Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device. The electrochemical device comprises a positive pole piece, a negative pole piece and electrolyte, the negative pole piece comprises a negative pole material layer, and the negative pole material layer comprises a negative pole active material; the negative electrode active material comprises first silicon-carbon particles and second silicon-carbon particles, the particle size Ra of the first silicon-carbon particles is greater than or equal to 6 microns, and the particle size Rb of the second silicon-carbon particles is less than or equal to 5.5 microns; the average particle size of the first silicon carbon particles is R1 [mu] m, 6.6 < = R1 < = 11.2, the average particle size of the second silicon carbon particles is R2 [mu] m, 1.1 < = R2 < = 4.2; based on the sum of the number of the first silicon-carbon particles and the number of the second silicon-carbon particles, the number proportion of the first silicon-carbon particles is P1%, and P1 is larger than or equal to 10 and smaller than or equal to 18; the number ratio of the second silicon-carbon particles is P2%, and P2 is larger than or equal to 82 and smaller than or equal to 90. The electrochemical device provided by the invention has relatively high energy density and good quick charge performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry technology, and particularly to an electrochemical device and an electronic device. Background Art

[0002] Currently, due to advantages such as high energy density, long cycle life, low self-discharge, and environmental friendliness, lithium-ion batteries have been widely used in various consumer electronic devices such as mobile phones, laptops, and tablet computers. And how to improve the fast charging performance and cycle performance of the electrochemical device while increasing the energy density of the electrochemical device is what the industry has been constantly pursuing and urgently needs to break through. Summary of the Invention

[0003] The purpose of the present application is to provide an electrochemical device and an electronic device, which can increase the energy density of the electrochemical device while improving the fast charging performance and cycle performance of the electrochemical device.

[0004] The first aspect of the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material; the negative electrode active material contains a first silicon-carbon particle and a second silicon-carbon particle. The particle size of the first silicon-carbon particle is R a , R a ≥6μm, and the particle size of the second silicon-carbon particle is R b , R b ≤5.5μm; the average particle size of the first silicon-carbon particle is R1μm, 6.6≤R1≤11.2, and the average particle size of the second silicon-carbon particle is R2μm, 1.1≤R2≤4.2; based on the sum of the numbers of the first silicon-carbon particle and the second silicon-carbon particle, the number proportion of the first silicon-carbon particle is P1%, 10≤P1≤18; the number proportion of the second silicon-carbon particle is P2%, 82≤P2≤90. The negative electrode sheet includes the above characteristics, and by regulating the average particle sizes and number proportions of the first silicon-carbon particle and the second silicon-carbon particle within the scope of the present application, the ion transport path can be shortened, the solid-phase diffusion ability can be improved, thereby improving the fast charging performance and cycle performance of the electrochemical device; at the same time, the pore utilization rate of the negative electrode sheet is increased, the space utilization of the negative electrode sheet is improved, thereby increasing the energy density of the electrochemical device.

[0005] In some embodiments of the present application, 2≤R1 / R2≤7. When 2≤R1 / R2≤7, it is beneficial to shorten the ion transport path, improve the solid-phase diffusion ability, thereby further improving the fast charging performance and cycle performance of the electrochemical device; at the same time, the average particle sizes of the first silicon-carbon particle and the second silicon-carbon particle match each other, increasing the pore utilization rate of the negative electrode sheet, improving the space utilization of the negative electrode sheet, thereby further increasing the energy density of the electrochemical device.

[0006] In some embodiments of the present application, X = P1 / P2, and 0.12 ≤ X ≤ 0.2. By adjusting the value of X within the scope of the present application, the first silicon-carbon particles and the second silicon-carbon particles match each other, improving the packing density and the pore utilization rate of the negative electrode sheet, thereby further increasing the energy density of the electrochemical device.

[0007] In some embodiments of the present application, based on the sum of the masses of silicon and carbon elements in the first silicon-carbon particles, the mass percentage of silicon element in the first silicon-carbon particles is A1%, and 37.3 ≤ A1 ≤ 44.7. By adjusting A1 within the scope of the present application, it is beneficial to the capacity per gram of the first silicon-carbon particles, improving the energy density of the electrochemical device. At the same time, it can also improve the interfacial stability of the first silicon-carbon particles, thereby improving the interfacial transfer impedance of the first silicon-carbon particles, and further enhancing the fast charging performance and cycling performance of the electrochemical device.

[0008] In some embodiments of the present application, based on the sum of the masses of silicon, carbon, and oxygen elements in the second silicon-carbon particles, the mass percentage of silicon element in the second silicon-carbon particles is A2%, and 8.7 ≤ A2 ≤ 24.7; based on the sum of the masses of silicon, carbon, and oxygen elements in the second silicon-carbon particles, the mass percentage of oxygen element in the second silicon-carbon particles is C%, and 1.1 ≤ C ≤ 2.1. By adjusting the mass percentages of silicon and oxygen elements in the second silicon-carbon particles within the scope of the present application, it is beneficial to improve the electronic conductivity and ionic conductivity of silicon in the second silicon-carbon particles, which is beneficial to the capacity per gram of the second silicon-carbon particles, thereby increasing the energy density of the electrochemical device. At the same time, it is beneficial to improve the interfacial stability of the second silicon-carbon particles and improve the interfacial transfer impedance of the negative electrode active material, thereby further enhancing the fast charging performance and cycling performance of the electrochemical device.

[0009] In some embodiments of the present application, the average roundness of the first silicon-carbon particles is M1, and 0.83 ≤ M1 ≤ 0.98; the average roundness of the second silicon-carbon particles is M2, and 0.91 ≤ M2 ≤ 0.99. By adjusting the average roundness of the first silicon-carbon particles and the second silicon-carbon particles within the scope of the present application, the distribution positions and packing modes of the first silicon-carbon particles and the second silicon-carbon particles in the negative electrode sheet can be optimized, thereby enhancing the fast charging performance and energy density of the electrochemical device; at the same time, it can also improve the stability of the bonding network of the negative electrode sheet during the cycling process, thereby improving the cycling performance of the electrochemical device.

[0010] In some embodiments of the present application, 0.86 ≤ M1 / M2 ≤ 0.95. By adjusting the value of M1 / M2 within the scope of the present application, the distribution positions and packing modes of the first silicon-carbon particles and the second silicon-carbon particles in the negative electrode sheet can be further optimized, and the energy density, fast charging performance, and cycling performance of the electrochemical device can be better improved.

[0011] In some embodiments of the present application, the porosity of the negative electrode sheet is from 20.2% to 39.1%. By regulating the porosity of the negative electrode sheet within the scope of the present application, while the negative electrode sheet has a relatively high energy density, the electron transport and ion transport performances are improved, and further the fast charging performance and cycle performance of the electrochemical device are improved.

[0012] In some embodiments of the present application, when the electrochemical device is discharged to 2.5 V, the thickness of the negative electrode material layer is H μm, 32.1 ≤ H ≤ 100.2; in some embodiments of the present application, 40.8 ≤ H ≤ 62.1. The thickness of the negative electrode material layer after discharge is within the above range, indicating that the thickness of the negative electrode material layer of the present application is relatively thin, the electrochemical device has a relatively high energy density, and in addition, the diffusion path of lithium ions in the negative electrode can be made shorter, thereby further improving the fast charging performance and cycle performance of the electrochemical device.

[0013] In some embodiments of the present application, the coating weight of the negative electrode sheet is W mg / cm 2 , 2.27 ≤ W ≤ 8.21. By regulating the coating weight W of the negative electrode sheet within the scope of the present application, a relatively high proportion of the negative electrode active material in the electrochemical device and a relatively short diffusion path of lithium ions in the negative electrode can be obtained, thereby further improving the fast charging performance and cycle performance of the electrochemical device and increasing the energy density at the same time.

[0014] In some embodiments of the present application, the electrolyte contains a first component, and the first component contains at least one of lithium difluorophosphate, lithium nitrate or dimethyl sulfoxide. The electrolyte contains at least one of the first components, which can optimize the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles, improve the stability and ion transport ability of the SEI film, and thereby improve the cycle performance and fast charging performance of the electrochemical device.

