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 silicon elements and carbon elements; based on the total number of atoms of the silicon element and the carbon element in the first area, the percentage of the number of atoms of the silicon element in the first area is A%, and A is larger than or equal to 19.4 and smaller than or equal to 36.7; based on the total number of atoms of the silicon element and the carbon element in the second area, the percentage of the number of atoms of the silicon element in the second area is B%, and B is larger than or equal to 23.8 and smaller than or equal to 31.8. By regulating the values of A and B in the application range, the fast charging performance and room-temperature storage performance of the electrochemical device can be improved, and the lithium precipitation of the negative electrode is improved.

Description

Technical Field

[0001] The present 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 materials are considered to be one of the most promising graphite alternative materials due to their ultra-high theoretical specific capacity and suitable working voltage.

[0003] However, when silicon materials are used as negative electrode materials, they are prone to excessive expansion rates during charging, which leads to a decline in the cycling performance of lithium-ion batteries. One of the main reasons for the above problems is the uneven distribution of silicon elements in silicon material particles. The regions with high silicon concentration have a larger expansion rate after lithium intercalation, while the regions with low silicon concentration have a relatively smaller expansion rate after lithium intercalation. This non-uniformity results in uneven lithium intercalation stress distribution inside the silicon material particles, ultimately causing the problem of excessive expansion or even rupture of the silicon material particles, thereby affecting the cycling and expansion performance of lithium-ion batteries. Solving these problems is crucial for improving the performance of lithium-ion batteries. Summary of the Invention

[0004] 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 fast charging performance and room temperature storage performance of the electrochemical device and to improve lithium plating on the negative electrode.

[0005] It should be noted that in the summary of the invention of the present application, lithium-ion batteries are used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to 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 and carbon element; based on the total number of silicon and carbon atoms in the first region, the atomic percentage of silicon element in the first region is A%, and 19.4 ≤ A ≤ 36.7; based on the total number of silicon and carbon atoms in the second region, the atomic percentage of silicon element in the second region is B%, and 23.8 ≤ B ≤ 31.8. By adjusting the values of A and B within the above ranges, the specific capacity of the silicon-carbon particles can be increased, and the expansion of the silicon-carbon particles during cycling can be reduced; at the same time, the lithium intercalation stress inside and outside the silicon-carbon particles can be made more uniform, reducing the risk of lithium dendrite formation due to excessive local silicon element content, improving lithium deposition on the negative electrode, and enhancing the fast charging performance and room temperature storage performance of the electrochemical device.

[0007] In an embodiment of the present application, 0.66 ≤ B / A ≤ 1.58. When the value of B / A is within the above range, lithium deposition on the negative electrode can be improved, and the fast charging performance and room temperature storage performance of the electrochemical device can be further enhanced.

[0008] In an embodiment of the present application, 0.82 ≤ B / A ≤ 1.29. When the value of B / A is within the above range, lithium deposition on the negative electrode can be further improved, and the fast charging performance and room temperature storage performance of the electrochemical device can be further enhanced.

[0009] In an embodiment of the present application, the average particle size D1 of the silicon-carbon particles is 5.5 μm to 8.7 μm. By adjusting the average particle size D1 of the silicon-carbon particles within the above range, the lithium intercalation ability of the silicon-carbon particles can be increased, the expansion performance and cycling performance of the electrochemical device can be improved, and at the same time, the lithium ion transport efficiency can be increased, the kinetic performance of the electrochemical device can be enhanced, and lithium deposition on the negative electrode can be improved.

[0010] In an embodiment of the present application, the powder resistivity ρ of the silicon-carbon particles is 0.25 Ω·cm to 8.7 Ω·cm. When ρ is within the above range, the electron transport speed in the negative electrode material layer can be increased, the internal resistance of the electrochemical device can be reduced, and the utilization rate of the negative electrode active material can be improved, thereby enhancing the fast charging performance of the electrochemical device.

[0011] 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 380°C to 460°C, the time t1 of the first heat preservation treatment is 1 h to 3 h; the time t2 for introducing the silane-containing gas is 400 min to 1600 min; the flow rate V1 of the silane-containing gas is 0.5 L / min to 2 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 a first compound to obtain silicon-carbon particles; the temperature T2 of the second heat preservation treatment is 480°C to 600°C, the time t3 of the second heat preservation treatment is 0.5 h to 2 h; the time t4 for introducing the first compound is 120 min to 420 min; the flow rate V2 of the first compound is 3 L / min to 10 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 fast charging performance and room temperature storage 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. 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 the present application has good fast charging performance and room temperature storage performance, and lithium deposition on the negative electrode is improved.

[0013] In one embodiment of the present application, the tap density of the negative electrode material layer is F g / cm 3 , 1.65 ≤ F ≤ 1.79. Preferably, 1.73 ≤ F ≤ 1.79. When the value of F is within the above range, the negative electrode material layer has a suitable thickness and porosity, improving the energy density and fast charging performance of the electrochemical device.

[0014] In one embodiment of the present application, the thickness D2 of the negative electrode material layer is 32 μm to 66 μm. When the thickness D2 of the negative electrode material layer is within the above range, the energy density of the electrochemical device can be improved, and at the same time, the transmission distance of ions and electrons in the negative electrode material layer can be shortened, the film resistance of the negative electrode plate can be reduced, and the fast charging performance of the electrochemical device can be improved.

