A negative electrode plate, an electrochemical device and an electronic device comprising the negative electrode plate

Abstract

The present application provides a negative electrode plate, an electrochemical device and an electronic device including the negative electrode plate. The negative electrode plate includes a negative electrode material layer, and the negative electrode material layer includes a silicon-based composite material. The silicon-based composite material includes a porous carbon matrix and nano-silicon particles within the pores of the carbon matrix. The compaction density of the silicon-based composite material under a pressure of 5 tons is D0, and the mass content of silicon in the silicon-based composite material is C0, and 0.2 ≤ (1 + 0.053D0C0 - 0.753D0) / (D0C0) ≤ 1.3. The electrochemical device having the negative electrode plate of the present application has good cycle performance, a small cycle deformation rate, a high energy density and good rate performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and particularly to a negative electrode sheet, an electrochemical device including the negative electrode sheet, and an electronic device. Background Art

[0002] Lithium-ion batteries have many advantages such as large volumetric and mass energy densities, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, and are widely used in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, people's requirements for the energy density, safety, cycle performance, etc. of batteries are getting higher and higher, and the emergence of new lithium-ion batteries with comprehensively improved performance is expected.

[0003] Silicon materials have a high specific capacity and can significantly improve the energy density of lithium-ion batteries as negative electrode materials. However, when lithium ions are inserted into the negative electrode, silicon materials will undergo large volume expansion and contraction, consuming lithium ions and electrolytes in the lithium-ion battery, and even causing the negative electrode material to crack, seriously affecting the energy density and cycle performance of the lithium-ion battery. In addition, in order to alleviate the problem of volume expansion and contraction of silicon materials, the size of silicon particles is reduced. However, as the size of silicon particles decreases, the specific surface energy of silicon particles increases. Especially for nano-silicon particles, they are extremely easy to agglomerate, which affects the energy density and cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present application is to provide a negative electrode sheet, an electrochemical device including the negative electrode sheet, and an electronic device, so as to improve the energy density and cycle performance of the electrochemical device and reduce the deformation rate after multiple cycles of the electrochemical device.

[0005] It should be noted that in the following content, a lithium-ion battery is used as an example of the electrochemical device to explain the present application. However, the electrochemical device of the present application is not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a negative electrode sheet. The negative electrode sheet includes a negative electrode material layer. The negative electrode material layer includes a silicon-based composite material. The silicon-based composite material includes a porous carbon matrix and nano-silicon particles in the pores of the carbon matrix. The compaction density of the silicon-based composite material under a pressure of 5 tons is D 0 g / cm 3 , the mass content of silicon in the silicon-based composite material is C 0 , and 0.2 ≤ (1 + 0.053D 0 C 0 - 0.753D 0 ) / (D 0 C 0 ) ≤ 1.3, preferably 0.3 ≤ (1 + 0.053D 0C 0 -0.753C 0 ) / (D 0 C 0 ) ≤ 1.1

[0007] In the negative electrode sheet provided by the present application, the negative electrode material layer contains a silicon-based composite material, and the silicon-based composite material contains a porous carbon matrix and nano-silicon particles in the pores of the carbon matrix. The nano-silicon particles are in the pores of the carbon matrix, which can improve the problem that the nano-silicon particles are prone to agglomeration; by controlling the tap density D 0 and the mass content C of silicon in the silicon-based composite material 0 (based on the total mass of the silicon-based composite material), and 0.2 ≤ (1 + 0.053D 0 C 0 -0.753D 0 ) / (D 0 C 0 ) ≤ 1.3, so that during the charging and discharging processes of the electrochemical device, the space required for the expansion of the nano-silicon particles can be satisfied, thereby effectively alleviating phenomena such as material rupture caused by the expansion of the nano-silicon particles, and improving the energy density and cycle performance of the electrochemical device. In the present application, the nano-silicon particles may refer to silicon particles with an average particle size in the nanometer range. The present application does not particularly limit the particle size of the nano-silicon particles, as long as the purpose of the present application can be achieved. For example, the average particle size of the nano-silicon particles is not greater than 500 nm.

[0008] In the present application, let P = (1 + 0.053D 0 C 0 -0.753C 0 ) / (D 0 C 0),i.e., 0.2 ≤ P ≤ 1.3, preferably 0.2 ≤ P ≤ 1.1. For example, the lower limit value of the P value may include the following values: 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7; the upper limit value of the P value may include the following values: 0.8, 0.9, 1.0, 1.1, 1.2, or 1.3. Without being limited to any theory, when the P value is too small (e.g., less than 0.2), the porosity in the silicon-based composite material is too low to meet the space required for the expansion of the nanosilicon particles during the lithium insertion / extraction process, and the carbon matrix is difficult to withstand the huge expansion stress, which may cause the structure of the silicon-based composite material to be damaged or even cause the silicon-based composite material to rupture, thereby reducing the first efficiency, cycle performance, and energy density of the electrochemical device; when the P value is too large (e.g., greater than 1.3), the porosity in the silicon-based composite material is too high, and there are too many reserved pores in the silicon-based composite material, resulting in a decrease in the mechanical compressive strength of the silicon-based composite material. During the preparation of the electrochemical device, the structure of the silicon-based composite material is easily damaged or even causes the silicon-based composite material to rupture, thereby reducing the cycle performance and energy density of the electrochemical device.

[0009] In one embodiment of the present application, the compaction density of the silicon-based composite material under a pressure of 5 tons is 0.6 g / cm 3 ≤ D 0 ≤ 1.5 g / cm 3 , preferably 0.8 g / cm 3 ≤ D 0 ≤ 1.4 g / cm 3 . For example, the lower limit value of the compaction density D of the silicon-based composite material under a pressure of 5 tons may include the following values: 0.6 g / cm 0 、0.7 g / cm 3 、0.8 g / cm 3 、0.85 g / cm 3 、0.9 g / cm 3 、0.95 g / cm 3 、1.0 g / cm 3 、1.05 g / cm 3 or 1.05 g / cm 3 . The upper limit value of the compaction density D of the silicon-based composite material under a pressure of 5 tons may include the following values: 1.1 g / cm 0 、1.15 g / cm 3 、1.2 g / cm 3 、1.25 g / cm 3 、1.3 g / cm 3 、1.4 g / cm 3 、1.4 g / cm 3 or 1.5 g / cm 3 . Without being limited to any theory, when the compaction density D of the silicon-based composite material under a pressure of 5 tons 0Too small (e.g., less than 0.6 g / cm 3 ), resulting in too high porosity in the silicon-based composite material, leading to a decrease in the mechanical strength of the silicon-based composite material. During the preparation of the electrochemical device, the structure of the silicon-based composite material is easily damaged, and even the silicon-based composite material may rupture, thereby reducing both the initial efficiency and energy density of the electrochemical device; as the compaction density D of the silicon-based composite material under 5 tons of pressure 0 gradually increases, the initial efficiency of the electrochemical device increases accordingly. However, when the compaction density D of the silicon-based composite material under 5 tons of pressure 0 is too large (e.g., greater than 1.5 g / cm 3 ), the pore space in the silicon-based composite material cannot meet the space required for the expansion of nano-silicon particles during the lithium insertion and extraction process, resulting in a significant decrease in the cycling performance of the electrochemical device.

