Negative active material, negative plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative active material, a negative plate comprising the negative active material and a battery. The negative electrode active material comprises silicon-carbon composite particles, wherein the silicon-carbon composite particles comprise a porous carbon material and silicon; according to an XRD diffraction pattern of the negative electrode active material, a first diffraction peak exists when 2 theta is 20-30 degrees, and a second diffraction peak exists when 2 theta is 40-50 degrees; the half-peak width of the first diffraction peak is 1-5 degrees, and the half-peak width of the second diffraction peak is 3-10 degrees; the intensity I1 of the first diffraction peak and the intensity I2 of the second diffraction peak meet the condition that I1 / I2 is greater than or equal to 3. The porous carbon material in the negative electrode active material disclosed by the invention has relatively high strength and structural stability, so that the volume expansion of silicon can be effectively improved and the structural stability of the negative electrode active material can be improved while relatively high gram volume of the negative electrode active material is ensured. Comprising the negative electrode active material has relatively high first coulombic efficiency and cycling stability and relatively low cycling expansion rate.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode active material, a negative electrode sheet comprising the negative electrode active material, and a battery comprising the negative electrode active material and / or the negative electrode sheet. Background Art

[0002] Graphite anode materials occupy the dominant position in the lithium-ion battery anode market due to their high conductivity, strong stability and low cost. However, with the continuous development of technology, the actual application capacity of graphite materials is gradually approaching its theoretical capacity (372mAh / g), which can no longer meet people's demand for higher energy density. Silicon has a theoretical capacity of up to 4200mAh / g and is considered to be the most promising alternative to graphite and the best choice for the next generation of lithium-ion battery anode materials. However, silicon is prone to alloying reaction during lithium insertion to generate LiSi and Li 12 Si7、Li 13 Si4 and Li 22 Compounds such as Si5 experience a large volume expansion (about 300%) during the battery charge and discharge cycle, causing the silicon material to shatter and fail.

[0003] Composite silicon with porous carbon materials can make silicon nanoparticles evenly distributed in the porous carbon materials, thereby avoiding particle breakage caused by stress concentration. However, when silicon nanoparticles are loaded in the pores of porous carbon materials, the volume expansion of the material is still large after lithium is embedded, which seriously affects the cycle stability of the battery.

[0004] Therefore, it is very important to invent a negative electrode material that can achieve both high gram capacity and cycle stability. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and to provide a negative electrode active material, a negative electrode sheet including the negative electrode active material, and a battery including the negative electrode active material and / or the negative electrode sheet. The XRD diffraction pattern of the negative electrode active material of the present invention has a specific diffraction peak within a specific angle range, and the ratio of the diffraction peak intensity is within a specific range. At this time, the negative electrode active material has high strength and structural stability, and can effectively improve the volume expansion of silicon while ensuring a high gram capacity, thereby improving the stability of the negative electrode active material during the battery cycle. The battery including the negative electrode active material has a high first coulomb efficiency and cycle stability and a low cycle expansion rate.

[0006] In the related art, silicon-carbon materials (silicon nanoparticles are evenly distributed in porous carbon materials) still affect the cycle stability of the battery. After a lot of research, the inventors of the present invention found that the reason for the above problems is that the silicon nanoparticles deposited inside the pores of the porous carbon material still have a large volume expansion after lithium insertion, which will cause a large extrusion stress on the porous carbon matrix. When the extrusion stress exceeds the limit that the porous carbon matrix can withstand, it will cause the porous carbon matrix to break, and then cause the silicon nanoparticles to separate from the porous carbon matrix, causing the negative electrode active material to fail and the battery's cycle stability to deteriorate. Based on the above findings, the inventors of the present invention have conducted a large number of targeted studies and found that by improving the strength and structural stability of the porous carbon matrix, the extrusion stress of the silicon particles can be avoided to damage the porous carbon matrix and the problem of failure of the negative electrode active material caused by the separation of the silicon particles from the porous carbon matrix after lithium removal can be avoided. Thereby effectively improving the cycle stability of the battery and reducing the cycle expansion rate.

[0007] The first aspect of the present invention provides a negative electrode active material, which includes silicon-carbon composite particles, and the silicon-carbon composite particles include porous carbon material and silicon; the XRD diffraction spectrum of the negative electrode active material has a first diffraction peak at 2θ of 20°-30°, and a second diffraction peak at 2θ of 40°-50°; the half-peak width of the first diffraction peak is 1°-5°, and the half-peak width of the second diffraction peak is 3°-10°; the intensity of the first diffraction peak is I1, the intensity of the second diffraction peak is I2, and I1 and I2 satisfy: I1 / I2≥3.

[0008] A second aspect of the present invention provides a negative electrode sheet, which comprises the negative electrode active material described in the first aspect of the present invention.

[0009] A third aspect of the present invention provides a battery, the battery comprising the negative electrode active material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0010] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0011] (1) The negative electrode active material of the present invention has good structural stability while ensuring a high gram capacity, and can maintain a low volume expansion during the battery charge and discharge cycle;

[0012] (2) The battery of the present invention can achieve both good initial coulombic efficiency and cycle stability, and has a low cycle expansion rate.

[0013] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shown is a scanning electron microscope (SEM) image of the negative electrode active material in one example of the present invention.

[0015] Figure 2 Shown is the XRD (X-ray diffraction) spectrum of the silicon-carbon composite particles prepared in Preparation Example 1.

[0016] Figure 3 Shown are stress-strain curves of the silicon-carbon composite particles prepared in Preparation Example 1 and Comparative Preparation Example 1. DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0018] A first aspect of the present invention provides a negative electrode active material, which may include silicon-carbon composite particles. The silicon-carbon composite particles may include porous carbon material and silicon. The XRD diffraction spectrum of the negative electrode active material has a first diffraction peak at 2θ of 20°-30° and a second diffraction peak at 2θ of 40°-50°. The half-peak width of the first diffraction peak may be 1°-5°, and the half-peak width of the second diffraction peak may be 3°-10°. The intensity of the first diffraction peak is I1, and the intensity of the second diffraction peak is I2, and I1 and I2 satisfy: I1 / I2≥3, for example, 3, 4, 5, 6, 7, 8, 9 or 10.

[0019] The porous carbon material has a rich microporous structure and a large pore volume, which can accommodate more silicon particles, so that the silicon particles can be evenly dispersed in the micropores of the porous carbon material, thereby effectively inhibiting the aggregation of silicon particles and reducing stress concentration. And the porous carbon material has a certain lithium storage capacity, and can further improve the capacity of the silicon-carbon composite particles when the silicon content remains unchanged. In addition, when the negative electrode active material has a specific diffraction peak within a specific range, the half-peak width of the diffraction peak is within a specific range, and the ratio of the intensity of the diffraction peak is within a specific range, it indicates that the porous carbon material in the negative electrode active material has a highly graphitized characteristic. In the highly graphitized porous carbon material, the carbon atoms are arranged closely, and there are strong cross-linked chemical bonds between the carbon layers, so that it has high stability and high strength, and can withstand large expansion stress, thereby effectively inhibiting the volume expansion of silicon during the lithium insertion process; It can also avoid the failure of the negative electrode active material caused by the separation of silicon from the porous carbon material after lithium removal. The above jointly determine that the negative electrode active material of the present invention has a stable structure and a low expansion rate while having a high gram capacity.

[0020] In one example, the half-peak width of the first diffraction peak is 2°-4°.

[0021] In one example, the half-peak width of the second diffraction peak is 5°-8°.

[0022] In one example, 3≤I1 / I2≤6.

[0023] In the present invention, the term "half-peak width" has the conventional meaning in the art. It is generally believed that the half-peak width refers to the peak width at half the height of the diffraction peak in the XRD diffraction spectrum, that is, the distance between the two points where a straight line parallel to the bottom of the peak passes through the midpoint of the peak height and intersects the two sides of the peak.

[0024] In the present invention, the Raman spectrum of the negative electrode active material is at 1334 cm -1 -1346cm -1 There is a D peak at 1581cm -1 -1585cm -1 There is a G peak. The intensity of the D peak is 1 D , the intensity of the G peak is I G , I D and I G Satisfy: 0.6≤I D / I G ≤1.2, for example, 0.6, 0.7, 0.8, 0.9, 1, 1.1 or 1.2.

[0025] Raman spectrum at 1334 cm -1 -1346cm -1The D peak at 1581 cm-1 is derived from the defects or disordered extension of the sp3 domain in the carbon layer. -1 -1585cm -1 The existence of the G peak is related to the stretching vibration of the sp2 bond in the carbon lattice. Therefore, the intensity of the D peak is D The intensity of the G peak I G It is used to characterize the order of the structure of amorphous carbon materials and graphitized carbon materials. D / I G When within a specific range, it indicates that the porous carbon material in the negative electrode active material has high stability and high strength, and can withstand large expansion stress, which not only effectively inhibits the volume expansion of silicon during the lithium insertion process; it can also avoid the failure of the negative electrode active material caused by the separation of silicon from the porous carbon material after delithiation.

