Negative electrode material and battery

Abstract

A negative electrode material and a battery. The negative electrode material comprises a carbon material and silicon particles, the negative electrode material having pores. The average shape factor of the negative electrode material is F0, where 0.65≤F0<1. The average shape factor F0 of the negative electrode material is obtained by testing in the following manner: randomly acquiring 10 negative electrode material particles; measuring the cross-sectional area Sn and the perimeter Cn of each negative electrode material particle, where Fn=4×π×Sn / Cn 2, n being a natural number selected from 1 to 10; calculating the average value of shape factors Fn of the 10 particles; and recording the average value as the average shape factor F0 of the negative electrode material. The negative electrode material has a stable structure, reducing collapse of the structure of the negative electrode material caused by volume expansion of silicon particles during deintercalation and intercalation of lithium, and effectively reducing the occurrence of side reactions, thus improving the cycle performance of the negative electrode material.

Description

Anode materials and batteries

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on August 29, 2023, with application number 202311101191.6 and application name “Negative Electrode Materials and Batteries”; priority to the Chinese patent application filed with the State Intellectual Property Office on November 29, 2023, with application number 202311605506.0 and application name “Negative Electrode Materials and Batteries”; priority to the Chinese patent application filed with the State Intellectual Property Office on February 7, 2024, with application number 202410172027.2 and application name “Negative Electrode Materials and Batteries”; all contents of which are incorporated by reference into this application. Technical Field

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

[0003] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, long cycle life, low environmental impact, and lack of memory effect. However, the low theoretical specific capacity of conventional carbon anode materials (372 mAh / g) has limited their widespread use. To increase the energy density of lithium-ion batteries, researchers are searching for high-capacity anode materials. Silicon-based anode materials, with their theoretical specific capacity reaching 4200 mAh / g, have become a research hotspot.

[0004] However, the volume expansion of silicon-based negative electrode materials during the alloying process with lithium is quite serious, and as the cycle proceeds, silicon-based negative electrode materials will undergo attenuation mechanisms such as pulverization, contact loss with conductive agents and current collectors, and the formation of unstable solid electrolyte interfaces (SEI), thereby leading to the degradation of the electrochemical performance of the negative electrode materials.

[0005] Among them, carbon materials have excellent electrical conductivity and mechanical properties. When combined with silicon, they can not only effectively alleviate the volume expansion of silicon, but also improve the conductivity of the electrode and obtain a stable SEI film. Silicon-carbon composite materials are the first silicon-based negative electrode materials to enter commercialization. They can shorten the transmission distance of Li+ and help improve the kinetic performance of the material. However, nano-silicon particles have a large specific surface area, the SEI film easily consumes excessive lithium salts, and the volume effect easily causes electrical separation between particles, resulting in reduced reversible capacity and coulombic efficiency. Moreover, nano-sized silicon particles are easily agglomerated when distributed in carbon materials, resulting in a high volume expansion effect of the material and even causing the material to break, thereby reducing the structural stability and cycle performance of the negative electrode material.

[0006] Therefore, there is an urgent need for a silicon-carbon negative electrode material with low expansion, high capacity and excellent cycle performance.

[0007] Application Contents

[0008] The present application provides a negative electrode material and a battery. The negative electrode material has a stable structure, reduces the collapse of the negative electrode material structure caused by the volume expansion of silicon particles during the lithium insertion and extraction process, effectively reduces the occurrence of side reactions, and thus improves the cycle performance of the negative electrode material.

[0009] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a carbon material and silicon particles, the negative electrode material having pores;

[0010] The average shape factor of the negative electrode material is F0, 0.65≤F0<1;

[0011] The average shape factor F0 of the negative electrode material is obtained by testing in the following manner:

[0012] Randomly obtain 10 negative electrode material particles and measure the cross-sectional area S of each negative electrode material particle n and the perimeter C n , F n =4*π*S n / C n 2 , n is a natural number from 1 to 10, calculate the shape coefficient F of 10 particles n The average value is recorded as the average shape factor F0 of the negative electrode material.

[0013] The technical solution of this application has at least the following beneficial effects:

[0014] The negative electrode material provided in the present application includes carbon material and silicon particles. Controlling the shape coefficient of the negative electrode material can effectively reduce the obvious edges and corners of the particles and increase the isotropy of the negative electrode material particles. During the charge and discharge process, the negative electrode material can shrink and expand relatively uniformly along the radial direction, which can reduce the stress concentration problem caused by the volume expansion of the active material silicon particles in the negative electrode material, which is beneficial to maintaining the stability of the particle structure of the negative electrode material and reducing the pulverization of the particles of the negative electrode material; and can reduce the stress concentration problem near the edges and corners caused by the volume expansion of the silicon particles in the negative electrode material, which is beneficial to maintaining the stability of the particle structure of the negative electrode material. DETAILED DESCRIPTION

[0015] To better illustrate the present application and facilitate understanding of the technical solution of the present application, the present application is further described below. However, the following embodiments are merely simplified examples of the present application and do not represent or limit the scope of protection of the present application. The scope of protection of the present application shall be subject to the claims.

[0016] The embodiment of the present application provides a negative electrode material, the negative electrode material includes a carbon material and silicon particles, and the negative electrode material has pores;

[0017] The average shape factor of the negative electrode material is F0, 0.65≤F0<1;

[0018] The average shape factor F0 of the negative electrode material is obtained by testing in the following way:

[0019] Randomly obtain 10 negative electrode material particles and measure the cross-sectional area S of each negative electrode material particle n and the perimeter C n , F n =4*π*S n / C n 2 , n is a natural number from 1 to 10, calculate the shape coefficient F of 10 particles n The average value is recorded as the average shape factor F0 of the negative electrode material.

[0020] The negative electrode material provided in the present application includes carbon material and silicon particles. Controlling the shape coefficient of the negative electrode material can effectively reduce the obvious edges and corners of the particles and increase the isotropy of the negative electrode material particles. During the charging and discharging process of the battery prepared with the negative electrode material, the negative electrode material can shrink and expand relatively uniformly along the radial direction, which can reduce the stress concentration problem caused by the volume expansion of the active substances in the negative electrode material, such as silicon particles, and is beneficial to maintaining the stability of the particle structure of the negative electrode material and reducing the pulverization of the particles of the negative electrode material; and can also reduce the stress concentration problem near the edges and corners caused by the volume expansion of the silicon particles in the negative electrode material, which is beneficial to maintaining the stability of the particle structure of the negative electrode material.

[0021] Specifically, the average shape factor F0 of the negative electrode material can be 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.72, 0.73, 0.74, 0.75, 0.76, 0.78, 0.79, 0.8, 0.81, 0.82, 0.85, 0.89, 0.90, 0.92, 0.93, 0.94, 0.95, 0.96, 0.98, 0.99, etc., which are not limited here. The cross-sectional area S and perimeter C of the particles can be automatically picked up by the software, and the shape factor F n Used to characterize the roundness of particle boundaries. Therefore, controlling the average shape factor of the negative electrode material within the range of 0.65 to 1 effectively reduces the apparent angularity of the particles. Maintaining the average shape factor of the negative electrode material particles within the above range can reduce the gaps between the negative electrode material particles, ensuring that the electrolyte fully infiltrates the negative electrode material, while also helping to increase the compaction density of the negative electrode material and improve the cycle performance of the negative electrode material.

[0022] In some embodiments, the particle fractal dimension of the negative electrode material is X0, 1<X0<3; the particle fractal dimension X0 of the negative electrode material is obtained by testing in the following manner:

[0023] Randomly obtain 10 negative electrode material particles and measure the cross-sectional area S of each negative electrode material particle n and the perimeter C n , X n =(log(C n )-b)*2 / log(S n ), b is a constant, and the cross-sectional area S of each negative electrode material particle is n and perimeter C n Fill in the double logarithmic table and use the least square method to obtain the slope φ of the fitting line. The particle fractal dimension of the negative electrode material is X0=2*φ.

[0024] It can be understood that the particle fractal dimension X0 is used to characterize the self-similarity of the particle outline, and usually reflects the rate of change of length (such as perimeter) under different measurement scales (such as different areas). For negative electrode materials, the area perimeter method fractal dimension (X) is used to reflect the change pattern of its complexity with the area of ​​the particle. When X0=1, the fractal dimension of all particles of the negative electrode material is the same; when 3>X0>1, the fractal dimension of the particles of the negative electrode material decreases with the increase of the particle area, and the lower the morphological similarity of the particles. The particle fractal dimension of the negative electrode material in the present application is controlled within the above range, and the higher the morphological similarity of the particles, that is, the higher the uniformity of the particle morphology.

[0025] The negative electrode material provided in the present application controls the particle fractal dimension of the negative electrode material. The particle fractal dimension X0 is used to characterize the self-similarity of the particle contour. The higher the morphological similarity of the particles of the negative electrode material, the higher the uniformity of the particle morphology. During the charge and discharge process, the negative electrode material can shrink and expand relatively uniformly along the radial direction, which can reduce the stress concentration problem caused by the volume expansion of the active material silicon particles in the negative electrode material, is beneficial to maintaining the stability of the particle structure of the negative electrode material, reduces the pulverization of the particles of the negative electrode material, and is beneficial to the negative electrode material in the battery cell to exhibit excellent electrochemical performance.

[0026] In this application, a 1M nitric acid solution is added to the negative electrode material and soaked for 4 hours. Then, a 20% mass fraction HF acid solution is dripped into the negative electrode material drop by drop, which will produce yellow smoke. The dripping is repeated several times until no yellow smoke is produced in the solution. Finally, the residue is digested with a 1M nitric acid solution, and then washed and dried to obtain the negative electrode material after removing the silicon particles.

[0027] In some embodiments, when the negative electrode material satisfies 0.65≤F0<1, the negative electrode material and the negative electrode material after removing silicon particles are tested by N2 adsorption-desorption method, and the volume ratio of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume ratio of nitrogen adsorbed at 10% partial pressure is A, 1.3≤A≤2.5;

[0028] The ratio of the volume of nitrogen adsorbed by the negative electrode material after the silicon particles are removed at a 90% partial pressure to the volume of nitrogen adsorbed at a 10% partial pressure is B, 1≤B≤1.9; and A / B>1.

