Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material comprises an active material, the active material comprising a first matrix and a second matrix. The negative electrode material has pores, wherein the volume of the pores of the negative electrode material is M cm3 / g, the volume of the pores of the negative electrode material measured after being maintained for 1 h under a pressure of 80 Mpa is N cm3 / g, and the particle space collapse ratio of the negative electrode material is P, P＝(M-N) / M, wherein 0.002≤M≤0.12, and 0.05≤P≤0.85. In the present application, the rigidity of the negative electrode material is adjusted by means of controlling the pore volume of the negative electrode material before and after pressurization, thereby improving the electrochemical performance of the negative electrode material while ensuring the structural stability of the negative electrode material.

Description

Negative electrode material and battery

[0001] The present application claims priority to the Chinese patent application No. 202411131888.2, filed on August 19, 2024, entitled "Negative electrode material and battery", and the Chinese patent application No. 202411693736.1, filed on August 19, 2024, entitled "Negative electrode material and battery", the contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of battery materials, in particular to a negative electrode material and a battery using the same. BACKGROUND

[0003] Lithium ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, excellent output power, long cycle life, and low pollution to the environment. In order to further improve the energy density of the battery, the research and development of silicon negative electrode materials become particularly important.

[0004] However, the silicon negative electrode material will experience significant volume expansion during the process of deintercalating lithium, which leads to the silicon negative electrode material being easily pulverized and falling off from the current collector during the charging and discharging process. This situation will damage the electrical contact between the active material and the current collector, and further cause the decline of electrochemical performance, capacity attenuation and weakening of cycle stability, thereby making it difficult to be commercially applied.

[0005] SUMMARY

[0006] To solve at least one of the above technical problems, the present application provides a negative electrode material.

[0007] In addition, the present application also provides a battery comprising the aforementioned negative electrode material.

[0008] The present application provides a negative electrode material, comprising an active material, the active material comprising a first matrix and a second matrix, the negative electrode material having pores, the pore volume of the negative electrode material being M cm 3 / g, the pore volume of the negative electrode material measured after being pressed at a pressure of 80 MPa for 1 h being N cm 3 / g, and the particle space collapse ratio of the negative electrode material being P, P=(M-N) / M, wherein 0.002≤M≤0.12 and 0.05≤P≤0.85.

[0009] The present application also provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the aforementioned negative electrode material.

[0010] Compared with the prior art, the negative electrode material provided by the embodiment of the application controls the pore volumes M and N of the negative electrode material before and after pressing, adjusts the rigidity strength of the negative electrode material, and according to the pore volume M cm 3 / g of the negative electrode material before pressing, the pore volume of the negative electrode material is N cm 3 / g after the pressing treatment, controls the particle space collapse ratio P of the negative electrode material within a suitable range, adjusts the rigidity strength of the negative electrode material, thereby ensuring the stability of the structure of the negative electrode material while improving the various electrochemical performances of the negative electrode material, such as improving the cycle stability of the battery prepared by the negative electrode material, and solving the problems of easy breaking and cracking of the negative electrode material prepared in the pressing process, thereby improving the poor processing performance of the negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a process flow diagram of a preparation method of a negative electrode material provided by the embodiment of the application.

[0012] FIG. 2 is a structural schematic diagram of a battery provided by the embodiment of the application.

[0013] FIG. 3 is a scanning electron microscope image of the negative electrode material of the embodiment 1 of the application.

[0014] FIG. 4 is an X-ray diffraction diagram of the negative electrode material of the embodiment 1 of the application.

[0015] FIG. 5 is a cycle performance curve diagram of the battery prepared by the negative electrode material of the embodiment 1 of the application. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by a person skilled in the art without creative labor fall within the protection scope of the application.

[0017] In order to solve the problems of poor conductivity and cycle stability of the negative electrode material, researchers try to use the coating method. However, the existing coating preparation process is quite complex, and the simple coating layer will cause a large volume expansion and shrinkage of the negative electrode material during the charging and discharging process, which may cause the rupture and failure of the coating layer, cannot protect the negative electrode material from structural damage, and cannot effectively improve the electrochemical performance of the negative electrode material.

[0018] The applicant found that the changes in the number and volume of the pores of the negative electrode material before and after pressing have a great influence on the volume expansion and performance of the negative electrode material. Therefore, the embodiment of the application provides a negative electrode material, which comprises an active substance, the active substance comprises a first matrix and a second matrix, the negative electrode material has pores, and the pore volume of the negative electrode material is M cm3 N cm3 / g (i.e. the pore volume of the negative material in a natural state, or an unpressurized state), and the pore volume of the negative material measured after being pressed for 1 h under a pressure of 80 MPa is N cm3 / g 3 The particle space collapse ratio P of the negative material is defined by (M-N) / M, i.e. P = (M-N) / M, where 0.002≤M≤0.12, 0.05≤P≤0.85. By controlling the pore volumes M and N of the negative material before and after being pressed, and further adjusting the particle space collapse ratio P of the negative material to be within a suitable range, the rigidity of the negative material is adjusted, so as to improve the various electrochemical performances of the negative material while ensuring the stability of the structure of the negative material, such as improving the cycle stability of the battery prepared from the negative material; and solving the problems of the negative material prepared electrode sheet, such as being easily broken or cracked during the pressing process, and improving the poor processability of the negative material.

[0019] Specifically, by controlling the particle space collapse ratio P of the negative material to be within a range of 0.05-0.85 under a suitable pressure, the rigidity of the material can be improved, the pores in the negative material can be moderately reduced, the deformation of the outer surface of the negative material can be reduced, and a stable solid electrolyte film can be formed on the surface of the negative material, so as to improve the first coulombic efficiency of the negative material. If the particle space collapse ratio of the negative material is too low (less than 0.05), the huge stress generated after the first matrix (such as a silicon-based material) is lithiated can break the entire negative material, resulting in deterioration of the cycle performance of the battery prepared from the negative material; if the particle space collapse ratio of the negative material is too high (more than 0.85), the rigidity of the negative material is weak, and there are many internal pores, although the volume expansion of the first matrix can be effectively alleviated, but due to the large volume shrinkage of the negative material, the electrolyte can be absorbed into the material, causing an increase in the side reaction between the negative material and the electrolyte, thereby causing serious capacity attenuation of the battery prepared from the negative material.

[0020] The size of the pore volume M of the negative material directly affects the particle space collapse ratio P of the negative material. In order to control the particle space collapse ratio P to be within a range of 0.05-0.85, the negative material needs to have a suitable pore volume M.

[0021] The pore volume M of the negative electrode material needs to be controlled in the range of 0.002-0.12, because too large pore volume M (greater than 0.12) will result in too loose structure of the negative electrode material, and too small pore volume M (less than 0.002) will result in the active material such as silicon element being broken and pulverized due to the volume expansion of the active material being not effectively relieved by the negative electrode material particles. The battery prepared by the negative electrode material will cause significant volume change and lead to capacity attenuation due to the loose structure or particle pulverization of the negative electrode material during the cycle process. The pore volume M is controlled in the range of 0.002-0.12 in the present application, which can effectively prolong the service life and cycle stability of the battery prepared by the negative electrode material. Limiting the range of pore volume M can also adjust the specific surface area and ion diffusion path of the negative electrode material, which is beneficial to improve the electron transmission rate and ion diffusion rate of the negative electrode material, thereby improving the charge-discharge efficiency of the battery prepared by the negative electrode material.

[0022] The pore volume M of the negative electrode material is derived from the pores possessed by the negative electrode material. By adjusting the pore size of the pores inside the negative electrode material, the pore volume of the negative electrode material is adjusted, and the particle space collapse ratio of the negative electrode material is controlled to meet the requirements of stability and performance of the battery material during use.

[0023] In some embodiments, M is 0.002, 0.007, 0.009, 0.02, 0.04, 0.05, 0.06, 0.08, 0.09, 0.1, 0.11, 0.12, or any value within the range composed of any two of the above values, which is not limited herein. Preferably, 0.03≤M≤0.1.

[0024] In some embodiments, the space collapse ratio P of the negative electrode material is 0.05, 0.1, 0.15, 0.2, 0.22, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or any value within the range composed of any two of the above values, which is not limited herein. Preferably, 0.3≤P≤0.85.

