WO2025246176A1 - Secondary battery, electric device, lithium-rich manganese-based positive electrode active material and preparation method - Google Patents

Abstract

A secondary battery, an electric device, a lithium-rich manganese-based positive electrode active material and a preparation method. The positive electrode sheet in the secondary battery comprises a positive electrode current collector and a positive electrode active substance layer arranged on at least one side of the positive electrode current collector. The positive electrode active substance layer comprises a lithium-rich manganese-based positive electrode active material, and the lithium-rich manganese-based positive electrode active material comprises a substrate and a coating layer coating the substrate, wherein the substrate comprises a lithium-rich manganese-based compound containing a Q element, Q comprising at least one of F, S, Cl, Br and I; and the coating layer comprises a phosphate-containing inorganic salt. The secondary battery, the electric device, the lithium-rich manganese-based positive electrode active material and the preparation method can not only make the material have a relatively high gram capacity, but can also effectively improve the cycling stability and storage stability of the battery in a high-temperature and high-charge state.

Description

Secondary batteries, electrical devices, lithium-rich manganese-based positive electrode active materials and their preparation methods

This application claims priority to Chinese Patent Application No. 202410683697.0, filed on May 29, 2024, entitled "Secondary Battery, Electrical Device, Lithium-Rich Manganese-Based Positive Electrode Active Material and Preparation Method", the entire contents of which are incorporated herein by reference.

Technical Field

This application relates to the field of batteries, specifically to a secondary battery, an electrical device, a lithium-rich manganese-based positive electrode active material, and a preparation method thereof.

Background Technology

With the continuous development and progress of society, energy consumption demand is rising daily, and the successful commercialization of lithium-ion batteries has greatly changed people's energy consumption patterns. However, with the increasing popularity of large-scale energy storage grids and electric vehicles, people's requirements for lithium-ion batteries are becoming increasingly stringent. Lithium-rich manganese-based cathode active materials have the advantages of high specific capacity and high theoretical energy density, and their main component, manganese, is inexpensive, attracting the attention of many researchers and being considered a potential next-generation high-energy-density lithium-ion battery cathode material.

Existing lithium-rich manganese-based cathode active materials generally suffer from accelerated degradation in the later stages of cycling. Although surface coating modification can improve cycle stability and storage stability, conventional coating has a poor effect on improving cycle stability and storage stability under high temperature and high charge conditions, and may also have an adverse effect on the specific capacity of the material.

Summary of the Invention

This application provides a secondary battery, an electrical device, a lithium-rich manganese-based positive electrode active material, and a preparation method thereof, which not only enables the material to have a high specific capacity, but also effectively improves the cycle stability and storage stability of the battery under high temperature and high charge conditions.

The first aspect of this application provides a secondary battery, comprising:

A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector;

The positive electrode active material layer includes a lithium-rich manganese-based positive electrode active material, which includes a matrix and a coating layer covering the matrix.

The matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q includes at least one of F, S, Cl, Br and I;

The coating layer comprises an inorganic salt containing phosphate.

Therefore, this application uses anion-doped lithium-rich manganese-based compounds as the matrix and phosphate-containing inorganic salts as the coating layer to form a lithium-rich manganese-based positive electrode active material. Specifically, side reactions intensify under high temperature and high charge conditions. Due to the defective rock salt structure of conventional lithium-rich manganese-based positive electrode active materials, which has a large transition metal dissolution rate and irreversible O activity, the inorganic element Q introduced in this application is used as an anion dopant to replace part of the O in the lithium-rich manganese-based positive electrode active material. The Mn-Q bond energy is greater than the Mn-O bond energy, so the introduction of inorganic element Q can increase the stability of Mn in the bulk phase. Moreover, the phosphate-containing coating material can combine with the dissolved Mn element to form manganese phosphate, reducing the material damage caused by Mn ³⁺ disproportionation and dissolution in the electrolyte. Therefore, the lithium-rich manganese-based positive electrode active material of this application can suppress the dissolution of transition metal Mn and suppress material damage, which not only enables the material to have a high specific capacity, but also effectively improves the cycle stability and storage stability of the battery under high temperature and high charge conditions.

In any embodiment, the chemical formula of the lithium-rich manganese-based compound is Li[Li _a Ni _b Co _c Mn _d M _e ]O _2-f Q _f , where a+b+c+d+e＝1, a＞0, b＞0, c≧0, d＞0, e≧0, f＞0, and M includes at least one of Mg, Nb, Cr, Ce, Fe, Ta, Al, V, Ti, Zr, Sn, and Mo. The matrix may also incorporate at least one of Co and the metallic element M as needed; Co can enhance kinetics and specific capacity, while M acts as a dopant to improve the structural stability of the material.

In any embodiment, the value of f in the chemical formula of the lithium-rich manganese-based compound ranges from 0.1 to 0.6; by controlling the value of f within the above range, effective anion doping can be achieved, and the overall performance of the material can be improved.

And/or, Q includes at least one of F and Cl. The bond energies between F and Cl and Mn are relatively large, and the introduction of F and Cl can effectively increase the stability of Mn in the bulk phase.

In any embodiment, in the chemical formula of the lithium-rich manganese-based compound, e > 0;

M includes at least one of Mg, Nb, Cr, and Ce. Introducing the metallic element M can improve the structural stability of the material.

In any embodiment, the inorganic salt has the chemical formula _Nx ( _PO4 ) _y , where x>0, y>0, and N includes at least one of Li, Fe, Ni, Mg, Co, V, and Al.

