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, each silicon carbon particle comprises a first region and a second region, and the first region is a region from the surface of the silicon carbon particle to a depth of 100 nm from the surface of the silicon carbon particle; the second region is a region which is 200 nm away from the surface of the silicon carbon particle to 500 nm away 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 is A%, and A is larger than or equal to 4.04 and smaller than or equal to 16.89; 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 is B%, and B is larger than or equal to 15 and smaller than or equal to 20.88. The electrochemical device has good cycle performance and safety performance, and lithium precipitation of the negative electrode can be 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, which limits 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 high theoretical specific capacity and suitable working voltage.

[0003] However, when used as a negative electrode material, silicon materials are prone to a large expansion rate 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 large expansion rate after lithium intercalation, while the regions with low silicon concentration have a relatively small expansion rate. This non-uniformity leads to uneven lithium intercalation stress distribution inside silicon material particles, ultimately causing the problem of excessive expansion or even rupture of silicon material particles, thereby affecting the cycling performance and expansion performance of lithium-ion batteries. Solving the above 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 cycling performance and safety performance of the electrochemical device and improve lithium deposition 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. The silicon-carbon particles include a first region and a second region. The first region is the region from the surface of the silicon-carbon particle to a depth of 100 nm from the surface of the silicon-carbon particle; the second region is the region from a depth of 200 nm from the surface of the silicon-carbon particle to a depth of 500 nm from the surface of the silicon-carbon particle; the silicon-carbon particles include silicon elements and carbon elements; based on the total number of silicon atoms and carbon atoms in the first region, the atomic percentage of silicon elements in the first region is A%, and 4.04 ≤ A ≤ 16.89; based on the total number of silicon atoms and carbon atoms in the second region, the atomic percentage of silicon elements in the second region is B%, and 15 ≤ B ≤ 20.88. By adjusting the values of A and B within the above range, the cycling performance and safety performance of the electrochemical device can be improved, and lithium deposition on the negative electrode can be improved.

[0007] In an embodiment of the present application, 1.05 ≤ B / A ≤ 4.84. When the value of B / A is within the above range, the cycling performance of the electrochemical device can be improved.

[0008] In an embodiment of the present application, 1.2 ≤ B / A ≤ 3.8. When the value of B / A is within the above range, the cycling performance of the electrochemical device can be further improved.

[0009] In an embodiment of the present application, the specific surface area of the silicon-carbon particles is 0.7 m 2 / g to 6.21 m 2 / g. When the specific surface area of the silicon-carbon particles is within the above range, the cycling performance of the electrochemical device can be further improved.

[0010] In an embodiment of the present application, the size D1 of the silicon grains in the silicon-carbon particles is 0.91 nm to 6.37 nm. Preferably, the size D1 of the silicon grains in the silicon-carbon particles is 1.02 nm to 2.35 nm. When the size D1 of the silicon grains in the silicon-carbon particles is within the above range, the cycling performance of the electrochemical device is further improved.

[0011] In an embodiment of the present application, the average particle size D2 of the silicon-carbon particles is 7.5 μm to 9.2 μm. When the average particle size D2 of the silicon-carbon particles is within the above range, the cycling performance of the electrochemical device can be further improved.

[0012] 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 430 °C to 480 °C, and the time t1 of the first heat preservation treatment is 0.5 h to 2 h; the time t2 for introducing the silane-containing gas after the first heat preservation treatment is 300 min to 660 min, and the flow rate V1 of the silane-containing gas is 0.5 L / min to 3 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 silane-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 400 °C to 470 °C, and the time t3 of the second heat preservation treatment is 1 h to 2 h; the time t4 for introducing the silane-containing gas after the second heat preservation treatment is 160 min to 240 min, and the flow rate V2 of the silane-containing gas is 0.5 L / min to 1.5 L / min; (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 480 °C to 600 °C, and the time t5 of the third heat preservation treatment is 0.5 h to 2 h; the time t6 for introducing the first compound is 120 min to 400 min, and the flow rate V3 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 controlling each preparation parameter within the above range, when the prepared negative electrode material is applied to an electrochemical device, the cycle performance and safety performance of the electrochemical device can be improved, and negative electrode lithium plating can be improved.

[0013] The third aspect of the present application provides an electrochemical device. Among them, the electrochemical device includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes the negative electrode material in any of the foregoing embodiments. The electrochemical device of the present application has good cycle performance and safety performance, and can improve negative electrode lithium plating.

[0014] In one embodiment of the present application, the porosity of the negative electrode sheet is 17.7% to 24.8%. When the porosity of the negative electrode sheet is within the above range, the cycle performance of the electrochemical device can be further improved, and negative electrode lithium plating can be improved.

[0015] In one embodiment of the present application, the coating weight of the negative electrode material layer is 80.6 mg / 1540.25 mm 2To 100.5 mg / 1540.25 mm 2 When the coating weight of the negative electrode material layer is within the above range, the energy density of the electrochemical device can be improved.

[0016] In an embodiment of the present application, the electrolyte includes a first type of auxiliary salt and a second type of auxiliary salt. The first type of auxiliary salt includes at least one of lithium difluorophosphate, lithium difluoroborate, lithium tetrafluoroborate, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate; the second type of auxiliary salt includes at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethylsulfonyl)imide. When the electrolyte includes the above first type of auxiliary salt and the second type of auxiliary salt, the cycle capacity retention rate of the electrochemical device can be improved, thereby improving the cycle performance of the electrochemical device.