[0029] It can be understood that the physical and chemical state of the negative electrode material after removing the silicon particles is close to the physical and chemical state of the carbon material before filling the silicon particles, and its porosity is high. The volume of nitrogen adsorbed by the negative electrode material after removing the silicon particles at 90% partial pressure is P 90 The volume of nitrogen adsorbed at 10% partial pressure P 10 The ratio is between 1 and 1.9; the volume of nitrogen adsorbed by the negative electrode material after filling with silicon particles at 90% partial pressure P 90 The volume of nitrogen adsorbed at 10% partial pressure P 10 The ratio is between 1.3 and 2.5. Since silicon particles fill a large number of pores in the carbon material, especially micropores, the pore volume of the negative electrode material is significantly reduced, and the pores are mainly mesopores and macropores, and the A value increases.

[0030] In some embodiments, when the negative electrode material satisfies 0.65≤F0<1, the gas production of the negative electrode slurry prepared from the negative electrode material after being placed in a 25°C environment for 24 hours is ≤1 mL / g, and the gas production of the negative electrode slurry prepared from the negative electrode material after being placed in a 45°C environment for 24 hours is ≤2 mL / g.

[0031] Gas production value test method: disperse carboxymethyl cellulose CMC in water at a mass ratio of 1.4% for gluing. After uniform dispersion, take 10g of glue and mix it with 10g of negative electrode material to obtain a slurry; put the slurry into an aluminum-plastic film bag, and record the slurry mass; then seal it to form a sealed aluminum-plastic film bag, fix the sealed aluminum-plastic film bag at the bottom of the container, completely immerse it in water, and record the volume of the aluminum-plastic film bag; after fixing it for 24 hours, record the volume of the aluminum-plastic film bag again; calculate the gas production of the silicon negative electrode material based on the change in the volume of the aluminum-plastic film, unit: mL / g.

[0032] In some embodiments, the average pore size of the pores in the negative electrode material is 0.5 nm to 50 nm; illustratively, the average pore size of the pores in the negative electrode material can be 0.5 nm, 0.8 nm, 1.0 nm, 1.3 nm, 1.5 nm, 1.8 nm, 2.0 nm, 3.0 nm, 4.0 nm, 5.0 nm, 8.0 nm, 10.0 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm or 50 nm, etc., without limitation herein. Controlling the average pore size of the pores in the negative electrode material is beneficial for buffering the volume expansion of silicon particles and improving the structural stability of the negative electrode material while improving the rate performance of the negative electrode material. Preferably, the average pore size of the pores in the negative electrode material is 0.5 nm to 20 nm. Further preferably, the average pore size of the pores in the negative electrode material is 1.6 nm to 5 nm.

[0033] In some embodiments, the average pore size of the negative electrode material after removing the silicon particles is 1.7nm to 2.2nm. Specifically, it can be 1.7nm, 1.8nm, 1.9nm, 2.0nm, 2.1nm, 2.2nm, etc., which are not limited here. If the pore size of the carbon material is too small, the gaseous precursor of the silicon particles will find it difficult to penetrate into the pores, and it will easily aggregate on the surface of the carbon material to form a shell structure, resulting in a decrease in the silicon particle content inside the negative electrode material and a decrease in the specific capacity of the negative electrode material; when the pore size of the carbon material is too large, although it is conducive to the filling of silicon particles, it may cause problems such as uneven distribution of silicon particles and silicon segregation, thereby causing uneven expansion of the negative electrode material, excessive local expansion stress, particle breakage, etc., which in turn leads to a decrease in the electrochemical performance of the negative electrode material. Therefore, controlling the average pore size of the carbon material within the above range is conducive to the composite of the carbon material and silicon particles, while improving the rate performance of the negative electrode material, it is conducive to buffering the volume expansion of silicon particles and improving the structural stability of the negative electrode material.

[0034] In some embodiments, the total pore volume of the negative electrode material is 0.001 cm 3 / g~0.4cm 3 / g, the total pore volume of the negative electrode material can be specifically 0.001cm 3 / g, 0.002cm 3 / g, 0.005cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.03cm 3 / g, 0.04cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.1cm 3 / g, 0.2cm 3 / g or 0.4cm 3 / g, etc., and of course, other values ​​within the above range can also be used, which are not limited here. Preferably, the total pore volume of the negative electrode material is 0.001cm 3 / g~0.1cm 3 / g.

[0035] In some embodiments, the total pore volume of the negative electrode material after removing the silicon particles is 0.2 cm 3 / g~2.0cm 3 / g. Specifically, it can be 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 1.95cm 3 / g or 2cm 3 / g, etc., of course, it can also be other values ​​within the above range, which is not limited here. Compared with the negative electrode material after removing the silicon particles, the pore volume of the negative electrode material containing silicon particles is significantly reduced, indicating that the density of the negative electrode material is increased, and the specific capacity of the negative electrode material can be effectively improved. The present application controls the total pore volume of the negative electrode material filled with silicon particles and the negative electrode material without silicon particles within the above range, which can not only improve the specific capacity of the negative electrode material, but also ensure that the negative electrode material can reserve an appropriate amount of pores to alleviate the volume expansion caused by silicon particles during the lithium insertion and extraction process, which is beneficial to improving the cycle performance of the negative electrode material. Preferably, the total pore volume of the negative electrode material after removing the silicon particles is 0.5cm 3 / g~2.0cm 3 / g.

[0036] In some embodiments, the pores in the negative electrode material after removing the silicon particles include micropores, and the volume proportion of the micropores in all pores is ≥80%. Specifically, the volume proportion of micropores with a pore size of less than 2.0 nm in all pores can be 80%, 81%, 82%, 83%, 84%, 85%, 87%, 88%, 90%, 92%, 93%, 95%, 98% or 99%, etc., which are not limited here. It can be understood that the pores of the negative electrode material after removing the silicon particles are mainly micropores. The pore size distribution within this range is conducive to the deposition of silicon particles during the deposition process, which is beneficial to adjust the size of silicon particles and reduce silicon segregation, thereby improving the local expansion stress of the negative electrode material while improving the density of the negative electrode material.

[0037] In some embodiments, in the negative electrode material after removing the silicon particles, the volume proportion of pores with a pore size of 5.0 nm or less in the total pore volume is ≥90%. Specifically, the volume proportion of pores with a pore size of 5.0 nm or less in all pores can be 80%, 81%, 82%, 83%, 84%, 85%, 87%, 88%, 90%, 92%, 93%, 95%, 98% or 99%, etc., which are not limited here. It can be understood that the pores of the negative electrode material (carbon material) after removing the silicon particles are mainly pores below 5.0 nm. The pore size distribution within this range helps to form gas-phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, and thus improve the density of the negative electrode material.

[0038] In some embodiments, the porosity of the negative electrode material after removing the silicon particles is 40% to 60%. Specifically, the porosity can be 40%, 45%, 48%, 50%, 52%, 55%, 56%, 57%, 58%, or 60%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0039] In some embodiments, the pores in the negative electrode material include at least one of micropores, mesopores, and macropores.

[0040] In some embodiments, the volume proportion of micropores in all pores is ≤5%, which may be 5%, 4%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5% or 0.1%, etc., which is not limited here.

[0041] In some embodiments, the volume proportion of mesopores in all pores is 87% to 97%, specifically 87%, 88%, 89%, 90%, 92%, 93%, 94%, 95%, 96% or 97%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0042] In some embodiments, the volume proportion of macropores in all pores is ≤13%, and can be specifically 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3% or 1%, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0043] It is understandable that since the silicon particles fill a large number of pores in the carbon material, especially the micropores, the pores of the negative electrode material are mainly mesopores and macropores.

[0044] In some embodiments, the specific surface area of ​​the negative electrode material after removing the silicon particles is 1300 m 2 / g~2500m 2 / g. Specifically, the specific surface area of ​​the carbon material can be 1300m 2 / g、1500m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g or 2500m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0045] In some embodiments, the tap density of the negative electrode material after removing the silicon particles is ≥0.30 g / cm 3 , specifically 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.10g / cm 3 , 1.20g / cm 3 , 1.30g / cm 3 , 1.40g / cm 3 or 1.50g / cm 3 It is understandable that the carbon material has a large number of pores, the presence of which reduces the density of the carbon material, and sufficient pores are conducive to the deposition of silicon particles.

[0046] In some embodiments, the tap density of the negative electrode material is 0.5 g / cm 3 ~1.5g / cm 3 , specifically 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 or 1.5g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. It can be seen that because the silicon particles fill the pores of the carbon material, the density of the carbon material is increased, so that the tap density of the negative electrode material increases by 80% to 120% compared to the initial carbon material.

[0047] In some embodiments, the carbon material includes at least one of amorphous carbon, crystalline carbon, and mesocarbon microbeads. The carbon material can improve the conductivity of the negative electrode material.

[0048] In some embodiments, at least a portion of the silicon particles are filled within the pores of the carbon material. As can be appreciated, the filling of the silicon particles within the pores of the carbon material ensures a dispersed distribution of the silicon particles and the carbon material. This can, on the one hand, increase the specific capacity of the negative electrode material, and, on the other hand, reduce the porosity of the carbon material after the silicon particles are filled, thereby increasing the density of the negative electrode material, effectively reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and further improving the cycling performance of the material.

[0049] In some embodiments, the silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon; specifically, the silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, etc. Of course, it should be noted that in some cases, the silicon alloy includes elemental silicon particles and alloys.

[0050] In some embodiments, the silicon particles include amorphous silicon. It is understood that amorphous silicon expands isotropically during lithium insertion, which can reduce the collapse of the pore structure in the negative electrode material, inhibit the rapid decay of the specific capacity of the negative electrode material, and improve the lithium insertion cycle performance of the negative electrode material.

[0051] In some embodiments, the negative electrode material may further include other active materials. Active materials refer to substances that can react with lithium to deintercalate and deintercalate lithium. Specifically, the active material includes at least one of Li, Na, K, Sn, Ge, Fe, Mg, Ti, Zn, Al, P, and Cu. The active material may be a single metal.