[0025] In some embodiments, the average diameter of the pores of the negative electrode material is 0.5 nm to 20 nm. For example, the average diameter of the pores can be 0.5 nm, 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 15 nm, or 20 nm, or other values within the above range, without limitation. The diameter of the pores affects the specific surface area of the negative electrode material. Smaller pores generally have a higher specific surface area, which is conducive to the diffusion of electrolyte and ions. Larger diameter pores can improve the expansion performance of the negative electrode material, which is conducive to the stability and cycle life of the negative electrode material. Within the above range, the negative electrode material can maintain structural stability, promote the rapid diffusion of ions, and reduce the penetration of electrolyte into the negative electrode material, thereby reducing side reactions between the negative electrode material and the electrolyte. Further, the average diameter of the pores can be 2 nm to 15 nm, while further adjusting the pore volume and particle space collapse ratio of the negative electrode material.

[0026] In some embodiments, the first matrix includes a single substance or a combination of at least one of silicon, germanium, antimony, tin, and boron. For example, silicon is used as a component of the negative electrode active material, which can increase the specific capacity of the negative electrode material and thereby increase the energy density of the battery prepared from the negative electrode material.

[0027] In some embodiments, the first matrix includes a silicon-based material, and the silicon-based material includes a silicon single substance, which includes amorphous silicon, crystalline silicon, or a composite of crystalline silicon and amorphous silicon. For example, the first matrix includes amorphous silicon, which isotropically expands during lithium intercalation, which can reduce the collapse of pores in the negative electrode material and inhibit the rapid decay of the specific capacity of the negative electrode material, thereby more favorably improving the lithium intercalation cycle performance of the negative electrode material.

[0028] In some embodiments, the first matrix includes a silicon-based material, and the silicon-based material includes at least one of a silicon oxide and a silicon alloy.

[0029] In some embodiments, the silicon oxide includes silicon and oxygen elements, and the atomic ratio of the silicon and oxygen elements is 0 to 2, excluding 0. For example, the atomic ratio of the silicon and oxygen elements can be 0.05, 0.11, 0.21, 0.26, 0.31, 0.41, 0.51, 0.59, 0.61, 0.69, 0.71, 0.74, 0.76, 0.79, 0.89, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, or other values within the above range, without limitation. Preferably, the atomic ratio of the silicon and oxygen elements is 0 to 1, excluding 0.

[0030] In some embodiments, the chemical formula of the silicon oxide is SiO xwherein 0 < x < 2, x can be specifically 0.05, 0.11, 0.21, 0.26, 0.31, 0.41, 0.51, 0.59, 0.61, 0.69, 0.71, 0.74, 0.76, 0.79, 0.89, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2, etc., which are not limited herein. Preferably, 0 < x < 1.

[0031] In some embodiments, the morphology of the first matrix includes at least one of a point shape, a spherical shape, an ellipsoidal shape, and a sheet shape, which can be selected according to actual needs, which are not limited herein.

[0032] In some embodiments, the purity of the first matrix is greater than 99%. Taking silicon particles as an active substance as an example, high-purity silicon particles are more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of lithium ion batteries.

[0033] In some embodiments, the second matrix includes a carbon material, and the carbon material includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, and graphene, etc. The second matrix selects the above-mentioned materials, which can all play a role in forming a conductive network with the first matrix.

[0034] In some embodiments, the second matrix includes a non-carbon material, and the non-carbon material includes at least one of a metal element, a metal oxide, a silicide, a silicate, a phosphate, a titanate, and an aluminum borate, etc. It can be understood that the non-carbon material adopts the above-mentioned materials, which all have good strength and rigidity, so that the negative electrode material has a higher compaction density in the battery preparation process, which can improve the structural stability of the negative electrode material, reduce the particle breakage and pulverization of the negative electrode material, and is conducive to improving the cycle performance of the negative electrode material. At the same time, the non-carbon material has electronic insulation, and thus has good ionic conductivity, which can play a role similar to an artificial SEI film, can slow down the generation of a subsequent natural SEI film, reduce the direct contact between the negative electrode material and the electrolyte, and reduce the occurrence of side reactions.

[0035] In some embodiments, the metal element can include at least one of copper, silver, tin, lead, aluminum, and zinc.

[0036] In some embodiments, the metal oxide can include at least one of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide.

[0037] In some embodiments, the silicide can include at least one of silicon carbide and silicon nitride.

[0038] In some embodiments, the silicate can include at least one of cordierite, mullite, and zeolite. It can be appreciated that the silicate of the present application is mainly a natural silicate mineral, in which cordierite (magnesium-aluminum silicate), with a chemical formula of Mg2Al4Si5O 18 , can contain elements such as Na, K, Ca, Fe, and Mn, and H2O; mullite, with a chemical formula of 3Al2O3-2SiO2; and zeolite (aluminosilicate), with a chemical formula of A m B p O 2p nH2O, where A represents a cation, usually including monovalent or divalent metal ions such as Ca, Na, K, Ba, Sr, etc., B represents a basic unit constituting a framework structure of the zeolite, i.e., Si and Al atoms, p is the valence of the cation, m is the number of cations A, and n is the number of water molecules.

[0039] In some embodiments, the phosphate can include at least one of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0040] In some embodiments, the titanate can include at least one of calcium titanate, iron titanate, lithium titanate, and barium titanate.

[0041] In the negative electrode material, at least part of the particles of the second matrix are located inside the particles of the first matrix.

[0042] Exemplarily, the silicon-based material is selected as the first matrix, and the carbon material is selected as the second matrix. The silicon-based material exists in the form of silicon grains. A plurality of silicon-based material particles constitute a matrix of the negative electrode material. The silicon-based material serves as the matrix. The negative electrode material can adjust various performances of the negative electrode material by utilizing the nanostructure and pore distribution of the silicon-based material. At least part of the carbon material can be located in the pores of the silicon-based material and jointly form pores of the negative electrode material with the silicon-based material. In this way, the carbon material is filled into the pores of the silicon-based material. A certain pore volume is reserved to obtain a suitable particle space collapse ratio, so as to adjust the rigidity strength of the negative electrode material.

[0043] It can be appreciated that the carbon material can also be selected as the first matrix, and the silicon-based material can be selected as the second matrix. A plurality of carbon material particles constitute a matrix of the negative electrode material. The carbon material serves as the matrix. The negative electrode material can adjust various performances of the negative electrode material by utilizing the nanostructure and pore distribution of the carbon material. At least part of the silicon-based material can be located in the pores of the carbon material and jointly form pores of the negative electrode material with the carbon material. In this way, the silicon-based material is filled into the pores of the carbon material. A certain pore volume is reserved to obtain a suitable particle space collapse ratio, so as to adjust the rigidity strength of the negative electrode material.

[0044] In some embodiments, the average particle size of the primary particles of the silicon-based material can be 1 nm to 100 nm, for example, 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, or other values within the above range, without limitation. Controlling the average particle size of the silicon particles in the silicon-based material to be between 1 nm and 100 nm can adjust the specific surface area and electron transport path of the negative electrode material, which is beneficial to improving the electrochemical performance of the negative electrode material. Further, the average particle size of the primary particles of the silicon-based material can be 5 nm to 50 nm. In the present application, the expression "primary particles" refers to the primary structure of a single particle, and the expression "secondary particles" refers to aggregates of primary particles that are aggregated by physical or chemical bonding between the primary particles, i.e., the secondary structure, without intentionally performing the aggregation or combination process of the primary particles that constitute the secondary particles.

[0045] In some embodiments, the average size of the silicon grains in the silicon-based material can be 0.5 nm to 15 nm, for example, 0.5 nm, 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 12 nm, or 15 nm, or other values within the above range, without limitation. Smaller nanoscale silicon grain sizes generally have higher specific surface areas, which are beneficial to charge transport and ion diffusion of the negative electrode material, inhibit volume expansion, thereby improving the electrochemical performance of the negative electrode material and increasing the stability and cycle life of the negative electrode material. Further, the average size of the silicon grains in the silicon-based material can be 2 nm to 10 nm.

[0046] Further, the negative electrode material can further include a coating layer provided on at least part of the surface of the active material. The coating layer is beneficial to improving the structural stability and electrical conductivity of the negative electrode material. The synergistic effect of a suitable particle space collapse ratio of the negative electrode material and a uniform coating layer on the surface of the negative electrode material can further improve the structural stability of the negative electrode material during lithiation, reduce the expansion rate of the negative electrode material, be beneficial to the formation of a stable solid electrolyte film on the surface of the negative electrode material, and be beneficial to the improvement of the electrical conductivity of the negative electrode material, thereby improving the electrochemical performance of the negative electrode material.