[0015] In an embodiment of the present application, the sheet resistance R of the negative electrode sheet is from 9.2 Ω·cm to 28.7 Ω·cm. When the sheet resistance R of the negative electrode sheet is within the above range, the conductivity of the negative electrode sheet can be improved, and the cycle performance of the electrochemical device can be improved.

[0016] In an embodiment of the present application, the electrolyte includes lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage content of lithium difluorophosphate is G%, 0.01 ≤ G ≤ 2, and preferably, 0.05 ≤ G ≤ 0.95. When G is within the above range, the side reaction between the electrolyte and the negative electrode material can be reduced, thereby improving the cycle performance of the electrochemical device and prolonging the cycle life of the electrochemical device.

[0017] In an embodiment of the present application, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is E%, 7 ≤ E ≤ 20, and preferably, 10 ≤ E ≤ 15. When E is within the above range, the side reaction between the electrolyte and the negative electrode material can be reduced, thereby improving the cycle performance of the electrochemical device and prolonging the cycle life of the electrochemical device.

[0018] In an embodiment of the present application, the electrolyte includes vinylene carbonate. Based on the mass of the electrolyte, the mass percentage content of vinylene carbonate is H%, 0.01 ≤ H ≤ 2, and preferably, 0.01 ≤ H ≤ 0.85. When H is within the above range, the side reaction between the negative electrode material and the electrolyte can be effectively reduced, thereby improving the stability of the negative electrode material and prolonging the cycle life of the electrochemical device.

[0019] In an embodiment of the present application, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is E%, 1.6 ≤ A / E ≤ 2.9. When the value of A / E is within the above range, the side reaction between the negative electrode material and the electrolyte can be effectively reduced, the negative electrode material can be protected, and the cycle life of the electrochemical device can be prolonged.

[0020] 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 use performance.

[0021] Advantages of the present application:

[0022] 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 and carbon elements; based on the total number of silicon and carbon atoms in the first region, the atomic percentage of silicon in the first region is A%, and 19.4 ≤ A ≤ 36.7; based on the total number of silicon and carbon atoms in the second region, the atomic percentage of silicon in the second region is B%, and 23.8 ≤ B ≤ 31.8. By adjusting the values of A and B within the scope of the present application, the fast charging performance and room temperature storage performance of the electrochemical device can be improved, and lithium deposition on the negative electrode can be improved.

[0023] 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

[0024] 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 use in 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.

[0025] 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

[0026] The following will clearly and completely describe the technical solutions in the present application in conjunction with the embodiments of the present application and the drawings. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0027] It should be noted that in the specific implementation 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.

[0028] The first aspect of the present application provides a negative electrode material. Among them, 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 particle to a depth of 40 nm from the surface of the silicon-carbon particle; the second region 12 is the region from a depth of 60 nm from the surface of the silicon-carbon particle to a depth of 100 nm from the surface of the silicon-carbon particle; the silicon-carbon particle includes silicon element and carbon element; based on the total number of atoms of silicon element and carbon element in the first region, the atomic percentage of silicon element in the first region is A%, and 19.4 ≤ A ≤ 36.7; based on the total number of atoms of silicon element and carbon element in the second region, the atomic percentage of silicon element in the second region is B%, and 23.8 ≤ B ≤ 31.8. For example, the value of A can be 19.4, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, 25.2, 30.1, 32.5, 36.7 or a range composed of any two of these values; the value of B can be 23.8, 24.3, 25.8, 26.4, 27.8, 28.6, 30.6, 31.8 or a range composed of any two of these values.

[0029] The inventors' research found that when the values of A and B are too low, for example, when the value of A is lower than 19.4 and the value of B is lower than 23.8, the specific capacity of the negative electrode material is relatively low; when the values of A and B are too high, for example, when the value of A is higher than 36.7 and the value of B is higher than 31.8, it will cause an excessive amount of lithium insertion in the negative electrode, resulting in the cracking of the silicon-carbon particles due to uneven stress distribution. By controlling the values of A and B within the above ranges, the specific capacity of the silicon-carbon particles can be improved, and the expansion of the silicon-carbon particles during the cycling process can be reduced; at the same time, it can also make the lithium insertion stress inside and outside the silicon-carbon particles more uniform, reduce the risk of lithium dendrite formation caused by the aggregation of lithium ions due to too high local silicon element content, improve lithium deposition on the negative electrode, and improve the fast charging performance and room temperature storage performance of the electrochemical device.

[0030] In one embodiment of the present application, 0.66 ≤ B / A ≤ 1.58, preferably, 0.82 ≤ B / A ≤ 1.29. For example, the value of B / A can be 0.66, 0.7, 0.75, 0.78, 0.8, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.89, 0.91, 0.95, 1, 1.1, 1.2, 1.29, 1.35, 1.45, 1.58 or a range composed of any two of these values. The value of B / A reflects the distribution of silicon atoms on the surface of the silicon-carbon particle. When the value of B / A is within the above range, it can make the lithium insertion amount in different regions of the silicon-carbon particle during charging be more evenly distributed, thereby improving the phenomenon of excessive lithium insertion amount and high stress caused by too high local silicon content in the silicon-carbon particle, being beneficial to improving the solid-phase transmission rate of lithium ions inside the silicon-carbon particle, improving lithium deposition on the negative electrode, and further improving the fast charging performance and room temperature storage performance of the electrochemical device.