[0052] In some embodiments, the active material may specifically be Sn particles, Ge particles, or Al particles. In other embodiments, the active material may also be silicon-lithium alloy, silicon-magnesium alloy, etc. Of course, it should be noted that in some cases, the active material includes elemental particles and alloys.

[0053] In some embodiments, the average particle size of the silicon particles is less than 50 nm. Specifically, the average particle size of the silicon particles can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 46 nm, 47 nm, 48 nm, or 49 nm, etc., without limitation herein. Average particle size of silicon particles: Observe the silicon particles using a field emission scanning electron microscope or a transmission electron microscope, directly measure the particle size of 5-10 silicon particles using a scale, and take the average of the particle sizes as the average particle size of the silicon particles.

[0054] In some embodiments, the mass percentage of carbon in the negative electrode material is 40% to 80%, specifically 40%, 50%, 60%, 70%, or 80%, etc., and other values ​​within the above range are also possible and are not limited here. Preferably, the mass percentage of carbon in the negative electrode material is 40% to 60%.

[0055] In some embodiments, the mass content of silicon in the negative electrode material is 20% to 55%, specifically 20%, 25%, 30%, 35%, 40%, 45%, 50%, or 55%, etc., and other values ​​within the above range are also possible and are not limited here. Preferably, the mass content of silicon in the negative electrode material is greater than 35% and less than 55%.

[0056] In some embodiments, the mass ratio of silicon to carbon in the negative electrode material is 0.9 to 1.10, specifically 0.9, 0.92, 0.95, 0.98, 1.0, 1.01, 1.02, 1.05, 1.07, 1.08 or 1.10, etc., which are not limited here. When the mass ratio of silicon to carbon in the negative electrode material is ≤0.9, the specific capacity of the negative electrode material decreases, but the overall cycle performance improves. When the mass ratio of silicon to carbon in the negative electrode material is ≥1.1, the specific capacity of the negative electrode material increases with the increase of silicon content, but the volume expansion effect of silicon is obvious, and the cycle performance of the negative electrode material is affected. When controlled within the above range, it is beneficial to improve the comprehensive specific capacity and cycle stability of the negative electrode material.

[0057] In some embodiments, the mass content of oxygen in the negative electrode material is ≤6%. Specifically, the mass content of oxygen in the negative electrode material can be 1%, 2%, 3%, 4%, 5% or 6%, which is not limited here. It is understandable that if the mass proportion of oxygen is too high, the active material (such as silicon) in the negative electrode material will be partially oxidized, and the pores will be at least partially destroyed, thereby affecting the cycle stability of the material. Controlling the mass proportion of oxygen in the negative electrode material within the above range can ensure that a large amount of inactive SiO2 is not generated in the material, which leads to a decrease in the cycle performance of the negative electrode material. The presence of a small amount of oxygen can utilize surface-passivated silicon oxide to reduce the side reaction between the electrolyte and silicon particles. Preferably, the mass content of oxygen in the negative electrode material is ≤5%.

[0058] In some embodiments, the mass content of water in the negative electrode material is ≤5%, and specifically may be 5%, 4%, 3%, 2.5%, 2%, 1.5%, 1.0%, 0.5%, etc., which is not limited here.

[0059] In some embodiments, the ash content of the negative electrode material is ≤1%, specifically 1%, 0.9%, 0.8%, 0.6%, 0.5%, 0.4%, 0.2%, 0.1%, etc., which is not limited here.

[0060] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g~10m 2 / g. Specifically, the specific surface area of ​​the negative electrode material can be 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 400m 2 / g, or 10m 2 / g, etc., of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the specific surface area of ​​the negative electrode material is 1m 2 / g~10m 2 / g.

[0061] In some embodiments, in the aqueous solution of the negative electrode material, Fe≤100ppm, Na≤50ppm, K≤100ppm, Cu≤25ppm, Cr≤20ppm, Co≤1ppm, Ni≤5ppm, Al≤5ppm, Bi≤2ppm, Mg≤5ppm, Pb≤1ppm, Sb≤1ppm, Sn≤10ppm, Ti≤1ppm, V≤1ppm, S≤20ppm. Since metal impurity ions such as iron, nickel, sodium, and aluminum salts have a lower reduction potential than lithium ions, the metal impurity ions will first be embedded in the negative electrode during the charging process, which will reduce the position of lithium ions embedded in the negative electrode, affect the battery capacity of the negative electrode material, and cause the reversible capacity of the lithium battery to decrease; metal impurity ions such as iron, copper, and zinc will cause self-discharge, and the deposited iron ions can easily puncture the diaphragm, causing micro-short circuits and causing safety issues; and the precipitation of metal impurity ions will prevent the formation of an effective passivation layer on the electrode surface, causing damage to the entire battery. Therefore, controlling the content of the above-mentioned metal impurities is beneficial to improving the electrochemical performance of the negative electrode material.

[0062] In some embodiments, the aqueous solution of the negative electrode material contains Li ≤ 5 ppm, Mn ≤ 20 ppm, Na ≤ 10 ppm, Ca ≤ 20 ppm, K ≤ 1 ppm, and Sr ≤ 1 ppm. By controlling the residual amount of each impurity, the purity of the negative electrode material can be guaranteed and the impact of impurities on the electrochemical performance of the negative electrode material can be reduced.

[0063] In some embodiments, the particle size D of the negative electrode material is 50 , 2μm≤D 50 ≤20μm, and 0.9≤(D 90 -D 10 ) / D 50 ≤5. Specifically, (D 90 -D 10 ) / D 50 The specific value of the ratio can be 0.9, 1.0, 1.1, 1.3, 1.5, 1.6, 1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5, etc., and is not limited here. It is understandable that the larger the particle size of the negative electrode material, the longer the diffusion path of lithium ions. Fractures and other defects are inevitably present in the Si / C lattice structure. These defects increase as the lattice structure expands and contracts during charging. The probability of lithium ions encountering such defects when diffusing in large particles increases, making the diffusion kinetics more difficult and resulting in more irreversible lithium ions than diffusion in small particles. Smaller particles have relatively more defects, which increases the resistance to lithium ion diffusion and prevents some active lithium ions from escaping smoothly during charge and discharge, increasing the irreversible capacity. Fine particles also increase the contact area between the electrode and the electrolyte, which is detrimental to the battery's cycling performance. Taking these two factors into consideration, staying within the above range allows the negative electrode material to achieve better electrochemical performance. Furthermore, when the negative electrode material is prepared into a negative electrode sheet and the negative electrode sheet is used in a battery, the local current density of the negative electrode sheet is uniform in the early stage of discharge, but in the late stage of discharge, the local current density of particles of different sizes varies greatly, and the overpotential of large particles is large, that is, the polarization is larger. Therefore, controlling the uniform distribution of the particle size of the negative electrode material particles can reduce the aggravation of polarization caused by large particles in the late stage of discharge. Preferably, D 10 ≥1.5μm, 5μm≤D 50 ≤9μm, D 90 ≤20μm, and 0.9≤(D 90 -D 10 ) / D 50 ≤1.7.

[0064] In some embodiments, 0.7 ≤ F0 < 1. It is understood that the negative electrode material particles are closer to spherical particles, which can increase the isotropy of the negative electrode material particles. During the charge and discharge process, the negative electrode material can shrink and expand relatively more evenly in the radial direction, which can reduce stress concentration caused by the volume expansion of the active material in the negative electrode material, help maintain the stability of the negative electrode material particle structure, and reduce particle pulverization. Considering production costs, preferably, 0.7 ≤ F0 ≤ 0.8.

[0065] In some embodiments, when 0.7≤F0<1, the specific surface area of ​​the negative electrode material is S1m 2 / g, the total pore volume of the negative electrode material is P1cm 3 / g; C1=S1 / (P1*100), 8≤C1≤20.

[0066] In the present application, the negative electrode material satisfies 0.7≤F0<1 while satisfying 8≤C1≤20. By controlling the specific surface area and total pore volume of the negative electrode material, the negative electrode material has a suitable pore volume, and the negative electrode material has sufficient space to alleviate the volume expansion of the silicon particles in the negative electrode material. At the same time, the specific surface area of ​​the negative electrode material is not too large, thereby reducing the occurrence of side reactions between the negative electrode material and the electrolyte, thereby comprehensively improving various aspects of the negative electrode material performance. The negative electrode material of the present application controls the surface morphology of the negative electrode material and the distribution of pores inside the negative electrode material. The two work together to better alleviate the volume expansion of silicon particles, thereby improving the strength, structural stability and cycle performance of the negative electrode material, and comprehensively improving various aspects of the negative electrode material performance.

[0067] Specifically, the value of C1 can be 8, 9, 10, 11, 12, 15, 16, 18 and 20, etc., which are not limited here. The total pore volume and specific surface area are very important parameters for characterizing the performance of negative electrode materials. There is a close relationship between the total pore volume and the specific surface area. The larger the total pore volume, the more pores there are in the negative electrode material, and the larger the specific surface area. Therefore, the carbon material has a higher tendency to adsorb the gaseous precursor of silicon particles (such as silicon source gas), and the gaseous precursor of silicon particles is more likely to undergo decomposition and deposition reactions in the pores of the carbon material; however, the larger the specific surface area of ​​the negative electrode material, the lower the strength and hardness of the negative electrode material particles, the more side reactions of the negative electrode material, and the lower the cycle stability of the battery prepared with the negative electrode material. When the C1 value of the negative electrode material is too large, the total pore volume of the negative electrode material is too small, or the specific surface area of ​​the negative electrode material is too large, indicating that the pores of the negative electrode material are too few and the pore diameter is large, which reduces the loading amount of the active material in the negative electrode material, and is not conducive to alleviating the volume expansion of the negative electrode material during the charge and discharge process, resulting in a decrease in the capacity, rate performance and cycle performance of the negative electrode material. When the C1 value of the negative electrode material is too small, the total pore volume of the negative electrode material is too large or the specific surface area of ​​the negative electrode material is too small, indicating that the pores of the negative electrode material are too many and the pore diameter is small, the structural stability of the negative electrode material is reduced, and the structure of the negative electrode material is prone to collapse during the charge and discharge process, resulting in a decrease in the cycle performance of the negative electrode material, and an increase in the side reactions between the negative electrode material and the electrolyte, which increases the consumption of active lithium ions, resulting in a decrease in the first efficiency of the negative electrode material.

