A composite positive electrode material and its preparation method and application

Abstract

The present invention provides a composite positive electrode material, a preparation method and an application thereof. The composite positive electrode material comprises a positive electrode material core and a composite coating layer arranged on the surface of the positive electrode material core. The composite coating layer is obtained by a chemical addition reaction of a polyphosphate monoester compound and a polyepoxy compound on the surface of the positive electrode active material particles. In the composite positive electrode material of the present invention, the polyphosphate monoester compound and the polyepoxy compound are in situ polymerized on the surface of the positive electrode active material particles to form a coating layer. The coating layer can effectively seal the surface of the positive electrode active material particles when the positive electrode active material is at a high temperature, and effectively alleviate the contact between the positive electrode active material and the electrolyte or the negative electrode material, reducing the occurrence of side reactions, thereby providing excellent safety performance for the positive electrode material and its lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries and relates to a composite positive electrode material and a preparation method and application thereof. Background Art

[0002] Currently, lithium-ion batteries are increasingly pursuing high energy density and long-term cycle stability. However, lithium-ion batteries assembled with liquid electrolytes are prone to thermal runaway, which can lead to safety issues such as fire and even explosion. Safety has become a key obstacle to the development of lithium-ion batteries. Under conditions such as overcharging, overheating, extrusion, impact, or short circuit, the solid electrolyte passivation film on the negative electrode side is unstable and easily decomposes under thermal conditions. This causes the liquid electrolyte to come into direct contact with the negative electrode material, resulting in an exothermic reaction and increasing the internal temperature of the lithium-ion battery. The continued rise in temperature causes the positive electrode material to decompose and release heat, releasing oxygen and other combustion-supporting gases, which further react with the electrolyte in an exothermic reaction. This rapid generation of heat causes the lithium-ion battery to generate heat faster than it dissipates, leading to thermal runaway and ultimately fire and explosion.

[0003] CN114335420A discloses a lithium-replenishing safety coating, a positive electrode plate and a lithium-ion battery. The lithium-replenishing safety coating comprises a pore-forming agent, a binder, an inorganic filler and a conductive agent; the pore-forming agent comprises a self-sacrificial lithium salt.

[0004] CN106410268A discloses a multi-coating intelligent high-safety polymer lithium-ion secondary battery, including a negative electrode sheet, a positive electrode sheet, a polyvinylidene fluoride coated diaphragm paper, a colloidal electrolyte and a shell. The positive electrode sheet contains a temperature-controlled intelligent variable impedance coating; the negative electrode sheet and the positive electrode sheet are respectively stacked and arranged on both sides of the polyvinylidene fluoride coated diaphragm paper. The stacked negative electrode sheet, polyvinylidene fluoride coated diaphragm paper, and positive electrode sheet are wound to form a battery core. After the battery core is injected with electrolyte, it is thermally polymerized to form a colloidal electrolyte. The negative electrode sheet and the positive electrode sheet in the battery core are adhered to both sides of the polyvinylidene fluoride coated diaphragm paper to form a non-liquid polymer battery core. The battery core and the colloidal electrolyte are located in the shell.

[0005] In order to improve the safety of lithium-ion batteries, the above scheme adds a safety coating on the surface of the positive or negative electrode to absorb excess heat inside the lithium-ion battery. The main components of the safety coating are nano-inorganic particles and organic binders. The interface contact impedance between the safety coating and the electrode is usually large, which causes a large loss in the cycle life of the lithium-ion battery. At the same time, due to the rapid increase in the internal temperature of the lithium-ion battery, the side reactions involving the organic binder increase, and the safety coating structure is prone to collapse and loses its protective function. Summary of the Invention

[0006] The object of the present invention is to provide a composite positive electrode material, a preparation method and an application thereof. In the composite positive electrode material of the present invention, a polyphosphate monoester compound and a polyepoxide compound are in situ polymerized on the surface of the positive electrode active material particles to form a coating layer. The coating layer can effectively seal the surface of the positive electrode active material particles when the positive electrode active material is at a high temperature, and effectively alleviate the contact between the positive electrode active material and the electrolyte or the negative electrode material, reduce the occurrence of side reactions, and thus provide excellent safety performance for the positive electrode material and its lithium-ion battery.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a composite positive electrode material, comprising a positive electrode material core and a composite coating layer arranged on the surface of the positive electrode material core, wherein the composite coating layer is obtained by a chemical addition reaction of a polybasic phosphate monoester compound and a polybasic epoxide compound on the surface of the positive electrode active material particles, wherein the polybasic phosphate monoester compound includes a compound containing two or more polybasic phosphate monoester structures, and the polybasic epoxide compound includes a compound containing two or more three-membered cyclic ether structures.

