Composite cathode material, preparation method thereof and lithium ion battery

Abstract

The application discloses a composite positive electrode material, a preparation method thereof and a lithium ion battery. The method comprises the following steps: 1) grafting a lithium source on a carbon source to obtain a modified precursor; and 2) sintering modification of the positive electrode material by using the modified precursor to form a composite network comprising a graphitized carbon network and a lithium supplementing material on the surface of the positive electrode material, thereby obtaining the composite positive electrode material. The carbon source comprises an organic substance containing a cyclic structure. The method can effectively improve the voltage platform, rate performance and low-temperature cycle performance of the positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a composite cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as a type of energy storage battery, are increasingly widely used in modern life and are currently in a period of rapid development. The cathode material, as one of the key materials, directly affects the overall performance of the battery.

[0003] Generally, cathode materials need to meet the following requirements: allowing for a large number of lithium ions to insert and extract, possessing a high redox potential, small volume changes due to insertion and extraction, high lithium ion diffusion coefficient, and high electronic conductivity. Among these, electronic conductivity has a crucial impact on the performance of cathode materials. A common method to improve electronic conductivity is surface coating with a carbon layer. For example, a common method to improve the electronic conductivity of lithium manganese iron phosphate (LFP) involves sintering the cathode material / cathode precursor in an atmosphere furnace, introducing oxygen-containing organic matter, water vapor, and an inert gas, controlling the furnace temperature at 500-1300℃, reacting for 3-40 hours, and then cooling to room temperature to obtain a discontinuous graphene-coated lithium-ion battery electrode material. However, this method suffers from drawbacks such as high sintering temperature, long sintering time, and generally mediocre performance of the prepared LFP batteries.

[0004] Therefore, providing a method to improve the electronic conductivity of cathode materials and thus enhance their electrochemical performance is an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a composite cathode material, its preparation method, and a lithium-ion battery. The method of this invention can effectively improve the voltage plateau, rate performance, and low-temperature cycling performance of the cathode material.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a composite cathode material, the method comprising the following steps:

[0008] (1) A lithium source is grafted onto a carbon source to obtain a modified precursor;

[0009] (2) The modified precursor is used to sinter the cathode material to form a composite network containing a graphitized carbon network and a lithium supplement material on the surface of the cathode material, thereby obtaining a composite cathode material.

[0010] The carbon source includes organic compounds with cyclic structures.

[0011] In the method of this invention, grafting refers to chemically bonding a lithium source to a carbon source.

[0012] The method of this invention modifies the cathode material by grafting a lithium source onto a carbon source and then sintering it. This allows for the formation of a composite network on the surface of the cathode material, consisting of a graphitized carbon network and a lithium replenishing material. This improves the electronic conductivity of the cathode material. Simultaneously, the lithium ions embedded in the surface of the cathode particles effectively shorten the lithium ion transport path and replenish the lithium ions that cannot migrate freely within the cathode material, thus achieving a lithium replenishment effect. The composite cathode material prepared by this invention exhibits a high voltage plateau, good rate performance and low-temperature cycling performance, as well as a high energy density.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] Preferably, the cyclic organic compound is at least one of a benzene ring organic compound, a five-membered heterocyclic organic compound, a six-membered heterocyclic organic compound, or a fused-ring organic compound.

[0015] By way of example and not limitation, the cyclic organic compound may be at least one of furan, thiophene, pyrrole, thiazole, imidazole, pyridine, pyrazine, pyrimidine, pyridazine, tetraphenyl, pentaphenyl, ovobenzine, naphthalene, anthracene, phenanthrene, pyrene, indene, acenaphthene, fluorene, azulene, bromobenzene, chlorobenzene, diphenylmercuric acid, and phenylacetic acid.

[0016] Preferably, the cyclic organic compound includes at least one of tetraphenyl, pentaphenyl, ovobenzene, naphthalene, anthracene, phenanthrene, pyrene, indene, acenaphthene, fluorene, azulene, and phenylacetic acid.

[0017] Preferably, the carbon source in step (1) further includes a first organic compound, the type of which is different from the type of the organic compound containing a cyclic structure, and the first organic compound is an organic compound containing at least one of an ester group, an amino group, and a carboxylic acid group.

