Negative electrode material and preparation method thereof, electrochemical device and electronic device

Abstract

The invention provides a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device, the negative electrode material comprises silicon-carbon particles, the silicon-carbon particles comprise a first region and a second region, the first region is a region from the surface of the silicon-carbon particles to a depth of 40nm from the surface of the silicon-carbon particles, and the second region is a region from the surface of the silicon-carbon particles to a depth of 40nm from the surface of the silicon-carbon particles; the second region is a region from the depth of 60nm to the depth of 100nm from the surface of the silicon carbon particle; the silicon-carbon particles comprise a silicon element, a carbon element and an oxygen element; based on the total number of atoms of the silicon element, the carbon element and the oxygen element in the first area, the percentage of the number of atoms of the oxygen element in the first area is A%, and A is larger than or equal to 7.7 and smaller than or equal to 24.9; based on the total number of atoms of the silicon element, the carbon element and the oxygen element in the second region, the percentage of the number of atoms of the oxygen element in the second region is B%, and B is larger than or equal to 5.5 and smaller than or equal to 8.8. The electrochemical device has good first coulombic efficiency and safety performance, and lithium precipitation of the negative electrode can be improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical technologies, and particularly to a negative electrode material, a preparation method thereof, an electrochemical device, and an electronic device. Background Art

[0002] As the negative electrode material of traditional commercial lithium-ion batteries, graphite has a low capacity (372 mAh / g) and there are safety hazards of lithium dendrites. These problems limit its further application. Therefore, developing negative electrode materials for lithium-ion batteries with high energy density and high safety has become the focus of current technological development. Compared with carbon-based materials such as graphite, silicon is considered to be one of the most promising graphite alternative materials due to its ultra-high theoretical specific capacity and suitable working voltage.

[0003] However, the negative electrode material added with silicon is prone to a large expansion rate during charging, which leads to a decline in cycle performance. One of the main reasons for these problems is the uneven distribution of silicon elements in the silicon material particles. The area with a high silicon concentration has a larger expansion rate after lithium intercalation, while the area with a low silicon concentration is relatively smaller. This non-uniformity leads to uneven lithium intercalation stress distribution inside the silicon material particles, ultimately causing problems such as excessive particle expansion or even rupture, thereby affecting the cycle and expansion performance of lithium-ion batteries. Solving these problems is crucial for improving the performance and safety of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material, a preparation method thereof, an electrochemical device, and an electronic device to improve the first Coulomb efficiency and safety performance of the electrochemical device and improve lithium plating on the negative electrode.

[0005] It should be noted that in the summary of the invention of this application, a lithium-ion battery is used as an example of the electrochemical device to explain this application, but the electrochemical device of this 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 material. The negative electrode material includes silicon-carbon particles, which include a first region and a second region. The first region is the region from the surface of the silicon-carbon particles to a depth of 40 nm from the surface of the silicon-carbon particles; the second region is the region from a depth of 60 nm from the surface of the silicon-carbon particles to a depth of 100 nm from the surface of the silicon-carbon particles; the silicon-carbon particles include silicon element, carbon element and oxygen element; based on the total number of atoms of silicon element, carbon element and oxygen element in the first region, the atomic percentage of oxygen element in the first region is A%, and 7.7 ≤ A ≤ 24.9; based on the total number of atoms of silicon element, carbon element and oxygen element in the second region, the atomic percentage of oxygen element in the second region is B%, and 5.5 ≤ B ≤ 8.8. By regulating the values of A and B within the above ranges, the oxygen element has a suitable atomic percentage in the first region and the second region, that is, the oxygen element has a suitable mass percentage on the surface and inside of the silicon-carbon particles. The nano-silicon can be effectively oxidized, a relatively stable interface is formed between the negative electrode sheet and the electrolyte, the consumption of the electrolyte is reduced, the energy density and the first Coulomb efficiency of the electrochemical device are improved. At the same time, it can also reduce the safety risks of lithium deposition and thermal failure, improve the safety performance of the electrochemical device, and improve lithium deposition on the negative electrode.

[0007] In an embodiment of the present application, 0.35 ≤ B / A ≤ 0.71. When the value of B / A is within the above range, the spatial distribution of oxygen atoms in the silicon-carbon particles can be adjusted, so that the oxidation degree of the nano-silicon outside the silicon-carbon particles is higher than that of the nano-silicon inside. While reducing the erosion of the nano-silicon on the surface of the silicon-carbon particles by the electrolyte, the electrochemical activity of the nano-silicon inside is maintained, further improving the first Coulomb efficiency and energy density of the electrochemical device, and further improving the safety performance of the electrochemical device and improving lithium deposition on the negative electrode. Preferably, 0.38 ≤ B / A ≤ 0.71. Further preferably, 0.53 ≤ B / A ≤ 0.71.

[0008] In an embodiment of the present application, based on the mass of the silicon-carbon particles, the mass percentage content W of silicon element in the silicon-carbon particles Si is 46.9% to 53.8%. When the mass percentage content W of silicon element in the silicon-carbon particles Si is within the above range, it can cooperate with the atomic percentage of oxygen element in the first region and the second region to further improve the oxidation degree of nano-silicon, increase the specific capacity of the silicon-carbon particles, improve the first Coulomb efficiency of the electrochemical device, and at the same time reduce the possibility of lithium dendrites formed due to the excessive mass percentage content of silicon element, and improve lithium deposition on the negative electrode.

[0009] In an embodiment of the present application, the true density ρ1 of the silicon-carbon particles is 1.98 g / cm 3 to 2.06 g / cm 3When the true density ρ1 of the silicon-carbon particles is within the above range, there are more internal pore structures inside the silicon-carbon particles, which is beneficial to storing lithium ions or sodium ions, thereby further improving the energy density and the first Coulombic efficiency of the electrochemical device.

[0010] In an embodiment of the present application, the negative electrode material further includes graphite, and the true density ρ2 of the negative electrode material is 2.19 g / cm 3 to 2.28 g / cm 3 When the true density ρ2 of the negative electrode material is within the above range, it is beneficial to improve the deposition density and deposition uniformity of lithium metal in the negative electrode sheet during the long-term cycling process, delay the growth of lithium dendrites, and reduce the side reaction between lithium metal and the electrolyte, thereby further improving the first Coulombic efficiency of the electrochemical device and improving lithium deposition on the negative electrode.