In any embodiment, the N in the inorganic salt includes at least one of Fe, Ni, Mg, Co, V, and Al, and the enriched The phosphorus coating content of the lithium-manganese-based cathode active material is 3000–8000 ppm; the N in the inorganic salt includes Li, and the phosphorus coating content of the lithium-rich manganese-based cathode active material is 3000–11000 ppm. By controlling the coating content of the lithium-rich manganese-based cathode active material within a certain range, the overall performance of the material is improved.

In any embodiment, the N in the inorganic salt includes at least one of Li, Co, and Al.

In any embodiment, the Dv50 of the lithium-rich manganese-based positive electrode active material is 2.5–6.7 μm, the SPAN is 1.15–1.35, and the BET is 1.5–2.0 ^m² /g.

In any embodiment, the average particle size of the substrate is 6 to 7 μm, and the thickness of the coating layer is 10 to 25 nm.

In any embodiment, the Mn dissolution amount of the lithium-rich manganese-based cathode active material in the reducing solution is 80-120 ppm. The test method for Mn dissolution amount is as follows: the lithium-rich manganese-based cathode active material is added to the reducing solution at a concentration of 0.02 g/ml, magnetically stirred for 5 min, then allowed to stand for 24 min, and then magnetically stirred for 1 min, and the concentration of Mn element is tested. Based on the lithium-rich manganese-based cathode active material, this application, through doping and coating, can obtain a lithium-rich manganese-based cathode active material with a certain Mn dissolution amount. This lithium-rich manganese-based cathode active material has a good complexation effect on Mn and can improve the stability of Mn. In other words, by controlling the Mn dissolution amount of the lithium-rich manganese-based cathode active material, the Mn dissolution can be reduced, thereby reducing the impact on battery performance.

In any embodiment, the reducing solution is an aqueous solution of ascorbic acid, and the concentration of the aqueous solution of ascorbic acid is 0.01–1 wt%. This application uses ascorbic acid as the solute for the Mn dissolution test. Ascorbic acid has a reducing effect, which can simulate the working environment of the material in the electrolyte, accelerating the reduction of some ^Mn⁴⁺ to ^Mn²⁺ , thus achieving rapid characterization. This application uses an aqueous solution of ascorbic acid within a certain concentration range to test the Mn dissolution, which can achieve better Mn dissolution results, reduce testing errors caused by insufficient Mn dissolution due to low concentration, and reduce the problem of lack of distinguishability in Mn dissolution due to excessively high concentration.

In any embodiment, the micro-stress of the lithium-rich manganese-based cathode active material is 0.3–2%, and the micro-stress is calculated as (βhkl × Cosθhkl) / (4sinθhkl), where θhkl is the diffraction angle of the crystal plane in the XRD diffraction pattern of the lithium-rich manganese-based cathode active material, and βhkl is the full width at half maximum (FWHM) of the crystal plane. Within a certain range, the micro-stress of the lithium-rich manganese-based cathode active material can reduce stress accumulation in the cathode material particles during charge-discharge cycles, improve the secondary spherical breakage phenomenon caused by excessive stress in the cathode material particles, and thus enhance the stability of the cathode material.

The second aspect of this application provides an electrical device including the secondary battery provided in the first aspect.

A third aspect of this application provides a lithium-rich manganese-based cathode active material, comprising a matrix and a coating layer covering the matrix; the matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q comprises at least one of F, S, Cl, Br and I; the coating layer comprises an inorganic salt containing phosphate.

The fourth aspect of this application provides a method for preparing the lithium-rich manganese-based positive electrode active material of the foregoing embodiments, wherein the matrix and the coating raw materials of the corresponding coating layer are ball-milled and mixed, and then sintered.

In any embodiment, the coating material includes one of _Li3PO4 , _FePO4 , _LiFePO4 , _Ni3 ( _PO4 ) ₂ , _Mg3 ( _PO4 ) ₂ , _Co3 ( _{PO4 ) 2} , _Li3V2 ( _PO4 ) _{3 ,} and _AlPO4 ;

And/or, the ball-to-material ratio during ball milling is 25–80;

And/or, the sintering temperature is 450–530℃, the heating rate is 1–3℃/min, the sintering time is 12–20h, and the sintering atmosphere is air.

In any embodiment, the precursor raw materials of each metal element in the corresponding lithium-rich manganese-based compound and the anionic raw material of Q element in the corresponding lithium-rich manganese-based compound are ball-milled and sintered to obtain the matrix.

In any embodiment, the precursor raw material includes at least one of metal sulfate and metal carbonate, and the anionic raw material includes anionic lithium salt.

And/or, the ball-to-material ratio during ball milling is 25–80;

And/or, the sintering temperature is 800–900℃, the heating rate is 1–3℃/min, the sintering time is 20–75h, and the sintering atmosphere is air.

The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application.

Attached Figure Description

Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

Explanation of reference numerals in the attached figures:

1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly.

Detailed Implementation

The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, power-consuming device, lithium-rich manganese-based positive electrode active material, and preparation method of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, transported through the electrolyte, pass through the separator, and intercalate into the negative electrode active material. The positive electrode active material, as a crucial component of lithium-ion batteries, significantly influences their performance. Lithium-rich manganese-based positive electrode active materials possess advantages such as high specific capacity and high theoretical energy density, and their main component, manganese, is inexpensive, attracting considerable attention from researchers and considered a potential next-generation high-energy-density lithium-ion battery positive electrode material.

Existing lithium-rich manganese-based cathode active materials generally suffer from accelerated degradation in the later stages of cycling. Although surface coating modification can improve cycle stability and storage stability, conventional coating has a poor effect on improving cycle stability and storage stability under high temperature and high charge conditions, and may also have an adverse effect on the specific capacity of the material.

