Negative electrode material and preparation method therefor, and lithium-ion battery

Abstract

A negative electrode material and a preparation method therefor, and a lithium-ion battery. The negative electrode material comprises an inner core and a coating layer formed on at least part of the surface of the inner core, wherein the inner core comprises a silicon-based material. The negative electrode material has a hole structure. The differentiation ratio ΔΦ of the hole structure of the negative electrode material satisfies: 1×10-3≤ formula (I), wherein ΔS is the area of a hysteresis loop in an isothermal adsorption and desorption curve of the negative electrode material; s is the specific surface area of the negative electrode material; ΔP is the interval difference value of the relative pressure intensity P / P0 corresponding to the hysteresis loop; and Qmax is the maximum isothermal adsorption capacity of the negative electrode material. The preparation method for the negative electrode material comprises: subjecting a silicon-based material inner core to be coated to a CVD vapor deposition treatment, so as to obtain the negative electrode material having a hole structure. In the method, by forming a hole structure having a certain degree of complexity on the negative electrode material, the rate capability and cycle performance of the material are improved.

Description

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number CN202310809643X, entitled “Negative Electrode Material, Preparation Method Thereof, and Lithium-ion Battery,” filed with the Patent Office of China on June 30, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the technical field of lithium batteries, and in particular to a negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0004] Currently, graphite-based materials are commonly used as anode materials in mature commercial lithium-ion batteries. However, the theoretical lithium storage capacity of graphite-based materials is low, which cannot meet the demand for high-energy-density batteries. Silicon-based anode materials, on the other hand, have a very high theoretical capacity of approximately 4200 mAh / g, far exceeding the capacity of commercial graphite. Therefore, silicon-based anode materials have great application prospects in energy storage and are one of the most critical materials for high-energy-density lithium-ion batteries.

[0005] However, existing silicon-based anode materials suffer from significant expansion and poor rate performance, which severely hinder their widespread application in lithium-ion batteries. Therefore, suppressing expansion and improving the cycle and rate performance of silicon-based materials are prerequisites for their widespread application. Therefore, designing the particle structure of silicon-based anode materials to mitigate expansion and improve rate and cycle performance is an urgent challenge that needs to be overcome.

[0006] Summary of the Invention

[0007] The present disclosure provides a negative electrode material, comprising a core and a coating layer formed on at least a portion of the surface of the core, wherein the core comprises a silicon-based material and the negative electrode material has a porous structure;

[0008] The differential ratio of the pore structure Satisfaction: 1×10 -3 ≤ΔΦ≤0.5;

[0009] Wherein, ΔS is the area of ​​the hysteresis loop in the isothermal adsorption-desorption curve of the negative electrode material;

[0010] s is the specific surface area of ​​the negative electrode material;

[0011] ΔP is the interval difference of the relative pressure P / P0 corresponding to the hysteresis loop, 0<ΔP≤1;

[0012] Qmax is the maximum isothermal adsorption capacity of the negative electrode material.

[0013] Optionally, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, silicon nitride, silicon phosphide, silicon sulfide, and silicon alloy.

[0014] Optionally, the coating layer includes at least one of a carbon-containing material and a ceramic material.

[0015] Optionally, the mass of the coating layer is 0.5%-10% of the total mass of the negative electrode material.

[0016] Optionally, the coating layer has a thickness of 20 nm to 700 nm.

[0017] Optionally, the core further includes a carbon material.

[0018] Optionally, the core further includes doped metal elements.

[0019] Optionally, the differential ratio ΔΦ of the pore structure satisfies 5×10 -3 ≤ΔΦ≤0.5.

[0020] Optionally, the area ΔS of the hysteresis loop satisfies 4.5×10 -4 ≤ΔS≤3.0×10 -2 Optionally, the area ΔS of the hysteresis loop satisfies 4.5×10 -4 ≤ΔS≤2.5×10 -2 .

[0021] Optionally, the specific surface area s of the negative electrode material is 0.5 m 2 / g-15m 2 / g.

[0022] Optionally, the maximum isothermal adsorption capacity Q of the negative electrode material max ≤1.35mmol / g.

[0023] Optionally, the BJH average pore size of the negative electrode material is 5nm-20nm, and the BJH pore volume satisfies 1.0×10 -4 cm 3 / g≤V BJH ≤0.1cm 3 / g.

[0024] Optionally, the pH of the negative electrode material is 6.0-12.0.

[0025] Optionally, the carbon-containing material includes at least one of graphite, hard carbon, soft carbon, diamond-like carbon, carbon fiber, carbide, asphalt, and resin-based high molecular polymer.

[0026] Optionally, the ceramic material includes at least one of phosphate, silicate, nitride, and metal oxide.

[0027] Optionally, the carbon-based material includes at least one of soft carbon, hard carbon, graphite, graphene, carbon nanotubes, carbon fibers, and diamond-like carbon.

[0028] Optionally, the doping metal element includes at least one of Li, Mg, Al, Ti, Na, K, Ca, Be, La, Ce, V, and Ba.

[0029] Optionally, the mass percentage of the doped metal element in the negative electrode material is 2%-15%.

[0030] Optionally, the coating layer has the pore structure.

[0031] Optionally, the pore structure includes micropores, mesopores and macropores.

[0032] The present disclosure also provides a method for preparing a silicon-based negative electrode material, comprising:

[0033] The silicon-based material core to be coated is subjected to CVD vapor deposition coating treatment to obtain a negative electrode material with a porous structure.

[0034] The gas for vapor deposition includes auxiliary gas and carbon source gas. Among the gases, the volume proportion of the carbon source gas is 30%-95%, and the volume proportion of the auxiliary gas is 5%-70%.

[0035] Optionally, before the CVD vapor deposition process, the method further includes pre-treating the silicon-based material core to be coated.

[0036] Optionally, the temperature of the vapor deposition treatment is 400° C.-1200° C., and the time is 1 hour-12 hours.

[0037] Optionally, when performing the CVD vapor deposition process, it also includes: placing the silicon-based material core to be coated in a deposition chamber of a deposition furnace, the rotation speed of the deposition chamber is 0.1r / min-10r / min, and the gas pressure in the deposition furnace is 0.1MPa-10MPa.

[0038] Optionally, the carbon source gas includes at least one of methane, ethane, ethylene, acetylene, propane, formaldehyde, acetaldehyde, and methanol.

[0039] Optionally, the auxiliary gas includes at least one of H2, SO2, NH3, and Ar.

[0040] Optionally, the pretreatment includes: screening, grading, washing, and drying in sequence.

[0041] Optionally, the particle size D of the silicon-based material core to be coated obtained after the pretreatment is 50 =2.5μm-9.0μm.

[0042] Optionally, the specific surface area of ​​the silicon-based material core to be coated obtained after the pretreatment is 0.5m 2 / g-7.5m 2 / g.

[0043] Optionally, the cleaning includes: first washing with water and then rinsing with an organic solvent.

[0044] Optionally, the drying includes: air-drying the cleaned material using an inert gas, and then vacuum-drying the cleaned material in an environment of 60° C.-150° C. and below 1000 Pa.

