Carbon-based negative electrode material, preparation method, secondary battery and electric device

Abstract

The invention provides a carbon-based negative electrode material, a preparation method, a secondary battery and an electric device. The carbon-based negative electrode material is granular and comprises a carbon-based core and a composite coating layer, the composite coating layer is formed on the surface of the carbon-based core and comprises a fast ion conductor and a coating auxiliary agent, and the coating auxiliary agent is used for being connected with the fast ion conductor and the carbon-based core in a chemical bonding and / or physical adsorption mode. Therefore, the composite coating layer containing the fast ion conductor stably coats the carbon-based core. A negative electrode of a secondary battery includes a carbon-based negative electrode material. The power utilization device comprises a secondary battery. The composite coating layer effectively coats the surface of the carbon-based core with the fast ion conductor, can effectively ensure the integrity of the composite coating layer in the subsequent processing process of the carbon-based negative electrode material, keeps stable coating of the fast ion conductor on the surface of the carbon-based core, and improves the coating rate of the fast ion conductor on the surface of the carbon-based core; and it is ensured that desolvation and ion transmission of lithium ions at the interface of the carbon-based negative electrode material are effectively promoted in the process that the carbon-based core stores the lithium ions.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a carbon-based negative electrode material, a preparation method, a secondary battery and an electrical device. Background Art

[0002] Lithium-ion batteries have the highest energy density among existing commercial energy storage devices, and therefore occupy an increasingly large share in the market. With the rapid development of electric vehicles and mobile electronic devices, the demand for charging speed of energy storage devices and the demand for low-temperature charging and discharging capabilities of batteries are growing. In commercial lithium-ion batteries, carbon-based anodes have become the most widely used anode materials due to their low cost and high actual capacity. However, carbon-based anodes have some disadvantages, such as limited lithium ion embedding sites, unstable interfaces, difficulty in desolvation of lithium ions on the surface of materials, and poor lithium ion diffusion capacity. These disadvantages will lead to large potential polarization in fast charging or low-temperature scenarios, thereby reducing the reversible capacity of the battery. In severe cases, it may even cause metallic lithium to precipitate on the surface of the carbon-based anode, thereby shortening the battery life. These disadvantages of carbon-based anode materials are the main factors limiting the further improvement of fast charging and low-temperature performance of commercial lithium-ion batteries.

[0003] Fast ion conductors such as lithium silicate and lithium fluoride have excellent ionic conductivity and a high lowest unoccupied molecular orbital energy level (hereinafter referred to as "LUMO energy level"), which can effectively promote the transmission of lithium ions. The high LUMO energy level of fast ion conductors can effectively promote the desolvation of lithium ions. Forming a fast ion conductor coating on the surface of the carbon-based negative electrode is an effective strategy to improve the fast charging and low temperature performance of lithium-ion batteries.

[0004] However, on the one hand, it is difficult for fast ion conductors to effectively adhere to the surface of the carbon-based core, so it is difficult to form a uniform and stable coating layer; on the other hand, it is difficult for the fast ion conductor layer to remain intact during the production and manufacturing process of the electrode sheet, and the stirring and coating processes during the electrode manufacturing process may destroy its integrity.

[0005] Therefore, there is an urgent need for a new type of carbon-based negative electrode material, preparation method, secondary battery and electrical device. Summary of the invention

[0006] The first aspect of the present application provides a carbon-based negative electrode material in a granular form, comprising:

[0007] Carbon-based core;

[0008] A composite coating layer is formed on the surface of the carbon-based core. The composite coating layer includes a fast ion conductor and a coating auxiliary agent. The coating auxiliary agent is used to connect with the fast ion conductor and the carbon-based core by chemical bonding and / or physical adsorption, so that the composite coating layer containing the fast ion conductor can stably coat the carbon-based core.

[0009] In some optional embodiments of the first aspect of the present application, the geometric mean radius of the particles of the carbon-based negative electrode material is R, and the geometric mean radius of the outer contour of the carbon-based core and the geometric mean radius of the outer contour of the composite coating layer are L respectively. 1 and L 2 , L 1 , L 2 The relationship between and R satisfies: 80% ≤ L 1 / R <L 2 / R,L 2 / R=100%.

[0010] In some optional embodiments of the first aspect of the present application, the composite coating layer completely wraps the carbon-based core.

[0011] In some optional embodiments of the first aspect of the present application, the value range of R is 1 μm to 50 μm.

[0012] In some optional embodiments of the first aspect of the present application, L 1 The value range is 8μm~25μm.

[0013] In some optional embodiments of the first aspect of the present application, the value range of R is 9 μm to 25 μm.

[0014] In some optional embodiments of the first aspect of the present application, the carbon-based core includes one or more of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, and soft carbon.