[0011] The second aspect of the present application provides a preparation method of the negative electrode material in any one of the foregoing embodiments. Among them, the preparation method of the silicon-carbon particles includes the following steps: (1) providing a porous carbon matrix, performing a first heat preservation treatment on the porous carbon matrix in an inert atmosphere, and then introducing a silane gas to obtain a first intermediate; the temperature T1 of the first heat preservation treatment is 400 °C to 600 °C, and the time t1 of the first heat preservation treatment is 0.5 h to 3 h; the time t2 of introducing the silane gas is 400 min to 900 min, and the flow rate V1 of the silane gas is 1.5 L / min to 3.5 L / min; the silane gas includes at least one of silane, disilane, trisilane, phenylsilane or tolylsilane; (2) performing a second heat preservation treatment on the first intermediate in an inert atmosphere, and then introducing an oxygen-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 80 °C to 200 °C, and the time t3 of the second heat preservation treatment is 0.5 h to 3 h; the time t4 of introducing the oxygen-containing gas is 30 min to 150 min, and the flow rate V2 of the oxygen-containing gas is 0.2 L / min to 1 L / min; the oxygen-containing gas includes at least one of oxygen, ozone or carbon dioxide; (3) performing a third heat preservation treatment on the second intermediate in an inert atmosphere, and then introducing a first compound to obtain silicon-carbon particles; the temperature T3 of the third heat preservation treatment is 500 °C to 650 °C, and the time t5 of the third heat preservation treatment is 0.5 h to 3 h; the time t6 of introducing the first compound is 240 min to 600 min, and the flow rate V3 of the first compound is 0.5 L / min to 3.5 L / min; the first compound includes at least one of acetylene, propylene or toluene. By controlling each preparation parameter within the above range, when the prepared negative electrode material is applied to an electrochemical device, the first Coulombic efficiency and safety performance of the electrochemical device can be improved, and lithium deposition on the negative electrode can be improved.

[0012] The third aspect of the present application provides an electrochemical device, wherein the electrochemical device includes a negative electrode tab and an electrolyte. The negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes the negative electrode material in any of the foregoing embodiments. The electrochemical device of the present application has good initial Coulomb efficiency and safety performance, and can improve lithium deposition on the negative electrode.

[0013] In one embodiment of the present application, the coating weight of the negative electrode material layer is 75 mg / 1540.25 mm 2 to 110 mg / 1540.25 mm 2 . When the coating weight of the negative electrode material layer is within the above range, the transport distance of ions and electrons in the negative electrode tab can be shortened, and lithium deposition on the negative electrode can be improved. Preferably, the coating weight of the negative electrode material layer is 80.6 mg / 1540.25 mm 2 to 100.5 mg / 1540.25 mm 2 .

[0014] In one embodiment of the present application, the electrolyte includes fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is F%, 5 ≤ F ≤ 15. When the value of F is within the above range, the initial Coulomb efficiency and safety performance of the electrochemical device can be further improved.

[0015] In one embodiment of the present application, the electrolyte includes 1,3 - propane sultone, and based on the mass of the electrolyte, the mass percentage content of 1,3 - propane sultone is P%, 2.5 ≤ F / P ≤ 6. When the value of F / P is within the above range, the proportion of substances that are difficult to decompose and generate gas in the SEI film can be increased, and the structure of the SEI film can be stabilized, thereby further improving the initial Coulomb efficiency and safety performance of the electrochemical device.

[0016] The fourth aspect of the present application provides an electronic device, wherein the electronic device includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good performance in use.

[0017] Advantages of the present application:

[0018] The present application provides a negative electrode material, a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material includes silicon-carbon particles, which include a first region and a second region. The first region is a region from the surface of the silicon-carbon particles to a depth of 40 nm from the surface of the silicon-carbon particles; the second region is a region from a depth of 60 nm from the surface of the silicon-carbon particles to a depth of 100 nm from the surface of the silicon-carbon particles; the silicon-carbon particles include silicon, carbon and oxygen elements; based on the total number of atoms of silicon, carbon and oxygen elements in the first region, the atomic percentage of oxygen element in the first region is A%, and 7.7 ≤ A ≤ 24.9; based on the total number of atoms of silicon, carbon and oxygen elements in the second region, the atomic percentage of oxygen element in the second region is B%, and 5.5 ≤ B ≤ 8.8. By adjusting the values of A and B within the scope of the present application, the oxygen element has a suitable atomic percentage in the first region and the second region, and the nano-silicon can be effectively oxidized, forming a relatively stable interface between the negative electrode sheet and the electrolyte, reducing the consumption of the electrolyte, improving the energy density and the first Coulomb efficiency of the electrochemical device, and at the same time, it can also reduce the safety risks of lithium deposition and thermal failure, improve the safety performance of the electrochemical device, and improve lithium deposition on the negative electrode.

[0019] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic structural diagram of silicon-carbon particles in an implementation scheme of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The purpose of the present application is to provide a negative electrode material, a preparation method thereof, an electrochemical device and an electronic device to improve the thermal shock safety performance of the electrochemical device. The specific technical solutions are as follows:

[0023] The first aspect of the present application provides a negative electrode material, wherein the negative electrode material includes silicon-carbon particles, and the silicon-carbon particles include a first region and a second region, as Figure 1As shown, the first region 11 is the region from the surface of the silicon-carbon particles to a depth of 40 nm from the surface of the silicon-carbon particles; the second region 12 is the region from a depth of 60 nm from the surface of the silicon-carbon particles to a depth of 100 nm from the surface of the silicon-carbon particles; the silicon-carbon particles include silicon, carbon, and oxygen elements; based on the total number of atoms of silicon, carbon, and oxygen elements in the first region, the atomic percentage of oxygen element in the first region is A%, 7.7 ≤ A ≤ 24.9; based on the total number of atoms of silicon, carbon, and oxygen elements in the second region, the atomic percentage of oxygen element in the second region is B%, 5.5 ≤ B ≤ 8.8. For example, the value of A can be 7.7, 8, 10, 12, 14, 14.5, 15.7, 15.9, 16.3, 16.6, 16.8, 18, 20.6, 22, 24, 24.9 or a range composed of any two of these values; the value of B can be 5.5, 6.4, 6.5, 6.6, 6.8, 6.9, 7.2, 7.3, 7.5, 7.9, 8.5, 8.8 or a range composed of any two of these values.