[0018] Preferably, the first organic compound includes at least one selected from amino acids, acetic acid, methyl formate, and ethyl acetate.

[0019] In one embodiment, ethyl acetate is a liquid.

[0020] Preferably, the carbon source in step (1) is a mixture of an organic compound with a cyclic structure and the first organic compound. Based on the total mass of the carbon source being 100%, the mass percentage of the organic compound with a cyclic structure is 70-96%, for example, 70%, 73%, 75%, 77%, 80%, 82.5%, 85%, 88%, 90%, 92%, 93%, 94%, 95%, or 96%. The organic compound with a cyclic structure easily forms a graphitized carbon network after sintering, exhibiting better conductivity than amorphous carbon. Coating the surface of the cathode material particles with a graphitized carbon network is beneficial for improving electrical performance, reducing specific surface area, and improving processing performance. Simultaneously, a small amount of the first organic compound transforms into amorphous carbon after sintering, which can fill cracks in the carbon layer and improve the overall electrochemical performance of the composite cathode material. Furthermore, other organic carbon sources contain reducing groups, which can play a reducing role during the crystal growth process of the cathode material, promoting crystal growth and thus improving the electrochemical performance of the cathode material.

[0021] Preferably, the method for sintering and modifying the cathode material in step (2) is method one or method two, wherein,

[0022] The first method includes:

[0023] The cathode material precursor and the modified precursor are mixed and sintered to obtain a composite cathode material.

[0024] The second method includes:

[0025] The cathode material and the modified precursor are mixed and sintered to obtain a composite cathode material.

[0026] In this invention, Method 1 involves blending a cathode material precursor, a modified precursor, and a lithium compound to perform surface coating modification during the cathode material growth process. Method 2 directly modifies the surface of the cathode material through surface coating. Both methods can improve the electrochemical performance of the cathode material.

[0027] Preferably, the lithium source in step (1) includes at least one of lithium metal, lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium nitrite, lithium acetate, lithium oxide, and lithium oxalate.

[0028] Preferably, the grafting in step (1) is achieved by reacting a carbon source with the lithium source, or by converting the carbon source into a derivative of the carbon source and reacting it with the lithium source. For example:

[0029] For example, bromobenzene / chlorobenzene reacts with metallic lithium in an organic mixture to yield phenyllithium, thus achieving grafting. The organic mixture can be diethyl ether, or a mixture of diethyl ether and benzene.

[0030] For example, diphenylmercuric acid reacts with metallic lithium in toluene to achieve grafting.

[0031] For example, phenylacetic acid reacts with metallic lithium / lithium hydroxide to achieve grafting.

[0032] As a preferred technical solution of the method described in this invention, the amount of carbon source added in step (1) satisfies the following: based on the mass of the cathode material core as 100%, the content of graphitized carbon network in the composite network is 0.1-3%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.

[0033] Preferably, the amount of lithium source added in step (1) satisfies the following: based on the mass of lithium element in the core of the positive electrode material as 100%, the content of lithium element in the lithium supplement material is 0.1-5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc.

[0034] Preferably, in Method 1, the cathode material precursor includes at least one of lithium cobalt oxide precursor, lithium manganese oxide precursor, ternary cathode material precursor, lithium iron phosphate precursor, or lithium manganese iron phosphate precursor.

[0035] Preferably, in Method 2, the cathode material includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary cathode material, lithium iron phosphate, or lithium manganese iron phosphate.

[0036] Preferably, in either method one or method two, the sintering atmosphere is a protective atmosphere.

[0037] Preferably, the gas in the protective atmosphere includes, but is not limited to, at least one of nitrogen, argon, helium, or neon.

[0038] Preferably, in Method 1 or Method 2, the sintering temperature is independently 700-800℃, such as 700℃, 725℃, 750℃, 770℃, 780℃, or 800℃. Here, "independently" means that the specific values ​​of the sintering temperature in Method 1 and Method 2 can be the same or different, and the specific values ​​within each range are chosen independently.

[0039] Preferably, in Method 1 or Method 2, the sintering time is independently 5-8 hours, such as 5 hours, 5.2 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours. Here, "independently" means that the specific values ​​of the sintering temperature in Method 1 and the sintering time in Method 2 can be the same or different, and the specific values ​​within their respective ranges are chosen independently.

