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, the silicon-carbon composite particles comprise closed pores and open pores, the open pores comprise first open pores and second open pores, the pore diameter of the first open pores is d1, the pore diameter of the second open pores is d2, d1 is greater than or equal to 0.26 nm and less than 0.365 nm, and d2 is greater than or equal to 0.365 nm; the total volume of the first open pores is 0.001 cm < 3 > / g to 0.15 cm < 3 > / g; the total volume of the second open pores is 0.0001 cm < 3 > / g to 0.05 cm < 3 > / g; and the total volume of the closed pores is 0.001 cm < 3 > / g to 0.35 cm < 3 > / g. The negative electrode active material disclosed by the invention has relatively high ionic conductivity and electronic conductivity and relatively high structural stability while relatively high gram volume is ensured. Comprising the negative electrode active material disclosed by the invention can give consideration to relatively good rate capability, conductivity and cycling stability.

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. Background Art

[0002] With the development and progress of electrochemical devices such as lithium-ion batteries, lithium iron phosphate batteries, and ternary batteries, people have put forward increasingly higher requirements for their cycle life and energy density. At present, using silicon-based materials with higher theoretical lithium storage capacity to replace traditional graphite materials as battery negative electrode active materials is an important way to improve the energy density of lithium-ion batteries. However, existing silicon-based materials have problems such as high particle volume expansion rate, poor conductivity, and severe surface side reactions during the cycle process. These problems lead to shedding, peeling, and poor interface contact of silicon-based materials during the cycle process, which in turn affects the transmission of ions and electrons, accelerates battery cycle degradation, reduces service life, and seriously affects the battery's cycle performance and rate performance. Summary of the Invention

[0003] The present invention aims to overcome the aforementioned problems existing in the prior art and provides a negative electrode active material, including a negative electrode sheet and a battery containing the negative electrode active material. The negative electrode active material of the present invention comprises silicon-carbon composite particles having a certain volume of open and closed pore structures. By regulating the pore size and volume of the open pore structure, the negative electrode is not only effectively wetted by the electrolyte, thereby improving lithium ion transmission efficiency, but also provides a buffer space for volume expansion of the silicon-carbon composite particles, thereby improving the rate performance and cycling stability of the battery.

[0004] The silicon-carbon composite particles of the present invention are porous structures containing micropores (including open pores and closed pores) of a specific size, which can play a role in space release for the volume expansion of the silicon-carbon composite particles during the charge and discharge process, reduce stress concentration inside the particles, avoid the breakage and shedding of the silicon-carbon composite particles, and improve the cycle stability and service life of the battery. Among them, the open-pore structure can increase the contact area between the silicon-carbon composite particles and the electrolyte, improve the wettability of the electrolyte, promote the transmission of lithium ions, provide a convenient channel for the diffusion of lithium ions, ensure that lithium ions can be embedded and extracted more quickly, and effectively improve the charge and discharge efficiency of the battery. At the same time, the open-pore structure can also provide a certain buffer space for the volume expansion of the silicon-carbon composite particles, thereby improving the cycle stability of the battery. Compared with the open-pore structure, the closed-pore structure in the silicon-carbon composite particles can also provide a buffer space for its expansion, reduce the shedding of the negative electrode active material caused by the drastic volume change, and extend the cycle life of the battery. In addition, the closed-pore structure is not in contact with the outside world, which can reduce the contact area between the silicon-carbon composite particles and the electrolyte and reduce the occurrence of side reactions.

[0005] In addition, the pore size of the open pore structure of the silicon-carbon composite particles and the volume of the open pore structure with a specific pore size are also key factors affecting the performance of the electrode. Among them, the pore size of the first opening is small, which will form a physical barrier, resulting in the electrolyte rarely being able to enter the silicon-carbon composite particles through these tiny open pore structures, effectively limiting the direct contact between the electrolyte and the active sites inside the silicon-carbon composite particle structure, thereby reducing the occurrence of side reactions and the decomposition and loss of effective components in the electrolyte, thereby effectively improving the cycle stability of the battery. The second opening allows the electrolyte to moderately infiltrate the silicon-carbon composite particles, which can not only form a stable solid electrolyte interface (SEI) film in the pores of the silicon-carbon composite particles, effectively preventing further decomposition of the electrolyte, but also allow lithium ions to migrate quickly and evenly embed and remove from the silicon-carbon composite particles, ensuring the efficient transmission of lithium ions during the charge and discharge process, and enhancing the rate performance of the battery. At the same time, the second opening can also provide sufficient space for the volume expansion of the silicon-carbon composite particles, effectively alleviating the problems of battery capacity reduction and structural damage caused by the volume expansion of the silicon-carbon composite particles during the lithium insertion process, further improving the battery's cycle stability and extending the battery's cycle life.

[0006] When the total volume of the first opening is too large (e.g. > 0.1 cm 3 / g), it is impossible to effectively buffer the volume expansion of the silicon-carbon composite particles during the lithium insertion process, resulting in the stress inside the silicon-carbon composite particles being difficult to be effectively released during the charge and discharge process. After long-term cycling, the silicon-carbon composite particles may suffer from structural damage such as cracking and pulverization, reducing the cycle stability of the battery. In addition, if the total volume of the first opening is too large, the electrolyte will not be able to effectively enter these tiny opening structures, resulting in a significant decrease in the transmission rate and an increase in the internal resistance, thereby affecting the rate performance of the battery. When the total volume of the second opening is too large (for example, >0.01cm 3 / g), the area of ​​direct contact between the silicon-carbon composite particles and the electrolyte increases, making side reactions more likely, forming an unstable SEI film, consuming more lithium ions, and exacerbating battery capacity decay. Simultaneously, as side reactions increase, heat generation may also increase, causing the battery temperature to rise during operation, increasing the risk of thermal runaway and affecting battery safety. Therefore, by regulating the volume of the open-pore structure with a specific pore size within an appropriate range, not only can effective contact with the electrolyte be achieved, reducing the occurrence of side reactions and improving lithium ion transmission efficiency, but it can also provide sufficient buffer space for material volume expansion, significantly improving the battery's cycling stability and rate performance.