[0010] In one embodiment of the present application, the mass content C of silicon in the silicon-based composite material 0 is 20% to 60%. For example, the lower limit value of the mass content C of silicon in the silicon-based composite material 0 may include the following values: 20%, 25%, 30%, 35% or 38%. The upper limit value of the mass content C of silicon in the silicon-based composite material 0 may include the following values: 40%, 45%, 50%, 55% or 60%. Without being limited to any theory, when the mass content C of silicon in the silicon-based composite material 0 is too low (e.g., less than 20%), most of the pores in the carbon matrix of the silicon-based composite material are not occupied. During the processing of the carbon-based composite material, it is easy to cause the silicon-based composite material to rupture, exposing a large number of fresh interfaces, resulting in a decrease in the initial efficiency of the electrochemical device; as the mass content C of silicon in the silicon-based composite material 0 gradually increases, the initial efficiency of the electrochemical device also increases. However, when the mass content C of silicon in the silicon-based composite material 0 is too high (e.g., greater than 60%), the pore space in the silicon-based composite material cannot meet the space required for the expansion of nano-silicon particles during the lithium insertion and extraction process, resulting in a significant decrease in the cycling performance of the electrochemical device. By controlling the mass content C of silicon in the silicon-based composite material 0 within the above range, the initial efficiency and cycling performance of the electrochemical device can be improved.

[0011] In one embodiment of the present application, the porosity of the silicon-based composite material is α, and 0.2 ≤ 0.5α / (C 0 - αC 0 ) ≤ 1.6, preferably 0.4 ≤ 0.5α / (C 0 - αC 0) ≤ 1.2, and this value characterizes the relationship between the mass content of silicon and the porosity in the silicon-based composite material. For example, the lower limit value of 0.5α / (C 0 -αC 0 ) may include the following values: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8; the upper limit value of 0.5α / (C 0 -αC 0 ) may include the following values: 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.6. Without being limited to any theory, when 0.5α / (C 0 -αC 0 ) is too small (e.g., less than 0.2), that is, the porosity α of the silicon-based composite material is too large or the mass content C of silicon in the silicon-based composite material 0 is too much, the reserved pores in the silicon-based composite material are difficult to buffer the lithium insertion volume expansion of the nanosilicon particles. At this time, the mechanical strength of the carbon matrix is difficult to withstand the huge expansion stress, resulting in the fragmentation of the structure of the silicon-based composite material and deteriorating its electrochemical performance, such as the reduction of energy density and cycle performance; when 0.5α / (C 0 -αC 0 ) is too large (e.g., greater than 1.6), that is, the porosity α of the silicon-based composite material is too small or the mass content C of silicon in the silicon-based composite material 0 is too little, the reserved pores in the silicon-based composite material are too large, which not only deteriorates the mechanical compressive strength of the carbon matrix, causes the material to be easily fragmented during processing, exposes a large number of fresh interfaces, and deteriorates the first efficiency of the silicon-based composite material, but also leads to a decrease in the energy density and a deterioration of the cycle performance of the electrochemical device. By controlling 0.5α / (C 0 -αC 0 ) within the above range, the first efficiency, cycle performance, and rate performance of the electrochemical device can be improved.

[0012] In an embodiment of the present application, the porosity α of the silicon-based composite material is 10% to 60%, preferably 25% to 50%. For example, the lower limit value of the porosity α of the silicon-based composite material may include the following values: 10%, 15%, 20%, 25% or 30%; the upper limit value of the porosity α of the silicon-based composite material may include the following values: 35%, 40%, 45%, 50% or 60%. Without being limited to any theory, when the porosity α of the silicon-based composite material is too small (e.g., less than 10%), the space required for the expansion of the nanosilicon particles during the lithium insertion / extraction process cannot be satisfied, and the carbon matrix is difficult to withstand the huge expansion stress, which may cause the structure of the silicon-based composite material to be damaged, and even cause the silicon-based composite material to rupture, thereby reducing the cycle performance and energy density of the electrochemical device; when the porosity α of the silicon-based composite material is too large (e.g., greater than 60%), the mechanical strength of the silicon-based composite material decreases, and the structure of the silicon-based composite material is easily damaged during the preparation of the electrochemical device, and even causes the silicon-based composite material to rupture, thereby reducing the cycle performance and energy density of the electrochemical device. By controlling the porosity of the silicon-based composite material within the above range, the cycle performance and energy density of the electrochemical device can be improved. Among them, the porosity α of the silicon-based composite material refers to the ratio of the volume of the pores in the silicon-based composite material to the total volume of the silicon-based composite material.

[0013] In an embodiment of the present application, diffraction peaks exist in the XRD diffraction pattern of the silicon-based composite material in the range of 2θ angle from 12° to 38°. The total area of the diffraction peaks is A, and the area of the diffraction peaks in the range of 2θ angle from 12° to the 2θ angle corresponding to the peak value of the diffraction peaks is B, and 60% ≤ B / A ≤ 70%. By regulating the ratio of B / A, the pore uniformity and crystallinity of the carbon matrix in the silicon-based composite material can be adjusted to effectively relieve the volume expansion of the nanosilicon particles during the lithium insertion / extraction process, thereby improving the first efficiency, good cycle performance and rate performance of the electrochemical device at the same time. It can be understood that during the preparation process of the carbon matrix, the treatment temperature can affect the pore uniformity and crystallinity of the carbon matrix. In the present application, the treatment temperature of the carbon matrix during the preparation process is 400°C to 1600°C, preferably 600°C to 1200°C, and further preferably 700°C to 1000°C, all of which can achieve the purpose of the present application. Without being limited to any theory, when the treatment temperature is too high, it will cause partial pore structure shrinkage or collapse inside the carbon matrix, making the internal pore distribution uneven, and ultimately resulting in uneven distribution of nanosilicon particles in the carbon matrix, reducing the cycle performance of the electrochemical device and increasing the deformation rate after cycling; when the treatment temperature is too low, not only will there be some oxygen-containing functional groups remaining on the surface of the carbon matrix, which are likely to react with the electrolyte in the electrochemical device, consuming the electrolyte and deteriorating the cycle performance of the electrochemical device; but also the conductivity of the carbon matrix will be reduced, deteriorating the rate performance of the electrochemical device.

[0014] In the present application, the lower limit value of B / A may include the following values: 60%, 61%, 62%, 63%, or 64%; the upper limit value of B / A may include the following values: 65%, 66%, 67%, 68%, 69%, or 70%. Without being limited to any theory, when B / A is too small (e.g., less than 60%), carbon atoms in the carbon matrix mainly exist in the SP 3 hybridization form, and the conductivity of the carbon matrix is low, deteriorating the rate performance of the electrochemical device; when B / A is too large (e.g., greater than 70%), it will cause partial shrinkage and collapse of the internal pore structure, and the uniformity of pores in the carbon matrix is low, so that the distribution of nanosilicon particles in the carbon matrix is also uneven, resulting in a decrease in the cycle performance of the electrochemical device and an increase in the deformation rate after cycling of the electrochemical device. By controlling the value of B / A within the above range, a silicon-based composite material with excellent electrical conductivity and uniform distribution of nanosilicon particles can be obtained, effectively alleviating the volume expansion of nanosilicon particles during the lithium insertion and extraction process, and improving the first efficiency, cycle performance, and rate performance of the electrochemical device.

