Electrochemical device and electronic device

Abstract

The present application provides an electrochemical device and an electronic device. The electrochemical device includes a negative electrode plate, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a silicon-carbon composite material, the silicon-carbon composite material includes a porous carbon skeleton and a silicon material, the silicon-carbon composite material has a Dv50 of aμm, satisfying 3≤a≤15, the negative electrode material layer has a porosity of b%, and the electrochemical device satisfies 0.15≤a / b≤1. The electrochemical device provided by the present application has good cycling performance, expansion performance, and rate performance.

Description

Technical Field

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

[0002] Lithium-ion batteries offer advantages such as high energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, and excellent safety. They are widely used in various fields, including portable energy storage, electronic devices, and electric vehicles. The rapid development of lithium-ion batteries has also placed higher demands on their comprehensive performance, such as achieving both high energy density and good cycle performance.

[0003] Silicon materials have a high gram capacity (up to 4200 mAh / g), and their use as negative electrode active materials in lithium-ion batteries can significantly increase the energy density of lithium-ion batteries. However, during the lithium-ion intercalation and deintercalation process, silicon materials undergo significant volume expansion, specifically increasing to 300% to 400% of their original volume. This can easily lead to cracking or pulverization of the silicon material, which in turn causes pulverization of the negative electrode material layer in the negative electrode sheet, affecting the formation of the solid electrolyte interface (SEI) film, and reducing the cycling performance of the lithium-ion battery. Summary of the Invention

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device to improve the cycle performance of the electrochemical device.

[0005] In a first aspect, the present application provides an electrochemical device comprising a negative electrode plate, the negative electrode plate comprising a negative electrode material layer, the negative electrode material layer comprising a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carbon skeleton and a silicon material, the average particle size of the silicon-carbon composite material being aμm, satisfying 3≤a≤15, the porosity of the negative electrode material layer being b%, and the electrochemical device satisfying 0.15≤a / b≤1. The porous carbon skeleton has a porous structure, which can provide expansion space for the silicon material in the silicon-carbon composite material to buffer the expansion stress generated during the expansion process. At the same time, by regulating the average particle size of the silicon-carbon composite material and the ratio of the average particle size of the silicon-carbon composite material to the porosity of the negative electrode material layer within the above-mentioned range, not only can sufficient space be provided for the volume expansion of the silicon material in the silicon-carbon composite material, but also good electrical contact can be achieved between the particles of the silicon-carbon composite material, thereby improving the cycling performance and expansion performance of the electrochemical device and providing the electrochemical device with good rate performance.

[0006] In some embodiments of the present application, the porosity b% of the negative electrode material layer satisfies 15≤b≤35. By regulating the porosity of the negative electrode material layer within the above range, it is beneficial to improve the cycle performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have good rate performance.

[0007] In some embodiments of the present application, the compaction density of the negative electrode material layer is 1.2 g / cm 3 to 1.8g / cm 3 By regulating the compaction density of the negative electrode material layer within the above range, it is beneficial to improve the cycle performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have good rate performance.

[0008] In some embodiments of the present application, based on the mass of the silicon-carbon composite material, the mass percentage of carbon in the silicon-carbon composite material is d%, satisfying 15≤d≤75, the mass percentage of silicon in the silicon-carbon composite material is e%, satisfying 15≤e≤75, and the mass percentage of oxygen in the silicon-carbon composite material is 0.3% to 10%. By regulating the mass percentages of carbon, silicon, and oxygen in the silicon-carbon composite material within the above range, it is beneficial to improve the cycling performance and expansion performance of the electrochemical device, and enable the electrochemical device to have good rate performance, higher specific capacity, first-cycle reversible capacity, and first-cycle coulombic efficiency.

[0009] In some embodiments of the present application, the porous carbon framework has a pore volume of 0.5 ml / g to 2.0 ml / g, and the pore volume percentage of micropores and mesopores based on the pore volume of the porous carbon framework is 70% to 90%. The porous carbon framework has a large number of micropores and mesopores, and the silicon material in the silicon-carbon composite material is distributed within the micropores and mesopores. This provides expansion space for the silicon material in the silicon-carbon composite material, can buffer the expansion stress generated during the expansion process, and thus improve the cycling performance and expansion performance of the electrochemical device.

[0010] In some embodiments of the present application, the electrochemical device includes an electrolyte, wherein the electrolyte includes ethylene carbonate, and the mass percentage of the ethylene carbonate based on the total mass of the electrolyte is f%, satisfying 5≤f≤30. By regulating the mass percentage of the ethylene carbonate within the above range, the cycling performance and rate performance of the electrochemical device are improved.

[0011] In some embodiments of the present application, the electrochemical device satisfies 0.2≤a / f≤2. By regulating the value of a / f within the above range, a synergistic effect is formed between the silicon-carbon composite material and the ethylene carbonate in the electrolyte, thereby improving the cycling performance, expansion performance, and rate performance of the electrochemical device.

[0012] In some embodiments of the present application, the electrolyte includes propylene carbonate, and the mass percentage of the propylene carbonate is g%, based on the total mass of the electrolyte, and satisfies 5≤g≤40. By regulating the mass percentage of propylene carbonate within the above range, the cycling performance and rate performance of the electrochemical device are improved.

[0013] In some embodiments of the present application, the preparation method of the silicon-carbon composite material includes the following steps: (1) placing a porous carbon skeleton in a silane atmosphere for a first deposition reaction, wherein the pore volume of the porous carbon skeleton is 0.5 ml / g to 2.0 ml / g, and based on the pore volume of the porous carbon skeleton, the pore volume percentage of micropores and mesopores is 70% to 90%; the volume percentage of silane in the silane atmosphere is 1% to 30%, the temperature of the first deposition reaction is 400°C to 600°C, and the time is 1h to 12h; (2) then performing a second deposition reaction in an oxygen atmosphere to obtain a silicon-carbon composite material, wherein the volume percentage of oxygen in the oxygen atmosphere is 1% to 30%, the temperature of the second deposition reaction is 400°C to 800°C, and the time is 1h to 12h. The silicon-carbon composite material prepared by the preparation method provided in the present application has silicon material embedded in the micropores and mesopores of the porous carbon skeleton, which not only can give play to the advantage of the high specific capacity of the silicon material to improve the specific capacity of the electrochemical device, but also the porous carbon skeleton provides sufficient space for the volume expansion of the silicon material to alleviate the expansion stress generated by the volume expansion, which is beneficial to improving the cycle performance and expansion performance of the electrochemical device.

