Negative electrode material and battery

Abstract

A negative electrode material and a battery. The negative electrode material comprises secondary particles, wherein the secondary particles comprise silicon primary nanoparticles; each silicon primary nanoparticle comprises at least one silicon grain; the average particle size of the silicon grains is Ds nm; the average particle size of the silicon primary nanoparticles is Dn nm; and the crystalline state degree of the silicon primary nanoparticles is A, where A=Dn / Ds, and 1≤A≤200. By exploring the relationship between the size of the silicon primary nanoparticles and the size of the silicon grains, the problem of stress concentration caused by lithium intercalation and deintercalation of the silicon primary nanoparticles can be alleviated, thereby improving the structural stability of the negative electrode material and reducing the expansion rate of the negative electrode material; therefore, the electrochemical performance and cycle performance of the negative electrode material are improved.

Description

Anode materials and batteries

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on August 31, 2023, with application number 202311125354.4 and invention name “Negative electrode material, preparation method thereof, and battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and more specifically, to negative electrode materials and batteries. Background Art

[0003] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution.

[0004] To increase battery energy density, the research and development of silicon anode materials is becoming increasingly mature. However, the volume expansion of silicon anode materials during lithium insertion and removal is large (>300%). During the charge and discharge process, the silicon anode materials will pulverize and fall from the current collector, causing the active material to lose electrical contact with the current collector, resulting in poor electrochemical performance, capacity decay, and decreased cycle stability, making commercial application difficult. To improve the conductivity and cycle stability of silicon anode materials, carbon coating can be used. The existing carbon coating preparation method is complex, and simple carbon coating cannot effectively improve the electrochemical performance of silicon-carbon anodes.

[0005] Based on this, there is an urgent need to develop a silicon-carbon negative electrode material with long cycle and low expansion performance.

[0006] Application Contents

[0007] The present application proposes a negative electrode material and a battery, which enable the negative electrode material to have excellent cycle stability and good expansion performance.

[0008] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising secondary particles, the secondary particles comprising silicon nano primary particles;

[0009] The silicon nano primary particles include at least one silicon crystal grain, the average particle size of the silicon crystal grain is Ds nm, and the average particle size of the silicon nano primary particles is Dn nm;

[0010] The crystal attitude of the silicon nano primary particles is A, A=Dn / Ds, and 1≤A≤200.

[0011] The technical solution of this application has at least the following beneficial effects:

[0012] The negative electrode material provided by the present application, by exploring the relationship between the size of silicon nano primary particles and the size of silicon grains, controls the crystal attitude of silicon nano primary particles under the same silicon nano primary particle size, can better reduce the stress concentration problem generated by silicon nano primary particles during the lithium insertion and removal process, is conducive to uniform stress release, ensures the structural stability of silicon nano primary particles, and reduces particle pulverization. Under the same primary particle size, when the crystal attitude A of silicon nano primary particles is too large, it means that the size of silicon grains is too small. When the size of silicon grains is too small, the grain boundaries between silicon grains will gradually disappear during the lithiation process, and finally form large-sized grains, i.e. electrochemical sintering. After electrochemical sintering, the grain boundaries between silicon grains disappear, and silicon grains grow. After the negative electrode material is inserted with lithium, the local stress of silicon nano primary particles will increase, and the structural instability of the negative electrode material will increase, resulting in a decrease in the cycle performance and capacity of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG1 is a schematic structural diagram of the negative electrode material provided in this embodiment;

[0014] 2a and 2b are schematic structural diagrams of silicon nano primary particles in the negative electrode material provided in this embodiment;

[0015] 3a and 3b are schematic diagrams of another structure of silicon nano primary particles in the negative electrode material provided in this embodiment;

[0016] FIG4 is a schematic diagram of a method for preparing a negative electrode material provided in this embodiment;

[0017] FIG5 is a scanning electron microscope image of the negative electrode material provided in Example 1;

[0018] FIG6 is an XRD pattern of the negative electrode material provided in Example 1;

[0019] FIG7 is a cycle performance curve diagram of the negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0020] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0021] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0022] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0023] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0024] Currently, in lithium-ion batteries, the anode material is one of the key materials that influences their charge and discharge performance. To increase battery energy density, research and development of high-capacity anode materials is becoming increasingly mature. However, these anode materials experience significant volume expansion during alloying with lithium. During the charge and discharge process, the anode material pulverizes and falls off the current collector, resulting in a loss of electrical contact between the anode material and the current collector. This leads to poor electrochemical performance, capacity fade, and decreased cycle stability in batteries fabricated with these anode materials, making them difficult to commercialize.

[0025] Silicon materials undergo macroscopic structural changes during the lithium-ionization process. These changes are closely related to the silicon material's grain size, silicon particle size, and the size of the secondary particles it constructs. Currently, there is no optimal balance between the size ratios of silicon crystals, primary silicon particles, and secondary silicon particles. This leads to stress concentration in silicon-containing anode materials during the lithium-ionization process, which can easily cause anode material particle fracture and poor structural stability.

[0026] In a first aspect, the present application provides a negative electrode material. As shown in FIG1 , the negative electrode material includes secondary particles 12 , and the secondary particles 12 include silicon nano primary particles 11 .

[0027] As shown in FIG2a and FIG2b, the silicon nano primary particle 11 includes at least one silicon crystal grain 112. The average particle size of the silicon crystal grain 112 is Ds nm, and the average particle size of the silicon nano primary particle 11 is Dn nm. The crystal attitude of the silicon nano primary particle 11 is A, A=Dn / Ds, and 1≤A≤200.

[0028] In the above scheme, by exploring the relationship between the size of the silicon nano primary particles 11 and the size of the silicon crystal grains 12, under the same silicon nano primary particle size, controlling the crystal attitude A of the silicon nano primary particles 11 can better reduce the stress concentration problem generated by the silicon nano primary particles 11 during the lithium insertion and removal process, which is beneficial to the uniform stress release of the nano primary particles, ensuring the structural stability of the silicon nano primary particles 11, and reducing particle pulverization. Under the same silicon nano primary particle size, when the crystal attitude A of the silicon nano primary particles 11 is too large, it means that the size of the silicon crystal grains 12 is too small. If the size of the silicon crystal grains 12 is too small, the grain boundaries between the silicon crystal grains will gradually disappear during the lithiation process, and finally form large-sized grains, that is, electrochemical sintering. After electrochemical sintering, the grain boundaries between the silicon crystal grains disappear, the silicon grains grow, and the local stress of the silicon nano primary particles 11 will increase after the negative electrode material is inserted with lithium, and the structural instability of the negative electrode material will be enhanced, resulting in a decrease in the cycle performance and capacity of the negative electrode material. Current research has found that when the silicon grain size is less than 10nm, obvious electrochemical sintering will occur. The charging current must be controlled to reduce the degree of sintering, or the silicon grains or silicon particles must be isolated with carbon.

[0029] In some embodiments, the average particle size of the silicon nano primary particles 11 is Dn nm, 1≤Dn≤200; specifically, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 190 nm or 200 nm, etc., which is not limited here.

[0030] In some embodiments, the average particle size of the silicon grains 112 is Ds nm, 1≤Ds≤100, and can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., which is not limited here.

[0031] In some embodiments, the crystal state of the silicon nano primary particle 11 is A, A=Dn / Ds, and 1≤A≤200. The value range of A can be 1, 5, 10, 15, 20, 30, 40, 50, 80, 100, 120, 150, 180 or 200, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0032] In some embodiments, as shown in Figures 3a and 3b, the crystal attitude A of the silicon nano primary particles 11 is 1, and the silicon nano primary particles are single crystal silicon. The secondary particles 12 include a plurality of single crystal silicon primary particles 11a.

[0033] In some embodiments, the silicon nano primary particles have a crystalline attitude 1<A≤200, and the silicon nano primary particles include silicon grains, which include polycrystalline silicon.