[0047] In some embodiments, the material of the coating layer includes at least one of a metal oxide, a carbon material, a conductive polymer, a fluoride, a phosphate, and a nitride.

[0048] In some embodiments, the coating layer can include a carbon material, which can include at least one of graphene, soft carbon, and hard carbon. Reasonably designing the carbon material raw material of the negative electrode material can effectively inhibit the volume expansion of the negative electrode material, reduce the structural damage of the negative electrode material during the cycle process, and further enhance the mechanical strength and pressure resistance of the negative electrode material.

[0049] In some embodiments, the coating layer can include a metal oxide, which can include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0050] In some embodiments, the coating layer can include a nitride, which can include at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0051] In some embodiments, the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly(3-hexylthiophene), poly(p-phenylene vinylene), polypyridine, and polyphenylene vinylene.

[0052] In some embodiments, the fluoride includes at least one of fluoroethylene, fluoropolymer, lithium fluoride, sodium fluoride, potassium fluoride, fluorocarbon polymer, fluorosilicon polymer, hexafluorobutyl acrylate, polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride.

[0053] In some embodiments, the phosphate includes at least one of magnesium phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0054] In some embodiments, the thickness of the coating layer can be 0.1 nm to 100 nm. For example, the thickness of the coating layer can be 0.1 nm, 5 nm, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, or any value within a range between any two of the above values. The coating layer can reduce the solubility of the negative electrode material, thereby reducing the amount of gas generated by the reaction of the dissolved active material with the electrolyte. Controlling the thickness of the coating layer within the above range is beneficial to maintaining the stability of the particle structure of the negative electrode material during the cycle process, and can reduce the exposed active material on the surface of the negative electrode material. Further, the thickness of the coating layer can be 1 nm to 50 nm, and further, the thickness of the coating layer can be 1 nm to 20 nm, thereby facilitating the rapid reversible deintercalation of lithium ions.

[0055] In some embodiments, the coating layer can be a single-layer coating layer formed of a single material, a coating layer formed of a combination of multiple materials, a multi-layer coating layer formed of a single material, or a multi-layer coating layer formed of multiple materials, and the like, and the layer structure of the coating layer can be selected according to actual needs. It can be understood that the coating layer has a higher density when it is a multi-layer coating structure.

[0056] In some embodiments, the median particle size of the negative electrode material can be 0.2 μm to 15 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, or 15 μm, and of course, other values within the above range are also possible and are not limited herein. The median particle size of the negative electrode material directly affects the specific surface area and electron transport path of the negative electrode material. A smaller particle size generally means a larger specific surface area, which is conducive to the electrochemical reaction and rapid charge transport, thereby improving the power density and energy density of the battery; a smaller particle size can reduce the volume change of the material during lithium ion insertion / extraction cycles, which helps to reduce the stress and deformation of the structure, thereby prolonging the cycle life of the battery; the range of the median particle size can further affect the pore structure and pore volume of the negative electrode material, and affect the particle space collapse ratio of the negative electrode material. Further, the median particle size of the negative electrode material can be 1 μm to 10 μm.

[0057] In some embodiments, the specific surface area of the negative electrode material can be 0.8 m 2 / g to 15 m 2 / g, for example, 0.8 m 2 / g, 1 m 2 / g, 2 m 2 / g, 5 m 2 / g, 8 m 2 / g, 10 m 2 / g, or 15 m 2 / g, and of course, other values within the above range are also possible and are not limited herein. Within the above range, the electrochemical reaction is conducive to the electrochemical reaction and rapid charge transport, thereby improving the electrochemical performance of the negative electrode material. Further, the specific surface area of the negative electrode material can be 2 m 2 / g to 10 m 2 / g.

[0058] In some embodiments, the powder compaction density of the negative electrode material can be 0.8 g / cm 3 to 1.5 g / cm 3 , for example, 0.8 g / cm 3 , 0.9 g / cm 3 , 1 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , or 1.5 g / cm 3etc. within the above range, which are not limited herein. Within the above range of the compaction density, the negative electrode material has a suitable charge transfer rate and electrolyte contact area, and also has a suitable good structural stability. The powder compaction density of the negative electrode material can be 1 g / cm 3 ~1.2 g / cm 3 .

[0059] In some embodiments, the second matrix comprises a carbon material, and the content of carbon element in the negative electrode material can be 5% to 70% by mass percentage, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60% or 70%, etc. within the above range, which are not limited herein. Within the above range, by adjusting the content of carbon element in the negative electrode material, the electrochemical performance and structural stability of the negative electrode material can be optimized. The content of carbon element in the negative electrode material can be 10% to 60%.

[0060] In some embodiments, the negative electrode material also contains oxygen element, and the mass fraction of oxygen element in the negative electrode material can be less than or equal to 10% by mass percentage, for example, 1%, 3%, 5%, 8% or 10%, etc. within the above range, which are not limited herein. The introduction of a certain amount of oxygen element can affect the structure and chemical properties of the negative electrode material, and adjust the pore structure of the negative electrode material. In the synthesis process of the negative electrode material, the oxygen element within the above content range can form oxides or oxygen-containing functional groups with carbon and silicon elements, which can form pores in the negative electrode material or adjust the distribution and size of the pores in the negative electrode material; can also improve the mechanical properties and structural stability of the negative electrode material; can improve the electronic conduction performance and the kinetic characteristics of the electrochemical reaction of the negative electrode material, which is helpful to improve the charge and discharge efficiency of the battery prepared by the negative electrode material; in addition, it can also affect the surface chemical properties of the negative electrode material, such as the formation of surface active sites, further promote the interaction between the negative electrode material and the electrolyte, and optimize the overall performance of the battery.

[0061] Compared with the prior art, the negative electrode material provided by the embodiments of the present application has the following beneficial effects:

[0062] 1. The embodiment of the present application controls the pore volume M and N of the negative electrode material before and after pressing, controls the particle space collapse ratio P of the negative electrode material in the range of 0.05-0.85, and adjusts the rigidity strength of the negative electrode material. On the one hand, it improves the pulverization problem caused by excessive stress generated in the first matrix of the negative electrode material during lithium extraction, improves the structural stability of the negative electrode material during lithiation, and improves the cycle performance; on the other hand, it utilizes the collapsible ability inside the negative electrode material to guide the negative electrode material to tend to inward expansion, so that the overall particle external shape change is small, thereby improving the initial efficiency of the battery prepared by the negative electrode material, and also effectively reducing the expansion rate of the negative electrode material. Thus, the volume expansion effect of the negative electrode material is reduced, the external deformation of the negative electrode material is stabilized, the formation of a stable solid electrolyte membrane is promoted, and the electrochemical performance of the negative electrode material is improved, such as improving the cycle stability of the battery prepared by the negative electrode material; solve the problem of easy breaking and cracking of the negative electrode material prepared electrode sheet during the pressing process, and solve the problem of poor processability of the negative electrode material.

[0063] 2. The negative electrode material provided by the embodiment of the present application deposits a second matrix inside the first matrix and forms a pore, thereby adjusting the pore volume of the negative electrode material, controlling the particle space collapse ratio of the negative electrode material, and thereby reducing the expansion rate of the negative electrode material and improving the electrochemical performance of the negative electrode material; in addition, the negative electrode material also has a coating layer, and forming a coating layer on the surface of the negative electrode material can reduce the dissolution amount of the negative electrode material during the cycle process, thereby reducing the side reaction of the dissolved first matrix with the electrolyte.

[0064] Referring to FIG. 1, the preparation method of the negative electrode material provided by the embodiment of the present application specifically includes the following steps:

[0065] Step S1, sintering the first material once to obtain a first product.

[0066] Specifically, the first material is placed in a reaction device (for example, an atmosphere furnace), and after one sintering under a protective atmosphere, the first product is obtained after cooling. The main purpose of sintering the first material once is to pretreat the first material, reduce oxidation, and promote the pyrolysis and crystallization process of the first material, so that the structure of the first product is stabilized, and the subsequent chemical reaction and compounding steps are prepared, ensuring that the first product has a certain crystal structure and chemical activity.

[0067] In some embodiments, the first material can include at least one of a single substance or a combination selected from silicon, germanium, antimony, tin, and boron, etc. For example, silicon single substance is used as the first material, which can improve the specific capacity of the prepared negative electrode material, and thereby improve the energy density of the battery prepared by the negative electrode material.

