Negative electrode material, preparation method thereof, negative electrode sheet and lithium ion battery

Abstract

The present application relates to a negative electrode material and a preparation method thereof, a negative electrode sheet, and a lithium ion battery. The negative electrode material includes a silicon-based active substance and a carbon material. The oil absorption value of the negative electrode material is 0 mL / 100 g and the specific surface area is S m 2 / g, the particle size concentration of the negative electrode material is P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the physical rebound capacity of the negative electrode material is T, T = 0.01 * O * S / P1, 0.20 < T < 1.20. The negative electrode material of the present application has a low physical rebound capacity, and the volume of the electrode sheet made therefrom is not easy to rebound after compaction, thereby achieving a high compaction density and exerting excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of negative electrode materials, and particularly relates to a negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high energy density, long cycle life, small environmental pollution and no memory effect, and are widely used in electric vehicles and consumer electronic products. The negative electrode material is an important component of the lithium ion battery, which directly affects the key indicators such as the energy density, cycle life and safety performance of the battery. At present, the commercialized lithium ion battery mainly uses graphite-based negative electrode material, but its theoretical specific capacity is only 372 mAh / g, which is difficult to meet the demand of high energy density lithium ion battery. Silicon-based negative electrode material has a very high specific capacity and is one of the candidate materials for the next generation of high energy density lithium ion batteries. However, the silicon negative electrode will produce a huge volume change during the charge and discharge cycle, which will lead to the deterioration of the material / plate structure and the instability of the solid electrolyte interface film (SEI), thereby causing the sharp decline of the electrochemical performance.

[0003] At present, silicon-based materials are often compounded with carbon materials, but the existing compounding method is often simple mixing, which lacks reasonable matching of silicon-based materials and carbon materials, and has been unable to meet the market demand for obtaining negative electrode materials with high compaction density and good cycle performance. Therefore, it is necessary to explore the mechanism of the synergistic effect of various factors and develop a composite negative electrode material that meets the market demand. SUMMARY

[0004] The purpose of the present application is to provide a negative electrode material, a preparation method thereof, a negative electrode sheet and a lithium ion battery. The negative electrode material has a low physical rebound ability, and the volume of the sheet made of the negative electrode material is not easy to rebound after compaction, so that a high compaction density can be obtained, and excellent cycle performance can be achieved.

[0005] In a first aspect, the present application provides a negative electrode material, which comprises a silicon-based active substance and a carbon material, the oil absorption value of the negative electrode material is O mL / 100g, the specific surface area of the negative electrode material is S m 2 / g, the particle size concentration of the negative electrode material is P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the physical rebound ability of the negative electrode material is T, T=0.01*O*S / P1, 0.20

[0006] In some embodiments, the silicon-based active substance comprises at least one of elemental silicon and silicon oxide.

[0007] In some embodiments, the silicon-based active material further comprises a doping metal M, M is selected from at least one of Mg, Li, Fe, Al, Mn and Cu.

[0008] In some embodiments, the silicon-based active material further comprises a doping metal M, M is selected from at least one of Mg, Li, Fe, Al, Mn and Cu, M is dispersed in the silicon-based active material in at least one of elemental, oxide or silicate form.

[0009] In some embodiments, the silicon-based active material comprises silicon oxide, the general formula of the silicon oxide is SiO x , 0 < x < 2.

[0010] In some embodiments, the silicon-based active material has a median particle size of 1 μm to 10 μm.

[0011] In some embodiments, the carbon material comprises at least one of graphite, graphene, amorphous carbon, carbon nanotube and carbon fiber.

[0012] In some embodiments, the negative electrode material has an oil absorption value of O mL / 100g, 0 < 57.0.

[0013] In some embodiments, the negative electrode material has a specific surface area of S cm 2 / g, S < 3.50.

[0014] In some embodiments, the negative electrode material has a pH value of 6 to 12.

[0015] In some embodiments, the negative electrode material has a tap density > 0.90 g / cm 3 .

[0016] In some embodiments, the negative electrode material has a mass content of water ≤ 0.5 wt%.

[0017] In some embodiments, the negative electrode material has a mass content of silicon element of 0.5 wt% to 25 wt%.

[0018] In some embodiments, the negative electrode material has a particle size satisfying: 0.1 μm ≤ D 20 ≤ 12 μm, 0.2 μm ≤ D 50 ≤ 18 μm, 0.3 μm ≤ D 80 ≤ 25 μm.

[0019] In some embodiments, in the negative electrode material, the silicon-based active material and the carbon material are dispersed in the form of particles.

[0020] In some embodiments, the physical resilience of the negative electrode material is T, 0.2 < T < 0.7.

[0021] In some embodiments, the physical resilience of the negative electrode material is T, 0.70 < T < 1.20.

[0022] In some embodiments, the particle size concentration of the negative electrode material is P1, 1.2 < P1 < 2.0.

[0023] In the second aspect, the application provides a preparation method of a negative electrode material, comprising the following steps:

[0024] providing a composite containing a silicon-based active substance and a carbon material, the particle size concentration of the composite is P0, 1.2 < P0 < 2.0, P0 = (D 80 +D 50 ) / (D 50 +D 20 );

[0025] performing surface modification treatment on the composite by introducing a non-polymerizable gas in a vacuum environment, and then performing plasma reaction by introducing a polymerizable gas to obtain a precursor;

[0026] performing heat treatment on the precursor to obtain the negative electrode material, the oil absorption value of the negative electrode material is O mL / 100g, the specific surface area of the negative electrode material is S m 2 / g, the particle size concentration of the negative electrode material is P1, P1 = (D 80 +D 50 ) / (D 50 +D 20 ), and the physical resilience of the negative electrode material is T, T = 0.01 * O * S / P1, 0.20 < T < 1.20.

[0027] In some embodiments, the specific step of providing the composite containing the silicon-based active substance and the carbon material comprises: mixing the silicon-based active substance and the carbon material to obtain the composite.

[0028] In some embodiments, the mass ratio of the silicon-based active substance to the carbon material is (0.01-0.4):1.

[0029] In some embodiments, the silicon-based active substance comprises at least one of elemental silicon and silicon oxide.

[0030] In some embodiments, the silicon-based active substance further comprises a doped metal M, M is selected from at least one of Mg, Li, Fe, Al, Mn and Cu.

[0031] In some embodiments, the silicon-based active material further comprises a doped metal M, M is selected from at least one of Mg, Li, Fe, Al, Mn and Cu, M is dispersed in the silicon-based active material in at least one of elemental, oxide or silicate form.

[0032] In some embodiments, the silicon-based active material comprises silicon oxide, the general formula of the silicon oxide is SiO x , 0 < x < 2.

[0033] In some embodiments, the carbon material comprises at least one of graphite, graphene, amorphous carbon, carbon nanotube and carbon fiber.

[0034] In some embodiments, the silicon-based active material has a median particle size of 1 μm to 10 μm.

[0035] In some embodiments, the carbon material has a median particle size of 2 μm to 20 μm.

[0036] In some embodiments, the mixing method comprises at least one of grinding mixing, air flow mixing and mechanical mixing.

[0037] In some embodiments, the method further comprises: adjusting the particle size of the composite, and controlling the particle size concentration of the composite to be P0, 1.2 < P0 < 2.0, P0 = (D 80 + D 50 ) / (D 50 + D 20 ).

[0038] In some embodiments, the surface modification treatment has a temperature of 50°C to 200°C.

[0039] In some embodiments, the surface modification treatment has a gas pressure range of 50 Pa to 150 Pa.

[0040] In some embodiments, the surface modification treatment has a time of 10 min to 30 min.

[0041] In some embodiments, the non-polymerizable gas comprises at least one of argon, nitrogen and hydrogen.

[0042] In some embodiments, the plasma reaction has a temperature of 50°C to 200°C.

[0043] In some embodiments, the plasma reaction has a gas pressure range of 50 Pa to 150 Pa.

[0044] In some embodiments, the plasma reaction has a time of 20 min to 60 min.

[0045] In some embodiments, the polymerizable gas comprises at least one of styrene, cyclohexylamine, propylene amine, and methacrylate.

