Negative electrode material

Abstract

The present application relates to a negative electrode material. The negative electrode material comprises an inner core and a coating layer located on at least part of the surface of the inner core; the inner core comprises a carbon matrix and a silicon material, and at least part of the silicon material is located in the carbon matrix; and the mass content of the coating layer in the negative electrode material is A% and the powder conductivity of the negative electrode material at 20 kN is ρ S / cm, wherein 4≤A*ρ≤30. In the negative electrode material of the present application, the product relationship between the mass content of the coating layer and the powder conductivity of the negative electrode material is controlled to be within a certain range, thus achieving a balance between the thickness of the coating layer and the powder conductivity, and reducing the occurrence of powder conductivity decrease caused by excessive coating layer thickness, such that the negative electrode material can have good powder conductivity while maintaining the advantage, brought about by the coating layer, of a reduction in side reactions.

Description

Negative electrode material

[0001] The application claims priority to the Chinese patent application No. 202510180277.5, filed on February 18, 2025, and entitled "Negative electrode material", the content of which is incorporated herein by reference. TECHNICAL FIELD

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

[0003] Lithium ion batteries have the advantages of high energy density, long service life and no environmental pollution, and have been widely used in computer, communication and consumer electronics fields. With the development of the market, lithium ion batteries are not only widely used in mobile devices such as smart phones and portable computers, but also applied in large equipment fields such as electric vehicles and electric tools. In order to improve the energy density of the battery, the research and development of silicon-based negative electrode materials are becoming mature. However, the volume expansion of silicon during lithium extraction / insertion is as high as 420%, and the severe volume effect will cause significant degradation of its electrochemical performance, which limits its practical application.

[0004] In order to alleviate the adverse effects of volume expansion of silicon material during charging and discharging, silicon material can be compounded with metal, oxide, organic polymer, carbon and other materials to build a coating layer on the surface of silicon material to improve its electrochemical stability. The mass content of the coating layer and the electrical conductivity of the negative electrode material will affect the electrochemical performance of the negative electrode material, and how to balance the relationship between the two to improve the cycle stability of the negative electrode material is a problem that needs to be solved at present.

[0005] SUMMARY

[0006] The present application provides a negative electrode material, by controlling the product relationship between the mass content of the coating layer in the negative electrode material and the powder electrical conductivity of the negative electrode material under 20kN within a certain range, the balance between the mass content of the coating layer and the powder electrical conductivity of the negative electrode material can be achieved, and the battery prepared by the negative electrode material shows lower electrode polarization and higher cycle stability during the cycle process.

[0007] The present application provides a negative electrode material, the negative electrode material includes a core and a coating layer located on at least part of the surface of the core, the core includes a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix; the mass content of the coating layer in the negative electrode material is A%, and the powder electrical conductivity of the negative electrode material under 20kN is pS / cm, wherein 4≤A*p≤30.

[0008] Compared with the prior art, the technical scheme of the present application has at least the following beneficial effects:

[0009] The negative electrode material includes a core and a coating layer located on at least a portion of the core's surface. The core comprises a carbon matrix and silicon material, with at least a portion of the silicon material located within the carbon matrix. This helps mitigate the volume expansion of the silicon material during lithium insertion / extraction in the battery made from the negative electrode material. The coating layer covers the surface of the core, effectively improving the surface stability of the negative electrode material and reducing direct contact between the core and the electrolyte solution. Batteries made from this negative electrode material exhibit lower electrode polarization and higher cycle stability during cycling. If the coating layer content in the negative electrode material is too high, the specific capacity and lithium-ion transport rate between the negative electrode material particles will decrease. If the coating layer content is too low, the coating layer on the core surface will be discontinuous, allowing the electrolyte to still contact the silicon material through uncovered areas, and side reactions cannot be effectively suppressed. If the powder conductivity of the negative electrode material is too low, it indicates poor conductivity, resulting in high resistance, affecting the battery's charge / discharge efficiency, and extending the battery's charge / discharge time. If the powder conductivity is too high, it may lead to an excessively high electron concentration on the surface of the negative electrode material, thereby triggering more side reactions. Therefore, this application controls the mass content of the coating layer in the negative electrode material to A%, and the powder conductivity of the negative electrode material at 20 kN to ρS / cm, where 4 ≤ A*ρ ≤ 30. By controlling the product of the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material at 20 kN within the above range, a balance can be achieved between the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material. The battery prepared with the negative electrode material exhibits lower electrode polarization and higher cycle stability during cycling. Attached Figure Description

[0010] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application;

[0011] Figure 2 shows a cross-sectional view of the negative electrode material particles prepared using dual-beam focused ion beam microscopy (Dual Beam FIB-SEM). Detailed Implementation

[0012] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0013] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0014] The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting thereof. As used in the description of the embodiments and the appended claims herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0015] It should be understood that the term "and / or" as used herein merely describes associated objects, which can exist in three relationships, for example, A and / or B can represent three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0016] In a first aspect, the embodiments of the present application provide a negative electrode material, the negative electrode material comprising a core and a coating layer located on at least part of the surface of the core, the core comprising a carbon matrix and a silicon material, at least part of the silicon material being located in the carbon matrix;

[0017] The mass content of the coating layer in the negative electrode material is A%, and the powder conductivity of the negative electrode material under 20kN is pS / cm, wherein 4≤A*p≤30. In the present application, the core comprises an active material, and the active material comprises a carbon matrix and a silicon material.

[0018] In the above scheme, the negative electrode material includes an inner core and a coating layer located on at least part of the surface of the inner core. The inner core includes a carbon matrix and a silicon material. At least part of the silicon material is located in the carbon matrix, which can alleviate the volume expansion of the silicon material in the negative electrode material during the lithium intercalation and deintercalation process of the battery prepared from the negative electrode material. The coating layer is coated on the surface of the inner core, which can effectively improve the surface stability of the negative electrode material, reduce the direct contact of the inner core with the electrolyte solution, and the battery prepared from the negative electrode material exhibits lower electrode polarization and higher cycle stability during the cycle process. If the mass content of the coating layer in the negative electrode material is too high, the specific capacity of the negative electrode material and the transmission rate of lithium ions between the negative electrode material particles will decrease. If the mass content of the coating layer in the negative electrode material is too low, it will lead to discontinuity of the coating layer on the surface of the inner core, and the electrolyte can still contact the silicon material through the uncovered area, and the side reactions cannot be effectively inhibited. If the powder conductivity of the negative electrode material is too low, it indicates that the conductivity of the negative electrode material is poor, thereby generating high resistance, affecting the charge and discharge efficiency of the battery, and leading to the prolongation of the charge and discharge time of the battery, etc. If the powder conductivity is too high, it may lead to too high electron concentration on the surface of the negative electrode material, thereby causing more side reactions, for example, it may accelerate the decomposition of the electrolyte or the formation of the SEI film. These side reactions will consume lithium ions, reduce the coulombic efficiency and cycle life of the battery. Therefore, by controlling the mass content of the coating layer in the negative electrode material to be A%, and the powder conductivity of the negative electrode material under 20kN to be pS / cm, where 4≤A*p≤30, the product relationship between the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material is controlled within the above range, the balance between the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material can be achieved, the decrease of the powder conductivity of the negative electrode material caused by the excessive mass content of the coating layer in the negative electrode material is reduced, and the negative electrode material can have good powder conductivity while maintaining the reduction of side reactions brought by the coating layer.

[0019] In some embodiments, 4≤A*p≤30, specifically, it can be 4, 5, 8, 10, 12, 15, 16, 18, 20, 22, 25, 28 or 30, etc., of course, it can also be other values within the above range, which are not limited herein. By controlling the product relationship between the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material under 20kN within the above range, the battery prepared from the negative electrode material can exhibit lower electrode polarization and higher cycle stability during the cycle process.

[0020] In some embodiments, the mass content of the coating layer in the negative electrode material is A%, 1≤A≤10, and the mass content of the coating layer in the negative electrode material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., and can also be other values within the above range, which is not limited herein. The application controls the mass content of the coating layer within the above range, which is beneficial to control the coating integrity of the coating layer on the surface of the negative electrode material particles, reduce the direct contact between the core and the electrolyte solution, and improve the cycle stability of the negative electrode material.

