CN116190631B - A lithium-rich manganese-based positive electrode active material and battery - Google Patents
A lithium-rich manganese-based positive electrode active material and batteryInfo
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- CN116190631B CN116190631B CN202310321011.9A CN202310321011A CN116190631B CN 116190631 B CN116190631 B CN 116190631B CN 202310321011 A CN202310321011 A CN 202310321011A CN 116190631 B CN116190631 B CN 116190631B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
本发明提供一种富锂锰基正极活性材料和电池。本发明第一方面提供一种富锂锰基正极活性材料，包括基体颗粒和包覆在基体颗粒外表面的包覆层，基体颗粒的分子式为Lia‑b1Kc‑ b2MnxCoyNizMhO2‑dDd，基体颗粒具有锂空位和钾空位。本发明提供的富锂锰基正极活性材料使用钾元素占据部分锂位点，有助于降低锂源使用量，并提高材料的倍率性能和结构稳定性，同时，钾空位的形成有助于容纳放电过程中嵌回的锂离子，提高电池的放电比容量、首次库伦效率和循环寿命。
The present invention provides a lithium-rich manganese-based positive electrode active material and a battery. In a first aspect, the present invention provides a lithium-rich manganese-based positive electrode active material, comprising a base particle and a coating layer coated on the outer surface of the base particle, the molecular formula of the base particle is Li a‑b1 K c‑ b2 Mn x Co y Ni z M h O 2‑d D d , and the base particle has lithium vacancies and potassium vacancies. The lithium-rich manganese-based positive electrode active material provided by the present invention uses potassium to occupy part of the lithium sites, which helps to reduce the amount of lithium source used and improve the rate performance and structural stability of the material. At the same time, the formation of potassium vacancies helps to accommodate lithium ions embedded back during the discharge process, thereby improving the battery's discharge specific capacity, first coulomb efficiency and cycle life.
Description
Technical Field
The invention relates to a lithium-rich manganese-based positive electrode active material and a battery, and relates to the technical field of batteries.
Background
Along with the increasing requirements of new energy automobiles on the endurance mileage, the improvement of the energy density of the battery is one of the development targets in the battery field. As one of the important components of the battery, the specific energy thereof affects the energy density of the battery, and therefore, it is urgent to develop a positive electrode active material with high specific energy.
Compared with ternary high nickel and lithium iron phosphate, the lithium-rich manganese-based positive electrode active material has higher specific energy (> 1000 Wh/Kg), but has the problems of low initial coulomb efficiency, quick capacity and voltage decay in the circulating process and the like, and the commercialization application of the lithium-rich manganese-based positive electrode active material is hindered. Meanwhile, compared with the conventional ternary positive electrode active material, the dosage of a lithium source required by the lithium-rich manganese-based positive electrode active material [ xLi 2MnO3·(1-x)LiMO2, taking x=0.5 as an example ] in the synthesis process is approximately 50%, and the cost advantage of the lithium-rich manganese-based positive electrode active material is gradually reduced along with the continuous rising of lithium price, so that the method has important significance for improving the defects of low first-week coulomb efficiency, rapid cycle attenuation and the like while reducing the dosage of lithium.
Disclosure of Invention
The invention provides a lithium-rich manganese-based positive electrode active material, which uses potassium element to occupy part of lithium sites, is beneficial to reducing the use amount of a lithium source and improving the multiplying power performance and structural stability of the material, and meanwhile, the formation of potassium vacancies is beneficial to accommodating lithium ions intercalated back in the discharging process and improving the discharging specific capacity, the first coulomb efficiency and the cycle life of a battery.
The invention also provides a battery comprising the lithium-rich manganese-based positive electrode active material.
