Graphite negative electrode material and preparation method thereof, negative electrode sheet and electrochemical device

Abstract

The present application relates to a graphite negative electrode material and a preparation method thereof, a negative electrode sheet and an electrochemical device. The graphite negative electrode material includes secondary particles formed by granulation and carbonization of 20% to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent. In the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and the coating agent is carbonized to at least partially form amorphous carbon coating on the outer layer of the doped porous graphite precursor. The solution provided in the present application can compound the doped porous graphite precursor with hard carbon particles and a coating agent to obtain a graphite negative electrode material with high capacity and fast charging performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a graphite negative electrode material and a preparation method thereof, a negative electrode sheet and an electrochemical device. Background Art

[0002] Graphite negative electrode materials are currently the main negative electrode materials for lithium-ion batteries and are used in various fields such as power, energy storage, and consumer electronics. With the increasingly higher requirements for energy density of terminals, the capacity and compaction performance of graphite negative electrode materials are also approaching the theoretical upper limit. Therefore, how to improve the capacity and fast charging performance of graphite is the main research direction.

[0003] In the related technology, a high-current pulsed electron beam is used to create pores in graphite, forming partial gaps in the graphite crystals to improve the material's rate performance. However, this increases the material's specific surface area, resulting in a shorter cycle life and unable to guarantee the fast charging performance of the graphite negative electrode material. Summary of the invention

[0004] In order to solve or partially solve the problems existing in the related art, the present application provides a graphite negative electrode material and a preparation method thereof, a negative electrode sheet and an electrochemical device, which can compound a doped porous graphite precursor with hard carbon particles and a coating agent to obtain a graphite negative electrode material with high capacity and fast charging performance.

[0005] The first aspect of the present application provides a graphite negative electrode material, which includes secondary particles formed by granulation and carbonization of 20% to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent, wherein the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and the coating agent is carbonized to at least partially form amorphous carbon coating on the outer layer of the doped porous graphite precursor filled with the hard carbon particles.

[0006] As an optional embodiment, the hard carbon particles include at least one of biomass hard carbon, resin hard carbon, and asphalt hard carbon.

[0007] As a preferred embodiment, the median particle size of the hard carbon particles is 1 μm to 10 μm.

[0008] As a preferred embodiment, the biomass hard carbon includes at least one of coconut shell carbon, bamboo carbon and straw carbon.

[0009] As a preferred embodiment, the resin hard carbon includes at least one of phenolic resin carbon, epoxy resin carbon and polyfurfuryl alcohol resin carbon.

[0010] As an optional embodiment, the asphalt-based hard carbon includes at least one of petroleum asphalt-based hard carbon and coal asphalt-based hard carbon.

[0011] As an optional embodiment, the doped porous graphite precursor is obtained by subjecting crushed graphite raw material to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor, and then the porous graphite precursor is successively subjected to heteroatom doping and graphitization treatment.

[0012] As an optional embodiment, the coating agent includes at least one of petroleum asphalt, coal tar asphalt, phenolic resin, and epoxy resin.

[0013] As a preferred embodiment, the graphite raw material includes at least one of green coke raw material and cooked coke raw material, preferably one or more of petroleum coke, coal-based coke, oil-based needle coke, and coal-based needle coke.

[0014] As a preferred embodiment, the pore-forming agent is an alkaline solution, preferably at least one of a KOH solution, a NaOH solution, and a LiOH solution.

[0015] As a preferred embodiment, the mass percentage concentration of the pore-forming agent is 10% to 30%.

[0016] As a preferred embodiment, the pores of the porous graphite precursor have a pore size of 1 μm to 5 μm.

[0017] As an optional embodiment, the heteroatom includes at least one of B, N, and P atoms, preferably a B atom.

[0018] As a preferred embodiment, the median particle size of the crushed graphite raw material is 7 μm to 15 μm.

[0019] The second aspect of the present application provides a method for preparing a graphite negative electrode material, comprising:

[0020] The crushed graphite raw material is subjected to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor;

[0021] After mixing the porous graphite precursor with an acid solution containing heteroatoms, graphitization is performed to obtain a doped porous graphite precursor doped with heteroatoms;

[0022] After mixing 20% ​​to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent, granulation and carbonization are performed to obtain secondary particles of graphite negative electrode material; in the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and the coating agent is carbonized to at least partially form amorphous carbon coating on the outer layer of the doped porous graphite precursor.

[0023] As an optional embodiment, the pore-making treatment temperature is 60° C. to 100° C., and the treatment time is 2 h to 10 h.

[0024] As an optional embodiment, the temperature of the graphitization treatment is 2600°C~3200°C.