[0040] In a second aspect, the present invention provides a composite cathode material prepared by the method described in the first aspect, the composite cathode material comprising a cathode material core and a composite network coating the surface of the cathode material core, the composite network comprising a graphitized carbon network and a lithium supplement material.

[0041] Thirdly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the composite positive electrode material described in the second aspect.

[0042] Compared with existing technologies, the present invention has the following beneficial effects:

[0043] The method of the present invention modifies the cathode material by grafting a lithium source onto a carbon source and then sintering it. This allows for the formation of a composite network containing a graphitized carbon network and a lithium replenishment material on the surface of the cathode material, thereby improving the electronic conductivity of the cathode material. Simultaneously, the lithium ions are embedded in the surface layer of the cathode particles, which can effectively shorten the lithium ion transport path. The composite cathode material exhibits better voltage plateau, rate performance, and low-temperature cycling performance. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0045] The embodiments of this invention are illustrated using lithium manganese iron phosphate as a cathode material, but this does not constitute a limitation of the invention. Other cathode materials are also applicable to this invention.

[0046] In this embodiment of the invention, the lithium manganese iron phosphate precursor is a mixture of iron phosphate (FePO4), manganese phosphate, lithium nitrate (LiNO3) and carbon source in the molar ratio of each element in the product, with the ratio of iron phosphate: manganese phosphate: lithium nitrate: carbon source (molar ratio) being 40%:60%:100%:2%.

[0047] Example 1

[0048] This embodiment provides a method for preparing a composite cathode material, including the following steps:

[0049] (1) Grafting metallic lithium onto benzene yields a carbon source for grafting lithium. The carbon source for grafting lithium is phenyl lithium. The specific grafting method is as follows:

[0050] Benzene and bromine water undergo an addition reaction in the presence of iron as a catalyst to produce bromobenzene;

[0051] The preparation of phenyllithium involves the following two steps: (a) under inert gas protection, sodium-lithium alloy and n-butyl ether are added to the system and stirred to obtain a sodium-lithium alloy dispersion; (b) at 30°C, bromobenzene is added dropwise to the sodium-lithium alloy dispersion obtained in step (a) with stirring, and the system temperature is controlled at 30°C. After the addition is complete, the reaction is maintained at this temperature and then treated to obtain a phenyllithium solution. The molar ratio of benzene to lithium is 1:3.

[0052] (2) Take the carbon of lithium manganese iron phosphate precursor and grafted lithium source and mix them evenly to obtain a mixture;

[0053] The mass ratio of carbon in the lithium manganese iron phosphate precursor to that in the grafted lithium source is 0.96:0.01.

[0054] (3) The mixture was placed in a tube furnace, nitrogen was introduced, and sintered at 700°C for 8 hours. After cooling and crushing, nano-sized lithium manganese iron phosphate, i.e. composite cathode material, was obtained.

[0055] The composite cathode material prepared in this embodiment includes a lithium manganese iron phosphate core and a composite network coated on the surface of the lithium manganese iron phosphate core. The composite network includes a graphitized carbon network and a lithium replenishment material.

[0056] Wherein, with the mass of the cathode material core being 100%, the content of the graphitized carbon network in the composite network is 1%;

[0057] With the mass of lithium element in the core of the cathode material being 100%, the lithium element content in the lithium replenishment material is 3%.

[0058] Example 2

[0059] This embodiment provides a method for preparing a composite cathode material, including the following steps:

[0060] (1) Grafting metallic lithium onto naphthalene yields carbon from the grafted lithium source, which is naphthalene lithium. The specific grafting method is as follows:

[0061] Naphthalene and lithium metal were mixed and stirred at room temperature under deoxygenated THF conditions to obtain lithium naphthalene, wherein the molar ratio of naphthalene to lithium was 1:3.

[0062] (2) Take the carbon of lithium manganese iron phosphate precursor and grafted lithium source and mix them evenly to obtain a mixture;

[0063] The mass ratio of carbon in the lithium manganese iron phosphate precursor to that in the grafted lithium source is 0.96:0.01.