[0015] In some optional embodiments of the first aspect of the present application, the fast ion conductor includes one or more of lithium silicate, lithium nitride, lithium borate, lithium fluoride, lithium carbonate, lithium hydroxide, lithium phosphate, lithium sulfate, lithium iodate, lithium sulfide, lithium phosphide, lithium acetate, lithium chloride, lithium bromide, lithium iodide, and lithium phosphosulfide; and / or

[0016] Lithium silicate includes Li 4 SiO 4 , Li 2 SiO 3 , Li 2 Si 2 O 5 , Li 6 Si 2 O 7 , Li 2 Si 5 O 11 One or more of; and / or

[0017] Lithium phosphosulfide includes Li 3 PS 4 , Li 2 PS 3, Li 7 P 3 S 11 , Li 10 GeP 2 S 12 , Li 9 SiPS 8 Cl, Li 6 PS 5 Cl, Li z PS x Cl y (where 0 < x, y ≤ 7, z = 2x + y - 5) or more of them.

[0018] In some alternative embodiments of the first aspect of the present application, the covalent bonds in the chemical bonding include one or more of C - O, C = O, C - P, C - S, Li - C, C - Si, C - F, C - N, C - B, C - I, C - O - P, C - O - Si, C - O - B, C - N - Si, C - P - Si.

[0019] In some alternative embodiments of the first aspect of the present application, the coating adjuvant includes one or more of hard carbon, soft carbon, graphite, and conductive polymers.

[0020] In some alternative embodiments of the first aspect of the present application, the conductive polymers include: one or more of polyaniline, polypyrrole, polythiophene, poly(p - phenylene ethynylene), polyacetylene, polyfluorene, poly(phenylene vinylene), polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, lithium polysilicate, lithium polysulfide, polyacrylonitrile, and their derivatives.

[0021] The second aspect of the present application provides a method for preparing the carbon - based anode material of the first aspect of the present application. The coating adjuvant includes one or more of hard carbon, soft carbon, and graphite. The method for preparing the carbon - based anode material includes:

[0022] S1: Disperse the carbon - based core, the precursor of the coating adjuvant, and the fast - ion conductor in a first solvent to obtain a mixed solution.

[0023] S2: Knead the mixed solution with a kneader for a first period of time, and then obtain an intermediate product after the first solvent in the mixed solution volatilizes and dries.

[0024] S3: Calcinate at a first temperature for a second period of time in an inert atmosphere to obtain the carbon - based anode material.

[0025] Alternatively, the coating adjuvant includes a conductive polymer. The method for preparing the carbon - based anode material includes:

[0026] S1': Disperse the carbon - based core, the precursor of the coating adjuvant, and the fast - ion conductor in a second solvent, and then add an initiator and stir - react for a third period of time to obtain a crude product.

[0027] S2': The crude product is washed, filtered and dried to obtain a carbon-based negative electrode material.

[0028] In some optional embodiments of the second aspect of the present application, the soft carbon is asphalt-based soft carbon.

[0029] In some optional embodiments of the second aspect of the present application, the first duration is 3 to 5 hours.

[0030] In some optional embodiments of the second aspect of the present application, the first temperature is 500°C to 3000°C.

[0031] In some optional embodiments of the second aspect of the present application, the second duration is 4 to 6 hours.

[0032] In some optional embodiments of the second aspect of the present application, the solvent in the mixed liquid in step S2 is dried by natural evaporation.

[0033] In some optional embodiments of the second aspect of the present application, the conductive polymer is polypyrrole, the precursor of the coating auxiliary agent includes pyrrole and phytic acid, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride.

[0034] In some optional embodiments of the second aspect of the present application, the third duration is 22 hours to 26 hours.

[0035] In some optional embodiments of the second aspect of the present application, in step S1 and step S1', the mass ratio of the carbon-based core and the fast ion conductor is (99.9:0.1) to (1:1), and the mass ratio of the fast ion conductor and the precursor of the coating auxiliary agent is (1:10) to (10:1).

[0036] In some optional embodiments of the second aspect of the present application, the mass ratio of the carbon-based core to the fast ion conductor is (99.5:0.5) to (95:5).

[0037] In some optional embodiments of the second aspect of the present application, the mass ratio of the precursors of the fast ion conductor and the coating auxiliary agent is (1:2) to (2:1).

[0038] A third aspect of the present application provides a secondary battery, wherein the negative electrode sheet of the secondary battery comprises the carbon-based negative electrode material of the first aspect of the present application,

[0039] Alternatively, the carbon-based negative electrode material in the negative electrode sheet of the secondary battery is prepared using the preparation method provided in the second aspect of the present application.

[0040] A fourth aspect of the present application provides an electrical device, comprising the secondary battery of the third aspect of the present application.

[0041] Beneficial effects:

[0042] The first aspect of the present application provides a carbon-based negative electrode material, which includes a carbon-based core and a composite coating layer, in which a coating auxiliary agent is used to connect with a fast ion conductor and a carbon-based core by chemical bonding and / or physical adsorption, and the fast ion conductor is compounded with some materials (coating auxiliary agents) that can better physically adsorb and / or chemically bond with the carbon-based core, so that a coating layer structure containing a fast ion conductor is more easily formed on the surface of the carbon-based core. The composite coating layer effectively coats the fast ion conductor on the surface of the carbon-based core, and can effectively ensure the integrity of the composite coating layer during the subsequent processing of the carbon-based negative electrode material, maintain the stable coating of the fast ion conductor on the surface of the carbon-based core and increase the coating rate of the fast ion conductor on the surface of the carbon-based core, ensuring that the desolvation and ion transport of lithium ions at the interface of the carbon-based negative electrode material are effectively promoted during the storage of lithium ions by the carbon-based core.

