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

Abstract

The invention relates to a negative electrode material and a preparation method thereof, a negative electrode plate and a lithium ion battery, the negative electrode material 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 is S m < 2 > / g, the particle size concentration ratio of the negative electrode material is P1, P1 is equal to (D80 + D50) / (D50 + D20), the physical rebound capacity of the negative electrode material is T, T is equal to 0.01 * O * S / P1, and T is greater than 0.20 and less than 1.20. The negative electrode material disclosed by the invention has relatively low physical rebound capability, and the volume of a pole piece prepared from the negative electrode material is not easy to rebound after compaction, so that relatively high compaction density can be obtained, and excellent cycle performance is exerted.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to negative electrode materials and preparation methods thereof, negative electrode plates, and lithium ion batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high cycle life, low environmental pollution and no memory effect, so they are widely used in electric vehicles and consumer electronic products. The negative electrode material is an important component of lithium-ion batteries, which directly affects key indicators such as battery energy density, cycle life and safety performance. At present, commercial lithium-ion batteries mainly use graphite negative electrode materials, but its theoretical specific capacity is only 372mAh / g, which is difficult to meet the needs of high energy density lithium-ion batteries. Silicon-based negative electrode materials have a high specific capacity as negative electrode materials for lithium-ion batteries and are 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, resulting in the degradation of the material / electrode structure and the instability of the solid electrolyte interface film (SEI), which leads to a sharp decline in its electrochemical performance.

[0003] At present, silicon-based materials and carbon materials are often compounded, but the existing compounding method is often a simple mixing, lacking a reasonable combination of silicon-based materials and carbon materials, and can no longer meet the market demand for negative electrode materials with high compaction density and good cycle performance. Therefore, it is necessary to explore the mechanism of action of multiple factors in coordination and develop composite negative electrode materials that meet market demand. Summary of the invention

[0004] The purpose of the present application is to provide a negative electrode material and a preparation method thereof, a negative electrode pole piece, and a lithium-ion battery. The negative electrode material of the present application has a low physical rebound ability, and the pole piece made therefrom is not easy to rebound in volume after compaction, thereby obtaining a higher compaction density and exerting excellent cycle performance.

[0005] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a silicon-based active substance and a carbon material, the oil absorption value of the negative electrode material is 0 mL / 100 g, 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.

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

[0007] In some embodiments, 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.

[0008] In some embodiments, 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.

[0009] In some embodiments, the silicon-based active material comprises silicon oxide, and the general formula of 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 includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes, and carbon fibers.

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

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

[0014] In some embodiments, the pH value of the negative electrode material is 6-12.

[0015] In some embodiments, the tap density of the negative electrode material is greater than 0.90 g / cm 3 .

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

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

[0018] In some embodiments, 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.

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

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

[0021] In some embodiments, the physical rebound capacity 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 a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0024] 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 );

[0025] 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;

[0026] 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 ​​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.

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

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

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

[0030] In some embodiments, 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.

[0031] In some embodiments, the silicon-based active material further includes a doped 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.

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

[0033] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes, and carbon fibers;

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

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

[0036] In some embodiments, the mixing method includes 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 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 ).

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

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

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

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

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

[0043] In some embodiments, the gas pressure of the plasma reaction ranges from 50Pa to 150Pa.

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

[0045] In some embodiments, the polymerizable gas includes at least one of styrene, cyclohexylamine, acrylamine, and methacrylate.

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

[0047] In some embodiments, the heat treatment time is 1 h to 20 h.

[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, wherein the protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0050] In a third aspect, the present application provides a negative electrode plate, which includes the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method of the negative electrode material described in the second aspect; under a rolling pressure of 3MPa, the plate rebound rate of the negative electrode plate is 2% to 10%.

[0051] In a fourth aspect, the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the negative electrode sheet described in the third aspect.

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

[0053] The negative electrode material provided in the present application comprises a silicon-based active substance and a carbon material, and the oil absorption value of the negative electrode material is 0 mL / 100 g and the specific surface area is S m 2 / g, particle size concentration 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 physical rebound capacity T of the negative electrode material can be used to measure the ability of the negative electrode material to physically rebound after rolling. In the present application, the balance between the oil absorption value, specific surface area and particle size concentration of the negative electrode material is controlled, so that the negative electrode material has a lower physical rebound capacity, and the silicon-based active material and the carbon material particles can be tightly combined, which is conducive to inhibiting the volume expansion of the silicon-based active material, so that the volume of the manufactured electrode is not easy to rebound after compaction, so as to obtain a higher compaction density, so that the negative electrode has both good cycle performance and rate performance.