[0026] In one example, 0.8≤I D / I G ≤1.

[0027] In the present invention, the Raman spectrum of the negative electrode active material is obtained, for example, using a RM2000 microscopic confocal Raman spectrometer (product of Reinshaw Company), and the excitation source is a He-Ne laser with a wavelength of 525 nm.

[0028] In the present invention, the crushing force of the silicon-carbon composite particles is F, Among them, D v10 , D v50 and D v90 is the particle size of the porous carbon material, D' v10 , D' v50 and D' v90 is the particle size of the silicon-carbon composite particles, and k is 50-200 (for example, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200).

[0029] The silicon-carbon composite particles are obtained by vapor deposition of silicon in the pores of porous carbon materials. Therefore, the stronger the compressive strength of the porous carbon material used, the higher the compressive strength of the silicon-carbon composite particles obtained after vapor deposition. v50 is the median particle size of the porous carbon material, D' v50 is the median particle size of silicon-carbon composite particles. Under the same pressure, silicon-carbon composite particles with larger particle sizes are more easily crushed and have lower strength. v90 -D v10 reflects the particle size concentration of porous carbon materials, D' v90 -D' v10It reflects the particle size concentration of silicon-carbon composite particles. The silicon-carbon composite particles with better particle size uniformity have higher compressive strength. D / I G It is smaller, indicating that the structural stability of the silicon-carbon composite particles is higher. Within a certain range, I1 / I2 can also represent the structural stability of the silicon-carbon composite particles. Therefore, by regulating the relationship between the above characteristics, the negative electrode active material can have higher pressure resistance and mechanical strength, so that it can withstand greater pressure during rolling, and the negative electrode active material is not easy to break after rolling, the compaction density is higher, and the thickness of the negative electrode sheet is thinner, thereby improving the volume energy density of the battery. At the same time, negative electrode active materials with high mechanical strength are more stable during the battery cycle, which can avoid particle breakage in the late cycle, and a large amount of SEI film is formed on the surface of small particles, which accelerates the expansion of the battery.

[0030] In one example, k is 80-140.

[0031] In the present invention, F may be 30 N / m-60 N / m, for example, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m, 55 N / m or 60 N / m.

[0032] In the present invention, the crushing force F of the silicon-carbon composite particles can be obtained by using a single-particle mechanical property test system. By squeezing the silicon-carbon composite particles and recording the pressure-displacement curve, the stress when the silicon-carbon composite particles are crushed and fail is the crushing force of the material. The specific test method is as follows: disperse the test sample into a liquid, drip it onto a glass slide, locate a single particle under an optical microscope, control the pressure head to press down at a uniform speed, collect the force and displacement curves during the particle compression process, and calculate the mechanical properties of the single particle.

[0033] In the present invention, the performance test of the porous carbon material is carried out, and the silicon in the silicon-carbon composite particles needs to be removed first, for example, by an alkali etching method. The etching principle is: at room temperature, carbon does not react with alkali, while silicon reacts with alkali to form soluble silicates, thereby separating silicon from the silicon-carbon composite particles. The reaction equation is as follows: Si+2KOH+H2O=K2SiO3+2H2↑. The specific removal method is as follows:

[0034] A certain mass of deionized water, KOH and silicon-carbon composite particles are added to a reaction container, wherein the mass ratio of KOH to silicon-carbon composite particles is greater than 2, and the concentration of KOH is higher than 1 mol / L; to ensure that silicon is completely removed, the etching time is not less than 3 days, and 5g-10g KOH is added to the reaction container every 24 hours; after etching is completed, the remaining sample is washed with deionized water until the pH value of the washing liquid is 7; after the washed sample is filtered and dried, a porous carbon material can be obtained.

[0035] In the present invention, the particle size D of the porous carbon material is v10 , D v50 and D v90 The particle size D' of the silicon-carbon composite particles v10 , D' v50 and D' v90 has the conventional meaning in this field. v10 and D' v10 They refer to the particle sizes of porous carbon materials and silicon-carbon composite particles arranged from small to large, and the particle size at the 10% volume position. v50 and D' v50 They refer to the particle sizes of porous carbon materials and silicon-carbon composite particles arranged from small to large, and the particle size at the 50% volume position. v90 and D' v90 They refer to the particle sizes of the porous carbon material and the silicon-carbon composite particles arranged from small to large, respectively, and the particle size at the 90% position of the volume.

[0036] In the present invention, the specific surface area of ​​the porous carbon material can be 1500m 2 / g-2500m 2 / g, for example 1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g, 2000m 2 / g, 2100m 2 / g, 2200m 2 / g, 2300m 2 / g, 2400m 2 / g or 2500m 2 / g.

[0037] In one embodiment, the specific surface area of ​​the porous carbon material is 1700 m 2 / g-2300m 2 / g.

[0038] In the present invention, the specific surface area of ​​the micropores in the porous carbon material can be 1200 m 2 / g-2400m 2 / g, for example, 1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g, 2000m 2 / g, 2100m 2 / g, 2200m 2 / g, 2300m 2 / g or 2400m 2 / g.

[0039] In one embodiment, the specific surface area of ​​the micropores in the porous carbon material is 1400 m 2 / g-2200m 2 / g.

[0040] When the specific surface area of ​​the porous carbon material and the specific surface area of ​​the micropores in the porous carbon material are within a specific range, the porous carbon material can provide more active sites for subsequent chemical vapor deposition, and the number of loaded silicon particles is relatively balanced, which can ensure the structural stability of the negative electrode active material while increasing the gram capacity of the negative electrode active material, thereby enabling the battery to take into account both energy density and cycle stability.

[0041] In the present invention, the pore volume of the porous carbon material can be 0.4 cm 3 / g-1.5cm 3 / g, for example 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g or 1.5cm 3 / g.

[0042] In one example, the pore volume of the porous carbon material is 0.6 cm 3 / g-1.3cm 3 / g.

[0043] In the present invention, the pore volume of the micropores in the porous carbon material can be 0.3 cm 3 / g-1.4cm 3 / g, for example 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm3 / g, 0.9cm 3 / g, 1cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g or 1.4cm 3 / g.

[0044] In one example, the pore volume of the micropores in the porous carbon material is 0.5 cm 3 / g-1.2cm 3 / g.

[0045] When the pore volume of the porous carbon material and the pore volume of the micropores in the porous carbon material are within a specific range, the porous carbon material can provide more active sites for subsequent chemical vapor deposition, and the number of loaded silicon particles is relatively balanced, which can ensure the structural stability of the negative electrode active material while increasing the gram capacity of the negative electrode active material, thereby enabling the battery to have both energy density and cycle stability.

[0046] In the present invention, the specific surface area and pore volume of the porous carbon material and the specific surface area and pore volume of the micropores in the porous carbon material can be tested by conventional methods in the art, such as by N2 constant temperature adsorption and desorption measurement, combined with BET, NLDFT and other model fitting calculations.

[0047] In the present invention, the electronic conductivity of the porous carbon material may be 10 S / cm-45 S / cm, for example, 10 S / cm, 20 S / cm, 30 S / cm, 40 S / cm or 45 S / cm.

[0048] In one example, the electronic conductivity of the porous carbon material is 25 S / cm-45 S / cm.

[0049] There are a large number of free electrons between graphitized carbon layers, and the p orbitals are parallel and overlapped with each other. The electrons in the p orbitals can move in the entire carbon atom plane, so that the porous carbon material has a high electronic conductivity. Therefore, the silicon-carbon composite particles prepared with the porous carbon material as the matrix have excellent electrical conductivity.

[0050] In the present invention, the electronic conductivity of the porous carbon material can be measured by conventional methods in the art, such as using a conductivity meter, through a two-probe / four-probe direct measurement method, and calculating the conductivity based on the relationship between resistance and conductivity.

[0051] In the present invention, the true density of the porous carbon material can be 1.9 cm 3 / g-2.6cm 3 / g, for example, 1.9 cm 3 / g, 2cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g, 2.4cm 3 / g, 2.5cm 3 / g or 2.6cm 3 / g.

[0052] In one example, the true density of the porous carbon material is 2.2 cm 3 / g-2.4cm 3 / g.

[0053] When the true density of the porous carbon material is within a specific range, the silicon-carbon composite particles obtained by subsequent chemical vapor deposition can obtain better comprehensive performance. 3 / g), it indicates that there are a large number of pore structures in the porous carbon material, which is not conducive to the structural stability of the material. In particular, when the number of mesopores and macropores is too large, it is easy to cause the internal structure of the porous carbon material to collapse. When the true density of the porous carbon material is large (for example, greater than 2.6 cm 3 / g), which indicates that the number of pore structures in the porous carbon material is small. In the subsequent chemical vapor deposition process, due to insufficient active sites, it is difficult to deposit more silicon particles in the porous carbon material, resulting in low silicon content and low gram capacity of the negative electrode active material.