[0007] Based on this, the inventors of the present invention proposed the following solution:

[0008] A first aspect of the present invention provides a negative electrode active material, comprising silicon-carbon composite particles, the silicon-carbon composite particles comprising closed pores and open pores, the open pores comprising first and second pores, the pore size of the first pore being d1, the pore size of the second pore being d2, 0.26 nm ≤ d1 < 0.365 nm, d2 ≥ 0.365 nm; the total volume of the first pore being 0.001 cm 3 / g-0.15cm 3 / g; the total volume of the second opening is 0.0001cm 3 / g-0.05cm 3 / g; the total volume of the closed pores is 0.001cm 3 / g-0.35cm 3 / g.

[0009] A second aspect of the present invention provides a negative electrode sheet, comprising the negative electrode active material according to the first aspect of the present invention.

[0010] A third aspect of the present invention provides a battery, comprising the negative electrode active material according to the first aspect of the present invention and / or the negative electrode sheet according to the second aspect of the present invention.

[0011] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0012] (1) The negative electrode active material of the present invention has good structural stability and can maintain low volume expansion during battery charge and discharge cycles;

[0013] (2) The battery of the present invention can achieve both good charge and discharge rate performance and cycle stability.

[0014] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and 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 to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Shown is a schematic structural diagram of silicon-carbon composite particles in one embodiment of the present invention.

[0016] Figure 2 Shown is a small-angle X-ray diffraction spectrum of silicon-carbon composite particles in one example of the present invention.

[0017] Figure 3 Shown is a scanning electron microscope (SEM) image of silicon-carbon composite particles in one example of the present invention. DETAILED DESCRIPTION

[0018] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0019] A first aspect of the present invention provides a negative electrode active material, comprising silicon-carbon composite particles, the silicon-carbon composite particles comprising closed pores and open pores, the open pores comprising first pores and second pores, the pore size of the first pores being d1, and the pore size of the second pores being d2.

[0020] In one example, 0.26 nm ≤ d1 < 0.365 nm, such as 0.26 nm, 0.27 nm, 0.28 nm, 0.29 nm, 0.30 nm, 0.31 nm, 0.32 nm, 0.33 nm, 0.34 nm, or 0.35 nm; d2 ≥ 0.365 nm, such as 0.365 nm, 0.375 nm, 0.385 nm, 0.395 nm, 0.405 nm, 0.415 nm, 0.425 nm, 0.435 nm, 0.445 nm, or 0.455 nm.

[0021] In one embodiment, the total volume of the first opening is 0.001 cm 3 / g-0.15cm 3 / g, for example 0.001cm 3 / g, 0.01cm 3 / g, 0.02cm 3 / g, 0.04cm 3 / g, 0.06cm 3 / g, 0.08cm 3 / g, 0.1cm 3 / g or 0.15cm 3 / g; the total volume of the second opening is 0.0001cm 3 / g-0.05cm 3 / g, for example 0.0001cm 3 / g, 0.001cm 3 / g, 0.002cm 3 / g, 0.004cm 3 / g, 0.006cm 3 / g, 0.008cm 3 / g, 0.01cm 3 / g or 0.05cm 3 / g; the total volume of closed pores is 0.001cm 3 / g-0.35cm 3 / g, for example 0.001cm 3 / g, 0.01cm 3 / g, 0.05cm 3 / g, 0.1cm 3 / g, 0.15cm 3 / g, 0.2cm 3 / g, 0.25cm 3 / g, 0.3cm 3 / g or 0.35cm 3 / g.

[0022] In the present invention, the open pores and the closed pores have the conventional meanings in the art; the open pores generally refer to pores connected to the outer surface of the silicon-carbon composite particles; the closed pores generally refer to pores inside the silicon-carbon composite particles that are not connected to the outer surface. Figure 1 The figure shows a schematic structural diagram of silicon-carbon composite particles. As can be seen from the figure, the silicon-carbon composite particles include first open pores 11, second open pores 12, closed pores 2, porous carbon 3, silicon material 4 and amorphous carbon 5.

[0023] In the present invention, the pore size of the first opening can be obtained by conventional methods in the field, for example, by using density functional theory (DFT), adopting the helium adsorption method, fitting the experimental isotherm, and using the DFT model library to perform mathematical fitting (such as non-negative least squares method) to obtain the total pore size of the first opening and the second opening, and then subtracting the second pore size to obtain the first pore size; the pore size of the second opening is obtained by using DFT, adopting the N2 adsorption method, fitting the experimental isotherm, and using the DFT model library to perform mathematical fitting to obtain the pore size of the second opening.

[0024] In the present invention, the total volume of the first opening and the total volume of the second opening can be measured using conventional methods in the art, such as low-temperature gas adsorption combined with a Tri Star II surface area analyzer, using nitrogen or helium as the adsorption gas to measure the pore volume of the silicon-carbon composite particles / negative electrode sheet. Nitrogen has a diameter of 0.365 nm, and the volume of nitrogen adsorbed by the sample is the total volume of the second opening. Helium has a diameter of 0.26 nm, and the total volume of the first opening is the volume of helium adsorbed by the sample minus the volume of nitrogen adsorbed by the sample.

[0025] In the present invention, the total volume of the closed pores can be measured by conventional methods in the art, for example, firstly the true density a of the material is measured by a helium displacement method; then the mass fraction w1 of Si and the mass fraction w2 of C in the silicon-carbon composite particles are measured by a carbon-sulfur analyzer; w1, w2 and the theoretical density of Si (2.31 g / cm 3 ) and the theoretical density of C (2.33 g / cm 3) Substitute into the formula: closed pore volume = 1 / a-W1 / 2.31-W2 / 2.33, and the total volume of the closed pores can be calculated.

[0026] In the present invention, the helium measured true density of the silicon-carbon composite particles is 1.5 g / cm 3 -2.2g / cm 3 , for example 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 or 2.2g / cm 3 The nitrogen measured true density of the silicon-carbon composite particles is 1.2 g / cm 3 -1.9g / cm 3 , for example 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or 1.9 g / cm 3 .

[0027] In one embodiment, the helium measured true density of the silicon-carbon composite particles is 1.8 g / cm 3 -2.1g / cm 3 .

[0028] In one embodiment, the nitrogen measured true density of the silicon-carbon composite particles is 1.4 g / cm 3 -1.7g / cm 3 .