[0054] The preparation method of the negative electrode material provided by the present application, firstly, by controlling the particle size concentration of the raw material, i.e., 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 evacuation, 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, the active groups on the surface of the composite particles can be combined 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, so that the oil absorption value and specific surface area of ​​the negative electrode material are reduced, and 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 is further described below in conjunction with the accompanying drawings and embodiments.

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

[0057] Figure 2 A comparison chart of cycle curves of 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 clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0062] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0063] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising 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.

[0064] The negative electrode material provided in the present application includes a silicon-based active material and a carbon material, and the oil absorption value of the negative electrode material is 0 mL / 100 g and the specific surface area is S m 2 / g, particle size concentration 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 physical rebound capacity T of the negative electrode material can be used to measure the ability of the negative electrode material to physically rebound after rolling. In the present application, the balance between the oil absorption value, specific surface area and particle size concentration of the negative electrode material is controlled, so that the negative electrode material has a lower physical rebound capacity, and the silicon-based active material and the carbon material particles can be tightly combined, which is conducive to inhibiting the volume expansion of the silicon-based active material, so that the volume of the manufactured electrode is not easy to rebound after compaction, so as to obtain a higher compaction density, so that the negative electrode has both good cycle performance and rate performance.

[0065] In some embodiments, the physical rebound capacity of the negative electrode material is T, 0.20<T<1.20, specifically 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, etc., of course, it can also be other values ​​within the above range, which are not limited here. It can be understood that after slurry adjustment, coating, and drying, the negative electrode material needs to be rolled under a certain pressure to increase the compaction density and finally obtain a usable negative electrode pole piece. The pole pieces made of different negative electrodes will physically rebound after being placed for a period of time after rolling, causing changes in the contact area of ​​the active material and the electrode porosity, showing different electrochemical properties. The physical rebound capacity T of the negative electrode material can be used to measure the ability of the pole piece made of the negative electrode material to physically rebound after rolling. The smaller the T value, the less likely the pole piece made of the negative electrode material will rebound during rolling, making the silicon-based active substance and the carbon material particles in the electrode more tightly combined, which is beneficial to suppressing the volume expansion of the negative electrode material during the charge and discharge process. When T ≥ 1.20, the pole piece made of the negative electrode material will rebound severely after rolling, making the combination between the silicon-based active substance and the carbon material particles loose and the contact area significantly reduced, which is not conducive to suppressing the volume expansion of the negative electrode material and the formation of a good conductive channel. When T ≤ 0.2, the pole piece made of the negative electrode material will rebound very little after rolling, and there is a lack of suitable pores between the silicon-based active substance and the carbon material particles in the electrode, which is not conducive to the infiltration and transmission of the electrolyte, resulting in the inability to fully exert the lithium storage capacity of the negative electrode material, reducing the cycle performance, and seriously degrading the rate performance.

[0066] In some embodiments, the physical rebound capacity 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 undergoes appropriate physical rebound after rolling, so that the silicon-based active material and the carbon material particles have good contact, and also have appropriate electrode porosity, so that the electrode sheet has both good cycle performance and rate performance.

[0067] In some embodiments, the physical rebound capacity of the negative electrode material is T, 0.2<T<0.7. When 0.2<T<0.7, the pole piece made of the negative electrode material undergoes a small physical rebound after rolling, so that the silicon-based active material and the carbon material particles are tightly combined, which can significantly inhibit the volume expansion of the negative electrode material, thereby having excellent cycle performance.

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

[0069] In some embodiments, 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.

[0070] In some embodiments, 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.

[0071] In some embodiments, the silicon-based active material comprises silicon oxide SiO x , 0<x<2. Specifically, SiO x Specifically, it can be SiO 0.2 、SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 Etc., no limitation is made here.

[0072] In some embodiments, the median particle size of the silicon-based active material is 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., and of course it can also be other values ​​within the above range, which is not limited here.

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

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

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

[0076] In some embodiments, the thickness of the carbon layer is 1nm to 1000nm, and can be specifically 1nm, 5nm, 10nm, 15nm, 20nm, 50nm, 80nm, 100nm, 150nm, 200nm, 400nm, 500nm, 700nm, 800nm, 900nm, 1000nm, etc., which are not limited here. If the carbon layer is too thick, the carbon content is too high, which is not conducive to obtaining a negative electrode material with a high specific capacity; if the carbon layer is too thin, it is not conducive to increasing the conductivity of the negative electrode material and has a weak performance in inhibiting the volume expansion of the material, resulting in poor long cycle performance. Preferably, the thickness of the carbon layer is 50nm to 800nm; more preferably, the thickness of the carbon layer is 100nm to 500nm.