[0015] In the present application, the interior of the carbon matrix has pores, and the porosity of the carbon matrix is not particularly limited as long as the object of the present application can be achieved. For example, the pore volume of the carbon matrix is 0.2 g / cc to 0.5 g / cc. It can be understood that the pores of the carbon matrix can include pores with different pore sizes. For example, it includes micropores with a pore size less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores larger than 50 nm. In the present application, the numbers of the above micropores, mesopores, and macropores are not particularly limited as long as the object of the present application can be achieved. Among them, the porosity of the carbon matrix refers to the ratio of the volume of pores in the carbon matrix to the total volume of the carbon matrix. In the present application, the type of the carbon matrix is not particularly limited as long as the object of the present application can be achieved. For example, the carbon matrix can be selected from at least one of hard carbon, soft carbon, and graphite. The above hard carbon can include resin carbon, carbon black, organic polymer pyrolysis carbon, and their combinations. The above soft carbon can include carbon fiber, carbon microspheres, and their combinations.

[0016] In an embodiment of the present application, the average particle size Dv50 of the silicon-based composite material is not greater than 20 μm, preferably 1 μm to 15 μm. For example, the average particle size of the silicon-based composite material can be any of the following data: 1 μm, 4 μm, 8 μm, 12 μm, 16 μm, or 20 μm. Without being limited to any theory, when the average particle size Dv50 of the silicon-based composite material is too large (e.g., greater than 20 μm), the space required for the expansion of the nanosilicon particles during the lithium insertion / extraction process is also too large, and the stress that the carbon-based material needs to bear is also too large. As a result, the stability of the obtained silicon-based composite material is low, leading to a reduction in the cycling performance of the electrochemical device; when the average particle size Dv50 of the silicon-based composite material is too small (e.g., less than 1 μm), the silicon-based composite material is prone to agglomeration, resulting in a reduction in the cycling performance of the electrochemical device. By controlling the average particle size of the silicon-based composite material within the above range, the cycling performance of the electrochemical device can be improved.

[0017] In an embodiment of the present application, the specific surface area of the silicon-based composite material is not greater than 50 m 2 / g, preferably not greater than 30 m 2 / g. For example, the specific surface area of the silicon-based composite material can be any of the following data: 1 m 2 / g, 10 m 2 / g, 20 m 2 / g, 30 m 2 / g, 40 m 2 / g, or 50 m 2 / g. Without being limited to any theory, when the specific surface area of the silicon-based composite material is too large (e.g., greater than 50 m 2 / g), it will cause a reduction in the energy density of the electrochemical device; when the specific surface area of the silicon-based composite material is too small, it cannot meet the space required for the expansion of the nanosilicon particles during the lithium insertion / extraction process, resulting in a sharp decline in the cycling performance of the electrochemical device. By controlling the specific surface area of the silicon-based composite material within the above range, the energy density and cycling performance of the electrochemical device can be improved.

[0018] In an embodiment of the present application, there is a D peak in the Raman spectrum of the silicon-based composite material in the range of a displacement of 1255 cm -1 to 1355 cm -1 and there is a G peak in the range of a displacement of 1575 cm -1 to 1600 cm -1There is a G peak within a certain range, and the peak intensity ratio of the D peak to the G peak is from 0.2 to 2. For example, the lower limit value of the peak intensity ratio of the D peak to the G peak may include the following values: 0.2, 0.4, 0.6, 0.8, or 1; the upper limit value may include the following values: 1.2, 1.4, 1.6, 1.8, or 2. Without being limited to any theory, by controlling the peak intensity ratio of the D peak to the G peak within the range of 0.2 to 2, the pores in the silicon-based composite material can meet the space required for the volume expansion of the nanosilicon particles during lithium deintercalation and intercalation, thereby effectively improving the expansion deformation of the electrochemical device during the cycling process and enhancing the cycling performance of the electrochemical device.

[0019] In one embodiment of the present application, the silicon-based composite material includes a protective layer. The silicon-based composite material may have a protective layer on at least a part of its surface, or may be entirely wrapped by the protective layer. The protective layer includes at least one of the elements C, Ti, Al, Zn, S, P, Li, B, and N. Without being limited to any theory, when the protective layer includes at least one of the elements C, Ti, Al, Zn, S, P, Li, B, and N, the setting of the protective layer enables the electrochemical device to effectively reduce the generation of by-products during the cycling process and has a certain protective effect on the nanosilicon particles in the silicon-based composite material, thereby being beneficial to improving the cycling performance of the electrochemical device.

[0020] In one embodiment of the present application, based on the total mass of the silicon-based composite material, the mass percentage content of the metal element in the protective layer of the silicon-based composite material is from 0.1% to 0.9%. For example, the lower limit value of the mass percentage content of the metal element in the protective layer may include the following values: 0.1%, 0.2%, 0.3%, 0.4%, or 0.47%; the upper limit value of the mass percentage content of the metal element in the protective layer may include the following values: 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%. Without being limited to any theory, when the mass percentage content of the metal element in the protective layer is too low (e.g., less than 0.1%), it is difficult to play the role of the protective layer and has basically no effect on the performance of the electrochemical device; when the mass percentage content of the metal element in the protective layer is too high (e.g., higher than 0.9%), the thickness of the protective layer also increases accordingly, resulting in excessive polarization of the electrochemical device and significantly decreasing the cycling performance of the electrochemical device. By controlling the mass percentage content of the metal element in the protective layer within the above range, the cycling performance of the electrochemical device can be further improved. The aforementioned metal element may include at least one of Ti, Al, Zn, or Li.

[0021] In an embodiment of the present application, the carbon (C) in the protective layer is selected from at least one of amorphous carbon, carbon nanotubes, graphene, and vapor deposition carbon fibers. Without being limited to any theory, including at least one of amorphous carbon, carbon nanotubes, graphene, and vapor deposition carbon fibers in the protective layer can increase the electronic conductivity of the silicon-based composite material, and at the same time increase the contact sites with other materials in the electrochemical device, effectively reducing the cyclic performance decay caused by contact failure, thereby improving the cyclic performance of the electrochemical device. The present application has no particular limitation on the content of C, as long as the object of the present application can be achieved. For example, based on the total mass of the silicon-based composite material, the mass percentage of C in the protective layer of the silicon-based composite material is 0.1% to 0.5%.

[0022] In the silicon-based composite material of the present application, there is no particular limitation on the elements contained in the silicon-based composite material, as long as the object of the present application can be achieved. For example, the silicon-based composite material may contain silicon element, carbon element, and oxygen element, and the mass ratio of the silicon element, carbon element, and oxygen element is 1:1:1 to 6:3:0. Without being limited to any theory, the silicon-based composite material containing silicon element, carbon element, and oxygen element can effectively improve the cyclic performance of the electrochemical device.