[0029] The silicon-carbon composite particles of the present invention contain open pore structures of different sizes. The appropriate pore size can ensure that helium can enter but nitrogen cannot enter. Helium and nitrogen are used as measuring media to measure the true density of the silicon-carbon composite particles. When the true density of the silicon-carbon composite particles is within the above range, it means that the volume of the open pore structure is moderate, which can provide sufficient buffer space for the expansion of the silicon-carbon particles during charging, thereby avoiding material failure due to excessive volume expansion. When nitrogen is used as the measuring medium, if the true density of the silicon-carbon composite particles is lower than the above range (for example, <1.2 g / cm 3), indicating that there are still many pores in the particles, the silicon-carbon particles are not fully deposited inside the material, and the low silicon content leads to a low gram capacity of the material; when helium is used as the measuring medium, the actual density of the silicon-carbon composite particles is higher than the above range (for example, >2.2g / cm 3 ), which means that the number of open pore structures in the material is small, which is not enough to buffer the volume expansion of the silicon-carbon composite particles, causing the active material to rupture and fall off, and reducing the battery cycle stability.

[0030] In the present invention, the true density of the silicon-carbon composite particles can be measured by conventional methods in the art, such as the gas displacement method. A sample of the silicon-carbon composite particles is placed in a container of known volume, and then gas (helium / nitrogen) is injected. The true volume of the sample is calculated by measuring parameters such as the pressure change or volume change of the gas, and then substituted into the ideal gas state equation to calculate the true density. The specific calculation formula is as follows: ρ = m / V, where ρ is the true density of the silicon-carbon composite particles, m is the mass content of the silicon-carbon composite particles, and V is the true volume of the silicon-carbon composite particles.

[0031] In the present invention, the average sphericity of the silicon-carbon composite particles is 0.5-1, for example, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0032] In one example, the average sphericity of the silicon-carbon composite particles is 0.75-1.

[0033] The average sphericity is an indicator that measures the gap between the particle morphology and the perfect sphere. When the morphology of the silicon-carbon composite particles is spherical or close to spherical, there are many advantages. First, silicon-carbon composite materials with a spherical structure usually have better packing density and higher specific surface area, which can improve the energy density of the battery, effectively alleviate the volume expansion problem of silicon-carbon particles during charging and discharging, reduce the internal stress during the battery cycle, reduce the damage to the electrode structure caused by volume change, and improve the cycle stability of the battery. Secondly, the surface of the spherical silicon-carbon composite particles is more regular, which is conducive to the formation of a stable solid electrolyte interface (SEI) film, reducing the occurrence of side reactions, and further improving the cycle performance of the battery. At the same time, it can also shorten the diffusion path of lithium ions, facilitate electron conduction and ion transport, and improve the conductivity and rate performance of the material.

[0034] In the present invention, the average sphericity of the silicon-carbon composite particles can be measured by conventional methods in the art. For example, after disassembling the battery, removing the negative electrode sheet, cleaning the negative electrode sheet with dimethyl carbonate (DMC) and drying it, polishing the cross-section of the negative electrode sheet with an argon ion milling instrument, and observing it in a SEM device using backscatter imaging mode; finding a silicon-carbon composite particle with a continuous and smooth contour, connecting any two points on the edge of the particle to form a straight line segment inside the particle, selecting the longest straight line segment within the particle, and recording its length as Z1; taking the midpoint of the longest straight line segment, drawing a straight line through the midpoint to form a straight line segment with both end points at the edge of the particle, selecting the shortest straight line segment, and recording its length as Z2. The sphericity of the particle is then Z2 / Z1. At least 10 silicon-carbon composite particles are selected, the sphericity is measured, and the average value is calculated.

[0035] In the present invention, the silicon-carbon composite particles may include a core-shell structure. Figure 1 Figure 1 shows a schematic diagram of the structure of a silicon-carbon composite particle. As can be seen from the figure, the silicon-carbon composite particle includes a first open pore 11, a second open pore 12, a closed pore 2, a porous carbon 3, a silicon material 4, and an amorphous carbon 5. The core of the core-shell structure includes the porous carbon 3 and the silicon material 4, and the outer shell of the core-shell structure includes the amorphous carbon 5.

[0036] In the present invention, silicon and carbon in the inner core of the silicon-carbon composite particles are both in an amorphous state, distributed relatively evenly and densely, without obvious phase interfaces, and the outer surface of the inner core has a shell of a certain thickness.

[0037] In the present invention, the core of the core-shell structure includes carbon and silicon, and the shell of the core-shell structure includes carbon.

[0038] In one example, the core includes porous carbon and silicon material located in the pores of the porous carbon.

[0039] In one example, the shell includes amorphous carbon.

[0040] In the present invention, the XRD diffraction pattern of the silicon-carbon composite particles has a characteristic diffraction peak at 4°-5°. The half-peak width L of the characteristic diffraction peak satisfies 0.05°≤L≤0.6°, for example, 0.05°, 0.1°, 0.15°, 0.2°, 0.25°, 0.3°, 0.35°, 0.4°, 0.45°, 0.5°, 0.55°, or 0.6°.

[0041] like Figure 2The figure shows a small-angle XRD test of silicon-carbon composite particles in an example of the present invention. It can be seen from the figure that there is a characteristic diffraction peak between 2θ=4°-5°, and the half-peak width L of the characteristic peak satisfies 0.05°≤L≤0.6°, indicating that a small amount of micropores exist in the silicon-carbon composite particles. Since the silicon material will undergo a large volume expansion during the cycle, the presence of micropores can reserve a certain buffer space for the expansion of silicon. When L<0.05°, the silicon-carbon material contains too many micropores, and the reaction interface between the electrolyte and the silicon-carbon composite particles is large, resulting in excessive consumption of electrolyte to form a passivation film, reducing the first effect of the battery and affecting the energy density of the battery; when L>0.6°, the silicon-carbon material contains too few micropores, and the space reserved for the expansion of the silicon-carbon composite particles is insufficient. The particle structure is easily squeezed and broken during the cycle process, affecting the cycle life of the battery.

[0042] In the present invention, the particle size Dv10 of the silicon-carbon composite particles is 4μm-6μm, for example, 4μm, 4.5μm, 5μm, 5.5μm or 6μm; Dv50 is 8μm-12μm, for example, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm or 12μm; Dv90 is 14μm-18μm, for example, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm or 18μm. The particle size Dn10 of the silicon-carbon composite particles is greater than 3 μm, for example, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm or 6 μm; Dn50 is 6 μm-8 μm, for example, 6 μm, 6.5 μm, 7 μm, 7.5 μm or 8 μm; Dn90 is 10 μm-12 μm, for example, 10 μm, 10.5 μm, 11 μm, 11.5 μm or 12 μm.