[0031] In an embodiment of the present application, the average particle size D1 of the silicon-carbon particles is from 5.5 μm to 8.7 μm. For example, the average particle size D1 of the silicon-carbon particles can be 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 8.7 μm, or a range composed of any two of these values. When the silicon-carbon particles are charged and discharged, lithium ions will go through two processes: ion transport through the solid electrolyte interface (SEI) and internal solid-phase ion transport. Both of the above transport processes will affect the kinetic performance and cycling performance of the lithium-ion battery. By regulating the average particle size D1 of the silicon-carbon particles within the above range, at this time, the silicon-carbon particles have a suitable specific surface area, the SEI film has a suitable thickness, the lithium intercalation ability of the silicon-carbon particles is improved, the expansion performance and cycling performance of the electrochemical device are improved. At the same time, the solid-phase transport distance of lithium ions inside the particles is short, which can improve the transport efficiency of lithium ions, improve the kinetic performance of the electrochemical device, and improve lithium deposition on the negative electrode.

[0032] In an embodiment of the present application, the powder resistivity ρ of the silicon-carbon particles is from 0.25 Ω·cm to 8.7 Ω·cm. For example, the powder resistivity ρ of the silicon-carbon particles can be 0.25 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 8.7 Ω·cm, or a range composed of any two of these values. When ρ is within the above range, the transport speed of electrons in the negative electrode material layer can be increased, the internal resistance of the electrochemical device can be reduced, and the utilization rate of the negative electrode active material can be improved, thereby improving the fast charging performance of the electrochemical device.

[0033] In an embodiment of the present application, based on the mass of the silicon-carbon particles, the mass percentage content of silicon element is from 43.5% to 64.2%, and the mass percentage content of carbon element is from 34.8% to 55.5%.

[0034] In an embodiment of the present application, the negative electrode material further includes a carbon material, and the carbon material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, or soft carbon; based on the mass of the negative electrode material, the mass percentage content of the silicon-carbon particles is from 10% to 15%, and the mass percentage content of the carbon material is from 85% to 90%. For example, based on the mass of the negative electrode material, the mass percentage content of the silicon-carbon particles can be 10%, 11%, 12%, 13%, 14%, 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 the carbon material can be 85%, 86%, 87%, 88%, 89%, 90%, or a range composed of any two of these values.

[0035] 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 380°C to 460°C, the time t1 of the first heat preservation treatment is 1 h to 3 h; the time t2 for introducing the silane-containing gas is 400 min to 1600 min; the flow rate V1 of the silane-containing gas is 0.5 L / min to 2 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 a first compound to obtain silicon-carbon particles; the temperature T2 of the second heat preservation treatment is 480°C to 600°C, the time t3 of the second heat preservation treatment is 0.5 h to 2 h; the time t4 for introducing the first compound is 120 min to 420 min; the flow rate V2 of the first compound is 3 L / min to 10 L / min; the first compound includes at least one of acetylene, propylene or toluene. By adjusting each preparation parameter within the above range, when the prepared negative electrode material is applied to an electrochemical device, the fast charging performance and room temperature storage performance of the electrochemical device can be improved, and lithium deposition on the negative electrode can be improved.

[0036] 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 10:90 to 15:85.

[0037] 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 argon or helium.

[0038] The present application has no particular limitation on the method for adjusting the value of A, as long as the purpose of the present application can be achieved. For example, the value of A can be adjusted by adjusting the temperature T1 of the first heat preservation treatment. Exemplarily, when T1 increases, the value of A increases, and when T1 decreases, the value of A decreases.

[0039] The present application has no particular limitation on the method for adjusting the value of B, as long as the purpose of the present application can be achieved. For example, the value of B can be adjusted by adjusting the flow rate V1 of the silane-containing gas. Exemplarily, when V1 decreases, the value of B increases, and when V1 increases, the value of B decreases.

[0040] The present application has no particular limitation on the method for adjusting the value of B / A, as long as the purpose of the present application can be achieved. For example, the value of B / A can be adjusted by adjusting the respective values of B and A, and the adjustment method is as described above.

[0041] The method for regulating the average particle size D1 of the silicon-carbon particles in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, porous carbon matrices with different average particle sizes can be selected according to needs to regulate the average particle size D1 of the silicon-carbon particles.

[0042] The method for regulating the powder resistivity ρ of the silicon-carbon particles in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the temperature T1 of the first heat preservation treatment, the time t2 for introducing the silane gas, the flow rate V1 of the silane gas, or the flow rate V2 of the first compound will affect the powder resistivity ρ of the silicon-carbon particles.

[0043] 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 fast charging performance and room temperature storage performance, and the lithium deposition on the negative electrode is improved.

[0044] In one embodiment of this application, the tap density of the negative electrode material layer is F g / cm 3 , 1.65 ≤ F ≤ 1.79. Preferably, 1.73 ≤ F ≤ 1.79. For example, the value of F can be 1.65, 1.67, 1.69, 1.71, 1.73, 1.75, 1.77, 1.79 or a range composed of any two of these numerical values. When the value of F is within the above range, the negative electrode material layer has appropriate thickness and porosity, improving the energy density and fast charging performance of the electrochemical device.