[0046] In some embodiments, the heat treatment is performed at a temperature of 500-700 DEG C.

[0047] In some embodiments, the heat treatment is performed for a time of 1-20 hours.

[0048] In some embodiments, the heat treatment is performed under a protective atmosphere.

[0049] In some embodiments, the heat treatment is performed under a protective atmosphere, and the protective atmosphere comprises at least one of nitrogen, helium, neon, and argon.

[0050] In a third aspect, the present application provides a negative electrode tab, comprising the negative electrode material prepared by the preparation method of the negative electrode material in the second aspect; and the negative electrode tab has a tab rebound rate of 2-10% under a rolling pressure of 3 MPa.

[0051] In a fourth aspect, the present application provides a lithium ion battery, comprising the negative electrode tab in the third aspect.

[0052] Compared with the prior art, the technical scheme of the present application has at least the following beneficial effects:

[0053] The negative electrode material provided by the present application comprises a silicon-based active substance and a carbon material, has an oil absorption value of O mL / 100 g, a specific surface area of S m 2 / g, and a particle size concentration P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), and has a physical rebound capacity T, T=0.01*O*S / P1, 0.20

[0054] The preparation method of the negative electrode material provided by the present application, first, by controlling the particle size concentration of the raw material, that is, the composite containing the silicon-based active substance and the carbon material, the close combination and stacking between the silicon-based active substance and the carbon material can be effectively achieved, and the particle size and quantity of the large particles and the small particles in the material can be well matched, which is conducive to the full dispersion of the particles and tends to form a close stacking structure in which the small particles are embedded in the contact gaps of the large particles; then, after vacuuming, a non-polymerizing gas is introduced to perform surface modification treatment on the composite, and then a polymerizing gas is introduced to continue the plasma reaction to obtain a precursor; the surface of the composite particles after the surface modification treatment has active groups, which are During the plasma reaction process, the active groups on the surface of the composite particles can combine with the polymerizable gas molecules to form a tightly bound polymer modification layer on the particle surface. After carbonization, the polymer modification layer undergoes structural cracking and reforming, effectively modifying the surface defects of the material. The surface defects of the negative electrode material are reduced, and the oil absorption value and specific surface area of ​​the negative electrode material are reduced. The physical rebound ability of the final negative electrode material can be controlled within the range of 0.20 to 1.20, so that the volume of the manufactured negative electrode plate is not easy to rebound after compaction, thereby obtaining a higher compaction density, so that the negative electrode plate has both good cycle performance and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be further described below with reference to the accompanying drawings and examples.

[0056] Figure 1 A schematic diagram of a process for preparing a negative electrode material according to an embodiment of the present application;

[0057] Figure 2 A comparison chart of the cycle curves of the negative electrode materials prepared in Example 2, Example 8, and Comparative Example 8 of the present application;

[0058] Figure 3 This is a comparison chart of the rate performance of the negative electrode materials prepared in Example 2, Example 8 and Comparative Example 8 of the present application. DETAILED DESCRIPTION

[0059] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0060] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0061] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0062] It should be understood that the term "and / or" as used herein merely describes associated objects, which can exist in three relationships, for example, A and / or B can represent three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0063] In a first aspect, the application provides a negative electrode material, the negative electrode material comprising a silicon-based active material and a carbon material, the negative electrode material having an oil absorption value of O mL / 100g, a specific surface area of S m 2 / g, and a particle size concentration of P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the negative electrode material having a physical rebounding capacity of T, T=0.01*O*S / P1, 0.20

[0064] The negative electrode material provided by the application comprises a silicon-based active material and a carbon material, the negative electrode material having an oil absorption value of O mL / 100g, a specific surface area of S m 2 / g, and a particle size concentration of P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the negative electrode material having a physical rebounding capacity of T, T=0.01*O*S / P1, 0.20

[0065] In some embodiments, the physical rebounding capability of the negative electrode material is T, 0.20 < T < 1.20, which can be 0.21, 0.25, 0.3, 0.4, 0.45, 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.95, 1.0, 1.1, 1.15, or 1.2, and the like, and can also be other values within the above range, which is not limited herein. Understandably, after the slurry mixing, coating, and drying, the negative electrode material needs to be rolled under a certain pressure to improve the compaction density, and finally obtain a usable negative electrode sheet. The electrode sheets made of different negative electrode materials will rebound physically after being rolled and placed for a period of time, which will change the active material contact area and electrode porosity, and exhibit different electrochemical performances. The physical rebounding capability T of the negative electrode material can be used to measure the physical rebounding capability of the electrode sheet made of the negative electrode material after rolling. The smaller the T value, the more difficult the electrode sheet made of the negative electrode material to rebound after rolling, which makes the combination of the silicon-based active material and the carbon material particles in the electrode more compact, which is beneficial to inhibit the volume expansion of the negative electrode material during the charging and discharging process. When T ≥ 1.20, the electrode sheet made of the negative electrode material rebounds seriously after rolling, which makes the combination of the silicon-based active material and the carbon material particles loose, and the contact area significantly decreases, which is not conducive to the inhibition of the volume expansion of the negative electrode material and the formation of good conductive channels. When T ≤ 0.2, the physical rebounding of the electrode sheet made of the negative electrode material after rolling is extremely small, and there is a lack of suitable pores between the silicon-based active material and the carbon material particles in the electrode, which is not conducive to the infiltration and transmission of the electrolyte, which leads to the inability of the lithium storage capacity of the negative electrode material to be fully utilized, reduces the cycle performance, and seriously deteriorates the rate performance.

[0066] In some embodiments, the physical rebounding capability of the negative electrode material is T, 0.70 ≤ T < 1.20. When 0.70 ≤ T < 1.20, the electrode sheet made of the negative electrode material rebounds appropriately after rolling, which makes the silicon-based active material and the carbon material particles have good contact, and also has appropriate electrode porosity, so that the electrode sheet has good cycle performance and rate performance.

[0067] In some embodiments, the physical rebounding capability of the negative electrode material is T, 0.2 < T < 0.7. When 0.2 < T < 0.7, the electrode sheet made of the negative electrode material rebounds slightly after rolling, which makes the silicon-based active material and the carbon material particles tightly combined, which can significantly inhibit the volume expansion of the negative electrode material, thereby having superior cycle performance.

[0068] In some embodiments, the silicon-based active material includes at least one of elemental silicon and silicon oxide. The elemental silicon can be amorphous silicon and / or crystalline silicon.

[0069] In some embodiments, the silicon-based active material further includes a doped metal M, and M is selected from at least one of Mg, Li, Fe, Al, Mn, and Cu.

[0070] In some embodiments, the silicon-based active material further comprises a doped metal M, M is selected from at least one of Mg, Li, Fe, Al, Mn and Cu, M is dispersed in the silicon-based active material in at least one of elemental, oxide or silicate form.

[0071] In some embodiments, the silicon-based active material comprises silicon oxide SiOx x , 0 < x < 2. Specifically, SiOx x Specifically, SiOx 0.2 , SiOx 0.5 , SiOx 0.7 , SiOx 0.9 , SiOx 1.2 , SiOx 1.5 , SiOx 1.8 , SiOx 1.9 , etc. without limitation.

[0072] In some embodiments, the silicon-based active material has a median particle size of 1 μm to 10 μm, specifically 1 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.6 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.8 μm, 8.5 μm, 9 μm, 9.8 μm or 10 μm, etc. without limitation.

[0073] In some embodiments, in the negative electrode material, the silicon-based active material and the carbon material are dispersed in the form of particles.

[0074] In some embodiments, the carbon material is present on the surface of the silicon-based active material and / or dispersed between the silicon-based active material particles. Specifically, the silicon-based active material particles can be embedded in the carbon material with the carbon material as the matrix.

[0075] In some embodiments, the carbon material is on the surface of the silicon-based active material to form a carbon layer.