[0023] In an embodiment of the present application, the negative electrode material layer further includes graphite particles and a conductive agent. Based on the total mass of the silicon-based composite material, graphite particles, and conductive agent, the mass percentage of the silicon-based composite material is 5% to 80%, preferably 15% to 60%. Without being limited to any theory, the addition of graphite particles can effectively regulate the specific capacity of the negative electrode material layer, and the access of the conductive agent can effectively regulate the conductivity of the negative electrode material layer. In the present application, based on the total mass of the silicon-based composite material, graphite particles, and conductive agent, there is no particular limitation on the mass percentage of the graphite particles and the mass percentage of the conductive agent, as long as the object of the present application can be achieved. For example, the mass percentage of the graphite particles is 20% to 95%, and the mass percentage of the conductive agent is 0.5% to 5%.

[0024] In the present application, when the material in the protective layer is an easily agglomerated material, a dispersant can be added simultaneously when adding the protective layer material to make the materials in the protective layer evenly dispersed. The type and content of the dispersant can be selected according to the specific protective layer material, as long as the object of the present application can be achieved. For example, the dispersant can be selected from at least one of sodium carboxymethyl cellulose, polyvinylpyrrolidone, sodium polyacrylate, and polyvinylidene fluoride. When preparing the protective layer, considering the material loss during the preparation process, the materials used for preparing the protective layer can be appropriately added in excess, as long as the content of the elements (such as at least one of C, Ti, Al, Zn, S, P, Li, B, and N) in the protective layer is within the scope of the present application and meets the object of the present application.

[0025] The preparation process of the silicon-based composite material of the present application is well-known to those skilled in the art, and the present application has no particular limitation. For example, an organic substance is carbonized to obtain a carbon matrix, and then the carbon matrix is placed in a silicon-containing gas atmosphere and then heat-treated to obtain a silicon-based composite material. It can be understood that increasing the carbonization temperature or prolonging the carbonization time can increase the porosity of the carbon matrix, thereby reducing the compaction density of the silicon-based composite material under a pressure of 5 tons; reducing the carbonization temperature or shortening the carbonization time can reduce the porosity of the carbon matrix, thereby increasing the compaction density of the silicon-based composite material under a pressure of 5 tons; prolonging the treatment time of the carbon matrix in the silicon-containing gas or increasing the heat treatment temperature can increase the mass content of silicon in the silicon-based composite material; shortening the treatment time of the carbon matrix in the silicon-containing gas or reducing the heat treatment temperature can reduce the mass content of silicon in the silicon-based composite material. The present application has no particular limitation on the carbonization temperature, carbonization time, treatment time of the carbon matrix in the silicon-containing gas, and heat treatment temperature during the preparation of the silicon-based composite material, as long as the object of the present application can be achieved. For example, the carbonization temperature is 400°C to 1600°C, the carbonization time is 2 h to 12 h, the treatment time of the carbon matrix in the silicon-containing gas is 2 h to 15 h, and the heat treatment temperature is 300°C to 800°C.

[0026] In the present application, the carbonization temperature of the carbon matrix during the preparation process is preferably 600°C to 1200°C, and more preferably 700°C to 1000°C. Without being limited to any theory, when the carbonization temperature is too high, it will cause partial shrinkage or collapse of the pore structure inside the carbon matrix, making the internal pore distribution uneven, and ultimately resulting in uneven distribution of nano-silicon particles in the carbon matrix, reducing the cycle performance of the electrochemical device and increasing the deformation rate after cycling; when the carbonization temperature is too low, not only will some oxygen-containing functional groups remain on the surface of the carbon matrix, which is likely to cause side reactions with the electrolyte in the electrochemical device, consuming the electrolyte and deteriorating the cycle performance of the electrochemical device; but also reduce the conductivity of the carbon matrix and deteriorate the rate performance of the electrochemical device.

[0027] The preparation process of the negative electrode sheet of this application is well-known to those skilled in the art, and this application has no special limitations. For example, a silicon-based composite material, graphite particles, and a conductive agent are mixed to obtain a mixture, the mixture, a binder, and a solvent are mixed to obtain a mixed slurry, and the mixed slurry is coated on the negative electrode current collector and then dried, cold-pressed, and slit to obtain a negative electrode sheet containing a negative electrode material layer. In this application, there are no special limitations on the current collector layer of the negative electrode, as long as the purpose of this application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, etc. In this application, there are no special limitations on the thickness of the current collector layer of the negative electrode, as long as the purpose of this application can be achieved. For example, the thickness of the current collector layer of the negative electrode is 4 μm to 12 μm. In this application, there are no special limitations on the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. In this application, based on the total mass of the mixture, binder, and solvent, the mass percentage content of the binder has no special limitations, as long as the purpose of this application can be achieved. For example, the mass percentage content of the binder is 1% to 6%.

[0028] There are no special limitations on the above-mentioned conductive agent, as long as the purpose of this application can be achieved. For example, the conductive agent can include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, or graphene, etc. The above-mentioned carbon nanotubes can include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The above-mentioned carbon fibers can include at least one of vapor-grown carbon fibers (VGCF) and nanofibers.

[0029] There are no special limitations on the above-mentioned binder, as long as the purpose of this application can be achieved. For example, the binder can include at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, and polyvinylidene fluoride. There are no special limitations on the above-mentioned solvent, as long as the purpose of this application can be achieved. For example, the solvent can include deionized water or N-methylpyrrolidone.

[0030] Optionally, the negative electrode sheet may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer has no special limitations and can be a commonly used conductive layer in the art. The conductive layer includes the above-mentioned conductive agent and the above-mentioned binder.

[0031] The second aspect of the present application provides an electrochemical device, which includes the negative electrode sheet described in the embodiments of the present application. This electrochemical device has good cycle performance and high energy density. 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: lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries, etc.

[0032] The electrochemical device of the present application further includes a positive electrode sheet. The positive electrode sheet in the present application is not particularly limited as long as it can achieve the purpose of the present application. For example, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode material layer. Among them, the positive electrode current collector is not particularly limited as long as it can achieve the purpose of the present application. For example, it may include aluminum foil, aluminum alloy foil, or a composite current collector, etc. The positive electrode material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited as long as it can achieve the purpose of the present application. For example, the positive electrode active material may include at least one of composite oxides of lithium and transition metal elements. The above-mentioned transition metal elements are not particularly limited as long as they can achieve the purpose of the present application. For example, the transition metal elements may include at least one of nickel, manganese, cobalt, and iron. Specifically, the positive electrode active material may include at least one of lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium manganese iron phosphate, or lithium titanate. In the present application, the thicknesses of the positive electrode current collector and the positive electrode material layer are not particularly limited as long as they can achieve the purpose of the present application. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0033] Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder.

[0034] The above-mentioned conductive agent is not particularly limited as long as it can achieve the purpose of the present application. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, or graphene, etc. The above-mentioned binder is not particularly limited, and any binder known in the art may be used as long as it can achieve the purpose of the present application. For example, the binder may include at least one of polyvinyl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride, polytetrafluoroethylene (PTFE), carboxymethyl cellulose, or sodium carboxymethyl cellulose (CMC-Na), etc. For example, styrene-butadiene rubber (SBR) may be selected as the binder.

