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 coating structure, the coating structure comprises a fast ion conductor layer and a stable modification layer which are sequentially arranged on the surface of the carbon-based core, the fast ion conductor layer is arranged on the surface of the carbon-based core, and the stable modification layer is arranged on the surface of the fast ion conductor layer; the stable modification layer has electron and ion transmission capability and has self-supporting performance through chemical bonding connection in the layer so as to protect the fast ion conductor layer. A negative electrode of a secondary battery includes a carbon-based negative electrode material. The power utilization device comprises a secondary battery. The stable modification layer has relatively good ion electron transmission capability and structural stability, and can improve the retention rate of the fast ion conductor layer in the negative electrode material processing process and the battery operation process, so that the structural integrity of the negative electrode active material is protected, and the stability of the battery performance is improved.

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 and sodium-ion batteries are currently the main energy storage devices for electric vehicles and mobile electronic devices. As the market share of lithium-ion and sodium-ion batteries continues to expand, the requirements for battery charging speed and low-temperature performance are increasing day by day. Carbon-based negative electrode materials are the most widely used negative electrode active materials in commercial lithium-ion and sodium-ion batteries due to their low cost, ideal lithium storage potential, and high theoretical specific capacity. However, due to the limited lithium insertion sites, poor lithium ion diffusion capacity, and serious interface problems of carbon-based negative electrode materials, the battery is highly polarized when charged at high current or low temperature, resulting in a decrease in the battery's charge and discharge capacity. In severe cases, the problem of metallic lithium precipitation on the negative electrode surface may even occur, posing a safety hazard to the battery. The above-mentioned shortcomings of carbon-based negative electrode materials are the main factors limiting the charging speed and low-temperature performance of current commercial lithium-ion batteries.

[0003] Coating the surface of the carbon-based negative electrode with a fast ion conductor with high lithium ion affinity and high metal ion diffusion coefficient can effectively promote the desolvation, transmission and embedding of lithium ions on the surface of the carbon-based negative electrode and stabilize the interface of the carbon-based negative electrode. This is an effective solution to improve the fast charging and low-temperature performance of lithium-ion batteries using carbon-based negative electrodes.

[0004] However, the fast ion conductor layer is not easy to keep intact during the process of electrode sheet manufacturing and lithium ion storage. Stirring and coating will damage it. It will be destroyed due to the expansion of the electrode volume during the electrode cycle, and the battery's fast charging and low temperature performance are difficult to maintain stable.

[0005] Therefore, there is an urgent need for a carbon-based negative electrode material, a preparation method, a secondary battery and an 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] The coating structure comprises a fast ion conductor layer and a stable modification layer sequentially arranged on the surface of the carbon-based core, wherein the fast ion conductor layer is arranged on the surface of the carbon-based core, and the stable modification layer is arranged on the surface of the fast ion conductor layer;

[0009] The stable modification layer has the ability to transport electrons and ions and is self-supporting through chemical bonding within the layer to protect the fast ion conductor layer.

[0010] 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 radii of the outer contours of the carbon-based core, the fast ion conductor layer and the stable modification layer are L 1 , L 2 and L 3 , L 1 , L 2 , L 3 The relationship between and R satisfies: 80% ≤ L 1 / R <L 2 / R <L 3 / R,L 3 / R=100%.

[0011] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer wraps the carbon-based core, and the stabilizing modification layer wraps the fast ion conductor layer.

[0012] In some optional embodiments of the first aspect of the present application, the carbon-based negative electrode material satisfies at least one of the following conditions:

[0013] (1) The value range of R is 1 μm to 50 μm;

[0014] (2)L 1 The value range is 8μm~39.5μm;

[0015] (3)L 2 The value range is 9μm~39.8μm.

[0016] In some optional embodiments of the first aspect of the present application, the value range of R is 9 μm to 40 μm.

[0017] 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.

[0018] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer is coated on the surface of the carbon-based core by first covalent bonding or physical adsorption; and / or

[0019] The stable modification layer is disposed on the surface of the fast ion conductor layer by covalent bonding and / or physical adsorption.

[0020] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer 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 or lithium phosphosulfide; and / or

[0021] Lithium silicate includes Li 4 SiO4 , 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

[0022] The lithium phosphorus sulfide 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 , Li z PS x Cl y (0 < x, y ≤ 7, z = 2x + y - 5) one or more of.