[0045] The method for regulating the tap density F of the negative electrode material layer in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the tap density F of the negative electrode material layer can be regulated by controlling the rolling pressure during the cold pressing process. Exemplarily, when the rolling pressure during the cold pressing process increases, the tap density F of the negative electrode material layer increases; when the rolling pressure during the cold pressing process decreases, the tap density F of the negative electrode material layer decreases.

[0046] In one embodiment of this application, the thickness D2 of the negative electrode material layer is 32 μm to 66 μm. For example, the thickness D2 of the negative electrode material layer can be 32 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 66 μm or a range composed of any two of these numerical values. When the thickness D2 of the negative electrode material layer is within the above range, the areal capacity of the negative electrode plate can be improved, the energy density of the electrochemical device can be increased, and at the same time, the transmission distance of ions and electrons in the negative electrode material layer can be shortened, the sheet resistance of the negative electrode plate can be reduced, and the fast charging performance of the electrochemical device can be improved. The thickness D2 of the above negative electrode material layer refers to the thickness of the single-sided negative electrode material layer after cold pressing.

[0047] The method for regulating the thickness D2 of the negative electrode material layer in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the thickness D2 of the negative electrode material layer can be regulated by regulating the coating weight of the negative electrode material layer. On the basis of a certain compaction density of the negative electrode material layer, when the coating weight of the negative electrode material layer increases, the thickness D2 of the negative electrode material layer increases; when the coating weight of the negative electrode material layer decreases, the thickness D2 of the negative electrode material layer decreases.

[0048] In an embodiment of this application, the sheet resistance R of the negative electrode tab is from 9.2 Ω·cm to 28.7 Ω·cm. For example, the sheet resistance R of the negative electrode tab can be 9.2 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 28.7 Ω·cm, or a range composed of any two of these values. When the sheet resistance R of the negative electrode tab is within the above range, the conductivity of the negative electrode tab can be improved, and the cycling performance of the electrochemical device can be improved.

[0049] The method for regulating the sheet resistance R of the negative electrode tab in this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the sheet resistance R of the negative electrode tab can be regulated by regulating the average particle size D1 of the silicon-carbon particles, or the sheet resistance R of the negative electrode tab can also be regulated by the mass ratio of the silicon-carbon particles to the carbon material. Exemplarily, when D1 increases, the value of R increases, and when D1 decreases, the value of R decreases; when the mass ratio of the silicon-carbon particles to the carbon material increases, the value of R increases, and when the mass ratio of the silicon-carbon particles to the carbon material decreases, the value of R decreases.

[0050] In this application, the negative electrode tab 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 above "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its thickness direction, or can be provided on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. This application has no special limitation, as long as the purpose of this application can be achieved.

[0051] This application has no special limitation on the negative electrode current collector, 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, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, or titanium-copper composite current collector, etc. This application has no special limitation on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is from 4 μm to 15 μm.

[0052] 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 objectives 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, 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. Those skilled in the art can select according to actual needs as long as the objectives of the present application can be achieved.

[0053] Optionally, in some embodiments of the present application, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be 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. For example, they may be at least one of the aforementioned conductive agents and the aforementioned binders.

[0054] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be 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. For example, they may be at least one of the aforementioned conductive agents and the aforementioned binders.

[0055] In an embodiment of the present application, the electrolyte includes lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage content of lithium difluorophosphate is G%, where 0.01 ≤ G ≤ 2. Preferably, 0.05 ≤ G ≤ 0.95. For example, G can be 0.01, 0.05, 0.1, 0.5, 0.95, 1, 1.5, 2, or a range composed of any two of these values. When G is within the above range, it is beneficial to obtain a fluorine-containing SEI film, which promotes the uniform deposition of lithium, reduces the side reaction between the electrolyte and the negative electrode material, thereby improving the cycling performance of the electrochemical device and prolonging the cycling life of the electrochemical device.

[0056] In an embodiment of the present application, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is E%, where 7 ≤ E ≤ 20. Preferably, 10 ≤ E ≤ 15. For example, E can be 7, 10, 12, 15, 17, 20, or a range composed of any two of these values. When E is within the above range, it is beneficial to obtain a fluorine-containing SEI film, which promotes the uniform deposition of lithium, reduces the side reaction between the electrolyte and the negative electrode material, thereby improving the cycling performance of the electrochemical device and prolonging the cycling life of the electrochemical device.

[0057] In an embodiment of the present application, the electrolyte includes vinylene carbonate. Based on the mass of the electrolyte, the mass percentage content of vinylene carbonate is H%, where 0.01 ≤ H ≤ 2. Preferably, 0.01 ≤ H ≤ 0.85. For example, H can be 0.01, 0.1, 0.5, 0.85, 1, 1.5, 2, or a range composed of any two of these values. When H is within the above range, a relatively stable and dense SEI film can be formed on the surface of the negative electrode sheet, which can effectively reduce the side reaction between the negative electrode material and the electrolyte, thereby improving the stability of the negative electrode material and prolonging the cycling life of the electrochemical device.