[0025] As an optional embodiment, the heteroatom-containing acid solution includes at least one of acid solutions containing B, N, and P, preferably at least one of boric acid, nitric acid, and phosphoric acid, and more preferably boric acid.

[0026] As an optional embodiment, the sum of the mass percentages of the porous graphite precursor and the acid solution containing heteroatoms is calculated to be 100%, and the mass percentage of the acid solution containing heteroatoms is 1% to 10%.

[0027] A third aspect of the present application provides a negative electrode sheet, comprising the aforementioned graphite negative electrode material, or a graphite negative electrode material prepared by the aforementioned method for preparing the graphite negative electrode material.

[0028] A fourth aspect of the present application provides an electrochemical device, comprising the aforementioned negative electrode sheet.

[0029] The technical solution provided by this application may have the following beneficial effects:

[0030] The present application obtains secondary particles of graphite negative electrode material by compounding a doped porous graphite precursor with hard carbon particles and a coating agent, and performing granulation and carbonization. In the secondary particles, the hard carbon particles are filled in the pores of the doped porous graphite precursor, which can improve the compaction and fast charging performance of the graphite negative electrode material while protecting the heteroatom doping interface inside the pores, thereby improving the capacity and cycle performance of the graphite negative electrode material; after carbonization of the coating agent, at least part of the amorphous carbon is formed to coat the outer layer of the doped porous graphite precursor filled with hard carbon particles, and the doped porous graphite precursor filled with hard carbon particles is filled with the amorphous carbon. The coating of the heteroporous graphite precursor can, on the one hand, alleviate the oxidation of hard carbon particles and heteroatoms in subsequent processes, and on the other hand, can seal the hard carbon particles in the pores of the doped porous graphite precursor, thereby improving the volume expansion buffering capacity of the secondary particles, and amorphous carbon can further fill the pores of the doped porous graphite precursor or seal the surface of the doped porous graphite precursor, reducing the specific surface area of ​​the doped porous graphite precursor while avoiding the oxidation of hard carbon particles and heteroatoms inside the doped porous graphite precursor, thereby achieving the advantages of high-capacity fast charging and long cycle life.

[0031] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. DETAILED DESCRIPTION

[0032] The embodiments of the present application will be described in more detail below. Although the embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0033] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0034] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0035] In the related technology, a high-current pulsed electron beam is used to create pores in graphite, forming partial gaps in the graphite crystals to improve the material's rate performance. However, this increases the material's specific surface area, resulting in a shorter cycle life and unable to guarantee the fast charging performance of the graphite negative electrode material.

[0036] In view of the above problems, an embodiment of the present application provides a graphite negative electrode material, which can obtain a graphite negative electrode material with high capacity and fast charging performance by compounding a doped porous graphite precursor with hard carbon particles and a coating agent.

[0037] An embodiment of the present application provides a graphite negative electrode material. The graphite negative electrode material includes, by mass percentage, secondary particles formed by granulation and carbonization of 20% to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent. In the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and after carbonization, the coating agent at least partially forms amorphous carbon coating on the outer layer of the doped porous graphite precursor filled with the hard carbon particles.

[0038] In the embodiment of the present application, the formula for preparing the secondary particles of the graphite negative electrode material is: 20% to 90% of the doped porous graphite precursor, 5% to 30% of the hard carbon particles and 5% to 50% of the coating agent. For example, the formula for preparing the secondary particles of the graphite negative electrode material in the embodiment of the present application can be: 70% of the doped porous graphite precursor, 10% of the hard carbon particles and 20% of the coating agent or any value within the above-defined range, and the present application is not limited to this.

[0039] In an embodiment of the present application, a doped porous graphite precursor can be obtained by subjecting a pulverized graphite raw material to a pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor, and then the porous graphite precursor is successively subjected to heteroatom doping and graphitization treatment. In an embodiment of the present application, by etching pores in the pulverized graphite raw material, the channels for lithium ions to be embedded in the graphite particles are increased, and at the same time, the path for lithium ion diffusion is shortened, thereby improving the fast charging performance of the graphite negative electrode material. On this basis, heteroatom doping is performed to increase the reactive active sites, which is more conducive to the adsorption and embedding of lithium ions while improving the conductivity of the graphite negative electrode material, thereby achieving the purpose of improving the gram capacity of the graphite negative electrode material.