[0045] Optionally, after the vapor deposition process, the method further includes: grading and drying the product obtained by the vapor deposition process.

[0046] The present disclosure also provides a lithium-ion battery, comprising the negative electrode material described above, or comprising the negative electrode material prepared by the preparation method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope of the present disclosure.

[0048] FIG1 is an isothermal adsorption-desorption curve of the negative electrode material prepared in Example 1;

[0049] FIG2 is an isothermal adsorption-desorption curve of the negative electrode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0050] As used herein:

[0051] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The conjunction "consisting of" excludes any unspecified element, step, or component.

[0052] When an amount, concentration, or other value or parameter is expressed as a range, an optional range, or a range limited by a series of upper and lower optional values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or optional value with any range lower limit or optional value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0053] In these examples, parts and percentages are by mass unless otherwise indicated.

[0054] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0055] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0056] Although silicon-based negative electrode materials have high energy density, they experience excessive volume expansion during the charge and discharge process, leading to problems such as poor cycle and rate performance. To address this issue, the inventors of the present invention designed the particle structure of the negative electrode material to improve the performance of the material. Research has shown that the pore structure in silicon-based negative electrode materials plays a key role.

[0057] In most studies, only some specifications are made for the specific surface area and pore size range of the negative electrode material, and the relationship between the pore size, pore shape, pore structure, etc. and the electrochemical performance is not studied in depth, so further improvements cannot be made. The pores on the surface of the negative electrode material serve as fast transmission channels for lithium transmission, core expansion space, and skeleton space for SEI deposition, which are conducive to alleviating core expansion, improving the cycle and rate performance of the negative electrode material as a battery material, stabilizing the SEI-active component interface, improving the cycle coulomb efficiency of the negative electrode material as a battery material, and reducing the loss of active silicon and lithium. Based on this, the inventors of the present disclosure have conducted in-depth research on the pore structure of silicon-based negative electrode materials, especially the coating layer.

[0058] Undoubtedly, different pore structures will have different effects on the cycle performance and rate performance of negative electrode materials. However, due to the relatively small pore diameter and large number of pores in the negative electrode material, combined with the complex specific pore configuration, it is actually very difficult to clearly describe the pore structure in words. For negative electrode materials, the size of the pore diameter, the distribution of the pores, and the specific surface area of ​​the material will affect the adsorption performance of the material, thereby presenting different isothermal adsorption and desorption curves. The inventors of the present disclosure have found through research on negative electrode materials that the difference in pore structure can be reflected by comprehensively analyzing the relevant parameters of the isothermal adsorption and desorption curves and the specific surface area. Based on this, the inventors of the present disclosure further improved the negative electrode material to obtain a negative electrode material with a special pore structure.

[0059] The optimal pore distribution and pore structure of silicon-based anode materials facilitate rapid electrolyte infiltration. This rapid infiltration enhances the rapid transport of lithium ions, shortens the lithium ion transport path, and improves lithium ion transport efficiency, thereby enhancing the rate performance of silicon-based anode materials. Furthermore, the coating layer in these silicon-based anode materials effectively isolates the co-embedding of small organic molecules in the electrolyte, reducing core material loss and improving cycling performance.

[0060] This disclosure provides a negative electrode material, a preparation method thereof, and a lithium-ion battery. By providing a negative electrode material with a special pore structure, the material can, on the one hand, isolate unnecessary exposure of the silicon-based material core, reduce the loss of active material and lithium, and improve cycle performance; on the other hand, the pore structure facilitates rapid electrolyte infiltration, improving the transmission efficiency of lithium ions and thus enhancing the material's rate performance.

[0061] An embodiment of the present disclosure provides a negative electrode material, including a core and a coating layer formed on at least a portion of the surface of the core, wherein the core includes a silicon-based material, and the negative electrode material has a porous structure.

[0062] Among them, the differentiation ratio of pore structure Satisfaction: 1×10 -3 ≤ΔΦ≤0.5, for example, ΔΦ can be 5×10 -3 -0.45, 0.015-0.4, 0.03-0.3 or 0.1-0.2, such as 0.001, 0.003, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, etc. or any value between 0.001-0.5 or a range between two arbitrary values. Optionally, ΔΦ satisfies 5×10 -3 ≤ΔΦ≤0.5.

[0063] Specifically, ΔS is the area of ​​the hysteresis loop in the isothermal adsorption-desorption curve of the negative electrode material, and ΔS is the area of ​​the hysteresis loop calculated using the integration method; s is the specific surface area of ​​the negative electrode material, and the value of s is in units of m 2 / g corresponds to the specific value; ΔP is the interval difference of the relative pressure P / P0 corresponding to the above hysteresis loop, 0<ΔP≤1, for example, if the relative pressure P / P0 corresponding to the hysteresis loop in the isothermal adsorption-desorption curve is in the range of 0.6-0.9, then ΔP=0.9-0.6=0.3, or if the relative pressure P / P0 corresponding to the hysteresis loop is in the range of 0.53-0.76, then ΔP=0.76-0.53=0.23; Q max It is the maximum isothermal adsorption capacity of the negative electrode material. This value is the specific value corresponding to the unit of mmol / g.

[0064] It should be noted that the present disclosure tests the negative electrode material by mercury intrusion and gas adsorption in accordance with GB / T 21650.3-2011. An accurately weighed sample of the negative electrode material to be tested is placed in a sample tube, and the system is vacuumed and degassed to achieve the desired vacuum. The sample tube is then immersed in a liquid nitrogen bath and filled with a known amount of gas (nitrogen). The sample adsorbs the gas, causing a pressure drop. After reaching adsorption equilibrium, the equilibrium pressure of the gas is measured, and the adsorption amount can be calculated based on the pressure change before and after adsorption. The amount of adsorbate gas is gradually increased to change the pressure, and the above operation is repeated to test the isothermal adsorption-desorption curve. The theoretical model is then used to equivalently determine the specific surface area, pore volume, and pore size distribution of the sample to be tested. The area of ​​the hysteresis loop is determined by integrating the adsorption curve and desorption curve in the isothermal adsorption-desorption curve, and then subtracting the data.

[0065] By studying the laws of adsorption curves, the inventors of the present disclosure discovered that the data curve characteristics of the hysteresis loop in the isothermal adsorption and desorption curve of the negative electrode material are highly correlated with the electrochemical performance. By comprehensively considering the hysteresis loop area and the corresponding relative pressure interval difference, the specific surface area of ​​the negative electrode material and the maximum isothermal adsorption amount, and combining them into a calculation formula, the differentiated ratio ΔΦ of the pore structure is obtained to describe the pore structure in the negative electrode material, and the contribution of the pore structure is converted into an equivalent ratio, which is expressed in a more intuitive form to determine the efficiency of mass transfer and charge transfer at the solid-liquid interface, thereby indicating the influence of the pore structure of the negative electrode material, especially the coating layer, on the electrochemical performance.