[0068] In some embodiments, the first material can include a silicon-based material, and the silicon-based material can include amorphous silicon, crystalline silicon, or a composite of crystalline silicon and amorphous silicon.

[0069] In some embodiments, the first material can include a silicon-based material, which can include at least one of silicon oxide and silicon alloy, etc.

[0070] In some embodiments, the morphology of the first material can include at least one of a point shape, a spherical shape, an ellipsoidal shape, and a sheet shape, etc.

[0071] In some embodiments, the purity of the first material can be greater than 99%. Taking silicon as the first material for example, high-purity silicon is more conducive to Li-Si alloying with lithium, thereby improving the cycle performance of the lithium ion battery.

[0072] In some embodiments, the median particle size D50 of the first material can be 0.1 μm to 20 μm, and exemplarily can be 0.1 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, or 20 μm, etc. Within the above limited range, it is helpful to ensure the uniformity and consistency of the first material during the heat treatment and chemical reaction process, and at the same time, a smaller particle size is helpful to improve the specific capacity of the battery, reduce the volume expansion of the negative electrode material, etc. Further, the median particle size D50 of the first material can be 2 μm to 15 μm. The particle size test method of the above first material can be tested by a Malvern laser particle size analyzer (Mastersizer 3000), and the volume-based cumulative particle size distribution determined by the laser diffraction method is measured, and D50 represents the particle size corresponding to the cumulative particle size distribution percentage of 50%.

[0073] In some embodiments, the first sintering is to rise to a first sintering temperature of 250°C to 1150°C at a temperature rising speed of 1°C / min to 20°C / min and keep the temperature for 3h to 12h. The first sintering temperature can further be 500°C to 1000°C, and exemplarily can be 250°C, 350°C, 400°C, 500°C, 600°C, 700°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1150°C, etc. Of course, it can also be other values within the above range, which is not limited herein. By the appropriate temperature rising speed, sintering temperature and holding time, it is helpful to form a certain crystal structure by pretreating the first material, thereby providing a basis for the subsequent reaction with the metal reducing agent.

[0074] In some embodiments, the protective atmosphere can include at least one of argon, nitrogen, and helium, etc., so as to reduce the reaction of the first material with oxygen at high temperature to form an oxide, thereby maintaining the purity and activity of the first material.

[0075] In step S2, the first product is mixed with the metal reducing agent and subjected to secondary sintering to obtain a second product.

[0076] Specifically, the first product is mixed with the metal reducing agent in a certain proportion, and then put into a reaction device (for example, a reaction furnace) to replace the air with protective gas, and then subjected to secondary sintering. After cooling, the second product is obtained. The addition of the metal reducing agent aims to react with the first product. For example, when silicon is used as the first material, the first product can react with the metal reducing agent to form a silicon metal compound or a silicon metal alloy. The secondary sintering process also helps to ensure the uniformity and stability of the negative electrode material.

[0077] In some embodiments, the metal reducing agent can include at least one of magnesium powder, aluminum powder, lithium powder, and the like. The above-mentioned metal reducing agents all have good reducing properties, which are beneficial to the reduction and alloying of the first product. At the same time, the introduction of the metal reducing agent also helps to improve the electrical conductivity, ion diffusion performance and cycle stability of the negative electrode material.

[0078] In some embodiments, the mass ratio of the first product to the metal reducing agent is 1:(0.2-1.2), which can be exemplarily 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1 or 1:1.2, and further can be 1:(0.2-0.8). A suitable ratio can achieve a better reaction of the first product with the metal reducing agent.

[0079] In some embodiments, the secondary sintering is to rise to a first sintering temperature of 250-950℃ at a temperature rising rate of 1-30℃ / min and keep the temperature for 1-48h, which can be exemplarily 250℃, 350℃, 400℃, 500℃, 600℃, 700℃, 800℃, 850℃, 900℃ or 950℃, and further can be 300-600℃, and of course can be other values within the above range, which are not limited in the present application. By using a suitable temperature rising rate, sintering temperature and holding time, the reaction can reach a sufficient temperature and time, which can promote the reaction of the first product with the metal reducing agent, and improve the crystallinity and stability of the crystal structure of the second product.

[0080] In step S3, the second product is etched to obtain a negative electrode material precursor.

[0081] Specifically, the second product obtained in step S2 is put into an etching liquid in a certain proportion, and then subjected to purification treatment under certain conditions. After washing and drying, the negative electrode material precursor is obtained. Acid etching can remove the metal, by-products and other impurities on the surface of the second product to form a negative electrode precursor, improve the purity and activity of the negative electrode material precursor, and reduce the influence of impurities on the electrochemical performance of the material. The clean negative electrode material precursor provides a good foundation for the formation of pores and the subsequent deposition of the second material.

[0082] In some embodiments, the etching solution can include one of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid. These acidic solutions can effectively remove the metal, byproducts, and other impurities on the surface of the second product, reducing the impact of impurities on the electrochemical performance of the subsequent prepared negative electrode material.

[0083] In some embodiments, the mass ratio of the second product to the etching solution can be 1:(5-20), and can exemplarily be 1:5, 1:8, 1:10, 1:15, or 1:20, and can further be other values within the above range, which are not limited herein. By controlling the ratio of the second product and the etching solution, the surface of the second product is fully exposed during etching, and the etching effect is optimized.

[0084] In some embodiments, the molar concentration of the etching solution can be 1-10 mol / L. The molar concentration of the etching solution affects the concentration of active ions or molecules in the etching solution, directly affecting the etching rate and effect. Selecting an appropriate molar concentration can achieve the desired etching effect in a shorter time, while avoiding excessive etching or incomplete etching.

[0085] In some embodiments, the etching reaction time can be 0.5-10 h, ensuring that the etching process is fully carried out, so that impurities and unwanted surface substances are completely removed.

[0086] In some embodiments, the etching reaction temperature is less than or equal to 35°C. Controlling a lower etching reaction temperature helps to avoid a too fast chemical reaction rate, maintaining the controllability and safety of the etching process.

[0087] In some embodiments, the mass content of oxygen in the negative electrode material precursor is less than 5%. Controlling the oxygen content can reduce the negative impact of impurities on the electrochemical performance of the material, ensuring the electrochemical activity and stability of the negative electrode material precursor.

[0088] In some embodiments, the mass content of water in the negative electrode material precursor can be less than 1.2%. A low water content helps to reduce the oxidation reaction of the negative electrode material precursor, maintaining the purity and stability of the negative electrode material precursor.

[0089] In some embodiments, the median particle size of the negative electrode material precursor can be 0.1-15 μm, and can exemplarily be 0.1 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, or 15 μm, and can further be 1-10 μm, and can further be other values within the above range, which are not limited herein. The median particle size affects the uniformity and surface area of the negative electrode material precursor. An appropriate particle size range helps to optimize the electrochemical reaction rate and energy storage capacity of the negative electrode material.

[0090] In some embodiments, the average silicon grain size of the negative electrode material precursor can be 0.2 nm to 15 nm, for example, 0.2 nm, 0.5 nm, 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 12 nm, or 15 nm, and further can be 2 nm to 15 nm, and of course can also be other values within the above range, which are not limited herein. Within the above range, the electrochemical reaction and the rapid charge transfer are facilitated, thereby improving the electrochemical performance of the negative electrode material.

[0091] In some embodiments, the porosity of the negative electrode material precursor can be 25% to 55%, for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2, and further can be 35% to 55%, and of course can also be other values within the above range, which are not limited herein. The moderate porosity is helpful to improve the specific surface area of the negative electrode material and the permeability of the electrolyte, and to facilitate the electrochemical reaction and the stability of the material, and on the other hand, provides a basis for the subsequent deposition of the second material and the formation of pores.

[0092] In some embodiments, the specific surface area of the negative electrode material precursor can be 250 m 2 / g to 550 m 2 / g, for example, 250 m 2 / g, 300 m 2 / g, 350 m 2 / g, 400 m 2 / g, 450 m 2 / g, 500 m 2 / g, or 550 m 2 / g, and further can be 200 m 2 / g to 500 m 2 / g, and of course can also be other values within the above range, which are not limited herein. Within the above range, the negative electrode material precursor has a higher specific surface area, which is helpful for the subsequent contact reaction with the second material.

