Negative electrode, electrochemical device including the negative electrode, and electronic device.

Abstract

This application provides a negative electrode sheet, an electrochemical device including the negative electrode sheet, and an electronic device. The negative electrode sheet includes a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector. The first negative electrode material layer is disposed between the negative electrode current collector and the second negative electrode material layer. The first negative electrode material layer includes a first negative electrode active material, which includes first graphite. The second negative electrode material layer includes a second negative electrode active material and nano-metal oxides. The second negative electrode active material includes silicon carbide and second graphite. The nano-metal oxides include at least one of aluminum oxide, zinc oxide, magnesium oxide, tin oxide, indium oxide, zirconium oxide, copper oxide, or silver oxide. Based on the mass of the second negative electrode material layer, the mass percentage of the nano-metal oxides is from 0.01% to 10%. Applying the negative electrode sheet of this application to an electrochemical device enables the electrochemical device to have good cycle performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a negative electrode, an electrochemical device including the negative electrode, and an electronic device. Background Technology

[0002] With rapid societal development, higher demands are being placed on the energy density of electrochemical devices such as lithium-ion batteries. Due to the extremely high theoretical specific capacity of silicon-based materials, mixing them with graphite as the negative electrode active material significantly improves the energy density of lithium-ion batteries. However, the high reactivity between silicon-based materials and the electrolyte leads to continuous and rapid electrolyte consumption. In the later stages of cycling, the silicon-based material breaks off from the electrolyte, losing its reactivity, ultimately resulting in accelerated capacity decay of the lithium-ion battery and affecting its cycle performance. Therefore, improving the cycle performance of lithium-ion batteries has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode, an electrochemical device including the negative electrode, and an electronic device to improve the cycle performance of the electrochemical device.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of an electrochemical device to explain the invention, the electrochemical device described herein is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0005] The first aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector, the first negative electrode material layer being disposed between the negative electrode current collector and the second negative electrode material layer; the first negative electrode material layer comprising a first negative electrode active material, which includes a first graphite; the second negative electrode material layer comprising a second negative electrode active material and a nano-metal oxide, the second negative electrode active material including silicon carbide and a second graphite, the nano-metal oxide including at least one selected from aluminum oxide, zinc oxide, magnesium oxide, tin oxide, indium oxide, zirconium oxide, copper oxide, or silver oxide; based on the mass of the second negative electrode material layer, the mass percentage content of the nano-metal oxide is from 0.01% to 10%. The negative electrode sheet of this application, by simultaneously disposing of a first negative electrode material layer and a second negative electrode material layer on the surface of the negative electrode current collector, and by mixing silicon carbide and a second graphite in the second negative electrode material layer as the second negative electrode active material, leverages the high capacity characteristics of silicon carbide to improve the energy density of the electrochemical device. The high reactivity between silicon-carbon materials and electrolytes necessitates a significant increase in electrolyte levels during the cycling process of electrochemical devices. This application addresses this by placing a second negative electrode material layer on the surface of the negative electrode sheet, where electrolyte transport is more efficient, thus ensuring a continuous replenishment of electrolyte around the silicon-carbon material. Furthermore, the addition of nano-metal oxides within the scope of this application to the second negative electrode material layer enhances its wettability with the electrolyte, promoting uniform electrolyte distribution within the pores of the layer. This reduces the probability of the silicon-carbon material losing its reactivity due to localized electrolyte deficiency, leading to a significant capacity drop in the later stages of the electrochemical device's cycle. Consequently, the cycling performance of the electrochemical device is improved, resulting in a higher energy density.

[0006] In some embodiments of this application, the mass percentage of nano-metal oxide is 0.1% to 6% based on the mass of the second negative electrode material layer. Controlling the mass percentage of nano-metal oxide within this range is beneficial for improving the wettability of the second negative electrode material layer to the electrolyte, thereby further improving the cycle performance of the electrochemical device.

[0007] In some embodiments of this application, the mass percentage of nano-metal oxide is 0.5% to 3% based on the mass of the second negative electrode material layer. Controlling the mass percentage of nano-metal oxide within this range is beneficial for further improving the cycle performance of the electrochemical device.

[0008] In some embodiments of this application, the particle size Dv50 of the nano-metal oxide is... -1 The particle size ranges from 10 nm to 1000 nm. The particle size Dv50 of the nano-metal oxides... -1Adjusting the parameters within the above range is beneficial for improving the wettability of nano-metal oxides to the electrolyte and enhancing the cycle performance of the electrochemical device.

[0009] In some embodiments of this application, the particle size Dv50 of the nano-metal oxide is... -1 The particle size ranges from 100 nm to 600 nm. The particle size Dv50 of the nano-metal oxides... -1 Regulating within the above range is beneficial to further improve the cycle performance of the electrochemical device.

[0010] In some embodiments of this application, the particle size of the first graphite is Dv50. -2 The particle size Dv50 of the second graphite ranges from 11.0 μm to 13.5 μm. -3 The particle size of the first graphite is 9 μm to 12 μm. -2 The particle size Dv50 of the second graphite -3 Within the above range, the electrochemical device exhibits high energy density while maintaining good cycle performance.

[0011] In some embodiments of this application, the particle size of the silicon-carbon material is Dv10, Dv50. -4 Dv90 satisfies: 5μm≤Dv10≤6μm, 8μm≤Dv50 -4 ≤10.5μm, 13μm≤Dv90≤17μm. The particle size of silicon-carbon materials is Dv10, Dv50. -4 With Dv90 controlled within the aforementioned range, the cycle performance and energy density of the electrochemical device are improved.

