Negative electrode material and battery

Abstract

A negative electrode material, which comprises an active material, the active material comprising a silicon material and a carbon matrix having pores, wherein at least part of the silicon material is located in the pores of the carbon matrix. The true density of the negative electrode material is ρ g / cm3, the total pore volume thereof is V cm3 / g, and the negative electrode material satisfies the following formula: M=ρV / (ρ+V), where 0.020≤M≤0.085. The negative electrode material has strong structural stability and a low volume expansion rate, and has characteristics such as a high capacity, high initial Coulombic efficiency and good cycling performance.

Description

Negative electrode material and battery Cross-reference to related applications

[0001] The present application claims priority to the Chinese patent application No. 202410424313.3, filed on April 10, 2024, and entitled "Negative electrode material and preparation method thereof, and battery". TECHNICAL FIELD

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

[0003] In recent years, 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 used in electric vehicles, power tools and other fields. Therefore, developing lithium ion batteries with higher energy density is a current trend. The positive and negative electrode materials are the core of the battery, which determines the working efficiency of the battery. At present, the commercial negative electrode material is graphite, and its capacity has approached the theoretical limit, so there is limited room for further improvement. Therefore, it is urgent to develop a new generation of high-energy-density negative electrode material.

[0004] Silicon-based negative electrode materials are generally considered to be the next generation of battery negative electrode materials, which have the advantages of high capacity, abundant source, and relative safety. However, silicon-based negative electrode materials have a severe volume expansion effect during the cycling process, which can cause the negative electrode material to pulverize and break, resulting in rapid cycle decay of the negative electrode material. In the prior art, in order to reduce the volume expansion effect of the silicon-based negative electrode material during the cycling process, the silicon-based negative electrode material is usually subjected to carbon coating treatment, so that the volume expansion effect of the silicon-based negative electrode material obtained by the treatment is alleviated to a certain extent, but there are still shortcomings such as unstable cycling and poor rate performance, which still need to be further improved and optimized. SUMMARY

[0005] The present application provides a negative electrode material and a battery, which can improve the cycling performance of the silicon-based negative electrode material while taking into account the capacity of the silicon-based negative electrode material.

[0006] In a first aspect, the present application provides a negative electrode material, which includes an active substance, the active substance including a silicon material and a carbon matrix having pores, at least part of the silicon material being located in the pores of the carbon matrix; the true density of the negative electrode material is ρg / cm 3 , the total pore volume is V cm 3 / g, and the negative electrode material satisfies the following formula: M = ρV / (ρ+V), 0.020≤M≤0.085. The silicon material may, for example, be silicon particles.

[0007] In a second aspect, the present application also provides a battery including the negative electrode material as described above.

[0008] Compared with the prior art, the technical solution has at least the following technical effects: the negative electrode material satisfies the relationship: 0.020≤M=ρV / (ρ+V)≤0.085, the negative electrode material has strong structural stability, low volume expansion rate, high capacity, high first coulomb efficiency, and excellent cycle performance, and the like. In the negative electrode material, the total pore volume V cm 3 / g refers to the space in the carbon matrix material that is not filled, the larger the V value, the larger the space reserved in the negative electrode material, and the more obvious the buffering effect of silicon expansion, which is beneficial to reducing the volume expansion rate of the negative electrode material. However, a too large V value will lead to a decrease in the capacity of the negative electrode material, and will also lead to a decrease in the pressure resistance of the negative electrode material and a decrease in the lithium ion transmission efficiency. The true density ρ g / cm 3 is the density of the negative electrode material particles divided by the volume excluding the internal and external voids of the particles, which is a standard value that is not related to the total pore volume V cm 3 / g. For the silicon-carbon composite negative electrode material of the present application, since the density of silicon and the density of carbon are different, the ρ value reflects the degree of filling of the carbon matrix by the silicon material. The more the pores in the carbon matrix are filled with silicon material, the larger the true density ρ value of the negative electrode material, and the more beneficial to improving the capacity and pressure resistance of the negative electrode material. However, it is also easy to cause the silicon material and the pore wall of the carbon matrix where the silicon material is distributed to be excessively matched, even to be interference fit, which is not conducive to providing a buffer space for the expansion of the silicon material, and will lead to an increase in the volume expansion rate of the negative electrode material, thereby leading to a decrease in the cycle performance of the negative electrode material. The present application considers the dual influence of the true density and the total pore volume of the negative electrode material, and includes ρ and V in the calculation formula of the comprehensive performance measurement parameter M of the negative electrode material. The inventors have found that when the negative electrode material satisfies the relationship: 0.020≤M=ρV / (ρ+V)≤0.085, it has high capacity, high first coulomb efficiency, and excellent cycle performance, and can meet the application requirements. The embodiments of the present application summarize the parameters affecting the capacity, first coulomb efficiency, and cycle performance of the negative electrode material into the calculation formula of the comprehensive performance measurement parameter M of the negative electrode material, and by adjusting and optimizing the related parameters in the calculation formula, the comprehensive performance measurement parameter M of the negative electrode material is within the above range, and the negative electrode material has high capacity, high first coulomb efficiency, and excellent cycle performance at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a process flow diagram of the preparation method of the present application in an embodiment;

[0010] FIG. 2 is an XRD diagram of the silicon-based negative electrode material prepared in Example 1 of the present application;

[0011] FIG. 3 is a first charge-discharge curve diagram of the silicon-based negative electrode material prepared in Example 1 of the present application;

[0012] FIG. 4 is a cycle performance curve of the silicon-based negative electrode material prepared in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0013] In order to better understand the technical solutions of the present application, the embodiments of the present application are described in detail as follows.