[0043] In the present invention, the particle size of the silicon-carbon composite particles satisfies the relationship: For example, 1.2, 1.1, 1, 0.9 or 0.8; For example, 1.35, 1.3, 1.25, 1.2, 1.15, 1.1, 1.05, 1, 0.95, 0.9, 0.85, 0.8 or 0.7.

[0044] In one example,

[0045] In one example,

[0046] Regulating the particle size of the silicon-carbon composite particles to satisfy a specific relationship and ensuring that the particle size of the silicon-carbon composite particles is within an appropriate range is beneficial to improving the structural stability of the negative electrode active material. When the particle size of the silicon-carbon composite particles is small, it means that they have a higher specific surface area and a larger contact area with the electrolyte. More active lithium is consumed during the first week of charging, resulting in a low first efficiency of the negative electrode material. When the particle size of the silicon-carbon composite particles is large, the diffusion path of lithium ions inside the material is longer, and the kinetic performance of the negative electrode material is poor. In addition, when the particle size is large, the gaps between the particles are also larger, and the packing density of the material is low, making it difficult to obtain a negative electrode sheet with a higher compaction density, resulting in a low volume energy density of the battery. Therefore, when the particle size of the silicon-carbon composite particles meets the above range, it indicates that the particle size concentration is high and the amount of fine powder is small, which is beneficial to improving the high-temperature cycle and high-temperature storage performance of the battery.

[0047] In the present invention, the particle sizes Dv10, Dv50 and Dv90 as well as Dn10, Dn50 and Dn90 of the silicon-carbon composite particles can be measured by conventional methods in the art, such as a laser particle size test method, specifically as follows: the silicon-carbon composite particles are measured using a Malvern particle size tester, and the test steps are as follows: the silicon-carbon composite particles are dispersed in deionized water containing a dispersant (e.g., nonylphenol polyoxyethylene ether) (the mass content of the dispersant is 0.02%-0.03%), ultrasonicated for 2 minutes, and then placed in a Malvern particle size tester for testing.

[0048] In the present invention, based on the total weight of the silicon-carbon composite particles, the content of the porous carbon is 20%-70%, for example, 20%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or 70%; the content of the silicon material is 20%-70%, for example, 20%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or 70%; the content of the amorphous carbon is 0.1%-20%, for example, 0.1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%.

[0049] In one example, the content of the porous carbon is 30%-60%, the content of the silicon material is 30%-69%, and the content of the amorphous carbon is 1%-10%.

[0050] In the present invention, the first-cycle dQ / dV curve of the button-type half-cell of the negative electrode active material has a characteristic peak 1 at 0.25V-0.3V and a characteristic peak 2 at 0.4V-0.45V; the ratio of the peak intensity of the characteristic peak 1 to the peak intensity of the characteristic peak 2 is 1.65-3, for example, 1.65, 2, 2.5 or 3.

[0051] When the silicon particles are agglomerated, the lithium ion migration path is lengthened, the delithiation potential is increased, and the capacity ratio in the range of 0.4V-0.45V is increased. Figure 3 The scanning electron microscope (SEM) image of the silicon-carbon composite particles in an example of the present application is shown. As can be seen from the image, the brightness of the silicon-carbon composite particles is uniform, and there is no white edge around the particles, indicating that there is no silicon particle agglomeration on the surface of the material. In combination with the dQ / dV curve test, it can be known that the silicon particles are uniformly deposited in the porous active carbon framework. When the silicon particles are uniformly dispersed in the porous active carbon framework, the stress generated by the expansion of the silicon particles during the intercalation process can be uniformly dispersed to each part of the silicon-carbon material, avoiding the particle breakage caused by excessive local stress. The silicon particles enriched on the surface of the silicon-carbon particles are not conducive to the electrochemical performance of the silicon-carbon material. Compared with the silicon particles deposited in the porous active carbon framework, the silicon particles enriched on the surface have strong crystallinity, and the reaction with lithium ions to form silicon-lithium alloy is an irreversible process, and the cell retention rate decays rapidly in the later cycle period. In addition, the particle size of the surface silicon particles is increased after agglomeration, the lithium ion diffusion migration path is lengthened, and the cell rate performance is poor. Therefore, by adjusting the content of silicon element on the surface of the silicon-carbon composite particles within a suitable range, the enrichment of silicon particles on the surface of the silicon-carbon material can be avoided, and the overall performance of the silicon-carbon material can be effectively improved.

[0052] In the present application, the first cycle dQ / dV curve of the button half-cell comprising the silicon-carbon composite particles can be obtained by a method conventional in the art, for example, the silicon-carbon composite particles are prepared to obtain a button half-cell, the button half-cell is discharged at 0.05C to 5mV and then charged at 0.05C to 1.5V, in the data processing software (for example, the data processing software of the Blue Cell Test System) of the button half-cell, "voltage-dQ / dV" is selected, and the ordinates of the highest points in the intervals of 0.25-0.3V and 0.4-0.45V of the dQ / dV curve corresponding to the first week delithiation section on the graph are taken to represent the intensities of the characteristic peaks one and two and to calculate the ratio thereof.

[0053] The preparation method of the button half-cell is as follows: the silicon-carbon composite particles, 4wt% polyacrylic acid aqueous solution and conductive carbon black are mixed in a mass ratio of 80:10:10 to prepare a slurry, which is coated on the surface of a copper foil, dried to obtain a single-sided negative electrode sheet, and then cut into small round pieces of 12mm by a slicing machine, a lithium sheet is used as a counter electrode, a 1mol / L lithium hexafluorophosphate-ethylene carbonate / dimethyl carbonate (volume ratio 1:1) solution is used as an electrolyte, and a Celgard separator is used to assemble a 2016 button half-cell, and when the dQ / dV curve is tested, the charging and discharging are carried out at a current density of 0.1C in the interval of 5mV-1.5V.