[0043] The second aspect of the present application provides a method for preparing a carbon-based negative electrode material. The operation is simple, and the carbon-based negative electrode material with a composite coating layer can be efficiently prepared. The composite coating layer contains a fast ion conductor and a coating auxiliary agent composited therewith. The addition of the coating auxiliary agent ensures that the fast ion conductor effectively, uniformly and stably coats the carbon-based core surface.

[0044] The third aspect of the present application provides a secondary battery, which uses the carbon-based negative electrode material provided in the first aspect of the present application as a negative electrode active material. In the carbon-based negative electrode material, a composite coating layer is provided on the surface of the carbon-based core, and the physical adsorption and / or chemical bonding between the coating auxiliary agent and the carbon-based core ensures that the fast ion conductor is stably coated on the carbon-based core. During the use of the secondary battery, the transmission speed of lithium ions in the carbon-based negative electrode material is increased and the desolvation of the surface of the carbon-based negative electrode material is effectively promoted, thereby improving the charging speed, low temperature performance and battery cycle stability of the secondary battery.

[0045] The fourth aspect of the present application provides an electric device, which includes the secondary battery in the second aspect of the present application. The electric device has a shorter charging waiting time, good safety in a low temperature environment, and a longer cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the cross-sectional structure of the carbon-based negative electrode material particles of the present application;

[0047] Figure 2 This is a schematic diagram of the polar coordinate distribution of the calculation of the geometric radius of irregular figures;

[0048] Figure 3 It is a comparison diagram of the fast ion conductor coverage of the carbon-based negative electrode material with a composite coating layer in Example 1 of the present application and the carbon-based negative electrode material with only a fast ion conductor layer in Comparative Example 1 after the negative electrode material is prepared;

[0049] Figure 4 It is a comparison diagram of the fast ion conductor coverage of the carbon-based negative electrode material with a composite coating layer in Example 1 of the present application and the carbon-based negative electrode material with only a fast ion conductor layer in Comparative Example 1 after simulated stirring of the negative electrode material;

[0050] Figure 5 is a SEM image of graphite with composite coating. DETAILED DESCRIPTION

[0051] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0052] The first aspect of the present application provides a carbon-based negative electrode material having a cross-sectional structure such as Figure 1 As shown, the carbon-based negative electrode material has a granular shape, including:

[0053] Carbon-based core;

[0054] A composite coating layer is formed on the surface of the carbon-based core. The composite coating layer includes a fast ion conductor and a coating auxiliary agent. The coating auxiliary agent is used to connect with the fast ion conductor and the carbon-based core by chemical bonding and / or physical adsorption, so that the composite coating layer containing the fast ion conductor can stably coat the carbon-based core.

[0055] like Figure 2 As shown, in some optional embodiments of the first aspect of the present application, the geometric mean radius of the particles of the carbon-based negative electrode material is R, which is calculated according to the following formula (1):

[0056]

[0057] In formula (1), R(θ) is the geometric radius when the angle is θ, and the geometric mean radius of the outer contour of the carbon-based core and the geometric mean radius of the outer contour of the composite coating are L 1 and L 2 , L 1 , L 2 The relationship between and R satisfies: 80% ≤ L 1 / R <L 2 / R,L 2 / R=100%.

[0058] Fast ion conductors can effectively promote lithium ion transport and desolvation, but fast ion conductors are difficult to effectively attach to the surface of the carbon-based core and form a uniform and stable coating. The stirring and coating processes during electrode manufacturing may destroy their integrity. Coating aids are used to connect the fast ion conductor and the carbon-based core by chemical bonding and / or physical adsorption. The fast ion conductor is compounded with some materials (coating aids) that can better physically adsorb and / or chemically bond with the carbon-based core, making it easier to form a coating structure containing a fast ion conductor on the surface of the carbon-based core. The composite coating effectively coats the fast ion conductor on the surface of the carbon-based core and can effectively ensure the integrity of the composite coating during the subsequent processing of the carbon-based negative electrode material.

[0059] In some optional embodiments of the first aspect of the present application, the composite coating layer completely wraps the carbon-based core.

[0060] In some optional embodiments of the first aspect of the present application, the value range of R is 1 μm to 50 μm.

[0061] In some optional embodiments of the first aspect of the present application, L 1 The value range is 8μm~25μm.

[0062] In some optional embodiments of the first aspect of the present application, the value range of R is 9 μm to 25 μm.

[0063] In some optional embodiments of the first aspect of the present application, the carbon-based core includes one or more of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, and soft carbon.

[0064] In some optional embodiments of the first aspect of the present application, the fast ion conductor includes one or more of lithium silicate, lithium nitride, lithium borate, lithium fluoride, lithium carbonate, lithium hydroxide, lithium phosphate, lithium sulfate, lithium iodate, lithium sulfide, lithium phosphide, lithium acetate, lithium chloride, lithium bromide, lithium iodide, and lithium phosphosulfide; and / or

[0065] Lithium silicate includes Li 4 SiO 4 , Li 2 SiO 3 , Li 2 Si 2 O 5 , Li 6 Si 2 O 7 , Li 2 Si 5 O 11 One or more of; and / or

[0066] Lithium phosphosulfide includes Li 3 PS 4, Li 2 PS 3 , Li 7 P 3 S 11 , Li 10 GeP 2 S 12 , Li 9 SiPS 8 Cl, Li 6 PS 5 Cl, Li z PS x Cl y (where 0 < x, y ≤ 7, z = 2x + y - 5) or more of them.