[0021] In some embodiments, the powder conductivity of the negative electrode material at 20 kN is pS / cm, 0.2≤p≤5, and the powder conductivity can be 0.2 S / cm, 0.5 S / cm, 1 S / cm, 1.5 S / cm, 2 S / cm, 3 S / cm, 4 S / cm, 4.5 S / cm, or 5 S / cm, etc., and can also be other values within the above range, which is not limited herein. If the powder conductivity of the negative electrode material is too low, it indicates that the conductivity of the negative electrode material is poor, thereby generating a higher resistance, affecting the charge and discharge efficiency of the battery, and causing the charge and discharge time of the battery to be prolonged, etc. If the powder conductivity is too high, it can cause the electronic concentration on the surface of the negative electrode material to be too high, thereby triggering more side reactions, for example, it can accelerate the decomposition of the electrolyte or the formation of the SEI film, which consumes lithium ions, reduces the coulombic efficiency and cycle life of the battery.

[0022] In some embodiments, the carbon matrix includes at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, porous carbon, and graphene. The carbon matrix selects the above materials, which can all play a supporting role, and also has good electrical conductivity to ensure the electrical conductivity of the negative electrode material.

[0023] In some embodiments, the mass content of carbon in the negative electrode material is 30% to 60%, and can be 30%, 35%, 40%, 45%, 50%, 55%, 56%, 57%, 58%, or 60%, etc., and can also be other values within the above range, which is not limited herein.

[0024] In some embodiments, in the negative electrode material after removal of the silicon material, the volume fraction of the pores with a pore size of less than 5 nm in the total pore volume is ≥ 90%, specifically, 90%, 91%, 93%, 95%, 96%, 97%, 98%, or 99%, and of course, it can also be other values in the above range, which is not limited here. Understandably, the volume fraction of the pores in the negative electrode material after removal of the silicon material is controlled in the above range, and the pores can accommodate most of the silicon material, reduce the silicon segregation formed by the deposition of the silicon material on the surface of the carbon matrix, improve the content and uniformity of the silicon material in the carbon matrix, and thus improve the specific capacity and mechanical properties of the negative electrode material.

[0025] In some embodiments, the total pore volume of the negative electrode material after removal of the silicon material is 0.5 cm 3 / g to 2.0 cm 3 / g, specifically, 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.2 cm 3 / g, 1.5 cm 3 / g, 1.6 cm 3 / g, 1.8 cm 3 / g, or 2.0 cm 3 / g, and of course, it can also be other values in the above range, which is not limited here. Understandably, the negative electrode material after removal of the silicon material has abundant pores, which can accommodate the silicon material and provide space for the volume expansion of the silicon material. Preferably, the total pore volume of all the pores in the negative electrode material after removal of the silicon material is 0.7 cm 3 / g to 1.4 cm 3 / g. In this application, the total pore volume of the negative electrode material containing the silicon material is greatly reduced compared to the negative electrode material after removal of the silicon material, because the silicon material is relatively uniformly filled, so that most of the pores are reduced in volume after filling the silicon material, which indicates that the pores of the carbon matrix are effectively and relatively uniformly filled with the silicon material, thereby improving the specific capacity of the negative electrode material.

[0026] In some embodiments, the coating layer comprises at least one of an oxide of M element and / or a carbon material. The M element comprises at least one of B, Zr, Ni, Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, Hf, Ta, Co, Cr and Zn. The oxide layer of the M element can be coated on the surface of the core in combination with the carbon layer, or the oxide layer of the M element and the carbon layer can be stacked on the surface of the core in sequence, so as to reduce the side reaction of the electrolyte and the silicon material.

[0027] In some embodiments, the coating layer comprises an oxide of M element. The M element comprises at least one of B, Zr, Ni, Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, Hf, Ta, Co, Cr and Zn. The coating layer of the oxide of the M element reacts with the electrolyte to generate a dense, stable and ion-conducting artificial interface layer (SEI), so as to reduce the continuous consumption of active lithium and electrolyte. The oxide coating layer of the M element can also reduce the direct contact between the silicon material and the electrolyte, and inhibit the repeated growth and thickening of the SEI film during the cycle process. In addition, the oxide coating layer of the M element can provide additional mechanical constraint for the core, and better inhibit the volume expansion of the negative electrode material.

[0028] In some embodiments, the coating layer comprises a carbon material. When the coating layer comprises the carbon material, the formed carbon coating layer is beneficial to improve the stability and conductivity of the core. The carbon coating layer can also coat the silicon material exposed on the surface of the core, reduce the continuous oxidation of the exposed silicon material during the placement process, and reduce the risk of reducing the specific capacity and the initial coulombic efficiency (ICE) of the negative electrode material. The carbon coating layer can also reduce the direct contact between the silicon material and the electrolyte, improve the stability of the SEI film, and thus improve the initial coulombic efficiency of the negative electrode material.

[0029] In some embodiments, the average thickness of the coating layer is d, and the median particle size of the negative electrode material is D 50 D, wherein the ratio of d / D ranges from 0.5% to 5%, and specifically can be 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, and of course can also be other values within the above range, which are not limited herein. The thickness ratio of the coating layer, i.e., d / D, within the above range is beneficial to balance the initial coulombic efficiency, cycle stability and capacity of the negative electrode material.

[0030] In some embodiments, the average thickness of the coating layer is d, where 5nm ≤ d ≤ 500nm. The specific value of d can be 5nm, 10nm, 50nm, 100nm, 200nm, 300nm, 400nm, or 500nm, or other values ​​within the above range, and is not limited here. An average coating layer within the above range, with an intact coating layer and a suitable thickness, can reduce direct contact between the core and the electrolyte, thereby reducing the solubility of the negative electrode material and the occurrence of side reactions on the surface of the negative electrode material, thus improving the cycle stability of the negative electrode material. Simultaneously, a suitable coating layer thickness also helps to maintain the powder conductivity and ion transport rate of the negative electrode material within an optimal range.

[0031] In some embodiments, the median particle size D of the negative electrode material 50 For D, 1μm≤D≤20μm, specifically it can be 1μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, or 20μm, etc., and of course, it can also be other values ​​within the above range, which are not limited here. The median particle size of the negative electrode material is within the above range, which is beneficial to the improvement of the cycle performance of the negative electrode material.

[0032] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.2cm 3 / g, specifically 0.001cm 3 / g, 0.005cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.05cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.18cm 3 / g or 0.2cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. After filling with silicon material, the remaining pores can reserve space for the volume expansion of silicon material, alleviate the expansion effect of the negative electrode material, improve the cycle stability of the negative electrode material, and can also adsorb or contain some of the small amount of gas generated by the side reaction between silicon material and electrolyte, improving the gas generation phenomenon of the negative electrode material. At the same time, if the total pore volume of the negative electrode material is within the above range, it can effectively reduce the amount of electrolyte that directly penetrates into the interior of the negative electrode material through the pore structure, reduce the side reaction that occurs when the electrolyte comes into contact with silicon material, and improve the cycle performance of lithium-ion batteries.

[0033] In some embodiments, the average pore size of the negative electrode material is 0.45 nm to 50 nm, and can be 0.45 nm, 0.5 nm, 0.8 nm, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 45 nm or 50 nm, or other values within the above range, which are not limited herein. If the pore size of the negative electrode material is too large, the tap density of the material will decrease, thereby reducing the volumetric energy density of the negative electrode material, and the electrolyte can be more easily decomposed in the pores. If the pore size of the negative electrode material is too small, the specific surface area is large, the contact area with the electrolyte is large, and the lithium and electrolyte consumed in the formation of the SEI film are large, thereby reducing the initial efficiency of the negative electrode material.

[0034] In some embodiments, the at least part of the silicon material is distributed on at least part of the surface of the carbon matrix.

[0035] In some embodiments, the silicon material includes at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, and composite particles of crystalline silicon and amorphous silicon, and the type of the silicon material can be selected as required, which is not limited herein.

[0036] In some embodiments, the silicon material includes amorphous silicon and / or crystalline silicon; preferably, the silicon material includes amorphous silicon, which isotropically expands during lithium intercalation, thereby reducing the collapse of the pore structure, inhibiting the rapid decay of the specific capacity of the battery prepared from the negative electrode material, and improving the lithium intercalation cycle performance of the battery prepared from the negative electrode material.

[0037] In some embodiments, the morphology of the silicon material includes at least one of a point shape, a spherical shape, an ellipsoidal shape, and a sheet shape, and the morphology of the silicon material can be selected as required, which is not limited herein.

[0038] In some embodiments, the mass content of silicon in the negative electrode material is 40% to 55%, and can be 40%, 42%, 45%, 48%, 50%, 51%, 52%, 53%, 54% or 55%, or other values within the above range, which is not limited herein. Controlling the mass content of silicon within the above range can effectively control the volume expansion of the negative electrode material and the capacity of the negative electrode material. Preferably, the mass content of silicon in the negative electrode material is 45% to 55%.