[0077] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers. Amorphous carbon can be soft carbon and / or hard carbon, and graphite can be artificial graphite and / or natural graphite. It is understandable that the carbon material can improve the conductivity of the silicon-based active material. Graphite is a material with high conductivity, small volume expansion, high first efficiency and stable cycle performance. Preferably, the carbon material is graphite.

[0078] In some embodiments, the oil absorption value of the negative electrode material is O mL / 100g, O<57.0, O can specifically 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., which are not limited here. The oil absorption value is related to the liquid absorption capacity of the negative electrode material, which reflects the absorption capacity of the particle clusters to the binder during the slurry preparation process, and is one of the material properties that measure the physical rebound ability of the pole piece. When the oil absorption value of the negative electrode material is O<57.0mL / 100g, the particle clusters of the negative electrode material can absorb an appropriate amount of binder during the slurry adjustment process, which is beneficial to enhance the bonding between the silicon-based active material and the carbon material. The obtained pole piece undergoes a small physical rebound after rolling, and it is easy to obtain a pole piece with a high compaction density. When the oil absorption value O of the negative electrode material is ≥57.0mL / 100g, the binder content absorbed by the negative electrode material particle clusters during the slurry mixing process is too high, which is not only not conducive to effective contact and filling of the particles, but also the excess binder in the particle clusters has greater elasticity, making the manufactured electrode prone to severe physical rebound after rolling, ultimately resulting in poor cycle performance.

[0079] In some embodiments, the specific surface area of ​​the negative electrode material is S cm 2 / g, S<3.50, specifically can be 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., of course, it can also be other values ​​within the above range, which are not limited here. It can be understood that the specific surface area is closely related to the surface energy and is positively correlated. Negative electrode materials with higher specific surface area have larger surface energy, and the interaction force between their particles is also larger, which can easily hinder the sliding of particles and is not conducive to the dense accumulation of particles. It is also one of the material properties to measure the physical rebound ability of the electrode. When the S of the silicon-based composite material is less than 3.50cm 2 / g, it has a suitable surface energy, which is conducive to the dense accumulation of particles, so that the electrode sheet is not easy to rebound. 2 / g, which has a large surface energy, making it difficult for the particles to form dense packing, resulting in a large physical rebound of the manufactured pole piece.

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

[0081] In some embodiments, the tap density of the negative electrode material is greater than 0.90 g / cm 3 The tap density of the negative electrode material can be specifically 0.91 g / 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 1.4 g / cm 3 Etc., no limitation is made here.

[0082] In some embodiments, the mass content of water in the negative electrode material is ≤0.5wt%, specifically 0.5wt%, 0.35wt%, 0.25wt%, 0.10wt%, 0.09wt%, 0.08wt%, 0.05wt% or 0.01wt%, etc., and of course it can also be other values ​​within 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% to 25wt%, specifically 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%, etc., and of course, it can also be other values ​​within the above range, which are not limited here. When the mass content of Si element is lower than 0.5wt%, the specific capacity of the negative electrode material is low and cannot meet the needs of high energy density lithium ion batteries. 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 deteriorates seriously.

[0084] In some embodiments, 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. It should be noted that the volume-based cumulative particle size distribution of the particle size distribution measured by laser diffraction method, D 20 Indicates the particle size corresponding to when the cumulative particle size distribution percentage reaches 20%. 50 Indicates the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%. 80 It indicates the particle size corresponding to when the cumulative particle size distribution percentage reaches 80%.

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

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

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

[0088] In some embodiments, the particle size concentration of the negative electrode material is P1, 1.2<P1<2.0, P1=(D 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 affect the physical rebound ability of the negative electrode sheet. Among them, D 50 ~D 80 The range represents the majority of the larger particles in the negative electrode material; D 20 ~D 50 The range represents the majority of smaller particles in the material; therefore, P1 = (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 good, which is conducive to the full dispersion of particles, and tends to form small particles embedded in the contact gaps of large particles to form 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 substance 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 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.