[0035] The electrochemical device itself further includes a separator. There is no particular limitation on the separator in this application, as long as it can achieve the purpose of this application. For example, at least one of polyolefin (PO) membranes mainly composed of polyethylene (PE), polypropylene (PP), and polytetrafluoroethylene, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex or aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, rolled membranes, spun membranes, etc. The separator in this application may have a porous structure, and there is no particular limitation on the size of the pore diameter, as long as it can achieve the purpose of this application. For example, the size of the pore diameter is from 0.01 μm to 1 μm. In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator is from 5 μm to 500 μm.

[0036] For example, the separator may include a base layer and a surface treatment layer. The base layer may be a non-woven fabric, a membrane, or a composite membrane having a porous structure, and the material of the base layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the base layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0037] For example, the inorganic layer includes inorganic particles and a binder. There is no particular limitation on the inorganic particles. For example, they may be selected from at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. There is no particular limitation on the binder. For example, it may be selected from one or a combination of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0038] The electrochemical device of this application further includes an electrolyte. The electrolyte of this application may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution. The electrolyte solution includes a lithium salt and a non-aqueous solvent. In some embodiments of this application, the lithium salt may include LiPF6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , at least one of LiBOB or lithium difluoroborate. For example, the lithium salt can be selected as LiPF 6 , because it can give a high ionic conductivity and improve the cycling performance.

[0039] The non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents or a combination thereof. The above-mentioned carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof. Examples of the above-mentioned chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) and combinations thereof. Examples of the cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene ethylene carbonate (VEC) and combinations thereof. Examples of the fluorinated carbonate compounds are 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, trifluoromethyl ethylene carbonate and combinations thereof. Examples of the above-mentioned carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and combinations thereof. Examples of the above-mentioned ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and combinations thereof. Examples of the above-mentioned other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate and phosphate esters and combinations thereof.

[0040] 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, the electrochemical device can be manufactured through the following process: overlapping the positive electrode plate and the negative electrode plate via a separator membrane, and after winding, folding, etc. as required, putting them into a housing, injecting the electrolyte into the housing and sealing it, wherein the separator membrane used is the above-mentioned separator membrane provided by this application. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing as required to prevent the pressure inside the electrochemical device from rising and overcharging and overdischarging.

[0041] The third aspect of this application provides an electronic device, which includes the electrochemical device described in the embodiments of this application, and this electronic device has good cycle performance and a relatively high energy density.

[0042] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop 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 headset stereo, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a minidisc, 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 moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, and a large household battery, etc.

[0043] The present application provides a negative electrode plate, an electrochemical device and an electronic device including the negative electrode plate. The negative electrode material layer of the negative electrode plate contains a silicon-based composite material, and the silicon-based composite material contains a porous carbon matrix and nano-silicon particles in the pores of the carbon matrix. By regulating the compaction density D 0 of the silicon-based composite material and the mass content C 0 of silicon in the silicon-based composite material, and 0.2 ≤ (1 + 0.053D 0 C 0 - 0.753D 0 ) / (D 0 C 0 ) ≤ 1.3, during the charging and discharging process of the electrochemical device, the space required for the expansion of the nano-silicon particles can be satisfied, thereby effectively alleviating phenomena such as material rupture caused by the expansion of the nano-silicon particles, and improving the energy density and cycle performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the drawings required for use in the embodiments and the prior art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application.

[0045] Figure 1 X-ray diffraction spectrum of the silicon-based composite material in Example 7 of the present application;

[0046] Figure 2 Raman spectrum of the silicon-based composite material in Example 7 of the present application;

[0047] Figure 3 Cyclic decay curve of the lithium-ion batteries in Example 7 of the present application and Comparative Example 1;

[0048] Figure 4 Swelling curve of the lithium-ion batteries in Example 7 of the present application and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] To make the objectives, technical solutions, and advantages of the present application clearer and more understandable, the following provides examples with reference to the accompanying drawings to further elaborate on the present application in detail. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0050] It should be noted that in the specific implementation manner of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application. However, the electrochemical device of the present application is not limited to lithium-ion batteries.

[0051] Embodiment

[0052] Hereinafter, embodiments and comparative examples are given to more specifically illustrate the implementation manner of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0053] Testing methods and equipment:

[0054] Testing the tap density of the silicon-based composite material:

[0055] Adopt GB / T 24533-2009 "Graphite Anode Materials for Lithium-Ion Batteries". Place a certain amount of silicon-based composite material on a special compaction mold (the diameter of the mold is known). There is a hollow in the middle of the mold, and there is a metal disc on each of the upper and lower sides. The powder is placed between the metal discs, and a metal cylinder is placed on the top. Place the mold on the test bench of a compression and flexure integrated testing machine (Sanshi Zongheng UTM7305), set the pressure to 5 tons, and the thickness of the silicon-based composite material under 5 tons of pressure can be read on the testing machine. Calculate the tap density of the silicon-based composite material under 5 tons of pressure through ρ = m / v.

[0056] Testing the specific surface area of the silicon-based composite material:

[0057] At a constant low temperature (-199°C to -193°C), after measuring the adsorption amount of gas on the solid surface at different relative pressures, based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), the monolayer adsorption amount of the sample is obtained, and thus the specific surface area of the solid is calculated.

[0058] BET formula:

[0059] Where: W --- the mass of the gas adsorbed by the solid sample under the relative pressure (P / P0), unit cm 3 / g; Wm --- the saturated adsorption amount of the gas covering a single molecular layer, unit cm 3 / g; C---Constant related to the adsorption heat and condensation heat of the first layer; Slope: (c - 1) / (WmC), Intercept: 1 / WmC, Total specific surface area: (Wm × N × Acs / M); Specific surface area: S = St / m, where m is the sample mass, Acs: Average area occupied by each N 2 The average area occupied by each molecule is 16.2 Å 2 .

[0060] Weigh 1.5 g to 3.5 g of the powder sample and put it into the test sample tube of TriStar II 3020. After degassing at 200 °C for 120 min, conduct the test.

[0061] Porosity test of silicon-based composite materials:

[0062] Use a scanning transmission electron microscope (STEM) to photograph the interface of the silicon-based composite material, and use the obtained STEM images to determine the porosity. Specifically: Use Image J software to perform binary processing on the STEM images. After calibrating the size according to the scale, use Analyze Particles to count the area of the pores. The ratio of the area of the pores to the cross-sectional area of the measured silicon-based composite material is the porosity of the measured silicon-based composite material; Take any 20 or more particles of the silicon-based composite material for the same test, and take the average value as the porosity of the silicon-based composite material.

[0063] Particle size test of silicon-based composite materials:

[0064] Add 0.02 g of the silicon-based composite material to a 50 mL clean beaker, then add 20 mL of deionized water, and then add 3 to 5 drops of a surfactant with a mass concentration of 1% to completely disperse the powder in water. Ultrasonic for 5 minutes in a 120 W ultrasonic cleaner, and use a laser particle size analyzer to test the particle size distribution. Dv50 is the diameter at which 50% of the cumulative volume-based distribution of the particles is obtained by testing with a laser scattering particle size analyzer.