[0014] The second aspect of the present application provides an electronic device comprising the electrochemical device of any of the aforementioned embodiments. The electrochemical device provided by the present application has good cycle performance, expansion performance, and rate performance, thereby having a long service life.

[0015] The present application provides an electrochemical device and an electronic device. The electrochemical device includes a negative electrode plate, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a silicon-carbon composite material, the silicon-carbon composite material includes a porous carbon skeleton and a silicon material, the average particle size of the silicon-carbon composite material is a μm, satisfying 3≤a≤15, the porosity of the negative electrode material layer is b%, and the electrochemical device satisfies 0.15≤a / b≤1. The porous carbon skeleton has a porous structure, which can provide expansion space for the silicon material in the silicon-carbon composite material to buffer the expansion stress generated during the expansion process. At the same time, by regulating the average particle size of the silicon-carbon composite material and the ratio of the average particle size of the silicon-carbon composite material to the porosity of the negative electrode material layer within the above range, not only can sufficient space be provided for the volume expansion of the silicon material in the silicon-carbon composite material, but also good electrical contact is achieved between the particles of the silicon-carbon composite material, thereby improving the cycling performance and expansion performance of the electrochemical device and providing the electrochemical device with good rate performance.

[0016] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any embodiment of the present application. DETAILED DESCRIPTION

[0017] The following will be combined with the examples in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0018] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of electrochemical devices to explain the present application, but the electrochemical devices of the present application are not limited to lithium-ion batteries.

[0019] A first aspect of the present application provides an electrochemical device comprising a negative electrode plate, the negative electrode plate comprising a negative electrode material layer, the negative electrode material layer comprising a silicon-carbon composite material, the silicon-carbon composite material comprising a porous carbon skeleton and a silicon material, the average particle size of the silicon-carbon composite material being a μm, satisfying 3≤a≤15, preferably 6≤a≤12, the porosity of the negative electrode material layer being b%, and the electrochemical device satisfying 0.15≤a / b≤1, preferably 0.3≤a / b≤1. For example, the average particle size of the silicon-carbon composite material can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any range therebetween, and the value of a / b can be 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any range therebetween.

[0020] The inventors of this application have found that when the average particle size of the silicon-carbon composite material is too small (for example, less than 3 μm), the specific surface area of ​​the silicon-carbon composite material increases, and it is easy to have side reactions with the electrolyte, thereby affecting the cycle performance of the electrochemical device. When the average particle size of the silicon-carbon composite material is too large (for example, greater than 15 μm), it is difficult to provide sufficient space for the volume expansion of the silicon material in the silicon-carbon composite material, and it is impossible to effectively buffer the expansion stress generated during the expansion process, thereby affecting the cycle performance and rate performance of the electrochemical device. When the value of a / b is too small (for example, less than 0.15) or too large (for example, greater than 1), it is not conducive to improving the cycle performance, expansion performance and rate performance of the electrochemical device. The porous carbon skeleton has a porous structure, which can provide expansion space for the silicon material in the silicon-carbon composite material to buffer the expansion stress generated during the expansion process. At the same time, by regulating the average particle size and a / b value of the silicon-carbon composite material within the above range, it not only provides sufficient space for the volume expansion of the silicon material in the silicon-carbon composite material, fully utilizing the high gram capacity advantage of the silicon material in the silicon-carbon composite material, but also enables the particles of the silicon-carbon composite material to have good electrical contact with each other, thereby improving the cycle performance and expansion performance (such as volume expansion rate) of the electrochemical device, and enabling the electrochemical device to have good rate performance.

[0021] In some embodiments of the present application, the porosity of the negative electrode material layer is b%, satisfying 15≤b≤35, preferably 18≤b≤30. For example, the porosity of the negative electrode material layer can be 15%, 20%, 25%, 30%, 35% or any range therebetween. When the porosity of the negative electrode material layer is too small (for example, less than 15%), it cannot provide sufficient space for the volume expansion of the silicon material in the silicon-carbon composite material, which will affect the cycle performance and expansion performance of the electrochemical device. When the porosity of the negative electrode material layer is too large (for example, greater than 35%), the electrical contact between the particles of the silicon-carbon composite material is reduced, which will affect the rate performance of the electrochemical device. By regulating the porosity of the negative electrode material layer within the above range, not only can sufficient space be provided for the volume expansion of the silicon material in the silicon-carbon composite material, but also good electrical contact can be provided between the particles of the silicon-carbon composite material, thereby improving the cycle performance and expansion performance of the electrochemical device, and enabling the electrochemical device to have good rate performance. The porosity of the negative electrode material layer refers to the percentage of the volume of the pores in the negative electrode material layer to the volume of the negative electrode material layer.

[0022] In some embodiments of the present application, the compaction density of the negative electrode material layer is 1.2 g / cm 3 to 1.8g / cm 3 , preferably 1.4 g / cm 3 to 1.8g / cm 3 For example, the compaction density of the negative electrode material layer can be 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 Or any range therebetween. When the compaction density of the negative electrode material layer is too small (e.g. less than 1.2 g / cm 3 ), the porosity of the negative electrode material layer increases, and the electrical contact between the particles of the silicon-carbon composite material decreases, which will affect the rate performance of the electrochemical device. When the compaction density of the negative electrode material layer is too large (for example, greater than 1.8 g / cm 3 ), the porosity of the negative electrode material layer decreases, which in turn prevents the silicon material from expanding and releasing the expansion stress generated during expansion, affecting the cycling and expansion performance of the electrochemical device. By regulating the compaction density of the negative electrode material layer within the above range, the cycling and expansion performance of the electrochemical device can be improved, as well as providing good rate performance.