[0067] In some optional embodiments of the first aspect of the present application, the covalent bonds in the chemical bonding include one or more of C - O, C = O, C - P, C - S, Li - C, C - Si, C - F, C - N, C - B, C - I, C - O - P, C - O - Si, C - O - B, C - N - Si, C - P - Si.

[0068] In some optional embodiments of the first aspect of the present application, the coating adjuvant includes one or more of hard carbon, soft carbon, graphite, and conductive polymer.

[0069] In some optional embodiments of the first aspect of the present application, the conductive polymer includes: one or more of polyaniline, polypyrrole, polythiophene, poly(phenylene vinylene), polyacetylene, polyfluorene, poly(phenylene ethylene), polyacrylic acid, polytetrafluoroethylene, poly(vinylidene fluoride), carboxymethyl cellulose, lithium polysilicate, lithium polysulfide, polyacrylonitrile, and their derivatives.

[0070] The second aspect of the present application provides a preparation method of the carbon - based anode material of the first aspect of the present application. The coating adjuvant includes one or more of hard carbon, soft carbon, and graphite. The preparation method of the carbon - based anode material includes:

[0071] S1: Dispersing the carbon - based core, the precursor of the coating adjuvant, and the fast - ion conductor in the first solvent to obtain a mixed solution.

[0072] S2: Kneading the mixed solution with a kneader for the first period of time, and then obtaining an intermediate product after the first solvent in the mixed solution volatilizes and dries.

[0073] S3: Calcining at the first temperature for the second period of time in an inert atmosphere to obtain the carbon - based anode material.

[0074] Alternatively, the coating adjuvant includes a conductive polymer. The preparation method of the carbon - based anode material includes:

[0075] S1': dispersing the carbon-based core, the precursor of the coating auxiliary agent and the fast ion conductor in the second solvent, adding an initiator and stirring the reaction for a third time to obtain a crude product;

[0076] S2': The crude product is washed, filtered and dried to obtain a carbon-based negative electrode material.

[0077] In some optional embodiments of the second aspect of the present application, the soft carbon is asphalt-based soft carbon.

[0078] In some optional embodiments of the second aspect of the present application, the first duration is 3 to 5 hours.

[0079] In some optional embodiments of the second aspect of the present application, the first temperature is 500°C to 3000°C.

[0080] In some optional embodiments of the second aspect of the present application, the second duration is 4 to 6 hours.

[0081] In some optional embodiments of the second aspect of the present application, the solvent in the mixed liquid in step S2 is dried by natural evaporation.

[0082] In some optional embodiments of the second aspect of the present application, when the conductive polymer is polypyrrole, the precursor of the coating auxiliary agent includes pyrrole and phytic acid, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride.

[0083] In some optional embodiments of the second aspect of the present application, the third duration is 22 hours to 26 hours.

[0084] In some optional embodiments of the second aspect of the present application, in step S1 and step S1', the mass ratio of the carbon-based core and the fast ion conductor is (99.9:0.1) to (1:1), and the mass ratio of the fast ion conductor and the precursor of the coating auxiliary agent is (1:10) to (10:1).

[0085] In some optional embodiments of the second aspect of the present application, the mass ratio of the carbon-based core to the fast ion conductor is (99.5:0.5) to (95:5).

[0086] In some optional embodiments of the second aspect of the present application, the mass ratio of the precursors of the fast ion conductor and the coating auxiliary agent is (1:2) to (2:1).

[0087] In some optional embodiments of the second aspect of the present application, the first solvent and the second solvent respectively include one or more of deionized water, anhydrous ethanol, NN dimethylacetamide, NN dimethylpyrrolidone, and tetrahydrofuran.

[0088] A third aspect of the present application provides a secondary battery, wherein the negative electrode sheet of the secondary battery comprises the carbon-based negative electrode material of the first aspect of the present application,

[0089] In some optional embodiments of the third aspect of the present application, the carbon-based negative electrode material in the negative electrode sheet of the secondary battery is prepared using the preparation method provided by the second aspect of the present application.

[0090] The secondary battery provided in the third aspect of the present application uses the carbon-based negative electrode material provided in the first aspect of the present application as the negative electrode active material, and has good fast charging performance, low temperature performance and battery cycle stability.

[0091] A fourth aspect of the present application provides an electrical device, comprising the secondary battery of the third aspect of the present application.

