WO2022134541A1 - Positive electrode material, preparation method therefor, and electrochemical device - Google Patents

Abstract

Provided in the present application are a positive electrode material, a preparation method therefor, and an electrochemical device. The positive electrode material comprises lithium cobalt oxide having a P6₃mc crystal structure, and lithium manganese oxide having a C2/m crystal structure; in an XRD graph of the positive electrode material, the characteristic peak-to-peak intensity located within a range of 17°-19° is I_A, and the characteristic peak-to-peak intensity located within a range of 19°-22° is I_B, wherein 0.1≤I_B/I_A≤0.5. The electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the positive electrode material of the present application. The positive electrode material has excellent structural stability, high capacity characteristics, and cycle stability.

Description

Positive electrode material, preparation method thereof, and electrochemical device technical field

The present application relates to the field of electrochemistry, and in particular, to a positive electrode material, a preparation method thereof, and an electrochemical device.

Background technique

Electrochemical devices, such as lithium-ion batteries, are widely used in portable electronic products, electric transportation, national defense and aviation, energy storage and other fields due to their advantages of high energy density, good cycle performance, environmental protection, safety and no memory effect. In order to meet the needs of social development, it is an urgent problem to seek lithium-ion batteries with higher energy density and power density, which requires the cathode materials used to have higher specific capacity and higher voltage platform.

At present, the most commercialized cathode material in the 3C field is LiCoO ₂ cathode material, which has an R-3m phase structure and a theoretical capacity of 273.8mAh/g. It has good cycle and safety performance, high compaction density and simple preparation process. . Since its commercialization by Sony in 1991, LiCoO ₂ cathode materials have dominated the lithium-ion battery materials market. In order to obtain higher specific energy, LiCoO ₂ is developing towards high voltage (>4.6Vvs.Li/Li ⁺ ). However, when LiCoO ₂ is charged to 4.5V, the capacity can only reach 190mAh/g. People try to achieve higher specific capacity by extracting more Li ⁺ from the crystal structure, but as the voltage is further increased, Li ⁺ is extracted in large quantities, and the crystal structure will undergo a series of irreversible phase transitions (O3 to H1-3 , H1-3 to O1), which greatly reduces the material cycle performance and safety performance. In addition, the interface side reactions are intensified under high voltage, and the Co metal is seriously dissolved, and the high-voltage electrolyte technology is difficult to match. The decomposition and failure of conventional electrolytes at high voltage are accelerated, so the capacity decay is very serious.

At present, metal cations such as Al, Mg, Ti, Zn, and Ni are generally used in the industry and scientific research community for bulk doping to improve the structural stability of R-3m phase LiCoO ₂ . The doping of most elements improves the structural stability of the material by delaying the irreversible phase transition, but the effect of this method on the structure stability is not obvious at voltages higher than 4.6V. In addition, as the doping amount increases, the theoretical capacity loss will increase. Therefore, there is an urgent need to find a cathode material for lithium-ion batteries with high specific capacity, high voltage platform, good structural reversibility, and interface stability at high voltage.

SUMMARY OF THE INVENTION

In view of the problems existing in the background art, the purpose of the present application is to provide a positive electrode material, which has good interface stability, high capacity and cycle stability.

In some embodiments, the present application provides a composite positive electrode material, including lithium cobalt oxide with a P6 ₃ mc crystal structure and lithium manganese oxide with a C2/m crystal structure; in the XRD pattern of the positive electrode material, it is located at 17° The characteristic peak intensity in the range of -19° is I _A , and the characteristic peak intensity in the range of 19°-22° is I _B , _0.1≤IB / _IA≤0.5 .

In some embodiments, the average particle diameter D1 of the lithium cobalt oxide having the P6 ₃ mc crystal structure and the average particle diameter D2 of the lithium manganese oxide having the C2/m crystal structure satisfy: 0.1≦D2/D1≦0.5.

In some embodiments, the average particle size D1 is 5 μm to 30 μm; the average particle size D2 is 1 μm to 5 μm.

In some embodiments, there are voids and/or cracks within the lithium cobalt oxide.

In some embodiments, the lithium cobalt oxide includes Li and Co elements and optionally includes at least one of M element or Na element, wherein M element includes Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of Cu, Nb, Cr, Y or Zr; the sum of the molar content of Co and M elements is n _Co+M , the molar content of Li element is n _Li , and the ratio x of n _Li to n _Co+M is 0.6<x<0.95, the molar content of M element is n _M , the ratio of n _M to n _Co+M y is 0≤y<0.15, the molar content of Na element is n _Na , the ratio of n _Na to n _Co+M z is 0≤z<0.03.