[0023] In some embodiments of the present application, based on the mass of the silicon-carbon composite material, the mass percentage of carbon in the silicon-carbon composite material is d%, satisfying 15≤d≤75, preferably 40≤d≤75, the mass percentage of silicon in the silicon-carbon composite material is e%, satisfying 15≤e≤75, preferably 40≤e≤75, and the mass percentage of oxygen in the silicon-carbon composite material is 0.3% to 10%, preferably 1% to 6%. For example, the mass percentage of carbon in the silicon-carbon composite material can be 15%, 20%, 30%, 40%, 50%, 60%, 70%, 75% or any range therebetween, the mass percentage of silicon in the silicon-carbon composite material can be 15%, 20%, 30%, 40%, 50%, 60%, 70%, 75% or any range therebetween, and the mass percentage of oxygen in the silicon-carbon composite material can be 0.3%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween. It is understandable that a small amount (mass percentage content less than 0.1%) of impurities may be present in the silicon-carbon composite material. For the convenience of discussion, the present application ignores the impurities, that is, the sum of the mass percentage content of silicon, carbon and oxygen in the silicon-carbon composite material is 100%.

[0024] The inventors of the present application have discovered that when the mass percentage of carbon in the silicon-carbon composite material is too low (for example, less than 15%), it cannot provide sufficient expansion space for the silicon material in the silicon-carbon composite material, thereby affecting the cycle performance and expansion performance of the electrochemical device. When the mass percentage of carbon in the silicon-carbon composite material is too high (for example, greater than 75%), the mass percentage of silicon is low at this time, and the high gram capacity advantage of the silicon material in the silicon-carbon composite material cannot be effectively exerted, which will affect the specific capacity of the battery. By regulating the mass percentage of carbon in the silicon-carbon composite material within the above range, it is beneficial to improve the cycle performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have a higher specific capacity.

[0025] When the mass percentage of silicon in the silicon-carbon composite material is too low (for example, less than 15%), it will affect the first-cycle reversible capacity of the electrochemical device, and it will not be able to effectively exert the high gram capacity advantage of the silicon material in the silicon-carbon composite material, which will affect the specific capacity of the battery. When the mass percentage of silicon in the silicon-carbon composite material is too high (for example, higher than 75%), the mass percentage of carbon is low at this time, which cannot provide sufficient expansion space for the silicon material in the silicon-carbon composite material, thereby affecting the cycle performance and expansion performance of the electrochemical device; in addition, the high mass percentage of silicon is not conducive to the transmission of lithium ions and electrons, thereby affecting the rate performance of the electrochemical device. By regulating the mass percentage of silicon in the silicon-carbon composite material within the above range, it is beneficial to improve the cycle performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have good rate performance, higher first-cycle reversible capacity and specific capacity.

[0026] The oxygen in the silicon-carbon composite material will form an inert layer with lithium ions on the surface of the silicon-carbon composite material, which can improve the expansion performance of the silicon material in the silicon-carbon composite material, and thus improve the cycle performance and expansion performance of the electrochemical device. However, when the mass percentage of oxygen in the silicon-carbon composite material is too high (for example, higher than 10%), the inert layer formed will affect the transmission of lithium ions, and thus affect the rate performance and first-cycle coulomb efficiency of the electrochemical device. By regulating the mass percentage of oxygen in the silicon-carbon composite material within the above range, it is beneficial to improve the cycle performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have good rate performance and a higher first-cycle coulomb efficiency.

[0027] Overall, by regulating the mass percentage of carbon, silicon and oxygen in the silicon-carbon composite material within the above range, it is beneficial to improve the cycling performance and expansion performance of the electrochemical device, and enable the electrochemical device to have good rate performance, higher specific capacity, first-cycle reversible capacity and first-cycle coulombic efficiency.

[0028] In some embodiments of the present application, the silicon-carbon composite material satisfies 0.5≤d / e≤5, preferably 0.8≤d / e≤3. For example, the value of d / e can be 0.5, 1, 2, 3, 4, 5, or any range therebetween. By regulating the value of d / e within the above range, it is beneficial to improve the cycling performance and expansion performance of the electrochemical device, and to enable the electrochemical device to have good rate performance.

[0029] In some embodiments of the present application, the pore volume of the porous carbon skeleton is 0.5 ml / g to 2.0 ml / g, preferably 0.8 ml / g to 2.0 ml / g, and the pore volume percentage of micropores and mesopores based on the pore volume of the porous carbon skeleton is 70% to 90%, preferably 80% to 90%. For example, the pore volume of the porous carbon skeleton can be 0.5 ml / g, 0.6 ml / g, 0.7 ml / g, 0.8 ml / g, 0.9 ml / g, 1.0 ml / g, 1.1 ml / g, 1.2 ml / g, 1.3 ml / g, 1.5 ml / g, 1.8 ml / g, 2.0 ml / g or any range therebetween, and the pore volume percentage of micropores and mesopores is 70%, 75%, 80%, 85%, 90% or any range therebetween. The porous carbon framework has a large number of micropores and mesopores. The silicon material in the silicon-carbon composite is distributed within the micropores and mesopores, providing expansion space for the silicon material in the silicon-carbon composite. This can buffer the expansion stress generated during the expansion process, thereby improving the cycling performance and expansion performance of the electrochemical device. The pore volume percentage of micropores and mesopores refers to the percentage of the sum of the pore volumes of micropores and mesopores to the pore volume of the porous carbon framework. Micropores refer to pores with a pore diameter of less than 2nm, and mesopores refer to pores with a pore diameter between 2nm and 50nm.

[0030] In some embodiments of the present application, the electrochemical device includes an electrolyte, the electrolyte includes ethylene carbonate (EC), and the mass percentage of ethylene carbonate based on the total mass of the electrolyte is f%, satisfying 5≤f≤30, preferably 10≤f≤30. For example, the mass percentage of EC can be 5%, 10%, 15%, 20%, 25%, 30% or any range therebetween. Adding EC to the electrolyte is beneficial to improving the rate performance of the electrochemical device due to its high dielectric constant. At the same time, when EC penetrates into the surface of the silicon-carbon composite material, it is beneficial to form a stable SEI film on the surface of the negative electrode sheet, thereby improving the cycle performance of the electrochemical device. However, when the mass percentage of EC is too high (for example, higher than 30%), the viscosity of the electrolyte increases, which is not conducive to the transmission of lithium ions, the conductivity of the electrolyte decreases, and EC will be embedded in the silicon-carbon composite material together with the lithium ions, so that the reversible capacity is reduced, thereby affecting the rate performance, cycle performance and capacity of the electrochemical device. By regulating the mass percentage of EC within the above range, it is beneficial to improve the cycle performance and rate performance of the electrochemical device.