Existing technology discloses a phosphate-coated lithium-rich layered cathode material, comprising a lithium-rich material and a coating layer on the lithium-rich material. The lithium-rich material has the general formula Li _{_1+a}M _{_1-a} O_₂ , and the coating layer material has the general formula Mn_{_x}P_{_y}O_{_z} . The coating Mn_{_x}P _{_y} _O _z contains Mn, which readily dissolves under high-voltage operating conditions, affecting the cathode material's performance.

Existing technology also discloses a method for preparing lithium-rich manganese-based cathode materials coated with phosphate polyanion composite manganese salt. The method involves first dissolving soluble phosphate and soluble manganese salt in water to form an aqueous solution, then adding the lithium-rich manganese-based cathode material to obtain a precursor solution. After drying, the solution is calcined in a muffle furnace to obtain the lithium-rich manganese-based cathode material coated with phosphate polyanion composite manganese salt. This method involves coating in an acidic solution environment, which easily leads to surface etching and an abnormal increase in specific surface area of the lithium-rich manganese-based cathode material, resulting in structural damage and performance deterioration.

Therefore, current lithium-rich manganese-based cathode active materials generally suffer from accelerated degradation in the later stages of cycling, falling short of the energy cycle performance of cathode materials. Although surface coating modification of cathode materials is beneficial to improving cycle stability and storage stability, high-temperature storage materials experience rapid energy degradation, and conventional coating has little effect on improving the material under high temperature and high SOC conditions. In addition, commonly used oxide and fluoride coatings are electrochemically inert, and while improving the structural stability of the material, they sacrifice the specific capacity and energy density.

To address the issue of poor cycle stability and storage stability of lithium-rich manganese-based cathode active materials under high temperature and high charge conditions, a cathode active material was designed. By doping and coating the lithium-rich manganese-based cathode active material, not only can the cathode active material have a high specific capacity, but the cycle stability and storage stability of the cathode active material under high temperature and high charge conditions can also be improved, thereby enhancing the cycle life and storage life of the battery.

Based on this, the first aspect of the present application provides a secondary battery, including: a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector;

The positive electrode active material layer includes a lithium-rich manganese-based positive electrode active material, which includes a matrix and a coating layer covering the matrix.

The matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q includes at least one of F, S, Cl, Br and I;

The coating layer consists of phosphate-containing inorganic salts.

The lithium-rich manganese-based cathode active material of this application is a coated and modified lithium-rich manganese-based cathode active material. The coating layer can be a complete coating on the substrate or a partial coating. This application does not impose any specific restrictions on this.

The lithium-rich manganese-based cathode active material of this application uses a lithium-rich manganese-based compound doped with Q as the matrix and an inorganic salt containing phosphate as the coating layer. Introducing the inorganic element Q into the matrix material increases the stability of Mn in the bulk phase and inhibits Mn dissolution. Furthermore, the phosphate-containing coating material can combine with the dissolved Mn to form manganese phosphate, reducing material damage caused by ^Mn³⁺ disproportionation in the electrolyte. Therefore, the lithium-rich manganese-based cathode active material of this application can inhibit the dissolution of transition metal Mn and suppress material damage, resulting in not only a high specific capacity but also effectively improving the cycle stability and storage stability of the battery under high temperature and high charge conditions.

According to some embodiments of this application, the chemical formula of the lithium-rich manganese-based compound is Li[Li _a Ni _b Co _c Mn _d M _e ]O _2-f Q _f , where a+b+c+d+e＝1, a＞0, b＞0, d＞0, f＞0, and M includes at least one of Mg, Nb, Cr, Ce, Fe, Ta, Al, V, Ti, Zr, Sn and Mo.

The aforementioned lithium-rich manganese-based compounds contain Li, Ni, Mn, and Q, and may also contain at least one of Co and M. Exemplarily, the lithium-rich manganese-based compounds include: Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.8 F _0.2 , Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.8 Cl _0.2 , Li _1.2 Mn _0.48 Ni _0.18 Mg _0.14 O _1.8 F _0.2 , Li _1.2 Mn _0.48 Co _0.14 Ni _0.18 O _1.8 F _0.2 , or one or a combination of other constituent materials. For lithium-rich manganese-based compounds containing both nickel (Ni) and manganese (Mn), as well as those containing both nickel (Ni), cobalt (Co), and manganese (Mn), nickel, cobalt, and manganese are all transition metal elements. They can provide higher electron transport and energy storage capabilities in cathode materials, thereby improving the energy density of the battery.

According to some embodiments of this application, in the chemical formula of the lithium-rich manganese-based compound, the value of f ranges from 0.1 to 0.6; and/or, Q includes at least one of F and Cl.

For example, the chemical formulas of lithium-rich manganese-based compounds are Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.8 F _0.2 , Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.8 Cl _0.2 , Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.4 F _0.6 , and Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.9 F _0.1 .

According to some embodiments of this application, in the chemical formula of the lithium-rich manganese-based compound, e > 0;

M includes at least one of Mg, Nb, Cr, and Ce. For example, the chemical formulas of lithium-rich manganese-based compounds are Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Mg _0.04 O _1.8 F _0.2 and Li _1.2 Mn _0.48 Co _0.1 Ni _0.18 Cr _0.04 O _1.8 F _0.2 .

According to some embodiments of this application, the inorganic salt has the chemical formula _Nx ( _PO4 ) _y , where x > 0, y > 0, and N includes at least one of Li, Fe, Ni, Mg, Co, V, and Al. Exemplarily, the inorganic salt includes at least one of _Li3PO4 , _Mg3 ( _PO4 ) ₂ , _Co3 ( _PO4 ) ₂ , _{AlPO4 ,} and other materials.