[0054] In the present invention, the true density of the porous carbon material can be tested by conventional methods in the art, such as by gas displacement method. The specific test method is as follows: use an analytical balance to weigh a certain mass of porous carbon material sample, seal the sample in a sample chamber of known volume, pass a certain amount of inert gas (such as helium, nitrogen, etc.) into the sample chamber and diffuse it into the expansion chamber, obtain the volume of the sample by the pressure difference before and after the gas diffusion, and then calculate the true density by the mass and volume of the sample.

[0055] In the present invention, the porous carbon material satisfies at least one of the following conditions:

[0056] (1) The 0.005V-1.5V lithium-free capacity can be 300mAh / g-500mAh / g, for example, 300mAh / g, 400mAh / g or 500mAh / g.

[0057] (2) The first-week lithium insertion capacity C0 and the first-week lithium removal capacity C1 satisfy: 0.2≤C1 / C0≤0.4, for example, 0.2, 0.3 or 0.4.

[0058] (3) The lithium removal capacity C2 at 0.005V-0.85V and the first-week lithium removal capacity C1 satisfy: 0.45≤C2 / C1≤0.8, for example, 0.45, 0.5, 0.6, 0.7 or 0.8.

[0059] (4) The first week lithium embedded capacity C0 can be 1000mAh / g-1500mAh / g, for example, 1000mAh / g, 1100mAh / g, 1200mAh / g, 1300mAh / g, 1400mAh / g or 1500mAh / g.

[0060] During the battery charge and discharge cycle, the combination of silicon and lithium ions to form a silicon-lithium alloy is the main way for the negative electrode active material to provide capacity. In addition, lithium ions can also be reversibly adsorbed and desorbed in the micropores within the porous carbon material to provide partial capacity. However, during the vapor deposition of silicon, most of the micropores of the porous carbon material are filled with silicon particles, and the lithium storage on the surface of the porous carbon material matrix is ​​limited and almost negligible. The porous carbon material of the present invention has a high degree of graphitization characteristics and has a lithium storage mechanism similar to that of graphite. During the battery charge and discharge process, lithium ions can be reversibly embedded / de-lithium in the graphite-like carbon layer, thereby providing additional capacity and further increasing the gram capacity of the negative electrode active material. In addition, the porous carbon material has a higher efficiency within 0.005V-0.85V, which means that the porous carbon material can provide more reversible capacity at a low voltage platform.

[0061] In the present invention, the silicon-carbon composite particles have a core-shell structure. The core of the core-shell structure includes the porous carbon material and the silicon. The shell of the core-shell structure includes a carbon material. Based on the total mass of the silicon-carbon composite particles, the content of the porous carbon material can be 29%-60% (for example, 29%, 30%, 40%, 50% or 60%), the content of the silicon can be 30%-70% (for example, 30%, 40%, 50%, 60% or 70%), and the content of the carbon material can be 1%-10% (for example, 1%, 2%, 3%, 4%, 5% or 10%).

[0062] When the silicon-carbon composite particles have a core-shell structure and the content of each substance in the silicon-carbon composite particles is within a specific range, the obtained silicon-carbon composite particles have better comprehensive performance. Using porous carbon materials as a substrate can make the silicon particles evenly dispersed in the porous carbon material, thereby buffering the volume expansion of the silicon particles caused by lithium embedding during battery charging. Silicon particles have a high theoretical gram capacity, and depositing silicon particles in porous carbon materials can significantly improve the electrochemical energy storage performance of silicon-carbon composite particles. The carbon material on the surface of the silicon-carbon composite particles can improve the structural stability of the silicon-carbon composite particles, and also help to improve their electrical conductivity.

[0063] In one example, based on the total mass of the silicon-carbon composite particles, the content of the porous carbon material is 38%-55%, the content of the silicon is 40%-60%, and the content of the carbon material is 2%-5%.

[0064] In the present invention, the particle size D of the porous carbon material is v50 The average particle size of the silicon may be 0.1 nm-2000 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 500 nm, 1000 nm or 2000 nm. The particle size D' of the silicon-carbon composite particles may be 5 μm-15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm. The average particle size of the silicon may be 0.1 nm-2000 nm, for example, 0.1 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 500 nm, 1000 nm or 2000 nm. v50 It may be 5 μm-15 μm, for example 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0065] In one example, the particle size D of the porous carbon material is v50 7μm-13μm.

[0066] In one example, the average particle size of the silicon is 1 nm-100 nm.

[0067] In one example, the particle size D' of the silicon-carbon composite particles is v50 7μm-13μm.

[0068] When the particle size D' of the silicon-carbon composite particles v50 and the particle size D of the porous carbon material constituting the silicon-carbon composite particles v50 When the average particle size of silicon is within a specific range, it is beneficial to improve the overall electrochemical performance of the negative electrode active material. This is because a smaller particle size means a high specific surface area and a large contact area with the electrolyte, which results in more active lithium being consumed during the first week of charging, resulting in a low first coulombic efficiency of the negative electrode active material. A larger particle size means a longer diffusion path for lithium ions inside the material, resulting in poor kinetic performance of the negative electrode active material. In addition, the large gaps between large-size particles result in a lower packing density of the material, making it difficult to obtain a negative electrode sheet with a higher compaction density, resulting in a low volume energy density of the battery.

[0069] In the present invention, the particle size D of the porous carbon material is v10 , D v50 and D v90 , the average particle size of the silicon and the particle size D' of the silicon-carbon composite particles v10 , D' v50 and D' v90It can be obtained by conventional methods in the art, for example, the particle size D of the porous carbon material v10 , D v50 and D v90 And the particle size D' of silicon-carbon composite particles v10 , D' v50 and D' v90 The average particle size of silicon is obtained by testing with a laser particle size analyzer, and the average particle size of silicon is obtained by testing with a transmission electron microscope (TEM). Specifically, at least 20 silicon particles are selected in the mirror image, the particle sizes are measured, and the average value is taken.

[0070] In one example, the carbon material includes amorphous carbon.

[0071] In one example, the silicon includes nano-silicon.

[0072] In the present invention, the thickness of the shell may be 2nm-20nm, for example 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm or 20nm.

[0073] In one example, the shell has a thickness of 5 nm-10 nm.

[0074] The shell on the surface of the silicon-carbon composite particles can effectively prevent direct contact between silicon and the electrolyte, thereby reducing the occurrence of side reactions and improving the structural stability of the negative electrode active material. At the same time, the shell can also inhibit the agglomeration of silicon, avoid the failure of the negative electrode active material caused by stress concentration, and improve the cycle stability of the battery. In addition, since silicon is a semiconductor, the conductivity of the porous carbon material is significantly reduced after being composited with silicon. The surface coating of the carbon-containing shell helps to improve the overall conductivity of the silicon-carbon composite particles, thereby improving the rate performance of the battery.

[0075] In the present invention, the thickness of the shell can be tested by conventional methods in the art, such as using TEM, randomly selecting at least 10 silicon-carbon composite particles, selecting at least 5 sites on each silicon-carbon composite particle, measuring the thickness of the shell at each site, and taking the average value.

[0076] In the present invention, the specific surface area of ​​the silicon-carbon composite particles can be 0.1 m 2 / g-10m 2 / g, for example 0.1m 2 / g, 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g or 10m 2 / g.

[0077] In one embodiment, the specific surface area of ​​the silicon-carbon composite particles is 1 m 2 / g-5m 2 / g.

[0078] In the present invention, the pore volume of the silicon-carbon composite particles can be 0.0001 cm 3 / g-0.004cm 3 / g, for example, 0.0001cm 3 / g, 0.0002cm 3 / g, 0.0003cm 3 / g, 0.0004cm 3 / g, 0.0005cm 3 / g, 0.0006cm 3 / g, 0.0007cm 3 / g, 0.0008cm 3 / g, 0.0009cm 3 / g, 0.001cm 3 / g, 0.002cm 3 / g, 0.003cm 3 / g or 0.004cm 3 / g.

[0079] In one example, the pore volume of the silicon-carbon composite particles is 0.0005 cm 3 / g-0.002cm 3 / g.

[0080] On the premise that the specific surface area and pore volume of the porous carbon material are within a specific range, when the specific surface area and pore volume of the silicon-carbon composite particles are within a specific range, the negative electrode active material can have a higher gram capacity while effectively reducing the contact between the negative electrode active material and the electrolyte and reducing the formation of the SEI film, thereby improving the battery's initial efficiency and capacity retention rate.

[0081] In the present invention, the specific surface area and pore volume of the silicon-carbon composite particles can be measured by conventional methods in the art, such as by N2 isothermal adsorption and desorption measurement, combined with BET, NLDFT and other model fitting calculations.