[0031] In some embodiments of the present application, the electrochemical device satisfies 0.2≤a / f≤2, preferably 0.2≤a / f≤1.5. For example, the value of a / f can be 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.5, 2 or any range therebetween. When the value of a / f is too small (for example, less than 0.2), that is, the average particle size of the silicon-carbon composite material is small or the mass percentage of EC is high, both will affect the rate performance of the electrochemical device. When the value of a / f is too large (for example, greater than 2), that is, the average particle size of the silicon-carbon composite material is large or the mass percentage of EC is low, the cycle performance, expansion performance and rate performance of the electrochemical device will be affected. By regulating the value of a / f within the above range, it is beneficial for the silicon-carbon composite material to form a synergistic effect with EC in the electrolyte to improve the cycle performance, expansion performance and rate performance of the electrochemical device.

[0032] In some embodiments of the present application, the electrolyte includes propylene carbonate (PC), and the mass percentage of propylene carbonate is g%, based on the total mass of the electrolyte, and satisfies 5≤g≤40, preferably 10≤g≤30. For example, the mass percentage of PC can be 5%, 10%, 20%, 30%, 40% or any range therebetween. Adding PC to the electrolyte is beneficial to improving the rate performance of the electrochemical device due to its high dielectric constant. At the same time, when PC penetrates into the surface of the silicon-carbon composite material, it is beneficial to form a stable SEI film on the surface of the negative electrode sheet, thereby improving the cycle performance of the electrochemical device. However, when the mass percentage of PC is too high (for example, higher than 40%), the viscosity of the electrolyte increases, which is not conducive to the transmission of lithium ions, the conductivity of the electrolyte decreases, and there is a risk of PC precipitation, thereby affecting the cycle performance, expansion performance and rate performance of the electrochemical device. By regulating the mass percentage of PC within the above range, it is beneficial to improve the cycle performance and rate performance of the electrochemical device.

[0033] In some embodiments of the present application, the preparation method of the silicon-carbon composite material includes the following steps: (1) placing a porous carbon skeleton in a silane atmosphere for a first deposition reaction, wherein the pore volume of the porous carbon skeleton is 0.5 ml / g to 2.0 ml / g, and based on the pore volume of the porous carbon skeleton, the pore volume percentage of micropores and mesopores is 70% to 90%; the volume percentage of silane in the silane atmosphere is 1% to 30%, the temperature of the first deposition reaction is 400°C to 600°C, and the time is 1h to 12h; (2) then performing a second deposition reaction in an oxygen atmosphere to obtain a silicon-carbon composite material, wherein the volume percentage of oxygen in the oxygen atmosphere is 1% to 30%, the temperature of the second deposition reaction is 400°C to 800°C, and the time is 1h to 12h. The silicon-carbon composite material prepared by the above preparation method has silicon embedded in the micropores and mesopores of the porous carbon framework. This not only leverages the high gram capacity of silicon to improve the specific capacity of the electrochemical device, but also provides sufficient space for the volume expansion of the silicon material to alleviate the expansion stress generated by volume expansion, which is beneficial for improving the cycling performance and expansion performance of the electrochemical device. The siloxane atmosphere and oxygen atmosphere also include an inert gas, which may include but is not limited to at least one of nitrogen, argon, or helium.

[0034] When preparing a silicon-carbon composite material, the average particle size of the silicon-carbon composite material can be adjusted by adjusting the average particle size of the porous carbon skeleton. Generally, increasing the average particle size of the porous carbon skeleton increases the average particle size of the silicon-carbon composite material; decreasing the average particle size of the porous carbon skeleton decreases the average particle size of the silicon-carbon composite material. This application does not particularly limit the average particle size of the porous carbon skeleton, as long as it meets the average particle size of the silicon-carbon composite material described above. For example, the average particle size of the porous carbon skeleton is 1 μm to 20 μm.

[0035] The temperature and duration of the first and second deposition reactions typically affect the performance of silicon-carbon composites. For example, increasing the temperature of the first deposition reaction can increase the degree of crystallization of the silicon material, which is beneficial for improving the first-cycle coulombic efficiency of the electrochemical device, but it can affect its expansion performance. Increasing the temperature of the second deposition reaction can increase the thickness of the passivation layer on the surface of the silicon material, thereby improving the processing stability of the silicon-carbon composite. Prolonging the time of the first deposition reaction can increase the silicon content of the silicon-carbon composite, which is beneficial for improving the specific capacity of the electrochemical device, but an excessively high silicon content can affect the expansion performance of the electrochemical device. Prolonging the time of the second deposition reaction can increase the thickness of the passivation layer on the surface of the silicon material and improve the processing stability of the silicon-carbon composite. Lowering the temperature of the first deposition reaction can reduce the degree of crystallization of the silicon material, affecting the first-cycle coulombic efficiency of the electrochemical device. Lowering the temperature of the second deposition reaction is not conducive to the formation of a stable passivation layer on the surface of the silicon material. Shortening the time of the first deposition reaction can correspondingly reduce the silicon content. An appropriate silicon content can improve the cycling performance and expansion performance of the electrochemical device. Shortening the time of the second deposition reaction can affect the thickness of the stable passivation layer formed on the surface of the silicon material. By regulating the temperature and time of the first deposition reaction and the second deposition reaction within the above ranges, the surface stability of the silicon-carbon composite material is improved, thereby improving the first-cycle coulombic efficiency, cycling performance, and expansion performance of the electrochemical device. For example, the porous carbon framework may include, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon, and the silicon material may include, but is not limited to, at least one of crystalline silicon or amorphous silicon.

[0036] In the present application, the negative electrode sheet also includes a negative electrode current collector. The present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or composite current collector, etc. The negative electrode material layer can be arranged on one surface or two surfaces along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved. In the present application, there is no special restriction on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness is 4μm to 12μm.