In some embodiments, the lithium cobalt oxide includes Li _x Na _z Co _{1-y My} O ₂ , 0.6<x<0.95, 0≤y<0.15, 0≤z<0.03, and M includes Al, Mg, Ti, At least one of Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y, and Zr.

In some embodiments, the lithium manganese oxide includes Li _2±h Mn _1-g T _g O _k , 0≤h≤1, 0≤g≤0.5, 0<k<5, T includes Ti, Sn, Ru, At least one of Ni, Co and Al.

In some embodiments, the present application further provides an electrochemical device including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet includes the positive electrode material of the present application.

In some embodiments, the electrolyte includes a carboxylate.

In some embodiments, the carboxylates include at least one of the following: pentasodium diethylenetriaminepentaacetate, sodium nitrilotriacetate, sodium edetate, sodium gluconate.

In some embodiments, the mass percentage content of the carboxylate is 0.01% to 0.15% based on the mass of the electrolyte.

The beneficial effects of the present application are as follows: the cathode material provided by the present application has good interface stability, high capacity characteristics and cycle stability.

Detailed ways

It is to be understood that the disclosed embodiments are merely exemplary of the application, which may be embodied in various forms, and therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a A representative basis is provided for teaching one of ordinary skill in the art to variously implement the application.

In the description of this application, terms and professional terms that are not explicitly described are common knowledge of those skilled in the art, and methods that are not explicitly described are conventional methods known to those skilled in the art.

In the description of this application, the "average particle size" means that the material powder is photographed and observed by a SEM scanning electron microscope, and then, 10 material particles are randomly selected from the SEM photograph using image analysis software, and these The respective areas of the material particles, and then, assuming that the material particles are spherical, the respective particle diameters R (diameter) are obtained by the following formula:

R=2×(S/π) ^1/2 ; wherein, S is the area of the material particle;

The process of obtaining the particle diameter R of the material particles was performed on 10 SEM images, and the particle diameters of the obtained 100 (10×10) material particles were arithmetically averaged to obtain the average particle diameter of the material particles.

The positive electrode material of the present application, the preparation method thereof, and the electrochemical device of the present application will be described in detail below.

[Positive electrode material]

In some embodiments, the cathode material of the present application includes lithium cobalt oxide with a P6 ₃ mc crystal structure and lithium manganese oxide with a C2/m crystal structure; in the XRD pattern of the cathode material, it is located in the range of 17°-19° The peak intensity of the characteristic peak (P6 ₃ mc structure peak) within 19°-22° is I _A , and the characteristic peak intensity (C2/m peak) in the range of 19°-22° is I _B , _0.1≤IB / _IA≤0.5 .

Lithium cobalt oxide with P6 ₃ mc crystal structure has a stable oxygen structure, is not easy to release oxygen at high voltage, has a stable structure, and thus has good cycle performance. In addition, it has lithium ion accepting ability, which can absorb additional lithium ions. The theoretical capacity (>300mAh/g) of lithium manganese oxide with C2/m crystal structure is higher _than that of P6 ₃ mc cathode material. The lithium cobalt oxides of mc are compounded together, which can well combine the advantages of the two materials and solve their respective shortcomings. In the XRD pattern of the cathode material, the characteristic peak intensity (P63mc structure peak) in the range of 17°-19° is _IA , and the characteristic peak intensity (C2/m peak) in the range of 19°-22° is When I _B , 0.1<I _B /I _A ≤ 0.5, on the one hand, there is a sufficient amount of lithium manganese oxide in the positive electrode material to provide lithium ions for the lithium cobalt oxide with P6 ₃ mc crystal structure, and to supplement the formation of the SEI film. On the other hand, the excess of lithium manganese oxide is avoided, thereby greatly improving the cycle stability of the cathode material.

In some embodiments, the average particle size D1 of the lithium cobalt oxide having the P6 ₃ mc structure and the average particle size D2 of the lithium manganese oxide having the C2/m crystal structure satisfy: 0.1≦D2/D1≦0.5. Satisfying the above particle size relationship, the small particles of lithium manganese oxide that play the role of supplementing lithium can mainly exist in the pores between the large particle size lithium cobalt oxides, reducing the change of the lithium manganese oxide structure due to the cycle process. It adversely affects the active connections between Li-Co oxides, thereby maintaining high cycling stability.