[0024] The inventors' research found that when the value of A and / or B is too low, for example, the value of A is lower than 7.7 and / or the value of B is lower than 5.5, the mass percentage of oxygen element on the surface and inside of the silicon-carbon particles is too low, and the nanosilicon is not effectively oxidized, resulting in the direct contact of highly active nanosilicon with the electrolyte, which will cause a large number of irreversible side reactions, resulting in excessive consumption of the electrolyte and causing the safety risks of lithium deposition and thermal failure; when the value of A and / or B is too high, for example, the value of A is higher than 24.9 and / or the value of B is higher than 8.8, the nanosilicon is largely oxidized, resulting in a low initial Coulombic efficiency of the material, which will lead to a low energy density of the electrochemical device. By regulating the values of A and B within the above range, the oxygen element has a suitable atomic percentage in the first region and the second region, the nanosilicon can be effectively oxidized, a relatively stable interface is formed between the negative electrode sheet and the electrolyte, the consumption of the electrolyte is reduced, the energy density and the initial Coulombic efficiency of the electrochemical device are improved; at the same time, it can also reduce the safety risks of lithium deposition and thermal failure, improve the safety performance of the electrochemical device, and improve lithium deposition on the negative electrode.

[0025] In an embodiment of the present application, 0.35 ≤ B / A ≤ 0.71. For example, the value of B / A can be 0.35, 0.38, 0.4, 0.43, 0.44, 0.45, 0.46, 0.5, 0.53, 0.55, 0.6, 0.65, 0.7, 0.71 or a range composed of any two of these numerical values. For example, in some embodiments of the present application, 0.38 ≤ B / A ≤ 0.71. In some embodiments of the present application, 0.53 ≤ B / A ≤ 0.71. When the value of B / A is within the above range, the spatial distribution of oxygen atoms in the silicon-carbon particles can be adjusted so that the oxidation degree of the nano-silicon outside the silicon-carbon particles is higher than that of the nano-silicon inside, while reducing the erosion of the nano-silicon on the surface of the silicon-carbon particles by the electrolyte and maintaining the electrochemical activity of the internal nano-silicon, further improving the initial Coulombic efficiency and energy density of the electrochemical device, as well as further improving the safety performance of the electrochemical device and improving lithium deposition on the negative electrode.

[0026] In an embodiment of the present application, based on the mass of the silicon-carbon particles, the mass percentage content W of silicon element in the silicon-carbon particles Si is 46.9% to 53.8%. For example, the mass percentage content W of silicon element in the silicon-carbon particles Si can be 46.9%, 47%, 48%, 49%, 49.7%, 49.9%, 50%, 50.1%, 50.2%, 50.4%, 50.5%, 50.6%, 51%, 52%, 53%, 53.8% or a range composed of any two of these numerical values. When the mass percentage content W of silicon element in the silicon-carbon particles Si is within the above range, the specific capacity of the silicon-carbon particles can be improved, the initial Coulombic efficiency of the electrochemical device can be improved, and at the same time, the possibility of forming lithium dendrites due to excessive mass percentage content of silicon element leading to lithium ion aggregation can be reduced, and lithium deposition on the negative electrode can be improved.

[0027] In an embodiment of the present application, based on the mass of the silicon-carbon particles, the mass percentage content of oxygen element in the silicon-carbon particles is 0.5% to 6.1%, and the mass percentage content of carbon element in the silicon-carbon particles is 40.1% to 52.5%. For example, the mass percentage content of oxygen element in the silicon-carbon particles can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.1% or a range composed of any two of these numerical values; the mass percentage content of carbon element in the silicon-carbon particles can be 40.1%, 42%, 44%, 46%, 48%, 50%, 52%, 52.5% or a range composed of any two of these numerical values.

[0028] In an embodiment of the present application, the true density ρ1 of the silicon-carbon particles is 1.98 g / cm 3 to 2.06 g / cm3 For example, the true density ρ1 of the silicon carbide particles can be 1.98 g / cm 3 、1.99 g / cm 3 、2.01 g / cm 3 、2.02 g / cm 3 、2.03 g / cm 3 、2.05 g / cm 3 、2.06 g / cm 3 or a range composed of any two of these values. The true density refers to the actual volume of solid matter within the volume of the material in an absolutely dense state, excluding internal pores or voids between particles. When the true density ρ1 of the silicon carbide particles is within the above range, the silicon carbide particles have more internal pore structures, which is beneficial for storing lithium ions or sodium ions, thereby further improving the energy density and initial Coulombic efficiency of the electrochemical device.

[0029] In an embodiment of the present application, the negative electrode material further includes graphite, and the true density ρ2 of the negative electrode material is 2.19 g / cm 3 to 2.28 g / cm 3 For example, the true density ρ2 of the negative electrode material can be 2.19 g / cm 3 、2.2 g / cm 3 、2.22 g / cm 3 、2.24 g / cm 3 、2.26 g / cm 3 、2.28 g / cm 3 or a range composed of any two of these values. The true density of the negative electrode material reflects the mixing ratio of the silicon carbide particles and graphite. When the true density ρ2 of the negative electrode material is within the above range, applying the negative electrode material to the negative electrode plate is beneficial for the negative electrode plate to provide a good conductive channel, uniform the current during charge and discharge, form a more uniform electric field, which is beneficial for improving the deposition density and deposition uniformity of lithium metal in the negative electrode plate during long-term cycling, delaying the growth of lithium dendrites, reducing the side reaction between lithium metal and the electrolyte, thereby further improving the initial Coulombic efficiency of the electrochemical device and improving lithium metal deposition on the negative electrode.

[0030] In an embodiment of the present application, based on the mass of the negative electrode material, the mass percentage content of the silicon carbide particles is 5% to 15%, and the mass percentage content of graphite is 85% to 95%. For example, based on the mass of the negative electrode material, the mass percentage content of the silicon carbide particles can be 5%, 7%, 9%, 11%, 13%, 15% or a range composed of any two of these values; based on the mass of the negative electrode material, the mass percentage content of graphite can be 85%, 87%, 89%, 91%, 93%, 95% or a range composed of any two of these values.