[0058] In an embodiment of the present application, the electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is E%, and 1.6 ≤ A / E ≤ 2.9. For example, the value of A / E can be 1.6, 1.9, 2.2, 2.5, 2.7, 2.9, or a range composed of any two of these values. When the value of A / E is within the above range, a relatively stable and dense SEI film can be formed on the surface of the negative electrode material. The SEI film is mainly composed of inorganic salts (such as lithium carbonate and lithium oxide) and organic substances (such as polymers), which can effectively reduce the side reaction between the negative electrode material and the electrolyte, protect the negative electrode material, and prolong the cycling life of the electrochemical device.

[0059] 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, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. There is no particular limitation on the mass percentage content of the lithium salt in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the lithium salt may be 8% to 20%.

[0060] The present application places no particular limitation on the non-aqueous solvent, 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, methylcyclobutanesulfone, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application places no particular limitation on the mass percentage content of the non-aqueous solvent in the electrolyte, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the non-aqueous solvent may be 56% to 84%.

[0061] In one embodiment of the present application, the electrolyte may include fluorinated ethylene carbonate, lithium difluorophosphate, vinylene carbonate, a lithium salt, and a non-aqueous solvent. The mass percentage contents of fluorinated ethylene carbonate, lithium difluorophosphate, vinylene carbonate, and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 56% to 84%. The electrochemical device including the above electrolyte has good fast charging performance and room temperature storage performance, and can improve lithium deposition on the negative electrode.

[0062] In the present application, the electrochemical device includes a positive electrode tab, which 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.

[0063] There is no special limitation on the positive electrode current collector in the present application, 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 can 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.

[0064] In the present application, the positive electrode material layer includes a positive electrode active material. There is no special limitation on the positive electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode active material can 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 cobaltate (LiCoO2), lithium manganate, 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.

[0065] In the present application, the positive electrode material layer can further include a conductive agent and a binder. There is no special limitation on the types of the conductive agent and the binder in the present application, 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. There is 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. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0066] There is no special limitation on the thicknesses of the positive electrode current collector and the positive electrode material layer in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 150 μm.

[0067] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The 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. This application does not particularly limit 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.

[0068] In this application, the electrochemical device further includes a separator. This application does not particularly limit the separator, as long as it can achieve the purpose of this application. 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), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendared film, or a spun film.

[0069] In some embodiments of this 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.

[0070] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments of this application, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit 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. This application does not particularly limit the binder. For example, the binder may be at least one of the aforementioned binders. In some embodiments of this 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).

[0071] In this application, the thickness of the separator is not particularly limited as long as it can achieve the purpose of this application. For example, the thickness of the separator may be 3 μm to 30 μm.

[0072] In the present application, the electrochemical device further includes a housing for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of electrochemistry. The present application does not limit the above-mentioned other components. The present application has no special limitation on the housing, and it can be a housing well-known in the art as long as the purpose of the present application can be achieved. For example, the housing can be a hard-shell housing or a flexible housing. The material of the hard-shell housing can be metal, and the present application does not limit the type of metal. Any known metal hard-shell housing in the art can be used as long as the purpose of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0073] The present application has no special 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: lithium metal electrochemical devices, lithium ion electrochemical devices (lithium ion batteries), lithium polymer electrochemical devices, or lithium ion polymer electrochemical devices (lithium ion polymer batteries), etc.

[0074] 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 special limitation. For example, the preparation process of the electrochemical device can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing operations such as winding and folding according to needs to obtain a wound electrode assembly. Then, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. Or, stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly. Placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the housing according to needs to prevent the pressure inside the electrochemical device from rising and overcharging and overdischarging.

[0075] 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 use performance.

[0076] The type of the electronic device in this application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments of this application, 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 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.

[0077] Examples

[0078] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of this application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0079] Testing method and device:

[0080] Test of the values of A and B:

[0081] 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 silicon elements in the first region from 0 nm to 40 nm on the sample surface is measured. The above silicon-carbon particles are continuously etched, and the etching depth is from 60 nm to 100 nm. Then, the atomic percentage B of silicon elements 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 PHI5000 Versaprobe II type X-ray photoelectron spectrometer, and the X-ray excitation source is Al target Kα ray.

[0082] Test of the average particle size of silicon-carbon particles:

[0083] The negative electrode plate is longitudinally cut along the thickness direction by plasma, polished using argon ion polishing technology to obtain a flat cross-section. Then, a scanning electron microscope (SEM, model: OXFORD·EDS) is used to take SEM photos at a magnification of 50,000 times to observe the silicon-carbon particles. Then, using image analysis software, 30 silicon-carbon particles are randomly selected from the SEM photos, and the areas of these silicon-carbon particles are obtained. Then, assuming that the silicon-carbon particles are spherical, the respective particle sizes D (diameters) are calculated by the following formula: D = 2×(S1 / π) 1 / 2; where S1 is the area of the silicon-carbon particles; and the average particle size of the obtained 30 silicon-carbon particles is taken as the average particle size D1 of the silicon-carbon particles.