The first aspect of the present invention provides a lithium-rich manganese-based positive electrode active material, which comprises a base particle and a coating layer coated on the outer surface of the base particle, wherein:
The molecular formula of the matrix particles is Li a-b1Kc-b2MnxCoyNizMhO2-dDd, the matrix particles have lithium vacancies and potassium vacancies, the molar quantity of the lithium vacancies is b1, and the molar quantity of the potassium vacancies is b2,1＜(a+c)≤1.5,a+c+x+y+z+h＝2,4＜a/c＜30,0.05＜(b1+b2)≤0.25,0.15<(c-b2)/(b1+b2)＜0.35,x＞(y+z+h),0≤h≤0.1,0≤d≤0.25;
M is selected from one or more of Ti, mo, te, W, nb, ta, V, sb, sn, si, zr, cr, al, la, Y, sr, mg, zn, D is selected from one or more of F, S, P, N, B;
The coating layer comprises one or more of oxides, fluorides, polyanion salts containing one or more elements of Al, co, P, B, si, zr, W, te, zn, mg, ti, ta, la, nb, sb, V, Y, ce, bi.
The lithium-rich manganese-based positive electrode active material provided by the invention comprises matrix particles, wherein the molecular formula of the matrix particles is Li a-b1Kc-b2MnxCoyNizMhO2-dDd, wherein a and c respectively represent the molar quantity of lithium ions and potassium ions in the particle material before forming lithium vacancies and potassium vacancies, and the sum (a+c) of the molar quantity of the lithium ions and the potassium ions is more than 1 and less than or equal to 1.5. The matrix particles provided by the invention occupy part of lithium sites by using potassium, can generate a lithium layer strut effect, are favorable for increasing the layer-by-layer spacing of lithium, promoting lithium ion diffusion, inhibiting transition metal ion migration and improving the multiplying power performance and structural stability of the material, and in addition, the cheaper potassium is used for replacing lithium, so that the use amount of a lithium source is reduced, the preparation cost of an anode active material is reduced, and meanwhile, in order to ensure the molar quantity of lithium ions in the matrix particles, the molar ratio a/c of the lithium ions and the potassium ions is more than 4 and less than 30.
The matrix particles provided by the invention also comprise lithium vacancies and potassium vacancies, and the formation of the potassium vacancies is favorable for accommodating lithium ions intercalated back in the discharging process, so that the specific discharge capacity, the first coulomb efficiency and the cycle life of the battery are improved, and the invention uses b1 and b2 to respectively represent the molar quantity of the lithium vacancies and the potassium vacancies. The molar quantity of Li/TM and K/TM can be calculated by the molar quantity of Li/TM and K/TM before and after the formation of the vacancy, specifically, the molar quantity of Li, K and transition metal TM in the particles before the formation of the vacancy is tested, the molar quantity of Li/TM and K/TM is calculated and is recorded as Li/TM Before the vacancy and K/TM Before the vacancy , the molar quantity of Li, K and transition metal TM in the finished positive electrode active material is tested, the molar quantity of Li/TM and K/TM is calculated and is recorded as Li/TM Finished product and K/TM Finished product , the molar quantity of Li vacancy b1 is calculated and obtained by the formula 1, the molar quantity of potassium vacancy b2 is calculated and the sum of the molar quantity of Li vacancy b1 and the molar quantity of potassium vacancy b2 is the molar quantity of total vacancy;
b1 = [ Li/TM Before the vacancy -Li/TM Finished product ] 1
B2 = [ K/TM Before the vacancy -K/TM Finished product ] formula 2.
The molar amounts of Li, K and transition metals in the particulate material before vacancy formation and the finished positive electrode active material can be obtained by ICP (Inductively coupled PLASMA MASS sputtering) test.
In order to ensure the dosage of lithium ions and the molar ratio of the total vacancies, the invention provides matrix particles in which the molar amount of the total vacancies, b1+b2, is greater than 0.05 and less than or equal to 0.25, and the molar ratio of the residual potassium ions (c-b 2) to the total vacancies, b1+b2, is greater than 0.15 and less than 0.35.
Further, in the matrix particles provided by the invention, b < 1+b2 > is more than or equal to 0.08 and less than or equal to 0.18, b < 2/(b < 1+b2) < 1.0, and the molar quantity of total vacancies and the duty ratio of potassium vacancies are limited, so that the capacity exertion is prevented from being influenced by the excessively low lithium consumption on the basis of reducing the lithium source consumption and improving the first coulombic efficiency of the positive electrode active material.