[0093] In some embodiments, the pore volume of the negative electrode material precursor can be 0.28 cm 3 / g to 0.56 cm 3 / g, for example, 0.28 cm 3 / g, 0.3 cm 3 / g, 0.4 cm 3 / g, 0.5 cm 3 / g, or 0.56 cm 3 / g, and further can be 0.3 cm 3 / g to 0.5 cm3 / g, of course, but also other values within the above range, which are not limited herein. The higher pore volume in the negative electrode material precursor provides space for the subsequent deposition of the second material and ensures sufficient space to form the necessary pores to optimize the performance and stability of the negative electrode material.

[0094] In step S4, the second material is deposited inside the particles of the negative electrode material precursor by pulse chemical vapor deposition to obtain the negative electrode material.

[0095] Specifically, the negative electrode material precursor with a pore structure is placed in a reaction device (for example, a reaction furnace), the air therein is replaced with a protective gas, and after being heated to a certain temperature, the gas-phase second material is introduced in a pulse manner. By controlling the amount of gas introduced for a short time, the deposition rate and efficiency of the second material inside are changed, and then the second material is continuously introduced in a sustained manner to continue depositing the carbon source in the pores inside the particles of the negative electrode material precursor. After a certain holding time, the second material undergoes a thermal cracking reaction, the second material is deposited inside the negative electrode material precursor, and a hole is reserved inside the negative electrode material precursor to obtain the negative electrode material.

[0096] This step deposits the second material inside the negative electrode material precursor and reserves a hole by pulse chemical vapor deposition. By using a pulse gas inlet method, the deposition rate of the second material inside the negative electrode material precursor can be accurately controlled, and the deposition rate from inside to outside can be sequentially increased. A part of the hole can be reserved inside the negative electrode material precursor, and then the pore volume of the negative electrode material can be adjusted, and the particle space collapse ratio of the negative electrode material can be controlled.

[0097] In some embodiments, the second material can include a carbon material, which can include at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, and graphene, etc. The second material selected from the above materials can form a conductive network inside the negative electrode material precursor.

[0098] In some embodiments, the second material can include a non-carbon material, which can include at least one of a metal, a metal oxide, a silicide, a silicate, a phosphate, a titanate, and an aluminum borate, etc.

[0099] In some embodiments, the metal oxide can include at least one of aluminum oxide, zirconium oxide, germanium dioxide, and manganese dioxide.

[0100] In some embodiments, the silicide can include at least one of silicon carbide and silicon nitride.

[0101] In some embodiments, the silicate can include at least one of cordierite, mullite, and zeolite. It can be appreciated that the silicate of the present application is mainly a natural silicate mineral, in which cordierite (magnesium-aluminum silicate) has a chemical formula of Mg2Al4Si5O 18 , which can contain elements such as Na, K, Ca, Fe, and Mn, and H2O; mullite has a chemical formula of 3Al2O3-2SiO2; and zeolite (aluminosilicate) has a chemical formula of A m B p O 2p nH2O, where A represents a cation, usually including monovalent or divalent metal ions such as Ca, Na, K, Ba, Sr, etc., B represents a basic unit constituting the framework structure of the zeolite, i.e., Si and Al atoms, p is the valence of the cation, m is the number of cations A, and n is the number of water molecules.

[0102] In some embodiments, the phosphate can include at least one of aluminum phosphate, magnesium phosphate, calcium phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate, etc.

[0103] In some embodiments, the titanate can include at least one of calcium titanate, iron titanate, lithium titanate, and barium titanate, etc.

[0104] In some embodiments, the temperature rising rate of the gas-phase carbon deposition can be 1-30°C / min. Controlling the temperature rising rate can affect the transmission and decomposition rate of the second material in the reaction device. A proper temperature rising rate can uniformly heat the negative electrode material precursor in the reaction chamber to reach a reaction temperature suitable for the thermal cracking of the second material, while avoiding non-uniform deposition or other adverse effects caused by too fast temperature rising.

[0105] In some embodiments, the reaction temperature of the gas-phase deposition can be 200-1050°C, exemplarily 200°C, 300°C, 350°C, 400°C, 500°C, 600°C, 700°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or 1050°C, etc., and of course can also be other values within the above range, which are not limited in the present application, and can further be 500-1000°C. The reaction temperature is a key parameter affecting the thermal cracking reaction rate and deposition quality of the second material, and performing the reaction within a proper temperature range can control the thermal cracking rate of the second material to deposit the second material inside the negative electrode material precursor and form the required pores.

[0106] In some embodiments, the holding time of the gas-phase deposition can be 1-24h, and sufficient holding time is beneficial to ensure uniform deposition of the second material inside the negative electrode material precursor to form a stable structure and pore distribution.

[0107] In some embodiments, the gaseous carbon source can include at least one of acetylene, methane, ethylene, propane, toluene, cyclohexane, ethanol, ethylene, propylene, pyrrole, and acetonitrile, etc.

[0108] In some embodiments, the flow rate of the gaseous carbon source can be 0.1 L / min to 10 L / min, and exemplarily can be 0.1 L / min, 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, or 10 L / min, etc., and of course can also be other values within the above range, which are not limited herein, and further can be 0.5 L / min to 5 L / min. Controlling the flow rate of the gaseous carbon source can adjust the rate and concentration of the carbon source entering the reaction device, so as to accurately control the carbon deposition rate of the carbon source inside the anode material precursor.

[0109] In some embodiments, the pulse frequency can be 10 Hz to 500 Hz, and specifically can be 10 Hz, 50 Hz, 100 Hz, 150 Hz, 200 Hz, 300 Hz, 400 Hz, 450 Hz, or 500 Hz, etc., and of course can also be other values within the above range, which are not limited herein. The pulse duration can be 10 ms to 800 ms, and specifically can be 10 ms, 50 ms, 100 ms, 150 ms, 300 ms, 500 ms, 600 ms, 700 ms, or 800 ms, etc., and of course can also be other values within the above range, which are not limited herein. The pulse gas inlet can control the short-time high-concentration input of the second material, and by adjusting the pulse frequency and duration, the deposition process of the second material can be accurately controlled.

[0110] In some embodiments, the pulse duration can be 1 h to 8 h, and specifically can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h, etc., and of course can also be other values within the above range, which are not limited herein. The pulse duration affects the deposition amount of the second material and the persistence of the reaction, and appropriate pulse duration can achieve sufficient deposition of the second material, form the required pores, and thus optimize the electrochemical performance and cycle stability of the prepared anode material.

[0111] Further, the coating material can also be deposited on the surface of the anode material precursor by the pulse chemical vapor deposition method, to form a coating layer on the surface of the anode material precursor, which is beneficial to reducing the dissolution amount of the active material in the anode material during the cycle, and further reducing the side reaction of the dissolved silicon particles with the electrolyte; and is also beneficial to relieving the volume expansion of the anode material.

[0112] In some embodiments, the negative electrode material precursor can be coated by a coating material to obtain the negative electrode material.

[0113] In some embodiments, the coating material can include a carbon material, and the carbon material can include at least one of graphene, soft carbon, and hard carbon. Reasonable design of the carbon material raw material of the negative electrode material can effectively inhibit the volume expansion of the silicon particles, reduce the structural damage of the negative electrode material during the cycle process, and enhance the mechanical strength and pressure resistance of the negative electrode material.

[0114] In some embodiments, the coating material can include a metal oxide, and the metal oxide can include at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0115] In some embodiments, the coating layer can include a nitride, and the nitride layer can include at least one of titanium nitride, vanadium nitride, cobalt nitride, nickel nitride, and carbon nitride.

[0116] In some embodiments, the coating material includes a conductive polymer, and the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly-p-phenylenevinylene, polypyridine, and polyphenylvinylene.

[0117] In some embodiments, the coating material includes a fluoride, and the fluoride includes at least one of fluoroethylene, fluoropolymer, lithium fluoride, sodium fluoride, potassium fluoride, fluorocarbon polymer, fluorosilicon polymer, hexafluorobutyl acrylate, polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride.

[0118] In some embodiments, the coating material includes a phosphate, and the phosphate includes at least one of magnesium phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, chromium phosphate, cobalt phosphate, nickel phosphate, germanium phosphate, zirconium phosphate, niobium phosphate, molybdenum phosphate, tantalum phosphate, tungsten phosphate, and lanthanum phosphate.

[0119] The suitable particle space collapse ratio of the negative electrode material and the uniform coating layer on the surface of the negative electrode material can improve the structural stability of the negative electrode material during the lithiation process, reduce the expansion rate of the negative electrode material, be conducive to the formation of a stable solid electrolyte film on the surface of the negative electrode material, and be conducive to the improvement of the conductivity of the negative electrode material, thereby improving the electrochemical performance of the negative electrode material.