[0040] In the embodiment of the present application, a doped porous graphite precursor is compounded with hard carbon particles and a coating agent, and granulated and carbonized to obtain secondary particles of the graphite negative electrode material. In the secondary particles, the hard carbon particles are filled in the pores of the doped porous graphite precursor, which can improve the compaction and fast charging performance of the graphite negative electrode material while protecting the heteroatom doping interface inside the pores, thereby improving the capacity and cycle performance of the graphite negative electrode material; after the coating agent is carbonized, at least part of the amorphous carbon is formed to coat the outer layer of the doped porous graphite precursor filled with the hard carbon particles, and the hard carbon particles are filled with the amorphous carbon. The coating of the doped porous graphite precursor can, on the one hand, alleviate the oxidation of hard carbon particles and heteroatoms in subsequent processes, and on the other hand, seal the hard carbon particles in the pores of the doped porous graphite precursor, thereby improving the volume expansion buffering capacity of the secondary particles, and amorphous carbon can further fill the pores of the doped porous graphite precursor or seal the surface of the doped porous graphite precursor, reducing the specific surface area of ​​the doped porous graphite precursor while avoiding the oxidation of hard carbon particles and heteroatoms inside the doped porous graphite precursor, thereby achieving the advantages of high-capacity fast charging and long cycle life.

[0041] As an optional embodiment, the hard carbon particles include particles crushed from at least one of biomass hard carbon, resin hard carbon, and asphalt hard carbon.

[0042] The hard carbon particles in the embodiments of the present application refer to carbon particles that are difficult to graphitize, and the selected materials belong to the same carbon material as the doped porous graphite precursor. Hard carbon particles belong to carbon materials, with low graphitization degree, large interlayer spacing, and good fast charging performance. The fast charging performance of graphite negative electrode materials can be improved by compounding hard carbon particles with doped porous graphite precursors. Compared with silicon dioxide materials, silicon dioxide materials belong to silicon materials, with higher capacity but inferior fast charging performance to carbon materials.

[0043] As an optional embodiment, the median particle size of the hard carbon particles is 1 μm to 10 μm.

[0044] In the embodiments of the present application, the median particle size (D50) refers to the particle size corresponding to when the cumulative particle size distribution percentage reaches 50% in a particle size distribution. The median particle size of the hard carbon particles can be 1 μm, 3 μm, 5 μm, 7 μm, 10 μm or any value within the above-defined range, and the present application does not limit this.

[0045] The median particle size of the hard carbon particles in the embodiment of the present application can match the average pore size of the pores of the doped porous graphite precursor, so that most of the hard carbon particles can be filled in the pores of the doped porous graphite precursor to seal the pores and protect the pores.

[0046] As a preferred embodiment, the biomass hard carbon includes at least one of coconut shell carbon, bamboo carbon and straw carbon.

[0047] The internal crystal arrangement of biomass hard carbon is disordered and the interlayer spacing is large, which allows the hard carbon negative electrode to store more charge under the same volume, and lithium ions are easier to embed and extract, thereby improving the energy density and endurance of the battery.

[0048] As a preferred embodiment, the resin hard carbon includes at least one of phenolic resin, epoxy resin and polyfurfuryl alcohol resin carbon.

[0049] Resin-based hard carbon materials excel in mechanical strength and structural stability, have high compressive strength and structural stability, and have a simple preparation process and low cost.

[0050] As a preferred embodiment, the asphalt-based hard carbon includes at least one of petroleum asphalt-based hard carbon and coal asphalt-based hard carbon.

[0051] Pitch-based hard carbon has good electrochemical properties, high specific capacity and stable potential platform. Its large interlayer spacing is conducive to the insertion and extraction of lithium ions, thereby improving the energy density and endurance of the battery.

[0052] As an optional embodiment, the doped porous graphite precursor is obtained by subjecting the crushed graphite raw material to pore-forming treatment with a pore-forming agent to obtain the porous graphite precursor, and then the porous graphite precursor is successively subjected to heteroatom doping and graphitization treatment.

[0053] The steps for preparing the doped porous graphite precursor in the embodiment of the present application may include:

[0054] The crushed graphite raw material is subjected to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor; the porous graphite precursor is mixed with an acid solution containing heteroatoms, and then graphitized to obtain a doped porous graphite precursor doped with heteroatoms.

[0055] The pulverized graphite raw material in the embodiment of the present application can be obtained by pulverizing and granulating the graphite raw material. This is because the graphite raw material is generally in block form and has a large volume. After being pulverized into particles, it is convenient for pore formation and doping. The pulverized graphite raw material can be granular, with a median particle size of 7μm~15μm. The graphite raw material particles within this particle size range can balance high capacity and fast charging performance.

[0056] The embodiment of the present application creates pores in the crushed graphite raw material to provide lithium ion embedding channels, thereby improving the rate performance. At the same time, the use of heteroatom doping, hard carbon composite and coated carbonization can reduce the negative reactions caused by the pores, provide more reaction sites for the embedding and adsorption of lithium ions, and improve the energy density and fast charging performance of the graphite negative electrode material.