[0054] The present application also provides a method for preparing the above-mentioned silicon-carbon composite particles, which comprises at least the following steps:

[0055] (1) The carbon source and KOH are mixed evenly and placed in a first heating device, heated to 600°C-1000°C under a N2 atmosphere, kept warm for 1h-3h, and a porous carbon material is obtained by particle shaping;

[0056] (2) placing the porous carbon material prepared in step (1) in a second heating device, heating it to 400° C.-800° C. in a N2 atmosphere, and maintaining it in a (10%-30%) SiH4-N2 mixed atmosphere for 0.5 h-2 h;

[0057] (3) The composite material prepared in step (2) is placed in a third heating device, heated to 400°C-800°C under a N2 atmosphere, and acetylene gas with a flow rate of 50 sccm-300 sccm is introduced, and the temperature is kept for 0.5h-2h.

[0058] In the present invention, in step (1), the carbon source comprises at least one of needle petroleum coke, resin, and coconut shell. The mass ratio of the carbon source to KOH is (1-5):1, for example, 1:1, 2:1, 3:1, 4:1, or 5:1. The first heating device comprises, for example, a tubular furnace.

[0059] In the present invention, in step (2), the second heating device includes, for example, a tube furnace.

[0060] In the present invention, in step (3), the third heating device includes, for example, a tube furnace.

[0061] A second aspect of the present invention provides a negative electrode sheet, comprising the negative electrode active material according to the first aspect of the present invention.

[0062] In one embodiment, in the negative electrode sheet, the total volume of the first opening is 0.14 cm 3 / g-0.24cm 3 / g, for example 0.14cm 3 / g, 0.16cm 3 / g, 0.18m 3 / g, 0.2cm 3 / g, 0.22cm 3 / g or 0.24cm 3 / g; the total volume of the second opening is 0.06cm 3 / g-0.1cm 3 / g, for example 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g or 0.1cm 3 / g.

[0063] In the present invention, in the negative electrode sheet, the total volume of the first openings and the total volume of the second openings are tested in the same manner as the total volume of the first openings and the total volume of the second openings in the silicon-carbon composite particles, and are not described in detail here.

[0064] 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, wherein the negative electrode active material layer includes the negative electrode active material.

[0065] In the present invention, the negative electrode active material layer may further 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, polyethylene oxide, polyacrylic acid, and derivatives thereof.

[0066] 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.

[0067] In the present invention, based on the total mass of the negative electrode active material layer, the content of the negative electrode active material may be 80%-99.8% (for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99% or 99.8%), the content of the negative electrode conductor may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%), and the content of the negative electrode binder may be 0.1%-10% (for example, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.1%).

[0068] A third aspect of the present invention provides a battery, which may include the negative electrode active material according to the first aspect of the present invention and / or the negative electrode sheet according to the second aspect of the present invention.

[0069] In the present invention, the battery further comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, and a lithium-rich manganese-based material.

[0070] In the present invention, the battery further comprises a separator, which may comprise a separator commonly used in the art, for example, at least one of polypropylene, polyethylene and polyvinylidene fluoride.

[0071] In the present invention, the battery also includes an electrolyte, and the electrolyte includes an organic solvent and an electrolyte salt, and the organic solvent includes a carbonate solvent and / or a carboxylate solvent. The carbonate solvent may include a cyclic carbonate solvent and a chain carbonate solvent. The cyclic carbonate solvent may include a cyclic carbonate conventionally used in the art, for example, including at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC) and butylene carbonate (BC). The chain carbonate solvent may include a chain carbonate conventionally used in the art, for example, including at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC). The carboxylate solvent may include carboxylate commonly used in the art, for example, at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB). The electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium, or lithium bis(trifluoromethylsulfonyl)imide.

[0072] In one example, the battery comprises a lithium-ion battery.

[0073] In one example, the battery comprises a lithium-ion secondary battery.

[0074] 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 usage methods, and do not represent a difference in order.

[0075] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0076] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0077] The following preparation examples are used to prepare the silicon-carbon composite particles of the present invention.

[0078] Preparation Example 1

[0079] Silicon-carbon composite particles were prepared as follows:

[0080] (1) Needle-shaped petroleum coke and KOH were mixed in a mass ratio of 1:2 and placed in a tube furnace. The mixture was heated to 800 °C under a nitrogen atmosphere and kept at this temperature for 2 h. The mixture was then washed and dried, and porous carbon (sphericity of 0.85) was obtained by particle shaping.

[0081] (2) placing the porous carbon material prepared in step (1) in a tube furnace, heating it to 600°C in a N2 atmosphere, and then introducing a 30% SiH4-N2 mixed atmosphere and maintaining it for 2 hours;

[0082] (3) The material prepared in step (2) was placed in a tube furnace, N2 was introduced and the temperature was raised to 600°C, and then acetylene gas with a flow rate of 60 sccm was introduced and kept warm for 2 hours; silicon-carbon composite particles were obtained.

[0083] Wherein, 0.26nm≤d1<0.365nm, d2≥0.365nm; the total volume of the first opening of the silicon-carbon composite particle is 0.06cm 3 / g, and the total volume of the second opening is 0.002cm 3 / g, the total volume of closed pores is 0.12cm 3 / g; the silicon-carbon composite particles include a core-shell structure, with a porous carbon content of 60%, a silicon material content of 30%, and an amorphous carbon content of 10%; Dv10 is 4.1μm, Dv50 is 8.5μm, Dv90 is 14.1μm, Dn10 is 2μm, Dn50 is 6.1μm, and Dn90 is 10.2μm. is 1.18, is 1.34.

[0084] Preparation Example 2

[0085] Silicon-carbon composite particles were prepared as follows:

[0086] (1) Needle-shaped petroleum coke and KOH were mixed in a mass ratio of 1:2.5 and placed in a tube furnace. The mixture was heated to 850°C under a nitrogen atmosphere and kept warm for 2 h. The mixture was taken out, washed, and dried, and porous carbon (sphericity of 0.75) was obtained by particle shaping.

[0087] (2) The porous carbon material prepared in step (1) was placed in a tube furnace, heated to 550° C. in a N 2 atmosphere, and then introduced into a 10% SiH 4 -N 2 mixed atmosphere and maintained for 2.5 h;

[0088] (3) The material prepared in step (2) was placed in a tube furnace, N2 was introduced and the temperature was raised to 500°C, and then acetylene gas with a flow rate of 120 sccm was introduced and kept warm for 2 hours; silicon-carbon composite particles were obtained.