[0084] Compaction density test of the negative electrode material layer:

[0085] After charging the lithium-ion battery to 4.45 V at 0.2 C and then discharging it to 3.0 V at 0.2 C, record the discharge capacity as C1. Then charge the lithium-ion battery to the C1 / 2 capacity cut-off at 0.2 C. At this time, the lithium-ion battery is in a half-charged state. Disassemble the lithium-ion battery to obtain the negative electrode plate in the half-charged state. Clean the negative electrode plate with dimethyl carbonate (DMC) and vacuum dry it, then cut a negative electrode plate sample with an area of S cm 2 The thickness of the negative electrode plate sample is measured as Y1 cm and the mass is M1 g. Then peel off the negative electrode material layer of the negative electrode plate sample, and the thickness of the negative electrode current collector is measured as Y2 cm and the mass is M2 g. The compaction density F of the negative electrode material layer can be calculated as F = (M1 - M2) / (S×(Y1 - Y2)), and the unit is g / cm 3 .

[0086] Film resistance test of the negative electrode plate:

[0087] After cleaning the negative electrode plate with dimethyl carbonate (DMC) and vacuum drying it, obtain a dry negative electrode plate. Cut the negative electrode plate into a test sample of 60 mm×80 mm, and use a film resistance meter to test the film resistance R of the negative electrode plate under a test pressure of 0.4 T and a pressure holding time of 10 s.

[0088] Powder resistivity test of the silicon-carbon particles:

[0089] In a drying room, use a powder resistivity meter to test the powder resistivity of the silicon-carbon particles in each example and comparative example.

[0090] Room temperature storage performance test:

[0091] Charge the lithium-ion battery at a constant current of 0.2 C to 4.45 V at 25 °C, then charge it at a constant voltage of 4.45 V to 0.05 C, let it stand for 5 minutes, and then discharge it at a constant current of 0.2 C to 3.0 V, and record the discharge capacity at this time as C0. Then charge the lithium-ion battery at a constant current of 0.2 C to 4.45 V, then charge it at a constant voltage of 4.45 V to 0.05 C, and then place the lithium-ion battery in a constant temperature oven at 25 °C for 120 days. Take out the lithium-ion battery, let it stand for 30 minutes, and discharge the lithium-ion battery at a constant current of 0.2 C to 3.0 V, and record the discharge capacity at this time as C2. The discharge capacity retention rate (%) of the lithium-ion battery after storage at 25 °C for 120 days = C2 / C0×100%.

[0092] Ten lithium-ion batteries are tested in each group. If the discharge capacity retention rate of the lithium-ion batteries after storage at 25°C for 120 days is ≥80%, it is considered to pass the test. The passing rate of the room temperature storage test (%) = the number of batteries with a discharge capacity retention rate ≥80% after storage at 25°C for 120 days / 10 × 100%.

[0093] The higher the passing rate of the room temperature storage test, the better the room temperature storage performance of the lithium-ion battery.

[0094] Lithium plating test:

[0095] Take the tested lithium-ion battery, let it stand for 5 minutes at a test temperature of 0°C, charge it at a constant current of 0.2C to 4.45V, then charge it at a constant voltage of 4.45V to 0.05C. At this time, the lithium-ion battery reaches a fully charged state; let it stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V, and let it stand for 5 minutes. After repeating the above charge and discharge process 10 times, fully charge the lithium-ion battery, disassemble it in a drying room, and take pictures to record the state of the negative electrode.

[0096] Judgment of the degree of lithium plating: It is judged according to the state of the fully charged and disassembled negative electrode. When the area showing gray on the negative electrode is <2%, it is judged as no lithium plating; when the gray area on the negative electrode is ≥2% and <20%, it is judged as slight lithium plating; when the gray area on the negative electrode is ≥20% and <30%, it is judged as lithium plating; when the gray area on the negative electrode is ≥30%, it is judged as severe lithium plating.

[0097] Test of the charging capacity retention rate at different rates:

[0098] Under the condition of 25°C, charge the lithium-ion battery at 0.2C to 4.45V, record the charging capacity C3 at this time, let it stand for 5 minutes, and then discharge it at 0.2C to 3.0V; charge it at 2C to 4.45V, record the charging capacity C4 at this time, let it stand for 5 minutes, and then discharge it at 0.2C to 3.0V.

[0099] The charging capacity retention rate at 2C (%) = C4 / C3 × 100%.

[0100] The fast charging performance of the lithium-ion battery is characterized by the ratio of the charging capacity at 2C to the charging capacity at 0.2C of the lithium-ion battery. The higher the charging capacity retention rate at 2C, the better the fast charging performance of the lithium-ion battery.

[0101] Example 1-1

[0102] <Preparation of the negative electrode material>

[0103] (1) Provide a porous carbon matrix, conduct a first heat preservation treatment on the porous carbon matrix in a nitrogen atmosphere, and then introduce a silane gas to obtain a first intermediate. Among them, the average particle size of the porous carbon matrix is 7.8 μm; the temperature T1 of the first heat preservation treatment is 420 °C, the time t1 of the first heat preservation treatment is 2 h; the time t2 for introducing the silane gas is 800 min; the flow rate V1 of the silane gas is 1 L / min; the silane gas is silane.

[0104] (2) Conduct a second heat preservation treatment on the first intermediate in a nitrogen atmosphere, and then introduce a first compound to obtain silicon-carbon particles. Among them, the temperature T2 of the second heat preservation treatment is 540 °C, the time t3 of the second heat preservation treatment is 1 h; the time t4 for introducing the first compound is 240 min; the flow rate V2 of the first compound is 6 L / min; the first compound is acetylene.