[0068] In some embodiments, when 0.7≤F0<1, the specific surface area of ​​the negative electrode material after removing the silicon particles is S2m 2 / g, the total pore volume of the negative electrode material after removing silicon particles is P2cm3 / g, C2=S2 / (P2*100), 10≤C2≤25. Specifically, the value of C2 can be 10, 12, 13, 14, 15, 18, 20, 21, 23 and 25, etc., of course, it can also be other values ​​within the above range, which is not limited here. Controlling the C2 of the negative electrode material (i.e., carbon material) after removing the silicon particles within the above-mentioned limited range is beneficial to controlling the total pore volume and specific surface area of ​​the carbon material to be in a balanced state, so that the micropores and small-diameter mesopores (<5nm) inside the carbon material account for a large proportion, which is beneficial to increasing the loading amount and distribution uniformity of silicon particles in the carbon material, reducing local stress concentration, and alleviating the volume expansion of the active material during the charge and discharge process, and maintaining the morphology of the carbon material during charge and discharge. The negative electrode material of the present application controls the surface morphology of the negative electrode material and the distribution of the internal pores of the carbon material. The two work synergistically, which is beneficial to maintaining the morphology of the negative electrode material particles during the charge and discharge process, reducing the breakage of the negative electrode material particles, and better alleviating the volume expansion of silicon particles, thereby improving the strength, structural stability and cycle performance of the negative electrode material, and comprehensively improving all aspects of the performance of the negative electrode material.

[0069] In some embodiments, when 0.7≤F0<1, the tap density of the negative electrode material is 0.8 g / cm 3 ~1.3g / cm 3 Specific examples include 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 or 1.3 g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. It can be seen that due to the silicon particles and / or other active materials filling the pores of the carbon material, the tap density of the negative electrode material increases by 80% to 120% compared to the initial carbon material.

[0070] In some embodiments, when 0.65≤F0<0.7. At this time, although the average shape factor F0 of the negative electrode material decreases, the surface edges and corners of the negative electrode material particles tend to be gentle, or there are no obvious edges and corners. During the charge and discharge process, the negative electrode material can still shrink and expand relatively uniformly in the radial direction, which can reduce the stress concentration problem near the edges and corners caused by the volume expansion of the silicon particles in the negative electrode material, which is beneficial to maintaining the stability of the particle structure of the negative electrode material and reducing the pulverization of the negative electrode material particles; and the average shape factor of the negative electrode material particles is maintained within the above range, which can reduce the gaps between the negative electrode material particles, which is beneficial to improve the compaction density of the negative electrode material and improve the cycle performance of the negative electrode material.

[0071] In some embodiments, when 0.65 ≤ F0 < 0.7, the oil absorption value of the negative electrode material is Q1 mL / 100 g, 30 ≤ Q1 ≤ 80; the oil absorption value of the negative electrode material after removing the silicon particles is Q2 mL / 100 g, 120 ≤ Q2 ≤ 200; and (Q2 - Q1) / Q1 > 0.5. Specifically, the value of Q1 can be 30, 32, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, etc., without limitation here. The value of Q2 can be 120, 130, 140, 150, 160, 170, 180, 190, or 200, etc., without limitation here. The specific value of (Q2-Q1) / Q1 can be 0.51, 0.55, 0.6, 0.7, 0.8, 0.9, 0.95, 1.0, 1.2, 1.5, 1.8, 2.0 or 3, etc., and of course it can also be other values ​​within the above range.

[0072] In the present application, (Q2-Q1) / Q1>0.5 is controlled. Generally, the more developed the pores inside the material are, the greater the oil absorption value will be. Here, by limiting the change in the oil absorption value inside the material before and after deposition, the pores inside the material are limited to be effectively filled, which indirectly reflects the uniform dispersion distribution of silicon particles and carbon materials inside the material. The negative electrode material after removing the silicon particles, that is, the negative electrode material has developed pores before filling with silicon particles, which changes the oil absorption value of the negative electrode material before and after filling with silicon particles. In electrochemical devices, lithium ion intercalation and deintercalation not only require diffusion channels and reaction interfaces, but also require an electrolyte as a medium. According to experimental exploration, the applicant has found that while ensuring that the negative electrode material has excellent wetting properties, improving the filling of silicon particles can increase the specific capacity of the negative electrode material, so that the negative electrode material has both high specific capacity and excellent wetting properties.

[0073] In some embodiments, when 0.65≤F0<0.7, the compaction density of the negative electrode material is 0.80cm 3 / g~1.30cm 3 / g; specifically 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 or 1.3 g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. Controlling the compaction density of the negative electrode material within the above range is beneficial to improving the energy density of the negative electrode material and improving the cycle performance of the negative electrode material.

[0074] In some embodiments, when 0.65≤F0<0.7, the powder conductivity of the negative electrode material at 20 kN is 0.5 S / cm to 2.0 S / cm, specifically 0.5 S / cm, 0.6 S / cm, 0.71 S / cm, 0.75 S / cm, 0.79 S / cm, 0.8 S / cm, 0.9 S / cm, 1.0 S / cm, 1.1 S / cm, 1.2 S / cm, 1.4 S / cm, 1.5 S / cm, 1.8 S / cm, or 2.0 S / cm, etc., and of course other values ​​within the above range are also possible, and are not limited here. Preferably, the powder conductivity of the negative electrode material at 20 kN is greater than 0.7 S / cm and less than 1.5 S / cm.

[0075] Secondly, the present application also provides a method for preparing a negative electrode material using a chemical vapor deposition process. Chemical vapor deposition (CVD) is to place a carbon material in one or more precursor gases, and under set temperature and pressure conditions, the precursor gas reacts and / or decomposes on the surface of the carbon material to produce the desired deposit, thereby obtaining a high-performance negative electrode material.

[0076] The preparation method specifically comprises the following steps:

[0077] S10, providing a carbon material having pores.

[0078] In some embodiments, the preparation process of the carbon material includes the following steps: weighing a certain amount of carbon phenolic resin, adding a surfactant Span85 and mixing them evenly, the mass ratio of phenolic resin to surfactant is <6:1, the dispersion ratio (defined as the mass ratio of phenolic resin to 201 methyl silicone oil (used as a dispersant)) is 0.08-0.12, and then adding 201 methyl silicone oil, stirring evenly and placing in a three-necked flask. After stirring evenly, the temperature is raised to a curing temperature of 120-150°C, and the temperature is kept constant for a certain time (60 minutes) and then cooled to room temperature. Use a Soxhlet extractor to remove the 201 methyl silicone oil to obtain phenolic resin microspheres. The phenolic resin microspheres are placed in a box furnace and carbonized at 500-900°C for 0.5-2.5 hours to obtain a carbonized material. The carbonized material is heated to 500-800°C and activated with water vapor for 2-10 hours to obtain activated carbon. The activated carbon is charged into the furnace and heated to 400-600°C at a rate of 2-10°C / min, the deposition pressure is 0.05-10kPa, the deposition time is 2-1000h, and the silicon source gas flow rate is 0.1-10L / min.

[0079] In other embodiments, the preparation process of the carbon material comprises the following steps: placing the carbon source precursor in a pulverizer, crushing it and grinding it in an automatic mortar, then sieving it to less than 45 μm, and then placing it in a vacuum freeze dryer for freeze drying for 24 hours. The freeze-dried carbon source precursor is placed in a tube furnace, treated at 750°C for 120 minutes under an argon atmosphere, and then soaked in dilute hydrochloric acid (10wt%) for 6 hours to remove inorganic impurities in the carbon source precursor. Then, it is washed with deionized water and anhydrous ethanol until the filtrate is neutral, and placed in a 60°C forced air oven to fully dry to obtain an intermediate. The intermediate is placed in a quartz boat and placed in the middle of a quartz tube in a tube furnace. Before heating, high-purity argon is passed through for 30 minutes to remove the air in the tube, and then the temperature is raised to 700°C~1300°C at a heating rate of 10°C / min and a carbonization treatment is carried out at a constant temperature for 1 hour, and then cooled to room temperature to obtain a carbonized material. Finally, the carbonized material is dried with a mixture of a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 0.2 g / mol to 0.5 g / mol, and then heated to 800°C to 900°C for secondary carbonization treatment, and the secondary carbonization product is immersed in a hydrochloric acid solution. After pickling, the pickled product needs to be ultrasonically washed with ethanol or deionized water until the washing water is neutral, and the solid-liquid separation is carried out and the temperature is raised to 70°C to 90°C for drying. The dried carbon material is subjected to ball milling fluidized bed airflow pulverization, that is, gas is used to impact the carbon material so that the carbon material particles reach a preset particle size to obtain the carbon material.

[0080] In other embodiments, the carbon material can be directly purchased from existing carbon materials that meet the requirements.

[0081] In some embodiments, the specific surface area of ​​the carbon material is S2'm 2 / g, the total pore volume of the negative electrode material after removing silicon particles is P2'cm 3 / g, C2'=S2' / (P2'*100), 10≤C2'≤25. Specifically, the value of C2' can be 10, 12, 13, 14, 15, 18, 20, 21, 23 and 25, etc., of course, it can also be other values ​​within the above range, which is not limited here. Controlling the C2' of the carbon material within the above-mentioned limited range is beneficial to controlling the total pore volume and specific surface area of ​​the carbon material to be in a balanced state, so that the micropores and small-diameter mesopores (<5nm) inside the carbon material account for a large proportion, which is beneficial to increasing the loading amount and distribution uniformity of silicon particles in the carbon material, reducing local stress concentration, and alleviating the volume expansion of the active material during the charge and discharge process, and maintaining the morphology of the carbon material during charge and discharge.

[0082] In some embodiments, the oil absorption value of the carbon material is Q2'mL / 100g, 120≤Q2'≤200; specifically, the value of Q2' can be 120, 130, 140, 150, 160, 170, 180, 190 or 200, etc., which is not limited here.