[0057] As a preferred embodiment, the graphite raw material includes at least one of a green coke raw material and a cooked coke raw material.

[0058] Green coke raw materials are generally coke materials that are formed in the coking process without high-temperature calcination treatment, and cooked coke raw materials are generally coke materials that are formed after high-temperature calcination treatment in the coking process. The use of green coke raw materials and / or cooked coke raw materials as graphite raw materials can effectively reduce the production cost of the graphite negative electrode material of the present application, and effectively reduce the production difficulty, so that the graphite negative electrode material can meet the requirements of large-scale promotion and application.

[0059] Furthermore, the raw material for green coke can be one or more of petroleum coke, coal-based coke, oil-based needle coke, and coal-based needle coke; the raw material for cooked coke can be obtained by calcining one or more of petroleum coke, coal-based coke, oil-based needle coke, and coal-based needle coke.

[0060] As a preferred embodiment, the pore-forming agent is an alkaline solution.

[0061] The pore-forming agent in the embodiment of the present application is an alkaline solution. The alkaline solution penetrates into the graphite particles and generates holes through oxidation etching. The alkaline solution has a good pore-forming effect and is easy to clean. It does not introduce other metal impurities and reduces the occurrence of negative reactions.

[0062] Preferably, it is at least one of a KOH solution, a NaOH solution, and a LiOH solution.

[0063] KOH solution, NaOH solution, and LiOH solution are strong alkaline solutions, which can more easily penetrate into graphite, form deeper pores, and form pores more quickly and more evenly by oxidation. As a preferred embodiment, the mass percentage concentration of the pore former is 10% to 30%.

[0064] The mass percentage concentration of the pore-forming agent in the embodiments of the present application may refer to the percentage of the mass of the solute contained in the solution to the mass of the solution. The mass percentage concentration of the pore-forming agent may be 10%, 20%, 30% or any value within the above-defined range, and the present application does not limit this.

[0065] In the embodiments of the present application, the pore-forming agent is selected at an appropriate concentration to form pores of appropriate size. If the concentration is too low, pores may not be formed effectively. If the concentration is too high, the oxidation etching reaction may be uncontrollable and the degree of pore formation may be uncontrollable.

[0066] As a preferred embodiment, the pores of the porous graphite precursor have a pore size of 1 μm to 5 μm.

[0067] In the embodiment of the present application, the pore size of the pores of the porous graphite precursor is controlled to be 1 μm to 5 μm by controlling factors such as the type, concentration, and content of the pore-forming agent.

[0068] As a preferred embodiment, the heteroatom includes at least one of B, N, and P atoms.

[0069] The embodiments of the present application can dope B, N, and P into a porous graphite precursor to obtain a doped porous graphite precursor. Compared with transition metal and silicon doping, the doping of atoms such as B, N, and P can utilize their electron-deficient or multi-electron properties after hybridization and combination with carbon atoms to improve the conductivity and ion transport properties of the porous graphite precursor. At the same time, the defect sites generated also provide more reaction sites for the embedding and adsorption of lithium ions, thereby achieving the purpose of improving the gram capacity and fast charging performance of the graphite negative electrode material.

[0070] Preferably, the heteroatom in the embodiment of the present application is a B atom. This is because the doping of the B atom has electron-deficient characteristics after hybridization and combination with the carbon atom.

[0071] As an optional embodiment, the median particle size of the crushed graphite raw material is 7 μm to 15 μm.

[0072] In the embodiments of the present application, the median particle size of the crushed graphite raw material can be 7 μm, 10 μm, 12 μm, 15 μm or any value within the above-defined range, and the present application does not impose any limitation on this.

[0073] The size of the pulverized graphite raw material is between 7 μm and 15 μm, so that the graphite raw material after pore formation can maintain a larger particle size and serve as the main particles in the graphite negative electrode material.

[0074] As an optional embodiment, the coating agent includes at least one of petroleum asphalt, coal tar asphalt, phenolic resin, and epoxy resin.

[0075] In the embodiments of the present application, petroleum asphalt, coal tar asphalt, phenolic resin, and epoxy resin are all asphalt-based coating agents, which can reduce the impedance of the graphite negative electrode, increase the speed of lithium ion embedding, and improve the fast charging performance and low temperature performance.

[0076] When petroleum asphalt and coal tar asphalt are used as coating agents, the graphite negative electrode material can better adapt to the volume changes during the charging and discharging process, reduce the shedding and pulverization of the material, and thus improve the overall performance and service life of the battery.