The cation doping element M provided by the invention is one or more selected from Ti, mo, te, W, nb, ta, V, sb, sn, si, zr, cr, al, la, Y, sr, mg, zn, part of cation doping elements can occupy transition metal positions, the bond energy between the cation doping elements and oxygen is higher, the oxygen is restrained from being separated to stabilize the structure, and part of cation doping elements only stay at the grain boundary, but can also play roles in refining grains and improving the interface stability. Further, the cation doping element M is selected from one or more of Nb, W, P, mo, ta.
The anion doping element D provided by the invention is one or more selected from F, S, P, N, B, and has the effects of stabilizing lattice oxygen and improving structural stability. Further, the anionic doping element D is selected from one or more of F, P, S.
It is understood that the matrix particles provided by the invention do not include the cation doping element M and the anion doping element D, or include the cation doping element M and/or the anion doping element D, i.e. the molar amount h of the cation doping element M is 0 to 0.1, the molar amount D of the anion doping element D is 0 to 0.25, and h and D may be 0 at the same time or at least one of them is greater than 0.
The surface of the substrate particle provided by the invention comprises a coating layer, the coating layer is favorable for reducing interface side reaction, improving interface stability, inhibiting oxygen release and improving the stability of the positive electrode active material in charge and discharge under high voltage, and the coating layer comprises one or more of oxide, fluoride and polyanion salt containing one or more elements of Al, co, P, B, si, zr, W, te, zn, mg, ti, ta, la, nb, sb, V, Y, ce, bi.
Further, the cladding layer includes one or more of LiAlO 2、Al2O3、AlF3、AlPO4.
In a specific embodiment, the D50 of the lithium-rich manganese-based positive electrode active material is 3 to 14 μm, and D50 refers to a particle size corresponding to a case where the cumulative particle size distribution percentage of the positive electrode active material reaches 50%, and specifically is selected from a range consisting of 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, or any two thereof, and can be obtained by a particle size analyzer test.
In a specific embodiment, the compaction density of the lithium-rich manganese-based positive electrode active material at 3.5T is 2.3-3.3 g/m 3, specifically is 2.3g/m3、2.5g/m3、2.8g/m3、3.0g/m3、3.1g/m3、3.2g/m3、3.3g/m3 or a range formed by any two of the above materials, the compaction density can be obtained through a compaction densitometer test, in the test process, a certain weight of positive electrode active material powder is added into a hard die with a fixed diameter and a fixed height, the powder is moved and deformed under the pressure of 3.5T to form a compact with a certain density and strength, and the result is calculated according to the net weight and the compression volume of the powder.
In a specific embodiment, the specific surface area of the lithium-rich manganese-based positive electrode active material is 0.2-5 m 2/g, and the specific surface area is specifically selected from the range of 0.2m2/g、0.5m2/g、0.8m2/g、1.0m2/g、1.5m2/g、2.0m2/g、2.5m2/g、3.0m2/g、3.5m2/g、4.0m2/g、4.5m2/g、5.0m2/g or any two of the specific surface area and the specific surface area can be obtained by testing by adopting a BET test method.
In a specific embodiment, the matrix particles provided by the invention are obtained by washing a matrix particle precursor, wherein the molecular formula of the matrix particle precursor is Li aKcMnxCoyNizMhO2-dDd, and an aqueous solution containing potassium ions is used in the washing process.
The matrix particle precursor refers to a particle material before formation of lithium vacancies and potassium vacancies, and is specifically obtained by performing a first sintering treatment on a first mixed material, wherein the first mixed material comprises a lithium source, a potassium source, a nickel cobalt manganese precursor, a doping source containing a cation doping element M and a doping source containing an anion doping element D.
Further, the lithium source is selected from one or more of LiCO 3、LiOH、CH3COOLi、LiNO3, the potassium source is selected from one or more of K 2CO3、KOH、KNO3、CH3 COOK, the nickel cobalt manganese precursor is selected from one or more of carbonate, hydroxide and oxalate containing nickel, cobalt and manganese elements, and further, the nickel cobalt manganese precursor is selected from carbonate Ni xCoyMnzCO3 containing nickel, cobalt and manganese elements, hydroxide Ni xCoyMnz(OH)2 containing nickel, cobalt and manganese elements, (x+y+z=1).