[0083] In some embodiments, the ratio of the volume of nitrogen adsorbed by the carbon material at a 90% partial pressure to the volume of nitrogen adsorbed at a 10% partial pressure is B', where 1 ≤ B' ≤ 1.9; the value of B' can be 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or 1.9, among others, without limitation herein. It is understood that the carbon material, before being filled with silicon particles, has a high porosity and a relatively large pore size, which facilitates uniform deposition of the active material within the pores.

[0084] In some embodiments, the average pore size of the carbon material is 1.7 nm to 2.2 nm, specifically 1.7 nm, 1.8 nm, 1.9 nm, 2.0 nm, 2.1 nm, 2.2 nm, etc., which are not limited here. When the pore size of the carbon material is too small, the gaseous precursor of the active material (such as silicon oxygen gas) is difficult to penetrate into the pore, resulting in a decrease in the active material content in the negative electrode material and a decrease in the specific capacity of the negative electrode material; when the pore size of the carbon material is too large, although it is conducive to the filling of the active material, it may cause problems such as uneven distribution and segregation of the active material, thereby causing uneven expansion of the negative electrode material, excessive local expansion stress, and particle breakage, etc., which in turn leads to a decrease in the electrochemical performance of the negative electrode material. Therefore, controlling the average pore size of the carbon material within the above range is conducive to the composite of the carbon material and the active material, while improving the rate performance of the negative electrode material, it is conducive to buffering the volume expansion of the active material and improving the structural stability of the negative electrode material.

[0085] In some embodiments, the total pore volume of the carbon material is 0.2 cm 3 / g~2.0cm 3 / g. Specifically, it can be 0.2cm 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.2cm 3 / g, 1.5cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 1.95cm 3 / g or 2.0cm 3 / g, etc., and of course, other values ​​within the above range can also be used, which are not limited here. Preferably, the total pore volume of the negative electrode material after removing the silicon particles is 0.5cm 3 / g~2.0cm 3 / g.

[0086] In some embodiments, in the carbon material, the volume proportion of micropores with a pore size of less than 2.0 nm in the total pore volume is ≥80%. Specifically, the volume proportion of micropores with a pore size of less than 2.0 nm in all pores can be 80%, 81%, 82%, 83%, 84%, 85%, 87%, 88%, 90%, 92%, 93%, 95%, 98% or 99%, etc., which are not limited here. It can be understood that the pores of the carbon material are mainly micropores, and the pore size distribution within this range is conducive to the deposition of silicon particles during the deposition process, which is beneficial to adjust the size of silicon particles and reduce silicon segregation, thereby improving the local expansion stress while improving the density of the negative electrode material.

[0087] In some embodiments, in the carbon material, the volume proportion of pores with a pore diameter of 5.0 nm or less in the total pore volume is ≥ 90%. Specifically, the volume proportion of pores with a pore diameter of 5.0 nm or less in all pores can be 80%, 81%, 82%, 83%, 84%, 85%, 87%, 88%, 90%, 92%, 93%, 95%, 98% or 99%, etc., without limitation herein.

[0088] In some embodiments, in the carbon material, the volume proportion of pores with a pore diameter of less than 1.5 nm in the total pore volume is 20% to 25%, and the volume proportion of pores with a pore diameter of less than 1.6 nm in the total pore volume is 20% to 50%. It can be understood that the pores of the carbon material are mainly micropores. The pore size distribution within this range helps to form gas-phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, and thus improve the density of the negative electrode material.

[0089] In some embodiments, the porosity of the carbon material is 40% to 60%. Specifically, the porosity can be 40%, 45%, 48%, 50%, 52%, 55%, 56%, 57%, 58%, or 60%, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0090] In some embodiments, the carbon material has a specific surface area of ​​1300 m 2 / g~2500m 2 / g. Specifically, the specific surface area of ​​the carbon material can be 1300m 2 / g、1500m 2 / g、2000m 2 / g、2100m 2 / g、2200m2 / g、2300m 2 / g、2400m 2 / g or 2500m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here.

[0091] In some embodiments, the tap density of the carbon material is ≥ 0.30 g / cm 3 , specifically 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.10g / cm 3 , 1.20g / cm 3 , 1.30g / cm 3 , 1.40g / cm 3 or 1.50g / cm 3 It is understandable that the carbon material has a large number of pores, the presence of which reduces the density of the carbon material, and sufficient pores are conducive to the deposition of silicon particles.

[0092] In some embodiments, the carbon material includes at least one of amorphous carbon, crystalline carbon, and mesocarbon microbeads. The carbon material can improve the conductivity of the negative electrode material.

[0093] In some embodiments, the pH value of the carbon material is 6 to 9, specifically 6, 6.5, 7, 7.5, 8, 8.5 or 9, etc., which is not limited here.

[0094] In some embodiments, the mass content of hydrogen in the carbon material is 0.01% to 5%, specifically 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., which is not limited here.

[0095] In some embodiments, the mass content of oxygen in the carbon material is 0.01% to 10%, specifically 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., which is not limited here.

[0096] In some embodiments, the mass content of nitrogen in the carbon material is 0.01% to 0.5%, specifically 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., which is not limited here.

[0097] S20, introducing a reaction gas containing a silicon source gas, and performing vapor deposition on the carbon material to obtain a negative electrode material.

[0098] In some embodiments, the deposition temperature of the vapor deposition is 400° C. to 650° C. Specifically, the deposition temperature can be 400° C., 420° C., 450° C., 470° C., 490° C., 500° C., 530° C., 550° C., 580° C., 600° C., 610° C., 620° C., 630° C., 640° C., or 640° C., etc. Of course, other values ​​between 400° C. and 650° C. are also possible, and are not limited here.

[0099] In some embodiments, the heating rate of the vapor deposition is 2°C / min to 20°C / min, specifically 2°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 13°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min or 20°C / min, etc., which is not limited here.

[0100] In some embodiments, the deposition pressure of the vapor deposition is 0.05 kPa to 101 kPa. Specifically, the deposition pressure can be 0.05 kPa, 0.1 kPa, 0.5 kPa, 1 kPa, 5 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, 50 kPa, 80 kPa, or 101 kPa, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0101] In some embodiments, the deposition time of the vapor deposition is 2 hours to 1000 hours. Specifically, the deposition time can be 2 hours, 5 hours, 10 hours, 50 hours, 100 hours, 150 hours, 200 hours, 250 hours, 300 hours, 350 hours, 400 hours, 500 hours, 600 hours, 650 hours, 700 hours, 800 hours, 900 hours, or 1000 hours, etc. Of course, other values ​​between 2 hours and 1000 hours are also possible, and are not limited here. Preferably, the deposition time of the vapor deposition is 2 hours to 50 hours.

[0102] It can be understood that the process conditions of vapor deposition (such as deposition temperature, deposition pressure and deposition time) will affect the deposition of silicon-based materials in the pores of carbon materials. Controlling the temperature, pressure and time of vapor deposition within the above range can ensure that the reaction gas containing active substances does not decompose and deposit before entering the pores of the carbon material, but quickly decomposes and deposits after entering the pores.

[0103] In some embodiments, vapor deposition is performed under a protective atmosphere.

[0104] In some embodiments, the protective atmosphere includes at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0105] In some embodiments, the reaction gas includes a raw material for a silicon source gas, and the raw material for the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. It should be noted that when the raw material for the silicon source gas is monosilane, disilane, monochlorosilane, or dichlorosilane, it is gaseous at room temperature; when the raw material for the silicon source gas is trichlorosilane or tetrachlorosilane, it is liquid at room temperature. During the vapor deposition process, the liquid silicon source gas vaporizes and becomes a gaseous silicon source.

[0106] In some embodiments, the flow rate of the silicon source gas is 1 L / min to 20 L / min, specifically 1 L / min, 1.5 L / min, 2 L / min, 5 L / min, 6 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min or 20 L / min, etc., which is not limited here.

[0107] In some embodiments, the method further comprises cooling, washing, and drying the vapor-deposited reaction product.

[0108] In some embodiments, the washing method comprises ultrasonic cleaning.

[0109] In some embodiments, the washing solvent comprises anhydrous ethanol.

[0110] In some embodiments, the washing time is 30 min to 60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 51 min, 53 min, 55 min 56 min, 57 min, 58 min, 59 min or 60 min. Of course, it can also be other values ​​within the above range, which is not limited here.

[0111] In some embodiments, the drying time is 20 min to 100 min. Specifically, the drying time can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min or 100 min, etc., which is not limited here.

[0112] In some embodiments, the drying temperature is 70°C to 90°C, specifically 70°C, 75°C, 80°C, 81°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C. Of course, it can also be other values ​​between 70°C and 90°C, which are not limited here.

[0113] The present application also provides a battery comprising the above-mentioned negative electrode material.

[0114] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

[0115] Performance Testing

[0116] (1) Etching treatment of negative electrode materials:

[0117] Add a 1M nitric acid solution to the negative electrode material and soak it for 4 hours. Then, add a 20% mass fraction HF acid solution drop by drop into the negative electrode material, which will produce yellow smoke. Repeat the addition several times until no yellow smoke is produced in the solution. Finally, use a 1M nitric acid solution to digest the residue, then wash and dry it to obtain the negative electrode material after removing the silicon particles, that is, the carbon material.

[0118] (2) Test method for the specific surface area of ​​the negative electrode material or the negative electrode material after removing silicon particles:

[0119] The specific surface area was measured using a Micromeritics TriStar 3000 surface area and pore size analyzer.

[0120] (3) Method for testing the pore volume of the negative electrode material or the negative electrode material after removing silicon particles:

[0121] The test was carried out using the ASAP2460 equipment from American Micromeritics. The pore volume V was calculated using the BJH Desorption cumulative volume of pores model. Calculated within the pore size range.

[0122] Micropore and mesopore analysis was performed using the Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium amount of nitrogen adsorbed on a surface is correlated with properties such as pore size. By combining the relationship between the amount adsorbed and relative pressure during adsorption, various models can be fitted to calculate pore size. The software generates reports using density functional theory (DFT) to calculate pore size distribution, total pore volume, and pore volume within a specific range.

[0123] The true density P of the negative electrode material is tested, and the porosity of the negative electrode material is calculated to be V / (V+1 / P).

[0124] (4) Method for testing the pore size of the negative electrode material or the negative electrode material after removing silicon particles:

[0125] An appropriate amount of sample particles was taken and the pore diameter was measured under a transmission electron microscope (TEM).