[0120] Compared with the prior art, the preparation method of the negative electrode material provided by the embodiments of the present application has the following beneficial effects:

[0121] 1. The second material can be precisely controlled in the deposition rate inside the negative electrode material by the pulse chemical vapor deposition process, and the deposition rate from inside to outside is sequentially increased, so as to reserve a part of the hole while depositing the second material inside the negative electrode material precursor, and then accurately adjust the pore volume of the negative electrode material, control the particle space collapse ratio of the negative electrode material, improve the structural stability of the negative electrode material, and improve the cycle performance and rate performance of the negative electrode material.

[0122] 2. The uniform coating layer can be formed on the surface of the negative electrode material by the pulse chemical vapor deposition process. The uniform coating layer can further improve the structural stability of the negative electrode material during the lithiation process, reduce the expansion rate of the negative electrode material, be beneficial to the formation of stable solid electrolyte film on the surface of the negative electrode material to improve the cycle performance of the negative electrode material, and be beneficial to the improvement of the conductivity of the negative electrode material, thereby improving the electrochemical performance of the negative electrode material.

[0123] 3. The preparation method is simple, efficient and controllable, which is beneficial to the large-scale production of the negative electrode material and has excellent commercialization prospect.

[0124] Referring to FIG. 2, the application further provides a battery, which comprises a positive electrode sheet 10, a negative electrode sheet 20, a separator 30 and an electrolyte 40, wherein the negative electrode sheet 20 comprises a negative electrode active material, and the negative electrode active material is the negative electrode material as described above. The battery 100 prepared by using the negative electrode material has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance and low expansion.

[0125] The foregoing negative electrode material, preparation method and battery are further described through specific examples.

[0126] Test method:

[0127] (1) Test method of specific surface area and pore volume of negative electrode material:

[0128] An ASAP2460 surface area and pore size analyzer of American Micromeritics is used, and N2 is used as the adsorption gas. A certain amount of sample is weighed and loaded into a specific bubble tube for specific surface area, and is purged with nitrogen at 300°C for one hour in a degassing station. After degassing is completed, the sample is cooled to room temperature, and the actual mass of the sample is weighed. Then, the specific bubble tube loaded with the sample is installed into the specific surface area and pore size analyzer, and the specific surface area of the sample is measured after the sample mass is input. The measurement can be performed according to GB / T 19587-2004 “Gas adsorption BET method for measuring specific surface area of solid material” or the equipment instruction manual.

[0129] (2) Particle space collapse ratio P of negative electrode material is tested by the following method:

[0130] 1 kg of negative electrode material is taken, and the pore volume is measured as M cm3 / g, and then the negative electrode material was loaded into an aluminum plastic film bag, vacuum treatment was performed, the vacuum degree was controlled below 10 kPa, and the aluminum plastic film bag was sealed. The aluminum plastic film bag was placed in an isostatic pressing device, the pressure was set to 80 MPa, and the pore volume of the negative electrode material measured after pressure maintaining for 1 h under this pressure was N cm3 / g. The particle space collapse ratio P = (M-N) / M was calculated. 3

[0131] (3) Particle size of the negative electrode material:

[0132] The particle size test method referred to GB / T 19077-2016. The number cumulative particle size distribution of the negative electrode material was measured by a Malvern laser particle size analyzer (Mastersizer 3000) through laser diffraction method, and Dn(50) represented the particle size corresponding to 50% of the number cumulative particle size distribution.

[0133] (4) Test method of tap density:

[0134] A certain amount of sample was weighed by using a Bette tap density tester, and the tap density of the negative electrode material was tested at 300 times / min and 3000 times of vibration.

[0135] (5) Test method of oxygen content and carbon content:

[0136] The mass content of oxygen element in the negative electrode material was tested by using a Fourier infrared spectrum measuring instrument, and the mass content of carbon element in the negative electrode material was tested by using a thermal gravimetric analysis method.

[0137] (6) SEM test:

[0138] The scanning electron microscope characterization was performed on a transmission electron microscope at an operating voltage of 200 kV, and the structure of the negative electrode material was observed.

[0139] (7) Test method of primary particle average size:

[0140] The material was sectioned by using a FIB-SEM device, the size of 20 primary particles was measured in the SEM, the diameter of the smallest inscribed circle of the primary particle was taken as the size, and the average value was calculated, that is, the average size of the primary particle.

[0141] The material was sectioned by using a FIB-SEM device, and the thickness of the coating layer was measured in the SEM.

[0142] (8) Test method of silicon grain average size:

[0143] ​The XRD pattern of the sample was measured by an X-ray diffractometer, the half-height width of the diffraction peak of the sample and the corresponding Bragg angle were obtained by jade software, and the average size of the silicon grains was calculated by the Scherrer formula D=Kγ / B cosθ.

[0144] (9) Electrochemical performance test:

[0145] The negative electrode material was mixed with sodium carboxymethyl cellulose, butadiene rubber, and conductive graphite (KS-6) and carbon black (SP) according to a mass ratio of 92:2:2:2:2 to prepare a slurry, which was uniformly coated on a copper foil and dried to obtain a negative electrode sheet. A button cell CR2016 was assembled in an argon atmosphere glove box, a polypropylene microporous membrane was used as a separator, 1 mol / L lithium hexafluorophosphate (a mixed solution of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate as a solvent) was used as an electrolyte, and a metal lithium sheet was used as a counter electrode.

[0146] The batteries prepared in the above examples and comparative examples were subjected to discharge specific capacity test on a blue CT2001A battery test system, and the ratio of the electric quantity discharged in 1 hour to the battery capacity was the discharge specific capacity.

[0147] The batteries prepared in the above examples and comparative examples were subjected to first coulombic efficiency test on a blue CT2001A battery test system, and the charging and discharging current was 0.05C, and the first coulombic efficiency was measured.

[0148] The batteries prepared in the above examples and comparative examples were subjected to 50-cycle test on a blue CT2001A battery test system, and the charging and discharging current was 0.25C. After 50 cycles, the battery capacity after the cycle and the capacity retention rate after the cycle were tested and calculated, wherein the capacity retention rate after 50 cycles of 0.25C was the discharge capacity of the 50th cycle / the discharge capacity of the first cycle*100%.

[0149] Example 1

[0150] Step 1, the silicon monoxide material was placed in a gas furnace, heated to 950℃ at a heating rate of 3℃ / min under the protection of argon atmosphere, and then cooled to obtain a first product after 5h of heat preservation.

[0151] Step 2, the first product was mixed with aluminum powder in a mass ratio of 1:0.3, and then placed in a reaction furnace. After the air was replaced by protective gas, the mixture was heated to 650℃ at a heating rate of 3℃ / min, and then cooled to obtain a second product after 4h of heat preservation.

[0152] Step 3, the second product was put into an etching solution for purification treatment, the mass ratio of the second product to the etching solution was 1:5, the concentration of the etching solution was 6mol / L, the etching reaction time was 1.5h, and the etching reaction temperature was controlled at 25℃. After washing and drying, a negative electrode material precursor was obtained.

[0153] Step 4, 500g of the negative electrode material precursor was placed in a rotating atmosphere furnace, the air therein was replaced with inert gas, and then heated to 750℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. After that, the flow rate of acetylene gas was set to 2.5L / min, the carbon source was introduced into a pulse generator, the pulse frequency was set to 50Hz, the pulse duration was 200ms, and the pulse duration was 3h. After the pulse generator was turned off, the acetylene gas was continuously introduced at a flow rate of 2.5L / min for 2h, and then cooled to obtain the negative electrode material.

[0154] Example 2

[0155] Step 1, the silicon monoxide material was placed in an atmosphere furnace, heated to 970℃ at a heating rate of 3℃ / min under the protection of argon atmosphere, and then cooled to obtain the first product after holding for 6h.

[0156] Step 2, the first product was uniformly mixed with aluminum powder at a mass ratio of 1:0.3, and then placed in a reaction furnace. The air was replaced with protective gas, heated to 650℃ at a heating rate of 3℃ / min, and then cooled to obtain the second product after holding for 4h.

[0157] Step 3, the second product was placed in an etching solution for purification treatment. The mass ratio of the second product to the etching solution was 1:10, the concentration of the etching solution was 3mol / L, the etching reaction time was 2.5h, and the etching reaction temperature was controlled at 25℃. After washing and drying, the negative electrode material precursor was obtained.