The cation doping source containing doping element M is selected from one or more of an oxide, hydroxide, oxyhydroxide, fluoride or polyanion salt containing cations, such as TiO2、MoO3、WO3、TeO2、Nb2O5、Ta2O5、V2O5、Sb2O5、SnO2、SiO2、ZrO2、CrO2、Al2O3、Al(OH)3、Co4O3、CoOOH、AlPO4、AlF3、La2O3、Y2O3、SrO、MgO、ZnO.
The anion doping source containing doping element D is selected from one or more of the anion containing compounds, for example ,LiF、KF、NH4F、Li2S、K2S、BN、AlN、Si3N4、NH4H2PO4、(NH4)2HPO4、Li3PO4、K3PO4.
Weighing the compounds according to the chemical formula Li aKcMnxCoyNizMhO2-dDd, uniformly mixing to obtain a first mixed material, and performing first sintering treatment on the first mixed material. It should be noted that, during the weighing process, the lithium source should be weighed excessively according to the proportion of 0-6%, so as to reduce the lithium amount error caused by volatilization of lithium and generation of residual lithium during the first sintering process.
The first sintering treatment can be performed in one high-temperature heating device of a tube furnace, a muffle furnace, a box furnace, a roller kiln, a pusher kiln and a rotary kiln, and air or oxygen is introduced at the same time, the treatment process comprises a first stage and a second stage, the temperature rising rate of the first stage is 1-5 ℃ per minute, the temperature is 400-800 ℃ and the time is 0-8 h, the temperature rising rate of the second stage is 1-5 ℃ per minute, the temperature is 800-950 ℃ and the time is 10-20 h.
After the first sintering treatment is finished, a matrix particle precursor is obtained, the matrix particle precursor is cooled to room temperature and then placed in an aqueous solution containing potassium ions, and the potassium ions are more active relative to lithium ions and can preferentially undergo proton exchange reaction with hydrogen in the aqueous solution to cause the potassium ions to be separated out, so that potassium vacancies are formed.
The potassium ion concentration and the water washing time in the aqueous solution are controlled to realize the adjustment of the potassium vacancy content, specifically, the potassium ion concentration in the aqueous solution containing potassium ions is 0.005-0.05 mol/L, the temperature of the aqueous solution is 0-25 ℃, the mass ratio of the aqueous solution to the matrix particle precursor is 1:0.5-2, and the mixing time is 1-30 min.
After the treatment is finished, solid particles are collected through solid-liquid separation, and matrix particles containing potassium vacancies and lithium vacancies are obtained after drying.
Further, the solid-liquid separation can be performed by using any one of centrifugation, suction filtration and filter pressing, and the drying temperature is 90-130 ℃.
On the basis of obtaining the matrix particles, the matrix particles can be mixed with the coating substance to obtain a second mixed material, and the second sintering treatment is carried out to obtain the finished product of the lithium-rich manganese-based positive electrode active material.
Specifically, the coating substance is an oxide, hydroxide, oxyhydroxide, fluoride, or polyanion salt containing one or more elements of Al, co, P, B, si, zr, W, te, zn, mg, ti, ta, la, nb, sb, V, Y, ce, bi, such as Al 2O3、Al(OH)3、Co4O3、CoOOH、AlPO4、AlF3, and the like.
Further, the mass of the coating substance is 0.01-1wt% of the total mass of the substrate particles and the coating substance.
The second sintering treatment can be performed in one high-temperature heating device of a tube furnace, a muffle furnace, a van furnace, a roller kiln, a pusher kiln and a rotary kiln, the second sintering treatment is performed in an air atmosphere, the temperature rising rate is 1-5 ℃ per minute, the temperature is 200-500 ℃, and the time is 3-12 hours.