[0034] In some embodiments, as shown in FIG1 , the negative electrode material includes secondary particles 12 , and the secondary particles 12 include silicon nano primary particles 11 ; the average particle size of the silicon nano primary particles 11 is Dn nm, and the average particle size of the secondary particles 12 is Dm nm; the stacking degree of the secondary particles 12 is B, B=Dm / Dn, and 5≤B≤400.

[0035] In the above scheme, by exploring the relationship between the sizes of secondary particles and silicon nano primary particles, under the same silicon primary particle size, reducing the value of the stacking degree B can reduce the expansion rate of the negative electrode material. This is because the compressive stress and tensile stress exerted on the secondary particles after lithiation are cumulative stresses. The lower the stacking degree, the fewer primary particles, and the lower the cumulative stress. Therefore, the smaller the expansion rate of the negative electrode material, which is conducive to the formation of a stable solid electrolyte film on the surface of the negative electrode material, thereby improving the rate performance and cycle stability of the negative electrode material.

[0036] In some embodiments, the average particle size of the secondary particles 12 is Dm nm, 500≤Dm≤25000; specifically, it can be 500nm, 1000nm, 1500nm, 2000nm, 3000nm, 5000nm, 8000nm, 10000nm, 15000nm, 20000nm, 23000nm or 25000nm, etc., which is not limited here.

[0037] In some embodiments, the stacking degree of the secondary particles 12 is B, B=Dm / Dn, and 5≤B≤400. The specific value of B can be 5, 10, 20, 50, 80, 100, 150, 200, 300, 350 or 400, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Controlling the stacking degree of the secondary particles 12 can ensure the structural stability of the secondary particles, which is conducive to the formation of a stable SEI film, reducing the expansion rate of the entire negative electrode material, and improving the first efficiency and cycle performance of the negative electrode material. When the stacking degree of the secondary particles 12 is too large, the size of the silicon nano primary particles 11 is too small under the same secondary particle size, which will lead to an increase in the specific surface area of ​​the secondary particles 12 and the specific surface area of ​​the negative electrode material. In the process of lithium insertion and extraction, side reactions increase, and the consumption of active lithium ions increases, resulting in a decrease in the first coulombic efficiency of the negative electrode material. When the stacking degree of the secondary particles 12 is too small, the silicon nano primary particles are larger at the same secondary particle size, and the expansion stress of the secondary particles 12 is more concentrated, which can easily lead to the secondary particles breaking and pulverizing, which is not conducive to improving the structural stability of the negative electrode material and reduces the cycle stability of the battery prepared with the negative electrode material.

[0038] In some embodiments, the negative electrode material further includes a conductive layer 111 located on at least a portion of the surface of the silicon nanoparticles 11. This conductive layer 111 comprises at least one of an amorphous carbon material, a graphitized carbon material, and a conductive ceramic material. This conductive layer 111 has a porous structure that facilitates the transport of lithium ions and electrons. Furthermore, by constructing this conductive layer 111 on the surface of the silicon nanoparticles, it can enhance the conductivity of the silicon nanoparticles 11 and effectively mitigate volume expansion.

[0039] In some embodiments, the conductive layer 111 includes a graphitized carbon material, which is graphene. The number of graphene layers is less than 20. The number of graphene layers can be 1 layer, 2 layers, 3 layers, 5 layers, 8 layers, 10 layers, 12 layers, 15 layers, 18 layers or 19 layers, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0040] In some embodiments, the thickness of the conductive layer is 1 nm to 200 nm, and can be specifically 1 nm, 10 nm, 20 nm, 40 nm, 50 nm, 80 nm, 100 nm, 150 nm, 180 nm or 200 nm, etc., which is not limited here.

[0041] In some embodiments, the conductive ceramic material includes at least one of a metal oxide, a transition metal nitride, and a sulfide.

[0042] In some embodiments, the metal oxide includes at least one of V2O5, TiO2, Nb2O5, CdO, CsO, MoO3, WO3, BaO, SnO2, Cr2O3, MnO, Ag2O, CoO, NiO, Cu2O, and SnO.

[0043] In some embodiments, the transition metal nitride includes at least one of VN, TiN, CoN, Fe3N, Co4N, and WN.

[0044] In some embodiments, the sulfide includes at least one of CdS, Ag2S, Sb2S3, TiS2, and Li2S.

[0045] In some embodiments, the negative electrode material further includes a coating layer 121 located on at least a portion of the surface of the secondary particles 12 , and the coating layer 121 includes at least one of an amorphous carbon material, a graphitized carbon material, and a polymer.

[0046] It can be understood that a coating layer is constructed on the surface of the secondary particles, and the coating layer can further alleviate the volume expansion of the negative electrode material; the negative electrode material is synergistically modified using a conductive layer and a coating layer, and the conductivity of the conductive layer 111 and the alleviation of the volume expansion of the silicon nano primary particles are utilized to ensure that the negative electrode material still has excellent electrical contact performance after lithium insertion. Combined with the outermost coating layer 121, the side reactions of the silicon nano primary particles and the electrolyte can be effectively avoided, while enhancing the structural stability of the negative electrode material.

[0047] In some embodiments, the coating layer 121 includes a polymer. For example, the polymer may be at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0048] In some embodiments, the mass content of the polymer in the negative electrode material is 1% to 20%, and specifically can be 1%, 3%, 4%, 5%, 6%, 7%, 10%, 12%, 15%, 18%, or 20%, etc., without limitation herein. The thickness of the coating layer 121 is 5 nm to 300 nm, and specifically can be 5 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm, etc., without limitation herein.

[0049] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene and tannic acid. The polymer is preferably at least one of polypyrrole, polythiophene, polyaniline, polyaniline and polyacetylene.

[0050] In some embodiments, the coating layer 121 includes a graphitized carbon material, and the thickness of the coating layer is 5 nm to 100 nm, specifically 5 nm, 10 nm, 30 nm, 50 nm, 70 nm, 80 nm, 90 nm, or 100 nm, etc., which is not limited here.

[0051] In some embodiments, the coating layer 121 includes an amorphous carbon material, and the thickness of the coating layer is 10nm to 500nm; specifically, it can be 10nm, 50nm, 80nm, 100nm, 150nm, 200nm, 250nm, 300nm, 450nm or 500nm, etc., which is not limited here.

[0052] In some embodiments, the carbon content of the negative electrode material is 5% to 80% by weight. Specifically, it can be 5%, 8%, 10%, 15%, 20%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, or 80%, etc., without limitation. It should be noted that the carbon in the negative electrode material is derived from a carbon material.

[0053] In some embodiments, the tap density of the negative electrode material is 0.3 g / cm 3 ~1.3g / cm 3 , specifically 0.3g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.3g / cm 3 etc. Preferably 0.5g / cm 3 ~0.8g / cm 3 .

[0054] In some embodiments, the powder compaction density of the negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 , for example 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 or 1.8g / cm 3 etc., preferably 1.45 g / cm 3 ~1.75g / cm 3 .

[0055] In some embodiments, the median particle size of the negative electrode material is 0.5 μm to 25 μm. Optionally, the median particle size of the negative electrode material can be 0.5 μm, 1 μm, 3 μm, 4 μm, 5 μm, 7 μm, 10 μm, 13 μm, 15 μm, 20 μm, or 25 μm, etc., without limitation herein. The median particle size of the negative electrode material is preferably 0.5 μm to 10 μm, more preferably 1 μm to 5 μm.

[0056] In some embodiments, the specific surface area ratio of the negative electrode material is 1m 2 / g~50m 2 / g. Optionally, the specific surface area ratio of the negative electrode material can be 1m 2 / g、5m 2 / g、8m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g or 50m 2 / g, etc., which are not limited here; it can be understood that the smaller the specific surface area, the better. Too large a specific surface area is likely to lead to the formation of SEI film, consume too much irreversible lithium salt, and reduce the initial efficiency of the battery. Taking into account the cost of the preparation process, the specific surface area is controlled at 2m 2 / g~15m 2 / g.