[0076] In some embodiments, the carbon layer has a thickness of 1 nm to 1000 nm, specifically 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 400 nm, 500 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc. without limitation. If the carbon layer is too thick, the carbon content is too high, which is not conducive to obtaining a negative electrode material with high specific capacity; if the carbon layer is too thin, it is not conducive to increasing the conductivity of the negative electrode material and the volume expansion inhibition performance of the material is weak, resulting in poor long cycle performance. Preferably, the thickness of the carbon layer is 50 nm to 800 nm; more preferably, the thickness of the carbon layer is 100 nm to 500 nm.

[0077] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotube, and carbon fiber. The amorphous carbon can be soft carbon and / or hard carbon, and the graphite can be artificial graphite and / or natural graphite. Understandably, the carbon material can improve the conductivity of the silicon-based active material. Graphite is a material with high conductivity, small volume expansion, high initial efficiency, and stable cycle performance, and preferably, the carbon material is graphite.

[0078] In some embodiments, the oil absorption value of the negative electrode material is O mL / 100g, 0<57.0, 0 can be 20.0, 25.0, 30.0, 40.0, 43.0, 45.0, 46.0, 47.0, 48.0, 50.0, 52.0, 53.0, 55.0, 56.0, or 57.0, etc., without limitation herein. The oil absorption value is related to the liquid absorption capacity of the negative electrode material, and reflects the absorption capacity of the particle clusters to the binder during slurry preparation, and is one of the material properties for measuring the physical rebound capacity of the electrode sheet. When the oil absorption value of the negative electrode material is 0<57.0 mL / 100g, the particle clusters of the negative electrode material can absorb an appropriate amount of binder during slurry preparation, which is beneficial to enhancing the adhesion of the silicon-based active material and the carbon material, and the electrode sheet obtained after rolling has a small physical rebound, and a high-compactness-density electrode sheet is easily obtained. When the oil absorption value of the negative electrode material is 0≥57.0 mL / 100g, the particle clusters of the negative electrode material absorb too much binder during slurry preparation, which is not conducive to the effective contact and filling of the particles, and the excess binder in the particle clusters has a large elasticity, so that the electrode sheet prepared is prone to serious physical rebound after rolling, and finally the cycle performance is poor.

[0079] In some embodiments, the specific surface area of the negative electrode material is S cm 2 / g, S<3.50, specifically 3.49, 3.45, 3.35, 3.30, 3.25, 3.15, 3.10, 3.0, 2.85, 2.76, 2.23, 2.10, 1.98, 1.56, 1.47, 1.38, 1.24, 0.98, 0.87, or 0.64, etc., and of course can also be other values within the above range, without limitation herein. Understandably, the specific surface area is closely related to the surface energy and has a positive correlation. The negative electrode material with a higher specific surface area has a larger surface energy, and the interaction force between the particles is also larger, which easily hinders the sliding of the particles and is not conducive to the dense packing of the particles, and is one of the material properties for measuring the physical rebound capacity of the electrode sheet. When the silicon-based composite material has a specific surface area S<3.50 cm 2 / g, it has a suitable surface energy, which is conducive to the dense packing of the particles, so that the electrode sheet prepared is not prone to rebound. When the specific surface area of the negative electrode material is S≥3.50 cm 2 / g, which has a large surface energy, so that the particles are difficult to form a close packing, so that the physical rebound of the prepared pole piece is large.

[0080] In some embodiments, the pH value of the negative electrode material is 6-12, which can be specifically 6, 6.5, 7, 7.8, 8, 8.5, 9, 9.6, 10, 10.5, 11, 11.3, 11.8 or 12, and of course can also be other values in the above range, which is not limited here. Preferably, the pH value of the negative electrode material is 6.5-8.5.

[0081] In some embodiments, the tap density of the negative electrode material is >0.90g / cm 3 . The tap density of the negative electrode material can be specifically 0.91g / cm 3 , 0.95g / cm 3 , 0.99g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.13g / cm 3 , 1.18g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.3g / cm 3 , 1.38g / cm 3 or 1.4g / cm 3 , and the like, which is not limited here.

[0082] In some embodiments, the mass content of water in the negative electrode material is ≤0.5wt%, which can be specifically 0.5wt%, 0.35wt%, 0.25wt%, 0.10wt%, 0.09wt%, 0.08wt%, 0.05wt% or 0.01wt%, and of course can also be other values in the above range, which is not limited here.

[0083] In some embodiments, the mass content of Si element in the negative electrode material is 0.5wt%-25wt%, and can be 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 3wt%, 5.6wt%, 7.8wt%, 8.9wt%, 10wt%, 11.5wt%, 14.6wt%, 16.5wt%, 18.9wt%, 20wt% or 25wt%, and can also be other values within the above range, which is not limited herein. When the mass content of Si element is lower than 0.5wt%, the specific capacity of the negative electrode material is low, which cannot meet the demand of high energy density lithium ion battery. When the mass content of Si element is higher than 20wt%, the volume expansion of the negative electrode material is too large, and the cycle performance is seriously deteriorated.

[0084] In some embodiments, the particle size of the negative electrode material satisfies: 0.1μm≤D 20 ≤12μm, 0.2μm≤D 50 ≤18μm, 0.3μm≤D 80 ≤25μm. It should be noted that the particle size distribution is measured by laser diffraction method, and the volume-based cumulative particle size distribution is measured. D 20 represents the particle size corresponding to the cumulative particle size distribution percentage of 20%. D 50 represents the particle size corresponding to the cumulative particle size distribution percentage of 50%. D 80 represents the particle size corresponding to the cumulative particle size distribution percentage of 80%.

[0085] Specifically, D 20 can be 0.1μm, 0.5μm, 1μm, 1.5μm, 3μm, 5μm, 8μm, 10μm, 11μm or 12μm, and is not limited herein.

[0086] D 50 Specifically, can be 0.2μm, 0.5μm, 1μm, 1.8μm, 2.5μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm or 18μm, and is not limited herein.

[0087] D 80 Specifically, can be 0.3μm, 1.5μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 23μm or 25μm, and is not limited herein.

[0088] In some embodiments, the particle size concentration of the negative electrode material is P1, 1.2 80 +D 50 ) / (D 50 +D 20). Specifically, P1 can be 1.21, 1.26, 1.31, 1.34, 1.38, 1.43, 1.47, 1.5, 1.56, 1.67, 1.74, 1.86, 1.95, 1.98 or 1.99, etc., which are not limited here. The particle size concentration P1 of the negative electrode material is one of the material properties that affects the physical rebound ability of the negative electrode sheet. Among them, D 50 ~D 80 The range represents the majority of larger particles in the negative electrode material; D 20 ~D 50 The range represents the majority of smaller particles in the material; therefore, P1 can be used as (D 80 +D 50 ) / (D 50 +D 20 ) represents the size ratio of large particles to small particles in the negative electrode material. The closer the P1 value is to 1, the more concentrated the particle size distribution is. When the negative electrode material satisfies 1.2<P1<2.0, the particle size and quantity matching of large particles and small particles in the material is better, which is conducive to the full dispersion of particles, and tends to form small particles embedded in the contact gaps of large particles, forming a tightly packed structure, which helps to reduce the physical rebound of the pole piece after rolling. When P1≤1.2, the particle size of large particles and small particles in the material is very close, and there are large pores in the contact between particles, which is not conducive to the formation of a tightly packed structure. When P1≥2.0, the particle size and quantity of large particles and small particles in the material are quite different, among which a large number of small particles tend to agglomerate themselves and it is difficult to form a matching tightly packed structure with large particles, and the effect of improving the physical rebound of the pole piece cannot be achieved.

[0089] In a second aspect, the present application provides a method for preparing a negative electrode material, such as Figure 1 As shown, the following steps are included:

[0090] Step S100, providing a composite material containing a silicon-based active material and a carbon material, wherein the particle size concentration of the composite material is P0, 1.2<P0<2.0, P0=(D' 80 +D' 50 ) / (D' 50 +D' 20 );

[0091] Step S200, in a vacuum environment, introducing a non-polymerizable gas to perform surface modification on the composite, and then introducing a polymerizable gas to perform a plasma reaction to obtain a precursor;

[0092] Step S300: heat-treating the precursor to obtain a negative electrode material. The negative electrode material has an oil absorption value of 0 mL / 100 g and a specific surface area of ​​5 m 2 / g, the particle size concentration of the negative electrode material is P1, P1=(D 80+D 50 ) / (D 50 +D 20 ), the physical rebounding ability of the negative electrode material is T, T = 0.01 * O * S / P1, 0.20 < T < 1.20.