[0023] In some alternative embodiments of the first aspect of the present application, the stable modification layer includes one or more of hard carbon, soft carbon, graphite, and conductive polymer;

[0024] In some alternative embodiments of the first aspect of the present application, the conductive polymer includes one or more of polyaniline, polypyrrole, polythiophene, poly(phenylene ethynylene), polyacetylene, polyfluorene, poly(phenylene vinylene), polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, carboxymethyl cellulose, and their derivatives.

[0025] In some alternative embodiments of the first aspect of the present application, the covalent bond in the covalent bonding includes one or more of C - O, C = O, C - P, C - S, Li - C, C - Si, C - F, C - N, C - B, C - I, N - O, C - O - P, C - O - Si, C - O - B, C - N - Si, C - P - S.

[0026] The second aspect of the present application provides a method for preparing a carbon - based negative electrode material, including:

[0027] S1: Obtain a carbon - based core, place the carbon - based core and the fast ion conductor in a fusion machine and rotate and fuse at a first speed of 100 - 3000 rpm for a first duration, and then perform a heat treatment in an inert gas atmosphere at a first temperature T1 to obtain a carbon - based core uniformly coated with a fast ion conductor layer;

[0028] S2: dispersing the carbon-based core uniformly coated with the fast ion conductor layer in a solvent, and adding a precursor for forming a stable modification layer according to a preset mass ratio of 99.9:0.1 to 1:1 between the carbon-based core uniformly coated with the fast ion conductor layer and the precursor of the stable modification layer to obtain a mixture to be treated, and performing surface coating treatment on the mixture to obtain a carbon-based negative electrode material, wherein:

[0029] When the stable modification layer is a carbon-based stable modification layer, S2 includes S21,

[0030] S21: Surface coating treatment includes: kneading the mixture to be treated, drying the solvent, and finally calcining at a second temperature T2 in an inert atmosphere to obtain a carbon-based negative electrode material;

[0031] When the stable modified layer is a conductive polymer stable modified layer, S2 includes S22,

[0032] S22: The surface coating treatment includes: adding an initiator to the mixture to be treated and stirring the mixture to make the mixture to be treated react under the action of the initiator to form a conductive polymer and uniformly coat the outer peripheral side of the fast ion conductor layer.

[0033] In some optional embodiments of the second aspect of the present application, the first speed is 500-1000 rpm.

[0034] In some optional embodiments of the second aspect of the present application, the first duration is 8 to 12 hours.

[0035] In some optional embodiments of the second aspect of the present application, the first temperature T1 is 300-3000°C.

[0036] In some optional embodiments of the second aspect of the present application, the temperature is 600-1500°C.

[0037] In some optional embodiments of the second aspect of the present application, a kneading machine is used for kneading in step S21, and the kneading time is 8 hours to 12 hours.

[0038] In some optional embodiments of the second aspect of the present application, the calcination temperature in step S21 is 300-3000°C, and the further calcination temperature is 600-1500°C.

[0039] In some optional embodiments of the second aspect of the present application, the calcination time in step S21 is 3 hours to 6 hours.

[0040] In some optional embodiments of the second aspect of the present application, the precursor in step S21 includes one or more of asphalt, aramid, and resin.

[0041] In some optional embodiments of the second aspect of the present application, when the conductive polymer is polypyrrole, the precursor of the stable modification layer includes pyrrole and phytic acid, and the molar ratio of the two is 1:3 to 3:1. The mass ratio of the initiator to the precursor of the stable modification layer is 1:100 to 1:10, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride.

[0042] A third aspect of the present application provides a secondary battery, wherein the negative electrode sheet in the secondary battery includes the carbon-based negative electrode material provided in the first aspect of the present application.

[0043] A fourth aspect of the present application provides an electrical device, comprising the secondary battery provided in the third aspect of the present application.

[0044] Beneficial effects:

[0045] The first aspect of the present application provides a carbon-based negative electrode material having a carbon-based core and a coating structure. The coating structure sequentially arranges a stable modification layer and a fast ion conductor layer on the surface of the carbon-based core, wherein the fast ion conductor layer is arranged on the surface of the carbon-based core, and the stable modification layer is arranged on the surface of the fast ion conductor layer. The stable modification layer has good ion and electron transmission capability and structural stability, and can effectively protect the fast ion conductor layer during the processing of the negative electrode material and the operation of the lithium-ion battery, and improve the retention rate of the fast ion conductor layer, thereby protecting the structural integrity of the negative electrode active material on the battery production line and in the long-term use of the battery product.