[0066] Generally speaking, pores have different sizes and distribution states. In this application, ΔΦ is used to express the complexity of the pore structure in the negative electrode material. The smaller ΔΦ is, the more the pore structure is close to being single, the pore size is the same, the distribution is uniform, and there is less staggering between different pores. The larger ΔΦ is, the greater the difference in pore size is, the more staggered the pores are, and the more chaotic the distribution is. In this application, when ΔΦ is less than 1×10 -3 When ΔΦ is greater than 0.5, it means that the pores are less differentiated and the pore structure is simple, that is, the pore size and shape are single, and there are few combinations of different pore structures. Therefore, under the same specific surface area conditions, the negative electrode material with this pore structure has low expansion reduction efficiency, poor SEI interface stability, and low cycle performance, especially low cycle Coulomb efficiency. When ΔΦ is greater than 0.5, it means that the pore structure is more complex, with too many pores of different pore sizes combined with each other, strong mass transfer resistance, low mass transfer efficiency, poor rate, and at the same time aggravated concentration polarization during the electrochemical reaction. Therefore, at 1×10 -3 In the range of ≤ΔΦ≤0.5, it means that the pore structure of the negative electrode material has a suitable pore size and staggered distribution, which can ensure that the negative electrode material quickly transfers mass and charge while having sufficient pores to buffer the expansion of the core, stabilize the SEI interface, and improve the Coulombic efficiency.

[0067] In conjunction with the first aspect, in an optional embodiment, the silicon-based material in the negative electrode material of the present disclosure includes at least one of elemental silicon, silicon oxide, silicon carbide, silicon nitride, silicon phosphide, silicon sulfide, and a silicon alloy. Optionally, the silicon oxide may be a silicon-oxygen composite, which can be represented by the general formula SiOx, 0 < x ≤ 2. Optionally, the molar ratio of oxygen atoms to silicon atoms in the silicon oxide is (0.5-2):1.

[0068] In addition to the silicon-based material, the core may also include at least one of a carbon-based material and a doping metal element. When the silicon-based material core contains a doping metal element, the doping metal element may be at least partially present in the form of silicate.

[0069] For doped negative electrode materials, such as a core composed of doped metal elements combined with elemental silicon, or a core composed of silicate combined with silicon oxide, when having the pore structure characteristics of the present application, ΔΦ is closer to the center value of the range, effectively improving the electrochemical rate performance and the cycle capacity retention rate.

[0070] Optionally, the carbon-based material includes at least one of soft carbon, hard carbon, graphite, graphene, carbon nanotubes, carbon fibers, and diamond-like carbon.

[0071] Optionally, the doping metal element includes at least one of Li, Mg, Al, Ti, Na, K, Ca, Be, La, Ce, V, and Ba.

[0072] Optionally, the doping mass percentage of the doped metal element in the negative electrode material is 2%-15%, for example, it can be 3%-14%, 4%-12% or 5%-10%, such as 2%, 3%, 5%, 8%, 10%, 12%, 15%, etc. or any value between 2%-15% or a range between two arbitrary values.

[0073] In an optional embodiment, the coating layer in the negative electrode material of the present disclosure includes at least one of a carbonaceous material and a ceramic material.

[0074] Optionally, the carbon-containing material includes at least one of graphite, hard carbon, soft carbon, diamond-like carbon, carbon fiber, carbide, asphalt, and resin-based high molecular polymer.

[0075] Optionally, the ceramic material includes at least one of phosphate, silicate, nitride, and metal oxide.

[0076] In an optional embodiment, the mass of the coating layer is 0.5%-10% of the total mass of the negative electrode material, for example, 1%-9%, 2%-8%, or 3%-7%, such as 0.5%, 1%, 3%, 5%, 7%, 10%, or any value between 0.5% and 10%, or a range between two arbitrary values. Alternatively, the mass of the coating layer is 2.5%-8% of the total mass of the negative electrode material.

[0077] In an optional embodiment, the thickness of the coating layer is 20nm-700nm, for example, it can be 50nm-600nm, 90nm-550nm or 150nm-400nm, such as 20nm, 50nm, 100nm, 200nm, 300nm, 500nm, 700nm, etc., or any value between 20nm-700nm or a range between two arbitrary values.

[0078] In an optional embodiment, the differential ratio ΔΦ of the pore structure of the negative electrode material satisfies 5×10 -3 ≤ΔΦ≤0.5.

[0079] In an optional embodiment, there is a hysteresis loop in the isothermal adsorption-desorption curve of the negative electrode material, and the area ΔS of the hysteresis loop satisfies 4.5×10 -4 ≤ΔS≤3.0×10 -2 , for example, ΔS can be 4.5×10 -4 ≤ΔS≤2.7×10 -2 , 4.5×10 -4 ≤ΔS≤2.5×10 -2 , 4.5×10 -3 ≤ΔS≤1.5×10 -2etc., such as 0.00045, 0.0005, 0.001, 0.005, 0.01, 0.02, 0.025, 0.027, 0.03, etc. or any value between 0.00045-0.025 or a range between two arbitrary values. Optionally, ΔS satisfies 4.5×10 -4 ≤ΔS≤1.0×10 -2 .

[0080] In an optional embodiment, the specific surface area s of the negative electrode material is 0.5 m 2 / g-15m 2 / g, for example, it can be 1.0m 2 / g-12m 2 / g, 2.5m 2 / g-10m 2 / g or 5.0m 2 / g-7m 2 / g, etc., such as 0.5m 2 / g、1m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g、10m 2 / g、12m 2 / g、15m 2 / g or 0.5m 2 / g-15m 2 / any value between or a range between two arbitrary values. Optionally, s is 0.5m 2 / g-10m 2 / g.

[0081] In an optional embodiment, the maximum isothermal adsorption capacity Q of the negative electrode material is max ≤1.35mmol / g, for example, Q max ≤1.0mmol / g, Q max ≤0.45mmol / g or Q max ≤0.35 mmol / g, etc., such as 0.1 mmol / g, 0.3 mmol / g, 0.5 mmol / g, 0.8 mmol / g, 1.0 mmol / g, 1.2 mmol / g or 1.35 mmol / g, etc.

[0082] In an optional embodiment, the BJH average pore size of the negative electrode material is 5nm-20nm, for example, it can be 7nm-18nm, 9nm-16nm or 10nm-14nm, such as 5nm, 10nm, 15nm, 20nm, etc., or any value between 5nm-20nm or a range between two arbitrary values.

[0083] The BJH pore volume of the negative electrode material, also known as the BJH Adsorption cumulative volume of pores, meets the requirement of 1.0×10 -4 cm 3 / g≤V BJH ≤0.1cm 3 / g, such as V BJH It can be 5.0×10 -4 cm 3 / g-0.05cm 3 / g, 8×10 -4 cm 3 / g-0.01cm 3 / g or 0.008cm 3 / g-0.05cm 3 / g, etc., such as 0.0001cm 3 / g, 0.0005cm 3 / g, 0.001cm 3 / g, 0.005cm 3 / g, 0.01cm 3 / g, 0.05cm 3 / g, 0.1cm 3 / g or 1.0×10 -4 cm 3 / g-0.1cm 3 / g, or a range between two arbitrary values.