[0093] The preparation method of the negative electrode material provided in the application first realizes the close combination and accumulation of the silicon-based active substance and the carbon material by controlling the particle size concentration of the raw material, i.e., the composite containing the silicon-based active substance and the carbon material, so that the particle size and quantity matching of the large particles and the small particles in the material is good, which is beneficial to the full dispersion of the particles and tends to form a close accumulation structure in which small particles are embedded in the contact gaps between large particles; then, after vacuumizing, the composite is surface-modified by introducing a non-polymerizable gas, and a polymerizable gas is further introduced to continue the plasma reaction, so as to obtain a precursor; the surface of the composite particle after the surface modification treatment has active groups, which can be combined with the molecules of the polymerizable gas in the plasma reaction process, so as to form a polymer modification layer on the surface of the particle, and the polymer modification layer is carbonized to crack and reform, effectively modifying the surface defects of the material, reducing the surface defects of the negative electrode material, reducing the oil absorption value and the specific surface area of the negative electrode material, and controlling the physical rebounding ability of the negative electrode material to be in the range of 0.20-1.20, so that the volume of the negative electrode plate after compaction is not easy to rebound, thereby obtaining a high compaction density, and the negative electrode plate has good cycle performance and excellent rate performance.

[0094] The following specifically introduces the present scheme:

[0095] Step S100, providing a composite containing a silicon-based active substance and a carbon material, the particle size concentration of the composite is P0, 1.2 < P0 < 2.0, P0 = (D' 80 +D' 50 ) / (D' 50 +D' 20 ).

[0096] In some embodiments, the specific steps of providing the composite containing the silicon-based active substance and the carbon material include: mixing the silicon-based active substance and the carbon material to obtain the composite.

[0097] In some embodiments, the mass ratio of the silicon-based active substance to the carbon material is (0.01-0.4):1, and specifically can be 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1 or 0.4:1, etc., and of course can also be other values within the above range, which is not limited here.

[0098] In some embodiments, the silicon-based active material comprises at least one of elemental silicon and silicon oxide. The elemental silicon can be amorphous silicon and / or crystalline silicon.

[0099] In some embodiments, the silicon-based active material further comprises a doping metal M, M being selected from at least one of Mg, Li, Fe, Al, Mn and Cu.

[0100] In some embodiments, the silicon-based active material further comprises a doping metal M, M being selected from at least one of Mg, Li, Fe, Al, Mn and Cu, M being dispersed in the silicon-based active material in at least one of elemental, oxide or silicate form. Preferably, M is dispersed in the silicon-based active material in silicate (M x Si y O z ) form.

[0101] In some embodiments, the silicon-based active material comprises silicon oxide SiO x , 0 < x < 2. Specifically, SiO x may be SiO 0.2 , SiO 0.5 , SiO 0.7 , SiO 0.9 , SiO 1.2 , SiO 1.5 , SiO 1.8 , SiO 1.9 , etc., without limitation.

[0102] In some embodiments, the carbon material comprises at least one of graphite, graphene, amorphous carbon, carbon nanotube and carbon fiber. The amorphous carbon can be soft carbon and / or hard carbon, and the graphite can be artificial graphite and / or natural graphite. Understandably, the carbon material can improve the conductivity of the silicon-based active material. Graphite is a material with high conductivity, small volume expansion, high initial efficiency and stable cycle performance, and preferably, the carbon material is graphite.

[0103] In some embodiments, the silicon-based active material has a median particle size of 1 μm to 10 μm, which can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., without limitation.

[0104] In some embodiments, the carbon material has a median particle size of 2 μm to 20 μm. The carbon material can have a median particle size of 2 μm, 5 μm, 7 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm or 20 μm, etc., without limitation.

[0105] In some embodiments, the mixing method includes at least one of grinding mixing, airflow mixing, and mechanical mixing.

[0106] In some embodiments, the method further includes: adjusting the particle size of the composite, and controlling the particle size concentration of the composite to be P0, 1.2 < P0 < 2.0, P0 = (D 80 + D 50 ) / (D 50 + D 20 ). Understandably, the particle size concentration of the composite is controlled within the above range, which can make the particle size and quantity of large particles and small particles in the negative electrode material match well, and is beneficial to the full dispersion of the particles, and tends to form a close-packed structure in which small particles are embedded in the contact gaps between large particles. Specifically, the composite is placed in an airflow classifier, and the particle size of the composite is classified and adjusted by the airflow classifier, so that the particle size concentration P0 of the composite satisfies the above range.

[0107] In step S200, the composite is subjected to surface modification treatment in a vacuum environment by introducing a non-polymerizable gas, and then subjected to plasma reaction by introducing a polymerizable gas, to obtain a precursor.

[0108] In some embodiments, the surface modification treatment is performed at a temperature of 50-200°C, and specifically can be 50°C, 60°C, 70°C, 80°C, 100°C, 120°C, 150°C, 180°C, or 200°C. Understandably, the above temperature is not limited to the listed values, and other values not listed in the range are also applicable.

[0109] In some embodiments, the reaction system is first subjected to vacuum before the surface modification treatment, and the surface modification treatment is performed at a gas pressure of 50-150 Pa, and specifically can be 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 100 Pa, 120 Pa, or 150 Pa, or other values in the above range, which are not limited herein.

[0110] In some embodiments, the non-polymerizable gas includes at least one of argon, nitrogen, and hydrogen.

[0111] During the surface modification treatment, the non-polymerizable gas is blown at a high speed to remove impurities adsorbed on the surface of the composite. Since the carbon material in the composite contains some oxygen elements, the oxygen elements can introduce active groups such as hydroxyl, carboxyl, amino, aldehyde, imino, etc. under the attack of the non-polymerizable gas.

[0112] In some embodiments, the surface modification treatment of the composite in the non-polymerizable gas is performed for 10-30 minutes, and then the plasma reaction in the polymerizable gas is performed for 20-60 minutes to obtain the precursor. It can be understood that the composite in the non-polymerizable gas is first preheated and surface cleaned, and then the polymer gas is introduced, so that the polymer gas can be combined with the active groups (such as hydroxyl, carboxyl, amino, aldehyde, imino) on the surface of the composite particles, and a tightly combined polymer modification layer is formed on the surface of the composite particles.

[0113] It should be noted that the surface modification treatment of the composite in the non-polymerizable gas will cause a certain weak damage to the surface of the composite, that is, if the surface modification treatment time is too long, the specific surface area of the negative electrode material will increase, which is not conducive to improving the physical rebound ability of the negative electrode material. The longer the plasma reaction time in the polymerizable gas, the thicker the polymer modification layer deposited on the surface of the composite, and the lower the specific surface area and oil absorption value of the negative electrode material after subsequent heat treatment. Therefore, controlling the surface modification treatment time of the composite in the non-polymerizable gas and the plasma reaction time in the polymerizable gas is beneficial to controlling the balance between the specific surface area, oil absorption value and physical rebound ability of the negative electrode material, and improving the cycle performance and rate performance of the negative electrode material.

[0114] In some embodiments, the temperature of the plasma reaction is 50-200°C, and can be specifically 50°C, 60°C, 70°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C. It can be understood that the above-mentioned temperature is not limited to the listed values, and other values not listed in the range are also applicable.

[0115] In some embodiments, the gas pressure of the plasma reaction is 50-150 Pa, and can be specifically 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 100 Pa, 120 Pa or 150 Pa, and of course can also be other values in the above range, which are not limited herein.

[0116] In some embodiments, the polymerizable gas includes at least one of styrene, cyclohexylamine, vinyl chloride, propylene amine, and methacrylate. Exemplarily, the polymer modification layer can be polystyrene, polypropylene amine, polymethacrylate, polyvinyl chloride, etc., which are not limited herein.