[0009] In the composite material described in the present invention, the reaction of the polyphosphate monoester compound and the polyepoxy compound on the surface of the positive electrode active material particles is a multi-stage reaction. The first-stage reaction is the modification treatment of the polyphosphate monoester compound and the polyepoxy compound on the surface of the positive electrode active material particles, fixing the safety component on the surface of the positive electrode active material particles. When the positive electrode active material is at a high temperature, the polyphosphate monoester compound and the polyepoxy compound can quickly undergo a secondary curing reaction and seal the surface of the positive electrode active material particles, preventing the positive electrode active material from contacting the electrolyte or the negative electrode material, and reducing the occurrence of side reactions. When the temperature to which the positive electrode active material is subjected is further increased, the reaction product of the polyphosphate monoester compound and the polyepoxy compound will undergo dehydration and carbonization, forming a coke layer on the surface of the positive electrode active material particles, making it difficult for heat to be transferred to each other, and the coke layer can prevent the oxygen released by the decomposition of the positive electrode active material from entering the adjacent combustion area, thereby alleviating the thermal runaway behavior of the lithium-ion battery.

[0010] Preferably, the structural formula of the phosphate monoester structure is as shown in Formula I:

[0011]

[0012] Preferably, the polyphosphate monoester compound includes any one of propylene diphosphate, bisphenol A bis(diphenyl phosphate), pentaerythritol phosphate or diethylstilbestrol diphosphate, or a combination of at least two thereof.

[0013] Preferably, the structural formula of the three-membered cyclic ether structure is as shown in Formula II:

[0014]

[0015] Preferably, the polyvalent epoxy compound includes any one or a combination of at least two of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, isocyanuric acid triglycidyl ether, trimethylolethane triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether or epoxy resin.

[0016] Preferably, the positive electrode material core includes any one or a combination of at least two of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide or lithium-rich manganese-based positive electrode materials.

[0017] Preferably, the particle size of the core of the positive electrode material is 1 to 10 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm or 10 μm.

[0018] Preferably, the specific surface area of ​​the cathode material core is 0.1 to 1 m 2 / g, for example: 0.1m 2 / g, 0.2m 2 / g, 0.5m 2 / g, 0.8m 2 / g or 1m 2 / g, etc.

[0019] In a second aspect, the present invention provides a method for preparing the composite positive electrode material as described in the first aspect, the preparation method comprising the following steps:

[0020] (1) mixing a polybasic phosphate monoester compound, a positive electrode active material, and a solvent to obtain a mixed solution A, and mixing a polybasic epoxy compound and a solvent to obtain a mixed solution B;

[0021] (2) After heating the mixed solution A, the mixed solution B is added dropwise to the mixed solution A to react to obtain the composite positive electrode material.

[0022] Compared with the traditional direct addition method, the method of the present invention is more conducive to the uniform distribution of the polyphosphate monoester compound and the polyepoxide compound on the surface of the positive electrode active material particles, ensuring the timely response of the secondary curing reaction without affecting the basic performance of the positive electrode active material; at the same time, the process conditions of in-situ polymerization coating can be completed under conventional conditions, while other forms of coating (such as carbon coating, vapor deposition coating, etc.) usually require high-temperature sintering, high process energy consumption, and are not conducive to large-scale production and preparation.

[0023] Preferably, the mass ratio of the total mass of the polyvalent phosphate monoester compound and the polyvalent epoxy compound to the positive electrode active material in step (1) is (1-20):100, for example: 1:100, 5:100, 10:100, 15:100 or 20:100, etc.

[0024] Preferably, in step (1), the molar ratio of the phosphate monoester structure of the polyvalent phosphate monoester compound to the three-membered cyclic ether structure of the polyvalent epoxy compound is k, 0<k<1.

[0025] Preferably, the solvent includes any one or a combination of at least two of ethanol, n-butanol, acetone, dimethyl carbonate, ethyl methyl carbonate, N,N-dimethylformamide or N-methylpyrrolidone.

[0026] Preferably, stirring is performed while adding dropwise in step (2).

[0027] Preferably, the stirring speed is 1000-5000 rpm, for example, 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm or 5000 rpm.