[0046] The second aspect of the present application provides a method for preparing a carbon-based negative electrode material, which is simple and efficient to prepare a carbon-based negative electrode material with a coating structure, ensuring that the stable modification layer completely wraps the fast ion conductor layer, thereby effectively protecting the fast ion conductor layer.

[0047] The third aspect of the present application provides a secondary battery, the negative electrode sheet of the secondary battery uses the carbon-based negative electrode material provided in the first aspect of the present application, which can promote the desolvation of lithium ions and accelerate the transmission of lithium ions, thereby improving the fast charging performance and low temperature performance of the battery. The stable modification layer of the negative electrode active material improves the material interface stability, thereby producing the effect of improving the battery cycle stability.

[0048] The fourth aspect of the present application provides an electric device, comprising the secondary battery in the third aspect of the present application. The electric device provided in the fourth aspect of the present application has good cycle performance and low temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the cross-sectional structure of the carbon-based negative electrode material of the present application;

[0050] Figure 2This is a schematic diagram of the polar coordinate distribution of the calculation of the geometric radius of irregular figures;

[0051] Figure 3 It is a comparison chart of the retention rate of fast ion conductors in the negative electrode materials of Example 1 with double-layer coating and Comparative Example 1 with only one fast ion conductor layer after stirring in an aqueous solvent;

[0052] Figure 4 This is a comparison chart of the retention rate of fast ion conductors in the negative electrode materials of Example 1 and Comparative Example 1 of the present application after 1000 cycles in the battery;

[0053] Figure 5 is a SEM image of graphite with double-layer coating. DETAILED DESCRIPTION

[0054] 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, in granular form, comprising:

[0055] Carbon-based core;

[0056] The coating structure comprises a fast ion conductor layer and a stable modification layer sequentially arranged on the surface of the carbon-based core, wherein the fast ion conductor layer is arranged on the surface of the carbon-based core, and the stable modification layer is arranged on the surface of the fast ion conductor layer;

[0057] The stable modification layer has the ability to transport electrons and ions and is self-supporting through chemical bonding within the layer to protect the fast ion conductor layer.

[0058] 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):

[0059]

[0060] In formula (1), R(θ) is the geometric radius when the angle is θ, and the geometric average radii of the outer contours of the carbon-based core, the fast ion conductor layer and the stable modification layer are L 1 , L 2 and L 3 , L 1 , L 2 , L 3 The relationship between and R satisfies: 80% ≤ L 1 / R <L 2 / R <L 3 / R,L 3 / R=100%.

[0061] After the fast ion conductor layer is coated on the surface of the carbon-based core, it can effectively accelerate the desolvation and transmission of lithium ions on the surface of the negative electrode material. However, the fast ion conductor layer is easily damaged by stirring, coating and other operations during the manufacturing process of the negative electrode sheet; in addition, the negative electrode material will expand in volume during the operation of the secondary battery, which can easily damage the surface fast ion conductor layer. The stable modification layer has excellent ion and electron transmission performance and excellent structural stability, which can make the above-mentioned fast ion conductor layer stably exist on the surface of the negative electrode material during battery manufacturing and operation.

[0062] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer wraps the carbon-based core, and the stabilizing modification layer wraps the fast ion conductor layer.

[0063] In some optional embodiments of the first aspect of the present application, the value range of R is 1 μm to 50 μm.

[0064] In some optional embodiments of the first aspect of the present application, the value range of R is 9 μm to 40 μm.

[0065] In some optional embodiments of the first aspect of the present application, L 1 The value range is 8μm~39.5μm.

[0066] In some optional embodiments of the first aspect of the present application, L 2 The value range is 9μm~39.8μm.

[0067] 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.

[0068] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer is coated on the surface of the carbon-based core by first covalent bonding or physical adsorption; and / or

[0069] The stable modification layer is disposed on the surface of the fast ion conductor layer by covalent bonding and / or physical adsorption.

[0070] In some optional embodiments of the first aspect of the present application, the fast ion conductor layer 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 or lithium phosphosulfide; and / or

[0071] Lithium silicate includes Li 4 SiO 4 , Li 2 SiO 3 , Li 2 Si 2 O5 , Li 6 , Si 2 , O 7 , Li 2 , Si 5 , O 11 one or more of; and / or

[0072] The lithium phosphorus sulfide 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 z , PS x , Cl y (0 < x, y ≤ 7, z = 2x + y - 5) one or more of these.

[0073] In some alternative embodiments of the first aspect of the present application, the covalent bonds in the first covalent 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.