[0077] When phenolic resin and epoxy resin are used as coating agents, these materials have good mechanical properties, chemical stability and high temperature performance, can isolate the positive and negative electrodes of the battery, allow lithium ions to pass through, and prevent battery explosion caused by high temperature, thereby improving the energy density, environmental protection and safety of lithium-ion batteries.

[0078] Corresponding to the aforementioned application function realization method embodiment, the present application also provides a method for preparing a graphite negative electrode material, a negative electrode sheet, an electrochemical device and corresponding embodiments.

[0079] The present application also provides a method for preparing a graphite negative electrode material, comprising:

[0080] S1. The crushed graphite raw material is subjected to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor.

[0081] The crushed graphite raw material in the embodiment of the present application can be obtained by crushing and granulating the graphite raw material. This is because the graphite raw material is generally blocky and large in size, and it is convenient to make holes and dope after being crushed into particles. The crushed graphite raw material can be granular, with a median particle size of 7μm~15μm. The graphite raw material particles within this particle size range can balance high capacity and fast charging performance. Among them, the graphite raw material can include one or more of raw coke or cooked coke such as petroleum coke, coal-based coke, oil-based needle coke, coal-based needle coke and other coke raw materials.

[0082] The embodiment of the present application forms pores in the crushed graphite raw material to provide lithium ion embedding channels, thereby improving the rate performance.

[0083] The pore-forming agent in the embodiment of the present application may be an alkaline solution, preferably at least one of a KOH solution, a NaOH solution, and a LiOH solution, wherein the mass percentage concentration of the pore-forming agent may be 10% to 30%.

[0084] S2. After mixing the porous graphite precursor with an acid solution containing heteroatoms, graphitization treatment is performed to obtain a doped porous graphite precursor doped with heteroatoms.

[0085] In the embodiment of the present application, the acid solution containing heteroatoms may include at least one of the acid solutions containing B, N, and P.

[0086] In the embodiment of the present application, a porous graphite precursor is mixed with at least one of the acid solutions containing B, N, and P, and then graphitized to obtain a doped porous graphite precursor doped with at least one of B, N, and P. Compared with the doping of transition metals and silicon atoms, the doping of atoms such as B, N, and P can utilize their electron-deficient or multi-electron characteristics after hybridization and combination with carbon atoms to improve the conductivity and ion transport properties of the porous graphite precursor. At the same time, the defect sites generated also provide more reaction sites for the embedding and adsorption of lithium ions, thereby achieving the purpose of improving the gram capacity and fast charging performance of the graphite negative electrode material.

[0087] S3. After mixing 20% ​​to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent, the mixture is granulated and carbonized to obtain secondary particles of a graphite negative electrode material; in the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and after carbonization of the coating agent, at least part of the amorphous carbon is formed to coat the outer layer of the doped porous graphite precursor.

[0088] In the embodiment of the present application, 20% to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent are mixed and granulated and carbonized. The granulation can obtain secondary particles, and the carbonization can cause the coating agent to form amorphous carbon. In the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and the amorphous carbon formed by the coating agent is coated on the outer layer of the doped porous graphite precursor filled with the hard carbon particles, which can reduce the expansion rate of the graphite negative electrode material and improve the cycle performance of the graphite negative electrode material.

[0089] The preparation method of the graphite negative electrode material in the embodiment of the present application is simple and easy to control. By etching the crushed graphite raw material to form holes, the channels for lithium ions to embed into the graphite particles are increased, and the diffusion path of lithium ions is shortened, thereby improving the fast charging performance of the graphite negative electrode material. On this basis, at least one heteroatom of B, N, and P is doped to increase the reactive active sites. The electron-deficient structure of these heteroatoms improves the conductivity of the graphite negative electrode material and is also more conducive to the adsorption and embedding of lithium ions, thereby achieving the purpose of improving the gram capacity of the graphite negative electrode material. Finally, the composite hard carbon particles are filled in the pores of the doped porous graphite precursor, which can improve the compaction and fast charging performance of graphite while protecting the heteroatom doping interface inside the pores, thereby improving the capacity and cycle performance of the graphite negative electrode material; after the carbonization of the coating agent, at least part of the amorphous carbon is formed to coat the outer layer of the doped porous graphite precursor filled with hard carbon particles. The coating of the doped porous graphite precursor filled with hard carbon particles by amorphous carbon can, on the one hand, alleviate the oxidation of hard carbon particles and heteroatoms in subsequent processes, and on the other hand, can seal the hard carbon particles in the pores of the doped porous graphite precursor, thereby improving the volume expansion buffering capacity of the secondary particles, and the amorphous carbon can further fill the pores of the doped porous graphite precursor or seal the surface of the doped porous graphite precursor, thereby reducing the specific surface area of ​​the doped porous graphite precursor while avoiding the oxidation of hard carbon particles and heteroatoms inside the doped porous graphite precursor, thereby achieving the advantages of high capacity, fast charging and long cycle life.