In this application, the coating amount of the lithium-rich manganese-based cathode active material is related to the coating material. According to some embodiments of this application, the N in the inorganic salt includes at least one of Fe, Ni, Mg, Co, V, and Al, for example, the chemical formula of the inorganic salt is _AlPO4 or _Co3 ( _PO4 ) ₂ , and the phosphorus coating amount of the lithium-rich manganese-based cathode active material is 3000-8000 ppm. 1 ppm = 0.0001%, that is, the phosphorus content in the coating layer accounts for 0.3%-0.8% of the total mass of the lithium-rich manganese-based cathode active material. As an example, the coating amount of the lithium-rich manganese-based cathode active material is 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, or 8000 ppm, or any value within the above two numerical ranges.

According to some embodiments of this application, the N in the inorganic salt includes Li, for example, the chemical formula of the inorganic salt is _Li3PO4 , _and the phosphorus element coating of the lithium-rich manganese-based positive electrode active material is 3000 to 11000 ppm, that is, the coating layer accounts for 0.3% to 1.1% of the total mass of the lithium-rich manganese-based positive electrode active material.

According to some embodiments of this application, the N in the inorganic salt includes at least one of Li, Co, and Al.

According to some embodiments of this application, the Dv50 of the lithium-rich manganese-based cathode active material is 2.5–6.7 μm, the SPAN is 1.15–1.35, and the BET is 1.5–2.0 ^m² /g. As an example, the Dv50 of the lithium-rich manganese-based cathode active material is 2.5 μm, 3 μm, 4 μm, 5.5 μm, or... 6.7μm, or any value within the two numerical ranges mentioned above; SPAN is 1.15, 1.2, 1.25, 1.3 or 1.35, or any value within the two numerical ranges mentioned above; BET is ^1.5m² /g, ^1.6m² /g, ^1.8m² /g or ^2.0m² /g, or any value within the two numerical ranges mentioned above.

Dv50 refers to the particle size that corresponds to 50% of the cumulative volume in the volume-based particle size distribution of lithium-rich manganese-based cathode active materials, starting from the smallest particle size. It can represent the overall particle size of lithium-rich manganese-based cathode active materials.

Particle size distribution width Wherein, Dv0.9 is equivalent to Dv90, which refers to the particle size corresponding to 90% of the cumulative volume; Dv0.1 is equivalent to Dv10, which refers to the particle size corresponding to 10% of the cumulative volume; and Dv0.5 is equivalent to Dv50.

Specific surface area (BET) refers to the total surface area per unit mass of particulate matter.

According to some embodiments of this application, the average particle size of the substrate is 6–7 μm, and the thickness of the coating layer is 10–25 nm. As an example, the average particle size of the substrate can be 6 μm, 6.3 μm, 6.5 μm, 6.7 μm, or 7 μm, or any value within the above two numerical ranges; the thickness of the coating layer can be 10 nm, 15 nm, 20 nm, or 25 nm, or any value within the above two numerical ranges.

According to some embodiments of this application, the amount of Mn dissolved in the lithium-rich manganese-based cathode active material in a reducing solution is...

The concentration of Mn leaching is 80-120 ppm. The test method for Mn leaching is as follows: add lithium-rich manganese-based positive electrode active material to a reducing solution with a concentration of 0.02 g/ml, stir magnetically for 5 min, let stand for 24 min, stir magnetically for 1 min, and then test the concentration of Mn.

According to some embodiments of this application, the reducing solution is an aqueous solution of ascorbic acid, and the concentration of the aqueous solution of ascorbic acid is 0.01-1 wt%, preferably 0.1-0.3 wt%. The concentration of the solution (concentration of ascorbic acid) used for testing the Mn dissolution of lithium-rich manganese-based cathode active material is 0.01-1 wt%, preferably 0.1-0.3 wt%.

According to some embodiments of this application, the microstress of the lithium-rich manganese-based cathode active material is 0.3 to 2%, and can be selected as 0.3 to 1.2%. The microstress is calculated as (βhkl × Cosθhkl) / (4sinθhkl), where θhkl is the diffraction angle of the crystal plane in the XRD diffraction pattern of the lithium-rich manganese-based cathode active material, and βhkl is the half-width at half maximum (FWHM) of the crystal plane.

This application does not impose any particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion secondary battery, etc.

Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[Positive electrode plate]

The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer comprises the lithium-rich manganese-based positive active material of the aforementioned embodiments.

In some implementations, other layers, such as an adhesive layer, may be provided between the positive current collector and the positive active material layer.

In some embodiments, positive electrode active material layers are respectively provided on both sides of the positive electrode current collector; optionally, the positive electrode active material layers on both sides of the positive electrode current collector are symmetrical about the positive electrode current collector, that is, they contain the same positive electrode active material provided above.

In some embodiments, the positive electrode active material may include not only lithium-rich manganese-based positive electrode active materials, but also other positive electrode active materials, such as uncoated and/or unmodified positive electrode active materials. The mass percentage of the lithium-rich manganese-based positive electrode active material in the total positive electrode active material may be more than 50% or more than 90%.

In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. This application does not specifically limit the types of conductive agents and binders, and they can be selected according to actual needs. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. As an example, the binder may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

In some embodiments, the mass ratio of the positive electrode active material to the conductive agent and binder is (96-99):(0.5-2):

(0.5～2). Therefore, by using the positive electrode active material, conductive agent and binder formulated in the proportions of this application to form a positive electrode slurry, it is beneficial to the conductivity of the positive electrode active material layer and the bonding strength with the positive electrode current collector.