[0084] In an optional embodiment, the pH of the negative electrode material is 6.0-12.0, for example, it can be 7.0-11.0, 7.5-10.0 or 8.0-9.0, such as 6.0, 6.5, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, etc., or any value between 6.0-12.0 or a range between two arbitrary values.

[0085] In an optional embodiment, the negative electrode material has micropores, mesopores and macropores. Optionally, the pore structure is mainly mesopores. Optionally, the pore volume of the mesopores is in the range of 65% to 90%. Optionally, the pore volume of the macropores is in the range of 5% to 20%. Optionally, the pore volume of the micropores is in the range of 0.05% to 10%. When the negative electrode material meets the above requirements, during electrochemical charge and discharge in a battery containing the negative electrode material, the lithium ion diffusion interface, the diffusion path and the electrolyte degradation energy in the negative electrode material can reach a balance, so that the electrochemical rate performance can be well exerted while reducing the consumption of the electrolyte, reducing excessive SEI deposition, inhibiting the expansion of the electrode, and improving the cycle performance.

[0086] One embodiment of the present disclosure also provides a method for preparing a negative electrode material, comprising: performing CVD vapor deposition treatment on a silicon-based material core to be coated to obtain a negative electrode material with a porous structure; wherein the gas for the vapor deposition treatment includes a mixed gas including an auxiliary gas and a carbon source gas, and in the above-mentioned mixed gas, the volume proportion of the carbon source gas is 30%-95%, and the volume proportion of the auxiliary gas is 5%-70%.

[0087] In an optional embodiment, before the CVD vapor deposition process is performed, the silicon-based material core to be coated is also pre-treated.

[0088] Optionally, the pretreatment includes: screening, grading, washing, and drying in sequence.

[0089] Among them, cleaning includes: washing with water first, and then rinsing with an organic solvent; drying includes: air-drying the cleaned material with inert gas, and then vacuum drying in an environment of 60℃-150℃ and below 1000Pa;

[0090] Optionally, the core of the silicon-based material to be coated is vibrated and sieved to adjust the appropriate particle size (D 50 The particle size range is 2.5μm-9.0μm); then rinse with deionized water for 30 minutes, then rinse with ethanol for 30 minutes, and finally dry with argon. The dried material is further vacuum dried, requiring the vacuum environment to be maintained below 1000Pa, the drying temperature to be within the range of 60℃-150℃, and the drying time to be any value between 3h and 48h.

[0091] It should be noted that after the particle size of the silicon-based material core to be coated is pre-treated and sized, the specific surface area of ​​the silicon-based material core raw material is effectively controlled (the range of the optional specific surface area is 0.5m 2 / g-7.5m 2 / g), which has a certain control effect on the formation of pore structure after deposition.

[0092] In addition, cleaning methods such as water and alcohol washing can remove adsorbed materials from the core surface, reducing their impact on deposition and allowing the coating layer to form a close chemical bond with the core, facilitating rapid charge transfer and improving the material's conductivity. Furthermore, surface adsorbed materials can affect the deposition structure of the coating layer, increasing the uncertainty of negative electrode material formation and impacting material performance.

[0093] In an optional embodiment, the temperature of the CVD vapor deposition process is 400° C.-1200° C., for example, 500° C.-1100° C., 600° C.-1000° C., or 700° C.-900° C., such as 400° C., 600° C., 800° C., 1000° C., 1200° C., or any value between 400° C.-1200° C. Optionally, the time of the CVD vapor deposition process is 1 hour-12 hours, for example, 2 hours-11 hours, 3 hours-10 hours, or 4 hours-9 hours, such as 1 hour, 3 hours, 5 hours, 7 hours, 10 hours, 12 hours, or any value between 1 hour and 12 hours, or a range between two arbitrary values.

[0094] In an optional embodiment, the CVD vapor deposition process further includes placing the silicon-based material core to be coated in a deposition chamber of a deposition furnace, wherein the rotation speed of the deposition chamber is 0.1 rpm to 10 rpm, and the gas pressure in the deposition furnace is 0.1 MPa to 10 MPa.

[0095] It should be noted that the temperature of CVD vapor deposition can regulate the deposition efficiency, the gas pressure in the furnace can control the density of the coating layer, the deposition time can control the thickness of the coating layer, and the rotation of the deposition chamber can improve the uniformity of the deposition coating between particles.

[0096] In an optional embodiment, the carbon source gas used in the CVD vapor deposition process includes at least one of methane, ethane, ethylene, acetylene, propane, formaldehyde, acetaldehyde, and methanol.

[0097] Optionally, at least two different carbon source gases are used in the CVD vapor deposition process. This is because the dissociation temperatures and dissociation efficiencies of the different carbon source gases are different, resulting in differentiated deposition. A coating layer with a complex pore structure can be deposited using the differentiated deposition of different gas sources.

[0098] In an optional embodiment, the auxiliary gas used in the CVD vapor deposition process includes at least one of H2, CO2, NH3, and Ar.

[0099] Optionally, in the mixed gas, the volume proportion of the carbon source gas is 30%-95%, and the volume proportion of the auxiliary gas is 5%-70%. For example, the carbon source gas accounts for 30% and the auxiliary gas accounts for 70%; or the carbon source gas accounts for 50% and the auxiliary gas accounts for 50%; or the carbon source gas accounts for 80% and the auxiliary gas accounts for 20%; or the carbon source gas accounts for 95% and the auxiliary gas accounts for 5%.

[0100] It should be noted that by introducing different proportions of carbon source gas and auxiliary gas, the coating layer can be locally provided with more amorphous irregular branches, so that the organic (high hydrogen content carbon) and coating layer parts (carbon element parts such as graphite, diamond, graphene, etc.) in the coating layer are more uniform, further improving the complexity of the pore structure in the negative electrode material, and changing the pore structure, thereby changing the differentiation ratio of the pore structure and changing the electrochemical performance.

[0101] In an optional embodiment, after CVD vapor deposition, the obtained product needs to be classified and dried, and then packaged to form a finished negative electrode material.

[0102] In an optional embodiment, the negative electrode material of the present disclosure can also be obtained by liquid-phase coating or solid-phase coating of the silicon-based material core to be coated.

[0103] Optionally, liquid phase coating includes: dissolving the coating raw material in a solvent, and then mixing it with the silicon-based material core to be coated to obtain a precursor solution; evaporating the precursor solution, and then placing it in an inert gas for a first heat treatment to obtain a negative electrode material.

[0104] If the coating layer is a ceramic material, the coating raw material used in the liquid phase coating includes at least one of soluble silicates, phosphates, and metal salts, and the solvent used is water.

[0105] If the coating layer is a carbonaceous material, the coating raw material used in the liquid phase coating includes at least one of asphalt and resin-type high molecular organic compounds, and the solvent used includes at least one of n-hexane, benzene and toluene.