[0015] In some embodiments of the present application, based on the mass of the electrolyte, the mass proportion of lithium difluorophosphate is D1%, 0.02 ≤ D1 ≤ 2.11. By regulating the mass proportion of lithium difluorophosphate within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the stability and ion transport ability of the SEI film can be improved, and thereby the cycle performance and fast charging performance of the electrochemical device can be further improved.

[0016] In some embodiments of the present application, based on the mass of the electrolyte, the mass proportion of lithium nitrate is D2%, 0.005 ≤ D2 ≤ 1.62. By regulating the mass proportion of lithium nitrate within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the stability and ion transport ability of the SEI film can be improved, and thereby the cycle performance and fast charging performance of the electrochemical device can be further improved.

[0017] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of dimethyl sulfoxide is D3%, and 0.02 ≤ D3 ≤ 1.83. By adjusting D3 within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the stability and ion transport ability of the SEI film can be improved, and thus the cycle performance and fast charging performance of the electrochemical device can be further improved.

[0018] In some embodiments of the present application, the electrolyte includes lithium nitrate. Based on the mass of the electrolyte, the mass percentage of lithium nitrate is D2%, and 0.005 ≤ D2 ≤ 1.62. D2 and R2 satisfy: 0.015 ≤ D2 × R2 ≤ 4.9. The electrolyte includes lithium nitrate and adjusting D2 × R2 within the scope of the present application is beneficial to further improving the fast charging performance and cycle performance of the electrochemistry and increasing the energy density of the electrochemical device.

[0019] In some embodiments of the present application, X = P1 / P2, and D2 and X satisfy: 0.31 ≤ D2 / X ≤ 10.1. By adjusting D2 / X within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be further optimized, the stability and ion transport ability of the SEI film can be improved, and thus the cycle performance and fast charging performance of the electrochemical device can be further improved. The second aspect of the present application provides an electronic device, which includes the electrochemical device provided by the first aspect of the present application. Thus, the electronic device of the present application has a long service life and good performance in use.

[0020] Advantages of the present application:

[0021] The present application provides an electrochemical device and an electronic device. Among them, the electrochemical device includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material; the negative electrode active material contains first silicon-carbon particles and second silicon-carbon particles, and the particle size of the first silicon-carbon particles is R a , R a ≥ 6 μm, and the particle size of the second silicon-carbon particles is R b , R b≤5.5 μm; the average particle size of the first silicon-carbon particle is R1 μm, 6.6 ≤ R1 ≤ 11.2, the average particle size of the second silicon-carbon particle is R2 μm, 1.1 ≤ R2 ≤ 4.2; based on the sum of the numbers of the first silicon-carbon particle and the second silicon-carbon particle, the proportion of the number of the first silicon-carbon particle is P1%, 10 ≤ P1 ≤ 18; the proportion of the number of the second silicon-carbon particle is P2%, 82 ≤ P2 ≤ 90. By adjusting the average particle sizes and the proportion of the numbers of the first silicon-carbon particle and the second silicon-carbon particle within the above ranges, the pore utilization rate of the negative electrode sheet can be improved, the space utilization of the negative electrode sheet can be improved, thereby increasing the energy density of the electrochemical device, and at the same time, the ion transport path can be shortened, the solid-phase diffusion ability can be improved, the risk of damage to the positive electrode material layer can be reduced, and the fast charging performance and the cycle performance of the electrochemical device can be improved.

[0022] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Detailed implementation manners

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0024] It should be noted that, in the specific implementation manners of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery.

[0025] The first aspect of the present application provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material; the negative electrode active material includes a first silicon-carbon particle and a second silicon-carbon particle, and the particle size of the first silicon-carbon particle is R a , R a ≥ 6 μm, the particle size of the second silicon-carbon particle is R b , R b≤5.5 μm; the average particle size of the first silicon-carbon particle is R1 μm, 6.6 ≤ R1 ≤ 11.2, the average particle size of the second silicon-carbon particle is R2 μm, 1.1 ≤ R2 ≤ 4.2; based on the sum of the numbers of the first silicon-carbon particle and the second silicon-carbon particle, the proportion of the number of the first silicon-carbon particle is P1%, 10 ≤ P1 ≤ 18; the proportion of the number of the second silicon-carbon particle is P2%, 82 ≤ P2 ≤ 90. For example, R1 can be 6.6, 7, 8, 9, 10, 11, 11.2 or a range composed of any two of these values; R2 can be 1.1, 1.5, 2, 2.5, 3, 3.5, 4, 4.2 or a range composed of any two of these values; P1 can be 10, 11, 12, 13, 14, 15, 16, 17, 18 or a range composed of any two of these values; P2 can be 82, 83, 84, 85, 86, 87, 88, 89, 90 or a range composed of any two of these values. The negative electrode sheet includes the above characteristics, and the average particle sizes and the proportion of the numbers of the first silicon-carbon particle and the second silicon-carbon particle are adjusted within the scope of this application. The particle sizes and the number of particles of the first silicon-carbon particle and the second silicon-carbon particle are matched, which can shorten the ion transport path and improve the solid-phase diffusion ability, thereby improving the fast charging performance and the cycling performance of the electrochemical device. At the same time, it is beneficial to improve the pore utilization rate of the negative electrode sheet and the space utilization of the negative electrode sheet, thereby increasing the energy density of the electrochemical device.

[0026] In this application, the negative electrode active material further includes graphite, and the graphite may include at least one of natural graphite and artificial graphite. The negative electrode material layer of this application further includes a conductive agent and a binder. In this application, based on the mass of the negative electrode material layer, the mass proportion of the first silicon-carbon particle is 1.1% to 14%, the mass proportion of the second silicon-carbon particle is 4.2% to 67%, the mass proportion of graphite is 5% to 90%, the mass proportion of the conductive agent is 0.2% to 5%, and the mass proportion of the binder is 1% to 10%.

[0027] In some embodiments of this application, 2 ≤ R1 / R2 ≤ 7. For example, the value of R1 / R2 can be 2, 3, 4, 5, 6, 7 or a range composed of any two of these values. By adjusting the value of R1 / R2 within the scope of this application, it is beneficial to shorten the ion transport path and improve the solid-phase diffusion ability, thereby further improving the fast charging performance and the cycling performance of the electrochemical device; at the same time, the average particle sizes of the first silicon-carbon particle and the second silicon-carbon particle are matched with each other, improving the pore utilization rate of the negative electrode sheet and the space utilization of the negative electrode sheet, thereby further increasing the energy density of the electrochemical device.

[0028] In some embodiments of the present application, X = P1 / P2, and 0.12 ≤ X ≤ 0.2. For example, the value of X can be 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, or a range formed by any two of these numerical values. By controlling the value of X within the scope of the present application, the first silicon-carbon particles and the second silicon-carbon particles match each other, the packing density is increased, the porosity utilization rate of the negative electrode sheet is improved, and thus the energy density of the electrochemical device is further improved.

[0029] In some embodiments of the present application, the first silicon-carbon particles contain silicon and carbon elements; based on the sum of the masses of silicon and carbon elements in the first silicon-carbon particles, the mass percentage of silicon element in the first silicon-carbon particles is A1%, and 37.3 ≤ A1 ≤ 44.7, and the rest is carbon element. For example, A1 can be 37.3, 38, 39, 40, 41, 42, 43, 44, 44.7, or a range formed by any two of these numerical values. Controlling the mass percentage of silicon element can control the effective contact sites between silicon and carbon. By controlling A1 within the scope of the present application, it is beneficial to improve the electronic conductivity and ionic conductivity of silicon, which is beneficial to the capacity per gram of the first silicon-carbon particles, and thus the energy density of the electrochemical device can be improved. At the same time, by controlling A1 within the above range, the distribution sites of silicon and carbon can be optimized, and the expansion of the first silicon-carbon particles can be improved by arranging the reasonable distribution sites of silicon and carbon, which is beneficial to improving the interface stability of the first silicon-carbon particles, thereby improving the interface transfer impedance of the first silicon-carbon particles, and further improving the fast charging performance and cycling performance of the electrochemical device.