To meet actual production needs, the minimum coating weight for a single-layer positive electrode active material layer with a coating area of 1540.25 ^mm² is 50 mg, and it is generally 50–200 mg.

In some embodiments, the positive electrode current collector can be a conventional metal foil or a composite positive electrode current collector (a composite positive electrode current collector can be formed by depositing metal material on a polymer substrate). As an example, the metal foil may include one or more of aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil. The composite positive electrode current collector may include a polymer substrate and at least [missing information - likely a coating material]. A metal layer on a surface; composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the method for preparing the positive electrode sheet may include forming a positive active material layer on at least one side of the positive current collector. As an example, the positive active material is mixed with a conductive agent, a binder and a solvent (e.g., N-methylpyrrolidone NMP) to form a positive electrode slurry, and then the positive electrode slurry is coated onto the positive current collector, followed by processes such as roller coating and drying to remove the solvent, to obtain the positive electrode sheet.

[Negative electrode plate]

The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, this application does not specifically limit the type of negative electrode active material, and it can be selected according to actual needs. As an example, the negative electrode active material may include one or more of the following materials: This application does not specifically limit the type of negative electrode material, and it can be selected according to actual needs. As an example, the negative electrode active material may be selected from one or more of graphite, lithium metal, a negative electrode-free current collector, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[Isolation membrane]

This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[Electrolytes]

A battery also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid or gel-like.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and an organic solvent.

In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

In some embodiments, the organic solvent may be selected from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, including, for example, polypropylene, polybutylene terephthalate, and polybutylene succinate.

A second aspect of this application provides an electrical device including the secondary battery described in the foregoing embodiments.

In addition, the battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

In addition, this application also provides an electrical device, which includes the battery provided in this application. The battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

As an electrical device, batteries, battery modules, or battery packs can be selected according to their usage requirements.

Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

A third aspect of this application provides a lithium-rich manganese-based positive electrode active material, comprising a matrix and a coating layer covering the matrix; the matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q includes at least one of F, S, Cl, Br and I; the coating layer comprises an inorganic salt containing phosphate.

The lithium-rich manganese-based cathode active material of the present application embodiments may have any of the characteristics of the lithium-rich manganese-based cathode active material in the aforementioned secondary battery.

The fourth aspect of this application provides a method for preparing the lithium-rich manganese-based positive electrode active material of the foregoing embodiments, wherein the matrix and the coating raw materials of the corresponding coating layer are first ball-milled and mixed, and then sintered.

In some embodiments, the coating material includes one _{of Li3PO4} , _FePO4 , _LiFePO4 , _Ni3 ( _PO4 ) ₂ , _Mg3 ( _PO4 ) ₂ , _Co3 ( _PO4 ) ₂ , _Li3V2 ( _PO4 ) _{3 ,} and _AlPO4 ;

And/or, the ball-to-material ratio during ball milling is 25–80;

And/or, the sintering temperature is 450–530℃, the heating rate is 1–3℃/min, the sintering time is 12–20h, and the sintering atmosphere is air.

In some embodiments, the material obtained by mechanically grinding and vibrating sieving after sintering is referred to as lithium-rich manganese-based positive electrode active material.

In some embodiments, the precursor raw materials corresponding to each metal element in the lithium-rich manganese-based compound and the anionic raw material of element Q in the lithium-rich manganese-based compound are first ball-milled and then sintered to obtain a matrix. In some embodiments, the material obtained after mechanical grinding and vibrating sieving of the sintered material is referred to as a sintered material, which is then sintered with the coating raw material.

In some embodiments, the precursor raw material includes at least one of metal sulfate and metal carbonate, and the anionic raw material includes anionic lithium salt. The precursor raw material can be fed at a Li/N molar ratio of 1.0 to 1.05, where N is other metals, such as the total metal composition of nickel, cobalt, manganese, and M.

And/or, the ball-to-material ratio during ball milling is 25–80;

And/or, the sintering temperature is 800–900℃, the heating rate is 1–3℃/min, the sintering time is 20–75h, and the sintering atmosphere is air.

The ball milling conditions in this step can be the same as those described above for the ball milling conditions of the coated raw material, or they can be different.

The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

Example 1

(1) Preparation of lithium-rich manganese-based positive electrode active materials

According to the precise molar ratio of elements contained in the lithium-rich manganese-based positive electrode active material with the molecular formula Li _{1.2Mn 0.48Co 0.1Ni 0.18Mg 0.04O 1.8F 0.4,} the precursor raw materials were weighed out as follows: lithium salt Li _{2CO 3} , manganese salt MnSO ₄ ·H _2O , cobalt salt CoSO ₄ ·7H _2O , nickel salt NiSO ₄ , magnesium salt MgSO ₄ , and anionic raw material LiF. The raw materials (each precursor raw material and anionic raw material) were mixed with zirconium balls at a ball-milling ratio of 50:1 in a drum-type ball mill mixer to obtain a precursor mixture. The precursor mixture was then sintered in a muffle furnace under air atmosphere, with a heating rate of 2.5℃/min, a sintering temperature of 900℃, and a sintering time of 20h. The sintered material was then mechanically ground and sieved to obtain the material with the molecular formula Li _1.2Mn The matrix is a lithium-rich manganese-based sintered material consisting of _0.48 Co, _0.1 Ni, _0.18 Mg, _0.04 O, _1.8 F, _{and 0.4} .

A sintering material and a coating material _AlPO4 with a phosphorus stoichiometry (P stoichiometry) of 4000 ppm were mixed in a drum ball mill at a ball-to-material ratio of 60. The mixture was then placed in a muffle furnace for sintering in an air atmosphere at a heating rate of 2℃/min, at a sintering temperature of 500℃, and for 15 hours. The sintered material was then mechanically ground and sieved to obtain the lithium-rich manganese-based positive electrode active material.