[0106] It should be noted that the complex cross-linking and polymerization of various materials, such as asphalt and polymer monomers, dissolved in organic solvents, as well as their differentiated deposition, facilitate the synthesis of complex pore structures. Furthermore, the addition of soluble mixed organic monomers to polar solvents allows for the formation of polymers under certain pH conditions, followed by the synthesis and deposition of precursors.

[0107] In an optional embodiment of liquid-phase coating, the mass of the coating raw material is 0.5%-10% of the total mass of the coating raw material and the silicon-based material core to be coated, for example, 1%-9%, 2%-7%, or 3%-6%, such as 0.5%, 1%, 3%, 5%, 8%, 10%, or any value between 0.5% and 10%, or a range between two arbitrary values. This is mainly to ensure that the coating raw material can be uniformly deposited on the surface of the silicon-based material core.

[0108] Optionally, the ratio of the mass of the solvent to the mass of the silicon-based material core to be coated is (3-7.5):1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1, 7.5:1 or any value between (3-7.5):1 or a range between two arbitrary values.

[0109] The evaporation of the precursor solution includes heating the precursor solution in a water bath or oil bath for evaporation while stirring the precursor solution at a speed of 10-500 rpm. The temperature of the water bath or oil bath is within a range of 10-20°C below the boiling point of the solvent. For example, when the solvent is water, the water bath temperature is set in the range of 80-90°C. The precursor solution is stirred until the particles are completely dry and return to a powdery state.

[0110] After the evaporated material is placed in an inert atmosphere for a first heat treatment, the precursor undergoes a solid-phase reaction to form a silicate. Certain carbon-containing materials carbonize to form a coating, improving the conductivity of the negative electrode material. Alternatively, the precursor can form a ceramic coating through a solid-phase reaction. This is because the precursor material can be uniformly deposited on the surface of the active core through coprecipitation and sol-gel methods, resulting in uniform mixing of the various components. This can reduce the reaction temperature, improve reaction efficiency, and improve the efficiency of ceramic formation.

[0111] In an optional embodiment of liquid phase coating, the temperature for the first heat treatment is 500°C-1200°C, for example, 600°C-1100°C, 700°C-1000°C or 800°C-900°C, such as 500°C, 600°C, 800°C, 1000°C, 1200°C or any value between 500°C-1200°C or a range between two arbitrary values. Optionally, the time for the first heat treatment is 3h-24h, for example, 5h-20h, 8h-18h or 10h-15h, such as 3h, 5h, 10h, 15h, 20h, 24h or any value between 3h-24h or a range between two arbitrary values. The inert gas used includes at least one of argon, nitrogen and helium.

[0112] In an optional embodiment, when using a solid phase coating process, it can optionally include: solid-phase mixing of a solid coating material with a silicon-based material core to be coated to obtain a solid-phase precursor; and placing the solid-phase precursor in an inert gas for a second heat treatment to obtain a negative electrode material.

[0113] The solid coating material comprises at least one of solid asphalt, soft carbon, hard carbon, and a ceramic precursor material. Due to the differences in carbon structure among these coating materials, ball milling allows for uniform mixing of the various phases, resulting in a thorough bonding and uniform deposition on the surface of the silicon-based core. This lowers the reaction temperature and facilitates the subsequent sintering process, facilitating the internal pore structure of the various structures and forming a well-defined internal structure. The ball milling time is optionally 6-72 hours.

[0114] In an optional embodiment of solid phase coating, the temperature of the second heat treatment is 500° C.-1200° C., for example, 600° C.-1100° C., 700° C.-1000° C., or 800° C.-900° C., such as 500° C., 600° C., 800° C., 1000° C., 1200° C., or any value between 500° C.-1200° C., or a range between two arbitrary values. Optionally, the time of the second heat treatment is 3 h-24 h, for example, 5 h-20 h, 8 h-18 h, or 10 h-15 h, such as 3 h, 5 h, 10 h, 15 h, 20 h, 24 h, or any value between 3 h-24 h.

[0115] After the liquid phase coating or solid phase coating is completed, the process further includes: etching and water washing the obtained product. Optionally, after acid-base etching, water washing, and filtration, the obtained product is dried by purging with argon gas. The argon-dried product can then be graded and vacuum-dried to remove moisture, and then vacuum-packaged to form the finished negative electrode material.

[0116] It should be noted that by subjecting the product obtained after liquid-phase coating or solid-phase coating to acid-base etching, water washing, and grading, the unreacted soluble precursors in the product can be removed, further improving the pore structure of the product. Among them, grading the washed and dried product can break up the agglomeration of the powder and further control the graded negative electrode material to be within the optimized particle size range. In addition, because the negative electrode material with a porous structure easily absorbs moisture, it is further removed by vacuum drying to improve the electrochemical performance of the negative electrode material.

[0117] The present disclosure controls the pores of the negative electrode material by regulating the coating layer, especially the coating layer with a special characteristic pore structure, which can effectively alleviate the expansion of the negative electrode core, balance the stability of the SEI growth interface, improve the cycle coulomb efficiency, and ensure the performance of the negative electrode material.

[0118] The present disclosure provides a negative electrode material having a coating layer, wherein the negative electrode material has a pore structure. Research has found that the pore structure has a great influence on the electrochemical performance of the negative electrode material. Therefore, the pore structure of the negative electrode material is studied in detail. By studying the law of adsorption defects, it is found that the data curve characteristics of the hysteresis loop in the isothermal adsorption and desorption curve of the negative electrode material are highly correlated with the electrochemical performance, and there is an optional mathematical relationship range (pore structure differentiation ratio ΔΦ), which is 1×10 -3 In the range of ≤ΔΦ≤0.5, it means that the pore structure of the negative electrode material has a suitable pore size and staggered distribution, which can ensure the rapid mass-charge transfer of the negative electrode material while also having sufficient pores to buffer the expansion of the core, stabilize the SEI interface, and improve the coulombic efficiency. -3 When ΔΦ is greater than 0.5, the pore structure is highly complex, with too many channels of different pore sizes combining with each other, resulting in strong mass transfer resistance, low mass transfer efficiency, and poor rate performance. This also exacerbates concentration polarization during the electrochemical reaction.

[0119] The present disclosure provides a method for preparing a negative electrode material, which utilizes CVD vapor deposition to produce a negative electrode material having a porous structure. By introducing an auxiliary gas into the carbon source gas, the pore structure in the coating layer and the pore structure between the coating layer and the core can be regulated, further increasing the complexity of the pore structure in the coating layer. By changing the pore structure, the differential ratio of the pore structure is altered, thereby changing the electrochemical performance of the negative electrode material.

[0120] The lithium-ion battery provided by the present invention uses the above-mentioned negative electrode material. By utilizing the reasonable pore structure in the coating layer, the negative electrode material can quickly undergo mass-charge transfer. At the same time, the pores of the coating layer can also buffer the expansion of the negative electrode material, stabilize the SEI interface, and significantly reduce the deposition thickness of the SEI layer, thereby significantly improving the diffusion coefficient of the lithium core of the negative electrode material and improving the coulombic efficiency and rate performance of the battery.