[0014] It should be clear that the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0015] The terms used in the embodiments of the present application are merely for the purpose of describing the specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0016] It should be understood that the term "and / or" used herein is merely to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " herein generally represents an "or" relationship between the front and rear associated objects.

[0017] In a first aspect, the present application provides a negative electrode material.

[0018] In the embodiments of the present application, the negative electrode material comprises an active material, the active material comprises a silicon material and a carbon matrix having pores, and at least part of the silicon material is located in the pores of the carbon matrix; the true density of the negative electrode material is ρg / cm 3 , the total pore volume is V cm 3 / g, and the negative electrode material satisfies the formula: M=ρV / (ρ+V), 0.020≤M≤0.085. Specifically, M can be 0.020, 0.030, 0.035, 0.040, 0.045, 0.050, 0.055, 0.070, 0.080, 0.085.

[0019] The negative electrode material of the embodiments of the present application satisfies the relationship formula: 0.020≤M=ρV / (ρ+V)≤0.085, and has strong structural stability, low volume expansion rate, high capacity, high first coulombic efficiency, excellent cycle performance and other characteristics. In the negative electrode material, the total pore volume V cm 3V is the total pore volume of the negative electrode material, and g is the space in the carbon matrix material that is not filled. The greater the value of V, the greater the space reserved in the negative electrode material, and the more obvious the buffering effect of the expansion of the silicon material, which is beneficial to reducing the volume expansion rate of the negative electrode material. However, if V is too large, on the one hand, the capacity of the negative electrode material will be reduced, and on the other hand, the pressure resistance of the negative electrode material will be reduced, and the lithium ion transmission efficiency will be reduced. The true density ρ g / cm 3 is the density of the mass of the negative electrode material particles divided by the volume excluding the pores inside and outside the particles. The true density of the negative electrode material is a standard value that is not related to the total pore volume V cm 3 / g. For the silicon-carbon composite negative electrode material of the present application, because the density of silicon and the density of carbon are different, it can be understood that the existence form of the carbon matrix and the silicon material and other factors can also affect the true density ρ value. The size of the ρ value reflects the degree of filling of the carbon matrix by the silicon material. The more the pores in the carbon matrix are filled with silicon material, the greater the true density ρ value of the negative electrode material, and the more beneficial to improving the capacity and pressure resistance of the negative electrode material. However, it is also easy to cause the silicon material to excessively cooperate with the pore walls of the carbon matrix in which it is distributed, and even to be interference fit, which is not conducive to providing a buffer space for the expansion of the silicon material, and will cause the volume expansion rate of the negative electrode material to increase, thereby reducing the cycle performance of the negative electrode material. The present application takes into account the dual influence of the true density and the total pore volume of the negative electrode material, and includes both ρ and V in the calculation formula of the comprehensive performance measurement parameter M of the negative electrode material. The inventors have found that when the negative electrode material satisfies the relationship: 0.020≤M=ρV / (ρ+V)≤0.085, it has high capacity, high first coulomb efficiency, and excellent cycle performance, and can meet the application requirements. The embodiments of the present application summarize the parameters affecting the capacity, first coulomb efficiency, and cycle performance of the negative electrode material into the calculation formula of the comprehensive performance measurement parameter M of the negative electrode material, and by adjusting and optimizing the related parameters in the calculation formula, the comprehensive performance measurement parameter M of the negative electrode material is within the above range, and the negative electrode material has high capacity, high first coulomb efficiency, and excellent cycle performance at the same time.

[0020] In some embodiments, 0.001≤V≤0.1. When V is within this range, it is more beneficial to comprehensively improve the capacity, first coulomb efficiency, and cycle performance of the negative electrode material.

[0021] In some embodiments, 1.7≤ρ≤2.3. When ρ is within this range, it is more beneficial to comprehensively improve the capacity, first coulomb efficiency, and cycle performance of the negative electrode material.

[0022] In some embodiments, the mass percentage of silicon in the negative electrode material is 5% to 90% based on the mass of the negative electrode material, and can be 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, 90%, or any value therebetween. When the value of V is constant, the greater the mass percentage of silicon in the negative electrode material, the greater the value of p. When the mass percentage of silicon in the negative electrode material is within the above range, the value of p can be adjusted to an appropriate range.

[0023] In some embodiments, the silicon material has a gap between the silicon material and the pore wall of the pore of the carbon matrix. When the silicon material has a gap between the silicon material and the pore wall of the pore of the carbon matrix, the gap between the silicon material and the pore wall of the pore of the carbon matrix can provide a buffer space for the expansion of the silicon material, which can reduce the volume expansion rate of the negative electrode material, enhance the structural stability of the negative electrode material, and thus improve the cycle performance of the negative electrode material.

[0024] In some embodiments, the carbon matrix comprises at least one of hard carbon, soft carbon, graphite, mesocarbon microbeads, activated carbon, porous carbon, mesoporous carbon, and carbon gel.