In some embodiments, the average particle size D1 is 5 μm to 30 μm; the average particle size D2 is 1 μm to 5 μm.

In some embodiments, there are voids and/or cracks inside the lithium cobalt oxide having the P6 ₃ mc structure. In some embodiments, the method for confirming holes and gaps includes: using an ion polishing machine (JEOL-IB-09010CP) to process the material to obtain a cross-section; using SEM to photograph the cross-section with a shooting magnification of not less than 5.0K to obtain Grain images, in which closed areas of a different color than the surrounding are holes and cracks. The closed area refers to an area enclosed by closed lines in the image, and the line connecting any point inside the closed area and any point outside the area intersects the boundary of the area. In the image, connect any two points of a closed curve, the longest distance is the longest axis, and the shortest distance is the shortest axis. Among them, the hole selection requirements may be: in a single particle in the image, the ratio of the longest axis of the closed area to the longest axis of the particle is not higher than 10%, and the difference between the longest axis and the shortest axis of the closed area is less than 0.5 microns; The requirements for the selection of cracks can be as follows: the ratio of the longest axis of the closed region in a single particle to the longest axis of the particle is not less than 70%.

In some embodiments, the lithium cobalt oxide includes Li and Co elements and optionally includes at least one of M element or Na element, wherein M element includes Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of Cu, Nb, Cr, Y or Zr; the sum of the molar content of Co and M elements is n _Co+M , the molar content of Li element is n _Li , and the ratio x of n _Li to n _Co+M is 0.6<x<0.95, the molar content of M element is n _M , the ratio of n _M to n _Co+M y is 0≤y<0.15, the molar content of Na element is n _Na , the ratio of n _Na to n _Co+M z is 0≤z<0.03.

In some embodiments, the lithium cobalt oxide includes Li _x Na _z Co _{1-y My} O ₂ , 0.6<x<0.95, 0≤y<0.15, 0≤z<0.03, and M includes Al, Mg, Ti, At least one of Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y, and Zr.

In some embodiments, the lithium manganese oxide includes Li _2±h Mn _1-g T _g O _k , 0≤h≤1, 0≤g≤0.5, 0<k<5, T includes Ti, Sn, Ru, At least one of Ni, Co and Al.

[Preparation method of positive electrode material]

Next, the method for preparing the positive electrode material of the present application will be described.

In some embodiments, the method for preparing the positive electrode material of the present application comprises the steps of:

a. Dissolve soluble Co salts (such as cobalt nitrate) and M salts (such as M nitrates) into the solvent according to the molar ratio of Co:M=(1-y):y, add precipitating agent and complexing agent, adjust pH , to form a precipitate; then the precipitate is sintered and ground to _obtain (Co _{1- y My ) 3 O 4 powder ;} : The molar ratio of (1-y) is reacted at 700°C-900°C in an air atmosphere to obtain Nan Co _{1-y My} O ₂ , where _0≤y <0.15, 0.6≤n<1;

b. Use the _Nan Co _{1-y My} O ₂ obtained in step a as the precursor, mix it with the lithium-containing molten salt uniformly, and react at 200°C-400°C in an air atmosphere. After the reaction is completed, the reactant is subjected to Deionized water was washed several times, and after the molten salt was cleaned, the powder was dried to obtain Li _x Na _z Co _{1-y My} O ₂ with a hexagonal close-packed (HCP) oxygen structure, where 0.6<x<0.85, 0 ≤y<0.15, 0≤z<0.03;

c. Mix the lithium salt and M and N salts or M and N oxides according to the molar ratio of Li:Mn:N=2+h:1:g, and carry out one-step reaction sintering at 700℃-900℃ in an air atmosphere Li _{2 ±h} Mn _1-g N _g O _k is obtained, wherein 0≤h≤1, 0≤g≤0.5, and 0<k<5.

d. Mix the products obtained in step b and step c uniformly according to a certain proportion to obtain the positive electrode material of the present application.

In some embodiments, in step a, the M element is selected from at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y, and Zr.

In some embodiments, in step a, the precipitating agent comprises sodium carbonate.

In some embodiments, in step a, the complexing agent comprises aqueous ammonia.

In some embodiments, in step a, the pH is 5-9.

In some embodiments, in step c, the T element includes at least one of Ti, Sn, Ru, Ni, Co, and Al.

In some embodiments, in step d, the mass ratio of the product obtained in step c mixed with the product obtained in step b is m, and 0<m≤0.2.

[Electrochemical device]

Finally, the electrochemical device of the present application will be described.