[0074] In some alternative embodiments of the first aspect of the present application, the stable modification layer includes one or more of hard carbon, soft carbon, graphite, conductive polymer;

[0075] In some alternative embodiments of the first aspect of the present application, the conductive polymer includes one or more of polyaniline, polypyrrole, polythiophene, poly(phenylene ethynylene), polyacetylene, polyfluorene, poly(phenylene vinylene), polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, carboxymethyl cellulose and their derivatives.

[0076] In some alternative embodiments of the first aspect of the present application, the covalent bonds in the covalent 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, N - O, C - O - P, C - O - Si, C - O - B, C - N - Si, C - P - S.

[0077] The second aspect of the present application provides a method for preparing a carbon - based negative electrode material, comprising:

[0078] S1: obtaining a carbon-based core, placing the carbon-based core and a fast ion conductor in a fusion machine, rotating and fusing them at a first speed of 100 to 3000 rpm for a first time, and then performing a heat treatment at a first temperature T1 in an inert gas atmosphere to obtain a carbon-based core uniformly coated with a fast ion conductor layer;

[0079] S2: dispersing the carbon-based core uniformly coated with the fast ion conductor layer in a solvent, and adding a precursor for forming a stable modification layer according to a preset mass ratio of 99.9:0.1 to 1:1 between the carbon-based core uniformly coated with the fast ion conductor layer and the precursor of the stable modification layer to obtain a mixture to be treated, and performing surface coating treatment on the mixture to obtain a carbon-based negative electrode material, wherein:

[0080] When the stable modification layer is a carbon-based stable modification layer, S2 includes S21,

[0081] S21: Surface coating treatment includes: kneading the mixture to be treated, drying the solvent, and finally calcining at a second temperature T2 in an inert atmosphere to obtain a carbon-based negative electrode material;

[0082] When the stable modified layer is a conductive polymer stable modified layer, S2 includes S22,

[0083] S22: The surface coating treatment includes: adding an initiator to the mixture to be treated and stirring the mixture to make the mixture to be treated react under the action of the initiator to form a conductive polymer and uniformly coat the outer peripheral side of the fast ion conductor layer.

[0084] In some optional embodiments of the second aspect of the present application, the first speed is 500-1000 rpm.

[0085] In some optional embodiments of the second aspect of the present application, the first duration is 8 to 12 hours.

[0086] In some optional embodiments of the second aspect of the present application, the first temperature T1 is 300-3000°C.

[0087] In some optional embodiments of the second aspect of the present application, the temperature is 600-1500°C.

[0088] In some optional embodiments of the second aspect of the present application, a kneading machine is used for kneading in step S21, and the kneading time is 8 hours to 12 hours.

[0089] In some optional embodiments of the second aspect of the present application, the calcination temperature in step S21 is 300-3000°C, and the further calcination temperature is 600-1500°C.

[0090] In some optional embodiments of the second aspect of the present application, the calcination time in step S21 is 3 hours to 6 hours.

[0091] In some optional embodiments of the second aspect of the present application, the precursor in step S21 includes one or more of asphalt, aramid, and resin.

[0092] In some optional embodiments of the second aspect of the present application, when the conductive polymer is polypyrrole, the precursor of the stable modification layer includes pyrrole and phytic acid, and the molar ratio of the two is 1:3 to 3:1. The mass ratio of the initiator to the precursor of the stable modification layer is 1:100 to 1:10, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride.

[0093] A third aspect of the present application provides a secondary battery, wherein the negative electrode sheet in the secondary battery includes the carbon-based negative electrode material provided in the first aspect of the present application.

[0094] 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 can maintain good cycle performance and low temperature performance for a long time.

[0095] A fourth aspect of the present application provides an electrical device, comprising the secondary battery provided in the third aspect of the present application.

[0096] The electrical device provided in the fourth aspect of the present application has good cycle performance and low temperature performance. [Specific embodiment]

[0098] Hereinafter, 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.

[0099] 1. Preparation of batteries in embodiments and comparative examples:

[0100] [Example 1]

[0101] <Preparation of negative electrode active material>

[0102] The artificial graphite FSN-1 produced by Shanshan Technology (hereinafter referred to as "artificial graphite") was selected as the carbon-based core to be coated, lithium silicate was selected as the fast ion conductor layer material, and asphalt-based soft carbon was selected as the stable modification layer material. The specific preparation process is as follows:

[0103] S1: Use a classifier to classify the artificial graphite in the raw material, and select artificial graphite with a graded particle size of 10-20μm as the carbon-based core. Disperse artificial graphite and lithium silicate in a fusion machine at a mass ratio of 96:2, turn the fusion machine cylinder rotation speed to 500rpm, fuse for 10 hours, and calcine at 1000℃ for 5 hours in an argon atmosphere to obtain graphite uniformly coated with lithium silicate.