[0025] In some embodiments, the average pore diameter of the pores in the carbon matrix is 1 nm to 10 nm, and can be 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, or any value therebetween. The carbon matrix, i.e., the negative electrode material after removal of the silicon material, is prepared by the following steps: immersing the negative electrode material in a 1M nitric acid solution for 4h, then adding 150mL of 20% mass fraction HF acid solution dropwise into the negative electrode material, which produces yellow smoke, and the process is repeated multiple times until no yellow smoke is produced in the solution; finally, adding a 1M nitric acid solution to digest the residue, then washing and drying to obtain the negative electrode material after removal of the silicon material. The carbon matrix, i.e., the negative electrode material after removal of the silicon material, can also be prepared by the following steps: adding 150mL of 20% mass fraction HF acid solution dropwise into 10g of negative electrode material under stirring, which produces SiF4 and H2 gas and releases heat, and after no gas is produced, centrifuging to remove the supernatant acid solution, then adding 150mL of 20% mass fraction HF acid solution into the negative electrode material again, stirring for 12h, then centrifuging to remove the supernatant acid solution, then washing the negative electrode material with pure water until it is neutral and drying to obtain the negative electrode material after removal of the silicon material.

[0026] In some embodiments, the silicon material comprises at least one of crystalline silicon, amorphous silicon, and a composite of crystalline silicon and amorphous silicon. Preferably, the silicon material is amorphous silicon, which has a lower expansion than other types of silicon, and thus helps to improve the problem of large volume expansion of the silicon-carbon negative electrode material during lithium extraction. In some embodiments, the average particle size of the silicon material is 0.1 nm to 10 nm, and can be specifically 0.1 nm, 1 nm, 4 nm, 6 nm, 8 nm, 10 nm, or any value therebetween. By controlling the size of the silicon material within an appropriate range, the volume expansion of the silicon-based negative electrode material can be inhibited.

[0027] In some embodiments, the silicon material comprises silicon particles. The morphology of the silicon particles comprises at least one of a point shape, a spherical shape, an ellipsoidal shape, and a sheet shape.

[0028] In some embodiments, the mass content of silicon in the silicon material is ≥ 99%.

[0029] In some embodiments, the negative electrode material further comprises a coating layer, and the coating layer is at least partially located on the surface of the active material. The coating layer helps to further reduce the volume expansion rate of the negative electrode material.

[0030] In some embodiments, the coating layer comprises at least one of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0031] In some embodiments, the thickness of the coating layer is 1 nm to 500 nm, and can be specifically 1 nm, 10 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or any value therebetween. When the thickness of the coating layer is within the above range, the electrochemical performance of the negative electrode material, such as the capacity and the rate performance, can be considered, and the cycle performance of the negative electrode material can be improved.

[0032] In some embodiments, the specific surface area of the negative electrode material is ≤ 5.0 m 2 / g.

[0033] In some embodiments, the powder conductivity of the negative electrode material is ≥ 0.1 S / cm.

[0034] In a second aspect, the present application further provides a preparation method of a negative electrode material.

[0035] Referring to FIG. 1, in the embodiments of the present application, the preparation method comprises the following steps:

[0036] S1. preparing an active material comprising a silicon material and a carbon matrix, wherein the carbon matrix has pores, and at least part of the silicon material is located in the pores of the carbon matrix;

[0037] S2. etching the active substance with HF to obtain the negative electrode material, the true density of the negative electrode material being pg / cm 3 , the total pore volume being V cm 3 / g, the negative electrode material satisfying the following formula:

[0038] M = pV / (p+V), 0.020≤M≤0.085.

[0039] In the preparation method of the embodiments of the present application, the true density pg / cm 3 and the total pore volume V cm 3 / g of the negative electrode material are regulated so that the prepared negative electrode material satisfies the relationship: 0.020≤M = pV / (p+V)≤0.085. The prepared negative electrode material has strong structural stability, low volume expansion rate, high capacity, high first coulombic efficiency, and excellent cycle performance. The inventors have found that when the negative electrode material satisfies the relationship: 0.020≤M = pV / (p+V)≤0.085, it has high capacity, high first coulombic efficiency, and excellent cycle performance. In the preparation process of the negative electrode material of the present application, the p value and the V value of the active substance are regulated to the appropriate range through etching treatment, so that the M value of the prepared negative electrode material is within the above range. In the etching process, HF etches the silicon material in the pores of the carbon matrix, increasing the gap size between the silicon material and the pore wall of the carbon matrix in which it is distributed, i.e., providing more buffer space for the expansion of the silicon material, thereby reducing the volume expansion rate of the negative electrode material and further improving the cycle performance of the negative electrode material.

[0040] The preparation method of the embodiments of the present application is described in detail as follows:

[0041] S1. preparing an active substance containing silicon material and carbon matrix, wherein the carbon matrix has pores, and at least part of the silicon material is located in the pores of the carbon matrix.

[0042] In some embodiments, the preparation step of the active substance comprises placing the carbon matrix in a first atmosphere environment containing a silicon source gas for first heat treatment to obtain the active substance.

[0043] In a specific embodiment, the silicon source gas includes at least one of silane and halosilane, for example, monosilane (SiH4), disilane (Si2H6), silicon tetrafluoride (SiF4), etc., which can be selected by those skilled in the art according to actual conditions.