[0090] As an optional embodiment, the pore-making treatment temperature is 60° C. to 100° C., and the treatment time is 2 h to 10 h.

[0091] In the embodiment of the present application, the crushed graphite raw material can be immersed in a pore-forming agent at a temperature of 60° C. to 100° C. to react for 2 h to 10 h. After the reaction is completed, the porous graphite precursor can be obtained by washing.

[0092] As an optional embodiment, the temperature of the graphitization treatment is 2600°C~3200°C.

[0093] As an optional embodiment, the acid solution containing heteroatoms includes at least one of acid solutions containing B, N, and P.

[0094] In the embodiment of the present application, an acid solution containing B, N, and P is mixed with a porous graphite precursor and then graphitized to obtain a doped porous graphite precursor doped with B, N, and P atoms. An alkaline pore-forming agent that can form a good complex with the acid solution containing B, N, and P is added to the porous graphite precursor, and the hydroxyl groups in the pores of the porous graphite precursor are used to capture the carboxyl groups in the acid solution containing B, N, and P, and the B, N, and P heteroatoms are embedded in the pores to form a heteroatom-doped doped porous graphite precursor.

[0095] Preferably, it is at least one of boric acid, nitric acid and phosphoric acid. Boric acid, nitric acid and phosphoric acid are easy to obtain and basically do not contain other impurity elements, which is conducive to obtaining a pure doping product after doping and reducing the occurrence of negative reactions.

[0096] More preferably, boric acid is used, and the boric acid is mixed with the porous graphite precursor and then graphitized to obtain a doped porous graphite precursor doped with B atoms. As an optional embodiment, the sum of the mass percentages of the porous graphite precursor and the acid solution containing heteroatoms is 100%, and the mass percentage of the acid solution containing heteroatoms is 1% to 10%.

[0097] In the embodiments of the present application, the mass percentage of the acid solution containing heteroatoms can be 1%, 3%, 5%, 7%, 10% or any value within the above-defined range, and the present application does not impose any limitation on this.

[0098] If the amount of the acid solution containing heteroatoms added is too large, more defects will be formed in the crystal structure of the porous graphite precursor. More defect structures will intensify the side reaction with the electrolyte, causing faster cycle decay; if the amount of the acid solution containing heteroatoms added is too small, fewer defect structures will be formed, the material's specific capacity and conductivity will be slightly insufficient, and its energy density and rate performance will be relatively poor.

[0099] The embodiment of the present application also provides a negative electrode sheet, comprising the aforementioned graphite negative electrode material, or the graphite negative electrode material prepared by the aforementioned method for preparing the graphite negative electrode material.

[0100] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder, wherein the embodiment of the present application has no special restriction on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector, etc. The negative electrode active material is selected from the aforementioned graphite negative electrode material, or the graphite negative electrode material prepared by the aforementioned method for preparing the graphite negative electrode material.

[0101] The conductive agent and the binder in the negative electrode active material layer of the embodiment of the present application can be selected from conventional materials in the art.

[0102] An embodiment of the present application also provides an electrochemical device, comprising the aforementioned negative electrode sheet.

[0103] In the embodiment of the present application, the electrochemical device further includes a positive electrode sheet, an electrolyte and a diaphragm.

[0104] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector.

[0105] In a specific embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder. The conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, etc. The binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0106] In one embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc. and carbon materials such as carbon cloth, carbon paper, etc. Preferably, the positive electrode current collector is a metal material.

[0107] In a specific embodiment, the electrolyte further includes an electrolyte salt, and the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate; the molar concentration of the electrolyte salt in the electrolyte is 0.4 mol / L to 2.2 mol / L. When the selection and molar concentration of the electrolyte salt are within the above range, the conductivity and stability of the electrolyte can be further improved, thereby further improving the first coulomb efficiency, high temperature cycle performance, high temperature storage performance, and low temperature cycle performance of the battery.

[0108] In a specific embodiment, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, methyl acetate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether. When the organic solvent of the electrolyte is selected from the above organic solvent, the viscosity of the electrolyte is lower and the ion conductivity is higher, which is conducive to improving the migration rate of lithium ions, thereby improving the high and low temperature cycle performance of the battery, and the above organic solvent can improve the stability of the electrolyte, avoid the decomposition reaction of the electrolyte, thereby further improving the high temperature storage performance of the battery.

[0109] In a specific embodiment, the electrochemical device also includes a diaphragm. The embodiment of the present application has no particular restrictions on the material and shape of the diaphragm, as long as it does not significantly damage the effect of the present application. It may include porous sheet-like or non-woven fabric-like materials with excellent liquid retention, etc. The materials of the resin or glass fiber diaphragm include but are not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc., and can be specifically set according to needs.