[0039] In some embodiments, the tap density of the negative electrode material is 0.8 cm 3 / g to 1.5 cm 3 / g, and can be 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.1 cm 3 / g, 1.2 cm 3 / g, 1.3 cm / g.3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., can also be other values ​​within the above range, and are not limited here. Compacted density refers to the density of a material during the compaction process, and is commonly used to describe the compactness of battery materials. In the manufacturing process of lithium-ion batteries, compacted density has a significant impact on battery performance. The higher the compacted density, the higher the battery capacity is generally; therefore, compacted density is also considered one of the reference indicators for material energy density. Controlling the compacted density within the above range is beneficial for improving the capacity of the negative electrode material. If the compacted density is too low, the capacity of the negative electrode material will be too low. If the compacted density is too high, it may increase the internal resistance of the battery, thereby affecting the battery's charge and discharge efficiency.

[0040] In some implementations, the tap density of the negative electrode material is 0.5 cm⁻¹. 3 / g~1.5cm 3 / g, specifically 0.5cm 3 / g, 0.6cm 3 / g, 0.8cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g1.3 cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g, etc., and of course, other values ​​within the above range are also possible, and are not limited here. Tap density refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions. Tap density reflects the packing density of material particles, and a high tap density is beneficial for improving the volumetric energy density of the battery. Both excessively high and excessively low tap densities are detrimental to the processing performance of the negative electrode material.

[0041] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g, specifically 0.5m 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g or 10m 2etc., and of course can also be other values within the above range, which are not limited herein. The specific surface area of the negative electrode material will affect the contact area between the negative electrode material and the electrolyte. The specific surface area of the negative electrode material within the above range can reduce the amount of lithium ions consumed by the SEI film formed during the first charge-discharge process of the lithium ion battery, and reduce the irreversible capacity loss of the lithium ion battery.

[0042] In some embodiments, the negative electrode material 24h has a gas production amount ≤1 mL / g at room temperature, specifically 1 mL / g, 0.9 mL / g, 0.8 mL / g, 0.7 mL / g, 0.6 mL / g, 0.5 mL / g, 0.4 mL / g, 0.3 mL / g, 0.2 mL / g, 0.1 mL / g, or 0.05 mL / g, etc., and of course can also be other values within the above range, which are not limited herein. The gas production value of the negative electrode material of the present application is controlled within the above range, which shows that the negative electrode material has a high surface density. The coating layer of the negative electrode material has a high density and good coating effect, thereby effectively reducing the direct contact between the silicon material in the negative electrode material and the electrolyte, and reducing the side reaction between the dissolved silicon material in the negative electrode material and the electrolyte.

[0043] In a second aspect, the present application provides a preparation method of the above negative electrode material, comprising the following steps:

[0044] Step S100, preparing an inner core, the inner core comprising a carbon matrix and a silicon material, at least part of the silicon material being located in the carbon matrix;

[0045] Step S200, subjecting a mixed solution of the inner core and a hydrate of an oxide containing an M element to standing, washing, and drying treatment to obtain a precursor; wherein the molar ratio of the inner core to the hydrate of the oxide of the M element is 10:1-2:1, the concentration of the hydrate of the oxide of the M element is 1 mol / L-5 mol / L, and the M element comprises at least one of B, Zr, Ni, Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, Hf, Ta, Co, Cr, and Zn;

[0046] Step S300, subjecting the precursor to heat treatment at 200°C-600°C for 1h-5h under a protective atmosphere to obtain the negative electrode material, wherein the mass content of the coating layer in the negative electrode material is A%, and the powder conductivity of the negative electrode material under 20kN is pS / cm, wherein 4≤A*p≤30.

[0047] In the above scheme, first, the core is prepared, the core comprising a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix to alleviate the volume expansion of the silicon material in the negative electrode material during the lithium intercalation and deintercalation process of the battery prepared by the negative electrode material; then the mixture solution of the hydrate of the oxide containing the M element and the core is subjected to standing, washing and drying treatment to obtain a precursor. By controlling the molar ratio of the hydrate of the oxide of the M element to the core and the concentration of the hydrate of the oxide of the M element, the hydrate of the oxide of the M element has good stability and uniform dispersion, and the agglomeration of the hydrate of the oxide of the M element is reduced, so that the hydrate of the oxide of the M element can uniformly and completely coat the surface of the core, and the coating amount of the hydrate of the oxide of the M element on the surface of the core can also be controlled. Finally, the precursor is subjected to heat treatment, and the hydrate of the oxide of the M element can uniformly and completely coat the surface of the core and has a suitable coating amount. The hydrate of the oxide of the M element coated on the surface of the core is decomposed to form the oxide of the M element after heat treatment. By controlling the temperature and time of heat treatment, the oxide of the M element can form a uniform and complete coating layer with a suitable thickness on the surface of the core, which can effectively improve the surface stability of the negative electrode material, reduce the direct contact of the core with the electrolyte solution, thereby reducing the dissolution of the negative electrode material in the battery prepared by the negative electrode material during the cycle process, and further inhibiting the occurrence of the side reaction on the surface of the negative electrode material in the battery prepared by the negative electrode material during the continuous cycle process, greatly reducing the accumulation of the electrochemically inert byproduct on the electrode surface, thereby reducing the impedance when the electrode electrochemical reaction occurs in the subsequent cycle process, exhibiting lower electrode polarization and higher cycle stability during the cycle process, and effectively reducing the gas production value of the negative electrode material. The mass content A% of the coating layer in the negative electrode material and the product A*ρ of the mass content A% and the powder conductivity pS / cm of the negative electrode material at 20kN are between 4 and 30, which can balance the thickness of the coating layer and the powder conductivity, reduce the decrease of the powder conductivity caused by the over-thick coating layer, and make the negative electrode material have good powder conductivity while maintaining the advantage of reducing the side reaction caused by the coating layer.

[0048] The preparation method of the application will be specifically described below in combination with examples:

[0049] In step S100, the core is prepared, the core comprising a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix.

[0050] In some embodiments, the carbon matrix comprises at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, porous carbon and graphene. It can be understood that the carbon matrix is selected from the above-mentioned materials, which can all play a supporting role, and also has good electrical conductivity to ensure the electrical conductivity of the negative electrode material.

[0051] In some embodiments, the total pore volume of the carbon matrix is 0.5 cm 3 / g~2.0 cm 3 / g, specifically 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1.0 cm 3 / g, 1.2 cm 3 / g, 1.5 cm 3 / g, 1.6 cm 3 / g, 1.8 cm 3 / g, or 2.0 cm 3 / g, etc., and of course can also be other values within the above range, which are not limited herein. Understandably, the carbon matrix has abundant pores that can accommodate the silicon material and reserve space for the volume expansion of the silicon material. Preferably, the total pore volume of the carbon matrix is 0.7 cm 3 / g~1.4 cm 3 / g.

[0052] In some embodiments, the morphology of the silicon material includes at least one of a point, a sphere, an ellipsoid, and a sheet, which can be selected according to actual needs, which are not limited herein.

[0053] In some embodiments, the purity of the silicon material is greater than 99%, and it is understood that high-purity silicon material is conducive to Li-Si alloying with lithium and improves the cycle performance of the lithium ion battery.

[0054] In some embodiments, the step of preparing the core includes: depositing the silicon material on the carbon matrix having pores to obtain the core.

[0055] In some embodiments, the deposition of the silicon material is by gas-phase chemical deposition, and the step includes: introducing a gas-phase silicon source into the carbon matrix having pores to perform a gas-phase chemical deposition reaction.

[0056] In some embodiments, the gas-phase silicon source includes at least one of silane, disilane, trisilane, and tetrasilane, which can be selected according to actual needs, which are not limited herein.

[0057] In some embodiments, the introduced gas includes a silicon-containing gas source and an auxiliary carrier gas, which can dilute the silicon-containing gas source and help control the residence time of the silicon-containing gas source. The auxiliary carrier gas includes at least one of nitrogen, argon, helium, and hydrogen.

[0058] In some embodiments, the flow ratio of the silicon-containing gas source and the auxiliary carrier gas is 1:(0-10), which can be 1:0, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:10, or the like, and can also be other values within the range, which can be selected within the above range according to actual needs.

[0059] In some embodiments, the concentration of the silicon-containing gas source is 10%-80%, which can be 10%, 13%, 18%, 26%, 35%, 43%, 55%, 68%, 74%, 80%, or the like, and can also be other values within the range, which can be selected within the above range according to actual needs, which is not limited herein.

[0060] In some embodiments, the temperature of the gas-phase chemical deposition reaction is 400-600°C, which can be 400°C, 420°C, 450°C, 480°C, 500°C, 550°C, 600°C, or the like, and can also be other values within the range, which can be selected within the above range according to actual needs, which is not limited herein. Preferably, the temperature of the gas-phase chemical deposition reaction is 450-550°C.