[0092] The electrical device provided in the fourth aspect of the present application has a faster charging speed and a longer cycle life, and has good safety at low temperatures. [Specific embodiment]

[0094] The following specific examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0095] 1. Preparation of batteries in embodiments and comparative examples

[0096] [Example 1]

[0097] <Preparation of negative electrode active material>

[0098] The artificial graphite FSN-2 (hereinafter referred to as "artificial graphite") produced by Shanshan Technology was graded using a classifier, and artificial graphite with a particle size range of 10μm to 20μm was selected as the carbon-based core; lithium silicate was used as a fast ion conductor, and asphalt-based soft carbon was used as a coating auxiliary agent. The specific preparation process is as follows:

[0099] Artificial graphite, lithium silicate and asphalt are dispersed in N,N-dimethylformamide (DMF) in a mass ratio of 96:2:3, and kneaded for 3 hours using a kneader. After the DMF solvent evaporates and dries naturally, it is calcined at 1000°C in an argon atmosphere for 5 hours to obtain the carbon-based negative electrode material in Example 1. The internal and external particle structures of the carbon-based negative electrode material are respectively: the internal part is graphite as a carbon-based core, and the external part is a composite coating layer using lithium silicate as a fast ion conductor and asphalt-based soft carbon as a coating auxiliary agent. The carbon-based negative electrode material is used as the negative electrode active material.

[0100] <Preparation of negative electrode sheet>

[0101] The negative electrode active material prepared according to the steps in <Preparation of negative electrode active material>, Ketjen black as a conductive additive, styrene butadiene rubber (abbreviated as SBR) as a binder and sodium carboxymethyl cellulose (abbreviated as CMC) as a thickener are mixed in a mass ratio of 95:1.5:1.5:2, and an appropriate amount of deionized water is added as a solvent, and the mixture is stirred and mixed to form a uniform negative electrode slurry. The slurry is coated on the current collector copper foil, dried in a vacuum oven at 110°C, and then cold pressed using a roller press to obtain a negative electrode sheet.

[0102] <Preparation of positive electrode sheet>

[0103] The positive electrode is selected from lithium cobalt oxide (chemical formula: LiCoO 2 ) is used as the positive electrode active material, and the positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (abbreviated as PVDF) as a binder are fully stirred and mixed in a proper amount of N-methylpyrrolidone (abbreviated as NMP) solvent in a mass ratio of 95:3:2 to form a uniform positive electrode slurry; the slurry is coated on the current collector aluminum foil, and dried and cold pressed in the same way as the negative electrode sheet to obtain the positive electrode sheet.

[0104] <Preparation of Electrolyte>

[0105] In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC:EMC:DMC=1:1:1, dissolved, and stirred thoroughly before adding lithium salt LiPF 6 , and then mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, LiPF 6 The mass percentage is 12.5%.

[0106] <Diaphragm>

[0107] Polypropylene (PP) porous polymer film was selected as the separator.

[0108] <Preparation of lithium-ion batteries>

[0109] The negative electrode sheet and the positive electrode sheet prepared according to the above steps are separated by an isolation film, and the battery cell is packaged with an aluminum-plastic film, and then the above electrolyte is added, packaged, and left to stand. The entire battery production process is carried out in a dry room or a glove box with an argon atmosphere where the water and oxygen content are less than 0.01ppm.

[0110] [Example 2]

[0111] The difference between Example 2 and Example 1 is that: <Preparation of negative electrode active material> is replaced by:

[0112] Graphite, lithium silicate, pyrrole, and phytic acid were dispersed in water in a mass ratio of 96:2:0.2:1.8, and ammonium persulfate was added as an initiator, with a mass ratio of ammonium persulfate to pyrrole of 1:20. After stirring and reacting for 24 hours, the particles were washed with deionized water, filtered, and dried in sequence to obtain a carbon-based negative electrode material having a particle structure of graphite as a carbon-based core and a composite coating layer of lithium silicate as a fast ion conductor and polypyrrole as a coating auxiliary agent. The carbon-based negative electrode material was used as the negative electrode active material.

[0113] The rest is the same as Example 1.

[0114] [Example 3]

[0115] Compared with Example 1, Example 3 is different in that lithium silicate in the raw material is replaced with lithium fluoride. The rest is the same as Example 1.

[0116] [Example 4]

[0117] Compared with Example 2, Example 4 is different in that lithium silicate in the raw material is replaced with lithium fluoride. The rest is the same as Example 2.

[0118] [Example 5]

[0119] Compared with Example 1, Example 5 is different in that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Example 1.

[0120] [Example 6]

[0121] Compared with Example 2, Example 6 is different in that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Example 2.

[0122] [Example 7]

[0123] Compared with Example 3, Example 7 is different in that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Example 3.

[0124] [Example 8]

[0125] Compared with Example 4, Example 8 is different in that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Example 4.

[0126] [Example 9]

[0127] Compared with Example 1, Example 9 is different in that the mass ratio of artificial graphite, lithium silicate and asphalt is changed to 88:10:2. The rest is the same as Example 1.

[0128] [Example 10]

[0129] Compared with Example 2, Example 10 is different in that the mass ratio of artificial graphite, lithium silicate, pyrrole and phytic acid is changed to 88:10:0.2:1.8. The rest is the same as Example 2.

[0130] [Examples 11 to 14]

[0131] Compared with Example 1, the differences of Examples 11 to 14 are as follows:

[0132] The mass ratios of artificial graphite, lithium silicate and asphalt in Example 11, Example 12, Example 13 and Example 14 were changed to 85:10:5, 80:10:5, 75:10:5 and 70:10:5 respectively.

[0133] The rest is the same as Example 1.