[0057] In some embodiments, the mass content of oxygen in the negative electrode material is less than 15%, and may be 5%, 6%, 8%, 10%, 12%, 13%, 14%, or 15%, etc., which is not limited here.

[0058] The present application also provides a method for preparing a negative electrode material, as shown in FIG4 , the method comprising the following steps:

[0059] S10, preparing silicon nano primary particles, the silicon nano primary particles comprising at least one silicon crystal grain; the average particle size of the silicon crystal grains is Ds nm, 1≤Ds≤100, the average particle size of the silicon nano primary particles is Dn nm, 1≤Dn≤200; the crystal attitude of the silicon nano primary particles is A, A=Dn / Ds, and 1≤A≤200;

[0060] S20, assembling silicon nano primary particles to form secondary particles to obtain a negative electrode material.

[0061] In this scheme, by exploring the relationship between the size of silicon nano primary particles and the size of silicon grains, as well as the balance between the size of secondary particles and silicon nano primary particles, the stress concentration generated during the lithiation of silicon nano primary particles can be weakened, the structural stability of silicon nano primary particles during the lithiation process can be improved, and the expansion rate of the negative electrode material can be reduced, which is conducive to the formation of a stable solid electrolyte film on the surface of the negative electrode material, so that the negative electrode material has low expansion, high cycle stability, high rate capability and high first coulombic efficiency.

[0062] The preparation method of the negative electrode material provided in this application can not only improve the electrochemical properties of the material, but also be suitable for large-scale production. The prepared negative electrode material can effectively improve the rate performance and cycle stability of lithium batteries.

[0063] The preparation method of the present application is described in detail below with reference to the examples:

[0064] Step S10, preparing silicon nano primary particles, the silicon nano primary particles including at least one silicon crystal grain; the average particle size of the silicon crystal grains is Ds nm, 1≤Ds≤100, the average particle size of the silicon nano primary particles is Dn nm, 1≤Dn≤200; the crystal attitude of the silicon nano primary particles is A, A=Dn / Ds, and 1≤A≤200.

[0065] In some embodiments, the average particle size of the silicon nano primary particles is Dn nm, 1≤Dn≤200; specifically, it can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 190 nm or 200 nm, etc., which is not limited here.

[0066] In some embodiments, the average particle size of the silicon grains is Ds nm, 1≤Ds≤100, and can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., which is not limited here.

[0067] In some embodiments, the crystal state of the silicon nano primary particles is A, A=Dn / Ds, and 1≤A≤200. The value range of A can be 1, 5, 10, 15, 20, 30, 40, 50, 80, 100, 120, 150, 180 or 200, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0068] In some embodiments, the step of preparing silicon nano primary particles includes performing vapor deposition using a silicon source gas to obtain silicon nano primary particles.

[0069] In some embodiments, the silicon source gas includes at least one of silane, disilane, trichlorosilane, dichlorosilane, and silicon tetrachloride.

[0070] In some embodiments, the vacuum pressure before vapor deposition is less than 1.0 Torr, and specifically can be 0.9 Torr, 0.8 Torr, 0.7 Torr, 0.6 Torr, 0.5 Torr, 0.4 Torr, 0.3 Torr, or 0.1 Torr, etc., which are not limited here. It is understandable that before performing chemical vapor deposition, the pressure in the furnace can be evacuated to a vacuum state, which is conducive to improving the purity of the silicon nano primary particles. Then, heat and introduce an appropriate amount of silicon source gas as the growth raw material of the silicon nano primary particles, and deposit for a period of time to obtain the silicon nano primary particles.

[0071] In some embodiments, the heating rate during vapor deposition is 1° C. / min to 20° C. / min, and may be 1° C. / min, 3° C. / min, 5° C. / min, 8° C. / min, 10° C. / min, 15° C. / min, or 20° C. / min, without limitation.

[0072] In some embodiments, the temperature during vapor deposition is 300°C to 1000°C, specifically 300°C, 400°C, 500°C, 600°C, 700°C, 800°C or 1000°C, etc., which is not limited here.

[0073] In some embodiments, the temperature of vapor deposition is 600°C to 1000°C, specifically 400°C, 500°C, 600°C, 700°C, 800°C or 1000°C.

[0074] In some embodiments, the flow rate of the silicon source gas is 0.05 L / min to 10 L / min, specifically 0.05 L / min, 0.1 L / min, 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 5 L / min, 7 L / min, 8 L / min or 10 L / min, which is not limited here.

[0075] In some embodiments, the ventilation time of the silicon source gas (ie, the time of vapor deposition) is 0.1 h to 10 h, specifically 0.1 h, 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h or 10 h, which is not limited here.

[0076] In some embodiments, the pressure during vapor deposition is 100 Torr to 500 Torr, and specifically can be 100 Torr, 150 Torr, 200 Torr, 250 Torr, 300 Torr, 350 Torr, 400 Torr, 450 Torr or 500 Torr, etc., which is not limited here.

[0077] In other embodiments, silicon nano primary particles may be prepared by plasma heating, and the size ratio (crystal attitude A) of the silicon nano primary particles to the silicon grains may be controlled within the above range.

[0078] Furthermore, before step S20, the method further includes forming a conductive layer on the surface of the silicon nano primary particles, wherein the conductive layer includes at least one of an amorphous carbon material, a graphitized carbon material, and a conductive ceramic material.

[0079] In some embodiments, the step of forming a conductive layer on the surface of the silicon nano primary particles includes: depositing a first gas-phase carbon source on the surface of the silicon nano primary particles by vapor deposition under a protective atmosphere to form the conductive layer.

[0080] In some embodiments, the concentration of the first gaseous carbon source is 0.1 L / min to 10 L / min, specifically 0.1 L / min, 1 L / min, 3 L / min, 5 L / min, 8 L / min or 10 L / min, which is not limited here.

[0081] In some embodiments, the holding time of vapor deposition is 1 h to 48 h, and specifically can be 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, 24 h or 48 h, which is not limited here.

[0082] In some embodiments, the temperature of vapor deposition is 200°C to 1050°C, specifically 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 950°C or 1050°C, which is not limited here.

[0083] In some embodiments, the heating rate of vapor deposition is 1°C / min to 30°C / min, specifically 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min or 30°C / min, which is not limited here.

[0084] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0085] In some embodiments, the volume ratio of the protective atmosphere to the first gaseous carbon source is 10:(0.5-10), specifically 10:0.5, 10:1, 10:2, 10:3, 10:4, 10:5, 10:7, 10:8, 10:9 or 10:10, which is not limited here.

[0086] In some embodiments, the first gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0087] In some embodiments, the step of forming a conductive layer on the surface of the silicon nano primary particles includes: introducing a conductive material at a predetermined pulse frequency to form the conductive layer by atomic layer deposition on the surface of the silicon nano primary particles. It is understood that forming a conductive layer on the surface of the silicon nano primary particles via atomic layer deposition can improve the conductivity of the silicon nano primary particles, thereby enhancing the conductivity and rate capability of the negative electrode material.

[0088] Specifically, silicon nano primary particles can be placed in an atomic layer deposition chamber, evacuated and replaced with inert gas, then heated, and one or more conductive materials are introduced at a certain pulse frequency for a certain period of time as raw materials for the conductive layer. By controlling the amount of conductive material, one or more conductive layers are deposited on the surface of the silicon nano primary particles.

[0089] In some embodiments, the temperature of atomic layer deposition is 200°C to 750°C, specifically 200°C, 300°C, 400°C, 450°C, 500°C, 550°C, 600°C or 750°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0090] In some embodiments, the time for atomic layer deposition is 1 hour to 48 hours, and specifically can be 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 12 hours, 18 hours, 24 hours or 48 hours, which is not limited here.