[0082] In the present invention, the true density of the silicon-carbon composite particles can be 1.5 cm 3 / g-2.4cm3 / g, for example, 1.5 cm 3 / g, 1.6cm 3 / g, 1.7cm 3 / g, 1.8cm 3 / g, 1.9cm 3 / g, 2cm 3 / g, 2.1cm 3 / g, 2.2cm 3 / g, 2.3cm 3 / g or 2.4cm 3 / g.

[0083] In one example, the true density of the silicon-carbon composite particles is 1.8 cm 3 / g-2.1cm 3 / g.

[0084] When the true density of the silicon-carbon composite particles is within a specific range, it can provide sufficient buffer space for the volume expansion of silicon during charging while ensuring that the negative electrode active material has a high gram capacity, thereby avoiding the failure of the negative electrode active material due to excessive volume expansion. 3 / g), indicating that there are still many pores in the silicon-carbon composite particles, and silicon is not fully deposited inside the porous carbon material, resulting in a low gram capacity of the negative electrode active material; and when the true density of the silicon-carbon composite particles is large (for example, greater than 2.4cm 3 / g), indicating that the number of pore structures in the silicon-carbon composite particles is small. When the battery is charged, the silicon embedded with lithium will expand in volume. If the pore structure in the silicon-carbon composite particles is not sufficient to support the volume expansion of silicon, the structure of the negative electrode active material will be destroyed.

[0085] In the present invention, the true density of the silicon-carbon composite particles can be measured by conventional methods in the art, such as by a gas replacement method.

[0086] In the present invention, the silicon-carbon composite particles may contain element potassium. The mass content of element potassium in the silicon-carbon composite particles is less than or equal to 300 ppm, for example, 300 ppm, 200 ppm, 100 ppm, 90 ppm, 80 ppm, 70 ppm, 60 ppm, 50 ppm, 40 ppm, 30 ppm, 20 ppm or 10 ppm.

[0087] In one example, the mass content of element potassium in the silicon-carbon composite particles is less than or equal to 100 ppm.

[0088] In one example, the mass content of element potassium in the silicon-carbon composite particles is less than or equal to 50 ppm.

[0089] The inventors of the present invention have found that by regulating the mass content of elemental potassium in silicon-carbon composite particles, the structural stability of the negative electrode active material can be effectively improved. The reason is that KOH is required in the preparation process of porous carbon materials, which will inevitably cause elemental potassium to remain in the negative electrode active material. Elemental potassium will expand in volume during the battery charge and discharge cycle, thereby causing the crystal structure of the negative electrode active material to collapse and the negative electrode sheet to pulverize.

[0090] In the present invention, the mass content of element potassium in the silicon-carbon composite particles can be measured by conventional methods in the art, such as inductively coupled plasma spectrometer (ICP).

[0091] In the present invention, the pH value of the suspension of the silicon-carbon composite particle aqueous solution with a mass content of 1.96% may be 6-10, for example, 6, 7, 8, 9 or 10.

[0092] In one example, the pH value of the suspension of the silicon-carbon composite particle aqueous solution with a mass content of 1.96% is 7-9.

[0093] In the present invention, the pH value of the suspension of the silicon-carbon composite particle aqueous solution with a mass content of 1.96% can be tested by conventional methods in the art, specifically as follows: a certain mass of silicon-carbon composite particles is uniformly dispersed in deionized water, wherein the mass ratio of silicon-carbon composite particles to deionized water is 1:50, the mixed solution is boiled, and after standing for 30 minutes, the upper clear liquid is taken, and the pH value is measured with a pH meter.

[0094] When the pH value of the aqueous solution of silicon-carbon composite particles with a specific content meets the above range, it means that the surface of the silicon-carbon composite particles is covered with a dense shell, which is beneficial to improving the overall conductivity of the negative electrode sheet.

[0095] In the present invention, the difference between the mass content of silicon on the surface of the core and the mass content of silicon inside the core is ≤10%, for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%.

[0096] In one example, the difference between the mass content of silicon on the surface of the core and the mass content of silicon inside the core is ≤5%.

[0097] When the difference between the mass content of silicon on the surface of the core and the mass content of silicon inside the core is within a specific range, it means that in the silicon-carbon composite particle, the silicon can be uniformly deposited in the pores of the porous carbon material, and there is no silicon agglomeration on the surface of the core of the silicon-carbon composite particle. Figure 1Shown is a scanning electron microscope (SEM) image of the negative electrode active material in an example of the present invention. It can be seen from the figure that the negative electrode active material includes silicon-carbon composite particles. The brightness of the silicon-carbon composite particles is uniform and there is no white edge around them, indicating that there is no silicon agglomeration on the surface of the inner core of the silicon-carbon composite particles.

[0098] When silicon is evenly dispersed in the pores of porous carbon materials, the stress generated by the expansion of silicon during the lithium insertion process can be evenly dispersed to various parts of the silicon-carbon composite particles, thereby avoiding particle breakage and failure due to excessive local stress. If silicon is enriched on the surface of the inner core of the silicon-carbon composite particle, it will be detrimental to the overall electrochemical performance of the material. Compared with the silicon deposited inside the porous carbon material, the silicon enriched on the surface has strong crystallinity, and the reaction with lithium ions to form a silicon-lithium alloy is an irreversible process, which will cause the retention rate of the battery to decay too quickly in the later stage of the cycle. In addition, the particle size of the silicon on the surface increases after agglomeration, and the diffusion and migration path of lithium ions becomes longer, resulting in poor battery rate performance. Therefore, avoiding the enrichment of silicon on the surface of the inner core can effectively improve the overall performance of silicon-carbon composite materials.

[0099] In the present invention, the dQ / dV curve of the button battery including the negative electrode active material has a first characteristic peak at 0.25V-0.3V and a second characteristic peak at 0.4V-0.45V; the intensity Q1 of the first characteristic peak and the intensity Q2 of the second characteristic peak satisfy: Q2 / Q1≤1.5, for example, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5 or 0.4.

[0100] In one example, Q2 / Q1≤0.7.

[0101] The first characteristic peak at 0.25V-0.3V and the second characteristic peak at 0.4V-0.45V in the dQ / dV curve of the button battery correspond to Li 15 Si4 to Li x Transformation of Si and Li x When the button cell meets the above peak intensity ratio, it means that the negative electrode active material is Li 15 Si4 can be quickly converted into Si without accumulating too much Li x Si, thereby improving the rate performance of the battery.

[0102] The present invention also provides a method for preparing the silicon-carbon composite particles, the method comprising the following steps:

[0103] S1: activating the porous carbon precursor;

[0104] S2: performing a first vapor deposition on the material obtained in step S1;

[0105] Optional S3: subjecting the material obtained in step S2 to a second vapor deposition.

[0106] In the present invention, "optional S3" means that step S3 may or may not be present. For example, the method is S1 and S2; for another example, the method is S1, S2 and S3.

[0107] In the present invention, the porous carbon precursor may include at least one of coke, petroleum coke, needle coke, pitch coke, anthracite and metallurgical coke.

[0108] In the present invention, the activation uses an activator, which may include KOH.

[0109] In the present invention, the mass ratio of the activator to the porous carbon precursor may be (0.1-4):1, for example, 0.1:1, 0.5:1, 1:1, 2:1, 3:1 or 4:1.

[0110] When the mass ratio of the activator to the porous carbon precursor is controlled within a certain range, it can be ensured that the porous carbon precursor produces a suitable number of micropores during the activation process.

[0111] In the present invention, the activation time may be 1 h-4 h, such as 1 h, 2 h, 3 h or 4 h. The activation temperature may be 600°C-1200°C, such as 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.

[0112] In the present invention, a silicon source is used in the first vapor deposition. The silicon source may include at least one of silane, dichlorosilane, trichlorosilane and tetrachlorosilane. The atmosphere of the first vapor deposition is an inert gas. The inert gas may include at least one of nitrogen, argon and helium.

[0113] In the present invention, the first vapor deposition time may be 1 h-4 h, such as 1 h, 2 h, 3 h or 4 h. The first vapor deposition temperature may be 400°C-600°C, such as 400°C, 500°C or 600°C.

[0114] In the present invention, a carbon source is used in the second vapor deposition. The carbon source may include at least one of methane, ethylene and acetylene. The atmosphere of the second vapor deposition is an inert gas. The inert gas may include at least one of nitrogen, argon and helium.

[0115] In the present invention, the second vapor deposition time may be 0.5 h-1.5 h, such as 0.5 h, 1 h or 1.5 h. The second vapor deposition temperature may be 600° C.-800° C., such as 600° C., 700° C. or 800° C.

[0116] A second aspect of the present invention provides a negative electrode sheet, which may include the negative electrode active material described in the first aspect of the present invention.