[0065] First efficiency test of silicon-based composite materials:

[0066] Mix the silicon-based composite material, conductive carbon black, and binder polyacrylic acid (PAA) obtained in the examples according to a mass ratio of 8:1:1, then add deionized water to prepare a slurry with a solid content of 70%. Use a scraper to coat a 100 μm thick coating, dry it in a vacuum drying oven at 85 °C for 12 hours, and then cut it into 1 cm diameter circular pieces in a dry environment with a punching machine. Use a lithium metal sheet as the counter electrode in a glove box, select a polyethylene (PE) film (provided by Celgard company) as the separator, and add the electrolyte in Example 1 to assemble a coin cell. Use a BlueTEC (LAND) series battery test system to conduct charge-discharge tests on the battery and test its charge-discharge capacity.

[0067] First, discharge at 0.05C to 0.005V, then rest for 5 minutes. After that, discharge at 50μA to 0.005V, rest for another 5 minutes, and then discharge at 10μA to 0.005V to obtain the initial lithium insertion capacity of the material. Then, charge at 0.1C to 2V to obtain the initial lithium deinsertion capacity. Finally, divide the initial lithium deinsertion capacity by the initial lithium insertion capacity to get the initial efficiency of the silicon-based composite material.

[0068] Cycling performance test:

[0069] The test temperature is 25°C or 45°C. Charge the lithium-ion battery at a constant current of 0.7C to 4.4V, then charge at a constant voltage until the current reaches 0.025C. After standing for 5 minutes, discharge at 0.5C to 3.0V. Use the capacity obtained in this step as the initial capacity, and conduct a 0.7C charge / 0.5C discharge cycling test. Calculate the ratio of the capacity of each step to the initial capacity to obtain the capacity cycling decay curve. Record the number of cycles when the capacity retention rate reaches 90% at 25°C as the room-temperature cycling performance of the lithium-ion battery, and record the number of cycles when the capacity retention rate reaches 80% at 45°C as the high-temperature cycling performance of the lithium-ion battery. Compare the number of cycles in the above two cases to obtain the cycling performance of the material.

[0070] Discharge rate test:

[0071] At 25°C, discharge the lithium-ion battery at 0.2C to 3.0V, then rest for 5 minutes. After that, charge at 0.5C to 4.45V, charge at a constant voltage until the current reaches 0.05C, and then rest for 5 minutes. Adjust the discharge rate and conduct discharge tests at 0.2C, 0.5C, 1C, 1.5C, and 2.0C respectively to obtain the discharge capacity. Compare the capacity obtained at each rate with the capacity obtained at 0.2C, and compare the ratio of 2C to 0.2C to evaluate the rate performance.

[0072] Full charge expansion rate test of lithium-ion battery:

[0073] Use a micrometer to measure the thickness L1 of the fresh lithium-ion battery during half charge. When the lithium-ion battery reaches a full charge state after cycling 400 times (cls), use the micrometer to measure the thickness L2 of the lithium-ion battery at this time. Then, the full charge expansion rate of the lithium-ion battery is (L2 - L1) / L1 × 100%.

[0074] Energy density calculation:

[0075] After charging the lithium-ion battery to 4.45V at 25°C, discharge it at 0.2C to 3V to obtain the discharge capacity (C) and the average voltage platform (U) of the lithium-ion battery. Then, use a laser thickness gauge to measure the length, width, and height of the lithium-ion battery to obtain its volume (V). The volume energy density (ED) can be calculated by the following formula: ED = C × U / V.

[0076] Example 1

[0077] <Preparation of silicon-based composite material>

[0078] 110 g of resorcinol and 150 g of 40 wt% aqueous formaldehyde solution were added to a flask to obtain a first mixed solution. After heating to 40 °C, 40 mL of a Na 2 CO 3 solution with a molar concentration of 50 mmol / L was added, and the mixture was continuously stirred for 5 h to obtain a second mixed solution. Then, the second mixed solution was sealed and aged at 75 °C for 120 h, and the solvent was removed. After drying at 80 °C, a carbonaceous block was obtained. The carbonaceous block was crushed into a powder with a particle size Dv50 of 7.5 μm and then carbonized at a carbonization temperature T1 of 800 °C for a carbonization time t1 of 6 h to obtain a carbon matrix. The carbon matrix was placed in a tubular furnace, and a mixed gas of silane and H 2 (the volume ratio of silane and H 2 is 5:95) was introduced into the tubular furnace. The temperature T2 in the tubular furnace was 500 °C, and the gas introduction time t2 was 12 h. After cooling, the above-mentioned silicon-based composite material was obtained.

[0079] <Preparation of negative electrode sheet>

[0080] The silicon-based composite material, graphite particles, and nano-conductive carbon black prepared above were mixed in a mass ratio of 80:5:15 to obtain a mixed material. Then, the mixed material and the binder polyacrylic acid were mixed in a mass ratio of 1:50, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 70%. The slurry was stirred evenly. The slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 10 μm and dried at 110 °C to obtain a negative electrode sheet with a negative electrode material layer coated on one side and a coating thickness of 150 μm. The above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. Then, the negative electrode sheet was cut into a specification of 74 mm × 867 mm for use.

[0081] <Preparation of positive electrode sheet>

[0082] The cathode active material lithium cobaltate, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 95:2.5:2.5. Then, N-methylpyrrolidone (NMP) is added as a solvent to formulate a slurry with a solid content of 75%, and the mixture is stirred evenly. The slurry is uniformly coated on one surface of an aluminum foil cathode current collector with a thickness of 10 μm and dried at 90 °C to obtain a cathode electrode sheet with a coating thickness of 110 μm. After the above steps are completed, the single-sided coating of the cathode electrode sheet is finished. Subsequently, the above steps are repeated on the other surface of the cathode electrode sheet to obtain a cathode electrode sheet with both sides coated with the cathode active material. After coating, the cathode electrode sheet is cut into a size of 74 mm × 867 mm, and the tab is welded for later use.

[0083] <Preparation of electrolyte>

[0084] In a dry argon atmosphere, the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, the lithium salt lithium hexafluorophosphate (LiPF 6 ) is added to the organic solvent and dissolved and mixed evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0085] <Preparation of separator>

[0086] A polyethylene (PE) film with a thickness of 15 μm (provided by Celgard) is used.

[0087] <Preparation of lithium-ion battery>

[0088] The above-prepared cathode electrode sheet, separator, and anode electrode sheet are stacked in sequence, with the separator placed in the middle of the cathode and anode to play an isolation role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with the electrolyte. After processes such as vacuum packaging, standing, formation, degassing, and trimming, a lithium-ion battery is obtained.

[0089] In Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13, Example 14, and Example 15, the preparation steps of <Preparation of silicon-based composite material>, <Preparation of anode electrode sheet>, <Preparation of cathode electrode sheet>, <Preparation of electrolyte>, <Preparation of separator>, and <Preparation of lithium-ion battery> are the same as those in Example 1, and the changes in relevant parameters are shown in Table 1.