[0064] (3) The mixture is placed in a tube furnace, argon gas is introduced, and sintering is carried out at 800℃ for 5 hours. After cooling and crushing, nano-sized lithium manganese iron phosphate is obtained, which is also a composite cathode material.

[0065] The composite cathode material prepared in this embodiment includes a lithium manganese iron phosphate core and a composite network coated on the surface of the lithium manganese iron phosphate core. The composite network includes a graphitized carbon network and a lithium replenishment material.

[0066] Wherein, with the mass of the cathode material core being 100%, the content of the graphitized carbon network in the composite network is 1%;

[0067] With the mass of lithium element in the core of the cathode material being 100%, the lithium element content in the lithium replenishment material is 3%.

[0068] Example 3

[0069] This embodiment provides a method for preparing a composite cathode material, including the following steps:

[0070] (1) Grafting metallic lithium onto benzene yields carbon grafted with lithium source; 1) Benzene and bromine water undergo an addition reaction under iron catalysis to produce bromobenzene;

[0071] The preparation of phenyllithium involves the following two steps: (a) under inert gas protection, sodium-lithium alloy and n-butyl ether are added to the system and stirred to obtain a sodium-lithium alloy dispersion; (b) at 30°C, bromobenzene is added dropwise to the sodium-lithium alloy dispersion obtained in step (a) with stirring, and the system temperature is controlled at 30°C. After the addition is complete, the reaction is maintained at this temperature and then treated to obtain a phenyllithium solution. The molar ratio of bromobenzene to lithium is 1:1.

[0072] (2) Take the carbon of lithium manganese iron phosphate precursor and grafted lithium source and mix them evenly to obtain a mixture;

[0073] The mass ratio of carbon in the lithium manganese iron phosphate precursor to that in the grafted lithium source is 0.97:0.015.

[0074] (3) The mixture was placed in a tube furnace, nitrogen was introduced, and sintered at 725°C for 6.5 hours. After cooling and crushing, nano-sized lithium manganese iron phosphate, i.e. composite cathode material, was obtained.

[0075] The composite cathode material prepared in this embodiment includes a lithium manganese iron phosphate core and a composite network coated on the surface of the lithium manganese iron phosphate core. The composite network includes a graphitized carbon network and a lithium replenishment material.

[0076] Wherein, based on the mass of the cathode material core as 100%, the content of the graphitized carbon network in the composite network is 1.5%;

[0077] With the mass of lithium element in the core of the cathode material being 100%, the lithium element content in the lithium replenishment material is 1.5%.

[0078] Example 4

[0079] The difference from Example 1 is that benzene is replaced with a mixture of benzene and amino acids. In this example, the total mass of benzene and amino acids is the same as the mass of benzene in Example 1.

[0080] In this embodiment, with the total mass of benzene and amino acids being 100%, the mass percentage of benzene is 80%.

[0081] Example 5

[0082] The difference from Example 5 is that, based on the total mass of benzene and amino acids being 100%, the mass percentage of benzene is 65%.

[0083] Example 6

[0084] The difference from Example 5 is that, based on the total mass of benzene and amino acids being 100%, the mass percentage of benzene is 98%.

[0085] Example 7

[0086] The difference from Example 1 is that the content of grafted metallic lithium in step (1) is adjusted so that the content of lithium in the lithium supplement material is 0.05% based on the mass of lithium in the core of the cathode material being 100%.

[0087] Example 8

[0088] The difference from Example 1 is that the content of grafted metallic lithium in step (1) is adjusted so that the content of lithium in the lithium replenishment material is 6% based on the mass of lithium in the core of the cathode material being 100%.

[0089] Example 9

[0090] The difference from Example 5 is that the amino acids are replaced with methanol.

[0091] Comparative Example 1

[0092] This comparative example provides a lithium-ion battery composite cathode material coated with a discontinuous graphitized carbon network, comprising the following steps:

[0093] The positive electrode material lithium iron phosphate was sintered in an atmosphere furnace, and acetone, water vapor and inert gas (nitrogen and / or argon) were introduced. The volume fractions of oxygen-containing organic matter (methanol) and water vapor introduced were 10% and 2%, respectively. The temperature in the atmosphere furnace was controlled at 1000℃, and the reaction was carried out for 10 hours. After cooling to room temperature, a non-continuous graphene-coated lithium-ion battery composite positive electrode material was obtained.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that instead of grafting lithium metal onto benzene, benzene and sodium-lithium alloy were directly mixed in step (2).