[0117] In step S300, the precursor is heat-treated to obtain a negative electrode material, wherein the oil absorption value of the negative electrode material is O mL / 100g, and the specific surface area is S m 2 / g, and the particle size distribution concentration of the negative electrode material is P1, P1=(D 80 +D 50 ) / (D50 +D 20 ), the physical rebounding ability of the negative electrode material is T, T=0.01*O*S / P1, 0.20

[0118] It can be understood that, in the heat treatment process, the polymer modification layer is carbonized and then structure cracking and reorganization occur, the surface defects of the negative electrode material are effectively modified, the oil absorption value and the specific surface area of the negative electrode material are reduced, and the physical rebounding ability of the finally obtained negative electrode material can be controlled in the range of 0.20-1.20, and the negative electrode material has good cycle performance and excellent rate performance.

[0119] In some embodiments, the temperature of the heat treatment is 500-700°C, and can be specifically 500°C, 530°C, 550°C, 580°C, 600°C, 620°C, 650°C, 670°C, 680°C or 700°C, and can also be other values in the above range, which are not limited herein.

[0120] In some embodiments, the time of the heat treatment is 1-20h, and can be specifically 1h, 1.5h, 3h, 5h, 8h, 10h, 12h, 15h, 18h or 20h, and can also be other values in the above range, which are not limited herein.

[0121] In some embodiments, the heat treatment is carried out in a protective atmosphere.

[0122] In some embodiments, the heat treatment is carried out in a protective atmosphere, and the protective atmosphere comprises at least one of nitrogen, helium, neon and argon.

[0123] In the third aspect, the application provides a negative electrode tab, which comprises the above negative electrode material, and the tab rebounding rate of the negative electrode tab is 2%-10% under a rolling pressure of 3MPa. The tab rebounding rate can be specifically 2%, 2.5%, 3%, 3.8%, 5.6%, 6.7%, 7.8%, 8.9%, 9.6% or 10%, and the like, which are not limited herein. It can be understood that, when the tab rebounding rate of the negative electrode tab is in the above range, the tab rebounds appropriately after rolling, the silicon-based active material and the carbon material are in good contact, and the electrode porosity is also appropriate, so that the tab has good cycle performance and rate performance.

[0124] In the fourth aspect, the application provides a lithium ion battery, which comprises the above negative electrode tab.

[0125] Embodiment

[0126] Embodiment 1

[0127] (1) 30g SiO (D50 = 6 pm), 970 g artificial graphite (D 50 = 15 pm) were preliminarily mixed and then placed in an air flow pulverizer for collision, crushing and mixing treatment to obtain a composite.

[0128] (2) The composite was placed in an air flow classifier for particle size adjustment to control the particle size concentration P0= 1.34 ± 0.05 of the composite, P0= (D 80 + D 50 ) / (D 50 + D 20 ).

[0129] (3) The composite was added into a plasma device and vacuumized; argon gas was introduced and the gas pressure was controlled at 100 Pa, and the composite was surface-modified using argon gas for 20 min, and the reaction temperature was 180 °C; then propylene amine was introduced and the gas pressure was controlled at 100 Pa for plasma reaction for 40 min to obtain a precursor.

[0130] (4) The precursor was heat-treated under an argon gas atmosphere, the heat treatment temperature was 500 °C, and the heat treatment time was 10 hours to obtain a negative electrode material.

[0131] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0132] The other parameters of the negative electrode material are shown in Table 1.

[0133] Example 2

[0134] (1) 100 g SiO (D 50 = 6 pm), 900 g artificial graphite (D 50 = 15 pm) were preliminarily mixed and then placed in an air flow pulverizer for collision, crushing and mixing treatment to obtain a composite.

[0135] (2) The composite was placed in an air flow classifier for particle size adjustment to control the particle size concentration P0= 1.45 ± 0.05 of the composite, P0= (D 80 + D 50 ) / (D 50 + D 20 ).

[0136] (3) The composite was added into a plasma device and vacuumized; argon gas was introduced and the gas pressure was controlled at 100 Pa, and the composite was surface-modified using argon gas for 20 min, and the reaction temperature was 180 °C; then propylene amine was introduced and the gas pressure was controlled at 100 Pa for plasma reaction for 40 min to obtain a precursor.

[0137] (4) The precursor is heat-treated under an argon atmosphere, the heat treatment temperature is 500°C, and the heat treatment time is 10 hours, to obtain the negative electrode material.

[0138] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0139] The other parameters of the negative electrode material are shown in Table 1.

[0140] Example 3

[0141] (1) 300g SiO (D 50 = 6μm) and 700g artificial graphite (D 50 = 15μm) are preliminarily mixed and then placed in an air flow pulverizer for collision, crushing and mixing treatment, to obtain a composite.

[0142] (2) The composite is placed in an air flow classifier for particle size adjustment, to control the particle size concentration P0 of the composite to be 1.66±0.05, P0 = (D 80 + D 50 ) / (D 50 + D 20 ).

[0143] (3) The composite is added into a plasma device and vacuumized; argon is introduced and the gas pressure is controlled to be 100Pa, and the composite is surface-modified by argon for 20min, the reaction temperature is 180°C; then propylene amine is introduced and the gas pressure is controlled to be 100Pa for plasma reaction for 40min, to obtain a precursor.

[0144] (4) The precursor is heat-treated under an argon atmosphere, the heat treatment temperature is 500°C, and the heat treatment time is 10 hours, to obtain the negative electrode material.

[0145] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0146] The other parameters of the negative electrode material are shown in Table 1.

[0147] Example 4

[0148] (1) 100g Mg-doped SiO (D 50 = 6μm) and 900g artificial graphite (D 50 = 15μm) are preliminarily mixed and then placed in an air flow pulverizer for collision, crushing and mixing treatment, to obtain a composite.

[0149] (2) The compound is placed in an air flow classifier for particle size adjustment, and the particle size concentration P0 of the compound is controlled to be 1.62±0.05, P0=(D 80 +D’ 50 ) / (D 50 +D’ 20 ).

[0150] (3) The compound is added into a plasma device and vacuumized; argon gas is introduced and the gas pressure is controlled to be 100 Pa, and the compound is treated by surface modification using argon gas for 20 min, and the reaction temperature is 180℃; then propylene amine is introduced and the gas pressure is controlled to be 100 Pa to perform plasma reaction for 40 min, and a precursor is obtained.

[0151] (4) The precursor is heat-treated under an argon gas atmosphere, the heat treatment temperature is 500℃, and the heat treatment time is 10 hours, and a negative electrode material is obtained.

[0152] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO and Mg, wherein Mg is dispersed in the silicon-based active substance in the form of magnesium silicate, and the carbon material is artificial graphite.

[0153] The other parameters of the negative electrode material are shown in Table 1.

[0154] Example 5

[0155] (1) 100g of Li-doped SiO (D 50 =6μm) and 900g of artificial graphite (D 50 =15μm) are preliminarily mixed and then placed in an air flow pulverizer for collision, crushing and mixing treatment to obtain a compound.

[0156] (2) The compound is placed in an air flow classifier for particle size adjustment, and the particle size concentration P0 of the compound is controlled to be 1.58±0.05, P0=(D 80 +D’ 50 ) / (D 50 +D’ 20 ).

[0157] (3) The compound is added into a plasma device and vacuumized; argon gas is introduced and the gas pressure is controlled to be 100 Pa, and the compound is treated by surface modification using argon gas for 20 min, and the reaction temperature is 180℃; then propylene amine is introduced and the gas pressure is controlled to be 100 Pa to perform plasma reaction for 40 min, and a precursor is obtained.

[0158] (4) The precursor is heat-treated under an argon gas atmosphere, the heat treatment temperature is 500℃, and the heat treatment time is 10 hours, and a negative electrode material is obtained.

[0159] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material. The silicon-based active material is SiO and Li, wherein Li is dispersed in the silicon-based active material in the form of lithium silicate, and the carbon material is artificial graphite.

[0160] Other parameters of the negative electrode materials are detailed in Table 1.

[0161] Example 6

[0162] (1) Weigh 100g SiO(D 50 =6μm), 900g natural graphite (D 50 =15 μm) were preliminarily mixed and then placed in a jet mill for collision, crushing and mixing to obtain a composite.