[0093] The preparation method of the negative electrode material provided by the present application, firstly, by controlling the particle size concentration of the raw material, i.e., 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 evacuation, 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, the active groups on the surface of the composite particles can be combined 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, so that the oil absorption value and specific surface area of ​​the negative electrode material are reduced, and 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.

[0094] The following is a detailed introduction to this program:

[0095] Step S100, providing a composite material containing a silicon-based active substance 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 ).

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

[0097] In some embodiments, the mass ratio of silicon-based active substance to carbon material is (0.01-0.4):1, specifically 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. Of course, it can also be other values ​​within the above range, which is not limited here.

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

[0099] In some embodiments, 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.

[0100] In some embodiments, the silicon-based active material further comprises a doping metal M, wherein 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 of a simple substance, an oxide or a silicate. Preferably, M is in the form of a silicate (M x Si y O z ) in the form of dispersed in the silicon-based active material.

[0101] In some embodiments, the silicon-based active material comprises silicon oxide SiO x , 0<x<2. Specifically, SiO x Specifically, it can be SiO 0.2 、SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 Etc., no limitation is made here.

[0102] In some embodiments, the carbon material includes at least one of graphite, graphene, amorphous carbon, carbon nanotubes and carbon fibers. Amorphous carbon can be soft carbon and / or hard carbon, and graphite can be artificial graphite and / or natural graphite. It is understandable that the carbon material can improve the conductivity of the silicon-based active material. Graphite is a material with high conductivity, small volume expansion, high first efficiency and stable cycle performance. Preferably, the carbon material is graphite.

[0103] In some embodiments, the median particle size of the silicon-based active material is 1 μm to 10 μm, and may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc., which is not limited here.

[0104] In some embodiments, the median particle size of the carbon material is 2 μm to 20 μm. The median particle size of the carbon material can be 2 μm, 5 μm, 7 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm or 20 μm, etc., which is not limited here.

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

[0106] In some embodiments, 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 ). It can be understood that controlling the particle size concentration P0 of the composite within the above range can make the particle size and quantity of large particles and small particles in the negative electrode material match well, which is conducive to the full dispersion of particles and tends to form a close stacking 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 graded and adjusted by the airflow classifier, so that the particle size concentration P0 of the composite is controlled to meet the above range.

[0107] Step S200 , in a vacuum environment, non-polymerizable gas is introduced to perform surface modification treatment on the composite, and then polymerizable gas is introduced to perform plasma reaction to obtain a precursor.

[0108] In some embodiments, the temperature of the surface modification treatment is 50° C. to 200° C., specifically 50° C., 60° C., 70° C., 80° C., 100° C., 120° C., 150° C., 180° C. or 200° C. It is understood that the above temperature is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0109] In some embodiments, before surface modification treatment, the reaction system is first evacuated, and the pressure range of the surface modification treatment is 50Pa to 150Pa, specifically 50Pa, 60Pa, 70Pa, 80Pa, 90Pa, 100Pa, 120Pa or 150Pa, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

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

[0111] During the surface modification process, non-polymerizing gas is blown through the composite at 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, and imino groups under the attack of non-polymerizing gas.

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

[0113] It should be noted that surface modification of the composite under non-polymerizing gas will cause certain slight damage to the surface of the composite, that is, when 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 under polymerizing 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 time of surface modification treatment of the composite under non-polymerizing gas and the time of plasma reaction under polymerizing gas is conducive 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° C. to 200° C., specifically 50° C., 60° C., 70° C., 80° C., 100° C., 120° C., 150° C., 180° C. or 200° C. It is understood that the above temperature is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0115] In some embodiments, the gas pressure range of the plasma reaction is 50Pa to 150Pa, specifically 50Pa, 60Pa, 70Pa, 80Pa, 90Pa, 100Pa, 120Pa or 150Pa, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0116] In some embodiments, the polymerizable gas includes at least one of styrene, cyclohexylamine, vinyl chloride, acrylamine, and methacrylate. For example, the polymer modified layer may be polystyrene, polyacrylamine, polymethacrylate, polyvinyl chloride, etc., which are not limited here.

[0117] Step S300, heat-treating the precursor to obtain a negative electrode material, wherein the negative electrode material has an oil absorption value of 0 mL / 100 g and a specific surface area of ​​S m 2 / g, the particle size distribution concentration of the negative electrode material is P1, P1 = (D 80 +D 50 ) / (D50 +D 20 ), the physical rebound capacity of the negative electrode material is T, T = 0.01*O*S / P1, 0.20<T<1.20.