[0044] In an embodiment, the flow rate of the silicon source gas is 0.1 L / min to 500 L / min, and can be 0.1 L / min, 1 L / min, 100 L / min, 200 L / min, 300 L / min, 400 L / min, 500 L / min, or any value therebetween. When the flow rate of the silicon source gas is limited within the above range, it is beneficial to control the true density and total pore volume of the active material prepared to be within an appropriate range, and further beneficial to control the ρ value and V value of the negative electrode material to be within an appropriate range.

[0045] In an embodiment, the volume concentration of the silicon source gas in the first atmosphere environment is 1% to 100%, and can be 1%, 5%, 10%, 20%, 30%, 50%, 60%, 70%, 80%, 90%, 100%, or any value therebetween. By adjusting the volume concentration of the silicon source gas, the content of silicon deposited in the carbon matrix can be adjusted, thereby adjusting the total pore volume. If the concentration of the silicon source gas is too low, the silicon deposited in the carbon matrix will be less, and the total pore volume will increase. Although this can reserve more expansion space for the silicon-based negative electrode material, so that the expansion rate of the negative electrode material is reduced and the cycle performance is enhanced, it will also cause the capacity of the silicon-based negative electrode material prepared to be significantly reduced.

[0046] In an embodiment, the time of the first heat treatment is 100 min to 1000 min, and can be 100 min, 200 min, 400 min, 600 min, 800 min, 1000 min, or any value therebetween. By controlling the time of the first heat treatment within the above range, it is beneficial to control the true density and total pore volume of the active material prepared to be within an appropriate range, and further beneficial to control the ρ value and V value of the negative electrode material to be within an appropriate range.

[0047] In an embodiment, the heating rate of the first heat treatment is 1°C / min to 20°C / min, and can be 1°C / min, 2°C / min, 4°C / min, 8°C / min, 12°C / min, 16°C / min, 20°C / min, or any value therebetween. By controlling the heating rate of the first heat treatment within the above range, it is beneficial to control the true density and total pore volume of the active material prepared to be within an appropriate range, and further beneficial to control the ρ value and V value of the negative electrode material to be within an appropriate range.

[0048] In an embodiment, the first heat treatment includes any one of sintering, chemical vapor deposition, and chemical vapor infiltration. That is, the silicon material obtained by decomposition of the silicon source gas can be deposited on the carbon material by a sintering process, or the silicon material obtained by decomposition of the silicon source gas can be deposited on the carbon material by a chemical vapor deposition or chemical infiltration process.

[0049] In an embodiment, the first atmosphere environment further comprises a protective gas, which comprises at least one of nitrogen, hydrogen, argon and helium. By performing the first heat treatment in the protective gas environment, the purity of the silicon material in the negative electrode material is improved, and thus the electrochemical performance of the negative electrode material is improved.

[0050] In an embodiment, the total pore volume of the carbon matrix is 0.1 cm 3 / g to 1.8 cm 3 / g, specifically 0.1 cm 3 / g, 0.5 cm 3 / g, 1 cm 3 / g, 1.5 cm 3 / g, 1.8 cm 3 / g, or any value therebetween. When the total pore volume of the carbon matrix is within the above range, the content of the silicon material in the negative electrode material is controlled within an appropriate range, and thus the comprehensive improvement of the capacity and cycle performance of the negative electrode material is achieved.

[0051] In an embodiment, the average pore size of the carbon matrix is 1 nm to 10 nm, specifically 1 nm, 2 nm, 4 nm, 6 nm, 8 nm, 10 nm, or any value therebetween. When the average pore size of the carbon matrix is within the above range, the silicon material is uniformly dispersed in the pores of the carbon matrix, and thus more silicon material is left with expansion buffer space between the pore walls of the pores of the carbon matrix.

[0052] S2. The active material is etched using HF to obtain the negative electrode material.

[0053] In some embodiments, the specific steps of the etching treatment include performing a second heat treatment on the active material in a second atmosphere environment containing HF to obtain the negative electrode material.

[0054] In an embodiment, the volume concentration of hydrofluoric acid in the second atmosphere environment is 0.01% to 50%, specifically 0.01%, 1%, 10%, 20%, 30%, 40%, 50%, or any value therebetween. When the volume concentration of hydrofluoric acid is controlled within the above range, the etching rate is controlled within an appropriate range, and thus the ρ value and V value of the negative electrode material are controlled within an appropriate range.

[0055] In an embodiment, the second heat treatment is performed for 1 minute to 800 minutes, and specifically, 1 minute, 10 minutes, 100 minutes, 200 minutes, 300 minutes, 400 minutes, 500 minutes, 600 minutes, 700 minutes, 800 minutes, or any value therebetween. Preferably, the second heat treatment is performed for 10 minutes to 80 minutes. By controlling the second heat treatment within the above range, the ρ value and the V value of the negative electrode material can be adjusted to an appropriate range.

[0056] In an embodiment, the second heat treatment is performed at a temperature of 200°C to 800°C, and specifically, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, or any value therebetween. By controlling the second heat treatment within the above range, the etching rate can be controlled to an appropriate range, and thus the ρ value and the V value of the negative electrode material can be adjusted to an appropriate range.

[0057] In some embodiments, before the etching treatment, the method further comprises a coating treatment on the active material.