[0061] In some embodiments, the holding time of the gas-phase chemical deposition reaction is 1-20h, which can be 1h, 3h, 4h, 6h, 7h, 8h, 10h, 12h, 15h, 18h, 20h, or the like, and can also be other values within the range, which can be selected according to actual needs, which is not limited herein. Preferably, the holding time of the gas-phase chemical deposition reaction is 2-10h.

[0062] By controlling the reaction parameters of the gas-phase chemical deposition, the gas-phase silicon source can penetrate into the carbon matrix and decompose in the pores of the carbon matrix to form silicon materials with appropriate particle size.

[0063] In step S200, the mixture of the hydrate of the oxide of the M element and the core is subjected to standing, washing, and drying treatment to obtain a precursor. The molar ratio of the core to the hydrate of the oxide of the M element is 10:1-2:1, and the concentration of the hydrate of the oxide of the M element is 1-5 mol / L. The M element includes at least one of B, Zr, Ni, Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, Hf, Ta, Co, Cr, and Zn.

[0064] In some embodiments, the specific steps of preparing the mixed solution of the hydrate of the oxide of the M element and the core include: adding the hydrate of the oxide of the M element into water, then adding the core under stirring, and continuously stirring at 80-90°C for 1h to uniformly disperse the hydrate in the water.

[0065] The stirring temperature can be specifically 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, etc., without being limited herein. When the stirring temperature is greater than 90°C, the increased temperature increases the collision between the core particles, so that some of the core particles appear to be agglomerated, thus two or even more core particles can be coated at the same time, so that the average particle size of the coated negative electrode material increases.

[0066] In some embodiments, the molar ratio of the core to the hydrate of the oxide of the M element is 10:1 to 2:1, which can be specifically 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1 or 2:1, etc., and of course can also be other values within the above range, without being limited herein. If the molar ratio of the core to the hydrate of the oxide of the M element is greater than 10:1, i.e., the content of the hydrate of the oxide of the M element is too small, although its dispersibility in the mixed solution will be improved, the coating layer on the surface of the core will be incomplete, increasing the direct contact between the core and the electrolyte solution, thus increasing the side reaction between the negative electrode material and the electrolyte, resulting in the decrease of the cycle performance of the negative electrode material. If the molar ratio of the core to the hydrate of the oxide of the M element is less than 2:1, i.e., the content of the hydrate of the oxide of the M element is too much, the coating layer will be too thick, thus hindering the transport of lithium ions between the negative electrode material particles, affecting the electrochemical performance of the negative electrode material.

[0067] In some embodiments, the concentration of the hydrate of the oxide of the M element is 1-5 mol / L, and can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L, and can also be other values within the above range, which are not limited herein. When the concentration of the hydrate of the oxide of the M element reaches a certain value, the ionic strength of the solution increases and the surface potential of the hydrate of the oxide of the M element decreases due to the presence of the supersaturation concentration, and the oxide is more inclined to homogeneous nucleation rather than adhering to the surface of the inner core, so that the stress caused by the volume expansion of the block / floc oxide formed in the first charge-discharge process is too large, so that the oxide is separated from the current collector and becomes an inert substance, resulting in low reversible specific capacity of the negative electrode material. At the same time, when the concentration of the hydrate of the oxide of the M element is too high, the different inner core particles can be further bonded, so that the inner core is unstable and agglomerated before being coated, so that the oxide is coated with multiple inner core particles, resulting in an increase in the particle size of the negative electrode material after coating. When the concentration of the hydrate of the oxide of the M element is too low, part of the hydrate of the oxide is not deposited on the surface of the inner core particle, which can easily cause the coating layer on the surface of the inner core to be incomplete, so that part of the inner core is not completely protected and is exposed to the electrolyte solution, and the negative electrode material is easily reacted with the electrolyte solution and continuously generates unstable SEI film, consumes the electrolyte solution, and causes the electrochemical performance of the negative electrode material to decrease.

[0068] In some embodiments, the hydrate of the oxide of the M element can be H3BO3, ZrOCl2·8H2O, Na2SiO3·9H2O, Al(NO3)3·9H2O, Ni(NO3)2·6H2O, MgCl2·6H2O, Cu(NO3)2·6H2O, Co(CH3COO)2·4H2O, Fe(NO 3)3 ·9H2O, etc., which can be selected according to actual needs, which are not limited herein.

[0069] In some embodiments, before the mixed solution is subjected to the standing treatment, the above method comprises: adding a pH adjusting agent to the mixed solution to adjust the pH of the mixed solution to 3-6. Specifically, the pH of the mixed solution can be 3, 3.5, 3.8, 4, 4.5, 5, 5.1, 5.3, 5.6, 5.8 or 6, etc., which can be selected according to actual needs, and is not limited herein. It can be understood that the core will be dissolved out during the coating process, and the dissolution amount is closely related to the pH value of the reaction; the cycle stability of the product obtained under different pH conditions is different. When the coating process is carried out under alkaline conditions, a large amount of the core will be dissolved and lost, although the silicon material in the core is oxidized to form silicate during the alkaline coating process, which makes the cycle stability of the corresponding product (i.e. the negative electrode material) significantly improved, but it will lead to the decrease of the discharge capacity and the first coulomb efficiency of the negative electrode material. In order to maximize the cycle stability of the negative electrode material while not reducing its discharge capacity and first coulomb efficiency, it is appropriate to carry out wet coating under neutral to slightly acidic conditions.

[0070] In some embodiments, the pH adjusting agent comprises at least one of excess ground H2CO3, H3BO3, CH3COOH or H3PO4, which can be selected according to actual needs, and is not limited herein again. The addition amount of the pH adjusting agent is not specifically limited, as long as it can adjust the pH of the mixed solution to the range of 3-6.

[0071] In some embodiments, the standing is carried out at room temperature, and the standing time is 5h.

[0072] In some embodiments, the solvent used for washing is distilled water, and the washing is carried out 3 times.

[0073] In some embodiments, the drying treatment is carried out at a temperature of 80℃ for 24h.

[0074] Step S300, the precursor is subjected to heat treatment at 200℃-600℃ for 1h-10h under a protective atmosphere to obtain a negative electrode material, wherein the mass content of the coating layer in the negative electrode material is A%, and the powder conductivity of the negative electrode material under 20kN is pS / cm, wherein 4≤A*p≤30.

[0075] In some embodiments, the protective atmosphere comprises at least one of nitrogen, argon, helium, neon, which can be selected according to actual needs, and is not limited herein.

[0076] In some embodiments, the temperature of the heat treatment is 200-600°C, and can be specifically 200°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, and can also be other values within the above range, which are not limited herein. The heat treatment temperature affects the speed of hydrolysis of the coating agent (i.e. the oxide hydrate). As the heat treatment temperature increases, the hydrolysis rate increases, and the coating layer attached to the surface of the core particle becomes more and more dense. When the temperature is too high, the structure of the coating layer is likely to be destroyed, thereby affecting the transmission of lithium ions. When the heat treatment temperature is too low, the coating layer on the surface of the core particle is not completely or uniformly coated, and the coating layer on the surface of the core particle is easily detached during the charging and discharging process, thereby increasing the direct contact between the core and the electrolyte and continuously reacting with the electrolyte to generate an unstable solid electrolyte interface film (SEI film) to consume more lithium ions, thereby affecting the capacity of the negative electrode material, causing poor electrical contact of the negative electrode material, decreasing the stability of lithium ion transmission, and causing the capacity of the negative electrode material to fluctuate.

[0077] In some embodiments, the heat treatment time is 1-10h, and can be specifically 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 6h, 8h or 10h, and can also be other values within the above range, which are not limited herein. The heat treatment time can affect the particle size of the negative electrode material before and after coating and the efficiency in the actual production process. If the heat treatment time is too short, the coating material cannot be completely attached to the surface of the core particle, which can expose the core particle to the electrolyte and cause corrosion during the battery cycle to break the electrode structure. If the heat treatment time is too long, the roughness of the negative electrode material becomes more uniform, and the surface of the negative electrode material has more pores, which are beneficial to the infiltration of the electrolyte and the transmission of lithium ions to some extent, thereby improving the capacity and cycle stability of the negative electrode material. However, when the material heat treatment time is too long, the coating layer formed on the surface of the core particle is too thick, which hinders the transmission of lithium ions and affects the outward expansion of silicon when lithium is inserted, thereby limiting the depth of lithium insertion, decreasing the discharge capacity and the first coulombic efficiency of the negative electrode material, and affecting the electrochemical performance.