[0089] Among them, 0.26nm≤d1<0.365nm, d2≥0.365nm; the total volume of the first opening of the silicon-carbon composite particle is 0.09cm 3 / g, and the total volume of the second opening is 0.009 cm 3 / g, the total volume of closed pores is 0.25cm 3 / g; silicon-carbon composite particles include a core-shell structure, with a porous carbon content of 45%, a silicon material content of 50%, and an amorphous carbon content of 5%; Dv10 is 5.9μm, Dv50 is 11.8μm, Dv90 is 17.6μm, Dn10 is 5.5μm, Dn50 is 8μm, and Dn90 is 12μm. is 0.99, It is 0.81.

[0090] Preparation Example 3

[0091] Silicon-carbon composite particles were prepared as follows:

[0092] (1) Needle-shaped petroleum coke and KOH were mixed in a mass ratio of 1:3 and placed in a tube furnace. The mixture was heated to 900 °C under a nitrogen atmosphere and kept at this temperature for 2 h. The mixture was then washed and dried, and porous carbon (sphericity of 0.98) was obtained by particle shaping.

[0093] (2) placing the porous carbon material prepared in step (1) in a tube furnace, heating it to 500° C. in a N 2 atmosphere, and then introducing a 20% SiH 4 -N 2 mixed atmosphere and maintaining it for 3 h;

[0094] (3) The material prepared in step (2) was placed in a tube furnace, N2 was introduced and the temperature was raised to 550°C, and then acetylene gas with a flow rate of 100 sccm was introduced and kept warm for 2 hours; silicon-carbon composite particles were obtained.

[0095] Among them, 0.26nm≤d1<0.365nm, d2≥0.365nm; the total volume of the first opening of the silicon-carbon composite particle is 0.02cm 3 / g, and the total volume of the second opening is 0.005cm 3 / g, the total volume of closed pores is 0.02cm 3 / g; the silicon-carbon composite particles include a core-shell structure, the content of the porous carbon is 30%, the content of the silicon material is 69%, and the content of the amorphous carbon is 1%; the DvlO is 5.2 pm, the Dv50 is 10.6 pm, the Dv90 is 16.5 pm, the Dn10 is 2.7 pm, the Dn50 is 7.3 pm, and the Dn90 is 11.4 pm, was 1.07, was 1.19.

[0096] Preparation Example 4

[0097] for verifying the influence brought by the change of the "total volume of the first opening".

[0098] The preparation examples in this group are made with reference to Preparation Example 1, except that the total volume of the first opening is regulated by changing the temperature and time of step (2), as follows:

[0099] Preparation Example 4a, the total volume of the first opening is controlled to be 0.003 cm 3 / g;

[0100] Preparation Example 4b, the total volume of the first opening is controlled to be 0.14 cm 3 / g.

[0101] Preparation Example 5

[0102] for verifying the influence brought by the change of the "total volume of the second opening".

[0103] The preparation examples in this group are made with reference to Preparation Example 1, except that the total volume of the second opening is regulated by changing the temperature of step (1), as follows:

[0104] Preparation Example 5a, the total volume of the second opening is 0.001 cm 3 / g;

[0105] Preparation Example 5b, the total volume of the second opening is 0.03 cm 3 / g.

[0106] Preparation Example 6

[0107] for verifying the influence brought by the change of the "total volume of the closed opening".

[0108] The preparation examples in this group are made with reference to Preparation Example 1, except that the total volume of the closed opening is regulated by changing the temperature of step (2), as follows:

[0109] Preparation Example 6a, the total volume of the closed opening is 0.003 cm 3 / g;

[0110] Preparation Example 6b, the total volume of the closed opening is 0.32 cm 3 / g.

[0111] Preparation Example 7

[0112] Used to verify the impact of changes in "mean sphericity".

[0113] This group of preparation examples was carried out with reference to Preparation Example 1, except that the average sphericity of the silicon-carbon composite particles was controlled by changing the average sphericity of the porous carbon material, as follows:

[0114] In Preparation Example 7, the average sphericity of the porous carbon material is 0.52.

[0115] Preparation Example 8

[0116] Used to verify the impact of changes in the "core-shell structure".

[0117] This group of preparation examples was carried out with reference to Preparation Example 1, except that in step (3), acetylene gas was not introduced, thereby obtaining silicon-carbon composite particles (without a shell).

[0118] Preparation Example 9

[0119] Used to verify the impact of changes in the "content of porous carbon, silicon material and amorphous carbon in silicon-carbon composite particles".

[0120] This group of preparation examples was carried out with reference to Preparation Example 1, except that the contents of porous carbon, silicon material, and amorphous carbon were controlled by changing the mass of needle-shaped petroleum coke in step (1), the content of SiH4-N2 in step (2), and the flow rate of acetylene gas in step (3), as follows:

[0121] In Preparation Example 9, the content of porous carbon is 19%, the content of silicon material is 71%, and the content of amorphous carbon is 10%.

[0122] Preparation Example 10

[0123] This is used to verify the impact of changes in the particle size of silicon-carbon composite particles.

[0124] This group of preparation examples was carried out with reference to Preparation Example 3, except that Dv50 was 8.1 μm. is 1.4; Dn50 is 6.01μm, is 1.45.

[0125] Comparative Preparation Example 1

[0126] The preparation was carried out in accordance with Preparation Example 1, except that the total volume of the first opening was controlled by changing the temperature and time of step (2), as follows:

[0127] Comparative Example 1a, the total volume of the first opening is 0.0005 cm 3 / g;

[0128] Comparative Preparation Example 1b, the total volume of the first opening is 0.2 cm 3 / g.

[0129] Comparative Preparation Example 2

[0130] The preparation was carried out in accordance with Preparation Example 1, except that the total volume of the second opening was controlled by changing the temperature of step (1), as follows:

[0131] Comparative Example 2a, the total volume of the second opening is 0.00008 cm 3 / g;

[0132] Comparative Preparation Example 2b, the total volume of the second opening is 0.07 cm 3 / g.

[0133] Comparative Preparation Example 3

[0134] The preparation was carried out in accordance with Preparation Example 1, except that the total volume of the closed pores was controlled by changing the temperature of step (2), as follows:

[0135] Comparative Example 3a, the total volume of closed pores is 0.00007 cm 3 / g;

[0136] Comparative Preparation Example 3b, the total volume of closed pores is 0.45 cm 3 / g.