[0037] In the present application, the negative electrode material layer may include, in addition to the above-mentioned silicon-carbon composite material, other negative electrode active materials known in the art, for example, including but not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O12 or at least one of Li-Al alloys.

[0038] In the present application, the negative electrode material layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the negative electrode conductive agent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of a carbon-based material, a metal-based material or a conductive polymer. The above-mentioned carbon-based material is selected from at least one of natural graphite, artificial graphite, conductive carbon black, acetylene black, Ketjen black or carbon fiber. The above-mentioned metal-based material may include but is not limited to metal powder and / or metal fiber. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0039] In the present application, the negative electrode material layer may also include a negative electrode binder. The present application has no particular limitation on the negative electrode binder, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or at least one of nylon.

[0040] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. The conductive layer may include, but is not limited to, the aforementioned negative electrode conductive agent and the aforementioned negative electrode binder.

[0041] The electrolyte of the present application also includes a lithium salt and other non-aqueous solvents. The present application does not particularly limit the lithium salt, as long as it can achieve the purpose of the present application. For example, it may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. Preferably, the lithium salt includes LiPF6.

[0042] The application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the application can be achieved, for example, can include but not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. Above-mentioned carbonate compounds can include but not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. Above-mentioned linear carbonate compounds can include but not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC). Above-mentioned cyclic carbonate can include but not limited to at least one of butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 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 trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is 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, decanoic acid lactone, valerolactone, or caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent may include, but is 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 total mass of the electrolyte, the weight percentage of the other non-aqueous solvent is 17% to 83%, for example, 17%, 17.5%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 82.5%, 83%, or any range therebetween.

[0043] The electrochemical device of the present application may also include a positive electrode sheet. The present application has no special restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet generally includes a positive electrode collector and a positive electrode material layer. The positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode collector, or on two surfaces in the thickness direction of the positive electrode collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode collector or a partial area of ​​the positive electrode collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved. In the present application, there is no special restriction on the positive electrode collector, as long as the purpose of the present application can be achieved, for example, it can include but is not limited to aluminum foil, aluminum alloy foil or composite current collector, etc. In the present application, there is no special restriction on the thickness of the positive electrode collector, as long as the purpose of the present application can be achieved, for example, the thickness is 8μm to 12μm.

[0044] In the present application, the positive electrode material layer includes a positive electrode active material. The present application has no particular restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, it may include at least one of lithium or a composite oxide of a transition metal element. The present application has no particular restrictions on the above-mentioned transition metal elements, as long as the purpose of the present application can be achieved. For example, it may include at least one of nickel, manganese, cobalt or iron. Specifically, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0045] In the present application, the positive electrode material layer may also include a positive electrode conductive agent. The present application has no particular restrictions on the positive electrode conductive agent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, acetylene black, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. Preferably, the positive electrode conductive agent includes conductive carbon black and carbon nanotubes. 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 nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder 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 polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. In the present application, the positive electrode material layer may further include a positive electrode binder. The present application has no particular limitation on the positive electrode binder, as long as it can achieve the purpose of the present application. For example, it may include but is not limited to at least one of fluorine-containing resin, polypropylene resin, fiber-type binder, rubber-type binder or polyimide-type binder.

[0046] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a conductive layer commonly used in the art, for example, including but not limited to the above-mentioned positive electrode conductive agent and the above-mentioned positive electrode binder.

[0047] The electrochemical device of the present application may also include an isolating membrane. The present application has no particular restrictions on the isolating membrane, as long as the purpose of the present application can be achieved. The above-mentioned isolating membrane may include a substrate layer and a surface treatment layer. The present application has no particular restrictions on the substrate layer. For example, it may include but is not limited to polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin isolating membranes, polyester films (such as polyethylene terephthalate films), cellulose films, polyimide films, polyamide films, spandex, aramid films, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, rolled membranes or spun membranes. At least one of them is preferably polyethylene or polypropylene. They have a good effect on preventing short circuits and can improve the stability of the electrochemical device through the shutdown effect. The isolating membrane of the present application may have a porous structure. The size of the pore size is not particularly limited, as long as the purpose of the present application can be achieved. For example, the pore size can be 0.01 μm to 1 μm. In the present application, the thickness of the isolating membrane is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness can be 5 μm to 500 μm.

[0048] In the present application, a surface treatment layer is provided on at least one surface of the above-mentioned substrate layer. The present application has no particular restrictions on the surface treatment layer, and it can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer can include, but is not limited to, inorganic particles and an inorganic layer binder. The present application has no particular restrictions on the inorganic particles, for example, it can include but is not limited to at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the inorganic layer binder, for example, it can include but is not limited to at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The polymer layer contains a polymer. This application does not specifically limit the polymer. The material of the polymer may include but is not limited to at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0049] The electrochemical device of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium-ion battery.

[0050] The preparation process of the electrochemical device is well known to those skilled in the art and is not particularly limited in this application. For example, it may 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, and other operations as needed to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag 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 stacked structure with tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag, and sealing the bag to obtain the electrochemical device. In addition, as needed, overcurrent protection components, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging inside the electrochemical device.

[0051] The second aspect of the present application provides an electronic device comprising the electrochemical device of any of the aforementioned embodiments. The electrochemical device provided by the present application has good cycle performance, expansion performance, and rate performance, thereby having a long service life.

[0052] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, 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, an automobile, a motorcycle, a power-assisted bicycle, 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.

[0053] Example

[0054] The following examples and comparative examples are provided to more specifically illustrate the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are by mass.

[0055] Test methods and equipment:

[0056] Average particle size test:

[0057] It is particularly important to point out here that: in the negative electrode sheet, since the silicon-carbon composite material is mixed with graphite, binder, dispersant and conductive agent materials, in order to more accurately characterize the average particle size of the silicon-carbon composite material in the negative electrode sheet, the following definition is made to test and characterize the average particle size of the silicon-carbon composite material in the negative electrode sheet: combined with the scanning electron microscope test method, a scanning electron microscope (ZEISS Sigma-02-33) device is used in the backscatter mode (0.1KV to 30KV), at a magnification of 100K, the particles with the lightest color contrast are the particles corresponding to the silicon-carbon composite material, and the value of the longest distance between the two points in each of the above particles is used as the particle size of the particle. The particle sizes of all silicon-carbon composite materials at the 100K magnification are counted, and the average value is calculated based on the particle sizes of all silicon-carbon composite materials to obtain the average particle size of the silicon-carbon composite material.