[0028] Preferably, the reaction temperature is 25-120°C, for example, 25°C, 50°C, 80°C, 100°C or 120°C.

[0029] Preferably, the reaction time is 2 to 8 hours, for example, 2 hours, 3 hours, 5 hours, 6 hours or 8 hours.

[0030] In a third aspect, the present invention provides a positive electrode plate, which comprises the composite positive electrode material as described in the first aspect.

[0031] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet as described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] After the safety components polyphosphate monoester compound and polyepoxide compound used in the present invention complete the primary reaction on the surface of the positive electrode active material particles, there will be evenly distributed polar groups on the surface of the positive electrode active material particles. These groups provide electrostatic repulsion between the positive electrode active material particles, which is beneficial to alleviate the secondary agglomeration of the active material particles during the positive electrode production process. At the same time, it is beneficial to the contact between the active material and the conductive agent and binder, which can play a positive effect on reducing the electrode impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an SEM image of the composite positive electrode material described in Example 1 of the present invention.

[0035] Figure 2 This is an SEM image of the composite positive electrode material described in Comparative Example 1.

[0036] Figure 3 This is an SEM image of the composite positive electrode material described in Comparative Example 2.

[0037] Figure 4 3 is a comparison chart of the cycle performance of the positive electrode materials described in Example 1, Example 7 and Example 8 and Comparative Examples 1-3.

[0038] Figure 5 It is a comparison diagram of the DSC curves of the delithiation positive electrodes prepared by the positive electrode materials described in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Example 1

[0041] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0042] (1) 2.63 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 2.37 g of ethylene glycol diglycidyl ether was added to 50 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0043] (2) The mixed reaction liquid A was heated to 50° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 2 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0044] The SEM image of the composite cathode material is as follows Figure 1 shown.

[0045] Example 2

[0046] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0047] (1) 3.25 g of bisphenol A bis(diphenyl phosphate) and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at a speed of 2000 rpm to obtain a mixed reaction solution A. 1.75 g of triglycidyl isocyanurate was added to 50 g of ethanol and stirred at a speed of 500 rpm to obtain a mixed reaction solution B.

[0048] (2) The mixed reaction liquid A was heated to 65° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 4 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0049] Example 3

[0050] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0051] (1) 2.59 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 2.41 g of pentaerythritol tetraglycidyl ether was added to 50 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0052] (2) The mixed reaction liquid A was heated to 55° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 8 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0053] Example 4

[0054] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0055] (1) 2.77 g of pentaerythritol phosphate and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 2.23 g of ethylene glycol diglycidyl ether was added to 50 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0056] (2) The mixed reaction liquid A was heated to 55° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 8 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0057] Example 5

[0058] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0059] (1) 0.52 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 4.48 g of ethylene glycol diglycidyl ether was added to 50 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0060] (2) The mixed reaction liquid A was heated to 50° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 2 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0061] Example 6

[0062] (1) 1.85 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 250 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 3.15 g of ethylene glycol diglycidyl ether was added to 50 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0063] (2) The mixed reaction liquid A was heated to 50° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 2 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0064] Example 7

[0065] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0066] (1) 5.27 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 300 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 4.73 g of ethylene glycol diglycidyl ether was added to 70 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0067] (2) The mixed reaction liquid A was heated to 50° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 8 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0068] Example 8

[0069] This embodiment provides a composite positive electrode material, and the preparation method of the composite positive electrode material is as follows:

[0070] (1) 10.54 g of propylene diphosphate and 100 g of lithium nickel cobalt manganate active material were added to 500 g of ethanol and stirred at 2000 rpm to obtain a mixed reaction solution A. 9.46 g of ethylene glycol diglycidyl ether was added to 100 g of ethanol and stirred at 500 rpm to obtain a mixed reaction solution B.

[0071] (2) The mixed reaction liquid A was heated to 50° C., and the mixed reaction liquid B was added dropwise to the mixed reaction liquid A under an inert gas atmosphere and a stirring speed of 1000 rpm. The reaction was allowed to react for 8 hours to obtain a reaction product C. The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the composite positive electrode material.

[0072] Comparative Example 1

[0073] This comparative example directly uses the nickel cobalt manganese oxide active material described in Example 1 as the positive electrode material. The SEM image of the positive electrode material is as follows: Figure 2 shown.