The electrochemical device of the present application is, for example, a primary battery or a secondary battery. The secondary battery is, for example, a lithium secondary battery, and the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In some embodiments, the electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

<Positive electrode>

The positive electrode sheet is known in the art as a positive electrode sheet that can be used in electrochemical devices. In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. In some embodiments, the positive electrode sheet includes the positive electrode material described above in the present application.

In some embodiments, the structure of the positive electrode sheet is known in the art as the structure of the positive electrode sheet that can be used in an electrochemical device.

In some embodiments, the preparation method of the positive electrode sheet is known in the art and can be used for the preparation of the positive electrode sheet of the electrochemical device. In some embodiments, in the preparation of the positive electrode slurry, a positive electrode active material, a binder, and a conductive material and a thickener are added as required, and then the positive electrode slurry is dissolved or dispersed in a solvent. The solvent is evaporated and removed during the drying process. The solvent is known in the art and can be used as the positive electrode active material layer, such as but not limited to N-methylpyrrolidone (NMP).

<Negative electrode>

In some embodiments, the electrochemical devices of the present application include a negative electrode sheet. The negative electrode sheet is a negative electrode sheet known in the art that can be used in an electrochemical device. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. In some embodiments, the anode active material layer includes an anode active material and an anode binder.

The negative electrode active material can be selected from various conventionally known materials that can be used as negative electrode active materials of electrochemical devices that can intercalate and deintercalate active ions or conventionally known materials capable of doping and dedoping active ions. substance.

In some embodiments, the negative active material includes at least one of lithium metal, lithium metal alloy, transition metal oxide, carbon material, and silicon-based material.

In some embodiments, the anode binder may include various polymeric binders.

In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent. The negative electrode conductive agent is used to provide conductivity for the negative electrode and can improve the conductivity of the negative electrode. The negative electrode conductive agent is a conductive material known in the art that can be used as the negative electrode active material layer. The negative electrode conductive agent may be selected from any conductive material as long as it does not cause chemical changes.

In some embodiments, the structure of the negative electrode sheet is known in the art as the structure of the negative electrode sheet that can be used in an electrochemical device.

In some embodiments, the preparation method of the negative electrode sheet is known in the art for the preparation method of the negative electrode sheet that can be used in an electrochemical device. In some embodiments, in the preparation of negative electrode slurry, negative electrode active material and binder are usually added, and conductive material and thickener are added as required, and then dissolved or dispersed in a solvent to prepare negative electrode slurry. The solvent is evaporated and removed during the drying process. The solvent is known in the art and can be used as the negative electrode active material layer, and the solvent is, for example, but not limited to, water. Thickeners are known in the art and can be used as a thickener for the negative active material layer, such as, but not limited to, sodium carboxymethylcellulose.

<Isolation film>

In some embodiments, the electrochemical devices of the present application include a separator. The separator is a separator known in the art that can be used in electrochemical devices, such as, but not limited to, a polyolefin-based porous membrane. In some embodiments, the polyolefin-based porous film comprises polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methyl methacrylate Monolayer or multilayer film composed of one or more of ester copolymers.

The present application has no particular limitations on the shape and thickness of the separator. The preparation method of the separator is known in the art and can be used for the preparation of the separator of the electrochemical device.

<Electrolyte>

In some embodiments, the electrolyte includes an electrolyte salt. Electrolyte salts are those known to those skilled in the art that are suitable for use in electrochemical devices. Appropriate electrolyte salts can be selected for different electrochemical devices. For example, for lithium ion batteries, lithium salts are generally used as electrolyte salts.

In some embodiments, the electrolyte further includes an organic solvent. The organic solvent is an organic solvent known to those skilled in the art and suitable for electrochemical devices, for example, a non-aqueous organic solvent is generally used. In some embodiments, the non-aqueous organic solvent includes at least one of carbonate-based solvents, carboxylate-based solvents, ether-based solvents, sulfone-based solvents, or other aprotic solvents.

In some embodiments, the electrolyte further includes additives. The additives are known in the art and are suitable for electrochemical devices, and can be added according to the required performance of the electrochemical device. In some embodiments, the additive comprises a carboxylate. In some embodiments, the carboxylate comprises at least one of pentasodium diethylenetriaminepentaacetate, sodium nitrilotriacetate, sodium edetate, and sodium gluconate. In some embodiments, based on the mass of the electrolyte, the mass percentage of the carboxylate is 0.01%-0.15%. In some embodiments, based on the mass of the electrolyte, the mass percentage of the carboxylate may be 0.02%, 0.03%, 0.05%, 0.07%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%.