[0090] In Examples 16, 17, 18, 19, and 20, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Sheet>, <Preparation of Positive Electrode Sheet>, <Preparation of Electrolyte>, <Preparation of Separator>, and <Preparation of Lithium-ion Battery> are the same as those in Example 1, and the changes in relevant parameters are shown in Table 2.

[0091] Example 21

[0092] The silicon-based composite material obtained in the preparation step of <Preparation of Silicon-based Composite Material> and the dispersant polyvinylpyrrolidone (PVP) were added to absolute ethanol at a mass ratio of 500:11, and stirred for 0.5 h to obtain a uniform suspension. Then, aluminum isopropoxide was added to the suspension, stirred for 0.5 h, and then deionized water was added dropwise and reacted for another 4 h to obtain a mixed solution. Among them, the mass ratio of aluminum isopropoxide to the silicon-based composite material is 1:50, and the molar ratio of aluminum isopropoxide to deionized water is 1:3. The mixed solution was obtained as a powder by spray drying, and the powder was heated at 500 °C for 2 h, cooled to room temperature and then sieved to obtain a silicon-based composite material with a metal element protective layer. And the silicon-based composite material in the preparation step of <Preparation of Negative Electrode Sheet> was replaced with the silicon-based composite material with a metal element protective layer, and the preparation steps of <Preparation of Positive Electrode Sheet>, <Preparation of Electrolyte>, <Preparation of Separator>, and <Preparation of Lithium-ion Battery> are the same as those in Example 7.

[0093] In Examples 22, 23, 24, 25, 26, and 27, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Sheet>, <Preparation of Positive Electrode Sheet>, <Preparation of Electrolyte>, <Preparation of Separator>, and <Preparation of Lithium-ion Battery> are the same as those in Example 21, and the changes in relevant preparation parameters are shown in Table 3.

[0094] Example 28

[0095] The silicon-based composite material obtained in the preparation step of <Preparation of Silicon-based Composite Material> was added to a single-walled carbon nanotube (SCNT) solution containing the dispersant sodium carboxymethylcellulose (CMC-Na) and dispersed for 2 hours until a uniform mixed solution was formed. It was spray-dried to obtain a powder, crushed, and sieved through 400 meshes to obtain a silicon-based composite material with a protective layer, where the mass ratio of silicon-based composite material:SCNT:CMC-Na is 99.75:0.1:0.15. And the silicon-based composite material in the preparation step of <Preparation of Negative Electrode Sheet> was replaced with the silicon-based composite material with a protective layer, and the preparation steps of <Preparation of Positive Electrode Sheet>, <Preparation of Electrolyte>, <Preparation of Separator>, and <Preparation of Lithium-ion Battery> are the same as those in Example 2.

[0096] In Examples 29 to 40, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Positive Electrode Plate>, <Preparation of Electrolyte>, <Preparation of Separator Membrane> and <Preparation of Lithium-ion Battery> are the same as those in Example 29, and the changes in relevant preparation parameters are shown in Table 4.

[0097] In Comparative Examples 1 to 6, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Positive Electrode Plate>, <Preparation of Electrolyte>, <Preparation of Separator Membrane> and <Preparation of Lithium-ion Battery> are the same as those in Example 1, except that the carbonization temperature T1, carbonization duration t1, gas introduction duration t2 and heat treatment temperature T2 in <Preparation of Silicon-based Composite Material> are adjusted according to specific examples, and the changes in relevant parameters are shown in Table 1.

[0098] In Comparative Examples 7 to 10, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Positive Electrode Plate>, <Preparation of Electrolyte>, <Preparation of Separator Membrane> and <Preparation of Lithium-ion Battery> are the same as those in Example 1, except that the carbonization temperature T1, carbonization duration t1, gas introduction duration t2 and heat treatment temperature T2 in <Preparation of Silicon-based Composite Material> are adjusted according to specific examples, and the changes in relevant parameters are shown in Table 2.

[0099] In Comparative Example 11, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Positive Electrode Plate>, <Preparation of Electrolyte>, <Preparation of Separator Membrane> and <Preparation of Lithium-ion Battery> are the same as those in Example 21, and the changes in relevant preparation parameters are shown in Table 3.

[0100] In Comparative Examples 12 and 13, the preparation steps of <Preparation of Silicon-based Composite Material>, <Preparation of Negative Electrode Plate>, <Preparation of Positive Electrode Plate>, <Preparation of Electrolyte>, <Preparation of Separator Membrane> and <Preparation of Lithium-ion Battery> are the same as those in Example 29, and the changes in relevant preparation parameters are shown in Table 4.

[0101] The preparation parameters and test results of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13, Example 14, Example 15, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 are shown in Table 1; the preparation parameters and test results of Example 16, Example 17, Example 18, Example 19, Example 20, Comparative Example 7, Comparative Example 8, Comparative Example 9, and Comparative Example 10 are shown in Table 2; the preparation parameters and test results of Example 7, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, and Comparative Example 11 are shown in Table 3; the preparation parameters and test results of Example 2, Example 28, Example 29, Example 30, Example 31, Example 32, Example 33, Example 34, Example 35, Example 36, Example 37, Example 38, Example 39, Example 40, Comparative Example 12, and Comparative Example 13 are shown in Table 4.

[0102]

[0103]

[0104]

[0105]

[0106] It can be seen from Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2, Example 6, Example 7, Example 8, Example 9, Example 10, Comparative Example 3, Comparative Example 4, Example 11, Example 12, Example 13, Example 14, Example 15, Comparative Example 5, and Comparative Example 6 that as long as the P value (i.e., (1 + 0.053D 0 C 0 - 0.753D 0 ) / (D 0 C 0 )) is within the scope of this application, the cycle performance of the lithium-ion battery can be improved, and the deformation rate of the lithium-ion battery after multiple cycles can be reduced. It can be seen from Example 1, Example 2, Example 3, Example 4, and Example 5 that when the mass content C 0 of silicon in the silicon-based composite material remains unchanged, the P value increases within the scope of this application, and the compaction density D 0decreases, the specific capacity of the silicon-based composite material shows no obvious difference, the initial efficiency decreases slightly, the cycling performance of the lithium-ion battery first improves and then decreases, and the deformation rate after cycling first decreases and then increases. It can be seen from Example 1, Example 6, Example 11, Example 2, Example 7, Example 12, Example 3, Example 8, Example 13, Example 4, Example 9, Example 14, Example 5, Example 10, and Example 15 that when the P value remains unchanged, C 0 increases within the scope of the present application, D 0 has a small change range, the specific capacity and initial efficiency of the silicon-based composite material increase, the cycling performance of the lithium-ion battery decreases slightly, the deformation rate after multiple cycles increases slightly, and the rate performance improves slightly. However, as long as C 0 , D 0 are within the scope of the present application, a lithium-ion battery with high cycling performance and low deformation rate can be obtained.