[0163] (2) Place the composite in an airflow classifier for particle size adjustment, and control the composite particle size concentration P0 = 1.73 ± 0.05, P0 = (D' 80 +D' 50 ) / (D' 50 +D' 20 ).

[0164] (3) Add the complex into the plasma equipment and evacuate it; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification treatment on the complex for 20 minutes at a reaction temperature of 180°C; then introduce propyleneamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0165] (4) The precursor was heat-treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

[0166] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material, wherein the silicon-based active material is SiO, and the carbon material is natural graphite.

[0167] Other parameters of the negative electrode materials are detailed in Table 1.

[0168] Example 7

[0169] (1) Weigh 30g SiO(D 50 =6μm), 970g artificial graphite (D 50 =15 μm) were preliminarily mixed and then placed in a jet mill for collision, crushing and mixing to obtain a composite.

[0170] (2) Place the composite in an airflow classifier for particle size adjustment, and control the composite particle size concentration P0 = 1.34 ± 0.05, P0 = (D' 80 +D' 50 ) / (D'50 +D’ 20 )。

[0171] (3) The complex was added into a plasma device and vacuumized; argon was introduced and the gas pressure was controlled to be 100 Pa, and the complex was surface-modified by argon for 20 min, and the reaction temperature was 180℃; then propylene amine was introduced and the gas pressure was controlled to be 100 Pa to carry out plasma reaction for 25 min, to obtain a precursor.

[0172] (4) The precursor was heat-treated under an argon atmosphere, the heat treatment temperature was 500℃, and the heat treatment time was 10 hours, to obtain the negative electrode material.

[0173] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is natural graphite.

[0174] The other parameters of the negative electrode material are shown in Table 1.

[0175] Example 8

[0176] (1) 100g SiO (D 50 = 6μm) and 900g artificial graphite (D 50 = 15μm) were preliminarily mixed and then placed in an air flow pulverizer to carry out collision, crushing and mixing treatment, to obtain a complex.

[0177] (2) The complex was placed in an air flow classifier to adjust the particle size, and the particle size concentration P0 of the complex was controlled to be 1.45±0.05, P0 = (D 80 +D’ 50 ) / (D 50 +D 20 ).

[0178] (3) The complex was added into a plasma device and vacuumized; argon was introduced and the gas pressure was controlled to be 100 Pa, and the complex was surface-modified by argon for 20 min, and the reaction temperature was 180℃; then propylene amine was introduced and the gas pressure was controlled to be 100 Pa to carry out plasma reaction for 25 min, to obtain a precursor.

[0179] (4) The precursor was heat-treated under an argon atmosphere, the heat treatment temperature was 500℃, and the heat treatment time was 10 hours, to obtain the negative electrode material.

[0180] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0181] The other parameters of the negative electrode material are shown in Table 1.

[0182] Example 9

[0183] (1) Take 300g SiO (D 50 = 6 μm), 700g artificial graphite (D 50 = 15 μm) and mix them preliminarily, then put them into an air flow pulverizer for collision, crushing and mixing treatment to obtain a composite.

[0184] (2) Put the composite into an air flow classifier for particle size adjustment to control the particle size concentration P0 = 1.66 ± 0.05, P0 = (D 80 + D 50 ) / (D 50 + D 20 ).

[0185] (3) Put the composite into a plasma device and vacuumize it; introduce argon gas and control the gas pressure at 100 Pa, use argon gas to perform surface modification treatment on the composite for 20 min, the reaction temperature is 180℃; then introduce propylene amine and control the gas pressure at 100 Pa to perform plasma reaction for 25 min to obtain a precursor.

[0186] (4) Perform heat treatment on the precursor in an argon gas atmosphere, the heat treatment temperature is 500℃, the heat treatment time is 10 hours to obtain a negative electrode material.

[0187] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0188] The other parameters of the negative electrode material are shown in Table 1.

[0189] Example 10

[0190] The difference between this example and Example 1 is that:

[0191] (3) Put the composite into a plasma device and vacuumize it; introduce argon gas and control the gas pressure at 100 Pa, use argon gas to perform surface modification treatment on the composite for 30 min, the reaction temperature is 180℃; then introduce styrene and control the gas pressure at 100 Pa to perform plasma reaction for 40 min to obtain a precursor.

[0192] The negative electrode material prepared in this example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0193] The other parameters of the negative electrode material are shown in Table 1.

[0194] Example 11

[0195] The difference between this example and Example 2 is that:

[0196] (3) The composite is added into a plasma device and vacuumized; argon is introduced and the pressure is controlled at 100 Pa, and the composite is surface modified by argon for 30 min, and the reaction temperature is 180°C; then styrene is introduced and the pressure is controlled at 100 Pa to carry out plasma reaction for 40 min, to obtain the precursor.

[0197] The negative electrode material prepared in the example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0198] The other parameters of the negative electrode material are shown in Table 1.

[0199] Example 12

[0200] Different from Example 1 is that:

[0201] (1) 30 g of Si (D 50 = 6 μm) and 970 g of artificial graphite (D 50 = 15 μm) are preliminarily mixed and then placed in an air flow pulverizer to carry out collision, crushing and mixing treatment, to obtain a composite.

[0202] The negative electrode material prepared in the example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is Si, and the carbon material is artificial graphite.

[0203] The other parameters of the negative electrode material are shown in Table 1.

[0204] Comparative Example 1

[0205] 100 g of carbon-coated SiO and 900 g of artificial graphite are stirred and mixed to obtain a mixture; the mixture is placed in an air flow classifier to adjust the particle size, and the particle size distribution concentration P0 of the mixture is controlled at 1.45±0.05, to obtain a negative electrode material.

[0206] The other parameters of the negative electrode material are shown in Table 1.

[0207] Comparative Example 2

[0208] Different from Example 8 is that:

[0209] (3) The composite is added into a plasma device and vacuumized; argon is introduced and the pressure is controlled at 100 Pa, and the composite is surface modified by argon for 40 min, and the reaction temperature is 180°C; then styrene is introduced and the pressure is controlled at 100 Pa to carry out plasma reaction for 40 min, to obtain the precursor.

[0210] The negative electrode material prepared in the example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0211] The other parameters of the negative electrode material are shown in Table 1.

[0212] Comparative Example 3

[0213] Different from Example 2 is that:

[0214] (3) The composite was added into a plasma device and vacuumized; propylene amine was introduced and the gas pressure was controlled to be 100 Pa to carry out plasma reaction for 70 min, to obtain a precursor.

[0215] The negative electrode material prepared in the example comprises a silicon-based active substance and a carbon material, the silicon-based active substance is SiO, and the carbon material is artificial graphite.

[0216] The other parameters of the negative electrode material are shown in Table 1.

[0217] Comparative Example 4

[0218] Different from Example 2 is that:

[0219] (1) 500 g of SiO (D50 = 6 μm) and 500 g of artificial graphite (D50 = 15 μm) were weighed and mixed to obtain a mixture, and the mixture was placed in an air flow crusher to carry out collision, crushing and mixing treatment, to obtain an active material.

[0220] (2) The active material was placed in an air flow classifier to adjust the particle size, and the particle size distribution concentration P0 of the active material was controlled to be 2.03 ± 0.05.

[0221] The other parameters of the negative electrode material are shown in Table 1.

[0222] Comparative Example 5

[0223] Different from Example 2 is that:

[0224] (3) The composite was added into a plasma device and vacuumized; propylene amine was introduced and the gas pressure was controlled to be 100 Pa to carry out plasma reaction for 40 min, to obtain a precursor.

[0225] The other parameters of the negative electrode material are shown in Table 1.

[0226] Comparative Example 6

[0227] Different from Example 2 is that:

[0228] (3) The composite was added into a plasma device and vacuumized; argon was introduced and the gas pressure was controlled to be 100 Pa, and the composite was surface-modified by argon for 20 min at a reaction temperature of 180 ℃, to obtain a precursor.

[0229] The other parameters of the negative electrode material are shown in Table 1.