[0091] In some embodiments, the pulse frequency is 40 khz to 500 khz, specifically 40 khz, 60 khz, 80 khz, 100 khz, 150 khz, 200 khz, 250 khz, 300 khz, 400 khz or 500 khz, etc., which is not limited here.

[0092] In some embodiments, the pulse duration of the conductive material is 10ms to 800ms, and can be specifically 10ms, 50ms, 100ms, 200ms, 300ms, 400ms, 500ms, 600ms, 700ms or 800ms, etc., which is not limited here.

[0093] By controlling various parameters of atomic layer deposition, it is beneficial to form silicon nano primary particles with a ratio of silicon nano primary particle size to silicon grain size within an appropriate range, which is beneficial to alleviating the stress concentration problem of silicon nano primary particles.

[0094] In some embodiments, the conductive layer includes a conductive ceramic material, and the conductive ceramic material includes at least one of a metal oxide, a transition metal nitride, and a sulfide.

[0095] In some embodiments, the conductive material includes an organic oxygenate of a transition metal, and the organic oxygenate of the transition metal includes at least one of titanium tetramethoxide, vanadium acetate, tetrabutyl titanate, and niobium oxalate. A metal oxide can be formed on the surface of the silicon nano primary particles by atomic layer deposition, and the metal oxide includes at least one of V2O5, TiO2, Nb2O5, CdO, CsO, MoO3, WO3, BaO, SnO2, Cr2O3, MnO, Ag2O, CoO, NiO, Cu2O, and SnO.

[0096] In some embodiments, the conductive material includes a nitrogen-containing organic compound of a transition metal, and the nitrogen-containing organic compound of the transition metal includes at least one of ammonium metavanadate, ammonium titanate, ammonium cobaltate, ammonium trioxalatoferrate, tetraethylammonium tetrachlorocobaltate, and ammonium tungstate. A transition metal nitride can be formed on the surface of the silicon nanoparticles by atomic layer deposition, and the transition metal nitride includes at least one of VN, TiN, CoN, Fe3N, Co4N, and WN.

[0097] In some embodiments, the conductive material includes an organic transition metal compound and a sulfur-containing gas, wherein the sulfur-containing gas includes at least one of gaseous sulfur vapor, hydrogen sulfide, and sulfur dioxide. Sulfides can be formed on the surface of the silicon nanoparticles through an atomic layer deposition process. The sulfides include at least one of CdS, Ag2S, Sb2S3, TiS2, and Li2S.

[0098] Step S20: assemble the silicon nano primary particles into secondary particles to obtain a negative electrode material.

[0099] It should be noted that the silicon nano primary particles can be assembled into secondary particles by self-assembly, melt assembly, electrostatic adsorption, or spray granulation coating, etc., which is not limited here.

[0100] In some embodiments, the step of assembling silicon nano primary particles to form secondary particles includes: mixing a first solution containing silicon nano primary particles and anionic surfactant with a second solution containing silicon nano primary particles and cationic surfactant, and obtaining secondary particles after solid-liquid separation.

[0101] In some embodiments, the anionic surfactant includes at least one of cetyltrimethylammonium bromide, sodium cetyl sulfate, polyvinylpyrrolidone, and sodium polystyrene sulfonate.

[0102] In some embodiments, the cationic surfactant includes at least one of polydiallyldimethylammonium chloride, aminopropyltriethoxysilane, and a silane coupling agent.

[0103] In some embodiments, the mass ratio of the anionic surfactant to the silicon nano primary particles is (0.05-5):1, specifically 0.05:1, 0.08:1, 1:1, 1.5:1, 2:1, 3:1, 4:1 or 5:1, etc., which is not limited here.

[0104] In some embodiments, the mass ratio of cationic surfactant to silicon nano primary particles is (0.05-10):1, specifically 0.05:1, 0.08:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 8:1, 9:1 or 10:1, etc., which is not limited here.

[0105] In some embodiments, the first solution and / or the second solution includes a solvent, which may be a polar solvent. Specifically, the solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0106] In some embodiments, the mass ratio of the silicon nano primary particles in the first solution to the silicon nano primary particles in the second solution is 1:(0.5-1.5), specifically 1:0.5, 1:0.8, 1:0.9, 1:1, 1:1.2, 1:1.3 or 1:1.5, which is not limited here.

[0107] In some embodiments, the solid content in the first solution is 2% to 50%, specifically 2%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 30%, 40%, 45%, 49% or 50%, etc., which is not limited here.

[0108] In some embodiments, the solid content of the second solution is 0.5% to 25%, specifically 0.5%, 0.8%, 1%, 5%, 8%, 9%, 10%, 12%, 13%, 15%, 18%, 20%, 24% or 25%, etc., which is not limited here.

[0109] In some embodiments, the solid content of the mixed slurry is 5% to 60%, specifically 5%, 8%, 10%, 15%, 18%, 20%, 25%, 30%, 40%, 45%, 50%, 54%, 59% or 60%, etc., which is not limited here.

[0110] In some embodiments, the step of assembling silicon nano primary particles to form secondary particles includes: spraying and granulating a mixed slurry comprising silicon nano primary particles and an anionic surfactant or a cationic surfactant to obtain secondary particles.

[0111] It should be noted that the types and contents of the cationic surfactant and the anionic surfactant are as described above and will not be repeated here.

[0112] In some embodiments, the step of assembling silicon nano primary particles to form secondary particles further comprises: dispersing and centrifuging the mixed slurry, wherein the dispersion method comprises at least one of mechanical stirring and ultrasonic dispersion.

[0113] In some embodiments, the mixed slurry further includes a solvent, and the solvent is selected from at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0114] In some embodiments, the drying temperature of the spray granulation is 100°C to 200°C, specifically 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 180°C or 200°C, which is not limited here.

[0115] In some embodiments, the feed rate of spray granulation is 100 mL / min to 1000 mL / min, specifically 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 600 mL / min, 800 mL / min or 1000 mL / min, etc., which is not limited here.

[0116] In some embodiments, the secondary particles include silicon nano primary particles; the average particle size of the silicon nano primary particles is Dn nm, and the average particle size of the secondary particles is Dm nm; the packing degree of the secondary particles is B, B=Dm / Dn, and 5≤B≤400.

[0117] In the above scheme, by exploring the relationship between the sizes of secondary particles and silicon nano primary particles, under the same silicon primary particle size, reducing the value of the stacking degree B can reduce the expansion rate of the negative electrode material. This is because the compressive stress and tensile stress received by the secondary particles after lithiation are cumulative stresses. The lower the stacking degree, the fewer primary particles, and the lower the cumulative stress. Therefore, the smaller the expansion rate of the negative electrode material, which is conducive to the formation of a stable solid electrolyte film on the surface of the negative electrode material, thereby improving the rate performance and first coulombic efficiency of the negative electrode material.

[0118] In some embodiments, the average particle size of the secondary particles is Dm nm, 500≤Dm≤25000; specifically, it can be 500nm, 1000nm, 1500nm, 2000nm, 3000nm, 5000nm, 8000nm, 10000nm, 15000nm, 20000nm, 23000nm or 25000nm, etc., which is not limited here.

[0119] In some embodiments, the stacking degree of the secondary particles is B, B=Dm / Dn, and 5≤B≤400, and the specific value of B can be 5, 10, 20, 50, 80, 100, 150, 200, 300, 350 or 400, etc., and of course it can also be other values ​​within the above range, which is not limited here. Controlling the stacking degree of the secondary particles can ensure the structural stability of the secondary particles, which is conducive to the formation of a stable SEI film, reducing the expansion rate of the negative electrode material, and improving the first efficiency and cycle performance of the negative electrode material. When the stacking degree of the secondary particles is too large, under the same secondary particle size, the size of the silicon nano primary particles is too small, which will lead to an increase in the specific surface area of ​​the secondary particles and the specific surface area of ​​the negative electrode material. In the process of lithium insertion and extraction, the side reactions increase, and the consumption of active lithium ions increases, resulting in a decrease in the first coulombic efficiency of the negative electrode material. When the stacking degree of secondary particles is too small, the size of silicon nano primary particles is too large under the same secondary particle size, and the expansion stress of the secondary particles is more concentrated, which can easily lead to the secondary particles cracking and pulverization, which is not conducive to improving the structural stability of the negative electrode material and the cycle stability of the battery prepared with the negative electrode material decreases.