[0121] Example

[0122] The embodiments of the present disclosure will be described in detail below with reference to specific examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0123] Example 1

[0124] This embodiment provides a negative electrode material, and the preparation method thereof includes:

[0125] (1) Weigh 1000 g of lithium-doped silicon oxide, in which the mass proportion of lithium is 10% and the silicon / oxygen atomic ratio is between 1:0.9 and 1.1. Rinse with deionized water for 30 min, then rinse with ethanol for 30 min, and then blow with dry Ar until there is no obvious liquid and there is no adhesion or agglomeration between the particles. Then put it into a vacuum drying oven. When the pressure in the oven drops to 500 Pa, start heating and drying. The drying temperature is 100 ° C and the drying time is 24 h.

[0126] (2) The treated sample was placed in a vapor deposition furnace for coating. The coating gas was a mixture of methane, acetylene, and ethylene in a volume ratio of 1:1:1, and an NH3 auxiliary atmosphere was introduced. The volume ratio of the carbon source gas to the auxiliary gas was 1:1. The deposition temperature was 900°C, the deposition time was 5 hours, and the deposition chamber speed was 5 r / min. The pressure in the deposition chamber was regulated by a pressure valve and maintained at 0.5 MPa. The mass ratio of the coating layer was controlled to be (5±0.5)%.

[0127] (3) The samples after vapor deposition are graded, the materials are screened and regulated to the target particle size, and vacuum dried at 100°C for 24 hours to form the finished negative electrode material.

[0128] Example 2

[0129] This embodiment provides a negative electrode material, and the preparation method thereof includes:

[0130] (1) Weigh 1000 g of lithium-doped silicon oxide, in which the mass proportion of lithium is 10% and the silicon / oxygen atomic ratio is between 1:0.9 and 1.1. Rinse with deionized water for 30 min, then rinse with ethanol for 30 min, and then blow with dry Ar until there is no obvious liquid and there is no adhesion or agglomeration between the particles. Then put it into a vacuum drying oven. When the pressure in the oven drops to 500 Pa, start heating and drying. The drying temperature is 100 ° C and the drying time is 24 h.

[0131] (2) The treated sample was placed in a vapor deposition furnace for coating. The coating gas was a mixture of methane and acetylene with a volume ratio of 1:1, and an Ar auxiliary atmosphere was introduced. The ratio of carbon source gas to auxiliary gas was 1:1. The deposition temperature was 900°C, the deposition time was 5 hours, and the deposition chamber speed was 5 r / min. The pressure in the deposition chamber was regulated by a pressure valve and maintained at 0.3 MPa. The mass ratio of the coating layer was controlled to be (5±0.5)%.

[0132] (3) The samples after vapor deposition are graded, the materials are screened and regulated to the target particle size, and vacuum dried at 100°C for 24 hours to form the finished negative electrode material.

[0133] Example 3

[0134] This embodiment provides a negative electrode material, and its preparation method is similar to that of Example 1, except that: in step (1), 1000 g of silicon monoxide is weighed, wherein the silicon / oxygen atomic ratio is between 1:0.9 and 1.1.

[0135] Example 4

[0136] This embodiment provides a negative electrode material, and its preparation method is similar to that of Example 1, except that the ratio of carbon source gas to auxiliary gas is 1:3.

[0137] Example 5

[0138] This embodiment provides a negative electrode material, and its preparation method is similar to that of Example 1, except that the ratio of the carbon source gas to the auxiliary gas is 1:4.

[0139] Example 6

[0140] This embodiment provides a negative electrode material, and its preparation method is similar to that of Example 1, except that: in step (1), 1000g of magnesium-aluminum-doped silicon dioxide is weighed, the mass proportion of magnesium is 5%, the mass proportion of aluminum is 5%, and the silicon / oxygen atomic ratio is between 1:0.9 and 1.1.

[0141] Example 7

[0142] This embodiment provides a negative electrode material, and the preparation method thereof includes:

[0143] (1) Weigh 1000g of silicon 2 oxide, where the silicon / oxygen atomic ratio is between 1:0.9 and 1.1. Rinse with deionized water for 30 minutes, then rinse with ethanol for 30 minutes, and then purge with dry Ar until there is no obvious liquid and no adhesion or agglomeration between particles. Place in a vacuum drying oven, reduce the pressure in the oven to 500 Pa, and start heating and drying at 100°C for 24 hours.

[0144] (2) The treated sample was placed in a vapor deposition furnace for coating. Methane gas was selected as the coating gas, and H2 and SO2 auxiliary atmospheres were introduced. The volume ratio of the two auxiliary gases was 1:1, and the ratio of carbon source gas to auxiliary gas was 1:2. The deposition temperature was 900°C, the deposition time was 7 hours, and the deposition chamber speed was 5 r / min. The pressure in the deposition chamber was regulated by a pressure valve and maintained at 1 MPa. The mass ratio of the coating layer was controlled to be (5±0.5)%.

[0145] (3) The samples after vapor deposition are graded, the materials are screened and regulated to the target particle size, and vacuum dried at 100°C for 24 hours to form the finished negative electrode material.

[0146] Comparative Example 1

[0147] This comparative example provides a negative electrode material, the preparation method of which includes:

[0148] (1) 100 g of silicon 2 oxide (silicon dioxide) with a silicon / oxygen atomic ratio of 1:0.9 to -1.1 was added to a mixed organic solvent of 100 g of N-methylpyrrolidone and 20 g of polyimide, stirred for 30 min, and then vacuum dried at 100 ° C for 48 h to remove the solvent.

[0149] (2) The mixed precursors were transferred into a high-pressure reactor, heated to 900°C at a rate of 10°C / min under an argon atmosphere, and reacted for 12 hours.

[0150] (3) The samples after vapor deposition are graded, and the materials are screened and adjusted to the target particle size; the heat-treated materials are then placed in a hydrochloric acid solution with a pH of 2 for 30 minutes, rinsed with deionized water, and then placed in a lithium hydroxide solution with a pH of 11 for 30 minutes, washed with deionized water for 30 minutes, and further rinsed with ethanol and filtered for 30 minutes, and purged with dry argon. After the sample is obviously free of adherent liquid and agglomerated particles, it is placed in a vacuum drying oven and vacuum dried at 100°C for 24 hours to form a finished negative electrode material.

[0151] Comparative Example 2

[0152] This comparative example provides a negative electrode material, the preparation method of which includes:

[0153] (1) Weigh 100 g of lithium-doped silicon oxide, in which the lithium content is 10% by mass and the silicon / oxygen atomic ratio is between 1:0.9 and 1.1. Rinse with deionized water for 30 minutes, then rinse with ethanol for 30 minutes, and then blow with dry Ar until there is no obvious liquid and there is no adhesion or agglomeration between the particles. Then put it into a vacuum drying oven, the pressure in the oven drops to 500 Pa, and start heating and drying. The drying temperature is 100 ° C and the drying time is 24 hours.

