co _b Mn _c M _d N _e O ₂ , wherein 0.8＜a＜0.98, b＜0.2, c＜0.2, a+b+c+d+e=1, and the M includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, and Nb, and the N includes at least one of W, B, Mo, F, S, V, P, and Cl;

(2) The positive electrode material includes a base material and a coating layer located on at least a portion of the surface of the base material, wherein the base material is a composite oxide including Ni, Co, Mn and M elements, and the M element includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg and Nb.

3. The positive electrode material according to claim 1 is characterized in that the positive electrode material comprises a base material and a coating layer located on at least a portion of the surface of the base material, the coating layer comprises a lithium salt, and the chemical formula of the lithium salt is Li _x N _y O _z , wherein x, y, z>0, and the N comprises at least one of W, B, Mo, F, S, V, P and Cl.

4. The positive electrode material according to claim 1, characterized in that it satisfies at least one of the following characteristics:

(1)0.15%≤L ₁ ≤0.45%;

(2)0.02% _≤L2≤0.16 %;

(3) 8≤P≤50;

(4) 4≤A ₁ ≤25;

(5) 150 ≤ _{A 2} ≤ 250;

(6) The conductivity of the positive electrode material is 0.025 S/cm~0.080 S/cm;

(7) The compaction density of the positive electrode material is 3.10 g/cm ³ ~3.65 g/cm ³ ;

(8) The specific surface area of the positive electrode material is 0.4 m ² /g to 0.8 m ² /g.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that it comprises the following steps:

Adding a free lithium ion conversion agent to an aqueous solution of a base material for modification treatment, wherein the free lithium ion conversion agent is used to absorb residual lithium in the base material, and the amount of the free lithium ion conversion agent added is 0.6 wt %-1.2 wt % based on the mass of the base material as 100 wt %, to obtain a modified mixture, and performing solid-liquid separation on the modified mixture to obtain a precursor; wherein the base material is a nickel cobalt lithium oxide composite oxide;

The precursor is sintered to obtain a positive electrode material.

6. The preparation method according to claim 5, characterized in that it comprises at least one of the following features:

(1) In the aqueous solution of the matrix material, the mass of deionized water is 15% to 30% of the mass of the matrix material;

(2) The matrix material is a composite oxide comprising Li, Ni, Co, Mn and M elements, wherein the M element comprises at least one of Sr, Ti, Al, Zr, W, Ba, Mg and Nb;

(3) The preparation step of the matrix material includes: preparing a mixture including a ternary precursor, a lithium source and an M dopant, and sintering the mixture in an oxygen atmosphere to obtain the matrix material; wherein the M includes at least one of Sr, Ti, Al, Zr, W, Ba, Mg, and Nb.

7. The preparation method according to claim 6, characterized in that it also includes at least one of the following features:

(1) The chemical formula of the ternary precursor is Ni _a Co _b Mn _c (OH) ₂ , 0.8≤a≤0.98, 0.01≤b≤0.2, 0.01≤c≤0.2;

(2) the M dopant includes at least one of Sr(OH) ₂ , SrO, TiO ₂ , Al ₂ O ₃ , Al(OH) ₃ , ZrO ₂ , Zr(OH) ₄ , Ba(OH) ₂ , BaO, MgO, Mg(OH) ₂ , Nb ₂ O ₅ , Nb ₂ O ₃ , WO ₃ and CaWO ₄ ;

(3) The mass of the M dopant is 0.1% to 0.55% of the mass of the ternary precursor;

(4) The ternary precursor comprises first particles and second particles of different particle sizes, and the particle size D50 of the first particles is 12 μm-18 μm;

(5) The ternary precursor comprises first particles and second particles of different particle sizes, and the particle size D50 of the second particles is 2 μm-5 μm;

(6) The ternary precursor comprises first particles and second particles of different particle sizes, and the mass ratio of the first particles to the second particles is 1:(1-5);

(7) The molar ratio of the Li element in the lithium source to the ternary precursor is 0.95-1.25.

8. The preparation method according to claim 6, characterized in that it also includes at least one of the following features:

(1) The lithium source includes at least one of hydrated lithium hydroxide, lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate and lithium oxalate;

(2) The free lithium ion conversion agent contains N, and the N includes at least one of W, B, Mo, F, S, V, P and Cl;

(3) The modification treatment is carried out in an ultrasonic environment, the frequency of the ultrasonic wave is 20 kHz to 50 kHz, and the ultrasonic time of the ultrasonic wave is 20 min to 40 min.

9. The preparation method according to claim 5, characterized in that it also includes at least one of the following features:

(1) The step of preparing the aqueous solution of the matrix material comprises: mixing the matrix material with deionized water and stirring uniformly, wherein the stirring speed is 20 Hz to 50 Hz;

(2) The step of preparing the aqueous solution of the matrix material comprises: mixing the matrix material with deionized water and stirring them uniformly, wherein the stirring time is 20 min to 40 min;

(3) The sintering temperature of the sintering treatment is 250°C to 500°C;

(4) The sintering time of the sintering treatment is 6 h to 12 h;

(5) The solid-liquid separation comprises subjecting the modified mixed material to a filter press treatment, wherein the extrusion pressure of the filter press is 0.2 MPa-0.5 MPa;

(6) The solid-liquid separation comprises subjecting the modified mixed material to a filter press treatment, wherein the filter press time is 10 min to 30 min;

(7) The solid-liquid separation comprises successively subjecting the modified mixed material to filter pressing and drying treatment, wherein the drying temperature is 80-170° C.;

(8) The solid-liquid separation comprises successively subjecting the modified mixture to filter pressing and drying treatment, and the drying time is 1 to 3 hours.

10. A lithium-ion battery, characterized in that it comprises the positive electrode material according to any one of claims 1 to 4, or comprises the positive electrode material prepared by the preparation method according to any one of claims 5 to 9.