[0074] Comparative Example 2

[0075] This comparative example provides a positive electrode material, and the preparation method of the positive electrode material is as follows:

[0076] (1) Add 100 g of lithium nickel cobalt manganate active material to 300 g of ethanol and stir at 2000 rpm to obtain a mixed reaction solution A;

[0077] (2) adding 5.0 g of triethyl phosphite to 50 g of ethanol, stirring and mixing at a speed of 500 rpm to obtain a mixed reaction solution B;

[0078] (3) Add the mixed reaction solution B dropwise to the mixed reaction solution A under an inert gas atmosphere and a stirring speed of 1000 rpm, and continue stirring for 8 h to obtain a reaction product C;

[0079] (4) The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain a positive electrode material. The SEM image of the positive electrode material is as follows: Figure 3 shown.

[0080] Comparative Example 3

[0081] This comparative example provides a positive electrode material, and the preparation method of the positive electrode material is as follows:

[0082] (1) Add 100 g of lithium nickel cobalt manganate active material to 300 g of ethanol and stir at 2000 rpm to obtain a mixed reaction solution A;

[0083] (2) adding 5.0 g of polyethylene glycol glycidyl dodecyl ether to 50 g of ethanol, stirring and mixing at a speed of 500 rpm to obtain a mixed reaction solution B;

[0084] (3) Add the mixed reaction solution B dropwise to the mixed reaction solution A under an inert gas atmosphere and a stirring speed of 1000 rpm, and continue stirring for 8 h to obtain a reaction product C;

[0085] (4) The reaction product C was filtered and washed, and then vacuum dried for 24 hours to remove the residual solvent to obtain the positive electrode material.

[0086] Performance testing:

[0087] A positive electrode slurry was prepared by using 97 parts of the positive electrode materials prepared in the examples and comparative examples, 1.5 parts of SP, 0.5 parts of CNTs, and 1 part of PVDF in NMP as solvent. The slurry was coated on a 12 μm aluminum foil, and then baked, rolled, and die-cut to obtain a 51 mm × 96 mm positive electrode sheet. The surface density of the positive electrode sheet was 18.0 mg / cm 2 .

[0088] A negative electrode slurry was prepared by using 96 parts of graphite negative electrode material, 1.3 parts of SP, 0.2 parts of CNTs, 0.7 parts of CMC and 1.8 parts of SBR in deionized water as solvent. The slurry was coated on an 8 μm copper foil and then baked, rolled and die-cut to obtain a 55 mm × 100 mm negative electrode sheet with an area density of 10.8 mg / cm 2 .

[0089] The diaphragm is a commercial diaphragm, and the electrolyte is a commercial electrolyte.

[0090] The positive electrode sheet, negative electrode sheet and separator are assembled into a soft-pack lithium-ion battery, and then the electrolyte is injected, and high-temperature standing and formation treatment are performed.

[0091] The lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-3 were subjected to initial charge and discharge efficiency, 0.33C discharge gram capacity, and 1C rate charge and 1C rate discharge cycle performance tests at 25°C. At the same time, the ohmic impedance and charge transfer impedance of the lithium-ion batteries were tested using an electrochemical workstation. The test results are shown in Table 1:

[0092] Table 1

[0093]

[0094]

[0095] As can be seen from Table 1, it can be obtained from Examples 1-8 that the positive electrode active material prepared by the present invention using a polyphosphate monoester compound and a polyepoxide compound has a higher first charge and discharge efficiency and discharge gram capacity. By comparing the ohmic impedance and charge transfer impedance of the lithium-ion battery, it is found that the ohmic impedance and the charge transfer impedance are reduced, especially the charge transfer impedance, which is reduced by 21.41%. This shows that the modification of the positive electrode active material by the reaction of the polyphosphate monoester compound and the polyepoxide compound helps to disperse the positive electrode active particles in the positive electrode sheet. This is mainly because the polyphosphate monoester compound and the polyepoxide compound give a large number of hydroxyl groups to the surface of the positive electrode active material particles after the primary reaction. These active groups are conducive to the ion and electron transport and charge exchange on the surface of the positive electrode active material particles.

[0096] Figure 4 The figure is a comparison of the cycle performance of the positive electrode materials described in Examples 1, 7 and 8 and Comparative Examples 1-3. The test results of the cycle performance also show that Examples 1-8 are better than Comparative Examples 1-3. In addition, it can be found that the total amount of the monoester phosphate compound and the polyepoxy compound in Examples 1, 7 and 8 is 5%, 10% and 20% of the positive electrode active material, respectively, among which the amount of 20% shows a clear disadvantage. This shows that although the polyester phosphate compound and the polyepoxy compound are beneficial to improving the performance of the positive electrode material and its lithium-ion battery, the more they are introduced into the positive electrode as inactive components, the better.