[0120] After step S20 , the method further includes: forming a coating layer on the surface of the secondary particles, wherein the coating layer includes at least one of an amorphous carbon material, a graphitized carbon material, and a polymer.

[0121] In some embodiments, the step of forming a coating layer on the surface of the secondary particles comprises: spray-drying a mixed coating liquid comprising the secondary particles and a polymer, so that a coating layer is formed on the surface of the secondary particles, wherein the coating layer comprises the polymer.

[0122] In some embodiments, the solid content of the secondary particles in the mixed coating liquid is 5% to 50%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., which is not limited here.

[0123] In some embodiments, the mixed coating fluid includes a polar solvent.

[0124] In some embodiments, the polar solvent includes at least one of water, anhydrous ethanol, methanol, and isopropanol.

[0125] In some embodiments, the mass ratio of the secondary particles to the polymer is 10:(0.1-5), specifically 10:0.1, 10:1, 10:2, 10:3, 10:4 or 10:5, which is not limited here.

[0126] In some embodiments, the drying temperature of spray drying is 60°C to 200°C, specifically 60°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C.

[0127] In some embodiments, the polymer comprises at least one of a diblock copolymer, a triblock copolymer, and a multiblock copolymer.

[0128] In some embodiments, the polymer includes at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid.

[0129] In some embodiments, the step of forming a coating layer on the surface of the secondary particles includes: introducing a second gas-phase carbon source into the secondary particles, heating the second gas-phase carbon source until a thermal cracking reaction occurs, so that the surface of the secondary particles is deposited to form a coating layer, and the coating layer includes at least one of an amorphous carbon material and a graphitized carbon material.

[0130] In some embodiments, the second gaseous carbon source includes at least one of acetylene, methane, toluene, cyclohexane, ethanol, ethylene, and propylene.

[0131] In some embodiments, the heating rate of the thermal cracking reaction is 1°C / min to 20°C / min, for example, 1°C / min, 3°C / min, 5°C / min, 8°C / min, 10°C / min, 15°C / min or 20°C / min, which is not limited here.

[0132] In some embodiments, the temperature of the thermal cracking reaction is 600°C to 1000°C. Specifically, the reaction temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 890°C, 900°C, 960°C, or 1000°C. The applicant has found through multiple experiments that controlling the reaction temperature within the range of 600°C to 1000°C can improve reaction efficiency and form a uniform carbon layer on the surface of the secondary particles. The carbon layer can be amorphous carbon. Preferably, the reaction temperature is 700°C to 900°C.

[0133] In some embodiments, the holding time of the thermal cracking reaction is 1 h to 48 h; specifically, it can be 1 h, 4 h, 8 h, 12 h, 16 h, 24 h, 28 h, 32 h, 38 h or 48 h, which is not limited here.

[0134] In some embodiments, the concentration of the second gaseous carbon source is 0.1 L / min to 10 L / min; specifically, it can be 0.1 L / min, 0.4 L / min, 0.6 L / min, 0.8 L / min, 1.0 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 9 L / min or 10 L / min, etc., which is not limited here.

[0135] In some embodiments, the thermal cracking reaction is carried out under a protective atmosphere.

[0136] In some embodiments, the protective atmosphere includes at least one of helium, neon, argon, krypton, and xenon.

[0137] The present application also provides a battery using the negative electrode material provided in the above embodiments of the present application or the negative electrode material prepared using the method for preparing the negative electrode material provided in the above embodiments of the present application. The battery provided in the embodiment of the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., without limitation herein.

[0138] The following further illustrates the embodiments of the present application in multiple embodiments. The embodiments of the present application are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0139] Example 1

[0140] (1) After the chemical vapor deposition furnace was pumped down to 0.5 Torr, it was heated to 600°C at a heating rate of 3°C / min, and silane gas was introduced at a rate of 0.5 L / min. The vapor deposition pressure of the entire deposition furnace was controlled at 300 Torr, and the deposition duration was 2 h. After cooling, silicon nanoparticles were collected.

[0141] (2) The silicon nano primary particles were placed in a rotary atmosphere furnace, and under the protection of an argon atmosphere, heated to 950°C at a heating rate of 3°C / min, and then 0.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 4 hours, the precursor was cooled to obtain the silicon nano primary particles and a carbon layer located on the surface thereof.

[0142] (3) Disperse 10g of the precursor and hexadecyltrimethylammonium bromide in 200ml of deionized water at a mass ratio of 10:2, stir for 30 minutes, ultrasonicate for 10 minutes, and centrifuge to obtain the modified precursor A1. Dissolve 10g of the precursor and 1g of polydiallyldimethylammonium chloride in 100ml of deionized water, stir for 30 minutes, ultrasonicate for 20 minutes, and centrifuge to obtain the modified precursor B2. Dissolve 10g of the modified precursor A1 in 100ml of deionized water and stir for 10 minutes to obtain solution E. Disperse 10g of the modified precursor B2 in 100ml of deionized water and stir for 10 minutes to obtain solution F. Slowly drip solution E into solution F, continue to stir rapidly for 40 minutes, and centrifuge to obtain the complex.

[0143] (4) 10 g of the composite was dissolved in 100 g of anhydrous ethanol, 1 g of polyacrylic acid was added, and mechanical stirring was performed for 30 minutes. The composite material was spray-dried at a temperature of 100°C to coat the surface with the polymer, thereby obtaining a negative electrode material.

[0144] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is a polymer layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is an amorphous carbon layer, and the silicon nano primary particles include multiple silicon grains.

[0145] Figure 5 is a scanning electron microscope image of the negative electrode material prepared in this embodiment 1; Figure 6 is an XRD diagram of the negative electrode material prepared in this embodiment 1; Figure 7 is a cycle performance curve of the negative electrode material prepared in this embodiment 1, with a charge and discharge current of 1000 mA / g.

[0146] It can be seen from the scanning electron microscope image in Figure 5 that the surface of the prepared negative electrode material has a spherical structure and is wrapped with a dense coating layer.

[0147] From the XRD pattern in Figure 6, it can be seen that the three strong peaks at 28.4°, 47.3° and 56.1° correspond to the three strong peaks of silicon (JCPDS No. 27-1402), and there is basically no impurity phase. According to the Scherrer formula, the silicon grain size is calculated to be 5 nm;

[0148] As shown in Figure 7, the material has excellent cycle performance. After 100 cycles at a current of 0.25C, it still has a capacity of 1255mAh / g and a capacity retention rate of 75%.

[0149] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0150] Example 2

[0151] (1) After the chemical vapor deposition furnace was pumped down to 0.5 Torr, it was heated to 700°C at a heating rate of 3°C / min, and silane gas was introduced at a flow rate of 1.5 L / min. The pressure of the entire deposition furnace was controlled at 200 Torr, and the deposition duration was 2 h. After cooling, silicon nanoparticles were collected.

[0152] (2) The silicon nano primary particles were placed in a rotary atmosphere furnace, and under the protection of an argon atmosphere, heated to 950°C at a heating rate of 3°C / min, and then 1.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the precursor was cooled to obtain the precursor, which included the silicon nano primary particles and a carbon layer located on the surface thereof.