[0137] Test Case I

[0138] (1) True density test

[0139] The silicon-carbon composite particles prepared in the preparation examples were subjected to true density tests. The results showed that the true density of the silicon-carbon composite particles prepared in all the preparation examples was 1.5 g / cm 3 -2.2g / cm 3 The true density of nitrogen measured is within 1.2g / cm 3 -1.9g / cm 3 The true density of the silicon-carbon composite particles prepared in Preparation Example 1 measured by helium and nitrogen was 2 g / cm 3 and 1.4 g / cm 3 The true density of the silicon-carbon composite particles prepared in Example 2 was measured by helium and nitrogen respectively, and the true density was 2.1 g / cm 3 and 1.7 g / cm 3 The true density of the silicon-carbon composite particles prepared in Example 3 was measured by helium and nitrogen respectively, and the true density was 1.8 g / cm 3 and 1.5g / cm 3The true density of the silicon-carbon composite particles prepared in Example 4a and Example 4b was measured in helium, respectively, and was 1.55 g / cm 3 and 2.18 g / cm 3 The nitrogen measured true density of the silicon-carbon composite particles prepared in Example 5a and Example 5b was 1.23 g / cm 3 and 1.82 g / cm 3 .

[0140] (2) XRD test

[0141] The silicon-carbon composite particles prepared in Preparation Examples 1 to 3 were subjected to XRD testing, and the results are recorded in Table 1. The results of the remaining preparation examples all met the following requirements: a characteristic diffraction peak was present at 4°-5°, and the half-peak width L of the characteristic diffraction peak satisfied 0.05°≤L≤0.6°.

[0142] (3) dQ / dV curve

[0143] The button half-cells prepared with the silicon-carbon composite particles obtained in Preparation Examples 1 to 3 were subjected to first-cycle dQ / dV curve tests, and the results are recorded in Table 1. The results of the remaining preparation examples all met the following requirements: a characteristic peak 1 at 0.25V-0.3V, a characteristic peak 2 at 0.4V-0.45V, and a ratio of the peak intensity of the characteristic peak 1 to the peak intensity of the characteristic peak 2 of 1.65-3.

[0144] Table 1

[0145]

[0146] The following examples illustrate the batteries of the present invention.

[0147] Example 1

[0148] Prepare as follows:

[0149] (1) Preparation of negative electrode sheet

[0150] Artificial graphite, the silicon-carbon composite particles prepared in Preparation Example 1, sodium carboxymethyl cellulose, styrene-butadiene rubber, and Super P were mixed in a mass ratio of 87.7:8.8:1.6:1.6:0.3, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil, placed in an 80°C oven and dried for 12 hours, and then rolled and slit to obtain a negative electrode sheet.

[0151] (2) Preparation of positive electrode sheet

[0152] Lithium cobalt oxide, polyvinylidene fluoride, acetylene black and carbon nanotubes were mixed in a mass ratio of 96:2:1.5:0.5, N-methylpyrrolidone was added, and the mixture was stirred in a vacuum mixer until a uniform positive electrode slurry was formed. The positive electrode slurry was evenly coated on both sides of the aluminum foil, placed in an oven for baking, and then transferred to a 120°C oven for drying for 8 hours. After roller pressing and slitting, the positive electrode sheet was obtained.

[0153] (3) Preparation of lithium-ion batteries

[0154] The negative electrode sheet prepared in step (1), the diaphragm (a polyethylene film with a thickness of 8 μm) and the positive electrode sheet prepared in step (2) are stacked in order, ensuring that the diaphragm is located between the positive and negative electrode sheets to play an isolating role, and then a bare battery cell is obtained by winding; the bare battery cell is placed in an aluminum-plastic film shell, and an electrolyte (a mixed solution of lithium hexafluorophosphate dissolved in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) and 5 vol% fluoroethylene carbonate, wherein the concentration of lithium hexafluorophosphate is 1 mol / L) is injected into the dried bare battery cell, and a lithium ion battery is obtained through vacuum packaging, standing, forming, shaping, sorting and other processes.

[0155] (4) Preparation of button half-cell

[0156] The silicon-carbon composite particles prepared in Preparation Example 1, Super P, sodium carboxymethyl cellulose and styrene-butadiene rubber were mixed in a mass ratio of 96.5:1.6:1.6:0.3, deionized water was added, and the mixture was mixed evenly under the action of a vacuum mixer to obtain a buckle negative electrode slurry; the buckle negative electrode slurry was coated on a copper foil, dried in an 80°C oven, and then transferred to a 100°C vacuum oven for drying for 12 hours to obtain a surface density of about 3 mg / cm 2 negative electrode sheet; in a dry environment, the negative electrode sheet was punched into a negative electrode disc with a diameter of 12 mm using a sheet punching machine; in a glove box, the negative electrode disc was used as the working electrode, the metal lithium sheet was used as the counter electrode, and a polyethylene membrane with a thickness of 20 μm was used as the isolation membrane. An electrolyte (a mixed solution of lithium hexafluorophosphate dissolved in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) and 5 vol% fluoroethylene carbonate, in which the concentration of lithium hexafluorophosphate was 1 mol / L) was added to assemble a button half-cell.

[0157] Examples 2 to 9 and Comparative Examples 1 to 3 were prepared with reference to Example 1, and Example 10 was prepared with reference to Example 3; the difference being that silicon-carbon composite particles were prepared by replacing Preparation Example 1 with Preparation Example 3, as shown in Table 2.

[0158] Test Case II

[0159] (1) Cycle test

[0160] The lithium ion batteries prepared in the examples and comparative examples were subjected to cycle tests. The specific test methods are as follows:

[0161] At 45 ° C, the battery was charged at 1.2C at 4.2V and then 0.7C to 4.53V, with a cutoff current of 0.05C, and then allowed to stand for 10 minutes. The thickness of the battery at this time was recorded as the initial thickness; then discharged at a rate of 0.2C to a cutoff voltage of 3.0V, allowed to stand for 10 minutes, and the discharge capacity of the battery at this time was recorded as the initial capacity; the cycle process was: charged at 1.2C at 4.2V and then 0.7C to 4.53V, with a cutoff current of 0.05C, and then allowed to stand for 10 minutes, and then discharged at a rate of 0.7C to a cutoff voltage of 3.0V, allowed to stand for 10 minutes, and the above cycle process was repeated until the 500th cycle. After the 500th cycle charging process was completed and allowed to stand for 10 minutes, the thickness of the battery was tested and recorded as the thickness after the cycle, and then discharged at 0.7C to 3.0V, allowed to stand for 10 minutes, and the discharge capacity of the battery at this time was recorded as the capacity after the cycle. The cycle capacity retention rate = capacity after cycle × 100% / initial capacity, thickness expansion rate = (thickness after cycle - initial thickness) × 100% / initial thickness. The cycle capacity retention rate and thickness expansion rate are recorded in Table 2.