[0017] In an embodiment of the present application, based on the mass of the electrolyte, the mass percentage content P of the first type of auxiliary salt is 0.3% to 1%. When the mass percentage content P of the first type of auxiliary salt is within the above range, the cycle capacity retention rate of the electrochemical device can be further improved, thereby further improving the cycle performance of the electrochemical device.

[0018] In an embodiment of the present application, based on the mass of the electrolyte, the mass percentage content T of the second type of auxiliary salt is 1% to 5%. When the mass percentage content T of the second type of auxiliary salt is within the above range, the cycle capacity retention rate of the electrochemical device can be further improved, thereby further improving the cycle performance of the electrochemical device.

[0019] In an embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the first type of auxiliary salt is P, and the mass percentage content of the second type of auxiliary salt is T, 0.1 ≤ P / T ≤ 1, preferably, 0.2 ≤ P / T ≤ 0.8. When the value of P / T is within the above range, the first type of auxiliary salt and the second type of auxiliary salt have appropriate mass percentage contents, and the cycle capacity retention rate of the electrochemical device can be further improved, thereby further improving the cycle performance of the electrochemical device.

[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 100 nm from the surface of the silicon-carbon particles; the second region is a region from a depth of 200 nm from the surface of the silicon-carbon particles to a depth of 500 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 atoms of silicon element and carbon element in the first region, the atomic percentage of silicon element in the first region is A%, and 4.04 ≤ A ≤ 16.89; 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 15 ≤ B ≤ 20.88. By adjusting the values of A and B within the scope of the present application, the cycle performance and safety 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, and those of ordinary skill in the art can also obtain other embodiments 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, but 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, 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 carbide particles to a depth of 100 nm from the surface of the silicon carbide particles; the second region 12 is the region from a depth of 200 nm from the surface of the silicon carbide particles to a depth of 500 nm from the surface of the silicon carbide particles. The silicon carbide particles include 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 4.04 ≤ A ≤ 16.89; 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 15 ≤ B ≤ 20.88. For example, the value of A can be 4.04, 4.5, 6, 7.5, 9, 10.5, 12, 13.5, 15, 16.5, 16.89 or a range composed of any two of these values; the value of B can be 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 20.88 or a range composed of any two of these values.

[0029] 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 4.04 and / or the value of B is lower than 15, the specific capacity of the negative electrode material is low; when the value of A and / or B is too high, for example, the value of A is higher than 16.89 and / or the value of B is higher than 20.88, it will cause too much lithium insertion in the negative electrode, resulting in the cracking of the silicon carbide particles due to uneven stress distribution. By adjusting the values of A and B within the above range, the specific capacity of the silicon carbide particles can be improved; it can also make the stress of the particles after lithium insertion concentrate inside rather than on the surface, which is beneficial to restricting the expansion of the silicon carbide particles and improving the expansion performance and cycling performance of the electrochemical device; in addition, it is also beneficial to reduce the lithium dendrites formed by the aggregation of lithium ions in the part with too high mass percentage of silicon element, improve the lithium deposition on the negative electrode, and improve the safety performance of the electrochemical device.

[0030] In an embodiment of the present application, 1.05 ≤ B / A ≤ 4.84, preferably, 1.2 ≤ B / A ≤ 3.8. For example, the value of B / A can be 1.05, 1.1, 1.2, 1.5, 2, 2.5, 3, 3.5, 3.8, 4, 4.5, 4.84 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 carbide particles. When the value of B / A is within the above range, the lower atomic percentage of silicon atoms on the surface of the silicon carbide particles can make the surface of the silicon carbide particles have higher ionic and electronic conductivity; when the silicon on the surface of the silicon carbide particles is inserted with lithium to form a lithium-silicon alloy, the conductivity of the silicon carbide particles can be improved, which is beneficial to the lithium insertion in the internal region with a relatively high atomic percentage of silicon element, and further improves the cycling performance of the electrochemical device through the rapid lithium insertion on the surface of the particles during charging of the negative electrode material.

[0031] In an embodiment of the present application, the specific surface area of the silicon carbide particles is 0.7 m 2from 0.7 m² / g to 6.21 m² / g 2 / g. For example, the specific surface area of the silicon-carbon particles can be 0.7 m 2 / g, 1 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, 4.5 m 2 / g, 5 m 2 / g, 5.5 m 2 / g, 6 m 2 / g, 6.21 m 2 / g or a range composed of any two of these values. When the specific surface area of the silicon-carbon particles is within the above range, it is beneficial to increase the lithium-ion diffusion rate, thereby improving the current density and charge-discharge rate; at the same time, the silicon-carbon particles have an appropriate number of active sites on the surface, reducing the side reactions between the silicon-carbon particles and the electrolyte, thereby further improving the cycling performance of the electrochemical device.

[0032] In one embodiment of the present application, the size D1 of the silicon grains in the silicon-carbon particles is from 0.91 nm to 6.37 nm. Preferably, the size D1 of the silicon grains in the silicon-carbon particles is from 1.02 nm to 2.35 nm. For example, the size D1 of the silicon grains in the silicon-carbon particles can be 0.91 nm, 0.95 nm, 1.02 nm, 1.5 nm, 2 nm, 2.35 nm, 2.5 nm, 3 nm, 4 nm, 5 nm, 6 nm, 6.37 nm or a range composed of any two of these values. When the size D1 of the silicon grains in the silicon-carbon particles is within the above range, it is possible to reduce the volume stress of the silicon-carbon particles during cycling and reduce the structural damage of the silicon-carbon particles, and it is also possible to reduce the transmission distance of lithium ions inside the silicon grains, thereby further improving the cycling performance of the electrochemical device.