[0104] S2: The lithium silicate-coated graphite and asphalt synthesized in step S1 are dispersed in a small amount of N,N-dimethylformamide (DMF for short) in a mass ratio of 98:2, and kneaded with a kneader for 3 hours. After drying the DMF solvent, calcined at 1000°C for 5 hours under an argon atmosphere to obtain the carbon-based negative electrode material of Example 1. The particle structure of the carbon-based negative electrode material is, from the inside to the outside of the particle, graphite as a carbon-based core, a fast ion conductor layer formed by lithium silicate, and a stabilizing modification layer formed by asphalt-based soft carbon.

[0105] <Preparation of negative electrode sheet>

[0106] The negative electrode active material prepared according to the steps in <Preparation of negative electrode active material>, acetylene 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 then 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 Cu foil, dried, and cold pressed to obtain a negative electrode sheet roll.

[0107] <Preparation of positive electrode sheet>

[0108] The positive electrode is selected from lithium cobalt oxide (chemical formula: LiCoO 2 ) is used as the positive electrode active material, which is fully stirred and mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (abbreviated as PVDF) in an N-methylpyrrolidone (abbreviated as NMP) solvent at a mass ratio of 96.3:2.2:1.5 to form a uniform positive electrode slurry; the slurry is coated on the current collector Al foil, dried and cold pressed to obtain a positive electrode sheet.

[0109] <Preparation of Electrolyte>

[0110] 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%.

[0111] <Diaphragm>

[0112] Polypropylene (PP) porous polymer film was selected as the separator.

[0113] <Preparation of lithium-ion batteries>

[0114] The negative electrode sheet and the positive electrode sheet prepared according to the above steps are separated by a separator, and then the above electrolyte is added dropwise, and the battery core is encapsulated with an aluminum plastic film, and then the electrolyte is injected, allowed to stand, and formed. The manufacturing process of the lithium-ion secondary battery 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.

[0115] [Example 2]

[0116] The difference compared with Example 1 is that: <Preparation of negative electrode active material> Step S2 is: Take lithium silicate-coated graphite, pyrrole, and phytic acid in a mass ratio of 98:0.8:1.2 and disperse them in water (solid content 50%), add ammonium persulfate as an initiator, and the mass ratio of ammonium persulfate to pyrrole is 1:20. After stirring and reacting for 24 hours, filter, wash with deionized water, and dry in turn to obtain the carbon-based negative electrode material of Example 2. The particle structure of the carbon-based negative electrode material is, from the inside to the outside of the particle, graphite as a carbon-based core, a fast ion conductor layer formed by lithium silicate, and a stable modification layer formed by polypyrrole.

[0117] The rest is the same as Example 1.

[0118] [Example 3]

[0119] The difference compared with Example 1 is that in step S1 of <Preparation of Negative Electrode Active Material>, lithium silicate is replaced by lithium fluoride. The rest is the same as Example 1.

[0120] [Example 4]

[0121] The difference compared with Example 2 is that lithium silicate is replaced by lithium fluoride in step S1 of <Preparation of Negative Electrode Active Material>. The rest is the same as Example 2.

[0122] [Example 5]

[0123] The difference compared with Example 1 is that the artificial graphite in the raw material is replaced by hard carbon. The rest is the same as Example 1.

[0124] [Example 6]

[0125] The difference between Example 6 and Example 2 is that the artificial graphite in the raw material is replaced by hard carbon. The rest is the same as Example 2.

[0126] [Example 7]

[0127] Compared with Example 3, Example 7 replaces the artificial graphite in the raw materials with hard carbon, and the rest is the same as Example 3.

[0128] [Example 8]

[0129] The difference between Example 8 and Example 4 is that the artificial graphite in the raw material is replaced with hard carbon. The rest is the same as Example 4.

[0130] [Example 9]

[0131] The difference between Example 9 and Example 1 is that the mass ratio of artificial graphite to lithium silicate is changed to 88:10. The rest is the same as Example 1.

[0132] [Example 10]

[0133] The difference between Example 10 and Example 2 is that the mass ratio of artificial graphite to lithium silicate is changed to 88:10. The rest is the same as Example 2.