Further, the temperature of the second sintering treatment is 300-400 ℃, and along with the increase of the second sintering temperature, the vacancy area gradually transits from the lamellar phase to the spinel phase, so that the structural transition trend of the inert rock salt phase is finally formed, and the comprehensive performance of the battery is affected.
It should be noted that, the nickel-cobalt-manganese precursor is generally prepared by a coprecipitation process, but because the coprecipitation process generally uses Na 2CO3 or NaOH as a precipitant, na impurities are inevitably introduced, and a hetero-phase is generated when the Na content is too high in the sintering process, the structure and the performance of the matrix particles are affected, so that the Na content in the finished lithium-manganese-rich positive electrode active material needs to be controlled to be 50-5000 ppm.
In conclusion, the lithium-rich manganese-based positive electrode active material provided by the invention uses doped element potassium to occupy lithium sites, can play a role of a lithium layer support, is beneficial to increasing the layer-to-layer distance of lithium, promoting lithium ion diffusion, inhibiting transition metal ion migration, improving rate performance and structural stability, and is beneficial to reducing the use amount of a lithium source and reducing the preparation cost of the positive electrode active material by replacing lithium with cheaper potassium.
The second aspect of the invention provides a battery comprising any of the lithium-rich manganese-based positive electrode active materials described above.
Based on the characteristics of the lithium-rich manganese-based positive electrode active material provided by the first aspect of the invention, the battery provided by the invention has good rate capability and cycle life.
In one embodiment, the battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, the positive electrode current collector can be selected from positive electrode current collectors which are conventionally used in the field, such as aluminum foils and the like, the positive electrode active material layer comprises the lithium-rich manganese-based positive electrode active material provided by the first aspect of the invention, and a conductive agent, a binder and the like, the conductive agent and the binder are not particularly selected, and can be conventionally selected in the field, for example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fibers, carbon nanotubes, single-walled carbon nanotubes, multi-arm carbon nanotubes and carbon fibers, and the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and lithium Polyacrylate (PAALi).
The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode current collector can be selected from negative electrode current collectors which are conventionally used in the field, such as copper foil and the like, the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, and the negative electrode active material can be selected from one or more of silicon, silicon carbon, siOx (0 < X < 2), lithium silicon alloy, artificial graphite, natural graphite, hard carbon, soft carbon and mesophase carbon microspheres.
The electrolyte and the diaphragm are all conventional materials in the field, and can be selected according to actual needs.
The lithium-rich manganese-based positive electrode active material provided by the invention occupies lithium sites by using K element, can play a role of a lithium layer strut effect, is beneficial to increasing the layer-to-layer distance of lithium, promoting lithium ion diffusion, inhibiting transition metal ion migration and improving rate performance and structural stability, and in addition, cheaper potassium is used for replacing lithium, so that the use amount of a lithium source is reduced, and the preparation cost of the positive electrode active material is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it will be obvious that the drawings in the following description are some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort to a person skilled in the art.
Fig. 1 is an XRD detection result of the positive electrode active material provided in example 3 and comparative example 1 of the present invention;
FIG. 2 is a scanning electron microscope image of the positive electrode active material according to example 3 of the present invention;
FIG. 3 is a scanning electron microscope image of the positive electrode active material provided in comparative example 1 of the present invention;
Fig. 4 is a cycle performance test result of a battery including the positive electrode active material provided in example 3 and comparative example 1 of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The preparation method of the lithium-rich manganese-based positive electrode active material provided by the embodiment comprises the following steps:
Uniformly mixing a lithium source, a potassium source, nb 2O5 and a nickel cobalt manganese precursor (Ni: co: mn=33:1:66 in the nickel cobalt manganese precursor) to obtain a first mixed material, placing the first mixed material into a box-type furnace, heating to 500 ℃ at a heating rate of 2 ℃ per minute under an air atmosphere, preserving heat for 5 hours, heating to 850 ℃ at a heating rate of 2 ℃ per minute, preserving heat for 12 hours, and cooling to obtain a matrix particle precursor;
mixing a matrix particle precursor with a potassium carbonate aqueous solution (the concentration of potassium ions is 0.02 mol/L) to form a suspension, stirring for 10min, carrying out suction filtration, and placing a filter cake in a blast oven at 110 ℃ to obtain matrix particles;
Uniformly mixing the matrix particles with 0.3wt% of coating substance Al 2O3, placing in a box furnace, heating to 300 ℃ at a heating rate of 2 ℃ per min under the air atmosphere, preserving heat for 8 hours, cooling and sieving to obtain the lithium-rich manganese-based anode active material.