[0033] In one embodiment of the present application, the average particle size D2 of the silicon-carbon particles is from 7.5 μm to 9.2 μm. For example, the average particle size D2 of the silicon-carbon particles can be 7.5 μm, 7.8 μm, 8.1 μm, 8.4 μm, 8.7 μm, 9 μm, 9.2 μm or a range composed of any two of these values. When the average particle size D2 of the silicon-carbon particles is within the above range, the transmission distance of lithium ions inside the silicon-carbon particles is shortened, which is beneficial to improving the transmission rate of lithium ions; and at this time, the silicon-carbon particles have an appropriate specific surface area, which is beneficial to forming a solid electrolyte interface (SEI) film with an appropriate thickness, thereby further improving the cycling performance of the electrochemical device.

[0034] In an embodiment of the present application, based on the mass of the silicon-carbon particles, the mass percentage content of silicon element is 40% to 58%, and the mass percentage content of carbon element is 41% to 59%. In the present application, the silicon-carbon particles may further include oxygen element and / or impurities, and based on the mass of the silicon-carbon particles, the mass percentage content of oxygen element and / or impurities is less than or equal to 1%.

[0035] 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, mesophase 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 10% to 30%, and the mass percentage content of the carbon material is 70% to 90%. For example, based on the mass of the negative electrode material, the mass percentage content of the silicon-carbon particles may be 10%, 15%, 20%, 25%, 30% 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 may be 70%, 75%, 80%, 85%, 90% or a range composed of any two of these values.

[0036] 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 430°C to 480°C, and the time t1 of the first heat preservation treatment is 0.5 h to 2 h; the time t2 for introducing the silane-containing gas after the first heat preservation treatment is 300 min to 660 min, and the flow rate V1 of the silane-containing gas is 0.5 L / min to 3 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 silane-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 400°C to 470°C, and the time t3 of the second heat preservation treatment is 1 h to 2 h; the time t4 for introducing the silane-containing gas after the second heat preservation treatment is 160 min to 240 min, and the flow rate V2 of the silane-containing gas is 0.5 L / min to 1.5 L / min; (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 480°C to 600°C, and the time t5 of the third heat preservation treatment is 0.5 h to 2 h; the time t6 for introducing the first compound is 120 min to 400 min, and the flow rate V3 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 cycle performance and safety performance of the electrochemical device can be improved, and lithium deposition on the negative electrode can be improved.

[0037] 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 30:70.

[0038] The present application has no particular limitation on the inert atmosphere, as long as the object of the present application can be achieved. For example, the inert atmosphere can be at least one of nitrogen, argon, or helium.

[0039] The present application has no particular limitation on the method for regulating the value of A, as long as the object of the present application can be achieved. For example, the value of A can be regulated by regulating the time t4 for introducing the silane-containing gas after the second heat preservation treatment. Exemplarily, when t4 increases, the value of A increases, and when t4 decreases, the value of A decreases.

[0040] 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 t2 for introducing the silane gas after the first heat preservation treatment. Exemplarily, when t2 decreases, the value of B decreases, and when t2 increases, the value of B increases.

[0041] The method for regulating the value of B / A in this application is not particularly limited as long as the purpose of this application can be achieved. For example, the value of B / A can be regulated by regulating the respective values of B and A, and the regulation method is as described above.

[0042] The method for regulating the size D1 of silicon grains in 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 size D1 of silicon grains in the silicon-carbon particles can be regulated by regulating the temperature T1 of the first heat preservation treatment and the temperature T2 of the second heat preservation treatment. Exemplarily, when T1 and T2 increase, D1 increases, and when T1 and T2 decrease, D1 decreases.

[0043] The method for regulating the average particle size D2 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 D2 of the silicon-carbon particles.

[0044] The method for regulating the specific surface area 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 flow rate V1 of the silane gas introduced after the first heat preservation treatment, the time t2 for introducing the silane gas after the first heat preservation treatment, the flow rate V2 of the silane gas introduced after the second heat preservation treatment, or the time t4 for introducing the silane gas after the second heat preservation treatment will affect the specific surface area of the silicon-carbon particles. Alternatively, the specific surface area of the prepared silicon-carbon particles can also be tested by the "specific surface area test" method in this application, and silicon-carbon particles with the desired specific surface area can be selected.

[0045] In this application, the porous carbon matrix can be a commercially available porous carbon matrix or prepared according to needs. 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, and then carrying out a temperature-raising reaction after mixing evenly 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.

[0046] The third aspect of the present application provides an electrochemical device. 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 cycle performance and safety performance, and can improve lithium deposition on the negative electrode.

[0047] In the present application, 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 above-mentioned "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 own thickness direction, or can be provided on two surfaces of the negative 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 negative electrode current collector, or a partial area of the surface of the negative electrode current collector. The present application has no special limitation, as long as the purpose of the present application can be achieved.

[0048] In an embodiment of the present application, the porosity of the negative electrode plate is 17.7% to 24.8%. For example, the porosity of the negative electrode plate can be 17.7%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 24.8% or a range composed of any two of these values. When the porosity of the negative electrode plate is within the above range, the negative electrode plate can provide a good conductive channel, uniform the current during the charge and discharge process, form a more uniform electric field, which is beneficial to improving the deposition density and deposition uniformity of lithium metal in the negative electrode plate during the long-term cycle process, delaying the growth of lithium dendrites, and reducing the side reaction between lithium metal and the electrolyte, thereby further improving the cycle performance of the electrochemical device and improving lithium deposition on the negative electrode.