[0134] [Examples 11-14]

[0135] The difference between Examples 11-14 and Example 1 is that:

[0136] The mass ratios of artificial graphite to lithium silicate in Example 11, Example 12, Example 13 and Example 14 were changed to 85:10, 80:10, 75:10 and 70:10 respectively;

[0137] In Examples 11-14, the mass ratio of lithium silicate-coated graphite to asphalt in step S2 of <Preparation of Negative Electrode Active Material> was changed to 90:10.

[0138] The rest is the same as Example 1.

[0139] [Examples 15-18]

[0140] The difference between Examples 15-18 and Example 1 is that:

[0141] The classified particle sizes of the artificial graphite in Examples 15, 16, 17 and 18 were changed to 1-10 μm, 20-25 μm, 30-35 μm and 40-45 μm, respectively.

[0142] The rest is the same as Example 1.

[0143] [Comparative Example 1]

[0144] The difference compared with Example 1 is:

[0145] In <Preparation of Negative Electrode Active Material>, only step S1 is performed, and step S2 is not performed.

[0146] The rest is the same as Example 1.

[0147] [Comparative Example 2]

[0148] The difference compared with Example 1 is:

[0149] The lithium silicate in step S1 of <Preparation of Negative Electrode Active Material> is replaced with lithium fluoride;

[0150] The process of step S2 of <Preparation of Negative Electrode Active Material> was not performed.

[0151] The rest is the same as Example 1.

[0152] [Comparative Example 3]

[0153] The difference compared with Example 1 is:

[0154] The artificial graphite in step S1 of <Preparation of Negative Electrode Active Material> is replaced with hard carbon;

[0155] The process of step S2 of <Preparation of Negative Electrode Active Material> was not performed.

[0156] The rest is the same as Example 1.

[0157] [Comparative Example 4]

[0158] The difference compared with Example 1 is:

[0159] The artificial graphite in step S1 of <Preparation of Negative Electrode Active Material> is replaced with hard carbon, and the lithium silicate is replaced with lithium fluoride;

[0160] The process of step S2 of <Preparation of Negative Electrode Active Material> was not performed.

[0161] The rest is the same as Example 1.

[0162] [Comparative Examples 5-8]

[0163] The difference between Comparative Examples 5-8 and Example 1 is that:

[0164] The process of step S2 of <preparation of negative electrode active material> was not performed;

[0165] The graded particle sizes of the artificial graphite in Comparative Examples 5-8 were changed to: 1-10 μm, 20-25 μm, 30-35 μm and 40-45 μm, respectively.

[0166] The rest is the same as Example 1.

[0167] 2. Test methods and equipment:

[0168] 1. Gram capacity test

[0169] The gram capacity test can refer to the standard: GB / T 24533-2019. The negative electrode active material is made into a negative electrode sheet through mixing, coating, rolling, lamination, and drying. A lithium sheet is used as a counter electrode and assembled into 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.

[0170] 2. Constant current charge and discharge test

[0171] The lithium-ion secondary battery was subjected to a constant current rate test and a cycle test.

[0172] Rate testing means cycling the battery at the following rates for 5 cycles under the following parameters: 0.1C, 0.2C, 0.5C, 1C, 2C, 4C, 6C.

[0173] Cycle testing refers to testing the battery at a rate of 1C.

[0174] Low temperature performance test means putting the battery into a -10℃ constant temperature box for constant current charge and discharge test. And test the specific capacity of the battery negative electrode active material at 0.1C rate.

[0175] 3. Test of element content of negative electrode active material

[0176] The negative electrode active material is 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 is completely dissolved, a uniform solution is taken for inductively coupled plasma emission spectroscopy (ICP) testing to obtain the content of different elements in the negative electrode active material.

[0177] For example, for Example 1 and Comparative Example 1, the retention rate of the fast ion conductor layer can be determined by the content of silicon element therein.

[0178] 4. Test of active material element content on cycle electrode

[0179] Disassemble the battery after the cycle, take out the negative electrode sheet, and scrape off the active material on the surface of the negative electrode sheet. Stir the scraped material in aqua regia (hydrochloric acid: nitric acid = 3:1), and heat it in an oil bath at 80°C while stirring. After the solid in the solution is completely dissolved, take a uniform solution for inductively coupled plasma emission spectroscopy (ICP) testing to obtain the content of different elements in the negative electrode active material after the cycle.