[0117] In the present invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material. The negative electrode active material layer may also include a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes) and carbon fibers. The negative electrode binder may include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene and polyethylene oxide.

[0118] In the present invention, the negative electrode active material may further include a carbon-based material, which may include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon and hard carbon.

[0119] In the present invention, based on the total mass of the negative electrode active material layer, the content of the negative electrode active material can be 80-99.8 weight % (for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99 or 99.8 weight %), the content of the negative electrode conductor can be 0.1-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 weight %), and the content of the negative electrode binder can be 0.1-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5 or 0.1 weight %).

[0120] The third aspect of the present invention provides a battery, which may include the negative electrode active material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0121] In the present invention, the battery may further include a positive electrode sheet. The positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer on at least one side of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, and the positive electrode active material may include at least one of lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganese oxide (LMO), lithium nickel oxide, nickel manganese oxide binary material, lithium-rich manganese-based material and lithium iron manganese phosphate.

[0122] In one example, the positive electrode active material includes a first particle and a second particle. The first particle includes a chemical formula of Li a1 Ni b1 Co c1 Mn d1 M 1 e1 O2 substances, 0.8≤a1≤1.3, 0.8≤b1≤0.98, 0.02≤c1≤0.2, 0.01≤d1≤0.14, 0 <e1≤0.08,M 1 The first particles include at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb, and the first particles include single crystal particles. The second particles include a chemical formula of Li a2 Ni b2 Co c2 Mn d2 M 2 e2 O2 substances, 0.9≤a2≤1.3, 0.8≤b2≤0.98, 0.02≤c2≤0.3, 0.01≤d2≤0.12, 0 <e2≤0.1,M 2 The present invention comprises at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb, and the second particles comprise polycrystalline particles.

[0123] Single crystal particles have excellent structural stability due to the uniformity of their internal crystal structure and consistent grain orientation. The primary particle size of polycrystalline particles is small, which greatly shortens the Li + transmission distance, which is beneficial to Li +transmission, thereby improving the battery rate performance. Therefore, when single crystal particles and polycrystalline particles are mixed and used, they have better structural stability and rate performance. In addition, the side reaction activity between silicon and the electrolyte is strong under high temperature conditions, which will lead to a large volume expansion. When the positive electrode active material includes single crystal particles and polycrystalline particles, it has a lower discharge temperature rise. Lowering the temperature of the battery during charging and discharging can effectively inhibit the volume expansion of silicon, so that the battery has higher cycle performance and energy density. Therefore, when the positive electrode active material meets specific characteristics, it can be used in combination with the negative electrode active material provided in the present invention to further improve the overall energy density, rate performance and cycle performance of the battery.

[0124] In the present invention, the battery may further include an electrolyte. The electrolyte may be a non-aqueous electrolyte. The electrolyte may include a carbonate solvent and a lithium salt. The carbonate solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate, (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). The lithium salt may include at least one of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB and LiDFOB.

[0125] In the related art, the silicon-carbon material breaks into small particles due to stress concentration in the middle and late stages of the battery cycle, which increases the contact area between the negative electrode active material and the electrolyte, leading to more side reactions, and continuously generating more SEI films, which consumes more electrolyte. However, the negative electrode active material of the present invention has higher strength, and the particle structure is stable in the late stage of the cycle, and it does not break under higher volume expansion stress, which reduces the occurrence of side reactions and the formation of SEI films, thereby reducing the volume expansion of the negative electrode and improving the cycle stability of the battery.

[0126] In the present invention, the battery may further include a diaphragm. The diaphragm may include at least one of a base film, a ceramic layer and a glue layer. The base film may include at least one of polyethylene, polypropylene, polyimide, polyacrylonitrile and polyethersulfone. The base film may have a thickness of 3 μm-20 μm. The ceramic layer may have a thickness of 0.5 μm-5 μm. The ceramic layer faces the positive electrode. The glue layer may have a thickness of 0.5 μm-5 μm. The glue layer may face the negative electrode.

[0127] In the related art, due to the large expansion of silicon-carbon materials, the small particles produced after the particles are broken can easily puncture the diaphragm during the battery cycle, resulting in a micro short circuit, thereby causing large self-discharge of the battery and reducing the battery life. The negative electrode active material of the present invention has a stable particle structure during the battery cycle and does not break under high volume expansion stress, thereby reducing the K value of the battery cell, reducing self-discharge reactions, and improving cycle stability. At the same time, since the extrusion stress of the negative electrode on the diaphragm is reduced, a thinner diaphragm can be selected while ensuring that the diaphragm is not punctured, thereby improving the volume energy density of the battery.

[0128] In one example, the battery comprises a lithium-ion battery.

[0129] In one example, the battery includes a lithium-ion secondary battery.

[0130] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0131] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usages, and do not represent the difference in order.

[0132] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0133] The following preparation examples are used to illustrate silicon-carbon composite particles.

[0134] Preparation Example 1

[0135] Silicon-carbon composite particles were prepared as follows:

[0136] S1: petroleum coke and KOH were mixed evenly in a mass ratio of 1:2, placed in a porcelain boat and placed in a tube furnace, heated from room temperature to 900°C at a heating rate of 5°C / min under a N2 atmosphere, activated for 2h, then cooled to room temperature, washed twice with dilute hydrochloric acid, washed twice with deionized water, centrifuged, filtered and dried;

[0137] S2: placing the material obtained in step S1 in a tube furnace, heating the temperature from room temperature to 500°C at a heating rate of 5°C / min under a N2 atmosphere, introducing a SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 content of 20%, and maintaining the temperature at 500°C for 3 hours;

[0138] S3: Place the material obtained in step S2 in a tube furnace, heat it from room temperature to 700°C at a heating rate of 5°C / min under a N2 atmosphere, introduce acetylene gas at a flow rate of 100 sccm, and maintain it at 700°C for 1 hour.

[0139] The prepared silicon-carbon composite particles have a core-shell structure, wherein the core includes porous carbon material and silicon, and the shell includes carbon material (amorphous carbon). The mass content of porous carbon in the silicon-carbon composite particles is 50.2%, the mass content of silicon is 47.5%, and the mass content of carbon material is 2.3%. The average particle size of silicon is 10nm, and the thickness of the shell is 7.53nm.

[0140] Preparation Example 2

[0141] Silicon-carbon composite particles were prepared as follows:

[0142] S1: petroleum coke and KOH were mixed evenly in a mass ratio of 1:1, placed in a porcelain boat and placed in a tube furnace, heated to 900°C under a N2 atmosphere, activated for 2 hours, then cooled to room temperature, washed twice with dilute hydrochloric acid, then washed twice with deionized water, centrifuged, filtered and dried;

[0143] S2: placing the material obtained in step S1 in a tube furnace, heating the temperature from room temperature to 500°C at a heating rate of 5°C / min under a N2 atmosphere, introducing a SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 content of 20%, and maintaining the temperature at 500°C for 3 hours;

[0144] S3: Place the material obtained in step S2 in a tube furnace, heat it from room temperature to 700°C at a heating rate of 5°C / min under a N2 atmosphere, introduce acetylene gas at a flow rate of 100 sccm, and maintain it at 700°C for 1 hour.

[0145] The prepared silicon-carbon composite particles have a core-shell structure, wherein the core includes porous carbon material and silicon, and the shell includes carbon material (amorphous carbon). The mass content of porous carbon in the silicon-carbon composite particles is 51.2%, the mass content of silicon is 46.7%, and the mass content of carbon material is 2.1%. The average particle size of silicon is 12nm, and the thickness of the shell is 6.73nm.

[0146] Preparation Example 3

[0147] Silicon-carbon composite particles were prepared as follows:

[0148] S1: petroleum coke and KOH were mixed evenly in a mass ratio of 1:3, placed in a porcelain boat and placed in a tube furnace, heated to 900°C under a N2 atmosphere, activated for 2 hours, then cooled to room temperature, washed twice with dilute hydrochloric acid, then washed twice with deionized water, centrifuged, filtered and dried;

[0149] S2: placing the material obtained in step S1 in a tube furnace, heating the temperature from room temperature to 500°C at a heating rate of 5°C / min under a N2 atmosphere, introducing a SiH4-N2 mixed gas with a flow rate of 60 sccm and a SiH4 content of 20%, and maintaining the temperature at 500°C for 3 hours;

[0150] S3: Place the material obtained in step S2 in a tube furnace, heat it from room temperature to 700°C at a heating rate of 5°C / min under a N2 atmosphere, introduce acetylene gas at a flow rate of 100 sccm, and maintain it at 700°C for 1 hour.

[0151] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 48.4%, the mass content of silicon is 49.1%, and the mass content of carbon material is 2.5%. The average particle size of silicon is 11nm, and the thickness of the shell is 8.82nm.

[0152] Preparation Example 4

[0153] This group of preparation examples is used to verify the effects of changes in the specific surface area and pore volume of porous carbon materials.