[0105] (3) Mix the silicon-carbon particles and carbon material artificial graphite evenly according to a mass ratio of 12:88 to obtain a negative electrode material.

[0106] <Preparation of negative electrode sheet>

[0107] Mix the above-prepared negative electrode material, binder styrene-butadiene rubber (SBR), and thickener carboxymethyl cellulose (CMC) according to a mass ratio of 98:1.6:0.4, dissolve them in deionized water as a solvent, mix evenly, and make a negative electrode slurry with a solid content of 45 wt%. Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dry it at 85 °C for 4 h to obtain a negative electrode sheet with a single-sided coated negative electrode material layer. The coating weight of the negative electrode material layer is 99.73 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 double-sided coated negative electrode material layer. After cold pressing, slicing, and slitting, dry it in a vacuum 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, and the compaction density of the negative electrode material layer is 1.75 g / cm 3 .

[0108] <Preparation of positive electrode sheet>

[0109] Mix the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 96.3:2.2:1.5. After adding the solvent N-methylpyrrolidone, stir evenly to obtain a positive electrode slurry with a solid content of 75 wt%. Coat the positive electrode 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 single-sided coated positive electrode material layer. The coating weight of the positive electrode material layer is 231.29 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 double-sided coated positive electrode material layer. After cold pressing, cutting, and slitting, dry it under vacuum 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, and the tap density of the positive electrode material layer is 4.23 g / cm 3 。

[0110] <Preparation of electrolyte>

[0111] In an argon atmosphere glove box with a water content < 10 ppm, mix ethylene carbonate (EC) and dimethyl carbonate (DMC) evenly in a volume ratio of 1:1 to obtain a base solvent. Add fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, and lithium salt LiPF6 to the base solvent and stir evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content E of fluoroethylene carbonate is 12.5%, the mass percentage content G of lithium difluorophosphate is 0.5%, the mass percentage content H of vinylene carbonate is 0.4%, the mass percentage content of LiPF6 is 12.5%, and the mass percentage content of the base solvent is 74.1%.

[0112] <Separator>

[0113] Use a polypropylene (PP) separator with a thickness of 4.5 μm.

[0114] <Preparation of lithium-ion battery>

[0115] 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 a role in isolation, and then wind to obtain an electrode assembly. Place the electrode assembly in an aluminum-plastic film, place 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.

[0116] Examples 1-2 to Examples 1-9

[0117] Except for adjusting the preparation parameters with reference to Table 1 in <Preparation of Anode Material> such that the values of A and B are as shown in Table 1, the rest is the same as in Example 1-1.

[0118] Examples 1-10

[0119] Except for using disilane as the silane-containing gas in <Preparation of Anode Material> and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0120] Examples 1-11

[0121] Except for using propylene as the first compound in <Preparation of Anode Material> and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0122] Examples 1-12 to Examples 1-13

[0123] Except for adjusting the preparation parameters with reference to Table 1 in <Preparation of Anode Material> such that the powder resistivity ρ of the silicon-carbon particles is as shown in Table 1, the rest is the same as in Example 1-1.

[0124] Examples 1-14 to Examples 1-17

[0125] Except for adjusting the average particle size D1 of the silicon-carbon particles according to Table 1 in <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0126] Examples 1-18 to Examples 1-19

[0127] Except for adjusting the mass ratio of the silicon-carbon particles to the carbon material in <Preparation of Anode Material> such that the film resistance R of the anode electrode sheet is as shown in Table 2, the rest is the same as in Example 1-1.

[0128] Examples 1-20 to Examples 1-24

[0129] Except for adjusting the coating weight of the anode material layer according to Table 2 in <Preparation of Anode Material> such that the thickness D2 of the anode material layer is as shown in Table 1, the rest is the same as in Example 1-1.

[0130] Examples 2-1 to Examples 2-11

[0131] Except for adjusting the preparation parameters according to Table 3 in <Preparation of Electrolyte>, the rest is the same as in Example 1-1. Among them, when the mass percentage content of at least one of lithium difluorophosphate, fluoroethylene carbonate or vinylene carbonate changes, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the lithium salt and the volume ratio of each component in the base solvent remain unchanged.

[0132] Comparative Examples 1 to Comparative Examples 6

[0133] Except that in the <Preparation of Anode Material>, the preparation parameters are adjusted with reference to Table 1 so that the values of A and B are as shown in Table 1, the rest is the same as in Example 1-1.

[0134] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1, 2, and 3.

[0135] Table 1

[0136]

[0137]

[0138] Table 2

[0139]

[0140]

[0141] It can be seen from Example 1-1 to Example 1-24 and Comparative Example 1 to Comparative Example 6 that when the values of A, B, and the preparation parameters of the anode material are within the scope of the present application, applying the anode material of the present application to a lithium-ion battery results in a lithium-ion battery having good fast charging performance and room temperature storage performance, and the lithium deposition on the anode is improved.

[0142] It can be seen from Example 1-1 to Example 1-9 that when the value of B / A is within the scope of the present application, the obtained lithium-ion battery has good fast charging performance and room temperature storage performance, and the lithium deposition on the anode is improved.

[0143] It can be seen from Example 1-1, Example 1-12, and Example 1-13 that when the value of ρ is within the scope of the present application, the obtained lithium-ion battery has good room temperature storage performance, and the lithium deposition on the anode is improved.