[0058] Porosity test:

[0059] The porosity of the negative electrode material layer was measured using the gas displacement method: Porosity = (V - V0) / V × 100%, where the pore volume is V - V0, where V0 is the true volume of the sample being measured and V is the total volume of the sample. The test equipment was a fully automatic true density tester (AccuPyc II 1340), and helium was used as the test gas.

[0060] Pore ​​volume, micropore and mesopore volume percentage test of porous carbon skeleton:

[0061] Pore ​​volume test of porous carbon skeleton: The pore volume of porous carbon skeleton was measured using nitrogen adsorption-desorption method. At a constant temperature of -196°C (77K), the amount of nitrogen adsorbed on the surface of the porous carbon skeleton at different relative pressures was measured. The nitrogen adsorption amount when the relative pressure P0 / P was close to 1 (P0 / P>0.99) was regarded as the saturated adsorption amount Vs. The volume after condensation of the saturated nitrogen adsorption amount was taken as the pore volume of the porous carbon skeleton: V1=Vs×0.001547. Among them, P0 refers to normal pressure, and P refers to the pressure of the gas when the nitrogen is desorbed.

[0062] Calculation of the pore volume percentage of micropores and mesopores: 2 g of powder sample of silicon-carbon composite material was weighed and placed in the test sample tube of a fully automatic specific surface area and porosity analyzer (TriStar II 3020). After degassing at 200°C for 120 min, the nitrogen adsorption and desorption isotherm of the porous carbon skeleton was measured by the nitrogen adsorption and desorption method. The pore size distribution in the porous carbon skeleton was calculated using the nonlinear density functional theory (NLDFT theory). The pore size distribution curve was plotted with the pore size as the x-axis and the pore volume as the y-axis. The ratio of the area Sa covered under the pore size distribution curve in the range of pore size x>0 nm to the total area S covered under the distribution curve was taken: a=Sa / S×100% as the pore volume percentage of micropores and mesopores in the porous carbon skeleton.

[0063] Test of carbon mass percentage:

[0064] The silicon-carbon composite material is heated and burned at high temperature in a high-frequency furnace under oxygen-rich conditions, oxidizing the carbon into carbon dioxide. After treatment, it enters the corresponding absorption cell, absorbs the corresponding infrared radiation, and is then converted into a corresponding signal by the detector. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the carbon dioxide concentration. The values ​​obtained during the entire analysis process are then accumulated. After the analysis is completed, this accumulated value is divided by the weight value in the computer, multiplied by the correction factor, and the blank is subtracted to obtain the mass percentage of carbon in the sample. The test is performed using a high-frequency infrared carbon and sulfur analyzer (Shanghai Dekai HCS-140).

[0065] Test of silicon mass percentage:

[0066] Take 5g of silicon-carbon composite material, place it in a beaker made of polytetrafluoroethylene (PTFE), slowly add 10ml of concentrated nitric acid and 2ml of hydrofluoric acid, heat to 220°C, completely dissolve the silicon-carbon composite material to obtain a sample solution, then shake the sample solution, slowly pour it into a funnel with a single layer of filter paper, and rinse the beaker and filter residue three times. The water temperature is 20°C ± 5°C, the volume is fixed to 100ml, shake well, and use inductively coupled plasma (ICP) equipment (PE 7000DV). The mass of silicon in the test solution is x, then the mass percentage of silicon in the powder is y = x / 5×100%.

[0067] Compaction density test:

[0068] The compacted density Pa of the negative electrode material layer is calculated by the formula: Pa = ma / Va. In the formula, ma is the mass of the negative electrode material layer, unit: g; Va is the volume of the negative electrode material layer, unit: cm 3 , where the volume Va is the product of the area Sa of the negative electrode material layer and the thickness of the negative electrode material layer.

[0069] Cyclic performance test:

[0070] The lithium-ion battery is charged at a constant current of 0.7C to 4.4V at a test temperature of 25°C, then charged at a constant voltage of 4.4V to 0.025C. After standing for 5 minutes, it is discharged at a constant current of 0.5C to 3.0V. This is considered one cycle, and the capacity of the lithium-ion battery is recorded as the initial capacity. Then, multiple cycles are performed, and the capacity obtained in each cycle is compared with the initial capacity to obtain the capacity retention rate and capacity decay curve. The number of cycles at which the capacity retention rate decays to 90% is recorded as the number of cycles of the lithium-ion battery at 25°C.

[0071] The test steps are the same as those at 25°C, except that the test temperature is changed to 45°C and the number of cycles at which the capacity retention rate decays to 80% is recorded as the number of cycles of the lithium-ion battery at 45°C.

[0072] Expansion performance test:

[0073] At a test temperature of 25°C, a screw micrometer is used to measure the thickness of the lithium-ion battery at 50% state of charge (SOC), which is recorded as H0. Then, after 500 cycles according to the steps in the cycle performance test, the thickness of the lithium-ion battery at 100% SOC is measured, which is recorded as H1. 25°C cycle expansion rate = (H1-H0) / H0×100%.

[0074] Change the test temperature to 45℃ and follow the same test steps as at 25℃ to calculate the cyclic expansion rate at 45℃.

[0075] Rate performance test:

[0076] At a test temperature of 25°C, the lithium-ion battery was discharged at a constant current of 0.2C to 3.0V, allowed to stand for 5 minutes, charged at a constant current of 0.5C to 4.45V, charged at a constant voltage of 4.45V to 0.05C and allowed to stand for 5 minutes. The discharge rate was adjusted and discharge tests were performed at 0.2C and 2.0C respectively to obtain the corresponding discharge capacity. The percentage ratio of the discharge capacity at 2.0C to that at 0.2C was used as the basis for measuring rate performance.