[0078] In the present application, by controlling the heat treatment temperature / time, adjusting the content and concentration of the oxide hydrate of the M element in the mixed solution, the pH value of the mixed solution and the stirring temperature, etc., a complete and dense coating layer can be formed on the surface of the core particle. In addition, because the coating layer cannot be a completely dense structure, and considering the problem of electrolyte infiltration, by adjusting the above parameters, the porosity of the negative electrode material meets certain conditions, thereby ensuring the good performance of the coating layer.

[0079] In a third aspect, the present application provides a preparation method of the above negative electrode material, comprising the following steps:

[0080] Step S10, a mixed solution containing silicon particles and dispersant is prepared, the mixed solution is mixed with a flocculation solution, and solid-liquid separation is performed to obtain a first composite.

[0081] In some embodiments, the silicon particles include at least one of crystalline silicon, amorphous silicon, and silicon alloy.

[0082] The silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, or the like. In some cases, the silicon particles include amorphous silicon and silicon alloy. Preferably, the silicon particles include amorphous silicon, which isotropically expands during lithium intercalation, can reduce the collapse of the pore structure, inhibit the rapid decay of the specific capacity, and improve the lithium intercalation cycle performance.

[0083] In some embodiments, the average particle size of the silicon particles is 1 nm to 50 nm, and can be 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or 50 nm, or the like, without being limited herein.

[0084] In some embodiments, the dispersant includes at least one of stearic acid, sodium stearate, zinc stearate, magnesium stearate, calcium stearate, polyvinylpyrrolidone, carboxymethyl cellulose, and polyacrylic acid.

[0085] In some embodiments, the mass ratio of the silicon particles to the dispersant is 100:(20-100), and can be 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, or 100:100, or the like, or other values within the above range, without being limited herein. It can be understood that the appropriate dispersant can improve the dispersion degree of the silicon particles in the mixed solution, reduce the agglomeration of the silicon particles, and further improve the dispersion degree of the silicon particles in the first composite.

[0086] In some embodiments, the mixed solution further includes a solvent, and the solvent includes at least one of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, glycerol, n-butanol, isobutanol, amyl alcohol, and ethyl acetate.

[0087] In some embodiments, the mixing process is performed under stirring.

[0088] In some embodiments, the mixing process is performed for 0.5 h to 3 h, and can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, or the like, or other values within the above range, without being limited herein.

[0089] In some embodiments, the step of solid-liquid separation includes filtering the mixed solution after the flocculation solution is added, and freeze-drying to obtain the first composite.

[0090] In some embodiments, the mass ratio of the silicon particles to the flocculation liquid is 1:(1-1.3), which can be 1:1, 1:1.05, 1:1.08, 1:1.1, 1:1.2, 1.25 or 1:1.3, and can also be other values within the above range, which are not limited herein.

[0091] In some embodiments, the solid content of the flocculation liquid is 0.1%-0.5%, which can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, and can also be other values within the above range, which are not limited herein.

[0092] In some embodiments, the flocculation liquid comprises a flocculating agent, and the flocculating agent comprises at least one of an inorganic flocculating agent and an organic flocculating agent.

[0093] In some embodiments, the inorganic flocculating agent comprises at least one of aluminum sulfate, aluminum chloride, iron sulfate and iron chloride.

[0094] In some embodiments, the organic flocculating agent comprises at least one of polyaluminum chloride, polyaluminum sulfate and polyacrylamide.

[0095] In the present application, the flocculation liquid is added to the mixed liquid, so that the dispersed nanoscale silicon particles are precipitated in a flocculation state. However, due to the dispersant on the surface of the silicon particles, the silicon particles in the flocculation product still remain in a mutually independent dispersed state.

[0096] In some embodiments, the temperature of the freeze-drying is -20℃ to -30℃, which can be -20℃, -22℃, -24℃, -25℃, -27℃, -28℃ or -30℃, and is not limited herein.

[0097] In some embodiments, the time of the freeze-drying is 10h-24h, which can be 10h, 12h, 15h, 18h, 20h, 22h or 24h, and is not limited herein. Through the freeze-drying treatment, the nanoscale silicon particles can be uniformly dispersed in the dispersant.

[0098] In step S20, the first composite is mixed with a carbon source precursor and then subjected to a preheating treatment to obtain a second composite.

[0099] In some embodiments, the carbon source precursor comprises at least one of sucrose, glucose, polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride and pitch.

[0100] In some embodiments, the mass ratio of the silicon particles to the carbon source precursor is 100:(100-250), which can be 100:100, 100:115, 100:130, 100:150, 100:180, 100:200, 100:220, 100:230, or 100:250, and the like, and of course, other values within the above range are also possible, which are not limited herein.

[0101] In some embodiments, the temperature of the pre-heating treatment is 150-350°C, which can be 150°C, 200°C, 250°C, 280°C, 300°C, 320°C, or 350°C, and the like, which are not limited herein.

[0102] In some embodiments, the time of the pre-heating treatment is 2-15h, which can be 2h, 3h, 5h, 8h, 10h, 12h, or 15h, and the like, which are not limited herein.

[0103] In some embodiments, the pre-heating treatment is performed under stirring.

[0104] By controlling the temperature, time, and state of the pre-heating, the dispersant reaches the boiling point and volatilizes, and the carbon source precursor is sufficiently pre-heated, softened, and penetrated to replace the dispersant on the surface of the silicon particles.

[0105] In step S30, the second composite is subjected to carbonization treatment to obtain a core, which includes a silicon material and a carbon material.

[0106] In some embodiments, the temperature of the carbonization treatment is 700-1000°C, which can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 980°C, or 1000°C, and the like, and of course, other values within the above range are also possible, which are not limited herein.

[0107] In some embodiments, the time of the carbonization treatment is 1-10h, which can be 1h, 2h, 3h, 4h, 5h, 6h, 8h, 9h, or 10h, and the like, which are not limited herein.

[0108] In some embodiments, the heating rate of the carbonization treatment is 2-10°C / min, which can be 2°C / min, 4°C / min, 5°C / min, 6°C / min, 8°C / min, 9°C / min, or 10°C / min, and the like, which are not limited herein.

[0109] In some embodiments, the carbonization treatment is performed under a protective gas.

[0110] In some embodiments, the carbonization treatment is performed under a protective gas, which includes at least one of nitrogen, helium, neon, argon, and krypton.

[0111] In some embodiments, the method further comprises: shaping, sizing, and grading the carbonized product, the shaping comprising at least one of pulverizing, milling, ball milling, and jet milling.

[0112] In some embodiments, the core prepared in step S30 is subjected to the operations in steps S200-S300 of the method for preparing the negative electrode material of the second aspect described above, to obtain the negative electrode material.

[0113] In a fourth aspect, the embodiments of the present application also provide a battery. FIG. 1 is a schematic diagram of a discharging state of a battery provided by the embodiments of the present application. As shown in FIG. 1, the battery comprises a shell and an electrode assembly. The electrode assembly comprises a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is arranged between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly can be a laminated structure, which is formed by alternately stacking the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 in sequence. In other embodiments, the electrode assembly can also be a wound structure, which is formed by winding the positive electrode sheet, the separator, and the negative electrode sheet stacked in sequence.

[0114] In some embodiments, the positive electrode sheet 1 comprises a positive electrode current collector 101 and a positive electrode active layer 102 arranged on at least one surface of the positive electrode current collector 101.

[0115] In some embodiments, the positive electrode current collector 101 can be made of an aluminum foil or a nickel foil, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) and a polymer substrate. The positive electrode active layer 102 comprises a positive electrode active material, which includes a compound capable of reversibly intercalating and deintercalating metal ions.

[0116] In some embodiments, the positive electrode active material can include a lithium transition metal composite oxide, a sodium transition metal composite oxide, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0117] In some embodiments, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganate (LiNiMnO4), or lithium iron phosphate (LiFePO4). 4) 0.5 Mn 1.5 O4) or lithium iron phosphate (LiFePO4).

[0118] In some embodiments, the negative electrode sheet 2 comprises a negative electrode current collector 201 and a negative electrode active material layer 202 arranged on at least one surface of the negative electrode current collector.

[0119] ​In some embodiments, the negative current collector 201 can use at least one of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, or a carbon-based current collector, etc., and can also be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foils and polymer substrates. The negative active material layer 202 includes a negative electrode material, which is the negative electrode material of the first aspect described above or the negative electrode material prepared by the preparation method described above.

[0120] The battery provided by the embodiments 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.

[0121] Embodiment 1

[0122] (1) Put the carbon matrix with holes (porous carbon) into a chemical vapor deposition (CVD) device, then introduce a mixed gas of silane (concentration of 45%) and auxiliary carrier gas (N2, Ar, concentration of 55%) into the CVD device, heat to 500°C, and perform vapor deposition reaction for 10 h to obtain an inner core.