[0096] Comparative Example 3

[0097] This comparative example provides a method for preparing a composite cathode material, including the following steps:

[0098] (1) Grafting lithium nitrate onto a carboxylic acid group yields a carbon atom grafted with lithium source. The specific grafting method is as follows:

[0099] Lithium nitrate reacts with carboxylic acid at 60°C under acidic conditions to produce lithium carboxylate, wherein the molar ratio of carboxylic acid to lithium is 1:2.

[0100] (2) Take the carbon of lithium manganese iron phosphate precursor and grafted lithium source and mix them evenly to obtain a mixture;

[0101] The mass ratio of carbon in the lithium manganese iron phosphate precursor to carbon in the grafted lithium source is 1:0.02.

[0102] (3) The mixture was placed in a tube furnace, nitrogen was introduced, and sintered at 750°C for 6 hours. After cooling and crushing, nano-sized lithium manganese iron phosphate, i.e. composite cathode material, was obtained.

[0103] Battery performance testing: Using the composite cathode materials provided in the above embodiments and comparative examples, batteries were assembled as follows:

[0104] Preparation of positive electrode sheet: The composite positive electrode material, SP (conductive carbon black), PVDF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) are mixed evenly in a ball mill for 2 hours at a mass ratio of 93.5:2.5:4:100 to obtain a positive electrode slurry; the prepared positive electrode slurry is added to aluminum foil, evenly scraped with a scraper, dried at 130℃ and then rolled to obtain a positive electrode sheet.

[0105] Battery assembly process: The prepared positive electrode sheet is attached to the positive electrode metal shell with conductive adhesive, a lithium metal sheet is used as the negative electrode, a Celgard 2400 microporous membrane is used as the separator, and a 1.0 mol / L LiPF6 solution is used as the electrolyte. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1. The cells are assembled into coin cells in a glove box.

[0106] Using a LAND electrochemical tester, the electrochemical performance of the above-mentioned coin cells, including voltage plateau, rate performance, low-temperature cycling performance, and energy density, was tested under the conditions of a charging termination voltage of 4.2V and a discharging termination voltage of 2.0V. The test results are shown in Table 1 below.

[0107] Table 1

[0108]

[0109]

[0110] As shown in Table 1, by grafting a lithium source onto a carbon source and then sintering and modifying the cathode material, the present invention can coat the surface of the cathode material with a composite network containing a graphitized carbon network and a lithium replenishment material, thereby improving the electronic conductivity of the cathode material. At the same time, the lithium ions are embedded in the surface layer of the cathode particles, which can effectively shorten the lithium ion transport path. The composite cathode material has better voltage plateau, rate performance and low temperature cycling performance.

[0111] A comparison of Examples 1 and 4-6 shows that using a composite carbon source composed of an organic compound with a cyclic structure and a first organic compound with reducing groups for the preparation of composite cathode materials helps to fill cracks in the carbon layer and plays a reducing role during the crystal growth of the cathode material, promoting crystal growth and thus improving the battery's voltage plateau, rate performance, and low-temperature cycle performance. Furthermore, there is an optimal range for the content of the cyclic organic compound in the composite carbon source; when the mass percentage is 70-96%, the battery's electrochemical performance is better.

[0112] A comparison of Example 1 and Examples 7-8 shows that there is an optimal range for the lithium content in the lithium replenishment material, and the electrochemical performance of the battery is better when the content is in the range of 0.1-5%.

[0113] A comparison between Example 1 and Example 9 shows that using a first organic compound with reducing groups is more beneficial to improving the electrochemical performance of the composite cathode material.

[0114] A comparison between Example 1 and Comparative Example 1 shows that in the method of Comparative Example 1, the sintering temperature was too high, which caused the lithium manganese iron phosphate particles to become larger, the lithium ion transport channels to become longer, and the capacity to become worse.

[0115] The comparison between Example 1 and Comparative Example 2 shows that introducing carbon and lithium through grafting can better construct a composite network of graphitized carbon network and lithium replenishment material, thereby improving the electrochemical performance of the battery.