[0058] In an embodiment, the coating material of the coating treatment comprises at least one of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0059] In an embodiment, the coating treatment is a carbon coating treatment, and the carbon coating treatment comprises at least one of a solid-phase carbon coating, a liquid-phase carbon coating, and a gas-phase carbon coating.

[0060] In an embodiment, the solid-phase carbon source for the solid-phase carbon coating treatment comprises at least one of sucrose, fructose, glucose, pitch, phenol formaldehyde resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0061] In an embodiment, the gas-phase carbon source for the gas-phase carbon coating treatment comprises at least one of acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0062] In an embodiment, the coating treatment is performed at a temperature of 200°C to 800°C, and specifically, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, or any value therebetween.

[0063] In an embodiment, the coating treatment is performed for 1 minute to 800 minutes, and specifically, 1 minute, 100 minutes, 200 minutes, 300 minutes, 400 minutes, 500 minutes, 600 minutes, 700 minutes, 800 minutes, or any value therebetween.

[0064] In some embodiments, the step of preparing the carbon matrix comprises subjecting a mixture comprising an activating agent and a carbon-based raw material to an activation treatment to obtain the carbon matrix.

[0065] In a specific embodiment, the carbon-based raw material comprises at least one of coconut shell, nutshell carbon, straw carbon, resin carbon, pitch carbon, bamboo charcoal, rice husk, and sugar.

[0066] In a specific embodiment, the activating agent comprises at least one of water vapor, an alkaline substance, and a template agent.

[0067] In a specific embodiment, the alkaline substance comprises at least one of potassium hydroxide and sodium hydroxide.

[0068] In a specific embodiment, the template agent comprises at least one of calcium hydroxide, calcium oxide, magnesium oxide, magnesium hydroxide, melamine, and aluminum oxide.

[0069] In a specific embodiment, the activation treatment is a water vapor activation treatment, and the volume concentration of water vapor in the water vapor activation treatment is 0.01% to 80%, specifically 0.01%, 0.1%, 1%, 10%, 20%, 40%, 60%, 80%, or any value therebetween.

[0070] In a specific embodiment, the temperature of the activation treatment is 500°C to 2000°C, specifically 500°C, 1000°C, 1500°C, 2000°C, or any value therebetween.

[0071] In a specific embodiment, the temperature increasing rate of the activation treatment is 1°C / min to 20°C / min, specifically 1°C / min, 5°C / min, 10°C / min, 15°C / min, 20°C / min, or any value therebetween.

[0072] In a specific embodiment, the time of the activation treatment is 2h to 20h, specifically 2h, 4h, 8h, 12h, 16h, 20h, or any value therebetween.

[0073] In some embodiments, the step of preparing the carbon matrix further comprises subjecting the carbon-based raw material to a carbonization treatment before the activation treatment.

[0074] In a specific embodiment, the temperature of the carbonization treatment is 400°C to 1200°C, specifically 400°C, 600°C, 800°C, 1000°C, 1200°C, or any value therebetween.

[0075] In an embodiment, the carbonization treatment is performed for 2-20 hours, and can be 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, or any value therebetween.

[0076] In some embodiments, after the activation treatment, the step of preparing the carbon matrix further comprises a purification treatment on the material obtained from the activation treatment.

[0077] In an embodiment, the purification treatment comprises washing and drying the material obtained from the activation treatment.

[0078] In an embodiment, the step of preparing the carbon matrix further comprises a crushing and screening treatment on the material obtained from the activation treatment; preferably, the crushing and screening treatment is performed after the purification treatment.

[0079] In a third aspect, the present application further provides a lithium ion battery comprising the negative electrode material as above, or comprising the negative electrode material prepared by the method as above.

[0080] Those skilled in the art will understand that the above-described negative electrode material and the method for preparing the battery are only examples. Other methods commonly used in the art can be used without departing from the content disclosed in the present application.

[0081] The embodiments of the present application are further described in the following examples. The embodiments of the present application are not limited to the following specific examples. Changes can be made appropriately without departing from the scope of the claims.

[0082] Example 1

[0083] (1) Bamboo charcoal is used as a raw material to perform carbonization treatment at a carbonization temperature of 600°C, and then acid washing is performed at a hydrochloric acid concentration of 10 mol / L for 5 hours. The product of the acid washing is dried and then subjected to steam activation treatment by introducing a mixture of water vapor and nitrogen gas, wherein the volume concentration of the water vapor is 3.5%, the activation time is 13 hours, and the activation temperature is 900°C, to obtain a porous carbon material (carbon matrix, average pore diameter 1.8 nm);

[0084] (2) The porous carbon material is placed in a CVD device, and then silane (SiH4) is introduced into the CVD device, the volume concentration of the silane is controlled to be 25%, and the temperature is raised to 490°C, and the reaction is performed for 8 hours to obtain an active material;

[0085] (3) The active material is placed in a reaction furnace, and methane gas is introduced, the volume concentration of the methane is controlled to be 12%, and heat treatment is performed at 720°C for 2 hours to obtain a coated product.

[0086] (4) The reaction furnace is supplied with a mixed gas of HF and argon to etch the coated product, wherein the volume concentration of HF is 0.5%, the etching temperature is 400°C, and the etching time is 40 min; then the temperature is lowered, and the obtained etching product is screened and graded to obtain the negative electrode material.