[0154] This group of preparation examples was carried out with reference to Preparation Example 1, except that the specific surface area and pore volume of the porous carbon material were changed by "adjusting the mass ratio of petroleum coke and KOH", as follows:

[0155] Preparation Example 4a:

[0156] In step S1, the mass ratio of petroleum coke to KOH is 1:0.5;

[0157] The prepared silicon-carbon composite particles have a core-shell structure, wherein the core includes porous carbon material and silicon, and the shell includes carbon material (amorphous carbon). The mass content of porous carbon in the silicon-carbon composite particles is 51.3%, the mass content of silicon is 46.1%, and the mass content of carbon material is 2.6%. The average particle size of silicon is 10nm, and the thickness of the shell is 9.01nm.

[0158] Preparation Example 4b:

[0159] In step S1, the mass ratio of petroleum coke to KOH is 1:4;

[0160] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 46.4%, the mass content of silicon is 51.2%, and the mass content of carbon material is 2.4%. The average particle size of silicon is 9nm, and the thickness of the shell is 7.42nm.

[0161] Preparation Example 5

[0162] This preparation example is used to verify the effect of changes in the "core-shell structure of silicon-carbon composite particles".

[0163] The process is carried out in accordance with Preparation Example 1, except that step S3 is not performed, and the material prepared in step S2 is used as silicon-carbon composite particles.

[0164] The mass content of porous carbon in the silicon-carbon composite particles is 52.5%, the mass content of silicon is 47.5%, the average particle size of silicon is 10nm, and there is no shell.

[0165] Preparation Example 6

[0166] This group of preparation examples is used to verify the impact of changes in the mass content of porous carbon material, silicon and carbon material in silicon-carbon composite particles.

[0167] This group of preparation examples is carried out with reference to Preparation Example 1, except that the "mass contents of porous carbon material, silicon and carbon material in the silicon-carbon composite particles" are changed by the holding time in step S2 and / or step S3, as follows:

[0168] Preparation Example 6a:

[0169] In step S2, maintaining at 500° C. for 4 h;

[0170] The prepared silicon-carbon composite particles have a core-shell structure, wherein the core includes porous carbon material and silicon, and the shell includes carbon material (amorphous carbon). The mass content of porous carbon in the silicon-carbon composite particles is 36.1%, the mass content of silicon is 61.7%, and the mass content of carbon material is 2.2%. The average particle size of silicon is 10nm, and the thickness of the shell is 7.82nm.

[0171] Preparation Example 6b:

[0172] In step S3, maintaining at 700° C. for 2 h;

[0173] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 46.3%, the mass content of silicon is 46.5%, and the mass content of carbon material is 7.2%. The average particle size of silicon is 10nm, and the thickness of the shell is 14.3nm.

[0174] Preparation Example 7

[0175] This preparation example is used to verify the effect of changes in the "specific surface area of ​​silicon-carbon composite particles".

[0176] The preparation was carried out in accordance with Preparation Example 1, except that the "specific surface area of ​​the silicon-carbon composite particles" was changed by the holding time in step S3, as follows:

[0177] In step S3, maintaining at 700° C. for 0.5 h;

[0178] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 51%, the mass content of silicon is 47.3%, and the mass content of carbon material is 1.7%. The average particle size of silicon is 9nm, and the thickness of the shell is 6.12nm.

[0179] Preparation Example 8

[0180] This preparation example is used to verify the effect of changing the "mass content of element potassium in silicon-carbon composite particles".

[0181] This preparation example is carried out with reference to the preparation example 1, except that the "mass content of element potassium in the silicon-carbon composite particles" is changed by changing the number of acid washings in step S1, as follows:

[0182] In step S1, the substrate is directly washed twice with deionized water instead of using dilute hydrochloric acid for washing;

[0183] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 49.7%, the mass content of silicon is 47.8%, and the mass content of carbon material is 2.5%. The average particle size of silicon is 10nm, and the thickness of the shell is 7.66nm.

[0184] Comparative Preparation Example 1

[0185] The preparation was carried out in accordance with Preparation Example 1, except that the petroleum coke was replaced with coconut shell of the same mass;

[0186] The prepared silicon-carbon composite particles have a core-shell structure, the core includes porous carbon material and silicon, the shell includes carbon material (amorphous carbon), the mass content of porous carbon in the silicon-carbon composite particles is 50.3%, the mass content of silicon is 47.1%, and the mass content of carbon material is 2.6%. The average particle size of silicon is 9nm, and the thickness of the shell is 8.12nm.

[0187] The following examples are provided to illustrate the batteries of the present invention.

[0188] Example 1

[0189] Prepare the battery as follows:

[0190] (1) Preparation of negative electrode sheets for button batteries

[0191] The negative electrode active material (silicon-carbon composite particles prepared in Preparation Example 1), sodium carboxymethyl cellulose, styrene-butadiene rubber, carbon black and single-walled carbon nanotubes were mixed uniformly in a mass ratio of 85:2:5.5:7:0.5, deionized water was added, and mixed uniformly under the action of a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry was uniformly coated on a copper foil, and the surface density was controlled at 4 mg / cm 2 -8 mg / cm 2 Range; put it into an oven and dry it at 80°C, and then roll and cut it to obtain the negative electrode sheet.

[0192] (2) Preparation of negative electrode sheets used in lithium-ion batteries

[0193] The negative electrode active material (the silicon-carbon composite particles prepared in Preparation Example 1 and artificial graphite are mixed in a mass ratio of 1:9), sodium carboxymethyl cellulose, styrene-butadiene rubber, carbon black and single-walled carbon nanotubes are mixed in a mass ratio of 85:2:5.5:7:0.5, deionized water is added, and the mixture is mixed in a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on a copper foil, and the surface density is controlled at 4 mg / cm 2 -8 mg / cm 2 Range; put it into an oven and dry it at 80°C, and then roll and cut it to obtain the negative electrode sheet.

[0194] (3) Preparation of positive electrode sheet

[0195] The positive electrode active material (including a first particle and a second particle, wherein the first particle is a LiNi 0.9 Co 0.04 Mn 0.04 Al 0.02 O2 is a single crystal particle; the second particle is a LiNi 0.85 Co 0.08 Mn 0.04 Al 0.03 O2 material, which is a polycrystalline particle; the mass ratio of the first particle to the second particle is 85:15), polyvinylidene fluoride, acetylene black and single-walled carbon nanotubes are mixed evenly in a mass ratio of 96:2:1.5:0.5, N-methylpyrrolidone is added, and the mixture is mixed evenly under the action of a vacuum stirrer to obtain a positive electrode slurry, and the positive electrode slurry is evenly coated on an aluminum foil, and the surface density is controlled at 8 mg / cm 2 -15mg / cm 2 Range; put it into an oven and dry it at 120°C, and then roll and cut it to obtain the positive electrode sheet.

[0196] (4) Preparation of lithium-ion batteries

[0197] The negative electrode sheet, the separator (a polyethylene film with a thickness of 5 μm, a ceramic layer with a thickness of 1 μm on one side and a glue layer with a thickness of 2 μm on the other side, with the ceramic layer facing the positive electrode sheet) prepared in step (1) and the positive electrode sheet prepared in step (2) are stacked in order so that the separator is located between the positive electrode sheet and the negative electrode sheet; after winding, packaging, liquid injection (the carbonate solvent in the electrolyte is a combination of EC and FEC, and the lithium salt is LiPF6), secondary sealing, formation, sorting and other processes, a lithium-ion battery is obtained.

[0198] (5) Preparation of button cells

[0199] The negative electrode sheet prepared in step (1) is punched into a disc with a diameter of 16 mm as the negative electrode using a punching machine; the metal lithium sheet is punched into a disc with a diameter of 18 mm as the positive electrode; in a glove box, the spring sheet, gasket, negative electrode disc, cellulose diaphragm and positive electrode disc are sequentially placed in a button battery shell, an appropriate amount of electrolyte (the carbonate solvent in the electrolyte is a combination of EC and FEC, and the lithium salt is LiPF6) is added, and the shell is compacted and sealed using a tablet press to obtain a button battery.

[0200] Examples 2 to 8 were carried out with reference to Example 1, except that the negative electrode active material was replaced with the silicon-carbon composite particles prepared in Preparation Examples 2 to 8 of the same mass, respectively. See Table 6 for details.

[0201] Example 9

[0202] This example is used to verify the influence of the change of the “positive electrode active material”.

[0203] The process is carried out in accordance with Example 1, except that the positive electrode active material is replaced with lithium cobalt oxide, and the gram capacity of the positive electrode sheet of the battery is ensured to be the same as that in Example 1.

[0204] Comparative Example 1

[0205] The same method is used as in Example 1, except that the silicon-carbon composite particles are replaced with the silicon-carbon composite particles prepared in Comparative Preparation Example 1 of the same mass.