[0030] In some embodiments of the present application, the second silicon carbide particles contain silicon element, carbon element and oxygen element; based on the total mass of silicon element, carbon element and oxygen element in the second silicon carbide particles, the mass percentage of silicon element is A2%, 8.7 ≤ A2 ≤ 24.7; based on the total mass of silicon element, carbon element and oxygen element in the second silicon carbide particles, the mass percentage of oxygen element is C%, 1.1 ≤ C ≤ 2.1, and the rest is carbon element. For example, A2 can be 8.7, 10, 12, 14, 16, 18, 20, 22, 24, 24.7 or a range composed of any two of these values; for example, C can be 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.1 or a range composed of any two of these values. By adjusting the mass percentages of silicon element and oxygen element in the second silicon carbide particles within the scope of the present application, it is beneficial to improve the electronic conductivity and ionic conductivity of silicon in the second silicon carbide particles, which is beneficial to the capacity per gram of the second silicon carbide particles, thereby improving the energy density of the electrochemical device. At the same time, by adjusting A2 and C within the above range, the distribution sites of silicon and carbon can be optimized, and the expansion of the second silicon carbide particles can be improved by arranging the reasonable distribution sites of silicon and carbon, which is beneficial to improving the interfacial stability of the second silicon carbide particles, thereby improving the interfacial transfer impedance of the negative electrode active material, and further improving the fast charging performance and cycle performance of the electrochemical device.

[0031] In some embodiments of the present application, the average roundness of the first silicon carbide particles is M1, 0.83 ≤ M1 ≤ 0.98; the average roundness of the second silicon carbide particles is M2, 0.91 ≤ M2 ≤ 0.99. For example, M1 can be 0.83, 0.86, 0.89, 0.92, 0.95, 0.98 or a range composed of any two of these values; for example, M2 can be 0.91, 0.93, 0.95, 0.97, 0.99 or a range composed of any two of these values. By adjusting the average roundness of the first silicon carbide particles and the second silicon carbide particles within the scope of the present application, the distribution positions and stacking modes of the first silicon carbide particles and the second silicon carbide particles in the negative electrode sheet can be optimized, which is beneficial to improving the ionic transport network and electronic transport network of the negative electrode sheet, thereby improving the fast charging performance and energy density of the electrochemical device; at the same time, the stability of the adhesion network of the negative electrode sheet during the cycling process can also be improved, thereby improving the cycle performance of the electrochemical device.

[0032] In some embodiments of the present application, 0.86 ≤ M1 / M2 ≤ 0.95. For example, the value of M1 / M2 can be 0.86, 0.88, 0.90, 0.92, 0.94, 0.95, or a range composed of any two of these values. By adjusting the value of M1 / M2 within the scope of the present application, the average roundness of the first silicon-carbon particles and the second silicon-carbon particles matches each other, and the distribution position and stacking mode of the first silicon-carbon particles and the second silicon-carbon particles in the negative electrode sheet can be further optimized, which is beneficial to improving the ion transport network and electron transport network of the negative electrode sheet, thereby better improving the energy density and fast charging performance of the electrochemical device; at the same time, the stability of the bonding network of the negative electrode sheet during the cycling process can be further improved, thereby further improving the cycling performance of the electrochemical device.

[0033] In some embodiments of the present application, the porosity of the negative electrode sheet is 20.2% to 39.1%. For example, the porosity of the negative electrode sheet can be 20.2%, 22.2%, 24.3%, 26.5%, 28.0%, 30.2%, 32.8%, 34.5%, 36.0%, 38.2%, 39.1%, or a range composed of any two of these values. By adjusting the porosity of the negative electrode sheet within the scope of the present application, sufficient ion transport channels can be provided to achieve the rapid transport of lithium ions, making it easier for the negative electrode active material to deintercalate and intercalate lithium, thereby improving the fast charging performance and energy density of the electrochemical device. At the same time, it can also match the expansion coefficient of the negative electrode active material itself, making the bonding network and conductive network of the negative electrode sheet have good stability, thereby improving the cycling performance of the electrochemical device.

[0034] In some embodiments of the present application, when the electrochemical device is discharged at 0.2C to 2.5V, the thickness of the negative electrode material layer is H μm, and 32.1 ≤ H ≤ 100.2; in some embodiments of the present application, 40.8 ≤ H ≤ 62.1. For example, the value of H can be 32.1, 35.4, 40.0, 40.8, 45.2, 50.5, 55.4, 60.3, 62.1, 65.5, 70.0, 75.2, 80.0, 85.5, 90.4, 95.8, 100.0, 100.2, or a range composed of any two of these values. The thickness of the negative electrode material layer after discharge is within the above range, indicating that the thickness of the negative electrode material layer of the present application is relatively thin, and the electrochemical device has a high energy density. In addition, it can also make the diffusion path of lithium ions in the negative electrode shorter, thereby further improving the fast charging performance and cycling performance of the electrochemical device.

[0035] In some embodiments of the present application, the coating weight of the negative electrode sheet is W mg / cm 2, 2.27 ≤ W ≤ 8.21. For example, the value of W can be 2.27, 3.20, 3.51, 4.00, 4.50, 5.25, 5.50, 6.00, 6.50, 7.00, 7.55, 8.00, 8.21, or any range formed by any two of these numerical values. By controlling the coating weight W of the negative electrode sheet within the scope of this application, on the one hand, a higher proportion of the negative active material in the electrochemical device can be achieved, so that the electrochemical device has a higher energy density; on the other hand, the diffusion path of lithium ions can be made shorter, which is beneficial to improving the fast charging performance of the electrochemical device.

[0036] In this application, there is no particular limitation on the preparation method of the first silicon-carbon particles, as long as the purpose of this application can be achieved. For example, the preparation method of the first silicon-carbon particles can be: adding the first carbon precursor into a fluidized bed, introducing the first gas, and performing the first chemical vapor deposition to obtain the first silicon-carbon particles. The above-mentioned first gas is a mixture of silane and argon, the volume fraction of silane in the first gas is 30% to 50%, the temperature of the first chemical vapor deposition is 400°C to 600°C, and the time is 6h to 10h. The first carbon precursor is porous carbon, and the average particle size of the first carbon precursor is 6.6μm to 11.2μm, and the average roundness is 0.83 to 0.98.

[0037] In this application, there is no particular limitation on the preparation method of the second silicon-carbon particles, as long as the purpose of this application can be achieved. For example, the preparation method of the second silicon-carbon particles can be: adding the second carbon precursor into a fluidized bed, introducing the second gas, performing the second chemical vapor deposition, and then standing in the air. After standing for 8h to 16h, acetylene gas is introduced for the third chemical vapor deposition to obtain the second silicon-carbon particles. The above-mentioned second gas is a mixture of silane and argon, the volume fraction of silane in the second gas is 20% to 40%, the temperature of the second chemical vapor deposition is 400°C to 600°C, and the time is 4h to 10h. The temperature of the third chemical vapor deposition is 400°C to 600°C, and the time is 4h to 12h. The second carbon precursor is porous carbon, and the average particle size of the second carbon precursor is 1.1μm to 4.2μm, and the average roundness is 0.91 to 0.99.

[0038] This application has no particular limitation on the method of controlling the average particle size R1 of the first silicon-carbon particles and the average particle size R2 of the second silicon-carbon particles, as long as the purpose of this application can be achieved. For example, the average particle size of the first silicon-carbon particles can be controlled by classifying the first carbon precursor, and the average particle size of the second silicon-carbon particles can be controlled by classifying the second carbon precursor. This application has no particular limitation on the method of particle classification, as long as the purpose of this application can be achieved. The method of particle classification can be any known classification means in the art, such as jet classification and cyclone classification.

[0039] The method for regulating the average roundness M1 of the first silicon-carbon particles and the average roundness M2 of the second silicon-carbon particles in this application is not particularly limited as long as the purpose of this application can be achieved. For example, the average roundness of the first silicon-carbon particles can be regulated by ball-milling the first carbon precursor, and the average roundness of the second silicon-carbon particles can be regulated by ball-milling the second carbon precursor. Generally, when the ball-milling time is prolonged, the average roundness of the particles decreases, and vice versa; when the rotation speed of the ball-milling is increased, the average roundness of the particles decreases, and vice versa.