[0077] First cycle reversible capacity test:

[0078] At a test temperature of 25°C, the lithium-ion battery was discharged at a constant current of 0.2C to 3.0V, allowed to stand for 5 minutes, charged at a constant current of 0.5C to 4.45V, and charged at a constant voltage of 4.45V to 0.05C, then allowed to stand for 5 minutes. The charging capacity obtained from the test is the first-cycle reversible capacity.

[0079] First-round Coulomb efficiency test:

[0080] At a test temperature of 25°C, the lithium-ion battery was discharged at a constant current of 0.2C to 3.0V, allowed to stand for 5 minutes, charged at a constant current of 0.5C to 4.45V, and charged at a constant voltage of 4.45V to 0.05C, then allowed to stand for 5 minutes. The first-cycle charge capacity and first-cycle discharge capacity of the lithium-ion battery were tested, and the first-cycle coulombic efficiency was calculated according to the following formula: first-cycle coulombic efficiency = first-cycle charge capacity / first-cycle discharge capacity × 100%.

[0081] Example 1-1

[0082] <Preparation of positive electrode sheet>

[0083] The positive electrode active material, lithium cobalt oxide (LiCoO2), the positive electrode conductive agent, acetylene black, and the positive electrode binder, polyvinylidene fluoride, were mixed in a mass ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added and stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was evenly coated on one surface of a 12 μm thick positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet coated on one side with a 110 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. The sheet was then cold pressed and cut to obtain a 74 mm x 851 mm positive electrode sheet.

[0084] <Preparation of Silicon-Carbon Composite Material>

[0085] (1) placing the porous carbon skeleton in a silane atmosphere for a first deposition reaction, wherein the porous carbon skeleton has a pore volume of 1 ml / g, an average particle size of 3 μm, and a pore volume percentage of micropores and mesopores of 80%; the volume percentage of silane in the silane atmosphere is 20%, and the remainder is nitrogen; the temperature of the first deposition reaction is 500° C., and the time is 6 h;

[0086] (2) A second deposition reaction is then carried out in an oxygen atmosphere to passivate the material obtained in the first deposition reaction, and the silicon exposed in the first deposition reaction is oxidized by oxygen to obtain a silicon-carbon composite material, wherein the volume percentage of oxygen in the oxygen atmosphere is 20% and the rest is nitrogen. The temperature of the second deposition reaction is 500°C and the time is 5 hours.

[0087] The average particle size of the silicon-carbon composite material is 3 μm.

[0088] <Preparation of negative electrode sheet>

[0089] Graphite, the silicon-carbon composite material prepared above, conductive carbon black as a negative electrode conductor, polyacrylic acid as a negative electrode binder, and sodium carboxymethyl cellulose as a thickener were mixed in a mass ratio of 86.5:10:2:0.8:0.7. Deionized water was added and the mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry with a solids content of 75 wt%. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil and dried to obtain a negative electrode sheet coated on one side with a 130 μm thick negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. The sheet was then cold pressed and cut to obtain a negative electrode sheet measuring 76 mm x 867 mm.

[0090] <Preparation of Electrolyte>

[0091] In an argon atmosphere glove box with a water content of <10 ppm, a certain amount of EC and DEC were mixed to obtain an organic solvent. LiPF6, a lithium salt, was then added to the organic solvent and mixed thoroughly to obtain an electrolyte. Based on the total mass of the electrolyte, the weight percentage of the lithium salt was 12.5%, the weight percentage of EC was 25%, and the remainder was DEC.

[0092] <Preparation of Separator>

[0093] A polyethylene film with a thickness of 7 μm (supplied by Celgard) was used.

[0094] <Preparation of lithium-ion batteries>

[0095] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation, and wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, degassing, and trimming.

[0096] Example 1-2 to Example 1-6

[0097] Except for adjusting the average particle size of the porous carbon skeleton so that the average particle size of the silicon-carbon composite material and the porosity of the negative electrode material layer are as shown in Table 1, the rest is the same as Example 1-1.

[0098] Example 2-1 to Example 2-6

[0099] Except for adjusting the average particle size of the porous carbon skeleton so that the compaction density and porosity of the negative electrode material layer are as shown in Table 2, the rest is the same as Example 1-3.

[0100] Example 3-1 to Example 3-7

[0101] Except for adjusting the parameters in the first deposition reaction and the second deposition reaction so that the mass percentages of carbon and silicon in the silicon-carbon composite material are as shown in Table 3, the rest is the same as Example 2-3.

[0102] Example 4-1 and Example 4-2

[0103] Except for adjusting the mass percentage of EC and the average particle size of the silicon-carbon composite material as shown in Table 4, the rest is the same as Example 3-3.

[0104] Example 4-3 and Example 4-7

[0105] Except that PC was added when preparing the organic solvent in <Preparation of Electrolyte>, and the mass percentages of EC and PC and the average particle size of the silicon-carbon composite material were adjusted as shown in Table 4, the rest was the same as Example 3-3.

[0106] Example 5-1 to Example 5-5

[0107] Except for adjusting the porous carbon skeleton shown in Table 5 to prepare the silicon-carbon composite material, the rest is the same as Example 4-5.

[0108] Comparative Example 1-1 to Comparative Example 1-2

[0109] Except for adjusting the average particle size of the porous carbon so that the average particle size of the silicon-carbon composite material and the porosity of the negative electrode material layer are as shown in Table 1, the rest is the same as Example 1-1.

[0110] The preparation parameters and performance tests of various embodiments and comparative examples are shown in Tables 1 to 5.

[0111] Table 1

[0112]

[0113] It can be seen from Examples 1-1 to 1-6, Comparative Examples 1-1, and 1-2 that when the ratio of the average particle size of the silicon-carbon composite material to the porosity of the negative electrode material layer, as well as the average particle size of the silicon-carbon composite material, are both within the range of this application, the resulting electrochemical device simultaneously has better cycle performance, expansion performance, and rate performance. In addition, the porosity of the negative electrode material layer generally affects the performance of the electrochemical device. When the porosity of the negative electrode material layer is within the range of this application, the resulting electrochemical device simultaneously has better cycle performance, expansion performance, and rate performance.