[0206] Test Case I

[0207] (1) XRD test

[0208] The silicon-carbon composite particles prepared in the preparation examples and the comparative preparation examples were subjected to XRD tests, and the results are recorded in Table 1. Figure 2 Shown is the XRD spectrum of the silicon-carbon composite particles prepared in Preparation Example 1. It can be seen from the figure that the first diffraction peak is located at 27.3°, the second diffraction peak is located at 43.6°, the half-peak width of the first diffraction peak is 2.3°, the half-peak width of the second diffraction peak is 5.5°, and I1 / I2 is 5.1.

[0209] (2) Raman spectroscopy test

[0210] The silicon-carbon composite particles prepared in the preparation example and the comparative preparation example were subjected to Raman spectroscopy test, and the results are recorded in Table 2.

[0211] (3) Crushing force test

[0212] The silicon-carbon composite particles prepared in the preparation examples and the comparative preparation examples were subjected to a crushing force test, and the results are recorded in Table 2. Figure 3 The stress-strain curves of the silicon-carbon composite particles prepared in Preparation Example 1 and Comparative Preparation Example 1 are shown. It can be seen from the figure that the silicon-carbon composite particles obtained in the preparation example of the present invention have higher compressive strength.

[0213] (4) Particle size test

[0214] The porous carbon material obtained in step S1 of the preparation example and the comparative preparation example and the silicon-carbon composite particles obtained in step S3 were tested for particle size using a laser particle size analyzer, and the results are recorded in Table 3.

[0215] (5) Specific surface area and pore volume test

[0216] The porous carbon material obtained in step S1 of the preparation example and the comparative preparation example and the silicon-carbon composite particles obtained in step S3 were tested for specific surface area and pore volume, and the results are recorded in Table 4.

[0217] (6) Electronic conductivity test

[0218] The porous carbon material obtained in step S1 of the preparation example and the comparative preparation example was tested for electronic conductivity, and the results are recorded in Table 2.

[0219] (7) True density test

[0220] The porous carbon material obtained in step S1 of the preparation example and the comparative preparation example and the silicon-carbon composite particles obtained in step S3 were tested for true density, and the results are recorded in Table 2.

[0221] (8) Gram capacity test

[0222] The porous carbon material obtained in step S1 of the preparation example and the comparative preparation example was tested for gram capacity. The specific test method is as follows:

[0223] First, the porous carbon material is prepared into a button battery:

[0224] The porous carbon material, sodium carboxymethyl cellulose, styrene-butadiene rubber, carbon black and single-walled carbon nanotubes are mixed evenly in a mass ratio of 85:2:5.5:7:0.5, deionized water is added, and the mixture is mixed evenly under the action of a vacuum mixer to obtain a slurry; the slurry is evenly coated on a copper foil, put into an oven, and dried at 80°C, and the negative electrode sheet is obtained through rolling and slitting; the negative electrode sheet is punched into a disc with a diameter of 16 mm as the negative electrode by a punching machine; the metal lithium sheet is punched into a disc with a diameter of 18 mm as the positive electrode; in a glove box, the shrapnel, gasket, negative electrode disc, cellulose diaphragm and positive electrode disc are sequentially placed in a button battery shell, an appropriate amount of electrolyte is added (the carbonate solvent in the electrolyte is a combination of EC and FEC, and the lithium salt is LiPF6), and the shell is compacted and sealed by a tablet press to obtain a button battery.

[0225] At room temperature (25°C), the performance of the button cell prepared above was tested using the LAND test system. The specific test steps include:

[0226] 1-Discharge to 5mV at 0.025C and let stand for 10 minutes;

[0227] 2-Discharge to 5mV at 0.01C and let stand for 10 minutes;

[0228] 3- Charge to 1.5V at 0.02C and let stand for 10 minutes;

[0229] The 0.005V-1.5V lithium removal capacity, the first week lithium insertion capacity C0, C1 / C0 and C2 / C1 of the porous carbon material were obtained through the discharge curve and the charge curve, and the results are recorded in Table 5.

[0230] (9) Element potassium content test

[0231] The silicon-carbon composite particles prepared in the preparation example and the comparative preparation example were tested for element potassium content, and the results are recorded in Table 3.

[0232] (10) pH test

[0233] The pH value of the silicon-carbon composite particles prepared in the preparation example and the comparative preparation example was tested as follows: the silicon-carbon composite particles and deionized water were evenly dispersed in a mass ratio of 1:50, the mixed solution was boiled, and after standing for 30 minutes, the upper clear liquid was taken, and the pH value was measured with a pH meter. The results are recorded in Table 3.

[0234] (11) Test of silicon mass content in silicon-carbon composite particles

[0235] The silicon-carbon composite particles prepared in the preparation example were tested for silicon content. The specific test method is as follows: using a scanning electron microscope-energy dispersive spectrometer (SEM-EDS), 5 points were selected on the surface and inside of the core of the silicon-carbon composite particles, and the silicon content at each point was tested and the average value was taken. The results are: the silicon-carbon composite particles prepared in Preparation Example 5, the difference between the mass content of silicon on the surface and the mass content of silicon inside is ≤5%; the silicon-carbon composite particles prepared in Preparation Examples 1-4 and 6-8, the difference between the mass content of silicon on the surface of the core and the mass content of silicon inside is ≤5%.

[0236] Table 1

[0237]

[0238]

[0239] Table 2

[0240]

[0241]

[0242] Table 3

[0243] <![CDATA[D v10 ]]> <![CDATA[D v50 ]]> <![CDATA[D v90 ]]> <![CDATA[D’ v10 ]]> <![CDATA[D’ v50 ]]> <![CDATA[D’ v90 ]]> Element Potassium Content pH Preparation Example 1 5.12μm 9.52μm 16.22μm 5.21μm 9.61μm 16.53μm 25ppm 8.12 Preparation Example 2 3.24μm 7.14μm 13.46μm 3.41μm 7.31μm 13.61μm 34ppm 8.45 Preparation Example 3 6.32μm 12.41μm 20.18μm 6.57μm 12.71μm 20.51μm 31ppm 8.31 Preparation Example 4a 5.18μm 9.54μm 16.21μm 5.24μm 9.63μm 16.51μm 31ppm 8.24 Preparation Example 4b 4.97μm 9.41μm 16.01μm 5.11μm 9.54μm 16.23μm 37ppm 8.67 Preparation Example 5 5.07μm 9.64μm 16.3μm 5.12μm 9.71μm 16.38μm 36ppm 7.81 Preparation Example 6a 5.14μm 9.53μm 16.19μm 5.24μm 9.62μm 16.33μm 34ppm 8.24 Preparation Example 6b 5.21μm 9.77μm 16.47μm 5.47μm 9.89μm 16.68μm 35ppm 8.21 Preparation Example 7 5.04μm 9.41μm 16.14μm 5.12μm 9.55μm 16.31μm 34ppm 8.41 Preparation Example 8 5.08μm 9.43μm 16.17μm 5.17μm 9.52μm 16.65μm 246ppm 9.57 Comparative Preparation Example 1 5.27μm 9.5μm 16.07μm 5.39μm 9.64μm 16.31μm 31ppm 8.36

[0244] Table 4

[0245]

[0246]

[0247] Table 5

[0248] 0.005V-1.5V lithium-free capacity C0 C1 / C0 C2 / C1 Preparation Example 1 417mAh / g 1223mAh / g 0.341 0.781 Preparation Example 2 401mAh / g 1226mAh / g 0.327 0.765 Preparation Example 3 392mAh / g 1248mAh / g 0.314 0.754 Preparation Example 4a 352mAh / g 1205mAh / g 0.292 0.712 Preparation Example 4b 341mAh / g 1214mAh / g 0.281 0.724 Preparation Example 5 414mAh / g 1247mAh / g 0.332 0.761 Preparation Example 6a 410mAh / g 1217mAh / g 0.337 0.751 Preparation Example 6b 412mAh / g 1170mAh / g 0.352 0.792 Preparation Example 7 409mAh / g 1258mAh / g 0.325 0.774 Preparation Example 8 403mAh / g 1283mAh / g 0.314 0.721 Comparative Preparation Example 1 387mAh / g 1348mAh / g 0.287 0.691

[0249] Test Case II

[0250] (1) dQ / dV curve

[0251] The button cells prepared in the examples and comparative examples were subjected to dQ / dV curve tests. The specific test method is as follows: At room temperature (25° C.), the performance of the button cells was tested using a LAND test system. The specific test steps include:

[0252] 1-Discharge to 5mV at 0.025C and let stand for 10 minutes;

[0253] 2-Discharge to 5mV at 0.01C and let stand for 10 minutes;

[0254] 3- Charge to 1.5V at 0.02C and let stand for 10 minutes;

[0255] The dQ / dV curve was obtained and the results are recorded in Table 6.