[0040] Generally, the mass percentage A1% of silicon element in the first silicon-carbon particles can be regulated by controlling the volume fraction of silane in the first gas, the temperature and time of the first chemical vapor deposition. When other conditions remain unchanged, increasing the volume fraction of silane in the first gas, the value of A1 increases, and vice versa; when other conditions remain unchanged, increasing the temperature of the first chemical vapor deposition, the value of A1 increases, and vice versa; prolonging the time of the first chemical vapor deposition, the value of A1 increases, and vice versa.

[0041] Generally, the mass percentage A2% of silicon element in the second silicon-carbon particles can be regulated by controlling the volume fraction of silane in the second gas, the temperature and time of the second chemical vapor deposition. When other conditions remain unchanged, increasing the volume fraction of silane in the second gas, the value of A2 increases, and vice versa; when other conditions remain unchanged, increasing the temperature of the second chemical vapor deposition, the value of A2 increases, and vice versa; prolonging the time of the second chemical vapor deposition, the value of A2 increases, and vice versa.

[0042] Generally, the mass percentage C% of oxygen element in the second silicon-carbon particles can be regulated by controlling the standing time in air. When other conditions remain unchanged, prolonging the standing time in air, the value of C increases, and vice versa.

[0043] Generally, the porosity of the negative electrode sheet can be regulated by controlling the formation pressure of the electrochemical device. When other conditions remain unchanged, increasing the formation pressure, the porosity decreases, and vice versa.

[0044] In this application, the thickness of the negative electrode material layer can be adjusted by adjusting the porosity and coating weight of the negative electrode sheet. When other conditions remain unchanged, increasing the porosity of the negative electrode sheet, the thickness of the negative electrode material layer increases, and vice versa. When other conditions remain unchanged, increasing the coating weight of the negative electrode sheet, the thickness of the negative electrode material layer increases, and vice versa.

[0045] In some embodiments of the present application, the electrolyte contains a first component, and the first component contains at least one of lithium difluorophosphate, lithium nitrate, or dimethyl sulfoxide. By containing at least one of the first components in the electrolyte, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the stability of the SEI film and the ion transport ability can be improved, thereby improving the cycle performance and fast charging performance of the electrochemical device.

[0046] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is D1%, and 0.02 ≤ D1 ≤ 2.11. For example, D1 can be 0.02, 0.1, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.11 or a range composed of any two of these values. By controlling the mass percentage of lithium difluorophosphate within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the content of inorganic lithium salts in the SEI film can be increased, and the strength of the SEI film can be improved to adapt to the volume changes of the first silicon-carbon particles and the second silicon-carbon particles during charge and discharge. It is also beneficial to improve the stability of the SEI film and the ion transport ability, and thus further improve the cycle performance and fast charging performance of the electrochemical device.

[0047] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of lithium nitrate is D2%, and 0.005 ≤ D2 ≤ 1.62. For example, D2 can be 0.005, 0.01, 0.05, 0.1, 0.5, 0.8, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.62 or a range composed of any two of these values. By controlling the mass percentage of lithium nitrate within the scope of the present application, it is beneficial to optimize the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles, improve the stability of the SEI film and the ion transport ability, and improve the kinetics of the negative electrode sheet, thereby further improving the cycle performance and fast charging performance of the electrochemical device.

[0048] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of dimethyl sulfoxide is D3%, and 0.02 ≤ D3 ≤ 1.83. For example, D3 can be 0.02, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 1.83 or a range composed of any two of these values. By controlling D3 within the scope of the present application, the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles can be optimized, the stability of the SEI film and the ion transport ability can be improved, and it is also beneficial to enhance the ion transport ability between the first silicon-carbon particles and the second silicon-carbon particles, thereby further improving the cycle performance and fast charging performance of the electrochemical device.

[0049] In some embodiments of the present application, the electrolyte includes lithium nitrate. Based on the mass of the electrolyte, the mass percentage of lithium nitrate is D2%, where 0.005 ≤ D2 ≤ 1.62, and D2 and R2 satisfy: 0.015 ≤ D2 × R2 ≤ 4.9. For example, D2 × R2 can be 0.015, 0.02, 0.05, 0.08, 0.1, 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.2, 4.9, or a range composed of any two of these values. By adjusting D2 × R2 within the scope of the present application, the second silicon-carbon particles in the negative electrode active material and lithium nitrate in the electrolyte act synergistically, which is more conducive to the formation of the SEI film on the surface of the second silicon-carbon particles, optimizes the composition and structure of the SEI film on the surface of the second silicon-carbon particles, further improves the stability and ion transport ability of the SEI film, enhances the kinetics of the negative electrode sheet, and thus further improves the cycle performance and fast charging performance of the electrochemical device and increases the energy density of the electrochemical device.

[0050] In some embodiments of the present application, X = P1 / P2, and D2 and X satisfy: 0.31 ≤ D2 / X ≤ 10.1. For example, D2 / X can be 0.31, 0.5, 0.8, 1.0, 1.5, 2, 4, 6, 8, 10.1, or a range composed of any two of these values. By adjusting D2 / X within the scope of the present application, the first silicon-carbon particles, the second silicon-carbon particles in the negative electrode active material and lithium nitrate in the electrolyte act synergistically, which is beneficial to further optimizing the composition and structure of the SEI film on the surfaces of the first silicon-carbon particles and the second silicon-carbon particles, improving the stability and ion transport ability of the SEI film, enhancing the kinetics of the negative electrode sheet, and thus further improving the cycle performance and fast charging performance of the electrochemical device.

[0051] In the electrochemical device of the present application, the electrolyte further includes a lithium salt and a base solvent.

[0052] The present application has no particular limitation on the lithium salt, as long as the object of the present application can be achieved. For example, the lithium salt may include, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethylsulfonyl)methyl (LiC(SO2CF3)3), lithium hexafluorosilicate (LiSiF6), lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate (LiF2OB), or one or more of them. For example, the lithium salt can be selected as LiPF6 because it has high ionic conductivity and improves the cycling performance. The present application has no particular limitation on the content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass ratio of the lithium salt can be 8% to 20%. For example, the mass ratio of the lithium salt can be 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range composed of any two of these values. The electrolyte may further include fluoroethylene carbonate (FEC). Based on the mass of the electrolyte, the mass ratio of fluoroethylene carbonate can be 1% to 10%. For example, the mass ratio of fluoroethylene carbonate can be 1%, 2%, 5%, 6%, 8%, 10%, or a range composed of any two of these values.

[0053] The present application has no particular limitation on the base solvent, as long as the object of the present application can be achieved. For example, the base solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). The above cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. Based on the mass of the electrolyte, the mass ratio of the base solvent may be 64% to 90%. For example, the mass ratio of the base solvent may be 64%, 70%, 73%, 78%, 80%, 82%, 84%, 86%, 88%, 90% or any range composed of any two of these values.

[0054] In some embodiments, the electrolyte includes a base solvent and a lithium salt, and the mass percentage of the lithium salt is as described above. The mass percentage of the base solvent can be 80% to 92%. In some other embodiments, the electrolyte includes a base solvent and a lithium salt. Optionally, the electrolyte further includes at least one of the above-mentioned first components, and the mass percentages of the lithium salt and the first component are as described above. The mass percentage of the base solvent can be 78% to 91%. In some embodiments, the electrolyte includes a base solvent, a lithium salt, and FEC, and the mass percentages of the lithium salt and FEC are as described above. The mass percentage of the base solvent can be 70% to 91%. In some other embodiments, the electrolyte includes a base solvent, a lithium salt, and FEC. Optionally, the electrolyte further includes at least one of the above-mentioned first components, and the mass percentages of the lithium salt, FEC, and the first component are as described above. The mass percentage of the base solvent can be 76% to 90%. The electrolyte having the above characteristics can enable the electrochemical device to have better kinetic performance and cycling performance.

[0055] In the present application, the "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or can be a partial area of the surface of the negative electrode current collector. There is no particular limitation in the present application as long as the object of the present application can be achieved.

[0056] The present application places no particular limitation on the negative electrode current collector as long as the object of the present application can be achieved. For example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0057] The present application has no particular limitation on the types of conductive agents and binders in the negative electrode material layer, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above-mentioned metal materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0058] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0059] In the present application, the electrochemical device further includes a separator. The present application has no particular limitation on the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film.