[0118] It can be understood that during the heat treatment process, the polymer modified layer undergoes structural cracking and reforming after carbonization, which effectively modifies the surface defects of the material. The surface defects of the negative electrode material are reduced, which reduces the oil absorption value and specific surface area of ​​the negative electrode material, so that the physical rebound ability of the final negative electrode material can be controlled within the range of 0.20 to 1.20, and the negative electrode material has both good cycle performance and excellent rate performance.

[0119] In some embodiments, the heat treatment temperature is 500°C to 700°C, specifically 500°C, 530°C, 550°C, 580°C, 600°C, 620°C, 650°C, 670°C, 680°C or 700°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0120] In some embodiments, the heat treatment time is 1 h to 20 h, specifically 1 h, 1.5 h, 3 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h or 20 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0121] In some embodiments, the heat treatment is performed under a protective atmosphere.

[0122] In some embodiments, the heat treatment is performed under a protective atmosphere, and the protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0123] In the third aspect, the present application provides a negative electrode plate, the negative electrode plate includes the above-mentioned negative electrode material, and the plate rebound rate of the negative electrode plate is 2% to 10% under a rolling pressure of 3MPa. The plate rebound rate can specifically be 2%, 2.5%, 3%, 3.8%, 5.6%, 6.7%, 7.8%, 8.9%, 9.6% or 10%, etc., which is not limited here. It can be understood that the plate rebound rate of the negative electrode plate is within the above range, and the plate undergoes appropriate physical rebound after rolling, so that the silicon-based active material and the carbon material have good contact, and also have appropriate electrode porosity, so that the plate has both good cycle performance and rate performance.

[0124] In a fourth aspect, the present application provides a lithium-ion battery, comprising the above-mentioned negative electrode plate.

[0125] Example

[0126] Example 1

[0127] (1) Weigh 30 g SiO(D50 =6μm), 970g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0129] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0130] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0132] Other parameters of the negative electrode materials are shown in Table 1.

[0133] Example 2

[0134] (1) Weigh 100g SiO(D 50 =6μm), 900g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0136] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0137] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0139] Other parameters of the negative electrode materials are shown in Table 1.

[0140] Example 3

[0141] (1) Weigh 300g SiO(D 50 =6μm), 700g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0143] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0144] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0146] Other parameters of the negative electrode materials are shown in Table 1.

[0147] Example 4

[0148] (1) Weigh 100 g of Mg-doped SiO (D 50 =6μm), 900g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0150] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0151] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

[0152] 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 Mg, wherein Mg is dispersed in the silicon-based active material in the form of magnesium silicate, and the carbon material is artificial graphite.

[0153] Other parameters of the negative electrode materials are shown in Table 1.

[0154] Example 5

[0155] (1) Weigh 100 g Li-doped SiO(D 50 =6μm), 900g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0157] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa to perform plasma reaction for 40 minutes to obtain a precursor.

[0158] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

[0159] 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 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 shown in Table 1.

[0161] Example 6

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

[0163] (2) The composite was placed in an air flow classifier for particle size adjustment, and the particle size concentration of the composite was controlled to be P0 = 1.73 ± 0.05, P0 = (D' 80 +D' 50 ) / (D' 50 +D' 20 ).

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

[0165] (4) The precursor is 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 substance and a carbon material, wherein the silicon-based active substance is SiO, and the carbon material is natural graphite.

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

[0168] Example 7

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

[0170] (2) The composite was placed in an air flow classifier for particle size adjustment, and the particle size concentration of the composite was controlled to be P0 = 1.34 ± 0.05, P0 = (D' 80 +D' 50 ) / (D'50 +D' 20 ).

[0171] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa for plasma reaction for 25 minutes to obtain a precursor.

[0172] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0174] Other parameters of the negative electrode materials are shown in Table 1.

[0175] Example 8

[0176] (1) Weigh 100g SiO(D 50 =6μm), 900g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

[0177] (2) Place the composite in an air flow classifier for particle size adjustment, and control the particle size concentration of the composite to be P0 = 1.45 ± 0.05, P0 = (D' 80 +D' 50 ) / (D' 50 +D' 20 ).

[0178] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa for plasma reaction for 25 minutes to obtain a precursor.

[0179] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0181] Other parameters of the negative electrode materials are shown in Table 1.

[0182] Example 9

[0183] (1) Weigh 300g SiO(D 50 =6μm), 700g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

[0184] (2) The composite was placed in an air flow classifier for particle size adjustment, and the particle size concentration of the composite was controlled to be P0 = 1.66 ± 0.05, P0 = (D' 80 +D' 50 ) / (D' 50 +D' 20 ).