[0153] (3) 10 g of the precursor was dissolved in 200 ml of anhydrous ethanol, 2 g of polyvinyl pyrrolidone was added, and the mixture was stirred for 30 minutes and then ultrasonicated for 10 minutes to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation under drying conditions at 130°C to obtain composite H.

[0154] (4) 100 g of the composite was placed in a rotary atmosphere furnace. Under argon atmosphere protection, the temperature was raised to 900 °C at a rate of 3 °C / min, and then 0.5 L / min of methane gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 6 h, the acetylene gas was turned off and the anode material was obtained by cooling.

[0155] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is an amorphous carbon layer, and the silicon nano primary particles include multiple silicon grains.

[0156] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0157] Example 3:

[0158] (1) After the chemical vapor deposition furnace was pumped down to 0.5 Torr, it was heated to 600°C at a heating rate of 3°C / min, and silane gas was introduced at a flow rate of 0.5 L / min. The pressure of the entire deposition furnace was controlled at 300 Torr for 2 h. After cooling, silicon nanoparticles were collected.

[0159] (2) 100 g of silicon nanoparticles were placed in an atomic layer deposition chamber. After evacuation to 0.5 mbar, the chamber was heated to 250°C. Then, a pulser was used to inject titanium tetramethoxide gas as a conductive material into the chamber at a frequency of 500 Hz, with a pulse time of 200 ms and a flow rate of 200 sccm. Finally, the titanium tetramethoxide gas was turned off, and the residual reaction gas in the chamber was replaced with argon. After cooling, a precursor was obtained, which included silicon nanoparticles and a titanium oxide layer on their surface.

[0160] (3) 10 g of the precursor was dissolved in 300 ml of anhydrous ethanol, 2 g of polyvinyl pyrrolidone was added, and the mixture was stirred for 30 min and then ultrasonicated for 10 min to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation (feed rate of 500 mL / min) under drying conditions of 150 °C to obtain a composite.

[0161] (4) 100 g of the composite was placed in a rotary atmosphere furnace and heated to 950 °C at a heating rate of 5 °C / min under argon atmosphere protection. Then, 2.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 8:2. After keeping the temperature for 6 h, the acetylene gas was turned off and cooled to obtain the negative electrode material.

[0162] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is a titanium oxide layer, and the silicon nano primary particles include multiple silicon grains.

[0163] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0164] Example 4

[0165] (1) A silicon substrate coated with a thin layer of metallic copper was placed in a chemical vapor deposition furnace chamber. After the chemical vapor deposition furnace was pumped to 0.5 Torr, it was heated to 1000°C at a heating rate of 20°C / min. Silane gas was introduced at a flow rate of 0.5 L / min. The pressure of the entire deposition furnace was controlled at 100 Torr for 2 hours. After cooling, silicon nanoparticles were collected.

[0166] (2) 100 g of silicon nanoparticles were placed in an atomic layer deposition chamber. After evacuation to 0.5 mbar, the chamber was heated to 250°C. Gaseous titanium tetramethoxide was then injected into the chamber as a conductive material using a pulser at a frequency of 500 Hz, with a pulse duration of 200 ms and a flow rate of 200 sccm. Finally, the titanium tetramethoxide gas was shut off, and the residual reaction gas in the chamber was replaced with argon. After cooling, a precursor was obtained, which included silicon nanoparticles and a titanium oxide layer on their surface.

[0167] (3) 10 g of the precursor was dissolved in 300 ml of anhydrous ethanol, 2 g of polyvinyl pyrrolidone was added, and the mixture was stirred for 30 min and then ultrasonicated for 10 min to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation (feed rate of 300 mL / min) under drying conditions of 150 °C to obtain a composite.

[0168] (4) 100 g of the composite was placed in a rotary atmosphere furnace and heated to 950 °C at a heating rate of 5 °C / min under argon atmosphere protection. Then, 2.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 8:2. After keeping the temperature for 6 h, the acetylene gas was turned off and cooled to obtain the negative electrode material.

[0169] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is a titanium oxide layer, and the silicon nano primary particles are single crystal silicon particles.

[0170] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0171] Example 5

[0172] (1) A silicon substrate coated with a thin layer of metallic copper was placed in a chemical vapor deposition furnace chamber. After the chemical vapor deposition furnace was pumped to 0.5 Torr, it was heated to 1000°C at a heating rate of 20°C / min. Silane gas was introduced at a flow rate of 0.5 L / min. The pressure of the entire deposition furnace was controlled at 100 Torr for 2 hours. After cooling, silicon nanoparticles were collected.

[0173] (2) 100 g of silicon nano primary particles were placed in a rotary atmosphere furnace and heated to 1050 ° C at a heating rate of 3 ° C / min under the protection of argon atmosphere. Then, 0.5 L / min of methane gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 9:1. After keeping the temperature for 3 hours, the precursor was cooled to obtain the precursor, which included silicon nano primary particles and a graphitized carbon layer on the surface.

[0174] (3) 10 g of the precursor was dissolved in 300 ml of anhydrous ethanol, 2 g of polyvinyl pyrrolidone was added, and the mixture was stirred for 30 min and then ultrasonicated for 10 min to obtain a mixed slurry. The mixed slurry was sphericalized by spray granulation (feed rate of 800 mL / min) under drying conditions of 150 °C to obtain a composite.

[0175] (4) 100 g of the composite was placed in a rotary atmosphere furnace and heated to 950 °C at a heating rate of 5 °C / min under argon atmosphere protection. Then, 2.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 8:2. After keeping the temperature for 6 h, the acetylene gas was turned off and cooled to obtain the negative electrode material.

[0176] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is a graphitized carbon layer, and the silicon nano primary particles are single crystal silicon particles.

[0177] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0178] Example 6

[0179] The difference from Example 3 is that:

[0180] (2) 100g of silicon nanoparticles were placed in an atomic layer deposition (ALD) processing chamber. After evacuation to 0.5mbar, the chamber was heated to 250°C. Ammonium metavanadate was then injected into the chamber as a conductive material using a pulser at a frequency of 500kHz, with a pulse duration of 200ms and an ammonium metavanadate flow rate of 200sccm. Finally, the ammonium metavanadate was turned off, and the residual reaction gas in the chamber was replaced with argon. After cooling, a precursor was obtained, which included silicon nanoparticles and a vanadium nitride (VN) layer on their surface.

[0181] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0182] Example 7

[0183] The difference from Example 3 is that:

[0184] (2) 100 g of silicon nanoparticles were placed in a processing chamber of an atomic layer deposition apparatus. After evacuation to 0.5 mbar, the chamber was heated to 250°C. Then, gaseous titanium tetramethoxide and gaseous sulfur vapor were injected into the processing chamber as conductive materials at a frequency of 500 Hz using a pulser. The pulse time was 220 ms, the flow rate of the gaseous titanium tetramethoxide was 200 sccm, and the flow rate of the gaseous sulfur vapor was 100 sccm. Finally, the gaseous titanium tetramethoxide and gaseous sulfur vapor were turned off, and the residual reaction gas in the chamber was replaced with argon. After cooling, a precursor was obtained, which included silicon nanoparticles and a Li2S layer on their surface.

[0185] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0186] Example 8

[0187] The difference from Example 3 is that:

[0188] (2) The silicon nano primary particles were placed in a rotary atmosphere furnace, and under the protection of an argon atmosphere, heated to 1050°C at a heating rate of 3°C / min, and then 0.1 L / min of methane gas was introduced so that the volume ratio of argon to methane in the rotary atmosphere furnace was 9:1. After keeping the temperature for 2 hours, the precursor was cooled to obtain a precursor, which included silicon nano primary particles and a graphene carbon layer located on the surface thereof, and the number of graphene layers was 5.