[0087] The silicon-based negative electrode material of Example 1 is analyzed in combination with FIGS. 2-3. As shown in FIG. 2, the negative electrode material includes amorphous silicon. As shown in FIG. 3, the negative electrode material has a high initial coulombic efficiency, with an initial charge-discharge capacity of 1935 mAh / g and an initial coulombic efficiency of 92.8%. As shown in FIG. 4, the negative electrode material has excellent cycle performance, with a capacity retention rate of 92.4% after 50 cycles.

[0088] Example 2

[0089] (1) The shell is used as a raw material for carbonization treatment at a carbonization temperature of 800°C, followed by acid pickling at a hydrochloric acid concentration of 5 mol / L for 58 h; the pickled product is dried and then subjected to steam activation treatment by supplying a mixed gas of steam and nitrogen, wherein the volume concentration of steam is 2.5%, the activation time is 13 h, and the activation temperature is 900°C, to obtain a porous carbon material (carbon matrix, average pore diameter 1.9 nm);

[0090] (2) The porous carbon material is placed in a CVD device, and then silane (SiH4) is supplied in the CVD device, with the volume concentration of silane controlled at 15%, and the temperature is raised to 500°C, and the reaction is carried out for 7 h to obtain an active substance;

[0091] (3) The active substance is placed in a reaction furnace, and acetylene gas is supplied, with the volume concentration of acetylene controlled at 18%, and heat treatment is carried out at 680°C for 2 h to obtain a coated product.

[0092] (4) The reaction furnace is supplied with a mixed gas of HF and argon to etch the coated product, wherein the volume concentration of HF is 0.1%, the etching temperature is 500°C, and the etching time is 30 min; then the temperature is lowered, and the obtained etching product is screened and graded to obtain the negative electrode material.

[0093] Example 3

[0094] (1) The shell is used as a raw material for carbonization treatment at a carbonization temperature of 800°C, followed by acid pickling at a hydrochloric acid concentration of 5 mol / L for 58 h; the pickled product is dried and then subjected to steam activation treatment by supplying a mixed gas of steam and nitrogen, wherein the volume concentration of steam is 2.5%, the activation time is 13 h, and the activation temperature is 900°C, to obtain a porous carbon material (carbon matrix, average pore diameter 1.9 nm);

[0095] (2) Put the porous carbon material into CVD, then introduce silane (SiH4) into the CVD device, control the volume concentration of silane to be 35%, heat to 450°C, and react for 6 hours to obtain an active substance;

[0096] (3) Put the active substance into a reaction furnace, introduce propane gas, control the volume concentration of propane to be 12%, and heat treat at 670°C for 3 hours to obtain a coated product.

[0097] (4) Introduce a mixed gas of HF and argon into the reaction furnace to etch the coated product, wherein the volume concentration of HF is 1.1%, the etching temperature is 500°C, and the etching time is 40 minutes; then cool down, screen and grade the obtained etching product, and obtain a negative electrode material.

[0098] Example 4

[0099] (1) Take rice husk as raw material, perform carbonization treatment at a carbonization temperature of 950°C, then perform acid pickling at a hydrochloric acid concentration of 5.9 mol / L for 4 hours; after drying, perform water vapor activation treatment by introducing a mixed gas of water vapor and nitrogen, wherein the volume concentration of water vapor is 1.8%, the activation time is 15 hours, and the activation temperature is 850°C, to obtain a porous carbon material (carbon matrix, average pore size 2.2 nm);

[0100] (2) Put the porous carbon material into CVD, then introduce silane into the CVD device, control the volume concentration of silane to be 55%, heat to 550°C, and react for 4 hours to obtain an active substance;

[0101] (3) Put the active substance into a reaction furnace, introduce methane gas, control the volume concentration of methane to be 22%, and heat treat at 670°C for 2 hours to obtain a coated product.

[0102] (4) Introduce a mixed gas of HF and argon into the reaction furnace to etch the coated product, wherein the volume concentration of HF is 1.5%, the etching temperature is 450°C, and the etching time is 60 minutes; then cool down, screen and grade the obtained etching product, and obtain a negative electrode material.

[0103] Example 5

[0104] (1) Put commercial porous carbon (average pore size 1.6 nm) into CVD, then introduce silane into the CVD device, control the volume concentration of silane to be 60%, heat to 520°C, and react for 4 hours to obtain an active substance;

[0105] (3) Put the active substance into a reaction furnace, introduce ethylene gas, control the volume concentration of ethylene to be 26%, and heat treat at 690°C for 2 hours to obtain a coated product.

[0106] (4) Introducing a mixed gas of HF and argon into the reaction furnace, the volume concentration of HF being 0.92%, etching temperature being 600°C, and etching time being 10 min; then cooling, and sieving and grading the obtained etching product to obtain the negative electrode material.

[0107] Example 6

[0108] The difference from Example 1 is that: step (2): the volume concentration of silane is controlled to be 5%, and the deposition time is 15 h.

[0109] Example 7: The difference from Example 1 is that: step (4): the volume concentration of HF is 50%.

[0110] Example 8: The difference from Example 1 is that: step (2): the volume concentration of silane is controlled to be 65%, and the deposition time is 3 h.

[0111] Example 9: The difference from Example 1 is that: step (2): the volume concentration of silane is controlled to be 35%, and the deposition time is 6 h.

[0112] Comparative Example 1

[0113] The difference from Example 1 is that: step (4) is not performed.