[0031] The second aspect of the present application provides a method for preparing the negative electrode material in any of the foregoing embodiments. Among them, the method for preparing the silicon-carbon particles includes the following steps: (1) providing a porous carbon matrix, subjecting the porous carbon matrix to a first heat preservation treatment in an inert atmosphere, and then introducing a silane-containing gas to obtain a first intermediate; the temperature T1 of the first heat preservation treatment is 400°C to 600°C, and the time t1 of the first heat preservation treatment is 0.5 h to 3 h; the time t2 for introducing the silane-containing gas is 400 min to 900 min, and the flow rate V1 of the silane-containing gas is 1.5 L / min to 3.5 L / min; the silane-containing gas includes at least one of silane, disilane, trisilane, phenylsilane or tolylsilane; (2) subjecting the first intermediate to a second heat preservation treatment in an inert atmosphere, and then introducing an oxygen-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 80°C to 200°C, and the time t3 of the second heat preservation treatment is 0.5 h to 3 h; the time t4 for introducing the oxygen-containing gas is 30 min to 150 min, and the flow rate V2 of the oxygen-containing gas is 0.2 L / min to 1 L / min; the oxygen-containing gas includes at least one of oxygen, ozone or carbon dioxide; (3) subjecting the second intermediate to a third heat preservation treatment in an inert atmosphere, and then introducing a first compound to obtain silicon-carbon particles; the temperature T3 of the third heat preservation treatment is 500°C to 650°C, and the time t5 of the third heat preservation treatment is 0.5 h to 3 h; the time t6 for introducing the first compound is 240 min to 600 min, and the flow rate V3 of the first compound is 0.5 L / min to 3.5 L / min; the first compound includes at least one of acetylene, propylene or toluene. By regulating each preparation parameter within the above range, when the prepared negative electrode material is applied to an electrochemical device, the initial Coulomb efficiency and safety performance of the electrochemical device can be improved, and negative electrode lithium plating can be improved.

[0032] In one embodiment of the present application, the negative electrode material can be obtained by uniformly mixing silicon-carbon particles and a carbon material in a mass ratio of 5:95 to 15:85.

[0033] The present application has no particular limitation on the inert atmosphere, as long as the purpose of the present application can be achieved. For example, the inert atmosphere can be at least one of nitrogen, argon or helium.

[0034] The present application has no particular limitation on the method for regulating the value of A, as long as the purpose of the present application can be achieved. For example, the value of A can be regulated by regulating the time t4 for introducing the oxygen-containing gas. Exemplarily, when t4 increases, the value of A increases, and when t4 decreases, the value of A decreases.

[0035] The method for regulating the value of B in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the value of B can be regulated by regulating the time t4 for introducing the oxygen-containing gas. Exemplarily, when t4 decreases, the value of B decreases, and when t4 increases, the value of B increases.

[0036] This application has no particular limitation on the method for regulating the value of B / A, as long as the purpose of this application can be achieved. For example, the value of B / A can be regulated by regulating the time t4 for introducing the oxygen-containing gas, and the regulation method is as described above.

[0037] This application has no particular limitation on the method for regulating the mass percentage content W of silicon element in the silicon-carbon particles Si as long as the purpose of this application can be achieved. For example, the mass percentage content W of silicon element in the silicon-carbon particles can be regulated by regulating the time t2 for introducing the silane gas. Si Exemplarily, when t2 increases, W Si increases, and when t2 decreases, W Si decreases.

[0038] This application has no particular limitation on the method for regulating the true density ρ1 of the silicon-carbon particles, as long as the purpose of this application can be achieved. For example, the mass percentage content W of silicon element in the silicon-carbon particles Si , the first heat preservation treatment temperature T1 or the time t2 for introducing the silane gas will affect the true density ρ1 of the silicon-carbon particles. Alternatively, the true density of the prepared silicon-carbon particles can also be tested by the "true density test" method in this application, and the silicon-carbon particles with the desired true density can be selected.

[0039] This application has no particular limitation on the method for regulating the true density ρ2 of the negative electrode material, as long as the purpose of this application can be achieved. For example, the true density ρ2 of the negative electrode material can be regulated by regulating the mass ratio of the silicon-carbon particles to the graphite. Exemplarily, when the mass ratio of the silicon-carbon particles to the graphite increases, ρ2 decreases, and when the mass ratio of the silicon-carbon particles to the graphite decreases, ρ2 increases.

[0040] In this application, the porous carbon matrix can be a commercially available porous carbon matrix according to needs or obtained by preparation. The preparation method of the porous carbon matrix in this application is not particularly limited as long as the purpose of this application can be achieved. For example, the preparation method of the porous carbon matrix can include but is not limited to the following steps: adding a phenolic compound, formaldehyde, and ammonia into water and mixing them evenly, and then carrying out a temperature-raising reaction to obtain the porous carbon matrix. Among them, the molar ratio of the phenolic compound, formaldehyde, and ammonia can be 1:(1.5 to 2.6):(0.006 to 0.015); the phenolic compound can include but is not limited to at least one of phenol, cresol, nonylphenol, aralkylphenol, cashew phenol, octylphenol, bisphenol A, or xylenol; the temperature of the temperature-raising reaction can be 90°C to 120°C, and the time of the temperature-raising reaction can be 1 h to 5 h.

[0041] The third aspect of this application provides an electrochemical device. Among them, the electrochemical device includes a negative electrode plate and an electrolyte. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes the negative electrode material in any of the foregoing embodiments. The electrochemical device of this application has good initial Coulomb efficiency and safety performance, and can improve lithium deposition on the negative electrode.

[0042] In one embodiment of this application, the coating weight CW of the negative electrode material layer is 75 mg / 1540.25 mm 2 to 110 mg / 1540.25 mm 2 . For example, the coating weight CW of the negative electrode material layer can be 75 mg / 1540.25 mm 2 , 80.6 mg / 1540.25 mm 2 , 85 mg / 1540.25 mm 2 , 90 mg / 1540.25 mm 2 , 95 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 100.5 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 or a range composed of any two of these values. For example, in some embodiments of this application, the coating weight CW of the negative electrode material layer is 80.6 mg / 1540.25 mm 2 to 100.5 mg / 1540.25 mm 2 . When the coating weight CW of the negative electrode material layer is within the above range, the transmission distance of ions and electrons in the negative electrode plate can be shortened, and lithium deposition on the negative electrode can be improved.