The preparation methods of the lithium-rich manganese-based positive electrode active materials provided in examples 2 to 11 and comparative examples 1 to 6 are basically the same as example 1, except that the molar ratios of lithium ions and potassium ions added in examples 2 to 8 and comparative examples 1 to 3 are different, the molar ratios of lithium ions, potassium ions and transition metals in the matrix particle precursors are adjusted, the temperatures of the second sintering treatments are adjusted in examples 9 to 10 and comparative examples 4 to 5, and the concentrations of potassium ions in the potassium carbonate aqueous solutions are adjusted in examples 11 and comparative example 6, specifically with the differences as shown in table 1.
The molar amounts of Li, K and transition metal TM in the matrix particle precursor and the finished positive electrode active material were tested by ICP (Inductively coupled PLASMA MASS sputtering), the molar ratios of Li/TM and K/TM were calculated from the molar amounts of Li, K and TM in the matrix particle precursor, and were recorded as Li/TM Before the vacancy and K/TM Before the vacancy , the molar ratios of Li/TM and K/TM were calculated from the molar amounts of Li, K and transition metal TM in the finished positive electrode active material, and were recorded as Li/TM Finished product and K/TM Finished product , the calculation results were shown in Table 1, and the molar ratios of total vacancies and transition metal elements were calculated from formulas 1 to 2, and the calculation results were shown in Table 1.
TABLE 1
Adding the lithium-rich manganese-based positive electrode active materials provided in examples 1-11 and comparative examples 1-6, a conductive agent Super-P and an adhesive PVDF into an NMP solvent according to the ratio of 90:5:5, uniformly mixing to obtain positive electrode active material layer slurry, coating the positive electrode active material layer slurry on the surface of a positive electrode current collector aluminum foil, sequentially drying, punching and rolling to obtain a positive electrode plate, sequentially stacking a button cell stainless steel shell, the positive electrode plate, a PP diaphragm and a lithium plate, dropwise adding a certain amount of electrolyte, packaging and standing to obtain a half cell, and testing the discharge capacity, the first coulombic efficiency, the multiplying power performance, the capacity retention rate and the voltage attenuation condition of the half cell, wherein the testing method is as follows, and the testing result is shown in Table 2.
(One) 0.2C discharge capacity
And (3) after standing the assembled half battery for 5 hours, charging to 4.55V at a constant current of 0.2C, then charging to a constant voltage of 4.55V until the cut-off current is equal to 0.05C, and discharging to 2.5V at a constant current of 0.2C after standing for 5 minutes, wherein the obtained discharge capacity is the 0.2C discharge capacity.
(II) first coulombic efficiency
And (3) after standing the assembled half battery for 5 hours, charging to 4.55V by using a constant current of 0.2C, then charging to a constant voltage of 4.55V until the cut-off current is equal to 0.05C, and after standing for 5 minutes, discharging to 2.5V by using a constant current of 0.2C, and calculating by using the obtained discharge capacity/charge capacity to obtain the first coulombic efficiency.
(III) 1C/0.2C rate capability
And (3) charging and discharging the assembled half battery for 1 circle at the rate of 0.2C, and then charging and discharging for 1 circle at the rate of 1C, wherein the obtained 1C discharge capacity/0.2C discharge capacity is 1C/0.2C rate performance.
(IV) 1C cycle 100T Capacity Retention Rate
And (3) the assembled half battery is charged and discharged for 100 circles under the 1C multiplying power, and the discharge capacity of the 100 th circle/the discharge capacity of the 1 st circle is the 1C circulation 100T capacity retention rate.