[0114] Comparative Example 2

[0115] The difference from Example 1 is that: the etching time in step (4) is 800 min.

[0116] Comparative Example 3

[0117] The difference from Example 1 is that: step (1): the volume concentration of water vapor is 95%.

[0118] Comparative Example 4

[0119] The difference from Example 1 is that: step (2): the volume concentration of silane is controlled to be 0.65%.

[0120] Comparative Example 5

[0121] The difference from Example 1 is that: step (4): the volume concentration of HF is 0.005%.

[0122] Test Method:

[0123] 1. Particle size test:

[0124] Particle size is measured using Mastersizer 3000 laser diffraction technology. Particle size measurement is accomplished by measuring the intensity of scattered light as a laser beam passes through a dispersed particle sample. The data is then used to analyze and calculate the particle size distribution that forms the scatter plot. D50: the particle size corresponding to the cumulative particle size distribution percentage of 50% of a sample. Its physical meaning is that the particles with a particle size greater than it account for 50%, and the particles with a particle size less than it also account for 50%. D50 is also called the median particle size. D90 particle size, D50 particle size, and D10 particle size are the equivalent diameters of the largest particles in the distribution curve when the cumulative distribution is 90%, 50%, and 10%, respectively.

[0125] 2. Average particle size:

[0126] The nano-silicon particles are observed by field emission scanning electron microscopy or transmission electron microscopy. The particle size of 5-10 nano-silicon particles is directly measured by a scale, and the average of the particle sizes is taken as the final nano-silicon particle size.

[0127] 3. Test of the mass content of silicon in the negative electrode material:

[0128] The sample is burned in an oxygen atmosphere using a box-type atmosphere furnace (model: SA2-9-17TP) to make silicon and silicon monoxide in the sample react to form silicon dioxide, and carbon is burned to become carbon dioxide and discharged. The mass content of silicon in the negative electrode material is calculated by weighing.

[0129] 4. Test of the mass content of carbon in the negative electrode material: A German Bruker / German Eltra infrared carbon and sulfur analyzer G4ICARUS HF / CS-i is used. The sample is burned in a high-temperature oxygen-rich state, and the carbon elements contained therein are oxidized to carbon dioxide, enter the infrared detector with the carrier gas, and the content of the carbon elements is calculated by quantitatively analyzing the changes in the infrared absorption wavelength intensity of the carbon dioxide signal.

[0130] 5. Test method for the pore size and pore volume ratio of the carbon matrix:

[0131] The pore volume of the sample refers to the total pore volume possessed by a unit mass of the sample, which can be measured by gas adsorption. Nitrogen adsorption is a technique for characterizing the porosity and pore size distribution of a material by condensing gas in the pores of a solid. As the pressure increases, the gas first condenses in the pores with the smallest diameter, and the pressure increases 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 determination of the pore volume and pore size distribution, as well as the respective pore volumes of micropores, mesopores, and macropores in the total pore volume.

[0132] 6. Specific surface area: The specific surface area is measured using a U.S. Micromeritics TriStar 3000 specific surface area and pore size analyzer.

[0133] 7. Tap density: A certain amount of sample was weighed and tested for tap density using a Buret tap, at 300 times / min, with 3000 times of vibration.

[0134] 8. Coating layer thickness: The average thickness of the coating layer was measured by FIB-SEM equipment for section processing of the material in SEM.

[0135] 9. Powder conductivity: The volume resistivity of the negative electrode material powder was tested by four-probe method using MCP-PD51 powder resistance testing system of Mitsubishi Chemical, Japan. The resistance of the powder at five pressure points of 4, 8, 12, 16, and 20 KN was tested using the instrument, and then the conductivity and resistivity of the negative electrode material powder were automatically calculated by the computer.

[0136] 10. Qualitative determination of amorphous silicon in the negative electrode material: The diffraction peak measured by X-ray diffractometer (XRD) was used to confirm the type of silicon, and the characteristic peak at 2θ = 28.4° was the characteristic peak of amorphous silicon.

[0137] 11. True density (ρg / cm 3 ) test: The true density of the material was tested according to the test method in Appendix D of GBT 24533-2019.

[0138] 12. Pore volume (V cm 3 / g) test: The pore volume of the negative electrode material was tested according to GB / T 7702.20-2008.

[0139] 13. Electrochemical cycle performance test: The silicon-based negative electrode material prepared in each example and comparative example was mixed with conductive agent and binder at a mass percentage of 94:1:5, dissolved in a solvent, and the solid content was controlled at 50%. The mixture was coated on a copper foil current collector, vacuum dried, and a negative electrode sheet was prepared. Then, a ternary positive electrode sheet prepared by a conventional mature process, 1 mol / L LiPF6 / EC+DMC+EMC (v / v=1:1:1) electrolyte, Celgard2400 separator, and shell were assembled into a 18650 cylindrical single battery using a conventional production process. The charge-discharge test of the cylindrical battery was carried out on a LAND battery test system of Wuhan Jinuo Electronics Co., Ltd. at room temperature, with 0.2C constant current charge-discharge, and the charge-discharge voltage limit was 2.75V-4.2V. The test results of Examples 1-9 and Comparative Examples 1-5 are shown in Table 1 below.