[0123] (2) Add deionized water to the hydrated compound of the oxide (Na2SiO3·9H2O), then add the inner core under stirring, the molar ratio of the inner core to the hydrated compound of the oxide (Na2SiO3·9H2O) is 5:1, the concentration of the hydrated compound of the oxide (Na2SiO3·9H2O) is 2 mol / L, and continuously stir at 80°C for 1 h to obtain a mixed solution; then add excess ground H2CO3 to adjust the pH to 5, and place at room temperature for 5 h, then wash with distilled water for 3 times, and dry at 80°C for 24 h to obtain a precursor.

[0124] (3) Calcine the precursor at 400°C for 2 h under N2 protection to obtain a negative electrode material.

[0125] The negative electrode material prepared in this embodiment includes an inner core and a coating layer located on at least part of the surface of the inner core, the inner core includes a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0126] Embodiment 2

[0127] Different from embodiment 1, the hydrated compound of the oxide in step (2) is replaced by Al(NO3)3·9H2O, and the rest of the operations are the same as those in embodiment 1.

[0128] The negative electrode material prepared in this embodiment includes an inner core and a coating layer located on at least part of the surface of the inner core, the inner core includes a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is Al2O3, and the silicon material is amorphous silicon.

[0129] Example 3

[0130] The difference between Example 1 and this example is that the hydrate of the oxide in step (2) is replaced by Ni(NO3)2·6H2O, and the rest of the operations are the same as those in Example 1.

[0131] The negative electrode material prepared in this example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is NiO, and the silicon material is amorphous silicon.

[0132] Example 4

[0133] The difference between Example 1 and this example is that the hydrate of the oxide in step (2) is replaced by Cu(NO3)2·6H2O, and the rest of the operations are the same as those in Example 1.

[0134] The negative electrode material prepared in this example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is CuO, and the silicon material is amorphous silicon.

[0135] Example 5

[0136] The difference between Example 1 and this example is that the hydrate of the oxide in step (2) is replaced by MgCl2·6H2O, and the rest of the operations are the same as those in Example 1.

[0137] The negative electrode material prepared in this example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is MgO, and the silicon material is amorphous silicon.

[0138] Example 6

[0139] The difference between Example 1 and this example is that the hydrate of the oxide in step (2) is replaced by Co(CH3COO)2·4H2O, and the rest of the operations are the same as those in Example 1.

[0140] The negative electrode material prepared in this example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is CoO, and the silicon material is amorphous silicon.

[0141] Example 7

[0142] The difference between Example 1 and this example is that the hydrate of the oxide in step (2) is replaced by Fe(NO3)2·9H2O, and the rest of the operations are the same as those in Example 1.

[0143] The negative electrode material prepared in the embodiment comprises a core and a coating layer on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is in the carbon matrix, the coating layer is Fe2O3, and the silicon material is amorphous silicon.

[0144] Example 8

[0145] Different from Example 1, the hydrate of the oxide in step (2) is replaced by H3BO3, and the rest of the operations are the same as those in Example 1.

[0146] The negative electrode material prepared in the embodiment comprises a core and a coating layer on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is in the carbon matrix, the coating layer is B2O3, and the silicon material is amorphous silicon.

[0147] Example 9

[0148] Different from Example 1, the hydrate of the oxide in step (2) is replaced by ZrOCl2·8H2O, and the rest of the operations are the same as those in Example 1.

[0149] The negative electrode material prepared in the embodiment comprises a core and a coating layer on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is in the carbon matrix, the coating layer is ZrO2, and the silicon material is amorphous silicon.

[0150] Example 10

[0151] Different from Example 1, the molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 10:1, and the rest of the operations are the same as those in Example 1.

[0152] The negative electrode material prepared in the embodiment comprises a core and a coating layer on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0153] Example 11

[0154] Different from Example 1, the molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 3:1, and the rest of the operations are the same as those in Example 1.

[0155] The negative electrode material prepared in the embodiment comprises a core and a coating layer on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0156] Example 12

[0157] Different from Example 1, the stirring temperature in step (2) is 90°C.

[0158] The negative electrode material prepared in the comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0159] Example 13

[0160] Different from Example 1, the pH of the mixed solution in step (2) is 6.

[0161] The negative electrode material prepared in the comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0162] Example 14

[0163] Different from Example 1, (3) the precursor is calcined at 200°C for 2h under N2protection to obtain the negative electrode material.

[0164] The negative electrode material prepared in the comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0165] Example 15

[0166] Different from Example 1, (3) the precursor is calcined at 600°C for 2h under N2protection to obtain the negative electrode material.

[0167] The negative electrode material prepared in the comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0168] Example 16

[0169] Different from Example 1, (3) the precursor is calcined at 400°C for 10h under N2protection to obtain the negative electrode material.

[0170] The negative electrode material prepared in the comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0171] Example 17

[0172] The difference between Example 1 is that the molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 10:1, the pH of the mixed solution is 6, and the rest of the operation is the same as Example 1.

[0173] Example 18

[0174] The difference between Example 1 is that step (4) is increased.

[0175] (4) The precursor calcined at 400°C for 2h under N2protection is placed in a CVD device, then acetylene and N2are introduced into the CVD device, the volume ratio of acetylene and N2introduced is 2:3, the temperature is raised to 580°C for coating reaction, the reaction time is 10h, and the deposition pressure is set to 5kPa, to obtain the negative electrode material.

[0176] Example 19

[0177] (1) Take 1Kg of nano-silicon particles, disperse them in an aqueous solution, then add 500g of polyvinylpyrrolidone, stir and disperse for 1h, then add 1Kg of polyacrylamide solution with a solid content of 0.5% to it, stir for 10min, then stand for 5min, centrifuge the solution after standing, and freeze-dry the sample after centrifugation at -30°C for 24h to obtain a first composite.

[0178] (2) Place the first composite in a VC hybrid heating machine, add asphalt according to a mass ratio of nano-silicon: asphalt of 100:185, raise the temperature of the machine to 350°C under stirring, mix for 2h, then take out the material to obtain a second composite.

[0179] (3) Place the second composite in a box furnace, introduce nitrogen, then raise the temperature to 800°C at a rate of 3°C / min, keep the temperature for 3h, then naturally cool, crush the product with a mechanical crusher, and pass it through a 325 mesh sieve to obtain a core, which includes silicon material and carbon material.

[0180] (4) Add deionized water to the hydrate compound of the oxide (Na2SiO3·9H2O), then add the above-mentioned core under stirring, the molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) is 5:1, the concentration of the hydrate of the oxide (Na2SiO3·9H2O) is 2mol / L, and the stirring is continued at 80°C for 1h to obtain a mixed solution; then add an excess of ground H2CO3, adjust the pH to 5, stand at room temperature for 5h, then wash with distilled water for 3 times, and dry at 80°C for 24h to obtain a precursor.

[0181] (5) Calcine the precursor at 400°C for 2h under N2protection to obtain a negative electrode material.

[0182] Comparative Example 1

[0183] The molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 20:1, which is different from that in Example 1.

[0184] The negative electrode material prepared in the present comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0185] Comparative Example 2

[0186] The molar ratio of the core to the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 1:1, which is different from that in Example 1.

[0187] The negative electrode material prepared in the present comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0188] Comparative Example 3

[0189] The concentration of the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 0.5 mol / L, which is different from that in Example 1.

[0190] The negative electrode material prepared in the present comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0191] Comparative Example 4

[0192] The concentration of the hydrate of the oxide (Na2SiO3·9H2O) in step (2) is 10 mol / L, which is different from that in Example 1.

[0193] The negative electrode material prepared in the present comparative example comprises a core and a coating layer located on at least part of the surface of the core, the core comprises a carbon matrix and a silicon material, at least part of the silicon material is located in the carbon matrix, the coating layer is SiO2, and the silicon material is amorphous silicon.

[0194] Test Method

[0195] 1. Test method for pore volume and proportion of carbon matrix and negative electrode material after removal of silicon material:

[0196] The ASAP2460 device of American Micromeritics was used for testing, and the BET pore size distribution test method was used. The pore size distribution data of the material were obtained by DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen. The pore volume of the material refers to the total pore volume of the unit mass of the material, and the pore volume of the material can be measured by gas adsorption. Nitrogen adsorption is a technology for characterizing the porosity and pore size distribution of a material by condensing gas in the pores of a solid. As the pressure rises, the gas first condenses in the pores with the smallest diameter, and the pressure rises until it reaches the saturation point, at which point all the pores are filled with liquid. Then the nitrogen pressure is gradually reduced to evaporate the liquid from the system. Analysis of the adsorption and desorption isotherms enables the determination of pore volume and pore size distribution, as well as the respective pore volumes of micropores, mesopores, and macropores in the total pore volume.