[0134] [Examples 15 to 18]

[0135] Compared with Example 1, the differences of Examples 15 to 18 are as follows:

[0136] The classified particle sizes of the artificial graphite in Examples 15, 16, 17 and 18 were changed to 1 μm to 10 μm, 20 μm to 25 μm, 30 μm to 35 μm and 40 μm to 45 μm, respectively.

[0137] The rest is the same as Example 1.

[0138] [Comparative Example 1]

[0139] The difference between Comparative Example 1 and Example 1 is that: No asphalt as a precursor of the coating auxiliary agent is added in Comparative Example 1. The rest is the same as Example 1.

[0140] [Comparative Example 2]

[0141] Comparative Example 2 is different from Comparative Example 1 in that lithium silicate in the raw material is replaced with lithium fluoride. The rest is the same as Comparative Example 1.

[0142] [Comparative Example 3]

[0143] The difference between Comparative Example 3 and Comparative Example 1 is that the artificial graphite in the raw material is replaced by hard carbon. The rest is the same as Comparative Example 1.

[0144] [Comparative Example 4]

[0145] Comparative Example 4 is different from Comparative Example 2 in that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Comparative Example 1.

[0146] [Comparative Examples 5 to 8]

[0147] Compared with Comparative Example 1, Comparative Examples 5 to 8 are different in that:

[0148] The classified particle sizes of the artificial graphite in Comparative Examples 5, 6, 7 and 8 were changed to 1 μm to 10 μm, 20 μm to 25 μm, 30 μm to 35 μm and 40 μm to 45 μm, respectively.

[0149] The rest is the same as Comparative Example 1.

[0150] 2. Test methods and equipment:

[0151] 1. Gram capacity test

[0152] The gram capacity test can refer to the standard: GB / T 24533-2019. First, the negative electrode active material is made into a negative electrode sheet through the steps of mixing, coating, rolling, punching and drying. Then, a lithium sheet is used as a counter electrode to assemble a button battery for testing. The capacity of the button battery is tested at a small current rate of 0.1C to calculate the gram capacity of the material.

[0153] 2. Constant current charge and discharge test

[0154] The lithium-ion secondary battery was subjected to a constant current rate test and a cycle test.

[0155] Rate testing means cycling the battery 5 times at the following rates: 0.1C, 0.2C, 0.5C, 1C, 2C, 4C, and 6C.

[0156] Cycle testing refers to testing the battery at a rate of 1C.

[0157] Low temperature performance testing refers to placing the battery in a -10°C constant temperature box for constant current charge and discharge testing.

[0158] 3. Test of element content of negative electrode active material

[0159] The negative electrode active material was stirred in aqua regia (hydrochloric acid: nitric acid = 3:1) and heated in an oil bath at 80°C. After the solid in the solution was completely dissolved, a uniform solution was taken for inductively coupled plasma emission spectroscopy (ICP) testing to obtain the content of different elements in the negative electrode active material.

[0160] For Example 1 and Comparative Example 1, the actual coverage rate of lithium silicate on the carbon-based core surface was obtained by calculating the ratio of the silicon content of the negative electrode active material obtained by ICP test to the original silicon content of the lithium silicate actually fed during the synthesis process.

[0161] 4. Element content test after simulated stirring

[0162] After the negative electrode active material is heated and stirred at 70°C in deionized water for 24 hours, the material is vacuum filtered and dried. Then the materials of different particle sizes are graded with a classifier, and materials with commonly used particle sizes (10 microns to 20 microns) for commercial carbon-based negative electrodes are selected to remove residual impurities and avoid interference with element testing. The graded negative electrode active material is stirred in aqua regia and heated in an oil bath at 80°C. After the solid in the solution is completely dissolved, a uniform solution is taken for ICP testing to obtain the content of different elements in the active substance.

[0163] For Example 1 and Comparative Example 1, the actual coverage rate of lithium silicate on the carbon-based negative electrode surface after simulated stirring can be obtained by calculating the ratio of the silicon element content of the negative electrode active material obtained by ICP test and the original silicon content of the lithium silicate actually fed during the synthesis process.

[0164] 5. Negative electrode active material structure composition and size test

[0165] The active material was observed for morphology using a scanning electron microscope (SEM, magnification of 5000). Some particles (10 randomly selected) were selected and cut using a focused ion beam. After the cross section was cut, the cross section was subjected to a surface distribution test of the energy spectrum (EDS-mapping). In the above embodiments and comparative examples, the distribution area of ​​the carbon element was used to calibrate the distribution area of ​​the carbon-based core, the distribution area of ​​the silicon element was used to calibrate the distribution area of ​​lithium silicate, the distribution area of ​​the fluorine element was used to calibrate the distribution area of ​​lithium fluoride, the distribution area of ​​the nitrogen element was used to calibrate the distribution area of ​​polypyrrole, and the distribution area of ​​the sulfur element combined with the carbon element was used to calibrate the distribution area of ​​asphalt-based soft carbon. According to the above description of R and L in the irregular figure, 1 and L 2 The SEM images and EDS-mapping images collected from all particle tests were analyzed as follows: the R and L of each particle cross section were calculated using the artificial intelligence (AI) image recognition method and Matlab modeling. 1 and L 2 The relevant data are summarized in Table 1. The above test is performed on all particles selected from each sample to obtain the R and L of each particle. 1 and L 2 , and calculate the L of each particle 1 / R and L 2 / R, take the average value to get the L in each sample 1 / R and L 2 / R, the relevant data are summarized in Table 1.