[0230] Test method

[0231] (1) Particle size of the negative electrode material:

[0232] The particle size test method refers to GB / T 19077-2016. It can be conveniently measured by a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK. The particle size distribution range of the negative electrode material is tested by the Mastersizer 3000, and the volume-based cumulative particle size distribution of the particle size distribution measurement is measured by the laser diffraction method. D20 represents the particle size corresponding to the cumulative particle size distribution percentage of 20%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage of 50%, and D80 represents the particle size corresponding to the cumulative particle size distribution percentage of 80%.

[0233] (2) Test method of specific surface area of the negative electrode material:

[0234] Referring to GB / T 19587-2004 “Determination of the Specific Surface Area of Solid Substances by Gas Adsorption BET Method”, the adsorption amount of gas on the solid surface at different relative pressures is measured at a constant low temperature, and then the monolayer adsorption amount of the sample is obtained based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), so as to calculate the specific surface area of the material.

[0235] (3) Test method of tap density of the negative electrode material:

[0236] Referring to GB / T 5162-2006 / ISO 3953:1993 “Determination of Tap Density of Metal Powders”, the tap density T is tested by the Korna tap density analyzer (Korna DAT-4-220) of Anton Paar (Shanghai) Trading Co., Ltd. after 3000 vibrations, and the unit is g / cm 3 .

[0237] (4) Test of pH of the negative electrode material:

[0238] Referring to GB / T 24533-2019 “Graphite-based negative electrode material for lithium ion batteries” Appendix C “Determination of pH value”, the pH meter (Mettler Toledo FE20) is used for measurement.

[0239] (5) Test method of oil absorption value of the negative electrode material:

[0240] The oil absorption value Q is tested by using the ASAHI S-500 oil absorption value tester of Japan ASAHISOUKEN, and the oil absorption value Q is the amount of dibutyl phthalate dropped when the torque generated by the change in viscosity characteristics reaches 70% of the maximum torque, in units of mL / 100 g.

[0241] (6) Test method of mass content of water in negative electrode material:

[0242] Refer to GB / T 24533-2019 "Graphite-based negative electrode material for lithium ion battery" Appendix B "Determination method of moisture content" or equipment instruction manual. The Mettler DL39 type Karl Fischer coulometric titrator is used for measurement.

[0243] (7) Electrochemical performance test

[0244] The negative electrode materials prepared in Examples 1-12 and Comparative Examples 1-3 were assembled into button cells: the negative electrode material: conductive agent (SuTer T): sodium carboxymethyl cellulose (CMC): butadiene-styrene rubber (SBR) = 92:2:2:2 in mass ratio was mixed uniformly, and then coated on a copper foil current collector to obtain a negative electrode sheet for standby after drying. The dried negative electrode sheet was rolled under a pressure of 3 MPa, 6 MPa and 9 MPa respectively, and the thickness change rate of the sheet before and after rolling was measured, which was the physical rebound (sheet rebound rate) of the sheet. The negative electrode sheet was rolled under a pressure of 3 MPa, and the rolled negative electrode sheet was tested for button cell. The battery was assembled in an argon glove box, with lithium metal sheet as negative electrode, electrolyte being 1 mol / L lithium hexafluorophosphate LiPF6+ethylene carbonate (EC)+methyl ethyl carbonate (EMC), and the separator being a polyethylene / propylene composite microporous membrane. The electrochemical performance was tested on a battery tester, and the charge and discharge voltage was 0.01-1.5 V.

[0245] The cycle life of the battery was the number of charge and discharge cycles when the capacity retention rate decayed to 80%.

[0246] The first coulombic efficiency = the first circle discharge capacity / the first circle charge capacity.

[0247] The test results are shown in Tables 2 and 3.

[0248] Table 1 Performance test results of negative electrode material

[0249]

[0250]

[0251] Table 2 Negative electrode sheet rebound test results of negative electrode sheet under different rolling pressures

[0252]

[0253] Table 3 Electrochemical performance test results of negative electrode materials

[0254]

[0255]

[0256] According to the test data in Tables 1-3, controlling the balance among the oil absorption value, specific surface area and particle size concentration of the negative electrode material can control the physical rebound ability T of the negative electrode material in the range of 0.2-1.2, can tightly combine the silicon-based active material and the carbon material particles, is conducive to inhibiting the volume expansion of the silicon-based active material, so that the volume of the prepared electrode sheet is not easy to rebound after compaction, and a higher compaction density can be obtained, so that the negative electrode sheet has good cycle performance and rate performance.

[0257] Table 2 is the electrode sheet rebound test results of the negative electrode sheet prepared from the negative electrode material prepared in the application under different roll pressures. As shown in Table 2, the electrode sheet rebound rate of the negative electrode sheet prepared from the negative electrode material prepared in the application under the roll pressure of 3 MPa, 6 MPa and 9 MPa is in the range of 2%-10%, which can ensure that the silicon-based active material and the carbon material maintain good contact and can be tightly combined, and at the same time can ensure that the negative electrode material layer on the negative electrode sheet has a suitable porosity, which is conducive to the electrolyte infiltrating the negative electrode material layer and improving the lithium ion transmission efficiency, so that the electrode sheet has good cycle performance and rate performance. However, the applicant found that as the roll pressure increases, the electrode sheet rebound rate of the negative electrode sheet after roll pressing also increases. Therefore, when the roll pressure is 3 MPa, the electrode sheet rebound rate of the negative electrode sheet after roll pressing can be effectively reduced, the problem of loose combination of the silicon-based active material and the carbon material caused by excessive electrode sheet rebound rate can be reduced, and the volume expansion and particle pulverization effect of the negative electrode sheet during the charge and discharge cycle process can be further reduced.

[0258] The negative electrode material prepared in Comparative Example 1, as shown in Tables 1-3, has an oil absorption value of 1.5 g / g, a specific surface area of 1.5 m2 / g and a particle size concentration of 0.8, and the physical rebound ability T of the negative electrode material is greater than 1.2. The negative electrode material is prepared by simply mixing the silicon-based active material SiO and graphite by stirring and adjusting the particle size. The negative electrode material has an unbalanced relationship among the oil absorption value, specific surface area and particle size concentration, and the physical rebound ability of the negative electrode material is greater than 1.2. The negative electrode sheet prepared from the negative electrode material has a serious physical rebound after roll pressing, the combination ability between the silicon-based active material and the carbon material particles is reduced, the silicon-based active material has a serious volume expansion during the cycle process, the negative electrode material is pulverized and broken, the cycle attenuation of the battery is rapid, and the cycle life of the electrode sheet is greatly reduced. Figure 2 and Figure 3 As shown in Tables 1-3, the negative electrode material prepared in Comparative Example 2 has an oil absorption value of 1.5 g / g, a specific surface area of 1.5 m2 / g and a particle size concentration of 0.8, and the physical rebound ability T of the negative electrode material is greater than 1.2. The negative electrode material is prepared by simply mixing the silicon-based active material SiO and graphite by stirring and adjusting the particle size. The negative electrode material has an unbalanced relationship among the oil absorption value, specific surface area and particle size concentration, and the physical rebound ability of the negative electrode material is greater than 1.2. The negative electrode sheet prepared from the negative electrode material has a serious physical rebound after roll pressing, the combination ability between the silicon-based active material and the carbon material particles is reduced, the silicon-based active material has a serious volume expansion during the cycle process, the negative electrode material is pulverized and broken, the cycle attenuation of the battery is rapid, and the cycle life of the electrode sheet is greatly reduced.

[0259] The negative electrode material prepared in Comparative Example 2 has a long surface modification treatment time of the composite in the non-polymerizable gas, which causes a certain degree of damage to the surface of the composite, resulting in a high specific surface area of the negative electrode material. The relationship among the oil absorption value, the specific surface area and the particle size concentration of the negative electrode material is unbalanced, and the physical rebound capacity of the negative electrode material is greater than 1.2. The negative electrode sheet prepared from the negative electrode material has a serious physical rebound after rolling, the combination between the silicon-based active material and the carbon material particles is loose, the silicon-based active material has a severe volume expansion effect in the cycle process, and the negative electrode material is pulverized and broken in the cycle process, resulting in a decrease in the cycle performance of the battery and a significant decrease in the cycle life of the electrode sheet.