[0180] For example, for Example 1 and Comparative Example 1, the retention rate of the fast ion conductor layer in the negative electrode active material after the electrode cycle can be determined by the silicon content therein.

[0181] 5. Negative electrode active material structure composition and size test

[0182] The negative electrode active material was observed for morphology using a scanning electron microscope (SEM, magnification of 5000), and 10 particles were randomly selected and cut using a focused ion beam. After the cross section was cut, the cross section was subjected to an energy spectrum distribution test (EDS-mapping). In some embodiments and comparative examples, the distribution area of ​​the carbon element is used to calibrate the distribution area of ​​the carbon-based core, the distribution area of ​​the silicon element is used to calibrate the distribution area of ​​lithium silicate, the distribution area of ​​the fluorine element is used to calibrate the distribution area of ​​lithium fluoride, the distribution area of ​​the nitrogen element is used to calibrate the distribution area of ​​polypyrrole, and the distribution area of ​​the sulfur element combined with the carbon element is used to calibrate the distribution area of ​​the asphalt-based soft carbon. For each sample, 10 particles were randomly selected, and according to the above description of R, L in the irregular figure, 1 , L 2 and L 3 The artificial intelligence (AI) image recognition method was used to analyze the collected SEM images and EDS-mapping images, and Matlab modeling was used to calculate the R and L of each particle cross section. 1 , L 2 and L 3 The correlation values ​​of the 10 particles selected for each sample were averaged to further calculate the L in each sample. 1 / R, L 2 / R and L 3 / R, the relevant data are summarized in Table 1.

[0183] Table 1 Summary of structural composition and proportion of different regions in the examples and comparative examples

[0184]

[0185]

[0186] The following conclusions can be drawn from the data in Table 1:

[0187] The data of Examples 1 to 8 show that the fast ion conductor layer formed of different materials (such as lithium salts such as lithium silicate and lithium fluoride) and the stable modification layer formed of different materials (such as asphalt-based soft carbon and polypyrrole) can form a coating structure on a variety of carbon-based cores (such as graphite and hard carbon).

[0188] The data of Examples 9 to 18 show that the relative sizes of different regions of the negative electrode active material particles can be regulated by adjusting the mass ratio of the precursors forming different layer regions and the carbon-based core region, that is, by adjusting the L 1 / R, L 2 / R and L 3 / R size.

[0189] 3. Test results:

[0190] 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.

[0191] Table 2 Performance test results of each embodiment and each comparative example

[0192]

[0193]

[0194] 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 coated with the stable modification 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.

[0195] By analyzing the data of Example 1, Comparative Example 1, Examples 9, 11 to 14, and the data of Example 2, Comparative Example 1, and Example 10 in Table 2, it can be found that: when the relative size between different regions of the carbon-based core and the coating structure changes, the 6C capacity, -10°C capacity, and the capacity after 1000 cycles of 1C in each example are improved to varying degrees compared with the corresponding comparative example, that is, the fast charging and low temperature performance of the negative electrode material are still improved. When the coating layer ratio is too high, the carbon-based negative electrode ratio is too low, which affects the reversible capacity of the negative electrode. As shown in Example 14, when L 1 When / R<80%, the reversible capacity of the negative electrode active material at 0.1C rate is affected and drops to less than 300 mAh / 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.

[0196] By analyzing the data of Examples 1, 15 to 18 and Comparative Examples 1, 5 to 8 in Table 2, it can be found that: within the commonly used particle size range of commercial carbon-based negative electrode materials (R is within 0 to 50 μm, and further R is within 9 to 40 μm), the embodiments coated with a stable modification layer have greatly improved 6C capacity, 0.1C capacity at -10°C, and capacity after 1C cycle 1000 cycles, relative to their respective corresponding comparative examples, that is, the fast charging, low temperature and cycle performance of the secondary battery are significantly improved.

[0197] Combination Figure 3 and Figure 4It can be found that after high-temperature stirring in an aqueous solution and long battery cycles, the retention rate of the fast ion conductor layer in the embodiments is significantly improved compared to the comparative examples. It can be seen that the stable modification layer in the embodiments effectively protects the structural integrity of the fast ion conductor layer, 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. Due to the protective effect of the stable modification layer on the fast ion conductor layer, the interface stability of the negative electrode active material is improved during the operation of the battery, and the stability of the battery cycle performance is improved.

[0198] 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.

[0199] 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.