[0158] Step 4, 500g of the negative electrode material precursor was placed in a rotating atmosphere furnace, the air therein was replaced with inert gas, and then heated to 750℃ at a heating rate of 3℃ / min under the protection of argon atmosphere. After that, the flow rate of acetylene gas was set to 2.5L / min, the carbon source was introduced into a pulse generator, the pulse frequency was set to 50Hz, the pulse duration was 200ms, and the pulse duration was 3h. After the pulse generator was turned off, the acetylene gas was continuously introduced at a flow rate of 2.5L / min for 2h, and then cooled to obtain the negative electrode material.

[0159] Example 3

[0160] Step 1, the silicon monoxide material was placed in an atmosphere furnace, heated to 970℃ at a heating rate of 3℃ / min under the protection of argon atmosphere, and then cooled to obtain the first product after holding for 6h.

[0161] Step 2, the first product was uniformly mixed with aluminum powder at a mass ratio of 1:0.3, and then placed in a reaction furnace. The air was replaced with protective gas, heated to 650℃ at a heating rate of 3℃ / min, and then cooled to obtain the second product after holding for 4h.

[0162] Step 3, the second product is put into the etching solution for purification treatment, the mass ratio of the second product to the etching solution is 1:10, the concentration of the etching solution is 3 mol / L, the etching reaction time is 2.5 h, the etching reaction temperature is controlled at 25℃, and the negative electrode material precursor is obtained after washing and drying.

[0163] Step 4, 500g of the negative electrode material precursor is placed in a rotary atmosphere furnace, the air therein is replaced with inert gas, and the temperature is raised to 900℃ at a rate of 3℃ / min under the protection of argon atmosphere. Then, the carbon source is introduced into the pulse generator, the pulse frequency is set to 10Hz, the pulse duration is 800ms, the pulse duration is 4h, and after the pulse generator is turned off, the acetylene gas is continuously introduced at a flow rate of 1.5L / min for 2h. After cooling, the negative electrode material is obtained.

[0164] Example 4

[0165] Step 1, the silicon monoxide material is placed in an atmosphere furnace, and the temperature is raised to 950℃ at a rate of 3℃ / min under the protection of argon atmosphere. After holding for 5h, the first product is obtained after cooling.

[0166] Step 2, the first product is mixed with magnesium powder at a mass ratio of 1:0.2, and then placed in a reaction furnace. The air is replaced with protective gas, and the temperature is raised to 620℃ at a rate of 3℃ / min. After holding for 5h, the second product is obtained after cooling.

[0167] Step 3, the second product is put into the etching solution for purification treatment, the mass ratio of the second product to the etching solution is 1:10, the concentration of the etching solution is 5 mol / L, the etching reaction time is 1.5 h, the etching reaction temperature is controlled at 25℃, and the negative electrode material precursor is obtained after washing and drying.

[0168] Step 4, 500g of the negative electrode material precursor is placed in a rotary atmosphere furnace, the air therein is replaced with inert gas, and the temperature is raised to 950℃ at a rate of 3℃ / min under the protection of argon atmosphere. Then, the carbon source is introduced into the pulse generator, the pulse frequency is set to 10Hz, the pulse duration is 800ms, the pulse duration is 8h, and after the pulse generator is turned off, the acetylene gas is continuously introduced at a flow rate of 0.1L / min for 3h. After cooling, the negative electrode material is obtained.

[0169] Example 5

[0170] The specific process of the preparation process is referred to Example 1, the difference is that the pulse frequency in step 4 is 20Hz, and the rest of the negative electrode material preparation method is basically the same as Example 1, which is not described here.

[0171] Example 6

[0172] The specific process of the preparation process refers to Example 1, except that the pulse frequency in step 4 is 100 Hz, and the rest of the preparation method of the negative electrode material is basically the same as that of Example 1, which is not described here.

[0173] Example 7

[0174] The specific process of the preparation process refers to Example 1, except that the pulse duration in step 4 is 1 h, and the rest of the preparation method of the negative electrode material is basically the same as that of Example 1, which is not described here.

[0175] Example 8

[0176] The specific process of the preparation process refers to Example 1, except that the pulse duration in step 4 is 6 h, and the rest of the preparation method of the negative electrode material is basically the same as that of Example 1, which is not described here.

[0177] Example 9

[0178] The difference from Example 1 is that step 4 is:

[0179] Step 4, 500g of negative electrode material precursor is placed in a rotary atmosphere furnace, the air in it is replaced with inert gas, and under the protection of argon atmosphere, it is heated to 550℃ at a heating rate of 3℃ / min, then 1L / min of silane gas is introduced, and the temperature is raised to 750℃, then the flow rate of acetylene gas is set to 2.5L / min, the carbon source is introduced into the pulse generator, the pulse frequency is set to 50Hz, the pulse duration is 200ms, the pulse duration is 3h, after the pulse generator is turned off, the acetylene gas is continuously introduced at a flow rate of 2.5L / min for 2h, and the negative electrode material is obtained after cooling.

[0180] Example 10

[0181] The difference from Example 1 is that steps 1-3 are:

[0182] Step 1, the shell is carbonized at 500℃ for 5h, then the carbonized product is pickled with 5mol / L hydrochloric acid for 4h, dried and placed in a heat treatment furnace, and a mixture of water vapor and nitrogen gas (volume ratio 1:80) is introduced for activation treatment, the treatment temperature is 800℃, and the time is 12h, to obtain a first product with an average pore size of 2.1nm.

[0183] Step 2, the first product is placed in a 0.4mol / L tin chloride solution, mechanically stirred for 30min, then heated to 95℃, then slowly add 1.2mol / L urea solution, pour the solution into a beaker and cool, and age for 24h; the aged product is moved into a centrifuge tube, centrifuged, washed and dried to obtain a second product.

[0184] Step 3, the second product was placed in a rotary furnace under argon protection, heated to 700℃ at a heating rate of 3℃ / min, then 2L / min of hydrogen was introduced, and after 2h of heat preservation, it was cooled to room temperature to prepare the negative electrode material precursor.

[0185] Example 11

[0186] Step 1, germanium dioxide and magnesium powder were mixed uniformly according to a molar ratio of 1:2, then placed in a box-type atmosphere furnace under argon protection, heated to 75℃ at a heating rate of 3℃ / min, and heat preserved for 3h to obtain a first product.

[0187] Step 2, the first product was put into an etching solution for purification treatment, the mass ratio of the first product to the etching solution was 1:5, the concentration of the etching solution was 1mol / L, the etching reaction time was 2.5h, the etching reaction temperature was controlled at 25℃, and after washing and drying, a negative electrode material precursor was obtained.

[0188] Step 3, 500g of the negative electrode material precursor was placed in a rotary atmosphere furnace, the air therein was replaced with inert gas, and under argon atmosphere protection, it was heated to 700℃ at a heating rate of 3℃ / min, then acetylene gas was set to a flow rate of 2.5L / min, the carbon source was introduced into a pulse generator, the pulse frequency was set to 50Hz, the pulse duration was 200ms, the pulse duration was 3h, after the pulse generator was turned off, acetylene gas was continuously introduced at a flow rate of 2.5L / min for 2h, and then cooled to obtain a negative electrode material.

[0189] Example 12

[0190] Step 1, the silicon monoxide material was placed in an atmosphere furnace, heated to 950℃ at a heating rate of 3℃ / min under argon atmosphere protection, heat preserved for 5h, and then cooled to obtain a first product.

[0191] Step 2, the first product was put into an etching solution for purification treatment, the mass ratio of the first product to the etching solution was 1:10, the concentration of the etching solution was 3mol / L, the etching reaction time was 2.5h, the etching reaction temperature was controlled at 35℃, and after washing and drying, a negative electrode material precursor was obtained.

[0192] Step 3, 500g of the negative electrode material precursor was placed in a rotary atmosphere furnace, the air therein was replaced with inert gas, and under argon atmosphere protection, it was heated to 900℃ at a heating rate of 3℃ / min, then acetylene gas was set as the carbon source, the flow rate was 9.5L / min, introduced into a pulse generator, the pulse frequency was set to 10Hz, the pulse duration was 800ms, the pulse duration was 4h, after the pulse generator was turned off, acetylene gas was continuously introduced at a flow rate of 1.5L / min for 2h, and then cooled to obtain a negative electrode material.