(Fifth) 1C cycle 100T voltage decay
The assembled half cell was charged and discharged for 100 cycles at 1C magnification, and the average discharge voltage of the 100 th cycle-the average discharge voltage of the 1 st cycle was 1C cycle 100T voltage decay (average discharge voltage=discharge energy/discharge capacity).
Sixth material saving cost
The cost of raw materials A1 used in comparative example 1 was calculated, the cost of raw materials used in examples 1 to 11 and comparative examples 2 to 3 was A2, and the cost savings were calculated as (A1-A2)/A1 x 100%, wherein the cost of water-washed materials was negligible.
TABLE 2
According to the data provided in examples 1-8 and comparative examples 1-3, under the condition that the molar total amount of lithium ions and potassium ions is unchanged, the content of lithium ions is continuously reduced along with the continuous increase of the content of potassium ions, the material saving cost is continuously improved, the content of lithium ions in the finished lithium-rich manganese-based positive electrode active material is not obviously different from that of raw materials, but the content of residual potassium ions and the content of vacancies are gradually increased, and according to Table 2, the comprehensive performance of the battery provided in examples 1-8 is improved compared with that of comparative examples 1-3, so that the lithium-rich manganese-based positive electrode active material provided by the invention can improve the first coulombic efficiency, the specific discharge capacity, the multiplying power performance and the cycling stability of the battery while the material cost is reduced. Too low a molar amount of potassium ions in comparative example 2 resulted in higher material costs and poor battery integration, while too high a molar amount of potassium ions in comparative example 3 reduced active lithium, exhibited a low specific discharge capacity, and first coulombic efficiency exceeding 100%.
According to literature reports, for a layered positive electrode active material with vacancies, as the sintering temperature increases, the vacancy region gradually transits from the layered phase to the spinel phase, and finally the structure transition trend of an inert rock salt phase is formed, and the invention is also verified in terms of secondary sintering temperature by using examples 3, 9-10 and comparative examples 4-5, which shows that the comprehensive performance of the battery is continuously reduced as the secondary sintering temperature increases. In comparative examples 4 to 5, transition metal ion migration occurs in the layered structure having vacancies due to the excessively high secondary sintering temperature, that is, transition metal ions migrate to the lithium layer and are converted into a spinel or rock salt structure, resulting in no longer applicable lithium vacancy calculation mode.
Examples 3, 11 and comparative example 6 were subjected to gradient verification of the concentration of potassium ions in an aqueous solution containing potassium ions, and it was found that, by estimating the value of the vacancy content Va thereof, for a burned sample of the same potassium recombination amount, the K content and the vacancy content remaining after washing with water correlated with the concentration of potassium ions in the aqueous solution because the removal of potassium ions was affected by the concentration difference.
In addition, XRD and SEM test characterization are carried out on the lithium-rich manganese-based positive electrode active materials provided in the embodiment 3 and the comparative example 1, the characterization results are shown in figures 1-3, according to the results shown in figure 1, the XRD patterns of the positive electrode active materials provided in the embodiment 3 and the comparative example 1 are not obviously different, and it is shown that a good layered structure can be formed after the positive electrode active materials are compounded by using K instead of Li, according to the results shown in figures 2-3, the sphericity of the positive electrode active materials provided in the embodiment 3 is good, the surface is clean, and the appearance of the positive electrode active materials is consistent with that of the lithium-rich manganese-based positive electrode active materials provided in the prior art.
In addition, the assembled half cell was subjected to a 0.2C charge-discharge test, and the charge-discharge capacity mAh/g and the voltage V were recorded, as shown in fig. 4, and it can be seen that example 3 significantly improved the specific discharge capacity compared to comparative example 1, although the charge capacity was reduced, due to the fact that vacancies formed after the removal of potassium ions can serve as the sites for lithium ion intercalation, to accommodate more lithium ions, contributing to the improvement of the specific discharge capacity, the first coulomb efficiency and the cycle life of the cell.
It should be noted that the above embodiments are merely for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solution described in the above embodiments may be modified or some or all of the technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present invention.