[0049] In an embodiment of the present 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 . For example, the coating weight CW of the negative electrode material layer can be 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 2Or a range composed of any two of these values. When the coating weight CW of the negative electrode material layer is within the above range, the ion and electron transport distances in the negative electrode sheet can be shortened, the influence of internal polarization of the electrochemical device during charging on the charging capacity can be reduced, and at the same time, the energy density of the electrochemical device can also be increased.

[0050] The present application does not particularly limit the method for regulating the porosity of the negative electrode sheet as long as the object of the present application can be achieved. For example, the porosity of the negative electrode sheet can be regulated by regulating the mass ratio of the silicon-carbon particles and the carbon material . Exemplarily, when the mass ratio of the silicon-carbon particles and the carbon material increases, the value increases, and when the mass ratio of the silicon-carbon particles and the carbon material decreases, the value decreases.

[0051] 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, and when the coating amount of the negative electrode material layer slurry decreases, the value of CW decreases.

[0052] 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 or titanium-copper composite current collector, etc.

[0053] 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 are 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 are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers may include, but 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.

[0054] 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 objectives 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. Those skilled in the art can select according to actual needs as long as the objectives of the present application can be achieved.

[0055] 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 objectives 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.

[0056] 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 has no particular limitation on 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 has no particular limitation on the conductive agent and the binder in the conductive layer, as long as the object of the present application can be achieved. For example, it may be at least one of the aforementioned conductive agent and the aforementioned binder.

[0057] In one embodiment of the present application, the electrolyte includes a first type of auxiliary salt and a second type of auxiliary salt. The first type of auxiliary salt includes at least one of lithium difluorophosphate, lithium difluoroborate, lithium tetrafluoroborate, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate; the second type of auxiliary salt includes at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethylsulfonyl)imide. When the electrolyte includes the above-mentioned first type of auxiliary salt and the second type of auxiliary salt, it is beneficial to form a relatively stable SEI film on the surface of the negative electrode sheet, which can reduce the occurrence of side reactions, improve the cycle capacity retention rate of the electrochemical device, and thus improve the cycle performance of the electrochemical device.

[0058] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content P of the first type of auxiliary salt is 0.3% to 1%. For example, the mass percentage content P of the first type of auxiliary salt may be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of these values. When the mass percentage content P of the first type of auxiliary salt is within the above range, it is beneficial to form a relatively stable SEI film on the surface of the negative electrode sheet, which can reduce the occurrence of side reactions, further improve the cycle capacity retention rate of the electrochemical device, and thus further improve the cycle performance of the electrochemical device.

[0059] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content T of the second type of auxiliary salt is 1% to 5%. For example, the mass percentage content T of the second type of auxiliary salt may be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of these values. When the mass percentage content T of the second type of auxiliary salt is within the above range, it is beneficial to form a relatively stable SEI film on the surface of the negative electrode sheet, which can reduce the occurrence of side reactions, further improve the cycle capacity retention rate of the electrochemical device, and thus further improve the cycle performance of the electrochemical device.

[0060] In an embodiment of the present application, the electrolyte includes a first auxiliary salt and a second auxiliary salt. Based on the mass of the electrolyte, the mass percentage content P of the first auxiliary salt is 0.3% to 1%, and the mass percentage content T of the second auxiliary salt is 1% to 5%. For example, the mass percentage content P of the first auxiliary salt can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any two of these values; the mass percentage content T of the second auxiliary salt can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of these values. When the mass percentage content P of the first auxiliary salt and the mass percentage content T of the second auxiliary salt are within the above ranges, it is beneficial to form a relatively stable SEI film on the surface of the negative electrode sheet, which can reduce the occurrence of side reactions, further improve the cycle capacity retention rate of the electrochemical device, and thus further improve the cycle performance of the electrochemical device.

[0061] In an embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the first auxiliary salt is P, and the mass percentage content of the second auxiliary salt is T, 0.1 ≤ P / T ≤ 1. Preferably, 0.2 ≤ P / T ≤ 0.8. For example, the value of P / T can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range composed of any two of these values. When the value of P / T is within the above range, the first auxiliary salt and the second auxiliary salt have appropriate mass percentage contents, and the mass percentage contents of the first auxiliary salt and the second auxiliary salt match, which is beneficial to form a relatively stable SEI film on the surface of the negative electrode sheet, can reduce the occurrence of side reactions, further improve the cycle capacity retention rate of the electrochemical device, and thus further improve the cycle performance of the electrochemical device.

[0062] In this application, the electrolyte includes a lithium salt and a non-aqueous solvent. There is no particular limitation on the lithium salt in this application, as long as the purpose of this 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 of the lithium salt in the electrolyte in this application, as long as the purpose of this application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 20%. There is no particular limitation on the non-aqueous solvent in this application, as long as the purpose of this 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 fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. There is no particular limitation on the mass percentage of the non-aqueous solvent in the electrolyte in this application, as long as the purpose of this application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent may be 74% to 90.7%.

[0063] In one embodiment of the present application, the electrolyte may include a first auxiliary salt, a second auxiliary salt, a lithium salt, and a non-aqueous solvent. The mass percentage contents of the first auxiliary salt, the second auxiliary salt, and the lithium salt are as described above, and the mass percentage content of the non-aqueous solvent is 74% to 90.7%. The electrochemical device including the above electrolyte has good cycle performance and safety performance, and can improve lithium deposition on the negative electrode.