[0189] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0190] Example 9

[0191] The difference from Example 3 is that:

[0192] (4) 100 g of the composite was placed in a rotary atmosphere furnace and heated to 1050 °C at a heating rate of 10 °C / min under argon atmosphere protection. Then, 2.5 L / min of acetylene gas was introduced so that the volume ratio of argon to acetylene in the rotary atmosphere furnace was 8:2. After keeping the temperature for 6 h, the acetylene gas was turned off and cooled to obtain a negative electrode material, wherein the coating layer included graphitized carbon and amorphous carbon.

[0193] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0194] Example 10

[0195] (1) After the chemical vapor deposition furnace was pumped down to 0.5 Torr, it was heated to 600°C at a heating rate of 3°C / min, and silane gas was introduced at a rate of 0.5 L / min. The vapor deposition pressure of the entire deposition furnace was controlled at 300 Torr, and the deposition duration was 2 h. After cooling, silicon nanoparticles were collected.

[0196] (2) Disperse 10g of silicon nano primary particles and hexadecyltrimethylammonium bromide in 200ml of deionized water in a mass ratio of 10:2, stir for 30 minutes, ultrasonicate for 10 minutes, and centrifuge to obtain modified silicon nano primary particles A1. Dissolve 10g of silicon nano primary particles and 1g of polydiallyldimethylammonium chloride in 100ml of deionized water, stir for 30 minutes, ultrasonicate for 20 minutes, and centrifuge to obtain modified silicon nano primary particles B2. Dissolve 10g of modified silicon nano primary particles A1 in 100ml of deionized water and stir for 10 minutes to obtain solution E. Disperse 10g of modified silicon nano primary particles B2 in 100ml of deionized water and stir for 10 minutes to obtain solution F. Slowly drip solution E into solution F, continue rapid stirring for 40 minutes, and centrifuge to obtain secondary particles, i.e., obtain the negative electrode material.

[0197] The negative electrode material prepared in this embodiment includes secondary particles, wherein the secondary particles include silicon nano primary particles, and the silicon nano primary particles include a plurality of silicon crystal grains.

[0198] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0199] Example 11

[0200] The difference from Example 3 is that:

[0201] (1) After the chemical vapor deposition furnace is pumped down to 0.5 Torr, it is heated to 500°C at a heating rate of 3°C / min, and silane gas is introduced at a rate of 0.5 L / min. The pressure of the entire deposition furnace is controlled at 500 Torr for 2 hours. After cooling, silicon nanoparticles are collected.

[0202] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is a titanium oxide layer, and the silicon nano primary particles include multiple silicon grains.

[0203] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0204] Example 12

[0205] The difference from Example 3 is that:

[0206] (1) After the chemical vapor deposition furnace was pumped down to 0.5 Torr, it was heated to 500°C at a heating rate of 3°C / min, and silane gas was introduced at a flow rate of 3.5 L / min. The pressure of the entire deposition furnace was controlled at 100 Torr for 5 hours. After cooling, silicon nanoparticles were collected.

[0207] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least part of the surface of the secondary particles, and the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles and a conductive layer located on at least part of the surface of the silicon nano primary particles, and the conductive layer is a titanium oxide layer, and the silicon nano primary particles include multiple silicon grains.

[0208] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0209] Example 13

[0210] (1) 100 g of silica with an average particle size of 8 μm was mixed with 100 g of magnesium powder, and then the silica was reduced by magnesium thermal reduction. The mixture was placed in an atmosphere furnace filled with a protective atmosphere and heated to 650 °C at a heating rate of 3 °C / min. The mixture was kept at this temperature for 3 h and then cooled to room temperature to obtain micron silicon secondary particles composed of nano-silicon.

[0211] (2) The reaction product was dissolved in 1 mol / L dilute hydrochloric acid solution and stirred for 3 h, then filtered and dried to obtain micron silicon secondary particles.

[0212] (3) Take 100 g of acid-washed micron silicon secondary particles and put them into a rotary atmosphere furnace. Under the protection of argon atmosphere, heat them to 950 °C at a heating rate of 5 °C / min, and then introduce 2.5 L / min of acetylene gas so that the volume ratio of argon to acetylene in the rotary atmosphere furnace is 8:2. After keeping the temperature for 6 hours, turn off the acetylene gas and cool it to obtain the negative electrode material.

[0213] The negative electrode material prepared in this embodiment includes secondary particles and a coating layer located on at least a portion of the surface of the secondary particles, wherein the coating layer is an amorphous carbon layer; the secondary particles include silicon nano primary particles.

[0214] The parameters of the negative electrode material in this embodiment are detailed in Table 1.

[0215] Performance Testing

[0216] 1) Test method for specific surface area of ​​negative electrode material:

[0217] The equipment used is the TriStar3000&3020 fully automatic specific surface and pore size analyzer from Micromeritics Inc. of the United States, which complies with the national standard GB / T 19587-2017. At constant temperature and low temperature, the adsorption amount of gas on the solid surface at different relative pressures is measured, and the monolayer adsorption amount of the sample is obtained based on the Brownauer-Ettel-Taylor adsorption theory and its formula (BET formula), thereby calculating the specific surface area of ​​the material.

[0218] 2) Test method for tap density:

[0219] The tap density of the powder was tested using a DAT-6-220 powder tap density instrument from Quantachrome Inc. (USA). According to the national standard GB / T 5162-2006 / ISO 3953:1993, a certain amount of sample was weighed and vibrated 3000 times at 300 times / min to test the tap density.

[0220] 3) Test methods for oxygen content and carbon content:

[0221] The oxygen content was measured using a Nicolet Is10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, USA, and the carbon layer content was tested using thermogravimetric analysis.

[0222] 4) SEM test:

[0223] Scanning electron microscopy characterization was performed on a Hitachi S4800 field emission electron microscope with an operating voltage of 200 kV to observe the structure of the negative electrode material and to scale the thickness of the coating layer.

[0224] 5) Test method for average size of primary and secondary particles:

[0225] The average particle size was measured using an E3500 ion mill and an S4800 field emission electron microscope from Hitachi, Japan.

[0226] 6) Test method for average silicon grain size:

[0227] The XRD patterns of the samples were measured by a TD-3600 X-ray diffractometer from Tongda Company in Dandong, China. The half-maximum width of the diffraction peaks and the corresponding Bragg angles were obtained using jade software. The average grain size of nano-silicon was calculated using the Scherrer formula D = Kγ / Bcosθ.

[0228] 7) Test method for thickness of conductive layer and coating layer:

[0229] The material was sectioned using an E3500 ion mill and an S4800 field emission electron microscope from Hitachi, Japan, and the thickness of the particle modification layer and the protective layer were measured using SEM.

[0230] 8) Test method for particle size of negative electrode material:

[0231] The D50 was measured using a laser particle size analyzer and showed a symmetrical distribution similar to a normal distribution. In the volume-based distribution, the cumulative 50% diameter is D50, and so on, the cumulative 90% diameter is D90, and the cumulative 10% diameter is D10.

[0232] After the above tests, the negative electrode materials prepared in Examples 1 to 13 have sample numbers S1 to S13. The performance parameters of the negative electrode materials are shown in Table 1:

[0233] Table 1

[0234] 10) Electrochemical testing:

[0235] The negative electrode material was mixed with sodium carboxymethyl cellulose, styrene-butadiene rubber, conductive graphite (KS-6) and carbon black (SP) in a ratio of 92:2:2:2:2 to prepare a slurry, uniformly coated on copper foil and dried to form a negative electrode sheet, which was assembled into a button battery in an argon atmosphere glove box. The separator used was a polypropylene microporous membrane, the electrolyte used was 1 mol / L lithium hexafluorophosphate (the solvent was a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate), and the counter electrode used was a metal lithium sheet.

[0236] The above 13 battery groups were subjected to a discharge specific capacity test on a Blue Power CT2001A battery test system. The ratio of the discharge quantity in one hour to the battery capacity is the discharge specific capacity.

[0237] The above 13 groups of batteries were tested for their initial coulombic efficiency on a Blue Power CT2001A battery testing system with a charge and discharge current of 0.05C, and the initial coulombic efficiency was measured.