Claims (10)
1. The lithium-rich manganese-based positive electrode active material is characterized by comprising base particles and a coating layer coated on the outer surfaces of the base particles, wherein:
The molecular formula of the matrix particles is Li a-b1Kc-b2MnxCoyNizMhO2-dDd, the matrix particles have lithium vacancies and potassium vacancies, the molar quantity of the lithium vacancies is b1, and the molar quantity of the potassium vacancies is b2,1＜(a+c)≤1.5,a+c+x+y+z+h＝2,4＜a/c＜30,0.05＜(b1+b2)≤0.25,0.15<(c-b2)/(b1+b2)＜0.35,x＞(y+z+h),0≤h≤0.1,0≤d≤0.25;
M is selected from one or more of Ti, mo, te, W, nb, ta, V, sb, sn, si, zr, cr, al, la, Y, sr, mg, zn, D is selected from one or more of F, S, P, N, B;
The coating layer comprises one or more of oxides, fluorides, polyanion salts containing one or more elements of Al, co, P, B, si, zr, W, te, zn, mg, ti, ta, la, nb, sb, V, Y, ce, bi.
2. The lithium-rich manganese-based positive electrode active material according to claim 1, wherein 0.08≤b1+b2≤ 0.18,0.9≤b2/(b1+b2). Ltoreq.1.0.
3. The lithium-rich manganese-based positive electrode active material according to claim 1, wherein the D50 of the lithium-rich manganese-based positive electrode active material is 3 to 14 μm.
4. The lithium-rich manganese-based positive electrode active material according to claim 1, wherein the compaction density of the lithium-rich manganese-based positive electrode active material at 3.5T is 2.3-3.3 g/m 3, and the specific surface area is 0.2-5 m 2/g.
5. The lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 4, wherein the matrix particles are obtained by washing a matrix particle precursor, the molecular formula of the matrix particle precursor is Li aKcMnxCoyNizMhO2-dDd, and an aqueous solution containing potassium ions is used in the washing process.
6. The lithium-rich manganese-based positive electrode active material according to claim 5, wherein the concentration of potassium ions in the aqueous solution containing potassium ions is 0.005-0.05 mol/L, the mass ratio of the aqueous solution to the matrix particle precursor is 1:0.5-2, the water washing temperature is 0-25 ℃, and the time is 1-30 min.
7. The lithium-rich manganese-based positive electrode active material according to claim 5, wherein the matrix particle precursor is obtained by subjecting a first mixture to a first sintering treatment, the first mixture comprising a lithium source, a potassium source, a nickel cobalt manganese precursor, a doping source containing a cation doping element M, and a doping source containing an anion doping element D;
The first sintering treatment is performed in an air or oxygen atmosphere and comprises a first stage and a second stage, wherein the temperature rising rate of the first stage is 1-5 ℃ per minute, the temperature is 400-800 ℃ and the time is 0-8 h, the temperature rising rate of the second stage is 1-5 ℃ per minute, the temperature is 800-950 ℃ and the time is 10-20 h.
8. The lithium-rich manganese-based positive electrode active material according to claim 5, wherein the lithium-rich manganese-based positive electrode active material is obtained by subjecting a second mixed material to a second sintering treatment, the second mixed material including the base particles and a coating substance;
The second sintering treatment is performed in an air atmosphere, the temperature rising rate is 1-5 ℃ per minute, the temperature is 200-500 ℃ and the time is 3-12 hours.
9. The lithium-rich manganese-based positive electrode active material according to claim 8, wherein the mass of the coating substance is 0.01 to 1wt% of the total mass of the base particles and the coating substance.
10. A battery comprising the lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 9.
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| CN112340783A (en) * | 2020-09-30 | 2021-02-09 | 宜宾锂宝新材料有限公司 | Modification method for reducing residual alkali on surface of high-nickel ternary cathode material, high-nickel ternary cathode material prepared by modification method and lithium ion battery |
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| CN112340783A (en) * | 2020-09-30 | 2021-02-09 | 宜宾锂宝新材料有限公司 | Modification method for reducing residual alkali on surface of high-nickel ternary cathode material, high-nickel ternary cathode material prepared by modification method and lithium ion battery |
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