[0166] Table 1 Summary of the structural composition and proportions of the embodiments and comparative examples

[0167]

[0168] The following conclusions can be drawn from the data in Table 1:

[0169] The data of Examples 1 to 8 show that the combination of fast ion conductors made of different materials (such as lithium salts such as lithium silicate and lithium fluoride) and coating auxiliary agents made of different materials (such as asphalt-based soft carbon and polypyrrole) can form a composite coating layer on a variety of carbon-based cores (such as graphite and hard carbon).

[0170] The data of Examples 9 to 14 show that adjusting the mass ratio of the carbon-based core (with the same particle size range), the fast ion conductor and the precursor of the coating auxiliary agent can adjust the size between the carbon-based core and the composite coating layer, that is, adjust the L 1 / R size.

[0171] The data of Examples 15 to 18 show that when the mass ratio of the carbon-based core, the fast ion conductor and the precursor of the coating auxiliary agent is kept unchanged and the particle size range of the carbon-based core is adjusted, L 1 / R has a smaller range of variation, while R and L 2 It increases with the increase of the carbon-based core particle size range, that is, the overall particle size in the carbon-based negative electrode material increases.

[0172] 3. Test Results

[0173] The lithium ion batteries obtained in Examples 1 to 18 and Comparative Examples 1 to 8 were subjected to various performance tests and material characterizations according to the test methods in Part 2. The results are shown in Table 2 and Figures 3 to 5 shown.

[0174] Table 2 Performance test results of each embodiment and each comparative example

[0175]

[0176]

[0177] The test results of Examples 1 to 8 and Comparative Examples 1 to 4 in Table 2 are analyzed. Example 1 and Example 2 are compared with Comparative Example 1, Example 3 and Example 4 are compared with Comparative Example 2, and so on. The comparative example and the two groups of examples arranged thereon can be used as a comparison group. It can be found that the examples in which the coating auxiliary agent is added to form a composite coating layer have greatly improved 6C capacity, -10°C capacity and capacity after 1000 cycles of 1C, compared with the corresponding comparative examples, that is, the fast charging, low temperature and cycle performance of the secondary battery are significantly improved.

[0178] The data comparison of Example 1, Example 9 and Example 11 to Example 14 with Comparative Example 1 in Table 2 shows that the relative size between the carbon-based core and the composite coating layer (the coating auxiliary agent is asphalt-based soft carbon) has changed. Compared with the corresponding comparative example, the 6C capacity, -10℃ capacity and 1C capacity after 1000 cycles in Table 2 have been improved to varying degrees. 1 When / R is large, the fast charging, low temperature and cycle performance of the secondary battery are significantly improved. When the proportion of the composite coating layer is too high and the proportion of the carbon-based core is too low, the reversible capacity of the negative electrode will be affected. As shown in Example 14, when L 1 / R<80%, the reversible capacity of the negative electrode active material at 0.1C rate is affected and reduced to less than 290mAh / g (i.e., the 0.1C initial capacity in Table 2), but the purpose of improving the low temperature and fast charging performance of the secondary battery can also be achieved. The data comparison of Example 2, Example 10 and Comparative Example 1 in Table 2 also shows that when the relative size between the carbon-based core and the composite coating layer (the coating auxiliary agent is polypyrrole) changes, the 6C capacity, -10℃ capacity and the capacity after 1C cycle 1000 cycles of each embodiment are improved to varying degrees compared with the corresponding comparative example.

[0179] By analyzing the data of Example 1, Example 15 to Example 18 and Comparative Example 1, Comparative Example 5 to Comparative Example 8 in Table 2, it can be found that: within the commonly used particle size range of commercial carbon-based negative electrode materials (the value range of R is 1μm to 50μm), the embodiment of adding a coating auxiliary agent to form a composite coating layer has greatly improved the 6C capacity, the 0.1C capacity at -10°C, and the capacity after 1000 cycles of 1C, relative to the corresponding comparative examples, that is, the fast charging, low temperature and cycle performance of the secondary battery have been significantly improved. Further, when the value range of R is 9μm to 25μm, the fast charging, low temperature and cycle performance of the secondary battery are more significantly improved.

[0180] Combination Figure 3 and Figure 4 It can be found that after the initial preparation of the carbon-based negative electrode material is completed or after the carbon-based negative electrode material is prepared and stirred in an aqueous solution, the coverage rate of the fast ion conductor in the embodiment is significantly improved compared with the comparative example. It can be seen that the coating auxiliary agent in the embodiment effectively improves the adhesion ability of the fast ion conductor on the carbon-based core, and significantly improves the kinetic performance of the negative electrode active material in the process of storing metal ions, thereby improving the fast charging and low temperature performance of the battery.

[0181] It should be noted that, in this article, "includes", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such process, method or article.