[0064] 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 "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be disposed on one surface of the positive electrode current collector along its own thickness direction, or may be disposed on both surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the surface of the positive electrode current collector, or may be a partial area of the surface of the positive electrode current collector. There is no particular limitation in the present application, as long as the purpose of the present application can be achieved.

[0065] There is no particular 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 may be used. For example, the metal foil may include, but is not limited to, aluminum foil; the composite current collector may 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.

[0066] In the present application, the positive electrode material layer includes a positive electrode active material. There is no particular 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 may include, but is not limited to, lithium nickel cobalt manganese oxide (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 manganese oxide.

[0067] In the present application, the positive electrode material layer may further include a conductive agent and a binder. There is no particular 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 may be at least one of the aforementioned conductive agent and the aforementioned binder. There is no particular 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.

[0068] 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.

[0069] 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.

[0070] 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) based on 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.

[0071] 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, and 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.

[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 particular 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. 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 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 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.

[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 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 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, 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 discharging.

[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 performance in use.

[0076] 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 headset, a video recorder, a liquid crystal television, a hand-held 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, an electric motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor, etc.

[0077] Example

[0078] 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.

[0079] Testing method and device:

[0080] Test of the values of A and B

[0081] The silicon carbide particles in each example or comparative example are etched using an argon ion single-atom beam, the etching depth is from 0 nm to 100 nm, and then the atomic percentage A of silicon element in the first region from the sample surface to a depth of 100 nm from the sample surface is measured. The above silicon carbide particles are continuously etched using an argon ion single-atom beam, the etching depth is from 200 nm to 500 nm, and then the atomic percentage B of silicon element in the second region from a depth of 200 nm from the sample surface to a depth of 500 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.

[0082] Specific surface area test

[0083] A fully automatic specific surface area and porosity analyzer (model: ASAP2020 HD88) is used to measure the specific surface area of the silicon carbide particles in the examples or comparative examples by the nitrogen adsorption method.

[0084] Test of the size of silicon grains

[0085] Take out the sample holder, glass slide and spatula used for sample preparation. Load silicon carbide particle powder with a mass of M g into the groove of the sample holder. Use the spatula to flatten the silicon carbide particle powder and then gently press the surface of the silicon carbide particle powder with the glass slide to make the powder surface consistent with the surface of the sample holder. Use an X-ray powder diffractometer (model POWDIX600 / 300), set the test radiation source to Kα ray of Cu target, tube voltage to 40 kV, tube current to 30 mA, scanning speed to 8° / min, and 2θ range to 10° to 80°. Use the Scherrer formula to calculate the size D1 of the silicon crystal grains.

[0086] Measurement of the average particle size of silicon carbide particles

[0087] Perform plasma longitudinal cutting on the negative electrode plate along the thickness direction, polish it using argon ion polishing technology to obtain a flat cross-section. Then, use a scanning electron microscope (SEM, model OXFORD·EDS) to take SEM photos at a magnification of 50,000 times to observe the silicon carbide particles. Then, use image analysis software to randomly select 30 silicon carbide particles from the SEM photos, calculate the area of each of these silicon carbide particles. Then, assuming that the silicon carbide particles are spherical, calculate the particle size D (diameter) of each using the following formula: D = 2×(S1 / π) 1 / 2 ; where S1 is the area of the silicon carbide particle; and take the average value of the particle sizes of the obtained 30 silicon carbide particles, which is the average particle size D2 of the silicon carbide particles.

[0088] Measurement of the porosity of the negative electrode plate

[0089] Take the negative electrode plate in the example or comparative example, cut it into a negative electrode plate sample with dimensions of 50 mm×100 mm, place the negative electrode plate sample in a true density tester (model AccuPyc II 1340) to measure the true volume V of the negative electrode plate sample. Then, use a micrometer to measure the thickness T of the negative electrode plate sample, and calculate the apparent volume V0 of the negative electrode plate sample = 50×100×T. Then, the porosity of the negative electrode plate

[0090] Measurement of the 25°C cycle capacity retention rate of lithium-ion batteries

[0091] Charge the lithium-ion battery in the example or comparative example at a constant current of 0.2C to 4.45V at 25°C, then charge it at a constant voltage of 4.45V to 0.05C, let it stand for 5 minutes, and then discharge it at a constant current of 0.2C to 3.0V. This is one charge-discharge cycle, and record the discharge capacity at this time as C0. Repeat the above charge-discharge cycle 500 times, and record the discharge capacity after 500 cycles as C1. The 25°C cycle 500-cycle capacity retention rate (%) = C1 / C0×100%.

[0092] The cycle performance of a lithium-ion battery is characterized by the cycle capacity retention rate of the lithium-ion battery at 25°C. The higher the cycle capacity retention rate of the lithium-ion battery at 25°C, the better the cycle performance of the lithium-ion battery.

[0093] Lithium plating test

[0094] The lithium-ion battery in the example or comparative example is left standing for 5 minutes at a test temperature of 0°C, charged at a constant current of 0.2C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C. At this time, the lithium-ion battery reaches a fully charged state; it is left standing for 5 minutes, and then discharged at a constant current of 0.2C to 3.0V and left standing for 5 minutes. After repeating the above charge and discharge process 10 times, the lithium-ion battery is fully charged, disassembled in a drying room, and the state of the negative electrode sheet is photographed and recorded.