[0185] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa for plasma reaction for 25 minutes to obtain a precursor.

[0186] (4) The precursor is heat treated in an argon atmosphere at a temperature of 500° C. for 10 hours to obtain a negative electrode material.

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

[0188] Other parameters of the negative electrode materials are shown in Table 1.

[0189] Example 10

[0190] The difference from Example 1 is:

[0191] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 30 minutes at a reaction temperature of 180°C; then introduce styrene and control the gas pressure to 100 Pa for plasma reaction for 40 minutes to obtain a precursor.

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

[0193] Other parameters of negative electrode materials are shown in Table 1.

[0194] Embodiment 11

[0195] The difference from Example 2 is:

[0196] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 30 minutes at a reaction temperature of 180°C; then introduce styrene and control the gas pressure to 100 Pa for plasma reaction for 40 minutes to obtain a precursor.

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

[0198] Other parameters of negative electrode materials are shown in Table 1.

[0199] Example 12

[0200] The difference from Example 1 is:

[0201] (1) Weigh 30 g Si(D 50 =6μm), 970g artificial graphite (D 50 =15 μm) were initially mixed and placed in a jet mill for collision, crushing and mixing to obtain a composite.

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

[0203] Other parameters of negative electrode materials are shown in Table 1.

[0204] Comparative Example 1

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

[0206] Other parameters of negative electrode materials are shown in Table 1.

[0207] Comparative Example 2

[0208] The difference from Example 8 is that:

[0209] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 40 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa for plasma reaction for 25 minutes to obtain a precursor.

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

[0211] Other parameters of negative electrode materials are shown in Table 1.

[0212] Comparative Example 3

[0213] The difference from Example 2 is:

[0214] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, and use argon gas to perform surface modification on the composite for 20 minutes at a reaction temperature of 180°C; then introduce acrylamine and control the gas pressure to 100 Pa for plasma reaction for 70 minutes to obtain a precursor.

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

[0216] Other parameters of negative electrode materials are shown in Table 1.

[0217] Comparative Example 4

[0218] The difference from Example 2 is:

[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 a jet mill for collision, crushing, and mixing to obtain an active material.

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

[0221] Other parameters of negative electrode materials are shown in Table 1.

[0222] Comparative Example 5

[0223] The difference from Example 2 is:

[0224] (3) Add the composite into a plasma device and evacuate the device; introduce acrylamine and control the gas pressure to 100 Pa to carry out plasma reaction for 40 minutes to obtain a precursor.

[0225] Other parameters of negative electrode materials are shown in Table 1.

[0226] Comparative Example 6

[0227] The difference from Example 2 is:

[0228] (3) Add the composite into a plasma device and evacuate the device; introduce argon gas and control the gas pressure to 100 Pa, use argon gas to perform surface modification treatment on the composite for 20 minutes, and the reaction temperature is 180° C. to obtain a precursor.

[0229] Other parameters of negative electrode materials are shown in Table 1.

[0230] Test Method

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

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

[0233] (2) Testing method for specific surface area of ​​negative electrode materials:

[0234] With reference to GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method", after measuring the adsorption amount of gas on the solid surface at different relative pressures at constant temperature and low temperature, the monolayer adsorption amount of the sample is obtained based on the Brownauer-Etter-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

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

[0236] Refer to GB / T 5162-2006 / ISO 3953:1993 "Determination of tap density of metal powders", and use the Quantachrome tap density analyzer (Quantachrome DAT-4-220) of Anton Paar (Shanghai) Trading Co., Ltd. for testing. The tap density T is the value after 3000 vibrations, and the unit is g / cm 3 .

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

[0238] Refer to Appendix C "Determination of pH Value" of GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", and use a pH meter (Mettler-Toledo FE20) for measurement.

[0239] (5) Testing method for oil absorption value of negative electrode material:

[0240] With reference to GB / T 3780.2-2017 "Carbon Black Part 2: Determination of Oil Absorption", the oil absorption value Q is tested using the ASAHI S-500 oil absorption value tester of ASAHISOUKEN of Japan. The oil absorption value Q is the amount of dibutyl phthalate added when the torque generated by the change in viscosity characteristics reaches 70% of the maximum torque, and the unit is mL / 100g.