[0107] Figure 1 shows the X-ray diffraction pattern of the silicon-based composite material in Example 7. It can be seen from Figure 1 that diffraction peaks exist in the range of 2θ angle from 12° to 38°, and the B / A ratio is 63%. Figure 2 shows the Raman spectrum of the silicon-based composite material in Example 7. It can be seen from Figure 2 that a D peak exists in the range of displacement from 1255 cm -1 to 1355 cm -1 , a G peak exists in the range of displacement from 1575 cm -1 to 1600 cm -1 , and the peak intensity ratio of the D peak to the G peak is 1.2. Figure 3 shows the cycling decay curve of the lithium-ion batteries in Example 7 and Comparative Example 1. It can be seen from Figure 3 that when the capacity retention rate is the same, the number of cycling times of the lithium-ion battery prepared in Example 7 is significantly greater than that of the lithium-ion battery provided in Comparative Example 1. Figure 4 shows the swelling curve of the lithium-ion batteries in Example 7 and Comparative Example 1. It can be seen from Figure 4 that when the number of cycling times is the same, the deformation rate of the lithium-ion battery provided in Example 7 is significantly smaller than that of the lithium-ion battery provided in Comparative Example 1.

[0108] It can be seen from Example 16, Example 17, Example 18, Comparative Example 7, and Comparative Example 8 that as long as the ratio of B / A is within the scope of the present application, the cycling performance of the lithium-ion battery can be improved and the deformation rate of the lithium-ion battery after multiple cycles can be reduced. It can be seen from Example 16, Example 17, and Example 18 that when C 0When the value of B / A increases within the scope of the present application while remaining unchanged, the specific surface area of the silicon-based composite material gradually increases, the specific capacity remains basically unchanged, and the initial efficiency slightly decreases. The cycle performance of the lithium-ion battery first improves and then decreases, the deformation rate after multiple cycles first decreases and then increases, and the rate performance increases.

[0109] It can be seen from Example 17, Example 19, Example 20, Comparative Example 9, and Comparative Example 10 that as long as C 0 Within the scope of the present application, the cycle performance of the lithium-ion battery can be improved, and the deformation rate of the lithium-ion battery after multiple cycles can be reduced. It can be seen from Example 17, Example 19, and Example 20 that when the value of B / A remains unchanged, C 0 increases within the scope of the present application, the specific surface area of the silicon-based composite material gradually decreases, the specific capacity changes little, and the initial efficiency gradually increases. The cycle performance of the lithium-ion battery improves, and the deformation rate after multiple cycles increases.

[0110] It can be seen from Example 7, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, and Example 27 that by providing a protective layer on the surface of the silicon-based composite material, the cycle performance of the lithium-ion battery can be further improved, and the deformation rate of the lithium-ion battery after multiple cycles can be reduced. It can be seen from Example 21, Example 24, Example 25, Example 26, and Example 27 that as the content of the metal element in the protective layer gradually increases within the scope of the present application, the specific surface area of the silicon-based composite material gradually increases, and the specific capacity and the initial efficiency slightly decrease, but the lithium-ion battery still has good cycle performance and a small deformation rate. It can be seen from Example 21, Example 24, Example 25, Example 26, Example 27, and Comparative Example 11 that as long as the content of the metal element in the protective layer is within the scope of the present application, the obtained lithium-ion battery has both good cycle performance and a small deformation rate. It can be seen from Example 21, Example 22, and Example 23 that as long as the metal element in the protective layer is within the scope of the present application, the obtained lithium-ion battery has both good cycle performance and a small deformation rate after multiple cycles.

[0111] The type and content of the carbon material usually also affect the performance of the lithium-ion battery. It can be seen from Example 2, Example 28, Example 29, Example 30, Example 31, Example 32, Example 33, Example 34, Example 35, Example 36, Example 37, Example 38, Example 39, and Example 40 that as long as the type and content of the carbon material are within the scope of the present application, the cycle performance of the lithium-ion battery can be further improved, and the deformation rate of the lithium-ion battery after multiple cycles can be reduced.

[0112] It can be seen from Example 28, Example 31, Example 32, and Comparative Example 12 that when the content of the carbon material is too high (such as Comparative Example 12), it is impossible to prepare a lithium-ion battery, which may be because when the carbon material is too high, the slurry cannot be processed.

[0113] It can be seen from Example 28 and Comparative Example 13 that the addition of a dispersant can generally improve the agglomeration problem of the carbon material, so that a lithium-ion battery with good cycle performance and a small deformation rate after multiple cycles can be obtained.

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

Claims

1. A negative electrode sheet, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a silicon-based composite material, the silicon-based composite material includes a porous carbon matrix and nano-silicon particles within the pores of the carbon matrix, and the compaction density of the silicon-based composite material under a pressure of 5 tons is D 0 g / cm 3 , the mass content of silicon in the silicon-based composite material is C 0 , and 0.2 ≤ (1 + 0.053D 0 C 0 - 0.753D 0 ) / (D 0 C 0 ) ≤ 1.3, 0.6 g / cm 3 ≤ D 0 ≤ 1.3 g / cm 3 , Among them, in the XRD diffraction pattern of the silicon-based composite material, diffraction peaks exist in the range of 2θ angles from 12° to 38°. The total area of the diffraction peaks is A, and the area of the diffraction peaks in the range of 2θ angles from 12° to the 2θ angle corresponding to the peak value of the diffraction peaks is B, and 60% ≤ B / A ≤ 70%.

2. The negative electrode sheet according to claim 1, Among them, The mass content C of silicon in the silicon-based composite material 0 is 20% to 60%.

3. The negative electrode sheet according to claim 1, Among them, The porosity of the silicon-based composite material is α, and 0.2 ≤ 0.5α / (C 0 - αC 0 ) ≤ 1.

6.

4. The negative electrode sheet according to claim 1, Among them, the negative electrode sheet satisfies at least one of the following characteristics: (a) The porosity α of the silicon-based composite material is 10% to 60%; (b) The average particle size Dv50 of the silicon-based composite material is not greater than 20 μm; (c) The specific surface area of the silicon-based composite material is not more than 50 m 2 / g; (d) In the Raman spectrum of the silicon-based composite material, a D peak exists in the range of a displacement of 1255 cm -1 to 1355 cm -1 and a G peak exists in the range of a displacement of 1575 cm -1 to 1600 cm -1 The ratio of the peak intensity of the D peak to that of the G peak is 0.2 to 2.

5. The negative electrode sheet according to claim 1, Among them, the silicon-based composite material includes a protective layer, and the protective layer includes at least one of the elements C, Ti, Al, Zn, S, P, Li, B, and N.

6. The negative electrode sheet according to claim 5, Among them, Based on the total mass of the silicon-based composite material, the mass percentage content of the metal elements in the protective layer is 0.1% to 0.9%.

7. The negative electrode sheet according to claim 5, Among them, The C in the protective layer is selected from at least one of amorphous carbon, carbon nanotubes, graphene, and vapor deposition carbon fibers.

8. The negative electrode sheet according to claim 1, Among them, The negative electrode material layer further includes graphite particles and a conductive agent. Based on the total mass of the silicon-based composite material, graphite particles, and the conductive agent, the mass percentage content of the silicon-based composite material is 5% to 80%.

9. An electrochemical device, which includes the negative electrode sheet according to any one of claims 1 to 8.

10. An electronic device, which includes the electrochemical device according to claim 9.

Images