[0126] (5) Test method for oil absorption value of negative electrode material or negative electrode material after removing silicon particles:

[0127] Using the ASAHI SOUKEN S-500 Oil Absorption Tester from Japan, a predetermined mass of powder sample is placed in a mixing chamber. Oil (DBP) is then dripped into the sample at a constant rate while simultaneously stirring with a rotor at a constant speed. As the sample absorbs increasing amounts of oil, the mixture changes from a free-flowing state to a semi-plastic agglomerate. During this process, the viscosity of the mixture gradually increases and a peak value appears. The oil absorption value (mL / 100g) is calculated by measuring the amount of oil dripped at 70% of the maximum torque obtained from the torque curve generated by the viscosity change.

[0128] (6) Testing method for average particle size of silicon particles:

[0129] The nano-silicon particles are observed by a field emission scanning electron microscope or a transmission electron microscope, and the particle sizes of 5-10 nano-silicon particles are directly measured by a scale ruler, and the average value of the particle sizes is taken as the final particle size of the nano-silicon particles.

[0130] (7) Test method for particle size of negative electrode material:

[0131] The volume-based cumulative particle size distribution of the particle size distribution was measured using a laser particle size analyzer. 10 Indicates the particle size corresponding to the cumulative particle size distribution percentage of the powder reaching 10%, D 50 Indicates the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, D 90 It indicates the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

[0132] (8) Test method for the mass content of carbon in negative electrode materials:

[0133] Using Germany's Bruker's G4ICARUS HF infrared carbon and sulfur analyzer: the sample is burned in a high-temperature, oxygen-rich state, and the carbon and sulfur elements it contains are oxidized to carbon dioxide and sulfur dioxide, respectively. The generated gases enter the infrared detector with the carrier gas. By quantitatively analyzing the changes in the carbon dioxide signal and the sulfur dioxide signal, the carbon and sulfur content can be calculated respectively.

[0134] (9) Test method for the mass content of silicon in negative electrode materials:

[0135] Use Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace: burn in an oxygen atmosphere, so that the silicon and silicon oxide in the sample react to form silicon dioxide, and the carbon is burned and converted into carbon dioxide and discharged. The silicon content is calculated by weighing.

[0136] (10) Test method for the tap density of negative electrode materials or negative electrode materials after removal of silicon particles:

[0137] The tap density was tested by using a vibrator, weighing 100 g of sample and vibrating 3000 times at 300 times / min.

[0138] (11) Test method for the mass content of nitrogen, oxygen and hydrogen elements in the negative electrode material after removing silicon particles:

[0139] Using a German Verder ONH 2000 oxygen, nitrogen, and hydrogen analyzer, the sample is melted in an inert atmosphere while surrounded by flux. The oxygen it contains is reduced to carbon dioxide by the carbon in the graphite crucible. The resulting carbon dioxide enters the infrared detector along with the carrier gas. Quantitative statistics of changes in the carbon dioxide signal are used to calculate the oxygen content. The sample is also melted in an inert atmosphere while surrounded by flux. The nitrogen and hydrogen it contains decompose to form stable elemental nitrogen and hydrogen, respectively. The resulting nitrogen and hydrogen gases enter the thermal conductivity detector along with the carrier gas. Quantitative statistics of changes in the thermal conductivity cell heat allow the mass content of the nitrogen and hydrogen to be calculated, respectively.

[0140] (13) Negative electrode material compaction density test:

[0141] Using the American McNor CARVER 4350.22 powder compaction density tester, a sample of specified mass m is placed in a mold and a pressure of 1.0 T is applied. After maintaining the pressure for 30 seconds, the pressure is removed and the thickness is tested to calculate the compaction density.

[0142] (14) pH test of negative electrode material:

[0143] A Mettler-Toledo FE20 pH meter is used. The potential difference measured in the solution by a working electrode cell consisting of a measuring electrode and a reference electrode is converted to pH using an ammeter, utilizing the linear relationship between the pH value of the solution being tested and the potential of the working cell. A 5g sample is dispersed in 45mL of water, stirred, and ultrasonicated for 5 minutes, followed by 10 minutes of rest before testing.

[0144] (15) Gas production value test

[0145] Carboxymethyl cellulose (CMC) was dispersed in water at a mass ratio of 1.4% for gluing. After uniform dispersion, 10 g of the glue solution was mixed with 10 g of the negative electrode material to obtain a slurry. The slurry was placed in an aluminum-plastic film bag, and the mass of the slurry was recorded. The bag was then sealed to form a sealed aluminum-plastic film bag, which was fixed to the bottom of a container and completely immersed in water, and the volume of the aluminum-plastic film bag was recorded. After fixing for 24 hours, the volume of the aluminum-plastic film bag was recorded again. The gas production of the silicon negative electrode material was calculated based on the volume change of the aluminum-plastic film, in units of mL / g.

[0146] (16) Electrochemical performance test

[0147] 1) The first discharge capacity and first coulombic efficiency (ICE) were measured by preparing a negative electrode slurry containing the negative electrode material, conductive carbon black, and polyacrylic acid (PPA) in a mass ratio of 75:15:10. This slurry was then coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and button cells were assembled in an argon-filled glove box. The cells were charged and discharged at a current density of 0.1C over the 0.01V-5V range to determine their first discharge capacity and first coulombic efficiency (ICE).

[0148] 2) The test method for the capacity retention rate and the electrode thickness expansion rate after 50 cycles is as follows: a negative electrode material, conductive carbon black (Super-P), conductive graphite (KS-6), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are prepared into a negative electrode slurry in a mass ratio of 92:2:2:2:2, coated on copper foil, and dried to form a negative electrode electrode. The proportion of Si-C and graphite in the mixture of the negative electrode material with a carbon coating layer and graphite is determined by the initial reversible specific capacity of the two and the capacity required to be combined. A button cell is assembled in an argon-filled glove box using a metal lithium sheet as the counter electrode. The button cell is subjected to 50 repeated charge and discharge tests in the charge and discharge range of 0.01V-5V at a current density of 1C to obtain the capacity retention rate and electrode thickness expansion rate after 50 cycles of the battery.

[0149] (17) Full dissolution test method for negative electrode materials:

[0150] A PE / Agilent OPTIMA 8000 / 5000 inductively coupled plasma optical emission spectrometer and a Sigma SGM.M8 / 10A muffle furnace were used. After calcination in a muffle furnace to remove carbon (if any), HF was used to digest and remove silicon. The residue was then digested with nitric acid and the volume was fixed before analysis using an ICP spectrometer.

[0151] (18) ICP test method for negative electrode materials:

[0152] The negative electrode material sample was dissolved in aqua regia, filtered, fixed to volume, and the element content was tested by ICP spectrometer.

[0153] (19) Test method for particle fractal dimension of negative electrode materials:

[0154] Use the Fractal Box Count plug-in to measure the fractal dimension of the particles. Open the image, convert it to 8-bit, and binarize it (Image → Adjust → Threshold). Then open the plug-in (Analyze → Tools → Fractal Box Count). Initialize the parameters. After binarization, select Black Background so that the white portion (pixel value = 255) represents the desired signal and the black portion represents the background. Perform a linear regression on the data within the selected box to obtain the linear regression results and the binning dimension X0.

[0155] Example 1-1

[0156] (1) Select a specific surface area of ​​1800m 2 / g, pore volume 1.2cm 3 / g, the maximum pore size is 9 nm, the average pore size is 1.81 nm, the porosity is 50%, the pH is 8, and the tap density is 0.39 cm 3 / g porous carbon material; wherein pores with a pore diameter of less than 1.5nm account for 22% of the total pore volume, pores with a pore diameter of less than 1.6nm account for 35% of the total pore volume, pores with a pore diameter of less than 2nm account for 82% of the total pore volume, and pores with a pore diameter of less than 5nm account for 95% of the total pore volume; B' of the carbon material is 1.5, C2' of the carbon material is 18; and the average shape factor of the carbon material is 0.89.

[0157] (2) The porous carbon was placed in a chemical vapor deposition furnace, monosilane was used as the working gas, the deposition temperature was 500°C, the deposition time was 10 h, and the flow rate of monosilane was 2 L / min to obtain the negative electrode material;

[0158] The negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material, wherein the carbon material has pores, and at least a portion of the silicon-based material fills the pores. The average shape factor F0 of the negative electrode material is 0.9.

[0159] The remaining parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0160] Example 1-2:

[0161] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0162] Examples 1-3

[0163] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0164] Examples 1-4

[0165] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0166] Examples 1-5

[0167] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0168] Examples 1-6

[0169] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0170] Examples 1-7

[0171] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0172] Examples 1-8

[0173] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0174] Examples 1-9

[0175] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0176] Examples 1-10

[0177] The difference from Example 1-1 is that a carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1. The parameters of the negative electrode material in this example are shown in Table 2.

[0178] Examples 1-11

[0179] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0180] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0181] Examples 1-12

[0182] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0183] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0184] Examples 1-13

[0185] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0186] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0187] Examples 1-14

[0188] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0189] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0190] Examples 1-15

[0191] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0192] The porous carbon was placed in a chemical vapor deposition furnace, monosilane was used as the working gas, the deposition temperature was 550°C, the deposition time was 9 hours, and the flow rate of monosilane was 1 L / min to obtain the negative electrode material;

[0193] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0194] Examples 1-16

[0195] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0196] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0197] Examples 1-17

[0198] The difference from Example 1 is that a carbon material with pores is selected. The specific parameters of the pore structure of the carbon material are shown in Table 1.

[0199] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0200] Comparative Example 1-1

[0201] The difference from Example 1 is that:

[0202] A carbon material with pores is selected, and the specific parameters of the pore structure of the carbon material are shown in Table 1.