[0095] Judgment of the degree of lithium plating: It is judged according to the state of the fully charged and disassembled negative electrode sheet. 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 < 10%, it is judged as slight lithium plating; when the gray area on the negative electrode sheet ≥ 10% and < 50%, it is judged as lithium plating; when the gray area on the negative electrode sheet ≥ 50%, it is judged as severe lithium plating.

[0096] Overcharge test

[0097] Under the condition of 45°C, the lithium-ion battery in the example or comparative example is charged at a constant current of 0.2C to 4.45V, left standing for 5 minutes, then discharged at a constant current of 0.2C to 3.0V, left standing for 5 minutes, then charged at a constant current of 3C to 4.8V, and then charged at a constant voltage of 4.8V. The charging is stopped when the charging time is limited to 6 hours or the surface temperature of the battery is stable (temperature difference ≤ 2°C within 30 minutes). 10 lithium-ion batteries are tested in each group, and the state of the lithium-ion battery is observed during the test. The lithium-ion battery passes if it does not catch fire or explode. Overcharge test pass rate (%) = the number of lithium-ion batteries that do not catch fire or explode in the overcharge test / 10 × 100%.

[0098] The safety performance of a lithium-ion battery is characterized by the overcharge test pass rate of the lithium-ion battery. The higher the overcharge test pass rate, the better the safety performance of the lithium-ion battery.

[0099] Example 1-1

[0100] <Preparation of negative electrode material>

[0101] (1) Provide a porous carbon matrix, perform 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 8.4 μm; the temperature T1 of the first heat preservation treatment is 450 °C, the time t1 of the first heat preservation treatment is 1.5 h; the time t2 for introducing the silane gas after the first heat preservation treatment is 330 min; the flow rate V1 of the silane gas is 2 L / min; the silane gas is silane.

[0102] (2) Perform a second heat preservation treatment on the first intermediate in a nitrogen atmosphere, and then introduce a silane gas to obtain a second intermediate. Among them, the temperature T2 of the second heat preservation treatment is 440 °C, the time t3 of the second heat preservation treatment is 2 h; the time t4 for introducing the silane gas after the second heat preservation treatment is 220 min, the flow rate V2 of the silane gas is 1 L / min; the silane gas is silane.

[0103] (3) Perform a third heat preservation treatment on the second intermediate in 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 480 °C, the time t5 of the third heat preservation treatment is 1 h; the time t6 for introducing the first compound is 240 min, the flow rate V3 of the first compound is 6 L / min; the first compound is acetylene.

[0104] (4) Mix the silicon-carbon particles and artificial graphite of carbon material evenly according to a mass ratio of 15:85 to obtain a negative electrode material.

[0105] <Preparation of negative electrode plate>

[0106] 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, then dissolve them in deionized water as the negative electrode solvent, mix evenly, and make a negative electrode material layer slurry with a solid content of 45 wt%. Uniformly coat the negative electrode material layer slurry on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and perform a drying treatment at 85 °C for 4 h to obtain a negative electrode plate with a single-sided coated negative electrode material layer. The coating weight CW of the negative electrode 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 plate 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 plate with a specification of 76.6 mm × 875 mm for standby. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 37 μm, and the porosity of the negative electrode plate is 21.3%.

[0107] <Preparation of positive electrode plate>

[0108] The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 96.3:2.2:1.5, and after adding the positive electrode solvent N-methylpyrrolidone, they are stirred evenly to obtain a positive electrode material layer slurry with a solid content of 75 wt%. The positive electrode material layer slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13 μm, and dried at 85 °C to obtain a positive electrode plate with a single-sided coated positive electrode material layer. 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 plate with a double-sided coated positive electrode material layer. After cold pressing, slicing, and slitting, it is dried under vacuum conditions at 85 °C for 4 hours to obtain a positive electrode plate 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.

[0109] <Preparation of electrolyte>

[0110] In an argon atmosphere glove box with a water content < 10 ppm, ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed evenly at a volume ratio of 1:1 to obtain a basic solvent. Lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide as a second type of auxiliary salt, and lithium salt LiPF6 are added to the basic solvent and stirred evenly to obtain an electrolyte. Among them, based on the mass of the electrolyte, the mass percentage content P of the first type of auxiliary salt is 0.5% (the mass percentage content of lithium tetrafluoroborate is 0.3%, and the mass percentage content of lithium difluorophosphate is 0.2%), the mass percentage content T of the second type of auxiliary salt is 1%, the mass percentage content of lithium salt LiPF6 is 12.5%, and the mass percentage content of the basic solvent is 86%.

[0111] <Separator>

[0112] A polypropylene (PP) separator with a thickness of 4.5 μm is used.

[0113] <Preparation of lithium-ion battery>

[0114] The positive electrode plate after welding the tab, the separator, and the negative electrode plate after welding the tab are stacked in sequence, with the separator placed in the middle of the positive electrode plate and the negative electrode plate to play a role in isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film, dried in a vacuum oven at 80 °C for 12 hours to remove moisture, injected with the above-prepared electrolyte, and obtained a lithium-ion battery through processes such as vacuum packaging, standing, forming, degassing, and trimming.

[0115] Examples 1-2 to Examples 1-10

[0116] Except for adjusting and controlling the preparation parameters with reference to Table 1 in the <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.

[0117] Examples 1-11 to 1-16

[0118] Except for adjusting and controlling the preparation parameters with reference to Table 1 in the <Preparation of Anode Material> such that the size D1 of the silicon grains in the silicon-carbon particles is as shown in Table 2, the rest is the same as in Example 1-1.