[0162] (2) Discharge rate test

[0163] The lithium ion batteries prepared in the examples and comparative examples were subjected to discharge rate tests. The specific test methods are as follows:

[0164] The lithium-ion batteries prepared in the Examples and Comparative Examples were allowed to rest for 10 minutes at a temperature of (25±5)°C. They were then discharged at a standard constant current of 0.2C to a discharge cutoff voltage of 3.0V and allowed to rest for 10 minutes. Under constant temperature conditions, they were then charged at a standard constant current and constant voltage of 0.2C to a charge cutoff voltage of 4.53V, with a cutoff current of 0.02C, and allowed to rest for 10 minutes. The batteries were then discharged at a specific rate (0.2C / 0.5C) to a discharge cutoff voltage of 3.0V, respectively, to obtain the actual capacities C1 and C2 of the batteries. The batteries were then allowed to rest for 10 minutes. This cycle was repeated until all discharge rates were complete. C2 / C1 × 100% is the capacity retention at a rate of 0.5C. The results are reported in Table 2.

[0165] (3) Charging rate test

[0166] The lithium-ion batteries prepared in the examples and comparative examples were subjected to a charge rate test. The specific test method is as follows:

[0167] The lithium-ion batteries prepared in the examples and comparative examples were allowed to rest for 10 minutes at a temperature of (25±5)°C, discharged at a rate of 0.2C to a cutoff voltage of 3.0V, allowed to rest for 10 minutes, and then charged at a standard constant current and constant voltage of 1C to a charge cutoff voltage of 4.53V at a cutoff current of 0.02C, and allowed to rest for 10 minutes. The capacity when charged at a standard constant current of 1C to 4.53V is C3, and the capacity when charged at a standard constant current and constant voltage of 1C to 4.53V at a cutoff current of 0.02C is C4. Therefore, the constant current charge ratio at 1C is C3 / C4×100%. The results are recorded in Table 2.

[0168] Table 2

[0169]

[0170]

[0171] As can be seen from Table 2, the battery of the present invention has significantly improved 45°C cycle performance and charge-discharge rate performance compared with the comparative example.

[0172] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A negative electrode active material, characterized in that The negative electrode active material includes silicon-carbon composite particles, the silicon-carbon composite particles include closed pores and open pores, the open pores include first open pores and second open pores, the pore diameter of the first open pore is d1, the pore diameter of the second open pore is d2, 0.26nm≤d1<0.365nm, d2≥0.365nm; The total volume of the first opening is 0.001 cm 3 / g-0.15cm 3 / g; The total volume of the second opening is 0.0001 cm 3 / g-0.05cm 3 / g; The total volume of the closed pores is 0.001 cm 3 / g-0.35cm 3 / g.

2. The negative electrode active material according to claim 1, wherein The true density of the silicon-carbon composite particles measured in helium is 1.5 g / cm 3 -2.2g / cm 3 ; preferably 1.8g / cm 3 -2.1g / cm 3 The nitrogen measured true density of the silicon-carbon composite particles is 1.2 g / cm 3 -1.9g / cm 3 ; preferably 1.4g / cm 3 -1.7g / cm 3 ; And / or, the average sphericity of the silicon-carbon composite particles is 0.5-1, preferably 0.75-1.

3. The negative electrode active material according to claim 1 or 2, wherein The silicon-carbon composite particles include a core-shell structure; the core of the core-shell structure includes carbon and silicon, and the shell of the core-shell structure includes carbon; Preferably, the core comprises porous carbon and silicon material located in the pores of the porous carbon; Preferably, the shell comprises amorphous carbon.

4. The negative electrode active material according to claim 1 or 2, wherein The XRD diffraction pattern of the silicon-carbon composite particles has a characteristic diffraction peak at 4°-5°; the half-peak width L of the characteristic diffraction peak satisfies 0.05°≤L≤0.6°.

5. The negative electrode active material according to claim 1 or 2, wherein The particle size Dv10 of the silicon-carbon composite particles is 4 μm-6 μm, Dv50 is 8 μm-12 μm, and Dv90 is 14 μm-18 μm; And / or, the particle size Dn10 of the silicon-carbon composite particles is greater than 3 μm, Dn50 is between 6 μm and 8 μm, and Dn90 is between 10 μm and 12 μm.

6. The negative electrode active material according to claim 5, wherein The particle size of the silicon-carbon composite particles satisfies the relationship: Preferably 0.9-1.2; and / or, Preferably it is 0.8-1.

35.

7. The negative electrode active material according to claim 3, wherein Based on the total weight of the silicon-carbon composite particles, the content of the porous carbon is 20%-70%, the content of the silicon material is 20%-70%, and the content of the amorphous carbon is 0.1%-20%; Preferably, based on the total weight of the silicon-carbon composite particles, the content of the porous carbon is 30%-60%, the content of the silicon material is 30%-69%, and the content of the amorphous carbon is 1%-10%.

8. The negative electrode active material according to claim 1 or 2, wherein The first-cycle dQ / dV curve of the button-type half-cell of the negative electrode active material has a characteristic peak 1 at 0.25V-0.3V and a characteristic peak 2 at 0.4V-0.45V; the ratio of the peak intensity of the characteristic peak 1 to the peak intensity of the characteristic peak 2 is 1.65-3.

9. 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 8; preferably, in the negative electrode sheet, the total volume of the first opening is 0.14 cm 3 / g-0.24cm 3 / g, and the total volume of the second opening is 0.06cm 3 / g-0.1cm 3 / g.

10. A battery, characterized in that: The battery comprises the negative electrode active material according to any one of claims 1 to 8 and / or the negative electrode sheet according to claim 9.

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