(2) Preparation of positive electrode sheet

Lithium-rich manganese-based positive electrode active material was added to a 5L mixing tank and premixed for 30 minutes. Then, conductive agent acetylene black (SP) and binder polyvinylidene fluoride (PVDF) were added and mixed for 30 minutes for a second dry mixing. Finally, solvent N-methylpyrrolidone (NMP) was added and the mixture was rapidly stirred under vacuum to form a slurry. The mass ratio of positive electrode active material:acetylene black:polyvinylidene fluoride was 96:2:2, and the solid content of the slurry was 70% by weight. The slurry was uniformly coated on both sides of an aluminum foil with a thickness of 12μm. After coating, the foil was dried in an oven at 110℃ for half an hour and then cold-pressed through rollers to obtain the positive electrode sheet. The positive electrode active material loading was 21.5 mg/ ^cm² .

(3) Assembly of the full battery

Artificial graphite and hard carbon (negative electrode active materials), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were thoroughly mixed in a deionized water solvent system at a weight ratio of 90:5:2:2:1. The mixture was then coated onto copper foil, dried, and cold-pressed through rollers to obtain the negative electrode sheet. A porous polyethylene polymer film was used as the separator.

The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, and the prepared basic electrolyte (1 mol/L _LiPF6 /(EC+EMC+DMC, volume ratio 1:1:1)) is injected and sealed to obtain a full cell.

Examples 2-12 and Comparative Examples 1-7

Step (1) is slightly different from that in Example 1. See Table 1 for details.

Test methods and results

1. Parameter performance testing of lithium-rich manganese-based cathode active materials:

(1) Particle volume distribution particle sizes Dv10, Dv50, and Dv90: Particle size distribution was determined using the Malvern 3000 equipment, referring to GB/T 19077-2016/ISO 13320:2009 Particle size distribution by laser diffraction.

Particle size distribution width Span = (Dv90 - Dv10) / Dv50.

The test method for BET is as follows: refer to the national standard GB/T 19587-2004.

The Dv50 of all the lithium-rich manganese-based cathode active materials in the embodiments and comparative examples are in the range of 6.4 to 6.7 μm, the SPAN is in the range of 1.15 to 1.35, and the BET is in the range of 1.5 to 2.0 ^m² /g. Therefore, it can be seen that the doping and coating modification methods of the embodiments of this application have little impact on the above parameters of the lithium-rich manganese-based cathode active materials.

(2) Mn dissolution amount: ① Weigh 1 ± 0.01 g of sample and add it to a beaker; ② Add 50 ml of ultrapure water to a 150 ml beaker, slowly add an appropriate amount of ascorbic acid powder (VC), sonicate for 5 min until completely dissolved, and obtain VC solution. The concentration of VC solution is...

=0.2wt%; ③ Measure the prepared VC solution and add it to the beaker in ①. After adding a small magnetic stir bar, seal the beaker and perform magnetic stirring at a speed of 500 rpm. The process is as follows: magnetic stirring for 5 min - standing for 24 min - magnetic stirring for 1 min; ④ Take the stirred solution and filter 4 mL into a test tube; ⑤ Add 2 mL of nitric acid to a 100 mL glass volumetric flask, and then take 1 mL of filtrate from the test tube in the previous step and add it to the volumetric flask to make up the volume; ⑥ Use inductively coupled plasma optical emission spectroscopy (ICP-OES) to test the concentration of Mn element, input the dilution factor and the volume/sample mass, and record the experimental result Mn/ppm.

Furthermore, by changing the concentration of the ascorbic acid (VC) solution, the results for the Mn dissolution of the same sample varied. For the sample in Example 1: with a VC solution concentration of 0.2 wt%, the measured Mn dissolution was 93 ppm; with a VC solution concentration of 0.1 wt%, the measured Mn dissolution was 88 ppm; and with a VC solution concentration of 1 wt%, the measured Mn dissolution was 138 ppm. This demonstrates that the concentration of the ascorbic acid solution used to test Mn dissolution should not be too high; otherwise, the measured Mn dissolution would be too large, failing to accurately reflect the stability of Mn in the bulk phase. Therefore, to better reflect the differences in Mn stability among the samples, the concentration of the ascorbic acid solution was fixed at 0.2 wt%.

(3) Microstress testing of lithium-rich manganese-based cathode active materials:

The method for detecting micro-stress: X-ray diffraction pattern test of lithium-rich manganese-based positive electrode active material to obtain XRD diffraction pattern. XRD test refers to the general rule JIS K 0131-1996, including the following requirements: (1) the sample is dry; (2) the sample particle size is <10μm. If it is electrode scraping powder or block sample, it needs to be ground through a 200-mesh sieve before being sent.

Micro-stress = (βhkl × Cosθhkl) / (4sinθhkl), where θhkl is the diffraction angle of the (hkl) crystal plane of the lithium-rich manganese-based cathode active material in the XRD diffraction pattern, and βhkl is the full width at half maximum (FWHM) of the (hkl) crystal plane of the lithium-rich manganese-based cathode active material in the XRD diffraction pattern.

The micro-stress, or Strain, is calculated.

2. Battery cell cycle performance testing:

Using a single full-cell battery as the test object, under a constant temperature environment of 25℃, the battery was charged at a rate of 0.5C to 4.43V at a voltage range of 2.5V to 4.43V. Then, it was charged at a constant voltage of 4.43V until the current was ≤0.05mA. After standing for 5 minutes, it was discharged at a rate of 0.2C to 2.5V. The discharge capacity was recorded and the discharge capacity (mAh/g) was calculated. The previous process was repeated to obtain the capacity retention rate after 300 cycles. The capacity retention rate = discharge capacity in the first cycle / discharge capacity at the specified number of cycles × 100%, which is the cycle retention rate (%) of the single-cell battery.