[0119] Example 1-17

[0120] Except for using disilane as the silane-containing gas introduced after the first heat preservation treatment and the silane-containing gas introduced after the second heat preservation treatment in the <Preparation of Anode Material> and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0121] Example 1-18

[0122] Except for using propylene as the first compound in the <Preparation of Anode Material> and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0123] Examples 2-1 to 2-4

[0124] Except for adjusting the average particle size of the porous carbon matrix in the <Preparation of Anode Material> such that the average particle size D2 of the silicon-carbon particles is as shown in Table 3, the rest is the same as in Example 1-1.

[0125] Examples 2-5 to 2-8

[0126] Except for adjusting the mass ratio of the silicon-carbon particles to the carbon material in the <Preparation of Anode Material> such that the porosity of the anode electrode is as shown in Table 3, the rest is the same as in Example 1-1.

[0127] Examples 2-9 to 2-12

[0128] Except for adjusting the coating amount of the anode material layer slurry in the <Preparation of Anode Material> such that the coating weight CW of the anode material layer is as shown in Table 3, the rest is the same as in Example 1-1.

[0129] Examples 3-1 to 3-7

[0130] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as in Example 1-1. Among them, when the mass percentage content of a certain type of auxiliary salt changes, the mass percentage content of the base solvent changes accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage content of the lithium salt remains unchanged; when the mass percentage content of another type of auxiliary salt changes, the mass percentage content of the lithium salt changes accordingly, the mass ratio of each component of the base solvent and the mass percentage content of the base solvent remain unchanged; when the mass percentage contents of a certain type of auxiliary salt and another type of auxiliary salt change, the mass percentage contents of the base solvent and the lithium salt change accordingly, the sum of the mass percentage contents of the certain type of auxiliary salt and the base solvent remains unchanged, the sum of the mass percentage contents of the another type of auxiliary salt and the lithium salt remains unchanged, and the mass ratio of each component of the base solvent remains unchanged.

[0131] Comparative Examples 1 to 4

[0132] Except for referring to Table 1 to adjust the preparation parameters 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 in Example 1-1.

[0133] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 4.

[0134] Table 1

[0135]

[0136]

[0137] Table 2

[0138]

[0139] It can be seen from Example 1-1 to Example 1-18 and Comparative Examples 1 to 4 that when the values of A and 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 25°C cycle capacity retention rate and the overcharge test passing rate of the obtained lithium-ion battery are relatively high, and there is no lithium deposition phenomenon, indicating that the lithium-ion battery of this application has good cycle performance and safety performance, and the lithium deposition on the negative electrode is improved.

[0140] It can be seen from Example 1-1 to Example 1-10 that when the value of B / A is within the scope of this application, the 25°C cycle capacity retention rate and the overcharge test passing rate of the obtained lithium-ion battery are relatively high, and there is no lithium deposition phenomenon, indicating that the cycle performance of the lithium-ion battery of this application is improved, and at the same time it has good safety performance, and the lithium deposition on the negative electrode is improved.

[0141] It can be seen from Examples 1-1, 1-11 to 1-16 that when the value of D1 is within the scope of the present application, the lithium-ion battery has a high 25°C cycle capacity retention rate and overcharge test passing rate, and no lithium deposition phenomenon occurs, indicating that the cycle performance of the lithium-ion battery of the present application is improved, and it has good safety performance, and lithium deposition on the negative electrode is improved.

[0142]

[0143] It can be seen from Examples 1-1, 2-1 to 2-4 that when the value of D2 is within the scope of the present application, the lithium-ion battery has a high 25°C cycle capacity retention rate and overcharge test passing rate, and no lithium deposition phenomenon occurs in Examples 2-1 to 2-3, and slight lithium deposition occurs in Example 2-4, indicating that the cycle performance of the lithium-ion battery of the present application is improved, and it has good safety performance, and lithium deposition on the negative electrode is improved.

[0144] It can be seen from Examples 1-1, 2-5 to 2-8 that when the value is within the scope of the present application, the lithium-ion battery has a high 25°C cycle capacity retention rate and overcharge test passing rate, and no lithium deposition phenomenon occurs in Examples 2-6 to 2-8, and slight lithium deposition occurs in Example 2-5, indicating that the cycle performance of the lithium-ion battery of the present application is improved, lithium deposition on the negative electrode is improved, and it has good safety performance at the same time.

[0145] It can be seen from Examples 1-1, 2-9 to 2-12 that when the value of CW is within the scope of the present application, the lithium-ion battery has a high 25°C cycle capacity retention rate and overcharge test passing rate, and no lithium deposition phenomenon occurs in Examples 2-9 to 2-10, and slight lithium deposition occurs in Examples 2-11 to 2-12, indicating that the cycle performance of the lithium-ion battery of the present application is improved, and it has good safety performance, and lithium deposition on the negative electrode is improved.

[0146] Table 4

[0147]

[0148] Note: Taking Example 1-1 as an example, the "type of a kind of auxiliary salt" is "lithium tetrafluoroborate + lithium difluorophosphate", and "P(%)" is "0.3 + 0.2", indicating that the a kind of auxiliary salt includes lithium tetrafluoroborate and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of lithium tetrafluoroborate is 0.3%, and the mass percentage of lithium difluorophosphate is 0.2%. The same applies to other examples.