[0114] Table 2

[0115]

[0116]

[0117] The compaction density of the negative electrode material layer also affects the porosity of the negative electrode material layer, which in turn affects the performance of the electrochemical device. As can be seen from Examples 1-3 and 2-1 to 2-6, when the compaction density of the negative electrode material layer is within the range of this application, the resulting porosity of the negative electrode material layer is also within the range of this application, and the electrochemical device simultaneously exhibits good cycling performance, expansion performance, and rate performance.

[0118] Table 3

[0119]

[0120] The carbon and silicon content in the silicon-carbon composite material directly affects the performance of the electrochemical device. It can be seen from Examples 2-3 and 3-1 to 3-7 that when the mass percentages of carbon, oxygen and silicon in the silicon-carbon composite material are within the range of this application, the obtained electrochemical device has good cycle performance, expansion performance and rate performance, as well as a higher first-cycle reversible capacity.

[0121] Table 4

[0122]

[0123]

[0124] Note: “ / ” in Table 4 indicates that there is no corresponding parameter or substance.

[0125] The content of the organic solvent component in the electrolyte and the relationship between the solvent and the negative electrode active material usually affect the performance of the electrochemical device. It can be seen from Examples 3-3, 4-1 and 4-2 that when the electrolyte contains EC and the mass percentage of EC is within the range of this application, the obtained electrochemical device has good cycle performance, expansion performance and rate performance. It can be seen from Examples 4-3 to 4-7 that when the electrolyte contains EC and PC at the same time, and the mass percentage of EC and PC is within the range of this application, the obtained electrochemical device has good cycle performance, expansion performance and rate performance. It can be seen from Examples 3-3, 4-1 to 4-7 that when the value of a / f is within the range of this application, the obtained electrochemical device has good cycle performance, expansion performance and rate performance.

[0126] Table 5

[0127]

[0128] The porous carbon framework used to prepare the silicon-carbon composite directly affects the performance of the silicon-carbon composite, and thus the performance of the electrochemical device. As can be seen from Examples 4-5, 5-1, and 5-5, when the pore volume, micropore volume percentage, and mesopore volume percentage of the porous carbon framework are within the ranges of this application, the resulting electrochemical device exhibits improved cycling performance, expansion performance, and rate capability.

[0129] It should be noted that, in this document, relational terms such as first and second, etc., are used only 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 terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0130] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0131] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-carbon composite material, the silicon-carbon composite material comprises a porous carbon skeleton and a silicon material, the average particle size of the silicon-carbon composite material is a μm, satisfying 3≤a≤15, and the porosity of the negative electrode material layer is b%, 15≤b≤35; the electrolyte comprises ethylene carbonate, and the mass percentage of the ethylene carbonate based on the total mass of the electrolyte is f%, 5≤f≤30; The electrochemical device satisfies 0.15≤a / b≤1, and 0.2≤a / f≤0.

4.

2. The electrochemical device according to claim 1, wherein The compaction density of the negative electrode material layer is 1.2 g / cm 3 to 1.8g / cm 3 .

3. The electrochemical device according to claim 1, wherein Based on the mass of the silicon-carbon composite material, the mass percentage of carbon in the silicon-carbon composite material is d%, satisfying 15≤d≤75, the mass percentage of silicon in the silicon-carbon composite material is e%, satisfying 15≤e≤75, and the mass percentage of oxygen in the silicon-carbon composite material is 0.3% to 10%.

4. The electrochemical device according to claim 1, wherein The porous carbon skeleton has a pore volume of 0.5 ml / g to 2.0 ml / g, and a pore volume percentage of micropores and mesopores is 70% to 90% based on the pore volume of the porous carbon skeleton.

5. The electrochemical device according to claim 1, wherein The electrolyte includes propylene carbonate, and based on the total mass of the electrolyte, the mass percentage of the propylene carbonate is g%, satisfying 5≤g≤40.

6. The electrochemical device according to any one of claims 1 to 5, wherein Based on the mass of the silicon-carbon composite material, the mass percentage of carbon in the silicon-carbon composite material is d%, the mass percentage of silicon in the silicon-carbon composite material is e%, and the electrochemical device satisfies at least one of the following: (1) a satisfies: 6≤a≤15; (2) a / b satisfies: 0.3≤a / b≤1; (3) b satisfies: 18≤b≤30; (4) The compaction density of the negative electrode material layer is 1.4 g / cm 3 to 1.8g / cm 3 ; (5) d satisfies: 40≤d≤75; (6) The e satisfies: 40≤e≤75; (7) The d / e ratio satisfies: 0.8≤d / e≤3; (8) The mass percentage of oxygen in the silicon-carbon composite material is 1% to 6%; (9) The porous carbon skeleton has a pore volume of 0.8 ml / g to 2.0 ml / g; (10) The pore volume percentage of micropores and mesopores of the porous carbon skeleton is 80% to 90%; (11) f satisfies: 10≤f≤30; (12) The electrolyte includes propylene carbonate, and the mass percentage of the propylene carbonate is g% based on the total mass of the electrolyte, where g satisfies: 10≤g≤30.

7. The method for preparing an electrochemical device according to any one of claims 1 to 5, wherein: The preparation method of the silicon-carbon composite material comprises the following steps: (1) placing a porous carbon skeleton in a silane atmosphere for a first deposition reaction, wherein the pore volume of the porous carbon skeleton is 0.5 ml / g to 2.0 ml / g, and the pore volume percentage of micropores and mesopores based on the pore volume of the porous carbon skeleton is 70% to 90%; the volume percentage of silane in the silane atmosphere is 1% to 30%, and the temperature of the first deposition reaction is 400° C. to 600° C., and the time is 1 hour to 12 hours; (2) Then, a second deposition reaction is performed in an oxygen atmosphere to obtain a silicon-carbon composite material, wherein the volume percentage of oxygen in the oxygen atmosphere is 1% to 30%, the temperature of the second deposition reaction is 400° C. to 800° C., and the time is 1 hour to 12 hours.

8. An electronic device comprising the electrochemical device according to any one of claims 1 to 6 or the electrochemical device prepared by the preparation method according to claim 7.

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