[0060] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure. The material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In the present application, the thickness of the separator has no particular limitation, as long as the object of the present application can be achieved. For example, the thickness of the separator may be 4 μm to 30 μm.

[0061] In this application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or can be disposed on both surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector, or a partial area of the surface of the positive electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved.

[0062] There is no special limitation on the positive electrode current collector in this application, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector), etc.

[0063] There is no special limitation on the positive electrode active material in this application, as long as the purpose of this application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganate, spinel-type lithium nickel manganate, and lithium titanate

[0064] The positive electrode material layer can also include a positive electrode conductive agent and a positive electrode binder. There is no special limitation on the types of the positive electrode conductive agent and the positive electrode binder in this application, as long as the purpose of this application can be achieved. For example, the positive electrode conductive agent and the positive electrode binder can be at least one of the above-mentioned conductive agents and the above-mentioned binders. There is no special limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application can be achieved.

[0065] There is no special limitation on the thickness of the positive electrode current collector and the positive electrode material layer in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0066] Optionally, the positive electrode plate can further include a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the positive electrode conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The positive electrode conductive layer includes a positive electrode conductive layer conductive agent and a positive electrode conductive layer binder. There is no special limitation on the positive electrode conductive layer conductive agent and the positive electrode conductive layer binder in this application. For example, it can be at least one of the above-mentioned conductive agents and the above-mentioned binders.

[0067] The electrochemical device further includes a housing for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the above-mentioned other components. This application has no special limitation on the housing, and it can be a housing well-known in the art as long as it can achieve the purpose of this application. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. This application does not limit the type of metal, and a metal hard shell housing known in the art can be used as long as it can achieve the purpose of this application. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0068] The preparation process of the electrochemical device of this application is well-known to those skilled in the art, and this application has no special limitation. For example, the preparation process of the electrochemical device can include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. according to needs to obtain a wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. Or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the housing as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0069] The electrochemical device of this application is not particularly limited, and it can include any device that undergoes an electrochemical reaction. For example, the electrochemical device can include but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0070] The second aspect of this application provides an electronic device, which includes the electrochemical device provided in the first aspect of this application. Thus, the electronic device of this application has a long service life and good performance.

[0071] The electronic device of this application is not particularly limited, and it can be any electrical device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor, etc.

[0072] Example

[0073] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0074] Testing methods and equipment:

[0075] Testing of elemental mass fraction, average particle size, particle number, and average roundness:

[0076] Fix the negative electrode plate on the sample stage using conductive carbon paste, and place the sample stage on the bracket. Place the bracket and the sample stage into an electron cross-section polishing instrument (CP), evacuate to 10 -4 Pa, and then cut along the thickness direction of the negative electrode plate using argon gas. Place the cross-section of the sample after cutting by CP facing upwards on the SEM special sample stage, and use a Philips XL-30 type field emission scanning electron microscope (SEM) for testing. Set the acceleration voltage to 10 kV and the emission current to 10 mA. Observe the silicon-carbon particles using SEM. The criteria for determining whether the silicon-carbon particles are the first silicon-carbon particles or the second silicon-carbon particles are as follows: When the particle size of the silicon-carbon particles is greater than or equal to 6 μm, the silicon-carbon particles are the first silicon-carbon particles; when the particle size of the silicon-carbon particles is less than or equal to 5.5 μm, the silicon-carbon particles are the second silicon-carbon particles.

[0077] Testing elemental mass fraction: Using the X-ray energy spectrometer (EDS) equipped with SEM, observe under a magnification of 1000 times, identify the first silicon-carbon particles and the second silicon-carbon particles, then perform point scanning on the first silicon-carbon particles and the second silicon-carbon particles respectively, measure the mass fractions of silicon and carbon elements in the first silicon-carbon particles and the mass fractions of silicon, carbon, and oxygen elements in the second silicon-carbon particles, and finally calculate based on the sum of the masses of silicon and carbon elements in the first silicon-carbon particles, the mass fraction of silicon element in the first silicon-carbon particles is A1%, and based on the sum of the masses of silicon, carbon, and oxygen elements in the second silicon-carbon particles, the mass fraction of silicon element in the second silicon-carbon particles is A2% and the mass fraction of oxygen element is C%.

[0078] Testing average particle size: Using SEM, take pictures of the cross-sections of the negative electrode plates of 5 samples under a magnification of 1000 times, randomly select the first silicon-carbon particles and the second silicon-carbon particles, measure the particle sizes of a total of 100 first silicon-carbon particles and 100 second silicon-carbon particles, and calculate the arithmetic mean to obtain the average particle size of the first silicon-carbon particles and the average particle size of the second silicon-carbon particles respectively.

[0079] Testing the number of particles: Using SEM, take SEM photos of the cross-section of the negative electrode sheet under a magnification of 1000 times. Count the number of all the first silicon-carbon particles and the number of all the second silicon-carbon particles in the photos. Take 5 different cross-section samples of the negative electrode sheet, count the number of particles, and take the average value to obtain the number of the first silicon-carbon particles and the number of the second silicon-carbon particles. Calculate the sum of their numbers, the proportion P1% of the number of the first silicon-carbon particles, and the proportion P2% of the number of the second silicon-carbon particles.

[0080] Testing the average roundness: Using SEM, take photos of the cross-section of the negative electrode sheet under a magnification of 1000 times. Take photos of the cross-sections of 5 samples of the negative electrode sheet. Randomly select 20 particles of the first silicon-carbon particles and the second silicon-carbon particles respectively from the above 5 samples. Use the image tool in Image to select and mark the particles, and the radius r of the circumscribed circle of the particles and the actual area S of the particles can be obtained; the roundness of the particles = S / (πr 2 ), calculate the arithmetic mean of the test results of 20 particles, and obtain the average roundness M1 of the first silicon-carbon particles and the average roundness M2 of the second silicon-carbon particles respectively.

[0081] Porosity test of the negative electrode sheet:

[0082] Fix the negative electrode sheet on the sample stage with conductive carbon glue, and place the sample stage on the bracket. Place the bracket and the sample stage into the CP, evacuate to 10 -4 Pa, and then cut along the thickness direction of the electrode sheet with argon gas. Place the cross-section of the sample after cutting in the CP facing upwards on the SEM special sample stage, and take photos using SEM under the conditions of an acceleration voltage of 10 kV, an emission current of 10 mA, and a magnification of 1000 times. Use Image J software to perform binary processing on the image threshold (threshold), count the area of the pores and the area of the negative electrode sheet in the test area, obtain the proportion of the pore area, that is, the porosity. Perform the same test at any 20 positions in the negative electrode sheet, and take the average value to obtain the porosity of the negative electrode sheet.

[0083] Thickness test of the negative electrode material layer:

[0084] When the electrochemical device is discharged to 2.5 V, the thickness test of the negative electrode material layer includes the following steps: After discharging the lithium-ion batteries in the examples and comparative examples to 2.5 V at a discharge rate of 0.2 C, disassemble the lithium-ion batteries. Measure the thickness of the negative electrode sheet and the negative electrode current collector respectively with a micrometer. For the negative electrode sheet with double-sided coating, the thickness of the negative electrode material layer = (the thickness of the negative electrode sheet - the thickness of the negative electrode current collector) / 2. If it is a negative electrode sheet with single-sided coating, the thickness of the negative electrode material layer = the thickness of the negative electrode sheet - the thickness of the negative electrode current collector. The smaller the thickness of the above negative electrode material layer, the higher the energy density of the lithium-ion battery.

[0085] Energy density percentage test:

[0086] In an environment of 25 °C, charge and discharge the lithium-ion battery according to the following steps: perform constant-current charging at a charging current of 0.5C until the upper limit voltage of 4.53V, then perform constant-voltage charging until the current is 0.02C. After standing for 5 minutes, then perform constant-current discharge at a discharge current of 0.2C until the cut-off voltage of 2.5V to obtain the discharge capacity C of the lithium-ion battery x , and calculate the average discharge voltage U of the lithium-ion battery. Charge to 3.95V at 0.5C to obtain a 50% SOC (state of charge) state, and obtain the lithium-ion battery at 50% SOC. Measure the length, width, and thickness of each lithium-ion battery at 50% SOC, and calculate the volume V of the lithium-ion battery; calculate the volumetric energy density of the lithium-ion battery = C x ×U / V, and further calculate the energy density percentage (%) of each example or comparative example relative to Comparative Example 1. The larger the energy density percentage, the higher the energy density of the lithium-ion battery.