[0241] (6) Test method for water mass content in negative electrode materials:

[0242] Refer to Appendix B "Determination of moisture content" of GB / T 24533-2019 "Graphite anode materials for lithium-ion batteries" or the equipment manual for measurement. Use Mettler DL39 Karl Fischer coulometric titrator for measurement.

[0243] (7) Electrochemical performance test

[0244] The negative electrode materials prepared in Examples 1 to 12 and Comparative Examples 1 to 3 were assembled into button batteries: the negative electrode materials: conductive agent (SuTer T): sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) were mixed uniformly in a mass ratio of 92:2:2:2, and then coated on a copper foil current collector, and dried to obtain a negative electrode sheet for use. The dried negative electrode sheet was rolled at a pressure of 3MPa, 6MPa, and 9MPa, respectively, and allowed to stand for 48 hours after rolling. The thickness change rate of the sheet before and after standing was measured, which was the physical rebound of the sheet (sheet rebound rate). The negative electrode plate was placed under a rolling pressure of 3MPa for rolling treatment. After standing still, the negative electrode plate was tested for button cells. The battery was assembled in an argon glove box. The metal lithium plate was used as the negative electrode, the electrolyte was 1mol / L lithium hexafluorophosphate LiPF6 + ethylene carbonate (EC) + methyl ethyl carbonate (EMC), the diaphragm was a polyethylene / propylene composite microporous membrane, and the electrochemical performance was carried out on a battery testing instrument. The charge and discharge voltage was 0.01~1.5V.

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

[0246] First coulombic efficiency = first cycle discharge capacity / first cycle charge capacity.

[0247] The test results are detailed in Table 2 and Table 3.

[0248] Table 1 Negative electrode material performance test results

[0249]

[0250]

[0251] Table 2 Negative electrode sheet rebound test results 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 to 3, controlling the balance between the oil absorption value, specific surface area and particle size concentration of the negative electrode material can control the physical rebound capacity T of the negative electrode material within the range of 0.2 to 1.2, and can make the silicon-based active material and the carbon material particles tightly combined, which is beneficial to inhibiting the volume expansion of the silicon-based active material, so that the volume of the manufactured electrode is not easy to rebound after compaction, and a higher compaction density can be obtained, so that the negative electrode has both good cycle performance and rate performance.

[0257] Table 2 shows the results of the pole piece rebound test of the negative electrode sheet made of the negative electrode material prepared in the present application under different rolling pressures. As shown in Table 2, the pole piece rebound rate of the negative electrode sheet made of the negative electrode material prepared in the embodiment of the present application under the rolling pressure of 3MPa, 6MPa and 9MPa is 2% to 10%, which can ensure that the silicon-based active material and the carbon material maintain good contact and can be closely combined. At the same time, it can also ensure that the negative electrode material layer on the negative electrode sheet has a suitable porosity, which is conducive to the electrolyte infiltration of the negative electrode material layer and improves the lithium ion transmission efficiency, so that the pole piece has both good cycle performance and rate performance. However, the applicant found that as the rolling pressure increases, the pole piece rebound rate of the negative electrode sheet after rolling also increases. It can be seen that when the rolling pressure is 3MPa, the pole piece rebound rate after the negative electrode sheet rolling treatment can be effectively reduced in a targeted manner, reducing the loose combination problem of the silicon-based active material and the carbon material caused by the excessively high pole piece rebound rate, and can further reduce the volume expansion and particle pulverization effect of the negative electrode sheet during the charge and discharge cycle.

[0258] The negative electrode material prepared in Comparative Example 1 is as follows Figure 2 and Figure 3 As shown, compared with Example 2 and Example 8, the negative electrode material is prepared by adjusting the particle size after mixing the silicon-based active material SiO with graphite by simple stirring and mixing. The oil absorption value of the prepared negative electrode material is too high, and the relationship between the oil absorption value, specific surface area and particle size concentration of the negative electrode material is unbalanced. The physical rebound ability of the negative electrode material is greater than 1.2. The negative electrode plate made of the negative electrode material undergoes severe physical rebound after rolling, which reduces the bonding ability between the silicon-based active material and the carbon material particles. The silicon-based active material has severe volume expansion during the cycle process, which leads to pulverization and breakage of the negative electrode material, rapid cycle attenuation of the battery, and a significant reduction in the cycle life of the plate.