The configuration of the electrolyte can be prepared by methods known to those skilled in the art, and its composition can be selected according to actual needs.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In the following examples and comparative examples, the reagents, materials, etc. used can be obtained commercially or synthetically unless otherwise specified.

The lithium ion batteries of the examples and comparative examples were prepared according to the following methods.

(1) Preparation of negative electrode sheet:

The negative active material artificial graphite, binder styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a weight ratio of 96:2:2 and dispersed in deionized water to form a slurry. After stirring evenly, it is coated on copper with a thickness of 6 μm. The foil negative electrode current collector is dried to form a negative electrode active material layer, and is dried and cold pressed to obtain a negative electrode sheet.

(2) Preparation of positive electrode sheet:

A lithium cobalt oxide having a P6 ₃ mc crystal structure and a lithium manganese oxide having a C2/m crystal structure satisfying the compositional characteristics in Tables 1-4 were mixed as positive electrode materials. Then, the positive electrode material, conductive carbon black and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in the N-methylpyrrolidone solvent system in a mass ratio of 98:1:1 to obtain a positive electrode slurry, which is coated with On the aluminum foil of 12 μm, it was dried and sliced to obtain a positive electrode sheet.

(3) Preparation of isolation film:

A polyethylene porous polymer film with a thickness of 8 μm was used as the separator.

(4) Preparation of electrolyte:

In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate (1.15 mol/L) and a non-aqueous organic solvent (its composition is ethylene carbonate EC: propylene carbonate PC: diethyl carbonate DEC=1:1:1, weight ratio) mixed to obtain Example 1-1 to Example 1-16, Comparative Example 1-1 to Comparative Example 1-6, Example 2-1 to Example 2-5, Example 3-1 to Example 3- 3 and the base electrolyte used in Comparative Examples 4-2. The electrolytes used in Examples 4-1 to 4-7 and Comparative Example 4-1 were obtained by adding additives with corresponding contents on the basis of the above-mentioned basic electrolyte.

(5) Preparation of lithium ion battery:

The positive electrode sheet, the separator film and the negative electrode sheet are stacked in sequence, so that the separator film is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and the electrode assembly is obtained by winding. The electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80 °C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and shaping.

Next, the performance testing process of the lithium-ion battery is described.

First-round discharge capacity and cycle performance test: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged with a constant current of 0.5C to a voltage of 4.8V, then left for 5 minutes, and then discharged with a constant current of 0.5C To the voltage of 3.0V, let stand for 5min, this is a cycle charge and discharge process, the discharge capacity this time is recorded as the first cycle discharge capacity. The lithium-ion battery is subjected to N-cycle charge-discharge test according to the above method, and the discharge capacity of the N-cycle cycle is obtained by detection. The capacity retention rate (%) of the lithium-ion battery after N cycles = the discharge capacity of the Nth cycle/the discharge capacity of the first cycle × 100%.

The relevant parameters of the lithium ion batteries of the examples and comparative examples and the performance test results of the lithium ion batteries are shown in Table 1-Table 4.

Table 1 shows the effect of the composition of the cathode material and the peak intensity ratio on the performance of the lithium ion battery.

Table 2 shows the effect of the particle size relationship between lithium cobalt oxide with P6 ₃ mc crystal structure and lithium manganese oxide with C2/m crystal structure on the performance of lithium ion batteries.

Table ₃ demonstrates the effect of the void/crack structure of LiCoO with P63mc crystal structure on the performance of Li-ion batteries.

Table 4 shows the effect of the content of carboxylate in the electrolyte on the performance of Li-ion batteries.

By comparing Examples 1-1 to 1-16 and Comparative Examples 1-1 to 1-6 in Table 1, it can be seen that in the XRD pattern of the positive electrode material, when _0.1≤IB / _IA≤0.5 , compared with For Comparative Examples 1-1 to 1-4 without lithium manganese oxide, while maintaining a better cycle capacity retention rate, the discharge capacity in the first cycle was greatly improved; compared with the Comparative Examples with I _B /I _A >0.5 1-5 to 1-6, the cycle capacity retention is more excellent. This is because, _{0.1≤I B} /IA ≤0.5 is satisfied, on the one hand, the positive electrode material has a sufficient amount of lithium manganese oxide to provide lithium ions for the lithium cobalt oxide having the P6 ₃ mc crystal structure, and supplement the formation of SEI On the other hand, it can avoid too much unstable C2/m crystal structure, thus greatly reducing the cycle stability of the cathode material.