[0087] Lithium plating test:

[0088] At 25 °C, charge and discharge the lithium-ion battery with a first-step rate of 1C. The charging steps are: perform constant-current charging at a first-step rate of 1C until 4.53V, stand for 5 minutes, then perform constant-voltage charging until 0.02C, and then discharge at 0.2C to 2.5V. This is a charge-discharge cycle process. After charging and discharging in cycles 10 times according to the above process, disassemble the lithium-ion battery and observe the lithium plating state on the surface of the negative electrode. The non-lithium-plated area on the surface of the negative electrode is golden yellow, and the lithium-plated area is white or grayish white. If white or grayish white appears on the surface of the negative electrode, it is determined that lithium plating occurs; otherwise, it is determined that no lithium plating occurs. The maximum non-lithium-plating rate defined under the condition of no lithium plating is recorded as the maximum non-lithium-plating rate of the lithium-ion battery. If no lithium plating occurs on the surface of the negative electrode, the lithium-ion battery prepared by the same method will be charged and discharged in cycles with the first-step rate increased by 0.1C and the remaining charge-discharge parameters the same as the above charge-discharge steps. After 10 cycles of charging and discharging, disassemble the lithium-ion battery and observe the lithium plating state on the surface of the negative electrode. Repeat the above steps, with the first-step rate increased by 0.1C each time until the lithium plating on the surface of the negative electrode ends the test, and record the maximum non-lithium-plating rate of the lithium-ion battery. The larger the maximum non-lithium-plating rate, the better the fast-charging performance of the lithium-ion battery.

[0089] 30 °C cycle capacity retention test:

[0090] Place the lithium-ion battery in a constant-temperature test chamber at 30°C and let it stand for 30 minutes to reach a constant temperature. Charge it at a constant current of 0.5C until the upper limit voltage of 4.53V, then charge it at a constant voltage until the current reaches 0.02C, let it stand for 5 minutes, and discharge it at a constant current of 0.2C until the cut-off voltage of 2.5V. Record it as the initial discharge capacity C0. Repeat this step 200 cycles, record the discharge capacity C1 after 200 cycles, and calculate the 30°C cycle capacity retention rate of the lithium-ion battery. 30°C cycle capacity retention rate (%) = C1 / C0 × 100%.

[0091] Example 1-1

[0092] <Preparation of the first silicon-carbon particles>

[0093] Add the first carbon precursor (porous carbon, average diameter of 8.0 μm, average roundness of 0.90) to the fluidized bed, introduce the first gas, and perform the first chemical vapor deposition to obtain the first silicon-carbon particles. Among them, the first gas is a mixture of silane and argon, the volume fraction of silane in the first gas is 40%, the temperature of the first chemical vapor deposition is 500°C, and the time is 8h.

[0094] The first silicon-carbon particles include silicon and carbon elements. The mass fraction A1% of silicon element, the average particle size R1 are shown in Table 1, and the average roundness M1 is shown in Table 2.

[0095] <Preparation of the second silicon-carbon particles>

[0096] Add the second carbon precursor (porous carbon, average diameter of 3.0 μm, average roundness of 0.95) to the fluidized bed, introduce the second gas, perform the second chemical vapor deposition, take it out after cooling to room temperature, let it stand in the air for 12h, then continue to add it to the fluidized bed, and introduce acetylene gas to perform the third chemical vapor deposition to obtain the second silicon-carbon particles. Among them, the second gas is a mixture of silane and argon, the volume fraction of silane in the second gas is 30%, the temperature of the second chemical vapor deposition is 500°C, and the time is 6h, and the temperature of the third chemical vapor deposition is 500°C, and the time is 8h.

[0097] The second silicon-carbon particles include silicon, carbon and oxygen elements. The mass fraction A2% of silicon element, the mass fraction C% of oxygen element, the average particle size R2 are shown in Table 1, and the average roundness M2 is shown in Table 2.

[0098] <Preparation of the negative electrode sheet>

[0099] Graphite, first silicon-carbon particles, second silicon-carbon particles, binder lithium polyacrylate (PAA-Li), and conductive agent single-walled carbon nanotubes were mixed in a mass ratio of 88.4:1.6:8.4:1.2:0.4. Deionized water was added and mixed evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 30 wt%. The negative electrode slurry was evenly coated on one side surface of a negative electrode current collector copper foil with a thickness of 12 μm and dried at 120 °C to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. The above steps were repeated on the other side surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode material layer, which was then cold-pressed and slit to obtain a negative electrode sheet with a specification of 78 mm × 875 mm. Among them, the thickness of the single-sided negative electrode material layer after cold pressing was 48 μm, and the coating weight of the negative electrode material layer was 6 mg / cm 2 .

[0100] <Preparation of the positive electrode sheet>

[0101] The positive electrode active material lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5. The conductive carbon black was acetylene black, and then N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt% and stirred evenly. The slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm and dried at 90 °C. After the above steps were completed, the single-sided coating of the positive electrode sheet was completed. Then, the above steps were repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. After coating, the positive electrode sheet was cut into a specification of 74 mm × 867 mm and the tab was welded for later use. Among them, the thickness of the single-sided positive electrode material layer was 42 μm, and the coating weight of the positive electrode material layer was 17 mg / cm 2 .

[0102] <Preparation of the electrolyte>

[0103] In a dry argon atmosphere glove box, ethylene carbonate, dimethyl carbonate, and ethyl acetate were mixed in a mass ratio of 3:3:4 to obtain a base solvent, and then lithium hexafluorophosphate and fluoroethylene carbonate (FEC) were added and mixed evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass ratio of lithium hexafluorophosphate was 12.5%, the mass ratio of FEC was 6%, and the balance was the base solvent.

[0104] <Preparation of the separator>

[0105] A polyethylene (PE) film with a thickness of 15 μm was used.

[0106] <Preparation of the lithium-ion battery>

[0107] After connecting the prepared positive electrode sheet and negative electrode sheet to the electrode tabs respectively, stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed in the middle of the positive and negative electrodes to play an insulating role, and then wind them to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film, inject electrolyte after drying, and obtain a lithium-ion battery through processes of vacuum packaging, standing, forming (forming pressure is 1.0 Mpa), degassing, and trimming.

[0108] Examples 1-2 to Examples 1-9

[0109] Except for adjusting the average particle size of the first carbon precursor or the average particle size of the second carbon precursor so that R1 and R2 are as shown in Table 1, the rest is the same as Example 1-1. When R1 and / or R2 change, the sum of the numbers of the first silicon-carbon particles and the second silicon-carbon particles and their respective particle numbers change accordingly, while the mass percentages P1% and P2% of their respective numbers remain unchanged, and the mass percentage of silicon element in the negative electrode material layer remains unchanged.

[0110] Examples 1-10 to Examples 1-13

[0111] Except for adjusting the particle number percentage P1% of the first silicon-carbon particles and the particle number percentage P2% of the second silicon-carbon particles according to Table 1 as shown in Table 1, the rest is the same as Example 1-1. When P1% and / or P2% change, the sum of the numbers of the first silicon-carbon particles and the second silicon-carbon particles changes accordingly, while the mass percentage of silicon element in the negative electrode material layer remains unchanged.

[0112] Examples 1-14 to Examples 1-15

[0113] Except for adjusting the forming pressure to make the porosity of the negative electrode sheet as shown in Table 1, the rest is the same as Example 1-1.

[0114] Examples 1-16 to Examples 1-19

[0115] Except for adjusting the porosity of the negative electrode sheet to make the thickness of the negative electrode material layer after discharging as shown in Table 1, the rest is the same as Example 1-1.

[0116] Examples 1-20 to Examples 1-21

[0117] Except for adjusting the coating weight of the negative electrode sheet according to Table 1, the thickness of the negative electrode material layer changes accordingly, and the rest is the same as Example 1-1.