[0182] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0183] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A carbon-based negative electrode material, characterized in that: In granular form, including: Carbon-based core; A composite coating layer is arranged on the surface of the carbon-based core, and the composite coating layer includes a fast ion conductor and a coating auxiliary agent. The coating auxiliary agent is used to connect with the fast ion conductor and the carbon-based core by chemical bonding and / or physical adsorption, so that the composite coating layer containing the fast ion conductor can stably coat the carbon-based core.

2. The carbon-based negative electrode material according to claim 1, characterized in that The geometric mean radius of the particles of the carbon-based negative electrode material is R, The geometric mean radius of the outer contour of the carbon-based core and the geometric mean radius of the outer contour of the composite coating layer are L1 and L2 respectively, and the relationship between L1, L2 and R satisfies: 80%≤L1 / R <L2 / R,L2 / R=100%。 3. The carbon-based negative electrode material according to claim 1 or 2, characterized in that: The composite coating layer completely wraps the carbon-based core.

4. The carbon-based negative electrode material according to claim 2, characterized in that: The carbon-based negative electrode material satisfies at least one of the following conditions: (1) The value range of R is 1 μm to 50 μm; preferably, the value range of R is 9 μm to 25 μm; (2) The value range of L1 is 8μm to 25μm.

5. The carbon-based negative electrode material according to claim 1, characterized in that: The carbon-based core includes one or more of natural graphite, artificial graphite, mesophase carbon microbeads, hard carbon, and soft carbon.

6. The carbon-based negative electrode material according to claim 1, characterized in that: The fast ion conductor includes one or more of lithium silicate, lithium nitride, lithium borate, lithium fluoride, lithium carbonate, lithium hydroxide, lithium phosphate, lithium sulfate, lithium iodate, lithium sulfide, lithium phosphide, lithium acetate, lithium chloride, lithium bromide, lithium iodide, and lithium phosphosulfide; and / or The lithium silicate includes Li4SiO4, Li2SiO3, Li2Si2O5, Li6Si2O7, Li2Si5O 11 One or more of; and / or The lithium phosphorus sulfide includes Li3PS4, Li2PS3, Li7P3S 11 , Li 10 GeP2S 12 , Li9SiPS8Cl, Li6PS5Cl, Li z PS x Cl y (where 0 < x, y ≤ 7, z = 2x + y - 5) or one or more of them.

7. The carbon-based negative electrode material according to claim 1, characterized in that: The covalent bonds in the chemical bonding include one or more of CO, C=O, CP, CS, Li-C, C-Si, CF, CN, CB, CI, COP, CO-Si, COB, CN-Si, and CP-Si.

8. The carbon-based negative electrode material according to claim 1, characterized in that: The coating auxiliary agent includes one or more of hard carbon, soft carbon, graphite, and conductive polymer; Preferably, the conductive polymer includes one or more of polyaniline, polypyrrole, polythiophene, poly(p-phenylene vinylene), polyacetylene, polyfluorene, poly(phenylene vinylene), polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, lithium polysilicate, lithium polysulfide, polyacrylonitrile and their derivatives.

9. A method for preparing a carbon-based negative electrode material according to any one of claims 1 to 7, characterized in that: The coating auxiliary agent includes one or more of hard carbon, soft carbon and graphite, and the preparation method of the carbon-based negative electrode material includes: S1: dispersing the carbon-based core, the precursor of the coating auxiliary agent and the fast ion conductor in a first solvent to obtain a mixed solution, S2: kneading the mixed solution for a first period of time using a kneading machine, and then evaporating and drying the first solvent in the mixed solution to obtain an intermediate product, S3: calcining at a first temperature for a second time in an inert atmosphere to obtain the carbon-based negative electrode material, Preferably, the soft carbon is asphalt-based soft carbon. Preferably, the first duration is 3 to 5 hours. Preferably, the first temperature is 500°C to 3000°C, Preferably, the second duration is 4 to 6 hours; Preferably, the solvent in the mixed solution in step S2 is dried by natural evaporation; Alternatively, the coating auxiliary agent includes a conductive polymer, and the method for preparing the carbon-based negative electrode material includes: S1': dispersing the carbon-based core, the precursor of the coating auxiliary agent and the fast ion conductor in a second solvent, adding an initiator and stirring the reaction for a third time to obtain a crude product; S2': washing, filtering and drying the crude product to obtain the carbon-based negative electrode material; Preferably, the conductive polymer is polypyrrole, the precursor of the coating auxiliary agent includes pyrrole and phytic acid, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride; Preferably, the third duration is 22h to 26h; Preferably, in step S1 and step S1': The mass ratio of the carbon-based core to the fast ion conductor is (99.9:0.1) to (1:1), preferably, the mass ratio of the carbon-based core to the fast ion conductor is (99.5:0.5) to (95:5); the mass ratio of the fast ion conductor to the precursor of the coating auxiliary agent is (1:10) to (10:1), preferably, the mass ratio of the fast ion conductor to the precursor of the coating auxiliary agent is (1:2) to (2:1).

10. A secondary battery, characterized in that: The negative electrode sheet of the secondary battery comprises the carbon-based negative electrode material according to any one of claims 1 to 8, Alternatively, the carbon-based negative electrode material in the negative electrode sheet of the secondary battery is prepared by the method for preparing the carbon-based negative electrode material as claimed in claim 9.

11. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 10.

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