[0110] In a specific embodiment, the electrochemical device may include an outer package, which can be used to encapsulate the electrode assembly and the electrolyte.

[0111] In a specific embodiment, the outer packaging of the electrochemical device can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the electrochemical device can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0112] The present application has no particular limitation on the shape of the electrochemical device, which may be cylindrical, square, or any other shape.

[0113] The embodiment of the present application also provides an electronic device, comprising the electrochemical device described above. The electronic device has the same advantages as the electrochemical device described above, which will not be described in detail.

[0114] The electronic devices of the embodiments of the present application may be conventional electronic devices in the art. By way of example, the electronic devices may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., without particular limitation.

[0115] In order to further understand the present invention, the present application is described below in conjunction with embodiments. These embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0116] 1. Preparation of lithium-ion batteries

[0117] Example 1

[0118] (1) Preparation of electrolyte

[0119] EC / PC / EMC = 2 / 1 / 7 mass ratio was mixed as an organic solvent. Add additive FEC to the organic solvent and mix well, then add LiPF6 to obtain an electrolyte with a LiPF6 concentration of 1.1 mol / L. Among them, FEC is fluoroethylene carbonate.

[0120] (2) Production of positive electrode:

[0121] S1. Grind the graphite raw material to a median particle size of 12 μm, add a 20% mass percent concentration of KOH solution, soak at 80° C. for 5 h, then wash and dry to obtain a porous graphite precursor.

[0122] S2. After uniformly mixing 95% by mass of a porous graphite precursor and 5% by mass of boric acid, graphitization is performed at 2800° C. to obtain a boron-doped porous graphite precursor.

[0123] S3. Granulate and carbonize 70% of boron-doped porous graphite precursor, 10% of hard carbon particles and 20% of coating agent at 1000°C to obtain secondary particles of graphite negative electrode material, wherein the hard carbon particles are obtained by crushing coconut shell carbon to D50 of 2μm, and the coating agent is petroleum asphalt.

[0124] S4, the secondary particles of the graphite negative electrode material in step S3 are used as negative electrode active materials, and are fully stirred and mixed with the conductive agent CNT and the binder polyvinylidene fluoride in N-methylpyrrolidone solvent at a weight ratio of 97:1.5:1.5 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0125] (3) Production of negative electrode sheet:

[0126] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in a proper amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

[0127] (4) Production of lithium-ion batteries:

[0128] Stack the positive electrode sheet, separator and negative electrode sheet in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and then wind it into a bare cell. Put the bare cell in an outer packaging bag, inject the electrolyte into the dried battery, and complete the preparation of the lithium-ion battery through vacuum packaging, static, formation, shaping and other processes.

[0129] Example 2 to Example 30, Comparative Example 1 to Comparative Example 27:

[0130] The basic contents are the same as those of Example 1, and the differences are shown in Tables 1.1 to 1.10.

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141] 2. Performance Test

[0142] The lithium-ion batteries of the above-mentioned embodiments and comparative examples were subjected to a cyclic charge and discharge test, wherein the batteries were charged to 4.5V at 3C constant current and constant voltage, cut off at 0.05C, and discharged at 0.5C, and the 0.1C gram capacity, 3C rate charging constant current ratio, cycle expansion ratio, and cycle capacity retention ratio of each battery after 600 cycles of charge and discharge were tested. The relevant test data results of the batteries of each embodiment and comparative example are shown in Tables 2.1 to 2.3.

[0143]

[0144]

[0145]

[0146] Combined with the data in the above table, the gram capacity and fast charging performance of the graphite negative electrode can be effectively improved by using alkaline solution etching to create pores, boron doping and hard carbon particle composite methods. At the same time, the battery's cycle expansion and capacity retention rate are also significantly improved.

[0147] The appropriate degree of etching can create pores of about 3μm, which can increase the doping of boron elements in the pores, thereby increasing the battery capacity. Hard carbon particles of about 2μm can better fill the pores, improve fast charging while protecting the doping interface, and improve the fast charging and cycle stability of the battery.

[0148] In summary, the present application effectively improves the gram capacity and fast charging performance of graphite negative electrode materials through reasonable material structure design, the use of alkaline solution etching pore formation, boron doping and hard carbon particle composite methods, while ensuring the performance advantages of cycle expansion and capacity retention rate, and therefore has good practical application value. Although the present application has been described with reference to the preferred embodiment, those skilled in the art will understand that various changes can be made and equivalents can replace its elements, as long as they do not deviate from the scope of the present application. In addition, many improvements can be made to adapt specific situations or materials to the teachings of the present application, as long as they do not deviate from the substantive scope of the present application. Therefore, the present application is not intended to be limited to the specific embodiments disclosed as the best way to implement the present application as conceived, but the present application will include all embodiments that fall within the scope of the attached claims.