3. Battery cell storage performance testing:

Under a constant temperature environment of 25℃, let it stand for 5 minutes, discharge at 1/3C to 2.5V, let it stand for 5 minutes, charge at 1/3C to 4.5V, and then charge at 4.5V at a constant voltage until the current is ≤0.05mA. Let it stand for 5 minutes. The charging capacity at this time is recorded as C0. Then discharge at 1/3C to 2.8V. The discharge capacity at this time is the initial specific capacity, recorded as D0. The first efficiency is D0/C0*100%.

Then, the battery was charged from 0.33C constant current to 4.5V and constant voltage until the current ≤0.05mA, left to stand for 5 minutes, and finally placed in a 60℃ temperature chamber for 1 hour until the battery temperature reached the target temperature for 15 days. After 15 days, it was taken out and the previous process was repeated in a constant temperature environment of 25℃. The capacity Dn (n＝0, 1, 2……) was recorded every 15 days. The capacity retention rate after 60 days of storage was calculated as (D4-D0)/D0*100%, which is the battery cell storage retention rate (%).

The specific results are shown in Table 1:

Table 1 Battery Performance

Based on the results in Table 1, we can see that:

The lithium-rich manganese-based cathode active materials in Examples 1-12 use a specific lithium-rich manganese-based compound Li[Li _{_aNi_b} Co_c M_{_n}dMe_e]O_{_2-f}Q_{_f} as the matrix and are coated with a specific coating layer N _{_x}(PO _₄)_{_y}. This not only enables the material to have a high specific capacity but also effectively improves the cycle stability and storage stability of the battery under high temperature and high charge conditions. In contrast, the batteries formed by using other lithium-rich manganese-based compounds as the matrix in Comparative Examples 1-7, and those without coating or with other coating layers, exhibit poor cycle stability and storage stability under high temperature and high charge conditions.

According to Examples 1-6, the lithium-rich manganese-based cathode active material employs anion Q doping to replace part of the O, which can effectively improve the cycle stability and storage stability of the battery under high temperature and high charge conditions. In contrast, the lithium-rich manganese-based cathode active material in Comparative Example 2, which does not employ anion doping, exhibits significantly worse cycle stability and storage stability.

In Examples 1-3, the anions doped in the lithium-rich manganese-based compounds are selected from F and Cl, which can significantly improve the cycle stability and storage stability of the battery under high temperature and high charge conditions.

In Examples 1 and 4-6, the value of f in the chemical formula of the lithium-rich manganese-based compound ranges from 0.1 to 0.6, which can effectively improve the cycle stability and storage stability of the battery under high temperature and high charge conditions.

According to Examples 1 and 7-8, the lithium-rich manganese-based compound contains the metal elements Li, Ni, and Mn, which enables the material to have a high specific capacity and can effectively improve the cycle stability and storage stability of the battery under high temperature and high charge conditions. In Examples 1 and 8, the lithium-rich manganese-based compound is also doped with metal M, specifically Mg, which can significantly improve the cycle stability and storage stability of the battery under high temperature and high charge conditions.

According to Examples 1 and 10-11, coating the lithium-rich manganese-based compound with a specific coating layer _Nx ( _PO4 ) _y can give the material a higher specific capacity and effectively improve the cycle stability and storage stability of the battery under high temperature and high charge conditions. The N in the coating layer is selected from Co and Al, which have a better effect on improving the cycle stability and storage stability of the battery. In contrast, the batteries formed from the uncoated lithium-rich manganese-based positive electrode active materials in Comparative Examples 3 and 7, and the lithium-rich manganese-based positive electrode active material coated with other materials in Comparative Example 6, exhibit poor cycle stability and storage stability under high temperature and high charge conditions.

According to Examples 1 and 12, the inorganic salt coating layer is _AlPO4 , and the phosphorus element coating amount of the lithium-rich manganese-based positive electrode active material is 4000-6000ppm. Although increasing the coating amount will lead to a decrease in the specific capacity of the material, by controlling the coating amount, the material can still have a high specific capacity, and the cycle stability and storage stability of the battery under high temperature and high charge conditions can also be improved.

Comparing the lithium-rich manganese-based cathode active materials of Examples 1, 4-5 (coated with inorganic salts and doped with anions Q at different doping amounts, f = 0.2, 0.6, 0.1) with the lithium-rich manganese-based cathode active materials of Comparative Examples 3-5 (uncoated and doped with anions Q at different doping amounts, f = 0.2, 0.6, 0.1), it was found that: the lithium-rich manganese-based cathode active materials of Comparative Examples 3-5 were uncoated, and the doping of anions Q was changed... The performance difference of the batteries corresponding to the amount of anion doping is relatively small, indicating that the effect of using only anion doping on improving the performance of lithium-rich manganese-based cathode active materials is limited. After the lithium-rich manganese-based cathode active materials in Examples 1, 4-5 are coated with inorganic salt, the performance difference of the batteries corresponding to the amount of anion doping is larger, indicating that the simultaneous use of anion doping and coating modification can synergistically improve the performance of lithium-rich manganese-based cathode active materials, thereby significantly improving the cycle stability and storage stability of the battery under high temperature and high charge conditions.