[0154] (2) Place the treated sample in a vapor deposition furnace for coating. Pure acetylene is used as the coating gas for carbon source deposition. Plasma is used for acetylene decomposition deposition. The deposition time is 48 hours. The plasma source is generated by an electron sputtering radio frequency gun with graphite as the target. A bias voltage of -400V is set on the material stage in the deposition chamber to ensure the deposition of the carbon source. After the plasma is stabilized, the pressure in the chamber is controlled by a vacuum valve and maintained at 100 Pa.

[0155] (3) The samples after vapor deposition are graded and the materials are screened and adjusted to the target particle size; then placed in a vacuum drying oven and vacuum dried at 100°C for 24 hours to form a finished negative electrode material.

[0156] Comparative Example 3

[0157] This comparative example provides a negative electrode material, the preparation method of which includes:

[0158] (1) Weigh 100 g of magnesium-doped silicon dioxide, in which the lithium content is 8.5% by mass and the silicon / oxygen atomic ratio is between 1:0.9 and 1.1. Rinse with deionized water for 30 min, then rinse with ethanol for 30 min, and then blow with dry Ar until there is no obvious liquid and there is no adhesion or agglomeration between the particles. Then put it into a vacuum drying oven, the pressure in the oven drops to 500 Pa, and start heating and drying. The drying temperature is 100 ° C and the drying time is 24 h.

[0159] (2) Place the treated sample in a vapor deposition furnace for coating. Pure acetylene is used as the coating gas for carbon source deposition. Plasma is used for acetylene decomposition deposition. The deposition time is 48 hours. The plasma source is generated by an electron sputtering radio frequency gun with graphite as the target. A bias voltage of -400V is set on the material stage in the deposition chamber to ensure the deposition of the carbon source. After the plasma is stabilized, the pressure in the chamber is controlled by a vacuum valve and maintained at 100 Pa.

[0160] (3) The samples after vapor deposition are graded and the materials are screened and adjusted to the target particle size; then placed in a vacuum drying oven and vacuum dried at 100°C for 24 hours to form a finished negative electrode material.

[0161] Various performance tests were performed on the negative electrode materials in Examples 1-7 and Comparative Examples 1-3. The test results are shown in Table 1. The isothermal adsorption-desorption curves of the negative electrode materials prepared in Example 1 and Comparative Example 1 are also shown in Figures 1 and 2, respectively.

[0162] The isothermal adsorption-desorption curve is obtained by measuring the pore size distribution and porosity of the negative electrode material by mercury intrusion porosimetry and gas adsorption method in accordance with GB / T 21650.3-2011 standard.

[0163] Particle size test: The particle size test was conducted in accordance with the national standard GB / T 24533-2019 using a Malvern Mastersizer 3000 to obtain D50 data.

[0164] Tap density: Data obtained by testing in accordance with the method specified in the national standard GB / T 24533-2019.

[0165] Coating mass percentage test: Tested in accordance with the method specified in the national standard GB / T 20123-2006. For carbon-coated negative electrode materials: The sample is burned in a high-temperature furnace with oxygen to generate and release CO2 gas. This method is used to separate the C element from the metal element and its compounds. The carbon content in the sample is calculated by measuring the CO2 content. For ceramic coatings, the mass ratio of the ceramic raw materials during the synthesis process is used to convert the mass of the ceramic coating according to the final mass of the ceramic produced after firing. For example, ceramic precursors A and B react at high temperature to generate the target ceramic D and the by-product gas E. The reaction equation is A+B=D+E. By adding the masses of A and B, the mass of D m is obtained. D , the mass of silicon-based raw material is m Si , through the formula m D / (m Si +m D ) to obtain the mass percentage of ceramic coating layer.

[0166] Lithium content of doped metal elements ICP (ppm): The negative electrode material is burned in a muffle furnace to remove carbon, hydrofluoric acid is used to digest Si and heated, and then aqua regia is added for digestion. Post-processing is carried out in accordance with the method specified in the national standard GB / T 24533-2019 to obtain data.

[0167] Table 1 Test results of negative electrode materials of Examples 1-7 and Comparative Examples 1-3

[0168] The electrochemical performance tests were also conducted on the negative electrode materials in the above Examples 1-7 and Comparative Examples 1-3. The specific test results are shown in Table 2.

[0169] The battery sample fabrication process involved assembling button cells using the equipment and methods outlined in BTRTC / ZY / 01-020, "Button Cell Method Operating Instructions," based on the specific capacity of the negative electrode material and the initial charge and discharge coulombic efficiency. The counter electrode used a lithium metal sheet, and the separator was a PP-PE-PP composite film with a diameter of 19.2 mm. The electrolyte composition ratio was EC / EMC / DMC = 1:1:1, and the lithium salt (LiPF6) concentration was 1.05 mol / L.

[0170] Electrochemical performance test:

[0171] Material capacity test: Use button battery charging and discharging equipment, 0.1C constant current charging to 10mV, then 0.02C constant current charging to 5mV, and 0.1C constant current discharge to 1.5V cutoff.

[0172] Half-cell 50-week cycle test: using button cell charging and discharging equipment, in the first week, discharge at 0.1C to 0.01V, then discharge at 0.01C in asymmetric decreasing order to 0.01V, then discharge at 0.01C to 0.005V, and charge at 0.1C to 1.5V; in the second week, discharge at 0.2C to 0.01V, then discharge at 0.02C in asymmetric decreasing order to 0.01V, then discharge at 0.02C to 0.005V, and charge at 0.2C to 1.5V; in the third week, discharge at 0.5C to 0.0 1V, 0.05C discharge in equal steps to 0.01V, 0.05C discharge to 0.005V, 0.5C charge to 1.5V; from the 4th to the 50th week, 1C discharge to 0.01V, 0.1C discharge in equal steps to 0.01V, 0.1C discharge to 0.005V, 1C charge to 1.5V; in the 51st week, 0.1C discharge to 0.01V, 0.01C discharge in equal steps to 0.01V, 0.01C discharge to 0.005V.

[0173] Full battery performance test: Graphite is mixed into the negative electrode material to achieve a standard capacity of 450mAh / g. The capacity retention rate (2.75V-4.2V) is tested at a high temperature (60°C) for 7 consecutive days under 0.2C charge and discharge.

[0174] Table 2 Electrochemical performance test results of negative electrode materials of Examples 1-7 and Comparative Examples 1-3

[0175] It should be noted that the adsorption equilibrium curve and hysteresis loop area are numerical representations of the surface pore structure distribution, which can affect the electrochemical properties of the material. By fine-tuning the pore structure through appropriate synthesis techniques, the material's performance can be improved, and different cores also have a certain impact on the material.