[0197] The negative electrode material removes the silicon material in the following way: 150 mL of 20% mass fraction HF acid solution is added dropwise into 10 g of negative electrode material under stirring, SiF4 and H2 gas are generated, and heat is released. After no gas is generated, the supernatant acid solution is removed by centrifugation. 150 mL of 20% mass fraction HF acid solution is again added dropwise into the negative electrode material, and after stirring for 12 h, the supernatant acid solution is again removed by centrifugation. Then the negative electrode material is washed with pure water until it is neutral and dried to obtain the negative electrode material after removing the silicon material, i.e. the carbon matrix.

[0198] 2. The median particle size D50 of the negative electrode material 50 Test method:

[0199] The particle size distribution range of the negative electrode material is tested by a Malvern laser particle size analyzer (Mastersizer 3000). The volume-based cumulative particle size distribution of the particle size distribution is measured by laser diffraction method, D 10 represents the particle size corresponding to the cumulative particle size distribution percentage of 10%, D 50 represents the particle size corresponding to the cumulative particle size distribution percentage of 50%, D 90 represents the particle size corresponding to the cumulative particle size distribution percentage of 90%, so that the particle size distribution (D 90 -D 10 ) / D 50 .

[0200] 3. Coating layer thickness:

[0201] The cross-section of the material is processed by FIB-SEM equipment, and 10 particles are randomly selected in SEM, and the coating layer thickness is measured 3 times for each particle to obtain the average thickness of the coating layer.

[0202] 4. Powder conductivity test:

[0203] The method for measuring the volume resistivity of the sample by four-probe method. The powder conductivity meter MCP-PD51 of Mitsubishi Chemical of Japan can measure the conductivity of the powder at five pressure points of 4, 8, 12, 16 and 20KN, and then the computer automatically calculates the conductivity and resistivity of the powder.

[0204] 5. The method for testing the mass content of carbon element: the G4 ICARUS HF infrared carbon and sulfur analyzer of Bruker of Germany is used, the sample is burned in a high-temperature oxygen-rich state, the carbon element contained therein is oxidized into carbon dioxide, the generated gas enters the infrared detector with the carrier gas, and the content of the carbon element is calculated by quantitatively counting the change of the carbon dioxide signal.

[0205] 6. The method for testing the mass content of silicon element: the SA2-9-17TP box-type atmosphere furnace of Nanyang Xiyu is used, the sample is burned in an oxygen atmosphere, the silicon in the sample is reacted into silicon dioxide, and the carbon is burned into carbon dioxide and discharged, and the silicon content is calculated by weighing.

[0206] 7. The method for testing the mass content of the coating layer in the negative electrode material:

[0207] For the M oxide coating layer: the content of C element can be measured first (using the G4 ICARUS HF infrared carbon and sulfur analyzer of Bruker of Germany, the sample is burned in a high-temperature oxygen-rich state, the carbon element contained therein is oxidized into carbon dioxide, the generated gas enters the infrared detector with the carrier gas, and the content of the carbon element is calculated by quantitatively counting the change of the carbon dioxide signal), and then burned in an oxygen-rich environment, so that the amount of C reduction is known, and the mass of Si weight gain can be known according to the weight gain. The mass of the coating layer = total mass - mass of C element - mass of Si element.

[0208] For the carbon material coating layer: a section of the negative electrode material particle can be prepared by using a dual-beam focused ion beam microscope (Dual Beam FIB-SEM), and 10 sections of the negative electrode material particle are randomly selected, and the section is taken as a target area as shown in FIG. 2. The intersection of the longest diameter (or the longest diagonal) and the shortest diameter (or the shortest diagonal) in the target area is defined as the O point, two straight lines are drawn from the O point to intersect with the edges (the surface of the negative electrode material) of the target area, and the intersection points are M and N respectively. The intersection point of the straight line OM and the edge of the core in the negative electrode material is M', and the intersection point of the straight line ON and the edge of the core in the negative electrode material is N'. The area A1 is surrounded by M'M'N'N, and the area S1 of the area A1 is obtained. The area A2 is surrounded by M'N'O, and the area S2 of the area A2 is obtained. The mass content a1 of the carbon element in the target area A1 and the mass content a2 of the carbon element in the target area A2 are obtained by EDS scanning the above target area, and the mass content of the carbon material coating layer is [S1×a1 / (S1×a1+S2×a2)]×the mass content of the carbon element in the negative electrode material.

[0209] 8. Specific surface area test method: The specific surface area of the powder sample is tested by gas adsorption method (nitrogen adsorption multi-point BET) at low temperature under liquid nitrogen cooling control using the TriStar 3000 & 3020 specific surface area and pore size analyzer of American Micromeritics.

[0210] 9. Compacted density test method: The compacted density of the sample is tested by placing the sample of a specified mass in a mold and applying a pressure of 1.0T for 30S, then removing the pressure to test the thickness, and calculating the compacted density using the CARVER 4350.22 powder compacted density instrument of American Carver.

[0211] 10. Tapped density test method: The tapped density of the sample is tested by placing the sample of a specified mass in a measuring cylinder and vibrating according to a specified number of times (conventional test 3000 times of tapping), reading the volume of the measuring cylinder after tapping, and calculating the tapped density using the DAT-6-220 tapped density instrument of American CANT.

[0212] 11. Gas production value test method:

[0213] (1) Disperse carboxymethyl cellulose (CMC) uniformly in an appropriate amount of water to form a CMC glue solution with a solid content of 1.4%, then mix 10g of the CMC glue solution with 10g of the negative electrode material to form a slurry;

[0214] (2) Put the slurry into an aluminum plastic film bag and record the mass of the slurry;

[0215] (3) Then seal to form a sealed aluminum plastic film bag;

[0216] (4) Fix the sealed aluminum plastic film bag at the bottom of the container and completely immerse it in water, and record the volume of the aluminum plastic film bag;

[0217] (5) After a fixed time of 24 hours, record the volume of the aluminum plastic film bag again;

[0218] (6) Calculate the gas production of the negative electrode material according to the change in the volume of the aluminum plastic film, unit: mL / g.

[0219] 12. Electrochemical performance test:

[0220] The negative electrode material, conductive carbon black and acrylonitrile multi-copolymer (LA133 glue) were mixed in a mass ratio of 70:15:15 to prepare a negative electrode slurry, which was coated on a copper foil, dried and then formed into a negative electrode sheet. A polypropylene microporous membrane was used as a separator, 1 mol / L lithium hexafluorophosphate (solvent: a mixed slurry of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate) was used as an electrolyte, and a lithium metal sheet was used as a counter electrode to assemble a button cell in an Ar-filled glove box. The button cell was subjected to charge-discharge test at a current density of 0.1C in a charge-discharge interval of 0.01V-1.5V to obtain the initial reversible specific capacity and initial coulombic efficiency (ICE) of the button cell.

[0221] The negative electrode material and graphite mixture, conductive carbon black (Super-P), conductive graphite (KS-6), carboxymethyl cellulose (CMC) and butadiene rubber (SBR) were mixed in a mass ratio of 92:2:2:2:2 to prepare a negative electrode slurry, which was coated on a copper foil, dried and then formed into a negative electrode sheet. The proportion of the negative electrode material and graphite in the negative electrode material and graphite mixture was determined by the initial reversible specific capacity of the two and the capacity required for the two. A polypropylene microporous membrane was used as a separator, 1 mol / L lithium hexafluorophosphate (solvent: a mixed slurry of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate) was used as an electrolyte, and a lithium metal sheet was used as a counter electrode to assemble a button cell in an Ar-filled glove box. The button cell was subjected to repeated 50 times of charge-discharge test at a current density of 1C in a charge-discharge interval of 0.01V-1.5V to obtain the capacity retention rate and the thickness expansion rate of the electrode sheet after 50 cycles of the battery.

[0222] The test results are shown in Tables 1-3.

[0223] Table 1 Physical performance parameters of the negative electrode material (I)

[0224] Table 2 Physical performance parameters of the negative electrode material (II)

[0225] Table 3 Electrochemical performance test results of the examples and comparative examples

[0226] According to the test data in Tables 1-3, by controlling the mass content of the coating layer in the negative electrode material to A%, and the powder conductivity of the negative electrode material under 20 kN to pS / cm, where 4≤A*p≤20, the product of the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material under 20 kN is controlled within the above range, the balance between the mass content of the coating layer and the powder conductivity of the negative electrode material can be achieved, the decrease in the powder conductivity and ion transmission rate of the negative electrode material caused by excessive coating layer is reduced, and the negative electrode material can have good powder conductivity and ion transmission rate while maintaining the reduction in side reactions brought by the coating layer.