According to Examples 1-10, the Mn leaching amount of the lithium-rich manganese-based cathode active material in ascorbic acid solution is 80-120 ppm, and the strain is below 0.7%. This corresponds to good Mn stability and low leaching amount, which can effectively improve the specific capacity of the material and the cycle and storage stability of the battery. However, the Mn leaching amount and strain in Comparative Examples 1, 2, 3, and 7 are all too high, making it impossible to simultaneously achieve a high specific capacity and excellent cycle and storage stability of the battery.

The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims (18)

A secondary battery, characterized in that it comprises: A positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; The positive electrode active material layer includes a lithium-rich manganese-based positive electrode active material, which includes a matrix and a coating layer covering the matrix. The matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q includes at least one of F, S, Cl, Br and I; The coating layer comprises an inorganic salt containing phosphate. According to claim 1, the secondary battery is characterized in that the chemical formula of the lithium-rich manganese-based compound is Li[Li _a Ni _b Co _c Mn _d M _e ]O _2-f Q _f , wherein a+b+c+d+e＝1, a＞0, b＞0, c≧0, d＞0, e≧0, f＞0, and M includes at least one of Mg, Nb, Cr, Ce, Fe, Ta, Al, V, Ti, Zr, Sn and Mo. According to claim 2, the secondary battery is characterized in that, in the chemical formula of the lithium-rich manganese-based compound, the value of f ranges from 0.1 to 0.6. And/or, Q includes at least one of F and Cl. The secondary battery according to claim 2 or 3 is characterized in that, in the chemical formula of the lithium-rich manganese-based compound, e > 0; M includes at least one of Mg, Nb, Cr, and Ce. According to claim 1, the secondary battery is characterized in that the inorganic salt has the chemical formula _Nx ( _PO4 ) _y , where x>0, y>0, and N includes at least one of Li, Fe, Ni, Mg, Co, V, and Al. According to claim 5, the secondary battery is characterized in that the N in the inorganic salt includes at least one of Fe, Ni, Mg, Co, V, and Al, and the phosphorus coating amount of the lithium-rich manganese-based positive electrode active material is 3000-8000 ppm; the N in the inorganic salt includes Li, and the phosphorus coating amount of the lithium-rich manganese-based positive electrode active material is 3000-11000 ppm. The secondary battery according to claim 5 or 6 is characterized in that the N in the inorganic salt includes at least one of Li, Co, and Al. The secondary battery according to any one of claims 1 to 7 is characterized in that the Dv50 of the lithium-rich manganese-based positive electrode active material is 2.5 to 6.7 μm, the SPAN is 1.15 to 1.35, and the BET is 1.5 to 2.0 ^m² /g. The secondary battery according to any one of claims 1 to 8 is characterized in that the average particle size of the substrate is 6 to 7 μm and the thickness of the coating layer is 10 to 25 nm. The secondary battery according to any one of claims 1 to 9 is characterized in that the amount of Mn dissolved in the reducing solution by the lithium-rich manganese-based positive electrode active material is 80 to 120 ppm; the method for testing the amount of Mn dissolved is as follows: the lithium-rich manganese-based positive electrode active material is added to the reducing solution at a concentration of 0.02 g/ml, magnetically stirred for 5 min, then allowed to stand for 24 min, and then magnetically stirred for 1 min, and the concentration of Mn element is tested. According to claim 10, the secondary battery is characterized in that the reducing solution is an aqueous solution of ascorbic acid, and the concentration of the aqueous solution of ascorbic acid is 0.01-1 wt%. The secondary battery according to any one of claims 1 to 11 is characterized in that the micro-stress of the lithium-rich manganese-based positive electrode active material is 0.3 to 2%, and the micro-stress is (βhkl × Cosθhkl) / (4sinθhkl), where θhkl is the diffraction angle of the crystal plane in the XRD diffraction pattern of the lithium-rich manganese-based positive electrode active material, and βhkl is the half-width at half maximum (FWHM) of the crystal plane. An electrical device, characterized in that it comprises a secondary battery as described in any one of claims 1 to 12. A lithium-rich manganese-based positive electrode active material, characterized in that it comprises a matrix and a coating layer covering the matrix; the matrix comprises a lithium-rich manganese-based compound containing element Q, wherein Q includes at least one of F, S, Cl, Br and I; and the coating layer comprises an inorganic salt containing phosphate. A method for preparing a lithium-rich manganese-based positive electrode active material as described in claim 14, characterized in that the matrix and the coating material of the corresponding coating layer are ball-milled and mixed, and then sintered. The method for preparing lithium-rich manganese-based positive electrode active material according to claim 15 is characterized in that the coating raw material includes one of _Li3PO4 , _FePO4 , _LiFePO4 , _Ni3 ( _{PO4 ) 2} , _Mg3 ( _PO4 ) ₂ , _Co3 ( _{PO4 ) 2} , _Li3V2 ( _PO4 ) ₃ and _AlPO4 ; And/or, the ball-to-material ratio during ball milling is 25–80; And/or, the sintering temperature is 450–530℃, the heating rate is 1–3℃/min, the sintering time is 12–20h, and the sintering atmosphere is air. The method for preparing lithium-rich manganese-based positive electrode active material according to claim 15 is characterized in that the precursor raw materials corresponding to each metal element in the lithium-rich manganese-based compound and the anionic raw materials corresponding to the Q element in the lithium-rich manganese-based compound are ball-milled and sintered to obtain the matrix. The method for preparing lithium-rich manganese-based positive electrode active material according to claim 17 is characterized in that the precursor raw material includes at least one of metal sulfate and metal carbonate, and the anionic raw material includes anionic lithium salt. And/or, the ball-to-material ratio during ball milling is 25–80; And/or, the sintering temperature is 800–900℃, the heating rate is 1–3℃/min, the sintering time is 20–75h, and the sintering atmosphere is air.