[0043] The present application does not particularly limit the method for regulating the coating weight CW of the negative electrode material layer, as long as the object of the present application can be achieved. For example, the coating weight CW of the negative electrode material layer can be regulated by regulating the coating amount of the negative electrode material layer slurry. Exemplarily, when the coating amount of the negative electrode material layer slurry increases, the value of CW increases; when the coating amount of the negative electrode material layer slurry decreases, the value of CW decreases.

[0044] The present application does not particularly limit the negative electrode current collector, as long as the object of the present 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, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc.

[0045] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the object of the present application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The above-mentioned conductive carbon black may include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The above-mentioned carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above-mentioned metal materials may include, but is not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder may include, but is not limited to, at least one of polyacrylic acid, methyl polyacrylate, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. The present application does not particularly limit the mass ratio of the negative electrode material, the conductive agent, and the binder in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0046] In some embodiments of the present application, the negative electrode material layer may further include a binder and a thickener. The present application does not particularly limit the types of the binder and the thickener, as long as the purpose of the present application can be achieved. For example, it may be at least one of the aforementioned binders. The thickener may include but is not limited to at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode material, the binder, and the thickener in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0047] The present application does not particularly limit the thickness of the negative electrode current collector and the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 100 μm.

[0048] Optionally, the negative electrode plate 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 present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and the binder in the conductive layer, as long as the purpose of the present application can be achieved. For example, it may be at least one of the aforementioned conductive agent and the aforementioned binder.

[0049] In one embodiment of the present application, the electrolyte includes fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is F%, 5 ≤ F ≤ 15. For example, the value of F can be 5, 7, 9, 11, 13, 15, or a range composed of any two of these values. When the value of F is within the above range, the electrolyte can have a lower viscosity and a higher lithium ion conductivity, which is beneficial to the migration of ions in the electrolyte; at the same time, it is more beneficial to cooperate with the atomic percentage of oxygen elements in the first region of the silicon-carbon particles, form a stable and relatively uniform solid electrolyte interface (SEI) film on the surface of the silicon-carbon particles, further reduce the side reactions of the electrolyte, reduce the gas generation at the positive electrode interface and the negative electrode interface, make the positive electrode interface and the negative electrode interface have better interface stability, reduce the influence of gas molecules on the positive electrode interface and the negative electrode interface, and thus further improve the safety performance of the electrochemical device.

[0050] In one embodiment of the present application, the electrolyte includes 1,3 - propane sultone, and based on the mass of the electrolyte, the mass percentage content of 1,3 - propane sultone is P%, 0.83 ≤ P ≤ 6. For example, the value of P can be 0.83, 1, 2, 3, 4, 5, 6, or a range composed of any two of these values.

[0051] In an embodiment of the present application, the electrolyte includes 1,3 - propane sultone. Based on the mass of the electrolyte, the mass percentage content of 1,3 - propane sultone is P%, and 2.5 ≤ F / P ≤ 6. For example, the value of F / P can be 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range composed of any two of these values. When the value of F / P is within the above range, the reduction potential of fluorinated ethylene carbonate containing fluorine and 1,3 - propane sultone containing sulfur is relatively high, and it will preferentially reduce on the surface of silicon - carbon particles over non - aqueous solvents (such as carbonate compounds), matching the atomic percentage of oxygen elements in the first region of the silicon - carbon particles, and forming an appropriate amount of inorganic components lithium fluoride or lithium sulfate on the surface of the silicon - carbon particles. The above - mentioned inorganic components are distributed on the surface of the negative electrode material layer, which can improve the ionic conductivity and toughness of the SEI film, thereby further improving the safety performance of the electrochemical device.

[0052] In the present application, the electrolyte includes a lithium salt and a non-aqueous solvent. There is no particular limitation on the lithium salt in the present application, as long as the object of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, or Li2SiF6. There is no particular limitation on the mass percentage content of the lithium salt in the electrolyte in the present application, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the lithium salt is 8% to 20%. There is no particular limitation on the non-aqueous solvent in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. There is no particular limitation on the mass percentage content of the non-aqueous solvent in the electrolyte in the present application, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the non-aqueous solvent may be 59% to 86.17%.

[0053] In one embodiment of the present application, the electrolyte may include fluoroethylene carbonate, 1,3 - propane sultone, a lithium salt, and a non - aqueous solvent. The mass percentage contents of fluoroethylene carbonate, 1,3 - propane sultone, and the lithium salt are as described above, and the mass percentage content of the non - aqueous solvent is 59% to 86.17%. The electrochemical device including the above - mentioned electrolyte has good initial Coulombic efficiency and safety performance, and can improve lithium deposition on the negative electrode.

[0054] In the present application, the electrochemical device includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above - mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector or a partial area of the surface of the positive electrode current collector. There is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0055] The present application has no special limitation on the positive electrode current collector as long as the purpose of the present application can be achieved. For example, a metal foil or a composite current collector can be used. For example, the metal foil may include, but is not limited to, aluminum foil; the composite current collector can be obtained by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0056] In the present application, the positive electrode material layer includes a positive electrode active material. The present application has no special limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganate (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium - rich manganese - based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, lithium titanate, lithium nickel manganese aluminate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, or at least one of spinel - type lithium nickel manganate.

[0057] In the present application, the positive electrode material layer may further include a conductive agent and a binder. The present application has no special limitation on the types of the conductive agent and the binder as long as the purpose of the present application can be achieved. For example, it can be at least one of the aforementioned conductive agent and the aforementioned binder. The present application has no special limitation on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0058] The present application has no particular limitation on the thickness of the positive current collector and the positive electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 80 μm.

[0059] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive 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. The present application has no particular limitation on the conductive agent and the binder in the conductive layer. For example, it may be at least one of the aforementioned conductive agents and the aforementioned binders.

[0060] In the present application, the electrochemical device further includes a separator. The present application has no particular limitation on the separator, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0061] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular limitation on the inorganic particles. For example, the inorganic particles may include 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 or barium sulfate. The present application has no particular limitation on the binder. For example, the binder may be at least one of the aforementioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0062] In the present application, the electrochemical device further includes a housing for accommodating the positive electrode plate, the separator, the negative electrode plate, and the electrolyte, as well as other components known in the field of electrochemistry. The present application does not limit the above-mentioned other components. The present application has no particular limitation on the housing, and it can be a housing well-known in the art as long as it can achieve the purpose of the present application. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. The present application does not limit the type of metal, and a metal hard shell housing known in the art can be used as long as it can achieve the purpose of the present application. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0063] The present application has no particular limitation on the type of the electrochemical device, and it can include any device that undergoes an electrochemical reaction. In the present application, the electrochemical device can include, but is not limited to: a lithium metal electrochemical device, a lithium ion electrochemical device (lithium ion battery), a lithium polymer electrochemical device, or a lithium ion polymer electrochemical device (lithium ion polymer battery), etc.