[0203] The parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0204] Table 1. Parameters of carbon materials

[0205] Table 2. Parameters of negative electrode materials without silicon particles

[0206] Table 3. Parameters of negative electrode materials

[0207] Table 4. Performance test results of examples and comparative examples

[0208] According to the results shown in Tables 1 to 3, the negative electrode materials prepared in Examples 1-1 to 1-15 of the present application have high initial discharge specific capacity, initial coulombic efficiency, and capacity retention rate after 50 cycles, and the electrode thickness expansion rate after 50 cycles is low. This is because the particle shape of the negative electrode material prepared in this embodiment is close to spherical particles, and the spherical particles have a pore structure with an appropriate number and pore size distributed inside. The spherical particles can increase the isotropy of the negative electrode material. During the charge and discharge process, the negative electrode material can shrink and expand relatively uniformly along the radial direction, which can reduce the stress concentration problem caused by the volume expansion of the silicon-based material. At the same time, the average shape factor of the negative electrode material particles remains within the above range, indicating that the higher the morphological similarity of the individual negative electrode material particles, the more uniform the stress in all directions to which the individual negative electrode material particles in the negative electrode active material layer on the surface of the electrode sheet are subjected after the negative electrode material is coated to form the negative electrode sheet. This is conducive to the uniform release of expansion stress in all directions, which is conducive to maintaining the stability of the particle structure and reducing particle pulverization, thereby improving the cycle performance of the material.

[0209] According to the test data of Examples 1-1, 1-14 to 1-15, and 1-16 to 1-17, when the average shape factor F0 of the negative electrode material is controlled within the range of 0.65 to 1, the negative electrode material also satisfies 8≤C1≤20, indicating that the negative electrode material has an appropriate number and diameter of pores, so that there is sufficient space in the negative electrode material to alleviate the expansion of the active material in the negative electrode material. At the same time, the specific surface area of ​​the negative electrode material is not too large, thereby reducing the occurrence of side reactions between the negative electrode material and the electrolyte, thereby comprehensively improving various aspects of the negative electrode material performance. Therefore, the data of Example 1-16 is better than that of Example 1-17.

[0210] The average shape coefficient F0 of the negative electrode material of comparative example 1-1 is too small, and the particle shape has obvious more angular edges. During the electrode sheet rolling process, the negative electrode material particles are easily partially broken, resulting in increased side reactions between the negative electrode material and the electrolyte, increased consumption of active lithium ions, and a decrease in the initial efficiency of the negative electrode material; during the charge and discharge process, the local stress of the negative electrode material particles is concentrated, the particles are further broken and pulverized, and the cycle performance of the material is reduced.

[0211] Ideally, the closer the average shape factor of the negative electrode material is to 1, the closer the particles are to spherical, the more uniformly the negative electrode material can shrink and expand radially, and the less likely the particles of the negative electrode material will break. In Examples 1-1 to 1-17 above, the applicants were able to improve the average shape factor of the negative electrode material by pre-screening the carbon material and selecting a suitable carbon material for composite with silicon particles. However, this also leads to increased production costs. Furthermore, pre-screening the carbon material is time-consuming and labor-intensive.

[0212] Generally, in order to improve the average shape factor of the negative electrode material, the negative electrode material is spheroidized to improve the average shape factor of the negative electrode material. A large amount of heat is generated during the spheroidization process, which causes partial oxidation of the silicon particles in the negative electrode material and a decrease in the specific capacity of the negative electrode material. In addition, the spheroidization process will also cause part of the negative electrode material to be pulverized, and the side reactions of the negative electrode material will increase, affecting the cycle performance of the negative electrode material.

[0213] Therefore, based on further research and development of the negative electrode material, the applicant found that when the average shape factor F0 of the negative electrode material is controlled within the range of 0.65 to 0.79, the negative electrode material can also meet the expected usage requirements and can significantly reduce production costs.

[0214] Example 2-1

[0215] (1) Coconut shells were crushed in a crusher and ground in an automatic mortar, and then sieved to less than 45 μm for later use. The crushed coconut shells were freeze-dried in a vacuum freeze dryer for 24 hours, then placed in a tube furnace and treated at 750°C for 120 minutes under an argon atmosphere. The shells were then soaked in dilute hydrochloric acid (10 wt%) for 6 hours to remove inorganic impurities in the material. The material was then washed with deionized water and anhydrous ethanol until the filtrate was neutral, and placed in a forced air oven at 60°C overnight to obtain an intermediate.

[0216] (2) The intermediate is placed in a quartz boat and placed in the middle of a quartz tube in a tube furnace. Before heating, high-purity argon gas is passed through the tube for 30 minutes to purge the air inside the tube. The temperature is then raised to 1000°C at a rate of 10°C / min and carbonized for 1 hour at this temperature. The carbonized material is then cooled to room temperature to obtain the carbonized material.

[0217] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:2, and evaporated at 60°C for 24 h to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 h, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10 wt%) and soaked for 24 h; after washing and drying, it was ball milled and fluidized bed air flow pulverized to obtain the carbon material.

[0218] (4) The carbon material was placed in a chemical vapor deposition furnace, monosilane was used as the working gas, the deposition temperature was 500°C, the deposition time was 10 h, and the flow rate of monosilane was 2 L / min to obtain the negative electrode material.

[0219] The negative electrode material prepared in this embodiment includes a carbon material and silicon particles. The carbon material has pores, and at least a portion of the silicon particles are filled in the pores. The average shape factor F0 of the negative electrode material is 0.7.

[0220] The remaining parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0221] Example 2-2:

[0222] (1) Coconut shells were crushed in a crusher and ground in an automatic mortar, and then sieved to less than 45 μm for later use. The crushed coconut shells were freeze-dried in a vacuum freeze dryer for 24 hours, then placed in a tube furnace and treated at 750°C for 120 minutes under an argon atmosphere. The shells were then soaked in dilute hydrochloric acid (10 wt%) for 6 hours to remove inorganic impurities in the material. The material was then washed with deionized water and anhydrous ethanol until the filtrate was neutral, and placed in a forced air oven at 60°C overnight to obtain an intermediate.

[0223] (2) The intermediate is placed in a quartz boat and placed in the middle of a quartz tube in a tube furnace. Before heating, high-purity argon is passed through the tube for 30 minutes to purge the air. The temperature is then raised to 700°C at a rate of 10°C / min and held constant for 1 hour. The carbonized material is then cooled to room temperature to obtain the carbonized material.

[0224] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:4, and evaporated at 60°C for 24 hours to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 hours, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10wt%) and soaked for 24 hours; after washing and drying, it was ball milled and fluidized bed air flow pulverized to obtain the carbon material.

[0225] (4) The carbon material was placed in a chemical vapor deposition furnace, disilane was used as the working gas, the deposition temperature was 450°C, the deposition time was 16 h, and the disilane flow rate was 3 L / min to obtain the negative electrode material.

[0226] The negative electrode material prepared in this embodiment includes a carbon material and silicon particles. The carbon material has pores, and at least a portion of the silicon particles are filled in the pores. The average shape factor F0 of the negative electrode material is 0.73.

[0227] The remaining parameters of the negative electrode material in this embodiment are detailed in Table 2.

[0228] Example 2-3

[0229] (1) Coconut shells were crushed in a crusher and ground in an automatic mortar, and then sieved to less than 45 μm for later use. The crushed coconut shells were freeze-dried in a vacuum freeze dryer for 24 hours, then placed in a tube furnace and treated at 750°C for 120 minutes under an argon atmosphere. The shells were then soaked in dilute hydrochloric acid (10 wt%) for 6 hours to remove inorganic impurities in the material. The material was then washed with deionized water and anhydrous ethanol until the filtrate was neutral, and placed in a forced air oven at 60°C overnight to obtain an intermediate.

[0230] (2) The intermediate is placed in a quartz boat and placed in the middle of a quartz tube in a tube furnace. Before heating, high-purity argon is passed through the tube for 30 minutes to purge the air. The temperature is then raised to 1300°C at a rate of 10°C / min and held constant for 1 hour. The carbonized material is then cooled to room temperature to obtain the carbonized material.

[0231] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:6, and evaporated at 60°C for 24 hours to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 hours, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10wt%) and soaked for 24 hours; after washing and drying, it was ball milled and fluidized bed air flow pulverized to obtain the carbon material.

[0232] (4) The carbon material was placed in a chemical vapor deposition furnace, monosilane was used as the working gas, the deposition temperature was 550°C, the deposition time was 6 hours, and the flow rate of monosilane was 1 L / min to obtain the negative electrode material.

[0233] The negative electrode material prepared in this embodiment includes a carbon material and silicon particles. The carbon material has pores, and at least a portion of the silicon particles are filled in the pores. The average shape factor F0 of the negative electrode material is 0.66.

[0234] Examples 2-4

[0235] (1) Coconut shells were crushed in a crusher and ground in an automatic mortar, and then sieved to less than 45 μm for later use. The crushed coconut shells were freeze-dried in a vacuum freeze dryer for 24 hours, then placed in a tube furnace and treated at 750°C for 120 minutes under an argon atmosphere. The shells were then soaked in dilute hydrochloric acid (10 wt%) for 6 hours to remove inorganic impurities in the material. The material was then washed with deionized water and anhydrous ethanol until the filtrate was neutral, and placed in a forced air oven at 60°C overnight to obtain an intermediate.

[0236] (2) The intermediate is placed in a quartz boat and placed in the middle of a quartz tube in a tube furnace. Before heating, high-purity argon is passed through the tube for 30 minutes to purge the air. The temperature is then raised to 900°C at a rate of 10°C / min and held constant for 1 hour. The carbonized material is then cooled to room temperature to obtain the carbonized material.

[0237] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:2, and evaporated at 60°C for 24 h to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 h, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10 wt%) and soaked for 24 h; after washing and drying, it was ball milled and fluidized bed air flow pulverized to obtain the carbon material.

[0238] (4) The carbon material was placed in a chemical vapor deposition furnace, monosilane was used as the working gas, the deposition temperature was 400°C, the deposition time was 18 hours, and the flow rate of monosilane was 3 L / min to obtain the negative electrode material.

[0239] The negative electrode material prepared in this embodiment includes a carbon material and silicon particles. The carbon material has pores, and at least a portion of the silicon particles are filled in the pores. The average shape factor F0 of the negative electrode material is 0.79.

[0240] Examples 2-5

[0241] The difference from Example 2-1 is that:

[0242] The carbon source precursors used are different; bamboo is used as the carbon source precursor.

[0243] Examples 2-6

[0244] The difference from Example 2-1 is that:

[0245] Step (1) is not performed.