[0097] Figure 5The following are the DSC results of the positive electrode active materials obtained by disassembling the lithium ion batteries prepared in Example 1 and Comparative Examples 1-3 at 100% SOC. The exothermic enthalpy values ​​of Example 1 and Comparative Examples 1-3 are 767.95 J / g, 1710.28 J / g, 1272.04 J / g, and 1712.70 J / g, respectively. By comparing the exothermic enthalpy values, it can be seen that the positive electrode active material prepared using the polyvalent phosphate monoester compound and the polyvalent epoxy compound can effectively reduce the heat release of the positive electrode active material in the delithiation state, which indicates that the safety component can effectively seal the particle surface of the positive electrode active material when it is at a high temperature, and effectively alleviate the contact between the positive electrode active material and the electrolyte or the negative electrode material, reducing the occurrence of side reactions, thereby providing excellent safety performance for the positive electrode material and its lithium ion battery.

[0098] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A composite positive electrode material, characterized in that The composite positive electrode material includes a positive electrode material core and a composite coating layer arranged on the surface of the positive electrode material core. The composite coating layer is obtained by a chemical addition reaction of a polybasic phosphate monoester compound and a polybasic epoxide compound on the surface of the positive electrode active material particles. The polybasic phosphate monoester compound includes a compound containing two or more phosphate monoester structures, and the polybasic epoxide compound includes a compound containing two or more three-membered cyclic ether structures.

2. The composite cathode material according to claim 1, wherein The structural formula of the phosphate monoester structure is shown in Formula I: Formula I.

3. The composite cathode material according to claim 1, wherein The polyphosphate monoester compound includes any one of propylene diphosphate, bisphenol A bis(diphenyl phosphate), pentaerythritol phosphate or diethylstilbestrol diphosphate, or a combination of at least two thereof.

4. The composite cathode material according to claim 1, wherein The structural formula of the three-membered cyclic ether structure is shown in Formula II: Formula II.

5. The composite cathode material according to claim 1, wherein The polyvalent epoxy compound includes any one of ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, isocyanuric acid triglycidyl ether, trimethylolethane triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether or epoxy resin, or a combination of at least two thereof.

6. The composite cathode material according to claim 1, wherein The positive electrode material core includes any one or a combination of at least two of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide or lithium-rich manganese-based positive electrode materials.

7. The composite cathode material according to claim 1, wherein The particle size of the positive electrode material core is 1-10 μm.

8. The composite cathode material according to claim 1, wherein The specific surface area of ​​the core of the positive electrode material is 0.1~1m 2 / g.

9. A method for preparing the composite positive electrode material according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) a polybasic phosphate monoester compound, a positive electrode active material, and a solvent are mixed to obtain a mixed solution A, and a polybasic epoxy compound and a solvent are mixed to obtain a mixed solution B; (2) After heating the mixed solution A, the mixed solution B is added dropwise to the mixed solution A to react to obtain the composite positive electrode material.

10. The preparation method according to claim 9, characterized in that The mass ratio of the total mass of the polyvalent phosphate monoester compound and the polyvalent epoxy compound to the positive electrode active material in step (1) is (1-20):

100.

11. The preparation method according to claim 9 or 10, characterized in that: In step (1), the molar ratio of the phosphate monoester structure of the polyvalent phosphate monoester compound to the three-membered cyclic ether structure of the polyvalent epoxy compound is k, 0<k<1.

12. The preparation method according to claim 9, wherein The solvent includes any one of ethanol, n-butanol, acetone, dimethyl carbonate, ethyl methyl carbonate, N,N-dimethylformamide or N-methylpyrrolidone, or a combination of at least two thereof.

13. The preparation method according to claim 9, wherein Stirring is performed while adding dropwise in step (2).

14. The preparation method according to claim 13, wherein The stirring speed is 1000-5000 rpm.

15. The preparation method according to claim 13, wherein The reaction temperature is 25-120°C.

16. The preparation method according to claim 13, wherein The reaction time is 2 to 8 hours.

17. A positive electrode plate, characterized in that: The positive electrode plate comprises the composite positive electrode material according to any one of claims 1 to 8.

18. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 17 .

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