[0259] For the negative electrode material prepared in Comparative Example 2, the time for the surface modification treatment of the composite in the non-polymerizing gas is too long during the preparation process, which causes a certain degree of damage to the surface of the composite, making the specific surface area of ​​the negative electrode material higher, and the relationship between the oil absorption value, specific surface area and particle size concentration in the negative electrode material is unbalanced, making the electrode sheet rebound ability of the negative electrode material greater than 1.2. The negative electrode electrode sheet made of the negative electrode material undergoes severe physical rebound after rolling, which loosens the bonding between the silicon-based active substance and the carbon material particles. The silicon-based active substance has a drastic volume expansion effect during the cycle process, resulting in pulverization and breakage of the negative electrode material during the cycle process, the cycle performance of the battery is reduced, and the cycle life of the electrode sheet is greatly reduced.

[0260] In the negative electrode material prepared in Comparative Example 3, the time for the composite to undergo plasma reaction in the polymerizing gas is too long during the preparation process, and the polymer modification layer deposited on the surface of the composite is relatively thick. After the composite is heat treated, the oil absorption value and specific surface area of ​​the negative electrode material are low, so that the physical rebound capacity T of the negative electrode material is less than 0.2. Therefore, the physical rebound of the negative 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 substance and the carbon material particles in the electrode, which is not conducive to the infiltration and transmission of the electrolyte, resulting in the inability to fully exert the lithium storage capacity of the negative electrode material, reducing the cycle performance, and at the same time deteriorating the rate performance of the negative electrode material.

[0261] In the negative electrode material prepared in Comparative Example 4, the content of silicon-based active substance SiO2 used in the preparation process is relatively high, the mass content of silicon element 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 during the cycle process, resulting in a decrease in the cycle performance and rate performance of the negative electrode material, and a significant decrease in the cycle life of the electrode piece.

[0262] In the negative electrode material prepared in Comparative Example 5, the composite is not surface-modified in a non-polymerizing gas during the preparation process. During the plasma reaction, it is difficult for the polymer gas to form a tightly bonded 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 a high oil absorption value, which makes the physical rebound capacity T of the negative electrode material too large. The negative electrode sheet made of the negative electrode material undergoes severe physical rebound after rolling, and the binding force between the silicon-based active substance and the carbon material particles decreases. The silicon-based active substance undergoes drastic volume expansion during the cycle process, the cycle performance of the negative electrode sheet deteriorates, and the cycle life is greatly reduced.

[0263] In the negative electrode material prepared in Comparative Example 6, the composite was not plasma treated in a polymerizing gas during the preparation process, the surface defects of the negative electrode material were not modified, the negative electrode material had many surface defects, and its oil absorption value and specific surface area were high, which made the negative electrode material have a high physical rebound ability. The negative electrode sheet made of the negative electrode material experienced severe physical rebound after rolling, the bonding ability between the silicon-based active substance and the carbon material was poor, and the silicon-based active substance underwent severe volume expansion during the cycle, resulting in pulverization and breakage of the negative electrode material during the cycle, severe deterioration of the cycle performance of the negative electrode sheet, and a significant reduction in the cycle life.

[0264] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises 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 Sm 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.

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, wherein 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, 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 of a simple substance, an oxide or a 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 features (1) to (7): (1) The oil absorption value of the negative electrode material is 0 mL / 100 g, O<57.0; (2) The specific surface area of ​​the negative electrode material is S cm 2 / g, S<3.50; (3) The pH value of the negative electrode material is 6 to 12; (4) The tap density of the negative electrode material is greater than 0.90 g / cm 3 ; (5) The mass content of water in the negative electrode material is ≤0.5wt%; (6) The mass content of silicon in the negative electrode material is 0.5wt% to 25wt%; (7) 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 (4): (1) In the negative electrode material, the silicon-based active material and the carbon material are dispersed 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; (4) The particle size concentration of the negative electrode material is P1, 1.2<P1<2.

0.

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 capacity of the negative electrode material is T, T = 0.01*O*S / P1, 0.20<T<1.

20.

6. The preparation method according to claim 5, characterized in that: The specific step of providing a composite containing a silicon-based active substance and a carbon material comprises: mixing the silicon-based active substance and the carbon material to obtain a composite, and the preparation method comprises 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, wherein 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 of a simple substance, an oxide or a 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 comprises 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 gas pressure range of the surface modification treatment is 50Pa to 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 to 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 comprises at least one of the following features (1) to (4): (1) The temperature of the heat treatment is 500° C. to 700° C.; (2) The heat treatment time is 1 h to 20 h; (3) The heat treatment is carried out under a protective atmosphere; (4) The heat treatment is performed 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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