[0149] It can be seen from Example 1-1, Example 3-1, Examples 3-3 to 3-5, and Example 3-7 that when the types of the first type of auxiliary salt and the second type of auxiliary salt are within the scope of the present application, the 25°C cycle capacity retention rate and the overcharge test passing rate of the obtained lithium-ion battery are relatively high. Moreover, no lithium deposition phenomenon occurred in Example 1-1, Example 3-1, and Examples 3-4 to 3-5, and slight lithium deposition occurred in Example 3-7, indicating that the cycle performance of the lithium-ion battery of the present application is improved, while having good safety performance, and the lithium deposition on the negative electrode is improved.

[0150] It can be seen from Example 1-1, Example 3-1 to Example 3-6 that when the mass percentage content P of the first type of auxiliary salt and the mass percentage content T of the second type of auxiliary salt are within the scope of the present application, the 25°C cycle capacity retention rate and the overcharge test passing rate of the obtained lithium-ion battery are relatively high. Moreover, no lithium deposition phenomenon occurred in Example 1-1, Example 3-1 to Example 3-5, and slight lithium deposition occurred in Example 3-6, indicating that the cycle performance of the lithium-ion battery of the present application is improved, while having good safety performance, and the lithium deposition on the negative electrode is improved.

[0151] It can be seen from Example 1-1, Example 3-1 to Example 3-7 that when the value of P / T is within the scope of the present application, the 25°C cycle capacity retention rate and the overcharge test passing rate of the obtained lithium-ion battery are relatively high. Moreover, no lithium deposition phenomenon occurred in Example 1-1, Example 3-1 to Example 3-5, and slight lithium deposition occurred in Example 3-6 and Example 3-7, indicating that the cycle performance of the lithium-ion battery of the present application is improved, while having good safety performance, and the lithium deposition on the negative electrode is improved.

[0152] 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 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 also includes elements inherent to such process, method or article.

[0153] 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 differences between each embodiment and other embodiments are emphasized in each embodiment.

[0154] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode material, wherein: The negative electrode material includes silicon carbon particles, and the silicon carbon particles 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 100 nm from the surface of the silicon carbon particles; the second region is a region from a depth of 200 nm from the surface of the silicon carbon particles to a depth of 500 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%, 4.04≤A≤16.89; 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%, 15≤B≤20.

88.

2. The negative electrode material according to claim 1, wherein 1.05≤B / A≤4.

84.

3. The negative electrode material according to claim 2, wherein 1.2≤B / A≤3.

8.

4. The negative electrode material according to claim 1, wherein The specific surface area of ​​the silicon carbon particles is 0.7 m 2 / g to 6.21m 2 / g.

5. The negative electrode material according to claim 1, wherein The size D1 of the silicon grains in the silicon-carbon particles is 0.91 nm to 6.37 nm. Preferably, the size D1 of the silicon grains in the silicon-carbon particles is 1.02 nm to 2.35 nm.

6. The negative electrode material according to claim 1, wherein The average particle size D2 of the silicon-carbon particles is 7.5 μm to 9.2 μm.

7. A method for preparing the negative electrode material according to any one of claims 1 to 6, 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 430° C. to 480° C., and the time t1 of the first heat preservation treatment is 0.5 h to 2 h; the time t2 of introducing the silane-containing gas after the first heat preservation treatment is 300 min to 660 min, and the flow rate V1 of the silane-containing gas is 0.5 L / min to 3 L / min; the silane-containing gas comprises 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 the silane-containing gas to obtain a second intermediate; the temperature T2 of the second heat preservation treatment is 400° C. to 470° C., and the time t3 of the second heat preservation treatment is 1 h to 2 h; the time t4 of introducing the silane-containing gas after the second heat preservation treatment is 160 min to 240 min, and the flow rate V2 of the silane-containing gas is 0.5 L / min to 1.5 L / min; (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 480°C to 600°C, and the time t5 of the third insulation treatment is 0.5h to 2h; the time t6 for introducing the first compound is 120min to 400min, and the flow rate V3 of the first compound is 3L / min to 10L / min; the first compound includes at least one of acetylene, propylene or toluene.

8. 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 6.

9. The electrochemical device according to claim 8, wherein: The negative electrode sheet satisfies at least one of the following conditions: (1) Porosity of the negative electrode sheet 17.7% to 24.8%; (2) The coating weight of the negative electrode material layer is 80.6 mg / 1540.25 mm 2 Up to 100.5mg / 1540.25mm 2 .

10. The electrochemical device according to claim 8, wherein The electrolyte includes a first type of auxiliary salt and a second type of auxiliary salt, wherein the first type of auxiliary salt includes at least one of lithium difluorophosphate, lithium difluoroborate, lithium tetrafluoroborate, lithium dioxalatoborate or lithium difluorooxalatoborate; and the second type of auxiliary salt includes at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

11. The electrochemical device according to claim 10, which satisfies at least one of the following conditions: (1) Based on the mass of the electrolyte, the mass percentage P of the first type of auxiliary salt is 0.3% to 1%; (2) Based on the mass of the electrolyte, the mass percentage T of the second type of auxiliary salt is 1% to 5%.

12. The electrochemical device according to claim 10, wherein: Based on the mass of the electrolyte, the mass percentage of the first type of auxiliary salt is P, the mass percentage of the second type of auxiliary salt is T, 0.1≤P / T≤1, preferably, 0.2≤P / T≤0.

8.

13. An electronic device, wherein: The electronic device comprises the electrochemical device according to any one of claims 8 to 12.

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