[0238] The above 13 groups of batteries were cycled for 100 cycles on a Blue Power CT2001A battery testing system with a charge and discharge current of 0.2C. After 100 cycles, the post-cycle battery capacity and post-cycle capacity retention rate were calculated.

[0239] The capacity retention rate after 100 cycles at 0.2C = discharge capacity at the 100th cycle / discharge capacity at the first cycle * 100%. The results are shown in Table 2.

[0240] Table 2 Parameter performance comparison of each battery

[0241] As shown in Table 2, the negative electrode materials prepared in Examples 1 to 9 can reduce the stress concentration generated during the lithiation process of the silicon nano primary particles and improve the structural stability of the silicon nano primary particles by controlling the size relationship between the silicon nano primary particles and the silicon grains. Controlling the size relationship between the secondary particles and the silicon nano primary particles can improve the structural stability of the negative electrode material during the lithiation process, reduce the expansion rate of the material, and facilitate the formation of a stable solid electrolyte film on the surface of the negative electrode material. By constructing a conductive layer on the surface of the silicon nano primary particles and constructing a coating layer on the surface of the secondary particles, the negative electrode material is synergistically modified using the conductive layer and the coating layer, and the conductivity of the conductive layer and the mitigation effect on the volume expansion of the silicon nano primary particles are utilized to ensure that the negative electrode material still has excellent electrical contact performance after lithium insertion. The outermost coating layer can effectively reduce the side reactions between the silicon nano primary particles and the electrolyte, while enhancing the structural stability of the negative electrode material, so that the battery prepared from the negative electrode material has low expansion, high cycle stability, high rate capability and first coulombic efficiency.

[0242] In Example 10, since there is no conductive layer on the surface of the primary particles of the negative electrode material and no coating layer on the surface of the secondary particles, although the first coulombic efficiency of the negative electrode material is comparable to that of Example 1, its cycle capacity retention rate and capacity after 200 cycles are lower than those of Example 1. This is because the lack of protection of the coating layer increases the side reactions between the electrolyte and the negative electrode material, intensifies the volume expansion of the negative electrode material, and significantly reduces the electrochemical performance.

[0243] During the preparation process of the negative electrode material of Example 11, the stacking degree B of the secondary particles is too large, indicating that the size of the silicon nano primary particles is relatively small, which will lead to an increase in the specific surface area of ​​the secondary particles and the specific surface area of ​​the negative electrode material. During the process of lithium insertion and removal from the negative electrode material, the side reactions between the negative electrode material and the electrolyte increase, and the consumption of active lithium ions increases, resulting in a decrease in the first coulombic efficiency of the battery prepared with the negative electrode material.

[0244] During the preparation process of the negative electrode material of Example 12, the crystal attitude A of the silicon nano primary particles is too large, indicating that the size of the silicon grains is too small, and electrochemical sintering is easily caused on the surface of the silicon nano primary particles. After sintering, the silicon grains grow, and the local stress of the silicon nano primary particles becomes larger after the negative electrode material is embedded with lithium. The instability of the entire structure is enhanced, resulting in a decrease in the cycle performance and capacity of the negative electrode material, and a deterioration in the electrochemical performance of the negative electrode material.

[0245] During the preparation process of the negative electrode material of Example 13, the stacking degree B of the secondary particles is too small, the size of the silicon nano primary particles is too large, and the expansion stress of the secondary particles is more concentrated, which easily leads to the cracking and pulverization of the secondary particles, which is not conducive to improving the structural stability of the negative electrode material, and reduces the cycle stability of the battery prepared with the negative electrode material.

[0246] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed process equipment and process flow of the present application, the present application is not limited to the above-mentioned detailed process equipment and process flow, which does not mean that the present application must rely on the above-mentioned detailed process equipment and process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A negative electrode material, characterized in that: comprising secondary particles, wherein the secondary particles include silicon nano primary particles; The silicon nano primary particles include at least one silicon crystal grain, the average particle size of the silicon crystal grain is Ds nm, and the average particle size of the silicon nano primary particles is Dn nm; The crystal attitude of the silicon nano primary particles is A, A=Dn / Ds, and 1≤A≤200.

2. The negative electrode material according to claim 1, characterized in that The crystal attitude A of the silicon nano primary particle is 1, and the silicon nano primary particle is single crystal silicon.

3. The negative electrode material according to claim 1, characterized in that The crystal attitude of the silicon nano primary particles is 1<A≤200, and the silicon nano primary particles include polycrystalline silicon.

4. The negative electrode material according to claim 1, characterized in that Contains at least one of the following characteristics: (1) The average particle size of the silicon grains is Ds nm, 1≤Ds≤100; (2) The average particle size of the silicon nano primary particles is Dn nm, 1≤Dn≤200.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that: The average particle size of the secondary particles is Dm nm; the stacking degree of the secondary particles is B, B=Dm / Dn, and 5≤B≤400.

6. The negative electrode material according to claim 5, characterized in that The average particle size of the secondary particles is Dm nm, 500≤Dm≤25000.

7. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a conductive layer located on at least a portion of the surface of the silicon nano primary particles.

8. The negative electrode material according to claim 7, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The conductive layer comprises at least one of an amorphous carbon material, a graphitized carbon material and a conductive ceramic material; (2) The conductive layer comprises a graphitized carbon material, wherein the graphitized carbon material is graphene, and the number of graphene layers is less than 20; (3) The thickness of the conductive layer is 1 nm to 200 nm; (4) The conductive layer comprises a conductive ceramic material, and the conductive ceramic material comprises at least one of a metal oxide, a transition metal nitride, and a sulfide; (5) the conductive layer comprises a conductive ceramic material, the conductive ceramic material comprises a metal oxide, and the metal oxide comprises at least one of V2O5, TiO2, Nb2O5, CdO, CsO, MoO3, WO3, BaO, SnO2, Cr2O3, MnO, Ag2O, CoO, NiO, Cu2O and SnO; (6) The conductive layer includes a conductive ceramic material, the conductive ceramic material includes a transition metal nitride, and the transition metal nitride includes at least one of VN, TiN, CoN, Fe3N, Co4N and WN.

9. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a coating layer located on at least a portion of the surface of the secondary particles, wherein the coating layer includes at least one of an amorphous carbon material, a graphitized carbon material, and a polymer; and the negative electrode material satisfies at least one of the following characteristics: (1) The mass content of carbon in the negative electrode material is 5% to 80%; (2) The coating layer comprises a polymer, and the polymer comprises at least one of polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polydopamine, xanthan gum, polypyrrole, polythiophene, polyphenylene vinylene, polyaniline, polyacetylene, and tannic acid; (3) The coating layer comprises a polymer, and the mass content of the polymer in the negative electrode material is 1% to 20%; (4) The coating layer comprises a graphitized carbon material, and the thickness of the coating layer is 5 nm to 100 nm; (5) The coating layer comprises an amorphous carbon material, and the thickness of the coating layer is 10 nm to 500 nm; (6) The coating layer comprises a polymer, and the thickness of the coating layer is 5 nm to 300 nm.

10. The negative electrode material according to claim 1, characterized in that The tap density of the negative electrode material is 0.3 g / cm 3 ~1.3g / cm 3 .

11. The negative electrode material according to claim 1, characterized in that The powder compaction density of the negative electrode material is 1.2 g / cm 3 ~1.8g / cm 3 .

12. The negative electrode material according to claim 1, characterized in that The median particle size of the negative electrode material is 0.5 μm to 25 μm.

13. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is 1.0 m 2 / g~50m 2 / g.

14. The negative electrode material according to claim 1, characterized in that The mass content of oxygen in the negative electrode material is less than 15%.

15. A battery, characterized in that: The negative electrode material comprises the negative electrode material as claimed in any one of claims 1 to 14.

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