[0064] The preparation process of the electrochemical device of the present application is well-known to those skilled in the art, and the present application has no particular limitation. For example, the preparation process of the electrochemical device can include, but is not limited to, the following steps: stacking the positive electrode plate, the separator, and the negative electrode plate in sequence, and performing operations such as winding and folding according to needs to obtain a wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. Or, stacking the positive electrode plate, the separator, and the negative electrode plate in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the housing according to needs to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0065] The fourth aspect of the present application provides an electronic device, wherein the electronic device includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good performance in use.

[0066] 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 head-mounted stereo earphone, a video recorder, a liquid crystal 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 machine, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0067] Example

[0068] Hereinafter, examples and comparative examples will be given to more specifically illustrate the embodiments 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.

[0069] Testing method and device:

[0070] Test of the values of A and B:

[0071] The silicon-carbon particles in each example or comparative example are etched using an argon ion single-atom beam, and the etching depth is from 0 nm to 40 nm. Then, the atomic percentage A of oxygen element in the first region from the sample surface to a depth of 40 nm from the sample surface is measured. The above silicon-carbon particles are continuously etched using an argon ion single-atom beam, and the etching depth is from 60 nm to 100 nm. Then, the atomic percentage B of oxygen element in the second region from a depth of 60 nm from the sample surface to a depth of 100 nm from the sample surface is measured. The equipment used for the test is a PHI 5000 Versaprobe II type X-ray photoelectron spectrometer, and the X-ray excitation source is Al target Kα ray.

[0072] Test of the mass percentage content of silicon element:

[0073] The mass percentage content W of silicon element in the silicon-carbon particles in each example or comparative example is measured by area scanning using an energy dispersive spectrometer (EDS) equipped with a scanning electron microscope of model OXFORD·EDS under the conditions of an acceleration voltage of 10 kV and an emission current of 10 mA. Si .

[0074] True density test:

[0075] Place the samples of silicon-carbon particles or anode materials prepared in each example and comparative example in a true density tester (model AccuPyc II 1340) to measure the true density ρ1 of the silicon-carbon particles and the true density ρ2 of the anode material.

[0076] Measurement of the initial Coulombic efficiency:

[0077] At 25 °C, discharge the lithium-ion batteries in the examples or comparative examples at a constant current of 0.2C to 3.0V, let them stand for 5 minutes, charge them at a constant current of 0.2C to 4.45V, charge them at a constant voltage of 4.45V until the current reaches 0.05C, and then let them stand for 5 minutes. Measure the first-cycle charge capacity and the first-cycle discharge capacity of the lithium-ion batteries, and calculate the initial Coulombic efficiency according to the following formula:

[0078] Initial Coulombic efficiency (%) = First-cycle charge capacity / First-cycle discharge capacity × 100%.

[0079] Lithium plating test:

[0080] Let the lithium-ion batteries in the examples or comparative examples stand for 5 minutes at a test temperature of 0 °C, charge them at a constant current of 0.2C to 4.45V, and then charge them at a constant voltage of 4.45V until the current reaches 0.05C. At this time, the lithium-ion batteries reach a fully charged state; let them stand for 5 minutes, and then discharge them at a constant current of 0.2C to 3.0V and let them stand for 5 minutes. After repeating the above charge-discharge process 10 times, fully charge the lithium-ion batteries, disassemble them in a drying room, and take pictures to record the state of the negative electrode sheets.

[0081] Judgment of the degree of lithium plating: It is judged according to the state of the fully charged and disassembled negative electrode sheets. When the area showing gray on the negative electrode sheet < 2%, it is judged as no lithium plating; when the gray area on the negative electrode sheet ≥ 2% and < 20%, it is judged as slight lithium plating; when the gray area on the negative electrode sheet ≥ 20% and < 30%, it is judged as lithium plating; when the gray area on the negative electrode sheet ≥ 30%, it is judged as severe lithium plating.

[0082] Thermal shock test:

[0083] Take 5 lithium-ion batteries from each group of examples or comparative examples. At 25 °C, charge the lithium-ion batteries at a constant current of 0.2C to 4.45V, and then charge them at a constant voltage of 4.45V until the current reaches 0.05C. At this time, the lithium-ion batteries reach a fully charged state; then place the lithium-ion batteries in an incubator at 135 °C for 30 minutes. The passing standard for the thermal shock test is that the lithium-ion batteries do not catch fire or explode during the thermal shock test. Thermal shock test passing rate (%) = Number of lithium-ion batteries that do not catch fire or explode during the thermal shock test / 5 × 100%.

[0084] The safety performance of a lithium-ion battery is characterized by the passing rate of its thermal shock test. The higher the passing rate of the thermal shock test of the lithium-ion battery, the better its safety performance.

[0085] Example 1-1

[0086] <Preparation of Anode Material>

[0087] (1) Provide a porous carbon matrix, perform a first heat preservation treatment on the porous carbon matrix under a nitrogen atmosphere, and then introduce a silane gas to obtain a first intermediate. Among them, the temperature T1 of the first heat preservation treatment is 500 °C, the time t1 of the first heat preservation treatment is 1.5 h; the time t2 for introducing the silane gas is 550 min; the flow rate V1 of the silane gas is 2.5 L / min; the silane gas is silane.

[0088] (2) Perform a second heat preservation treatment on the first intermediate under a nitrogen atmosphere, and then introduce an oxygen-containing gas to obtain a second intermediate. Among them, the temperature T2 of the second heat preservation treatment is 140 °C, the time t3 of the second heat preservation treatment is 1.5 h; the time t4 for introducing the oxygen-containing gas is 90 min, the flow rate V2 of the oxygen-containing gas is 0.6 L / min; the oxygen-containing gas is oxygen.

[0089] (3) Perform a third heat preservation treatment on the second intermediate under a nitrogen atmosphere, and then introduce a first compound to obtain silicon-carbon particles. Among them, the temperature T3 of the third heat preservation treatment is 575 °C, the time t5 of the third heat preservation treatment is 1.5 h; the time t6 for introducing the first compound is 420 min, the flow rate V3 of the first compound is 2 L / min; the first compound is acetylene.