[0256] (2) First Coulomb efficiency

[0257] The lithium-ion batteries prepared in the examples and comparative examples were subjected to the first coulombic efficiency test. The specific test method is as follows: at room temperature (25° C.), the button battery performance was tested using a LAND test system. The specific test steps include:

[0258] 1-Discharge to 5mV at 0.025C and let stand for 10 minutes;

[0259] 2-Discharge to 5mV at 0.01C and let stand for 10 minutes;

[0260] 3- Charge to 1.5V at 0.02C and let stand for 10 minutes;

[0261] The 0.005V-1.5V lithium removal gram capacity and the first-week lithium insertion gram capacity of the silicon-carbon composite particles are obtained through the discharge curve and the charge curve. The ratio of the first-week lithium removal gram capacity to the first-week lithium insertion gram capacity is calculated as the first coulombic efficiency, and the results are recorded in Table 6.

[0262] (3) Cycle test

[0263] The lithium ion batteries prepared in the examples and comparative examples were subjected to cycle tests, and the specific test methods are as follows:

[0264] At room temperature (25°C), using the LAND test system, the specific test steps include:

[0265] 1- Charge at 1.5C constant current to 4.48V, charge at 0.1C constant voltage, and let stand for 10 minutes;

[0266] 2-Discharge at 1C to 3V and let stand for 10 minutes;

[0267] The weekly capacity retention rate of the battery is calculated based on the initial discharge capacity and weekly discharge capacity of the battery. Before the cycle starts, the initial thickness of the battery is tested and recorded using a PPG thickness gauge. After each 100 cycles, the battery is fully charged and the current thickness is tested using a PPG thickness gauge. The thickness change rate is calculated based on the initial thickness.

[0268] Table 6

[0269]

[0270]

[0271] It can be seen from Table 6 that the battery prepared by the negative electrode active material of the present invention has higher first coulomb efficiency and cycle capacity retention rate and lower thickness expansion rate than the comparative example.

[0272] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A negative electrode active material, characterized in that: The negative electrode active material includes silicon-carbon composite particles, which include porous carbon material and silicon; the XRD diffraction spectrum of the negative electrode active material has a first diffraction peak at 2θ of 20°-30°, and a second diffraction peak at 2θ of 40°-50°; the half-peak width of the first diffraction peak is 1°-5°, and the half-peak width of the second diffraction peak is 3°-10°; the intensity of the first diffraction peak is I1, and the intensity of the second diffraction peak is I2, and I1 and I2 satisfy: I1 / I2≥3.

2. The negative electrode active material according to claim 1, wherein The half-peak width of the first diffraction peak is 2°-4°; And / or, the half-peak width of the second diffraction peak is 5°-8°; And / or, 3≤I1 / I2≤6.

3. The negative electrode active material according to claim 1 or 2, wherein The Raman spectrum of the negative electrode active material is 1334 cm -1 -1346cm -1 There is a D peak at 1581cm -1 -1585cm -1 There is a G peak; the intensity of the D peak is I D , the intensity of the G peak is I G , I D and I G Satisfy: 0.6≤I D / I G ≤1.2; Preferably, 0.8≤I D / I G ≤1.

4. The negative electrode active material according to claim 3, wherein The crushing force of the silicon-carbon composite particles is F, Among them, D v10 , D v50 and D v90 is the particle size of the porous carbon material, D' v10 , D' v50 and D' v90 is the particle size of the silicon-carbon composite particles, k is 50-200; preferably, k is 80-140; And / or, F is 30N / m-60N / m.

5. The negative electrode active material according to claim 1 or 2, wherein: The specific surface area of ​​the porous carbon material is 1500 m 2 / g-2500m 2 / g; preferably 1700m 2 / g-2300m 2 / g; And / or, the specific surface area of ​​the micropores in the porous carbon material is 1200m 2 / g-2400m 2 / g; preferably 1400m 2 / g-2200m 2 / g; And / or, the pore volume of the porous carbon material is 0.4 cm 3 / g-1.5cm 3 / g; preferably 0.6cm 3 / g-1.3cm 3 / g; And / or, the pore volume of the micropores in the porous carbon material is 0.3 cm 3 / g-1.4cm 3 / g; preferably 0.5cm 3 / g-1.2cm 3 / g; And / or, the electronic conductivity of the porous carbon material is 10S / cm-45S / cm; preferably 25S / cm-45S / cm; And / or, the true density of the porous carbon material is 1.9 cm 3 / g-2.6cm 3 / g; preferably 2.2cm 3 / g-2.4cm 3 / g.

6. The negative electrode active material according to claim 1 or 2, wherein: The porous carbon material satisfies at least one of the following conditions: (1) 0.005V-1.5V lithium-free capacity is 300mAh / g-500mAh / g; (2) The first-week lithium insertion capacity C0 and the first-week lithium removal capacity C1 satisfy the following conditions: 0.2≤C1 / C0≤0.4; (3) The lithium removal capacity C2 at 0.005V-0.85V and the lithium removal capacity C1 in the first week satisfy: 0.45≤C2 / C1≤0.8; (4) The first week of lithium embedding capacity C0 is 1000mAh / g-1500mAh / g.

7. The negative electrode active material according to claim 1 or 2, wherein: The silicon-carbon composite particles have a core-shell structure, the core of the core-shell structure comprises the porous carbon material and the silicon, and the shell of the core-shell structure comprises a carbon material; Preferably, based on the total mass of the silicon-carbon composite particles, the content of the porous carbon material is 29%-60%, the content of the silicon is 30%-70%, and the content of the carbon material is 1%-10%; more preferably, based on the total mass of the silicon-carbon composite particles, the content of the porous carbon material is 38%-55%, the content of the silicon is 40%-60%, and the content of the carbon material is 2%-5%; Preferably, the particle size D of the porous carbon material is v50 The average particle size of the silicon is 0.1nm-2000nm; the particle size D' of the silicon-carbon composite particles is v50 More preferably, the particle size D of the porous carbon material is 5 μm-15 μm. v50 The average particle size of the silicon is 1nm-100nm; the particle size D' of the silicon-carbon composite particles is v50 7μm-13μm; Preferably, the carbon material comprises amorphous carbon; Preferably, the silicon comprises nano-silicon; Preferably, the thickness of the shell is 2nm-20nm; more preferably 5nm-10nm.

8. The negative electrode active material according to claim 1 or 2, wherein The specific surface area of ​​the silicon-carbon composite particles is 0.1 m 2 / g-10m 2 / g; preferably 1m 2 / g-5m 2 / g; And / or, the pore volume of the silicon-carbon composite particles is 0.0001cm 3 / g-0.004cm 3 / g; preferably 0.0005cm 3 / g-0.002cm 3 / g; And / or, the true density of the silicon-carbon composite particles is 1.5 cm 3 / g-2.4cm 3 / g; preferably 1.8cm 3 / g-2.1cm 3 / g.

9. The negative electrode active material according to claim 1 or 2, wherein: The silicon-carbon composite particles contain element potassium, and the mass content of the element potassium in the silicon-carbon composite particles is less than or equal to 300 ppm; preferably, the mass content of the element potassium in the silicon-carbon composite particles is less than or equal to 50 ppm; And / or, the pH value of the suspension of the silicon-carbon composite particle aqueous solution with a mass content of 1.96% is 6-10; preferably 7-9.

10. The negative electrode active material according to claim 1 or 2, wherein The dQ / dV curve of the button battery including the negative electrode active material has a first characteristic peak at 0.25V-0.3V and a second characteristic peak at 0.4V-0.45V; the intensity Q1 of the first characteristic peak and the intensity Q2 of the second characteristic peak satisfy: Q2 / Q1≤1.5; Preferably, Q2 / Q1≤0.

7.

11. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode active material according to any one of claims 1 to 10.

12. A battery, characterized in that: The battery comprises the negative electrode active material according to any one of claims 1 to 10 and / or the negative electrode sheet according to claim 11.

13. The battery according to claim 12, wherein: The battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material; the positive electrode active material comprises a first particle and a second particle; The first particle includes a chemical formula of Li a1 Ni b1 Co c1 Mn d1 M 1 e1 O2 substances, 0.8≤a1≤1.3, 0.8≤b1≤0.98, 0.02≤c1≤0.2, 0.01≤d1≤0.14, 0 <e1≤0.08,M 1 comprising at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb, wherein the first particles comprise single crystal particles; The second particle includes a chemical formula of Li a2 Ni b2 Co c2 Mn d2 M 2 e2 O2 substances, 0.9≤a2≤1.3, 0.8≤b2≤0.98, 0.02≤c2≤0.3, 0.01≤d2≤0.12, 0 <e2≤0.1,M 2 The present invention comprises at least one of Al, Zr, B, Y, Sr, W, Ti, Mg and Nb, and the second particles comprise polycrystalline particles.

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