[0144] It can be seen from Example 1-1, Example 1-14 to Example 1-17 that when the value of D1 is within the scope of the present application, the lithium deposition on the anode of the obtained lithium-ion battery is improved, and at the same time, it has good fast charging performance and room temperature storage performance.

[0145] It can be seen from Example 1-1, Example 1-18, and Example 1-19 that when the value of R is within the scope of the present application, the fast charging performance of the obtained lithium-ion battery is improved, and at the same time, it has good room temperature storage performance, and the lithium deposition on the anode is improved.

[0146] It can be seen from Example 1-1, Example 1-20, and Example 1-24 that when the value of F is within the scope of the present application, the fast charging performance of the obtained lithium-ion battery is improved, and at the same time, it has good room temperature storage performance, and the lithium deposition on the anode is improved.

[0147] As can be seen from Example 1-1, Example 1-20, and Example 1-24, when the value of D2 is within the scope of the present application, the fast charging performance of the obtained lithium-ion battery is improved, and it has good room temperature storage performance, and lithium deposition on the negative electrode is improved.

[0148] Table 3

[0149]

[0150] As can be seen from Example 1-1, Example 2-1 to Example 2-4, when the mass percentage content G of lithium difluorophosphate is within the scope of the present application, the fast charging performance of the lithium-ion battery is improved, and it has good room temperature storage performance, and lithium deposition on the negative electrode is improved.

[0151] As can be seen from Example 1-1, Example 2-5 to Example 2-8, when the mass percentage content E of fluoroethylene carbonate is within the scope of the present application, the fast charging performance and room temperature storage performance of the obtained lithium-ion battery are improved, and lithium deposition on the negative electrode is improved.

[0152] As can be seen from Example 1-1, Example 2-5 to Example 2-8, when the value of A / E is within the scope of the present application, the fast charging performance and room temperature storage performance of the obtained lithium-ion battery are improved, and lithium deposition on the negative electrode is improved.

[0153] As can be seen from Example 1-1, Example 2-9 to Example 2-11, when the mass percentage content H of vinylene carbonate is within the scope of the present application, the fast charging performance of the obtained lithium-ion battery is improved, and it has good room temperature storage performance, and at the same time lithium deposition on the negative electrode is improved.

[0154] 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 actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are 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 also includes elements inherent to such process, method or article.

[0155] 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. The key point of each embodiment is to illustrate the differences from other embodiments.

[0156] 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 principles 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 and carbon; Based on the total number of atoms of silicon and carbon in the first region, the atomic percentage of silicon in the first region is A%, 19.4≤A≤36.7; Based on the total number of atoms of silicon and carbon in the second region, the atomic percentage of silicon in the second region is B%, 23.8≤B≤31.

8.

2. The negative electrode material according to claim 1, wherein 0.66≤B / A≤1.

58.

3. The negative electrode material according to claim 2, wherein 0.82≤B / A≤1.

29.

4. The negative electrode material according to claim 1, wherein The average particle size D1 of the silicon-carbon particles is 5.5 μm to 8.7 μm.

5. The negative electrode material according to claim 1, wherein The powder resistivity ρ of the silicon carbon particles is 0.25 Ω·cm to 8.7 Ω·cm.

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 380° C. to 460° C., the time t1 of the first heat preservation treatment is 1 h to 3 h; the time t2 of introducing the silane-containing gas is 400 min to 1600 min; the flow rate V1 of the silane-containing gas is 0.5 L / min to 2 L / min; the silane-containing gas comprises at least one of monosilane, disilane, trisilane, phenylsilane or tolylsilane; (2) The first intermediate is subjected to a second insulation treatment under an inert atmosphere, and then the first compound is introduced to obtain the silicon-carbon particles; the temperature T2 of the second insulation treatment is 480°C to 600°C, and the time t3 of the second insulation treatment is 0.5h to 2h; the time t4 for introducing the first compound is 120min to 420min; the flow rate V2 of the first compound is 3L / min to 10L / 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 negative electrode sheet satisfies at least one of the following conditions: (1) The compaction density of the negative electrode material layer is F g / cm 3 , 1.65≤F≤1.79, preferably, 1.73≤F≤1.79; (2) The thickness D2 of the negative electrode material layer is 32 μm to 66 μm; (3) The sheet resistance R of the negative electrode plate is 9.2 Ω·cm to 28.7 Ω·cm.

9. The electrochemical device according to claim 7, wherein: The electrolyte satisfies at least one of the following conditions: (1) The electrolyte comprises lithium difluorophosphate, and the mass percentage of lithium difluorophosphate is G%, 0.01≤G≤2, preferably, 0.05≤G≤0.95 based on the mass of the electrolyte; (2) The electrolyte comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is E%, 7≤E≤20, preferably, 10≤E≤15 based on the mass of the electrolyte; (3) The electrolyte includes vinylene carbonate, and the mass percentage of vinylene carbonate is H% based on the mass of the electrolyte, 0.01≤H≤2, preferably, 0.01≤H≤0.

85.

10. The electrochemical device according to claim 7, wherein: The electrolyte includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is E%, and 1.6≤A / E≤2.

9.

11. An electronic device, wherein: The electronic device comprises the electrochemical device according to any one of claims 7 to 10.

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