[0149] All ranges disclosed in this application are inclusive of the endpoints, and the endpoints are combinable with each other.

[0150] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A graphite negative electrode material, characterized in that: The graphite negative electrode material comprises secondary particles formed by granulating and carbonizing 20% ​​to 90% of a doped porous graphite precursor, 5% to 30% of hard carbon particles and 5% to 50% of a coating agent, wherein the hard carbon particles at least partially fill the pores of the doped porous graphite precursor, and the coating agent at least partially forms amorphous carbon after carbonization to coat the outer layer of the doped porous graphite precursor filled with the hard carbon particles; wherein the doped porous graphite precursor The porous graphite precursor is obtained by subjecting crushed graphite raw material to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor, and then the porous graphite precursor is successively subjected to heteroatom doping and graphitization treatment; the median particle size of the crushed graphite raw material is 7μm~15μm, the pore size of the porous graphite precursor is 1μm~5μm, the heteroatom includes at least one of B, N, and P atoms, and the median particle size of the hard carbon particles is 1μm~10μm.

2. The graphite negative electrode material according to claim 1, characterized in that The hard carbon particles include at least one of biomass hard carbon, resin hard carbon, and pitch hard carbon.

3. The graphite negative electrode material according to claim 2, characterized in that: The biomass hard carbon includes at least one of coconut shell carbon, bamboo carbon, and straw carbon; and / or the resin hard carbon includes at least one of phenolic resin carbon, epoxy resin carbon, and polyfurfuryl alcohol resin carbon; and / or the asphalt hard carbon includes at least one of petroleum asphalt-based hard carbon and coal asphalt-based hard carbon.

4. The graphite negative electrode material according to claim 1, characterized in that The coating agent includes at least one of petroleum asphalt, coal tar asphalt, phenolic resin and epoxy resin.

5. The graphite negative electrode material according to claim 4, characterized in that: The graphite raw material includes at least one of a raw coke raw material and a cooked coke raw material; and / or, The pore-forming agent is an alkaline solution; and / or, The mass percentage concentration of the pore-forming agent is 10% to 30%.

6. The graphite negative electrode material according to claim 5, characterized in that: The graphite raw material is one or more of petroleum coke, coal-based coke, oil-based needle coke, and coal-based needle coke; and / or, The pore-forming agent is at least one of KOH solution, NaOH solution and LiOH solution.

7. The graphite negative electrode material according to claim 1, characterized in that The heteroatom is a B atom.

8. A method for preparing a graphite negative electrode material, characterized in that: include: The crushed graphite raw material is subjected to pore-forming treatment with a pore-forming agent to obtain a porous graphite precursor; wherein the pore-forming treatment temperature is 60°C to 100°C, and the treatment time is 2h to 10h; the pore-forming agent is an alkaline solution, and the mass percentage concentration of the pore-forming agent is 10% to 30%; The porous graphite precursor is mixed with an acid solution containing heteroatoms, and then graphitized to obtain a doped porous graphite precursor doped with heteroatoms; wherein the acid solution containing heteroatoms includes at least one of acid solutions containing B, N, and P; the sum of the mass percentages of the porous graphite precursor and the acid solution containing heteroatoms is 100%, and the mass percentage of the acid solution containing heteroatoms is 1%~10%; 20%~90% of the doped porous graphite precursor, 5%~30% of hard carbon particles and 5%~50% of the coating agent are mixed, and then granulated and carbonized to obtain secondary particles of graphite negative electrode material; in the secondary particles, the hard carbon particles are at least partially filled in the pores of the doped porous graphite precursor, and the coating agent is carbonized to at least partially form amorphous carbon coating on the outer layer of the doped porous graphite precursor.

9. The preparation method according to claim 8, characterized in that: The temperature of the graphitization treatment is 2600°C to 3200°C.

10. The preparation method according to claim 9, characterized in that: The acid solution containing heteroatoms is at least one of boric acid, nitric acid and phosphoric acid.

11. The preparation method according to claim 10, characterized in that: The heteroatom-containing acid solution is boric acid.

12. A negative electrode sheet, characterized in that: The invention comprises the graphite negative electrode material according to any one of claims 1 to 7, or the graphite negative electrode material prepared by the method for preparing the graphite negative electrode material according to any one of claims 8 to 11.

13. An electrochemical device, characterized in that: Including the negative electrode sheet as claimed in claim 12.

Images