[0260] The negative electrode material prepared in Comparative Example 3 has a long plasma reaction time of the composite in the polymerizable gas, and the composite surface has a thick polymer modification layer. After the heat treatment of the composite, the oil absorption value and the specific surface area of the negative electrode material are low, and the physical rebound capacity T of the negative electrode material is less than 0.2. Therefore, the negative electrode sheet prepared from the negative electrode material has a minimal physical rebound after rolling, and the silicon-based active material and the carbon material particles in the electrode lack suitable pores, which is not conducive to the infiltration and transmission of the electrolyte, resulting in a failure to fully exert the lithium storage capacity of the negative electrode material, a decrease in the cycle performance, and a deterioration of the rate performance of the negative electrode material.

[0261] The negative electrode material prepared in Comparative Example 4 has a high content of the silicon-based active material SiO in the preparation process, and the mass content of silicon in the negative electrode material is significantly increased, and the specific capacity of the negative electrode material is also significantly increased. However, due to the excessive silicon content, the negative electrode material has a significant volume expansion in the cycle process, resulting in a decrease in the cycle performance and the rate performance of the negative electrode material and a significant decrease in the cycle life of the electrode sheet.

[0262] The negative electrode material prepared in Comparative Example 5 is not subjected to surface modification treatment of the composite in the non-polymerizable gas in the preparation process. In the plasma reaction process, the polymer gas is difficult to form a tightly combined modification layer on the surface of the composite particles, and the surface defects of the negative electrode material are difficult to be modified. The negative electrode material has many surface defects, and the oil absorption value is high, resulting in an excessive physical rebound capacity T of the negative electrode material. The negative electrode sheet prepared from the negative electrode material has a serious physical rebound after rolling, the bonding force between the silicon-based active material and the carbon material particles is decreased, the silicon-based active material has a severe volume expansion in the cycle process, the cycle performance of the negative electrode sheet is deteriorated, and the cycle life is significantly decreased.

[0263] The negative electrode material prepared in Comparative Example 6 is not subjected to plasma treatment in a polymerization gas during preparation, and the surface defects of the negative electrode material are not modified, so that the negative electrode material has more surface defects, higher oil absorption value and specific surface area, and higher physical rebounding capacity. The negative electrode sheet prepared from the negative electrode material has serious physical rebounding after rolling, the binding capacity between the silicon-based active material and the carbon material is poor, the silicon-based active material has serious volume expansion during the cycle process, the negative electrode material is pulverized and broken during the cycle process, the cycle performance of the negative electrode sheet is seriously deteriorated, and the cycle life is greatly attenuated.

[0264] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that The negative electrode material includes a silicon-based active material and a carbon material. The oil absorption value of the negative electrode material is 0 mL / 100 g and the specific surface area is S m 2 / g, the particle size concentration of the negative electrode material is P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the physical rebound ability of the negative electrode material is T, ,1.2<P1<2.0, 0.20<T<1.20; The oil absorption value of the negative electrode material is 0 mL / 100 g, O<57.0; the specific surface area of ​​the negative electrode material is S cm 2 / g, S<3.

50.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (6): (1) The silicon-based active material includes at least one of elemental silicon and silicon oxide; (2) The silicon-based active material further includes a doping metal M, where M is selected from at least one of Mg, Li, Fe, Al, Mn, and Cu; (3) The silicon-based active material further includes a doping metal M, where M is selected from at least one of Mg, Li, Fe, Al, Mn, and Cu, and M is dispersed in the silicon-based active material in the form of at least one element, oxide, or silicate; (4) The silicon-based active material includes silicon oxide, and the general formula of silicon oxide is SiO x , 0<x<2; (5) The median particle size of the silicon-based active material is 1 μm to 10 μm; (6) The carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers.

3. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following characteristics (1) to (5): (1) The pH value of the negative electrode material is 6 to 12; (2) The tap density of the negative electrode material is greater than 0.90 g / cm 3 ; (3) The mass content of water in the negative electrode material is ≤0.5wt%; (4) The mass content of silicon in the negative electrode material is 0.5 wt%~25 wt%; (5) The particle size of the negative electrode material satisfies: 0.1 μm ≤ D 20 ≤12μm, 0.2μm≤D 50 ≤18μm, 0.3μm≤D 80 ≤25μm.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that The negative electrode material satisfies at least one of the following characteristics (1) to (3): (1) In the negative electrode material, the silicon-based active material and the carbon material are dispersed in each other in the form of particles; (2) The physical rebound capacity of the negative electrode material is T, 0.2<T<0.7; (3) The physical rebound capacity of the negative electrode material is T, 0.70≤T<1.

20.

5. A method for preparing a negative electrode material, characterized in that: The following steps are involved: Provided is a composite containing a silicon-based active substance and a carbon material, wherein the particle size concentration of the composite is P0, 1.2<P0<2.0, P0=(D' 80 +D' 50 ) / (D' 50 +D' 20 ); In a vacuum environment, non-polymerizing gas is introduced to perform surface modification on the composite, and then polymerizing gas is introduced to perform plasma reaction to obtain a precursor; The precursor is heat-treated to obtain a negative electrode material having an oil absorption value of 0 mL / 100 g and a specific surface area of ​​5 m 2 / g, the particle size concentration of the negative electrode material is P1, P1=(D 80 +D 50 ) / (D 50 +D 20 ), the physical rebound ability of the negative electrode material is T, ,1.2<P1<2.0, 0.20<T<1.20; The oil absorption value of the negative electrode material is 0 mL / 100 g, O<57.0; the specific surface area of ​​the negative electrode material is S cm 2 / g, S<3.

50.

6. The preparation method according to claim 5, characterized in that The specific steps of providing a composite containing a silicon-based active substance and a carbon material include: mixing the silicon-based active substance and the carbon material to obtain a composite, and the preparation method includes at least one of the following features (1) to (10): (1) The mass ratio of the silicon-based active material to the carbon material is (0.01-0.4):1; (2) The silicon-based active material includes at least one of elemental silicon and silicon oxide; (3) The silicon-based active material further includes a doping metal M, where M is selected from at least one of Mg, Li, Fe, Al, Mn, and Cu; (4) The silicon-based active material further includes a doping metal M, where M is selected from at least one of Mg, Li, Fe, Al, Mn, and Cu, and M is dispersed in the silicon-based active material in the form of at least one element, oxide, or silicate; (5) The silicon-based active material includes silicon oxide, and the general formula of silicon oxide is SiO x , 0<x<2; (6) The carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers; (7) The median particle size of the silicon-based active material is 1 μm to 10 μm; (8) The median particle size of the carbon material is 2 μm to 20 μm; (9) The mixing method includes at least one of grinding mixing, air flow mixing, and mechanical mixing; (10) The method further comprises: adjusting the particle size of the composite to control the particle size concentration of the composite to be P0, 1.2<P0<2.0, P0=(D' 80 +D' 50 ) / (D' 50 +D' 20 ).

7. The preparation method according to claim 5, characterized in that The preparation method includes at least one of the following features (1) to (8): (1) The temperature of the surface modification treatment is 50°C to 200°C; (2) The air pressure range of the surface modification treatment is 50Pa~150Pa; (3) The surface modification treatment time is 10 min to 30 min; (4) The non-polymerizable gas includes at least one of argon, nitrogen, and hydrogen; (5) The temperature of the plasma reaction is 50°C to 200°C; (6) The gas pressure range of the plasma reaction is 50Pa~150Pa; (7) The plasma reaction time is 20 min to 60 min; (8) The polymerizable gas includes at least one of styrene, cyclohexylamine, acrylamine, and methacrylate.

8. The preparation method according to claim 5, characterized in that The preparation method includes at least one of the following features (1) to (4): (1) The heat treatment temperature is 500°C to 700°C; (2) The heat treatment time is 1h~20h; (3) The heat treatment is carried out under a protective atmosphere; (4) The heat treatment is carried out under a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, helium, neon and argon.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 5 to 8; under a rolling pressure of 3 MPa, the plate rebound rate of the negative electrode plate is 2% to 10%.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 9.

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