[0116] The comparison between Example 1 and Comparative Example 3 shows that the type of carbon source used for grafting lithium source has an important impact on improving the performance of composite cathode material. Since the carbon source used in Comparative Example 3 does not contain a ring structure, it cannot effectively form a composite network of graphitized carbon network and lithium supplementation material, thus leading to a decrease in electrochemical performance.

[0117] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a composite cathode material, characterized in that, The method includes the following steps: (1) A lithium source is grafted onto a carbon source to obtain a modified precursor; (2) The modified precursor is used to sinter the cathode material to form a composite network containing a graphitized carbon network and a lithium supplement material on the surface of the cathode material, thereby obtaining a composite cathode material. The carbon source includes organic compounds with cyclic structures; The cyclic organic compound is at least one of the following: benzene-ring organic compound, five-membered heterocyclic organic compound, six-membered heterocyclic organic compound, and fused-ring organic compound; The carbon source in step (1) also includes a first organic compound, the type of which is different from the type of the organic compound containing a cyclic structure. The first organic compound is an organic compound containing at least one of an ester group, an amino group, and a carboxylic acid group. The carbon source in step (1) is a mixture of an organic compound with a cyclic structure and the first organic compound. The total mass of the carbon source is 100%, and the mass percentage of the organic compound with a cyclic structure is 70-96%.

2. The method according to claim 1, characterized in that, The first organic compound includes at least one of amino acids, acetic acid, methyl formate, and ethyl acetate.

3. The method according to claim 1, characterized in that, The cyclic organic compounds include at least one of tetraphenyl, pentaphenyl, ovobenzene, naphthalene, anthracene, phenanthrene, pyrene, indene, acenaphthene, fluorene, azulene, bromobenzene, chlorobenzene, diphenylmercuric acid, and phenylacetic acid.

4. The method according to claim 1, characterized in that, The method for sintering and modifying the cathode material in step (2) is method one or method two, wherein, The first method includes: The cathode material precursor and the modified precursor are mixed and sintered to obtain a composite cathode material; The second method includes: The cathode material and the modified precursor are mixed and sintered to obtain a composite cathode material.

5. The method according to claim 1, characterized in that, The lithium source in step (1) includes at least one of lithium metal, lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide, lithium carbonate, lithium nitrate, lithium nitrite, lithium acetate, lithium oxide, and lithium oxalate.

6. The method according to claim 1, characterized in that, The grafting in step (1) is achieved by reacting a carbon source with the lithium source, or by converting the carbon source into a derivative of the carbon source and reacting it with the lithium source.

7. The method according to claim 1, characterized in that, The amount of carbon source added in step (1) satisfies the following: based on the mass of the cathode material as 100%, the content of graphitized carbon network in the composite network is 0.1-3%.

8. The method according to claim 1, characterized in that, The amount of lithium source added in step (1) satisfies the following: based on the mass of lithium element in the cathode material being 100%, the content of lithium element in the lithium replenishment material is 0.1-5%.

9. The method according to claim 4, characterized in that, In Method 1, the cathode material precursor includes at least one of lithium cobalt oxide precursor, lithium manganese oxide precursor, ternary cathode material precursor, lithium iron phosphate precursor, or lithium manganese iron phosphate precursor.

10. The method according to claim 4, characterized in that, In Method 2, the cathode material includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary cathode material, lithium iron phosphate, or lithium manganese iron phosphate.

11. The method according to claim 4, characterized in that, In either Method 1 or Method 2, the sintering atmosphere is a protective atmosphere.

12. The method according to claim 11, characterized in that, The protective atmosphere contains at least one of nitrogen, argon, helium, or neon.

13. The method according to claim 4, characterized in that, In either Method 1 or Method 2, the sintering temperature is independently 700-800℃.

14. The method according to claim 4, characterized in that, In either Method 1 or Method 2, the sintering time is independently 5-8 hours.

15. A composite cathode material prepared by the method according to any one of claims 1-14, characterized in that, The composite cathode material includes a cathode material core and a composite network coating the surface of the cathode material core, wherein the composite network comprises a graphitized carbon network and a lithium supplement material.

16. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes the composite positive electrode material as described in claim 15.

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