[0118] Examples 2-1 to Examples 2-2

[0119] Except for adjusting the time of the first vapor deposition so that the mass percentage A1% of silicon element in the first silicon-carbon particles is as shown in Table 2, the rest is the same as in Example 1-1. When A1% changes, the mass percentage of carbon element changes accordingly, and the sum of the two is 100%. P1%, P2%, and the sum of the numbers of the first silicon-carbon particles and the second silicon-carbon particles remain unchanged. At the same time, the mass percentages of the binder and the conductive agent remain unchanged, and the mass ratios of graphite to the first silicon-carbon particles and the second silicon-carbon particles change accordingly so that the mass percentage of silicon element in the negative electrode material layer remains unchanged.

[0120] Examples 2-3 to 2-4

[0121] Except for adjusting the time of the second vapor deposition and the time of standing in air so that the mass percentage A2% of silicon element and the mass percentage C% of oxygen element in the second silicon-carbon particles are as shown in Table 2, the rest is the same as in Example 1-1. When A2% and C% change, the mass percentage of carbon element changes accordingly, and the sum of the three is 100%. P1%, P2%, and the sum of the numbers of the first silicon-carbon particles and the second silicon-carbon particles remain unchanged. At the same time, the mass percentages of the binder and the conductive agent remain unchanged, and the mass ratios of graphite to the first silicon-carbon particles and the second silicon-carbon particles change accordingly so that the mass percentage of silicon element in the negative electrode material layer remains unchanged.

[0122] Examples 2-5 to 2-11

[0123] Except for regulating the average roundness of the first carbon precursor and / or the average roundness of the second carbon precursor so that M1 and M2 are as shown in Table 2, the rest is the same as in Example 1-1.

[0124] Example 3-1

[0125] Except for preparing the electrolyte according to the following steps for preparing the electrolyte, the rest is the same as in Example 1-1.

[0126] <Preparation of Electrolyte>

[0127] In an argon atmosphere glove box, ethylene carbonate, dimethyl carbonate, and ethyl acetate are mixed in a mass ratio of 3:3:4 to obtain a base solvent, and then lithium hexafluorophosphate, FEC, and the first component lithium difluorophosphate are added and mixed evenly to obtain the electrolyte. Among them, based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 12.5%, the mass percentage of FEC is 6%, the mass percentage of the first component lithium difluorophosphate is 0.02%, and the balance is the base solvent.

[0128] Examples 3-2 to 3-15

[0129] Except that the relevant parameters are adjusted according to Table 3, the mass ratio of the base solvent changes accordingly, and the mass ratios of the lithium salt and FEC remain unchanged, the rest is the same as in Example 3-1.

[0130] Comparative Example 1

[0131] Except that in the <preparation of the negative electrode sheet>, no first silicon carbide particles are added according to Table 1, and the particle number ratio of the second silicon carbide particles changes accordingly, the rest is the same as in Example 1-1. Among them, when the particle number ratio of the second silicon carbide particles changes, based on the mass of the negative electrode material layer, the mass ratio of silicon element remains unchanged, and the mass ratios of graphite, binder and conductive agent remain unchanged.

[0132] Comparative Example 2

[0133] Except that in the <preparation of the negative electrode sheet>, no second silicon carbide particles are added according to Table 1, and the particle number ratio of the first silicon carbide particles changes accordingly, the rest is the same as in Example 1-1. Among them, when the particle number ratio of the first silicon carbide particles changes, based on the mass of the negative electrode material layer, the mass ratio of silicon element remains unchanged, and the mass ratios of graphite, binder and conductive agent remain unchanged.

[0134] Comparative Examples 3 to 6

[0135] Except that the average particle size of the first carbon precursor or the average particle size of the second carbon precursor is adjusted so that R1 and R2 are as shown in Table 1, the rest is the same as in Example 1-1. When R1 and / or R2 change, the sum of the numbers of the first silicon carbide particles and the second silicon carbide particles and their respective particle numbers change accordingly, and their respective number ratios P1% and P2% remain unchanged, and the mass ratio of silicon element in the negative electrode material layer remains unchanged.

[0136] Comparative Examples 7 to 8

[0137] Except that the particle number ratio P1% of the first silicon carbide particles and the particle number ratio P2% of the second silicon carbide particles are adjusted as shown in Table 1, the rest is the same as in Example 1-1. When P1% and / or P2% change, the sum of the numbers of the first silicon carbide particles and the second silicon carbide particles changes accordingly, and the mass ratio of silicon element in the negative electrode material layer remains unchanged.

[0138] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0139] Table 1

[0140]

[0141]

[0142] Note: " / " in Table 1 indicates the non - existence of corresponding parameters or substances.

[0143] Referring to Table 1, it can be seen from Examples 1 - 1 to 1 - 21 and Comparative Examples 1 to 8 that the negative electrode active material includes the first silicon - carbon particles and the second silicon - carbon particles, and by controlling the average particle sizes R1, R2 and their quantity percentages P1%, P2% within the scope of this application, the thickness of the negative electrode material layer can be made thinner, and the lithium - ion battery has a higher energy density percentage, maximum non - lithium - precipitation rate and cycle capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycle performance. In Comparative Example 1, the negative electrode active material does not include the first silicon - carbon particles. In Comparative Example 2, the negative electrode active material does not include the second silicon - carbon particles. In Comparative Examples 3 to 8, at least one of R1, R2, P1%, P2% is not within the scope of this application, and the energy density percentage, maximum non - lithium - precipitation rate and cycle capacity retention rate of the lithium - ion battery are lower, indicating that the lithium - ion battery of this application has a low energy density and poor fast - charging performance and cycle performance.

[0144] The average particle size R1 of the first carbon precursor usually affects the energy density, fast - charging performance and cycle performance of the lithium - ion battery. It can be seen from Examples 1 - 1 to 1 - 4 and Comparative Examples 3 and 4 that by controlling the value of R1 within the scope of this application, the thickness of the negative electrode material layer can be made thinner, and the lithium - ion battery has a higher energy density percentage, maximum non - lithium - precipitation rate and cycle capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycle performance.

[0145] The average particle size R2 of the second carbon precursor usually affects the energy density, fast - charging performance and cycle performance of the lithium - ion battery. It can be seen from Example 1 - 1, Examples 1 - 5 to 1 - 9 and Comparative Examples 5 and 6 that by controlling the value of R2 within the scope of this application, the thickness of the negative electrode material layer can be made thinner, and the lithium - ion battery has a higher energy density percentage, maximum non - lithium - precipitation rate and cycle capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycle performance.

[0146] The value of R1 / R2 usually affects the energy density, fast - charging performance and cycle performance of the lithium - ion battery. It can be seen from Examples 1 - 1 to 1 - 9 that by controlling the value of R1 / R2 within the scope of this application, the thickness of the negative electrode material layer can be made thinner, and the lithium - ion battery has a higher energy density percentage, maximum non - lithium - precipitation rate and cycle capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycle performance.

[0147] The proportion P1% of the number of the first silicon-carbon particles and the proportion P2% of the number of the second silicon-carbon particles generally affect the energy density, fast charging performance and cycling performance of the lithium-ion battery. It can be seen from Example 1-1, Example 1-10 to Example 1-13, Comparative Example 7 and Comparative Example 8 that by adjusting the values of P1% and P2% within the scope of the present application, the thickness of the negative electrode material layer can be made thinner, and the lithium-ion battery has a higher energy density percentage, maximum non-lithium precipitation rate and cycling capacity retention rate, indicating that the lithium-ion battery of the present application has a high energy density while having good fast charging performance and cycling performance.

[0148] The value of X generally affects the energy density, fast charging performance and cycling performance of the lithium-ion battery. It can be seen from Example 1-1, Example 1-10 to Example 1-13 that by adjusting the value of X within the scope of the present application, the thickness of the negative electrode material layer can be made thinner, and the lithium-ion battery has a higher energy density percentage, maximum non-lithium precipitation rate and cycling capacity retention rate, indicating that the lithium-ion battery of the present application has a high energy density while having good fast charging performance and cycling performance.

[0149] The porosity of the negative electrode material layer generally affects the energy density, fast charging performance and cycling performance of the lithium-ion battery. It can be seen from Example 1-1 to Example 1-15 that by adjusting the porosity of the negative electrode material layer within the scope of the present application, the lithium-ion battery can have a higher energy density percentage, maximum non-lithium precipitation rate and cycling capacity retention rate, indicating that the lithium-ion battery of the present application has a high energy density while having good fast charging performance and cycling performance.