Table 2

By comparing Examples 2-1 to 2-5 in Table 2, it can be seen that when the particle size relationship between the lithium cobalt oxide having the P6 ₃ mc crystal structure and the lithium manganese oxide having the C2/m crystal structure satisfies 0.1≤D2 /D1≤0.5, the lithium-ion battery can have a more excellent cycle capacity retention rate. This is because: the small particles of lithium manganese oxide that play the role of supplementing lithium can mainly exist in the pores between the large particle size lithium cobalt oxides, reducing the effect of lithium manganese oxide on lithium cobalt due to the change of its own structure during the cycle process. Active linkages between oxides adversely affect maintaining high cycling stability.

table 3

By comparing Examples 3-1 to 3-3 in Table 3, it can be seen that the lithium cobalt oxide with the P6 ₃ mc crystal structure has both a hole and a crack structure. On the one hand, it can promote the extraction of lithium ions inside the active material, thereby greatly improving the The first cycle discharge capacity of lithium-ion batteries; on the other hand, the structure of pores and cracks can provide a buffer for stress and strain during cycling, improving the cycling stability of lithium-ion batteries.

Table 4

By comparing Examples 4-1 to 4-7 and Comparative Examples 4-1 to 4-2 in Table 4, it can be seen that adding an appropriate amount of carboxylate to the electrolyte can greatly improve the cycle capacity retention rate of lithium ion batteries. This is because an appropriate amount of carboxylate can stabilize transition metals such as Mn in the cathode material, thereby improving the cycling stability of Li-ion batteries.

The above is only an example of the present application, and is not intended to limit the present application in any form. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Within the scope of the technical solution of the present application, any changes or modifications made by using the technical content disclosed above are equivalent to equivalent implementation cases, and are all within the scope of the technical solution of the present application.

Claims (10)

1. A positive electrode material, characterized in that it comprises lithium cobalt oxide with a P6 ₃ mc crystal structure and a lithium manganese oxide with a C2/m crystal structure; in the XRD pattern of the positive electrode material, it is located in the range of 17°-19° The peak intensity of the characteristic peak within 19°-22° is _IB , and _{0.1≤IB / IA≤0.5} .
2. The positive electrode material according to claim 1, wherein the average particle size D1 of the lithium cobalt oxide having a P6 ₃ mc crystal structure and the average particle size D1 of the lithium manganese oxide having a C2/m crystal structure D2 satisfies: 0.1≤D2/D1≤0.5.
3. The positive electrode material according to claim 2, wherein the average particle size D1 is 5 μm to 30 μm; the average particle size D2 is 1 μm to 5 μm.
4. The cathode material according to claim 1, wherein there are holes and/or cracks inside the lithium cobalt oxide.
5. The positive electrode material according to claim 1, wherein the positive electrode material satisfies at least one of the following conditions:

   a) The lithium cobalt oxide includes Li and Co elements and optionally at least one of M element or Na element, wherein M element includes Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, At least one of Nb, Cr, Y or Zr; the sum of the molar contents of the Co and M elements is n _Co+M , the molar content of the Li element is n _Li , the n _Li and the n _Co The ratio x of _+M is 0.6<x<0.95, the molar content of the M element is n _M , the ratio y of the n _M to the n _Co+M is 0≤y<0.15, the mole of the Na element The content is n _Na , and the ratio z of the n _Na to the n _Co+M is 0≤z<0.03;

   b) The lithium manganese oxide includes Li _2±h Mn _1-g T _g O _k , 0≤h≤1, 0≤g≤0.5, 0<k<5, T includes Ti, Sn, Ru, Ni, At least one of Co and Al.
6. The cathode material according to claim 5, wherein the lithium cobalt oxide comprises Li _x Na _z Co _{1-y My} O ₂ , 0.6<x<0.95, 0≤y<0.15, 0≤z< 0.03, M includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y, and Zr.
7. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprising the positive electrode material according to any one of claims 1-6.
8. The electrochemical device of claim 7, wherein the electrolyte includes a carboxylate.
9. The electrochemical device of claim 8, wherein the carboxylate comprises at least one of the following:

   Pentasodium Diethylenetriaminepentaacetate, Sodium Nitrilotriacetate, Sodium EDTA, Sodium Gluconate.
10. The electrochemical device according to claim 8, wherein the mass percentage content of the carboxylate is 0.01% to 0.15% based on the mass of the electrolyte.