[0200] 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; The coating structure comprises a fast ion conductor layer and a stable modification layer sequentially arranged on the surface of the carbon-based core, wherein the fast ion conductor layer is arranged on the surface of the carbon-based core, and the stable modification layer is arranged on the surface of the fast ion conductor layer; The stable modification layer has the ability to transmit electrons and ions and is self-supporting through chemical bonding within the layer, so as to protect the fast ion conductor layer.

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, and the geometric mean radii of the outer contours of the carbon-based core, the fast ion conductor layer and the stable modification layer are L1, L2 and L3 respectively, and the relationship between L1, L2, L3 and R satisfies: 80%≤L1 / R <L2 / R<L3 / R,L3 / R=100%。 3. The carbon-based negative electrode material according to claim 1 or 2, characterized in that: The fast ion conductor layer wraps the carbon-based core, and the stabilizing modification layer wraps the fast ion conductor layer.

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 40 μm; (2) The value range of L1 is 8 μm to 39.5 μm; (3) The value range of L2 is 9μm~39.8μm.

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 layer is disposed on the surface of the carbon-based core by covalent bonding and / or physical adsorption; and / or, The stable modification layer is disposed on the surface of the fast ion conductor layer by covalent bonding and / or physical adsorption.

7. The carbon-based negative electrode material according to claim 1 or 6, characterized in that: The fast ion conductor layer comprises 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 or 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, Li z PS x Cl y (where 0 < x, y ≤ 7 and z = 2x + y - 5) or more than one of them.

8. The carbon-based negative electrode material according to claim 1, characterized in that: The stable modification layer 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, polyacrylonitrile, carboxymethyl cellulose and derivatives thereof.

9. The carbon-based negative electrode material according to claim 6, characterized in that: The covalent bonds in the covalent bonding include one or more of CO, C=O, CP, CS, Li-C, C-Si, CF, CN, CB, CI, NO, COP, CO-Si, COB, CN-Si, and CPS.

10. A method for preparing a carbon-based negative electrode material according to any one of claims 1 to 9, characterized in that: include: S1: obtaining a carbon-based core, placing the carbon-based core and a fast ion conductor in a fusion machine, rotating and fusing them at a first speed of 100 to 3000 rpm for a first time, and then performing a heat treatment at a first temperature T1 in an inert gas atmosphere to obtain a carbon-based core uniformly coated with a fast ion conductor layer; Preferably, the first speed is 500-1000 rpm; Preferably, the first duration is 8 to 12 hours; Preferably, the first temperature T1 is 300-3000°C, further 600-1500°C; S2: dispersing the carbon-based core uniformly coated with the fast ion conductor layer in a solvent, and adding a precursor for forming a stable modification layer according to a preset mass ratio of 99.9:0.1 to 1:1 between the carbon-based core uniformly coated with the fast ion conductor layer and the precursor of the stable modification layer to obtain a mixture to be treated, and performing surface coating treatment on the mixture to be treated to obtain the carbon-based negative electrode material, wherein: When the stable modification layer is a carbon-based stable modification layer, S2 includes S21, S21: the surface coating treatment comprises: kneading the mixture to be treated, drying the solvent, and finally calcining at a second temperature T2 in an inert atmosphere to obtain the carbon-based negative electrode material; Preferably, in step S21, a kneading machine is used for kneading, and the kneading time is 8 hours to 12 hours; Preferably, the calcination temperature in step S21 is 300-3000°C, and the further calcination temperature is 600-1500°C; Preferably, the calcination time in step S21 is 3 hours to 6 hours; Preferably, the precursor in step S21 includes one or more of asphalt, aramid, and resin; When the stable modified layer is a conductive polymer stable modified layer, S2 includes S22, S22: The surface coating treatment comprises: adding an initiator to the mixture to be treated and stirring the mixture to allow the mixture to react under the action of the initiator to form a conductive polymer and uniformly coat the outer peripheral side of the fast ion conductor layer; Preferably, when the conductive polymer is polypyrrole, the precursor of the stable modification layer includes pyrrole and phytic acid, and the molar ratio of the two is 1:3 to 3:

1. The mass ratio of the initiator to the precursor of the stable modification layer is 1:100 to 1:10, and the initiator includes one or more of ammonium persulfate, sodium persulfate, benzoyl peroxide, diisopropylbenzene peroxide, azobisisobutyronitrile, sulfuric acid, hydrochloric acid, and sodium hydride.

11. A secondary battery, characterized in that: The negative electrode sheet in the secondary battery comprises the carbon-based negative electrode material according to any one of claims 1 to 9, 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 10.

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

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