[0246] Examples 2-7

[0247] The difference from Example 2-1 is that:

[0248] (3) The carbonized material was mixed with KOH solution at a mass ratio of 1:10 (KOH concentration in the solution was 0.2 g / ml), and the dried mixed sample was obtained after evaporation at 60 °C for 24 h.

[0249] Examples 2-8

[0250] The difference from Example 2-1 is that:

[0251] (3) The carbonized material was mixed with KOH solution at a mass ratio of 1:0.2 (KOH concentration in the solution was 0.2 g / ml), and the dried mixed sample was obtained after evaporation at 60 °C for 24 h.

[0252] Examples 2-9

[0253] The difference from Example 2-3 is that:

[0254] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:1.5, and evaporated at 60°C for 24 h to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 h, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10 wt%) and soaked for 24 h; after washing and drying, it was ball milled in a fluidized bed air flow to obtain a carbon material.

[0255] Comparative Example 2-1

[0256] The difference from Example 2-1 is that:

[0257] (3) The carbonized material was mixed with a KOH solution (KOH concentration in the solution was 0.2 g / ml) in a mass ratio of 1:4, and evaporated at 60°C for 24 h to obtain a dry mixed sample. The mixed sample was placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min and maintained for 2 h, and then naturally cooled to room temperature. The black powder sample was placed in dilute hydrochloric acid (mass fraction of 10 wt%) and soaked for 24 h; after washing and drying, it was ball milled and pulverized by collision pin type air flow to obtain the carbon material.

[0258] Comparative Example 2-2

[0259] The difference from Example 2-1 is that:

[0260] (4) The carbon material is loaded into a chemical vapor deposition furnace, monosilane is used as the working gas, the deposition temperature is 500°C, the deposition time is 10 hours, the flow rate of monosilane is 2 L / min, and the deposited product is ball-milled and fluidized bed-type air flow pulverized to obtain the negative electrode material.

[0261] The negative electrode material prepared in this embodiment includes a carbon material and silicon particles. The carbon material has pores, and at least a portion of the silicon particles are filled in the pores. The average shape factor F0 of the negative electrode material is 0.86.

[0262] Table 5. Parameters of negative electrode materials after removing silicon particles

[0263] Table 6. Parameters of negative electrode materials

[0264] Table 7. Parameters of negative electrode materials

[0265] Table 8. Performance test results of examples and comparative examples

[0266] According to the results shown in Tables 4 to 6, the negative electrode materials prepared in the examples of the present application have high initial discharge specific capacity, initial coulombic efficiency, and capacity retention after 50 cycles, and the electrode thickness expansion rate after 50 cycles is low. This is because the average shape factor of the negative electrode materials prepared in this example is controlled within the range of 0.65 to 0.79, which can effectively reduce the obvious edges and corners of the particles. During the charge and discharge process, the negative electrode material can shrink and expand relatively uniformly along the radial direction, which can reduce the stress concentration problem near the edges and corners caused by the volume expansion of the silicon particles in the negative electrode material, and is conducive to maintaining the stability of the particle structure of the negative electrode material and reducing the pulverization of the negative electrode material particles. In addition, the average shape factor of the negative electrode material particles is maintained within the above range, which can reduce the gaps between the negative electrode material particles, which is conducive to increasing the compaction density of the negative electrode material, facilitating sufficient infiltration of the electrolyte, and improving the cycle performance of the negative electrode material.

[0267] According to the test data of Example 2-1 and the test data of Example 2-6, it can be seen that the impurity content of the negative electrode material prepared in Example 2-6 without performing step (1) is high. The high impurity content causes the electrical conductivity of the material to decrease. At the same time, part of the pores in the carbon material are occupied by impurity elements, which makes the content of Si deposited in the carbon material relatively low. Therefore, the first charge and discharge specific capacity and the first coulombic efficiency of the negative electrode material prepared in Example 2-6 are relatively low.

[0268] According to the test data of Examples 2-1 to 2-7 and the test data of Example 2-8, it can be seen that the oil absorption value of the carbon material in Example 2-8 is too small, which leads to the oil absorption value of the negative electrode material after filling with silicon particles being relatively small. While the specific capacity of the negative electrode material decreases, the wettability of the negative electrode material decreases, resulting in a decrease in the first coulombic efficiency of the negative electrode material compared to Example 2-1.

[0269] Comparative Example 2-1 uses ball mill collision nail-type airflow crushing, and the carbon material has obvious edges and corners. The average shape coefficient of the obtained negative electrode material is too small, that is, the particles have obvious edges and corners. During the charge and discharge process, the local expansion stress of the negative electrode material is too large, the stability of the particle structure of the negative electrode material decreases, and the expansion rate of the negative electrode material increases significantly.

[0270] In Comparative Example 2-2, after silicon vapor deposition, the deposited product is subjected to ball milling and fluidized bed air flow pulverization. Although the average shape coefficient of the negative electrode material is improved, a large amount of heat is generated during the spheroidization process, resulting in partial oxidation of the silicon particles in the negative electrode material and a decrease in the specific capacity of the negative electrode material. In addition, the spheroidization process will also cause part of the negative electrode material to be pulverized, and the side reactions of the negative electrode material will increase, affecting the cycle performance of the negative electrode material.

[0271] The test data from Examples 2-1 to 2-8 demonstrate that, by using a suitable preparation process to produce negative electrode materials and maintaining the average shape factor of the negative electrode material particles within the aforementioned range, stress concentration near corners caused by volume expansion of the silicon particles in the negative electrode material can be reduced, thereby maintaining the stability of the negative electrode material particle structure and reducing pulverization of the negative electrode material particles. Furthermore, the gaps between the negative electrode material particles can be reduced, which helps to increase the compaction density of the negative electrode material, facilitate sufficient electrolyte infiltration, and improve the cycle performance of the negative electrode material.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes a carbon material and silicon particles, and the negative electrode material has pores; The average shape factor of the negative electrode material is F0, 0.65≤F0<1; The average shape factor F0 of the negative electrode material is obtained by testing in the following manner: Randomly obtain 10 negative electrode material particles and measure the cross-sectional area S of each negative electrode material particle n and the circumference C n , F n =4*π*S n / C n 2 , n is a natural number from 1 to 10, calculate the shape coefficient F of 10 particles n The average value is recorded as the average shape factor F0 of the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material and the negative electrode material after removing silicon particles are tested by N2 adsorption-desorption method, and the volume ratio of nitrogen adsorbed by the negative electrode material at 90% partial pressure to the volume ratio of nitrogen adsorbed at 10% partial pressure is A, 1.3≤A≤2.5; The ratio of the volume of nitrogen adsorbed by the negative electrode material after the silicon particles are removed at a partial pressure of 90% to the volume of nitrogen adsorbed at a partial pressure of 10% is B, 1≤B≤1.9; and A / B>1.

3. The negative electrode material according to claim 1, characterized in that At least part of the silicon particles are filled in the pores of the carbon material; and / or, The silicon particles include at least one of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon.

4. The negative electrode material according to claim 1, characterized in that The total pore volume of the negative electrode material is 0.001 cm 3 / g~0.4cm 3 / g.

5. The negative electrode material according to claim 1, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The pores in the negative electrode material include micropores, wherein: The volume proportion of the micropores in all pores is ≤5%; (2) The pores in the negative electrode material include mesopores, wherein the volume proportion of the mesopores in all pores is 87% to 97%; (3) The pores in the negative electrode material include macropores, and the volume proportion of the macropores in all pores is ≤13%.

6. The negative electrode material according to claim 1, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The total pore volume of the negative electrode material after removing the silicon particles is 0.2 cm 3 / g~2.0cm 3 / g; (2) The pores in the negative electrode material after the silicon particles are removed include micropores, and the volume proportion of the micropores in all pores is ≥ 80%; (3) In the negative electrode material after the silicon particles are removed, the volume proportion of pores with a pore diameter of less than 5.0 nm in the total pore volume is ≥90%.

7. The negative electrode material according to claim 1, characterized in that The particle size D of the negative electrode material 50 , 2μm≤D 50 ≤20μm, and 0.9≤(D 90 -D 10 ) / D 50 ≤5.

8. The negative electrode material according to claim 1, characterized in that The gas production of the negative electrode slurry prepared from the negative electrode material after being placed in a 25° C. environment for 24 hours is ≤1 mL / g, and the gas production of the negative electrode slurry prepared from the negative electrode material after being placed in a 45° C. environment for 24 hours is ≤2 mL / g.

9. The negative electrode material according to any one of claims 1 to 8, characterized in that The average shape factor of the negative electrode material is F0, 0.65≤F0<0.

7.

10. The negative electrode material according to claim 9, characterized in that The oil absorption value of the negative electrode material is Q1mL / 100g, 30≤Q1≤80, the oil absorption value of the negative electrode material after removing the silicon particles is Q2mL / 100g, 120≤Q2≤200; and (Q2-Q1) / Q1>0.

5.

11. The negative electrode material according to claim 9, characterized in that The negative electrode material meets at least one of the following characteristics: (1) The compaction density of the negative electrode material is 0.80 cm 3 / g~1.30cm 3 / g; (2) The powder conductivity of the negative electrode material at 20 kN is 0.5 S / cm to 2 S / cm; (3) The mass content of carbon in the negative electrode material is 40% to 60%; (4) The mass content of silicon in the negative electrode material is 35% to 55%.

12. The negative electrode material according to any one of claims 1 to 8, characterized in that The average shape factor of the negative electrode material is F0, 0.7≤F0≤0.8, and the specific surface area of ​​the negative electrode material is S1 m 2 / g, the total pore volume of the negative electrode material is P1 cm 3 / g; C1=S1 / (P1*100), 8≤C1≤20.

13. The negative electrode material according to claim 12, characterized in that: The specific surface area of ​​the negative electrode material after removing silicon particles is S2 m 2 / g, the total pore volume of the negative electrode material after removing silicon particles is P2 cm 3 / g, C2=S2 / (P2*100), 10≤C2≤25.

14. The negative electrode material according to claim 13, characterized in that 0.5≤S1≤10, 0.001≤P1≤0.1; 1300≤S2≤2500, 0.5≤P2≤2.

0.

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

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