[0140] With reference to FIGS. 2-4, the above Table 1 is analyzed: it can be seen from the comparison of Examples 1-9 with Comparative Examples 1-5 that when the M value of the prepared negative electrode material is in the range of 0.020-0.085, the negative electrode material has a lower expansion rate, and at the same time has excellent cycle performance and a higher first coulomb efficiency. When the M value is too low, the expansion rate of the negative electrode material is relatively large, and its application is greatly limited. When the M value is too high, the capacity of the negative electrode material decreases, and the first coulomb efficiency decreases.

[0141] It can be seen from the comparison of Comparative Example 1 with Example 1 that no HF is used to etch the silicon material in the pores of the carbon matrix in Comparative Example 1, and the M value of the negative electrode material prepared in Comparative Example 1 is too low, which does not meet the range 0.020≤M≤0.085. Therefore, the volume expansion rate and cycle performance of the negative electrode material of Comparative Example 1 are poorer than those of Example 1.

[0142] It can be seen from the comparison of Comparative Example 2 with Example 1 that the etching time in step (4) of Comparative Example 2 is too long, which will cause the silicon material in the negative electrode material to be etched too much. The M value of the negative electrode material prepared in Comparative Example 2 is too high, which does not meet the range 0.020≤M≤0.085. Therefore, the capacity of the negative electrode material prepared in Comparative Example 2 is significantly reduced compared with the negative electrode material prepared in Example 1.

[0143] It can be seen from the comparison of Comparative Example 3 with Example 1 that the water vapor volume concentration in step (1) of Comparative Example 3 is too large, and the activated pores (average pore size) of the carbon matrix become larger (the average pore size of the carbon matrix in Example 1 and Comparative Example 3 is 1.9 nm and 4.5 nm, respectively, measured according to the test method described above). The M value of the negative electrode material prepared in Comparative Example 3 is too low, which does not meet the range 0.020≤M≤0.085. Therefore, the expansion and cycle performance of the negative electrode material prepared in Comparative Example 3 is poorer than that of the negative electrode material prepared in Example 1.

[0144] It can be seen from the comparison of Comparative Example 4 with Example 1 that the silane volume concentration in step (2) of Comparative Example 4 is reduced, and the time is unchanged, which causes less silicon to be deposited in the carbon matrix, and the total pore volume increases. The M value of the negative electrode material prepared in Comparative Example 4 is too high, which does not meet the range 0.020≤M≤0.085. Therefore, the capacity of the negative electrode material prepared in Comparative Example 4 is significantly reduced compared with the negative electrode material prepared in Example 1.

[0145] It can be seen from the comparison of Comparative Example 5 with Example 1 that the HF volume concentration in step (4) of Comparative Example 5 is too low, which causes the etching rate of the silicon material in the negative electrode material to be slow, and the pore-etching effect is not obvious. The M value of the negative electrode material prepared in Comparative Example 5 is too low, which does not meet the range 0.020≤M≤0.085. Therefore, the volume expansion rate of the negative electrode material prepared in Comparative Example 5 is increased, and the cycle performance is poorer than that of the negative electrode material prepared in Example 1.

[0146] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that The active material comprises a silicon material and a carbon matrix having pores, wherein at least a portion of the silicon material is located in the pores of the carbon matrix; The true density of the negative electrode material is ρg / cm 3 , the total pore volume is V cm 3 / g, the negative electrode material satisfies the following formula: M=ρV / (ρ+V), 0.020≤M≤0.

085.

2. The negative electrode material according to claim 1, wherein The silicon material includes silicon particles.

3. The negative electrode material according to any one of claims 1 to 2, characterized in that 0.001≤V≤0.1。 4. The negative electrode material according to any one of claims 1 to 3, characterized in that 1.7≤ρ≤2.

3.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that Based on the mass of the negative electrode material, the mass proportion of silicon element in the negative electrode material is 5% to 90%.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that There is a gap between at least a portion of the silicon material and the pore walls of the carbon matrix in which the silicon material is distributed.

7. The negative electrode material according to any one of claims 1 to 6, characterized in that The carbon matrix includes at least one of hard carbon, soft carbon, graphite, mesophase carbon microbeads, activated carbon, porous carbon, mesoporous carbon and carbon gel.

8. The negative electrode material according to any one of claims 1 to 7, wherein The average pore diameter of the pores in the carbon matrix is ​​1 nm to 10 nm.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that The silicon material includes at least one of crystalline silicon, amorphous silicon, and a composite of crystalline silicon and amorphous silicon.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that The average particle size of the silicon material is 0.1 nm to 10 nm.

11. The negative electrode material according to any one of claims 1 to 10, characterized in that The mass content of silicon element in the silicon material is ≥99%.

12. The negative electrode material according to any one of claims 1 to 11, wherein Possess at least one of the following characteristics: (1) The negative electrode material includes a coating layer, and the coating layer is at least partially located on the surface of the active material; (2) The negative electrode material includes a coating layer, and the coating layer includes at least one of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide; (3) The negative electrode material includes a coating layer, and the thickness of the coating layer is 1 nm to 500 nm.

13. The negative electrode material according to any one of claims 1 to 12, characterized in that The specific surface area of ​​the negative electrode material is ≤5.0m 2 / g.

14. The negative electrode material according to any one of claims 1 to 13, characterized in that The powder conductivity of the negative electrode material is ≥0.1S / cm.

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

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