[0176] As can be seen from Table 2, in Comparative Example 1, the pore structure changes are relatively simple, and the hysteresis loop area is relatively small. Outside the optimized range, this situation will cause the electrode to expand. This is because the pore structure is simple, which is conducive to electrolyte infiltration, but the surface side reactions are uncontrolled. In Example 7, by mixing the auxiliary gas into the carbon source gas, the pore structure in the carbon layer during the carbon deposition process and the pore structure between the carbon layers can be regulated, thereby forming different pore structures and pore distributions inside the coating layer, increasing the hysteresis loop area, and facilitating the expansion of the silicon-based material core and stabilizing the SEI growth interface. Compared with Comparative Example 1, the expansion rate of the buckled electrode sheet of Example 6 is significantly reduced, and the corresponding cycle capacity retention rate also shows a difference. Combined with the test results of Comparative Example 1 and Example 7 in Table 1, this shows that the differential ratio ΔΦ of the pore structure can describe the electrochemical changes caused by the pore structure of the negative electrode material. When ΔΦ is within the appropriate range, it can improve the electrolyte infiltration of complex pore structures and enhance the transfer of active lithium in the electrolyte to the negative electrode material, thereby improving the rate performance. The complex pore structure provides a weak polarization transmission barrier for the thermal conduction of lithium ions, which is beneficial to limit the degradation reaction at high temperature and improve the high-temperature storage capacity retention rate.

[0177] In the preparation methods of the negative electrode materials of Example 1 and Comparative Example 2, both use the same lithiated core, but different coating processes are used to regulate the pore structure of the surface coating layer, so that the differential ratio ΔΦ of the pore structure of the obtained negative electrode material is different. Although the hysteresis loop area ΔS of Comparative Example 2 is within the optional range, the calculated differential ratio ΔΦ of the pore structure exceeds the optional range and is 0.568. Combined with the electrochemical performance test results in Table 2, it can be seen that the pore structure in the coating layer of the negative electrode material prepared in Comparative Example 2 is very complex. During charging and discharging, a large amount of electrolyte degradation byproducts (SEI) exist in the pores of the surface coating layer of the negative electrode material. Then, after the volume expansion of the lithiated silicon-based core, it will destroy the pore structure filled with electrolyte, and then tear the coating layer on the surface of the negative electrode material, causing the electrolyte degradation to be out of control. Although the expansion rate of the negative electrode sheet is improved, the rate performance is reduced. In Table 2, the rate charging performance of Comparative Example 2 at three rates of 1C / 0.5C, 2C / 0.5C, and 3C / 0.5C is lower than that of Example 1 by 3.49%, 5.67%, and 5.75%, respectively.

[0178] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present disclosure.

[0179] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this disclosure and to form different embodiments. For example, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this disclosure and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art. Industrial Applicability

[0180] The present disclosure provides a negative electrode material, a preparation method thereof, and a lithium-ion battery. By providing a coating layer with a special pore structure on the negative electrode material, the diffusion coefficient of the lithium core of the negative electrode material is greatly improved, thereby improving the rate performance and cycle performance of the battery, thereby having excellent practical performance.

Claims

1. A negative electrode material, characterized in that: It comprises a core and a coating layer formed on at least a portion of the surface of the core, wherein the core comprises a silicon-based material, and the negative electrode material has a pore structure; The differential ratio of the pore structure Satisfaction: 1×10 -3 ≤ΔΦ≤0.5; Wherein, ΔS is the area of ​​the hysteresis loop in the isothermal adsorption-desorption curve of the negative electrode material; s is the specific surface area of ​​the negative electrode material; ΔP is the interval difference of the relative pressure P / P0 corresponding to the hysteresis loop, 0<ΔP≤1; Q max is the maximum isothermal adsorption capacity of the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that At least one of the following conditions is met: a. The silicon-based material includes at least one of elemental silicon, silicon oxide, silicon carbide, silicon nitride, silicon phosphide, silicon sulfide, and silicon alloy; b. The core further comprises a carbon material; c. The core also includes doped metal elements.

3. The negative electrode material according to claim 1, characterized in that At least one of the following conditions is met: a. The coating layer comprises at least one of a carbonaceous material and a ceramic material; b. The mass of the coating layer is 0.5%-10% of the total mass of the negative electrode material; c. The thickness of the coating layer is 20nm-700nm.

4. The negative electrode material according to claim 1, characterized in that The differential ratio ΔΦ of the pore structure satisfies 5×10 -3 ≤ΔΦ≤0.

5.

5. The negative electrode material according to claim 1, characterized in that The area of ​​the hysteresis loop ΔS satisfies 4.5×10 -4 ≤ΔS≤3.0×10 -2 .

6. The negative electrode material according to claim 1, characterized in that The maximum isothermal adsorption capacity Q of the negative electrode material max ≤1.35mmol / g.

7. The negative electrode material according to claim 1, characterized in that The BJH average pore size of the negative electrode material is 5nm-20nm, and the BJH pore volume satisfies 1.0×10 -4 cm 3 / g≤V BJH ≤0.1cm 3 / g.

8. The negative electrode material according to claim 3, characterized in that At least one of the following conditions is also met: a. The carbonaceous material comprises at least one of graphite, hard carbon, soft carbon, amorphous carbon, diamond-like carbon, carbon fiber, carbide, asphalt, and resin-based polymers; b. The ceramic material includes at least one of phosphate, silicate, nitride and metal oxide.

9. The negative electrode material according to claim 1, characterized in that The coating layer has the pore structure.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that: The pore structure includes micropores, mesopores and macropores.

11. A method for preparing a negative electrode material, characterized in that: include: The silicon-based material core to be coated is subjected to CVD vapor deposition coating treatment to obtain a negative electrode material with a porous structure. material; The gas for vapor deposition includes an auxiliary gas and a carbon source gas, wherein the volume proportion of the carbon source gas is 30%-95%, and the volume proportion of the auxiliary gas is 5%-70%; In the negative electrode material, the differential ratio of the pore structure Satisfies: 1×10-3≤ΔΦ≤0.5; Wherein, ΔS is the area of ​​the hysteresis loop in the isothermal adsorption-desorption curve of the negative electrode material; s is the specific surface area of ​​the negative electrode material; ΔP is the interval difference of the relative pressure P / P0 corresponding to the hysteresis loop, 0<ΔP≤1; Qmax is the maximum isothermal adsorption capacity of the negative electrode material.

12. The preparation method according to claim 11, characterized in that: At least one of the following conditions is met: A. The auxiliary gas includes at least one of H2, SO2, NH3, and Ar; B. In the mixed gas, the volume proportion of the carbon source gas is 30%-95%, and the volume proportion of the auxiliary gas is 5%-70%.

13. The preparation method according to claim 11, characterized in that: Before the CVD vapor deposition process is performed, the silicon-based material core to be coated is pre-treated.

14. The preparation method according to claim 13, characterized in that: At least one of the following conditions is met: C. The pretreatment comprises: screening, grading, cleaning and drying the silicon-based material core to be coated in sequence; D. The particle size D of the silicon-based material core to be coated obtained after the pretreatment 50 =2.5μm-9.0μm; E. The specific surface area of ​​the silicon-based material core to be coated obtained after the pretreatment is 0.5 m 2 / g-7.5m 2 / g.

15. A lithium ion battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 10, or comprises the negative electrode material prepared by the preparation method according to any one of claims 11 to 14.

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