[0150] The coating weight of the negative electrode material layer and the thickness of the negative electrode material layer generally affect the energy density, fast charging performance and cycling performance of the lithium-ion battery. It can be seen from Example 1-1, Example 1-16 to Example 1-21 that by adjusting the coating weight and thickness of the negative electrode material layer within the scope of the present application, the lithium-ion battery can have a higher energy density percentage, maximum non-lithium precipitation rate and cycling capacity retention rate, indicating that the lithium-ion battery of the present application has a high energy density while having good fast charging performance and cycling performance.

[0151] Table 2

[0152]

[0153] The mass percentage A1% of silicon element in the first silicon-carbon particles usually affects the energy density, fast charging performance, and cycling performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-1 to 2-2 that by adjusting the value of A1 within the scope of this application, the lithium-ion battery can have a high energy density percentage, the maximum non-lithium precipitation rate, and the cycling capacity retention rate, indicating that the lithium-ion battery of this application has a high energy density while having good fast charging performance and cycling performance.

[0154] The mass percentage A2% of silicon element and the mass percentage C% of oxygen element in the second silicon-carbon particles usually affect the energy density, fast charging performance, and cycling performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-3 to 2-4 that by adjusting the values of A2 and C within the scope of this application, the lithium-ion battery can have a high energy density percentage, the maximum non-lithium precipitation rate, and the cycling capacity retention rate, indicating that the lithium-ion battery of this application has a high energy density while having good fast charging performance and cycling performance.

[0155] The average roundness M1 of the first silicon-carbon particles usually affects the energy density, fast charging performance, and cycling performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-5 to 2-7 that by adjusting the value of M1 within the scope of this application, the lithium-ion battery can have a high energy density percentage, the maximum non-lithium precipitation rate, and the cycling capacity retention rate, indicating that the lithium-ion battery of this application has a high energy density while having good fast charging performance and cycling performance.

[0156] The average roundness M2 of the second silicon-carbon particles usually affects the energy density, fast charging performance, and cycling performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-8 to 2-9 that by adjusting the value of M2 within the scope of this application, the lithium-ion battery can have a high energy density percentage, the maximum non-lithium precipitation rate, and the cycling capacity retention rate, indicating that the lithium-ion battery of this application has a high energy density while having good fast charging performance and cycling performance.

[0157] The value of M1 / M2 usually affects the energy density, fast charging performance, and cycling performance of lithium-ion batteries. It can be seen from Examples 1-1, 2-5 to 2-11 that by adjusting the value of M1 / M2 within the scope of this application, the lithium-ion battery can have a high energy density percentage, the maximum non-lithium precipitation rate, and the cycling capacity retention rate, indicating that the lithium-ion battery of this application has a high energy density while having good fast charging performance and cycling performance.

[0158] Table 3

[0159]

[0160] Note: In Table 3, " / " indicates the non - existence of corresponding parameters or substances.

[0161] The type and mass percentage of the first component in the electrolyte usually affect the energy density, fast - charging performance, and cycling performance of lithium - ion batteries. It can be seen from Examples 1 - 1, 3 - 1 to 3 - 15 that when the electrolyte includes the first component within the scope of this application and its mass percentage is regulated within the scope of this application, the lithium - ion battery can have a high energy - density percentage, the maximum non - lithium - precipitation rate, and the cycling capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycling performance.

[0162] The values of D2×R2 and D2 / X usually affect the energy density, fast - charging performance, and cycling performance of lithium - ion batteries. It can be seen from Examples 3 - 5 to 3 - 9 that regulating the values of D2×R2 and D2 / X within the scope of this application can make the lithium - ion battery have a high energy - density percentage, the maximum non - lithium - precipitation rate, and the cycling capacity retention rate, indicating that the lithium - ion battery of this application has a high energy density while having good fast - charging performance and cycling performance.

[0163] It should be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non - exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0164] Each embodiment in this specification is described in a related manner. For the same or similar parts between each embodiment, reference can be made to each other, and the key point of each embodiment is to illustrate the differences from other embodiments.

[0165] The above - mentioned are only the preferred embodiments of this application, and are not intended to limit this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. An electrochemical device, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material; the negative electrode active material contains first silicon-carbon particles and second silicon-carbon particles. The particle size of the first silicon-carbon particle is R a , R a ≥6 μm, and the particle size of the second silicon-carbon particle is R b , R b ≤5.5 μm; The average particle size of the first silicon-carbon particles is R1 μm, 6.6 ≤ R1 ≤ 11.2, and the average particle size of the second silicon-carbon particles is R2 μm, 1.1 ≤ R2 ≤ 4.

2. Based on the sum of the numbers of the first silicon-carbon particles and the second silicon-carbon particles, the proportion of the number of the first silicon-carbon particles is P1%, 10 ≤ P1 ≤ 18; the proportion of the number of the second silicon-carbon particles is P2%, 82 ≤ P2 ≤ 90.

2. The electrochemical device according to claim 1, wherein 2 ≤ R1 / R2 ≤ 7.

3. The electrochemical device according to claim 1, wherein, X = P1 / P2, 0.12 ≤ X ≤ 0.

2.

4. The electrochemical device according to claim 1, wherein, Based on the sum of the masses of silicon element and carbon element in the first silicon-carbon particles, the mass proportion of silicon element in the first silicon-carbon particles is A1%, 37.3 ≤ A1 ≤ 44.

7.

5. The electrochemical device according to claim 1, wherein, Based on the sum of the masses of silicon element, carbon element and oxygen element in the second silicon-carbon particles, the mass proportion of silicon element in the second silicon-carbon particles is A2%, 8.7 ≤ A2 ≤ 24.

7. Based on the sum of the masses of silicon element, carbon element and oxygen element in the second silicon-carbon particles, the mass proportion of oxygen element in the second silicon-carbon particles is C%, 1.1 ≤ C ≤ 2.

1.

6. The electrochemical device according to claim 1, wherein, The average roundness of the first silicon-carbon particles is M1, 0.83 ≤ M1 ≤ 0.

98. The average roundness of the second silicon-carbon particles is M2, 0.91 ≤ M2 ≤ 0.

99.

7. The electrochemical device according to claim 6, wherein, 0.86 ≤ M1 / M2 ≤ 0.

95.

8. The electrochemical device according to claim 1, wherein The porosity of the negative electrode sheet is 20.2% to 39.1%.

9. The electrochemical device according to claim 1, wherein, When the electrochemical device is discharged to 2.5 V, the thickness of the negative electrode material layer is H μm, 32.1 ≤ H ≤ 100.2, preferably, 40.8 ≤ H ≤ 62.

1.

10. The electrochemical device according to claim 1, wherein, The coating weight of the negative electrode sheet is W mg / cm 2 , 2.27 ≤ W ≤ 8.

21.

11. The electrochemical device according to claim 1, wherein, The electrolyte contains a first component, and the first component includes at least one of lithium difluorophosphate, lithium nitrate or dimethyl sulfoxide.

12. The electrochemical device according to claim 11, wherein, The electrolyte satisfies at least one of the following conditions: i) Based on the mass of the electrolyte, the mass proportion of lithium difluorophosphate is D1%, 0.02 ≤ D1 ≤ 2.

11. ii) Based on the mass of the electrolyte, the mass proportion of lithium nitrate is D2%, 0.005 ≤ D2 ≤ 1.

62. iii) Based on the mass of the electrolyte, the mass proportion of dimethyl sulfoxide is D3%, 0.02 ≤ D3 ≤ 1.

83.

13. The electrochemical device according to claim 1, wherein, The electrolyte includes lithium nitrate. Based on the mass of the electrolyte, the mass proportion of lithium nitrate is D2%, 0.005 ≤ D2 ≤ 1.62, and D2 and R2 satisfy: 0.015 ≤ D2 × R2 ≤ 4.

9.

14. The electrochemical device according to claim 13, wherein, X = P1 / P2, and D2 and X satisfy: 0.31 ≤ D2 / X ≤ 10.

1.

15. An electronic device, which includes the electrochemical device according to any one of claims 1 to 14.

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