[0090] (4) Mix the silicon-carbon particles and graphite evenly according to a mass ratio of 15:85 to obtain the anode material.

[0091] <Preparation of Anode Plate>

[0092] Mix the above-prepared anode material, binder polymethyl acrylate, and thickener carboxymethyl cellulose according to a mass ratio of 98:1.6:0.4, dissolve them in deionized water as the anode solvent, mix evenly, and make an anode material layer slurry with a solid content of 45 wt%. Uniformly coat the anode material layer slurry on one surface of a 6-μm-thick anode current collector copper foil, and perform a drying treatment at 85 °C for 4 h to obtain an anode plate with a single-sided coated anode material layer. The coating weight CW of the anode material layer is 90.5 mg / 1540.25 mm 2。Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. After cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 12 hours to obtain a negative electrode sheet with a specification of 76.6 mm × 875 mm for use. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 37 μm.

[0093] <Preparation of the positive electrode sheet>

[0094] Mix the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) according to a mass ratio of 96.3:2.2:1.5, add the positive electrode solvent N-methylpyrrolidone, and stir evenly to obtain a positive electrode material layer slurry with a solid content of 75 wt%. Coat the positive electrode material layer slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, and dry it at 85 °C to obtain a positive electrode sheet with a positive electrode material layer coated on one side. The coating weight of the positive electrode material layer is 228.0 mg / 1540.25 mm 2 。Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a positive electrode material layer coated on both sides. After cold pressing, slicing, and slitting, it is dried under vacuum conditions at 85 °C for 4 hours to obtain a positive electrode sheet with a specification of 74 mm × 867 mm for use. Among them, the thickness of the single-sided positive electrode material layer after cold pressing is 35.5 μm.

[0095] <Preparation of the electrolyte>

[0096] In an argon atmosphere glove box with a water content < 10 ppm, mix ethylene carbonate (EC) and dimethyl carbonate (DMC) evenly according to a mass ratio of 1:1 to obtain a basic solvent. Add fluoroethylene carbonate, 1,3-propane sultone, and the lithium salt LiPF6 to the basic solvent and stir evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is 10%, the mass percentage content P of 1,3-propane sultone is 2.5%, the mass percentage content of LiPF6 is 12.5%, and the balance is the basic solvent.

[0097] <Separator>

[0098] Use a polypropylene (PP) separator with a thickness of 4.5 μm.

[0099] <Preparation of the lithium-ion battery>

[0100] Stack the positive electrode sheet after welding the tab, the separator, and the negative electrode sheet after welding the tab in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and then wind to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film, dry it in a vacuum oven at 80°C for 12 hours to remove moisture, inject the above-prepared electrolyte, and obtain a lithium-ion battery through processes such as vacuum packaging, standing, formation, degassing, and trimming.

[0101] Examples 1-2 to 1-5

[0102] Except that in the <preparation of the negative electrode material>, the time t4 for introducing the oxygen-containing gas is adjusted so that the values of A and B are as shown in Table 1, the rest is the same as Example 1-1.

[0103] Examples 1-6 and 1-7

[0104] Except that in the <preparation of the negative electrode material>, the time t2 for introducing the silane gas is adjusted so that the mass percentage content W of silicon element Si is as shown in Table 2, the rest is the same as Example 1-1.

[0105] Example 1-8

[0106] Except that in the <preparation of the negative electrode material>, disilane is used as the silane gas and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0107] Example 1-9

[0108] Except that in the <preparation of the negative electrode material>, carbon dioxide is used as the oxygen-containing gas and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0109] Example 1-10

[0110] Except that in the <preparation of the negative electrode material>, propylene is used as the first compound and the relevant preparation parameters are adjusted according to Table 1, the rest is the same as Example 1-1.

[0111] Example 1-11

[0112] Except that in the <preparation of the negative electrode material>, the mass ratio of silicon-carbon particles to graphite is adjusted so that the true density ρ2 of the negative electrode material is as shown in Table 2, the rest is the same as Example 1-1.

[0113] Examples 1-12 to 1-15

[0114] Except that in the <preparation of the negative electrode material>, the coating amount of the negative electrode material layer slurry is adjusted so that the coating weight CW of the negative electrode material layer is as shown in Table 2, the rest is the same as Example 1-1.

[0115] Examples 2-1 to 2-4

[0116] Except that the mass percentage contents of the components of the electrolyte are adjusted according to Table 3 in <Preparation of the electrolyte>, the rest is the same as that of Example 1-1. Among them, when the mass percentage content of at least one of vinyl fluorocarbonate or 1,3-propane sultone changes, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the lithium salt and the mass ratio of the components of the base solvent remain unchanged.

[0117] Comparative Examples 1 to 4

[0118] Except that the preparation parameters are adjusted according to Table 1 in <Preparation of the negative electrode material> so that the values of A and B are as shown in Table 1, the rest is the same as that of Example 1-1.

[0119] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 3.

[0120] Table 1

[0121]

[0122] Table 2

[0123]

[0124]

[0125] It can be seen from Example 1-1 to Example 1-15 and Comparative Examples 1 to 4 that when the values of A, B and the preparation parameters of the negative electrode material are within the scope of this application, when the negative electrode material of this application is applied to a lithium ion battery, the initial Coulomb efficiency and the passing rate of the thermal shock test of the obtained lithium ion battery are relatively high, and lithium deposition is improved. It shows that the lithium ion battery of this application has a relatively high initial Coulomb efficiency and good safety performance, and lithium deposition on the negative electrode is improved.

[0126] It can be seen from Table 1 and Table 2 that when the value of B / A is within the scope of this application, the initial Coulomb efficiency and the passing rate of the thermal shock test of the obtained lithium ion battery are relatively high, and lithium deposition is improved. It shows that the initial Coulomb efficiency of the lithium ion battery of this application is improved, and at the same time it has good safety performance, and lithium deposition on the negative electrode is improved.

[0127] It can be seen from Table 1 and Table 2 that when the value of W Si is within the scope of this application, the initial Coulomb efficiency and the passing rate of the thermal shock test of the obtained lithium ion battery are relatively high, and lithium deposition is improved. It shows that the initial Coulomb efficiency of the lithium ion battery of this application is improved, and lithium deposition on the negative electrode is improved, and at the same time it also has good safety performance.