[0193] Comparative Example 1

[0194] The specific process of the preparation process refers to Example 1, except that the carbon deposition in step 4 is a traditional chemical vapor deposition (CVD) technique. Specifically, 500 g of the negative electrode material precursor is placed in a rotary atmosphere furnace, the air therein is replaced with an inert gas, and under the protection of an argon atmosphere, the temperature is raised to 750°C at a rate of 3°C / min. After that, the flow rate of acetylene gas is set to 2.5 L / min, and the acetylene gas is continuously introduced for 5 h. The negative electrode material is obtained after cooling. The rest of the preparation method of the negative electrode material is basically the same as that of Example 1, which is not described in detail here.

[0195] The negative electrode materials obtained in Examples 1-12 (abbreviated as S1-S12) and Comparative Example 1 (abbreviated as D1) are subjected to the following tests.

[0196] 1. The negative electrode materials obtained in Examples 1-12 and Comparative Example 1 are subjected to tests of specific surface area, pore volume, particle space collapse ratio P, particle size, tap density, oxygen content, carbon content, scanning electron microscopy, X-ray diffraction, primary particle average size, and silicon grain average size related performance parameters. The results are shown in Table 1. For example, the scanning electron microscopy results of the negative electrode material in Example 1 are shown in Figure 3, and the X-ray diffraction spectrum results of the negative electrode material in Example 1 are shown in Figure 4.

[0197] Table 1. Preparation process parameters of negative electrode materials

[0198] Table 2

[0199] The above results show that:

[0200] Figure 3 is a scanning electron microscope image of the negative electrode material in Example 1. As can be seen from the scanning electron microscope image in Figure 3, the surface of the prepared negative electrode material is relatively smooth, and the particles of the negative electrode material do not appear to be broken. Figure 4 is an XRD graph of the negative electrode material in Example 1. As can be seen from the XRD graph in Figure 4, 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 are basically no impurity phases. According to the Scherrer formula, the silicon grain size is calculated to be 3.5 nm. After testing, the pore volume of the negative electrode material obtained in Example 1 is 0.09 cm 3 / g, the particle space collapse ratio P is 0.25, the average size of the silicon grains in the negative electrode material is 3.5 nm, the median particle size of the negative electrode material is 5 μm, the specific surface area is 5 m 2 / g, and the powder compaction density is 1.2 g / cm 3, the oxygen content is 5%, the mass percentage of carbon is 33%, and the average particle size of the silicon material in the negative electrode material is 10 nm. The results show that the negative electrode material obtained in Example 1 has a suitable pore volume and particle space collapse ratio P, and also has suitable specific surface area, high compaction density and other excellent performance parameters.

[0201] Figure 5 is a cycle performance curve of a button cell prepared using the negative electrode material in Example 1. As can be seen from Figure 5, the button cell prepared using the negative electrode material in Example 1 has excellent cycle performance, and the capacity retention rate can still reach 83.3% after 50 cycles at a current of 0.25C. This shows that the negative electrode material in this example has a suitable pore volume and particle space collapse ratio P, which not only improves the structural stability of the negative electrode material but also improves the cycle performance of the negative electrode material, thereby improving the electrochemical performance of the battery.

[0202] The negative electrode materials obtained in Examples 2-12 also have suitable pore volumes and particle space collapse ratios P, and also have suitable specific surface areas, high compaction densities and other excellent properties. The batteries prepared using the negative electrode materials obtained in Examples 2-12 also have high specific capacities and initial efficiencies, significantly improved volume retention rates and low expansion rates.

[0203] In Comparative Example 1, the traditional chemical vapor deposition technology is used. The carbon deposition rate of the carbon source in the material cannot be accurately controlled to adjust the pore volume of the composite negative electrode material and control the particle space collapse ratio of the composite negative electrode material. Therefore, the pore volume (0.21 cm 3 / g) of the negative electrode material in Comparative Example 1 is too large, which easily causes the outer surface of the negative electrode material to deform, thereby leading to capacity attenuation and reduced cycle stability of the prepared battery; and the particle space collapse ratio (0.95) is too high, the negative electrode material has weak rigidity, and there are many internal pores. Although the volume expansion of silicon can be effectively alleviated, the volume contraction of the negative electrode material is large, which causes the electrolyte to be absorbed into the material and causes a side reaction, resulting in severe capacity attenuation.

[0204] Therefore, compared with Comparative Example 1, the negative electrode materials obtained in Examples 1-12 all have suitable pore volumes and particle space collapse ratios P, and have excellent structural data and electrochemical test results, which shows that the negative electrode materials in the examples have good structural stability, can effectively reduce the expansion rate, and exhibit excellent electrochemical performance.

[0205] It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principles of the present application, but the present application is not limited thereto. Those skilled in the art can make various modifications and improvements without departing from the spirit and essence of the present application, and these modifications and improvements are also considered to be within the protection scope of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises an active substance, the active substance comprises a first matrix and a second matrix, the negative electrode material has pores, the pore volume of the negative electrode material is M cm 3 / g, the pore volume of the negative electrode material is N cm 3 / g measured after the negative electrode material is pressed under a pressure of 80 MPa for 1 h, the particle space collapse ratio of the negative electrode material is P, P=(M-N) / M, wherein 0.002≤M≤0.12, 0.05≤P≤0.

85.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) the M is 0.002, 0.007, 0.009, 0.02, 0.04, 0.05, 0.06, 0.08, 0.09, 0.1, 0.11, 0.12, or any value within a range defined by any two of the above values; (2) the space shrinkage ratio P of the negative electrode material is 0.05, 0.1, 0.15, 0.2, 0.22, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or any value within a range defined by any two of the above values.

3. The negative electrode material of claim 1, wherein, At least part of the second matrix is located inside the first matrix.

4. The negative electrode material of claim 1, wherein, The average diameter of the pores is 0.5 nm to 20 nm.

5. The negative electrode material of claim 1, wherein, The first matrix includes a single substance or a combination of at least one of silicon, germanium, antimony, tin, and boron.

6. The negative electrode material of claim 1, wherein, The first matrix includes a silicon-based material satisfying at least one of the following conditions: (1) the silicon-based material includes amorphous silicon, crystalline silicon, or a composite of crystalline silicon and amorphous silicon; (2) the silicon-based material includes at least one of silicon oxide and silicon alloy.

7. The negative electrode material of claim 1, wherein, The second matrix satisfies at least one of the following conditions: (1) the second matrix includes a carbon material including at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, and graphene; (2) the second matrix includes a non-carbon material including at least one of a metal single substance, a metal oxide, a silicide, a silicate, a phosphate, a titanate, and an aluminum borate.

8. The negative electrode material of claim 1, wherein, At least part of the particles of the second matrix is located inside the particles of the first matrix, and / or at least part of the particles of the first matrix is located inside the particles of the second matrix.

9. The negative electrode material of claim 1, wherein, The negative electrode material further includes a coating layer located on at least part of the surface of the active material, and a material of the coating layer includes at least one of a metal oxide, a carbon material, a conductive polymer, a fluoride, a phosphate, and a nitride.

10. The negative electrode material according to claim 9, characterized in that, The coating layer satisfies at least one of the following conditions: (1) the coating layer includes a carbon material including at least one of graphene, soft carbon, and hard carbon; (2) the thickness of the coating layer is 0.1 nm to 100 nm; (3) the thickness of the coating layer is 1 nm to 20 nm.

11. The negative electrode material of claim 6, wherein, The silicon-based material satisfies at least one of the following conditions: (1) the average particle size of primary particles of the silicon-based material is 1 nm to 100 nm; (2) the average size of silicon grains in the silicon-based material is 0.5 nm to 15 nm.

12. The negative electrode material of claim 1, wherein, The negative electrode material satisfies at least one of the following conditions: (1) the median particle size of the negative electrode material is 0.2 μm to 15 μm; (2) the specific surface area of the negative electrode material is 0.8 m 2 / g ~ 15 m 2 / g; (3) the powder compaction density of the negative electrode material is 0.8 g / cm 3 ~ 1.5 g / cm 3 .

13. The negative electrode material of claim 1, wherein, The second matrix includes a carbon material, and the content of carbon elements in the negative electrode material is 5% to 70% based on 100% of the mass of the negative electrode material.

14. The negative electrode material of claim 1, wherein, The content of oxygen elements in the negative electrode material is less than or equal to 10% based on 100% of the mass of the negative electrode material.

15. A battery, characterized by The battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the negative electrode sheet comprises the negative electrode material according to any one of claims 1-14.

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