[0227] According to the test data of Example 1 and Example 12, the stirring temperature in the preparation process (2) of the negative electrode material of Example 12 is too high, the core particles are agglomerated, and two or more cores are coated at the same time, which increases the median particle size of the negative electrode material, thereby limiting the storage capacity of the negative electrode material, reducing the contact area between large particles, slowing down the electron transmission, and reducing the cycle performance of the negative electrode material.

[0228] According to the test data of Example 1 and Example 13, the pH of the mixed solution in the preparation process (2) of the negative electrode material of Example 13 is too high, and when the coating process is carried out under alkaline conditions, a large amount of the core is dissolved, directly reducing the amount of the core participating in the electrochemical reaction, thereby reducing the initial specific capacity and the initial coulombic efficiency of the negative electrode material.

[0229] According to the test data of Example 1 and Example 14, the heat treatment temperature of the precursor in the preparation process (3) of the negative electrode material of Example 14 is too low, resulting in incomplete or uneven coating of the coating layer on the surface of the core, and the coating layer on the surface of the core is easy to fall off during charging and discharging, which increases the direct contact between the core and the electrolyte and continuously reacts with the electrolyte to generate unstable solid electrolyte interface film (SEI film) and consume more lithium ions, thereby reducing the electrochemical performance of the negative electrode material.

[0230] According to the test data of Example 1 and Example 15, the heat treatment temperature of the precursor in the preparation process (3) of the negative electrode material of Example 15 is too high, which destroys the structure of the coating layer, thereby affecting the transmission of ions, and reducing the initial specific capacity and the initial coulombic efficiency of the negative electrode material.

[0231] According to the test data of Example 1 and Example 16, it can be known that when the heat treatment time of the precursor in the preparation process of the negative electrode material of Example 16 is too long, the coating layer formed on the surface of the core will be too thick, which will hinder the transmission of lithium ions and affect the outward expansion of silicon during lithium intercalation, so that the lithium intercalation depth is limited, thereby causing the first discharge specific capacity and the first coulombic efficiency of the negative electrode material to decrease.

[0232] According to the test data of Example 1 and Example 17, it can be known that by changing the material of the coating layer, the powder conductivity of the negative electrode material can be effectively improved. Under the action of the coating layer, the side reaction is reduced, and the negative electrode material also has good powder conductivity.

[0233] According to the test data of Example 1 and Example 18 and 19, it can be known that when the coating layer includes SiO2 and carbon material, as long as the product of the mass content of the coating layer in the negative electrode material and the powder conductivity of the negative electrode material under 20 kN is controlled within the above range, the balance between the thickness of the coating layer and the powder conductivity of the negative electrode material can be achieved, the decrease of the powder conductivity of the negative electrode material caused by the over-thickness of the coating layer is reduced, and the negative electrode material can have good powder conductivity while maintaining the reduction of the side reaction caused by the coating layer.

[0234] According to the test data of Example 1 and Comparative Example 1, it can be known that the molar ratio of the core to the hydrate of the oxide of the M element in the negative electrode material of Comparative Example 1 in the preparation process is too high, that is, the addition amount of the hydrate of the oxide of the M element is too low, so that the mass content A of the coating layer in the negative electrode material is too low. Although the powder conductivity p of the negative electrode material increases, A*p is out of the range, the coating layer is difficult to completely cover the core, and the core is easily directly exposed to the electrolyte, which causes the side reaction between the negative electrode material and the electrolyte to increase, the expansion rate of the electrode sheet to increase, and thus the cycle performance of the negative electrode material to decrease.

[0235] According to the test data of Example 1 and Comparative Example 2, it can be known that the molar ratio of the core to the hydrate of the oxide of the M element in the negative electrode material of Comparative Example 2 in the preparation process is too low, that is, the addition amount of the hydrate of the oxide of the M element is too high, so that the mass content A of the coating layer in the negative electrode material increases, which causes the powder conductivity p of the negative electrode material to decrease, A*p is out of the range, the coating layer on the surface of the core is too thick, which causes the transmission of lithium ions to be hindered, and part of the lithium ions are difficult to effectively intercalate into the core, thereby causing the first coulombic efficiency of the negative electrode material to decrease significantly.

[0236] According to the test data of Example 1 and Comparative Example 3, the concentration of Na2SiO3·9H2O used in the preparation process of the negative electrode material of Comparative Example 3 is too low, so that part of the Na2SiO3·9H2O fails to deposit on the surface of the core particles, the mass content A of the coating layer in the negative electrode material decreases, although the powder conductivity p of the negative electrode material increases, A* p deviates from the range, the coating layer on the surface of the core is incomplete, which leads to that part of the core is not completely protected and exposed to the electrolyte solution, the negative electrode material is easy to react with the electrolyte solution and continuously generate unstable SEI film, consume the electrolyte solution, thereby leading to the decrease of the cycle performance of the negative electrode material.

[0237] According to the test data of Example 1 and Comparative Example 4, the concentration of Na2SiO3·9H2O used in the preparation process of the negative electrode material of Comparative Example 4 is too high, the mass content A of the finally formed coating layer in the negative electrode material is too high, which leads to the decrease of the powder conductivity p of the negative electrode material, A* p deviates from the range, and the initial specific discharge capacity, the initial coulombic efficiency and the cycle performance of the negative electrode material all decrease.

[0238] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises an inner core and a coating layer on at least part of the surface of the inner core, wherein the inner core comprises a carbon matrix and a silicon material, and at least part of the silicon material is located in the carbon matrix; The mass content of the coating layer in the negative electrode material is A%, and the powder conductivity of the negative electrode material under 20kN is ρS / cm, wherein 4≤A*ρ≤30.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material has at least one of the following characteristics: (1) A*ρ is any value in the range of 4, 5, 8, 10, 12, 15, 16, 18, 20, 22, 25, 28, 30 or any two of the above values; (2) 4.01≤A*ρ≤28.

32.

3. The negative electrode material of claim 1, wherein, 1≤A≤10; and / or, 0.2≤ρ≤5.

4. The negative electrode material of claim 1, wherein, The negative electrode material has at least one of the following characteristics: (1) The carbon matrix comprises at least one of artificial graphite, natural graphite, amorphous carbon, activated carbon, mesocarbon microbeads, carbon nanotubes, carbon nanofibers, porous carbon and graphene; (2) The mass content of carbon element in the negative electrode material is 30% to 60%.

5. The negative electrode material of claim 1, wherein, The negative electrode material has at least one of the following characteristics: (1) In the negative electrode material after removing the silicon material, the volume ratio of pores with a pore size of less than 5nm in the total pore volume is ≥90%; (2) the total pore volume of the negative electrode material after removal of the silicon material is 0.5 cm 3 / g ~ 2.0 cm 3 / g.

6. The negative electrode material of claim 1, wherein, The average thickness of the coating layer is d, the median particle size D of the negative electrode material is 50 D, and the negative electrode material has at least one of the following characteristics: (1) The ratio of d / D ranges from 0.5% to 5%; (2) 5nm≤d≤500nm; (3) 1μm≤D≤20μm.

7. The negative electrode material of claim 1, wherein, The coating layer comprises at least one of an oxide of M element and / or a carbon material; wherein the M element comprises at least one of B, Zr, Ni, Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, Hf, Ta, Co, Cr and Zn.

8. The negative electrode material of claim 1, wherein, The total pore volume of the negative electrode material is 0.001 cm 3 / g ~ 0.2 cm 3 The average pore diameter of the negative electrode material is 0.45 nm ~ 50 nm.

9. The negative electrode material of claim 1, wherein, At least part of the silicon material is distributed on at least part of the surface of the carbon matrix.

10. The negative electrode material of claim 1, wherein, The silicon material comprises at least one of crystalline silicon, silicon oxide, amorphous silicon, silicon alloy, composite particles of crystalline silicon and amorphous silicon.

11. The negative electrode material according to any one of claims 1 to 9, characterized by, The negative electrode material has at least one of the following characteristics: (1) The mass fraction of Si element in the negative electrode material is 40% to 55%; (2) the compaction density of the negative electrode material is 0.8 cm 3 / g ~ 1.5 cm 3 / g; (3) the tap density of the negative electrode material is 0.5 cm 3 / g ~ 1.5 cm 3 / g; (4) the specific surface area of the negative electrode material is 0.5 m 2 / g ~ 10 m 2 / g; (5) The gas production of the negative electrode material under normal temperature for 24h is ≤1mL / g.

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