[0128] As can be seen from Table 1 and Table 2, when the value of ρ1 is within the scope of the present application, the initial Coulombic efficiency of the lithium-ion battery obtained and the passing rate of the thermal shock test are relatively high, and lithium plating is improved. This shows that the initial Coulombic efficiency of the lithium-ion battery of the present application is improved, and at the same time, it has good safety performance, and lithium plating on the negative electrode is improved.

[0129] As can be seen from Table 1 and Table 2, when the value of ρ2 is within the scope of the present application, the initial Coulombic efficiency of the lithium-ion battery obtained and the passing rate of the thermal shock test are relatively high, and lithium plating is improved. This shows that the initial Coulombic efficiency of the lithium-ion battery of the present application is improved, and lithium plating on the negative electrode is improved, and at the same time, it also has good safety performance.

[0130] As can be seen from Table 1 and Table 2, when the value of CW is within the scope of the present application, the initial Coulombic efficiency of the lithium-ion battery obtained and the passing rate of the thermal shock test are relatively high, and lithium plating is improved. This shows that lithium plating on the negative electrode of the lithium-ion battery of the present application is improved, and at the same time, the initial Coulombic efficiency is improved, and it also has good safety performance.

[0131] Table 3

[0132]

[0133] As can be seen from Table 3, when the value of F is within the scope of the present application, the initial Coulombic efficiency of the lithium-ion battery obtained and the passing rate of the thermal shock test are relatively high, and lithium plating is improved. This shows that the safety performance of the lithium-ion battery of the present application is improved, and at the same time, it also has a relatively high initial Coulombic efficiency, and lithium plating on the negative electrode is improved.

[0134] As can be seen from Table 3, when the value of F / P is within the scope of the present application, the initial Coulombic efficiency of the lithium-ion battery obtained and the passing rate of the thermal shock test are relatively high, and lithium plating is improved. This shows that the safety performance of the lithium-ion battery of the present application is improved, and at the same time, it also has a relatively high initial Coulombic efficiency, and lithium plating on the negative electrode is improved.

[0135] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method or article.

[0136] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0137] 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 within the scope of protection of the present application.

Claims

1. A negative electrode material, wherein: The negative electrode material includes silicon carbon particles, and the silicon carbon particles include a first region and a second region, wherein the first region is a region from the surface of the silicon carbon particles to a depth of 40 nm from the surface of the silicon carbon particles; and the second region is a region from a depth of 60 nm from the surface of the silicon carbon particles to a depth of 100 nm from the surface of the silicon carbon particles; The silicon-carbon particles include silicon, carbon and oxygen; Based on the total number of atoms of silicon, carbon and oxygen in the first region, the atomic percentage of oxygen in the first region is A%, 7.7≤A≤24.9; Based on the total number of atoms of silicon, carbon and oxygen in the second region, the atomic percentage of oxygen in the second region is B%, and 5.5≤B≤8.

8.

2. The negative electrode material according to claim 1, wherein 0.35≤B / A≤0.

71.

3. The negative electrode material according to claim 1, wherein 0.38≤B / A≤0.71, preferably, 0.53≤B / A≤0.

71.

4. The negative electrode material according to claim 1, wherein Based on the mass of the silicon-carbon particles, the mass percentage of silicon in the silicon-carbon particles is W Si It ranges from 46.9% to 53.8%.

5. The negative electrode material according to claim 1, wherein The negative electrode material satisfies at least one of the following conditions: (1) The true density ρ1 of the silicon carbon particles is 1.98 g / cm 3 Up to 2.06g / cm 3 ; (2) The negative electrode material also includes graphite, and the true density ρ2 of the negative electrode material is 2.19 g / cm 3 Up to 2.28g / cm 3 .

6. A method for preparing the negative electrode material according to any one of claims 1 to 5, wherein: The method for preparing the silicon-carbon particles comprises the following steps: (1) providing a porous carbon substrate, subjecting the porous carbon substrate to a first heat preservation treatment under an inert atmosphere, and then introducing a silane-containing gas to obtain a first intermediate; the temperature T1 of the first heat preservation treatment is 400° C. to 600° C., and the time t1 of the first heat preservation treatment is 0.5 h to 3 h; the time t2 of introducing the silane-containing gas is 400 min to 900 min, and the flow rate V1 of the silane-containing gas is 1.5 L / min to 3.5 L / min; the silane-containing gas includes at least one of monosilane, disilane, trisilane, phenylsilane or tolylsilane; (2) subjecting the first intermediate to a second heat preservation treatment under an inert atmosphere, and then introducing an oxygen-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 80° C. to 200° C., and the time t3 of the second heat preservation treatment is 0.5 h to 3 h; the time t4 of introducing the oxygen-containing gas is 30 min to 150 min, and the flow rate V2 of the oxygen-containing gas is 0.2 L / min to 1 L / min; the oxygen-containing gas comprises at least one of oxygen, ozone or carbon dioxide; (3) The second intermediate is subjected to a third insulation treatment under an inert atmosphere, and then the first compound is introduced to obtain the silicon-carbon particles; the temperature T3 of the third insulation treatment is 500°C to 650°C, and the time t5 of the third insulation treatment is 0.5h to 3h; the time t6 of introducing the first compound is 240min to 600min, and the flow rate V3 of the first compound is 0.5L / min to 3.5L / min; the first compound includes at least one of acetylene, propylene or toluene.

7. An electrochemical device, wherein: The electrochemical device comprises a negative electrode sheet and an electrolyte. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer comprises the negative electrode material according to any one of claims 1 to 5.

8. The electrochemical device according to claim 7, wherein: The coating weight of the negative electrode material layer is 75 mg / 1540.25 mm 2 Up to 110mg / 1540.25mm 2 Preferably, the coating weight of the negative electrode material layer is 80.6 mg / 1540.25 mm 2 Up to 100.5mg / 1540.25mm 2 .

9. The electrochemical device according to claim 7, wherein: The electrolyte includes fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate is F% based on the mass of the electrolyte, 5≤F≤15.

10. The electrochemical device according to claim 9, wherein: The electrolyte includes 1,3-propane sultone, and based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone is P%, and 2.5≤F / P≤6.

11. An electronic device comprising the electrochemical device according to any one of claims 7 to 10.

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