[0012] In some embodiments of this application, the particle sizes Dv10 and Dv90 of the silicon-carbon material satisfy the following: 7.5 μm ≤ Dv90 - Dv10 ≤ 11.5 μm. Controlling the values ​​of Dv90-Dv10 within this range allows for a suitable gradient distribution of silicon-carbon materials of different particle sizes. This facilitates a tight and uniform distribution of the silicon-carbon material in the second negative electrode material layer, reduces the consumption of electrolyte by the silicon-carbon material, and improves the cycle performance of the electrochemical device while maintaining a high energy density.

[0013] In some embodiments of this application, the overall mass percentage of silicon-carbon material in the negative electrode is 10% to 30%, the mass percentage of silicon-carbon material in the second negative electrode active material is 20% to 80%, and the mass percentage of silicon in the silicon-carbon material is 30% to 60%. By controlling the overall mass percentage of silicon-carbon material in the negative electrode, the content of silicon-carbon material in the second negative electrode active material, and the content of silicon in the silicon-carbon material within the above-mentioned ranges, the electrochemical device can have good cycle performance and high energy density.

[0014] In some embodiments of this application, the specific surface area of ​​the silicon-carbon material is 0.5 m². 2 / g to 3.5m 2 / g. By controlling the specific surface area of ​​silicon-carbon materials within the above range, the electrochemical device exhibits good cycle performance and high energy density.

[0015] In some embodiments of this application, the specific surface area of ​​the silicon-carbon material is 1.0 m². 2 / g to 2.0m 2 / g. Controlling the specific surface area of ​​silicon-carbon materials within the above range is beneficial for further improving the cycle performance of electrochemical devices while maintaining high energy density.

[0016] A second aspect of this application provides an electrochemical device comprising the negative electrode as described in any of the foregoing embodiments. Therefore, the electrochemical device exhibits good cycle performance.

[0017] A third aspect of this application provides an electronic device comprising the electrochemical device described in any of the foregoing embodiments. Therefore, the electronic device exhibits excellent performance.

[0018] The beneficial effects of the embodiments of this application are as follows:

[0019] This application provides a negative electrode sheet, an electrochemical device including the negative electrode sheet, and an electronic device. The negative electrode sheet has a first negative electrode material layer and a second negative electrode material layer simultaneously disposed on the surface of the negative electrode current collector. The second negative electrode material layer on the surface of the negative electrode sheet contains graphite, silicon carbon material, and nano-metal oxides. The silicon carbon material is enriched on the surface of the negative electrode sheet, where the electrolyte is more easily transported, continuously replenishing the electrolyte around the silicon carbon material and allowing the silicon carbon material to provide more capacity to the negative electrode sheet. The addition of nano-metal oxides in the second negative electrode material layer improves the wettability of the negative electrode sheet to the electrolyte, ensuring uniform distribution of the electrolyte within the pores of the negative electrode sheet and reducing the probability of the silicon carbon material losing its reactivity due to localized electrolyte loss. Thus, applying the negative electrode sheet of this application to an electrochemical device can alleviate the problem of capacity drop in the later stages of the electrochemical device cycle due to rapid electrolyte consumption. Therefore, the cycle performance of the electrochemical device can be improved, and the electrochemical device can have a higher energy density.

[0020] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0022] Figure 1 This is a schematic cross-sectional view of the negative electrode sheet along its length and thickness in some embodiments of this application.

[0023] Figure label:

[0024] 10-Negative electrode sheet; 11-First negative electrode material layer; 12-Second negative electrode material layer; 13-Negative electrode current collector; 131-First surface; 132-Second surface. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0027] The first aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the first negative electrode material layer is disposed between the negative electrode current collector and the second negative electrode material layer. The aforementioned "first negative electrode material layer and second negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the first negative electrode material layer and the second negative electrode material layer can be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. The aforementioned "surface" refers to a portion or all of the surface of the negative electrode current collector. The first negative electrode material layer includes a first negative electrode active material, which includes a first graphite; the second negative electrode material layer includes a second negative electrode active material and a nano-metal oxide, wherein the second negative electrode active material includes silicon carbide and a second graphite, and the nano-metal oxide includes at least one selected from aluminum oxide, zinc oxide, magnesium oxide, tin oxide, indium oxide, zirconium oxide, copper oxide, or silver oxide; based on the mass of the second negative electrode material layer, the mass percentage content of the nano-metal oxide is from 0.01% to 10%.

[0028] For ease of understanding, in this application, the length direction of the negative electrode sheet is defined as X, and the thickness direction is defined as Z. It should be understood that the above definitions of direction are for the purpose of describing this application, and the directions defined in this application can be understood based on the relative positions of the elements in the accompanying drawings and the actual product. It is understood that the length and thickness directions of the negative electrode current collector, the first negative electrode material layer, and the second negative electrode material layer are the same as those of the negative electrode sheet. Figure 1 The following are schematic cross-sectional views of the negative electrode sheet along its length direction X and thickness direction Z in some embodiments of this application, such as... Figure 1 As shown, the negative electrode 10 includes a negative electrode current collector 13, a first negative electrode material layer 11, and a second negative electrode material layer 12. The negative electrode current collector 13 includes a first surface 131 and a second surface 132 disposed along its thickness direction Z. The first negative electrode material layer 11 and the second negative electrode material layer 12 are disposed on the two surfaces of the negative electrode current collector 13, namely the first surface 131 and the second surface 132, with the first negative electrode material layer 11 disposed between the negative electrode current collector 13 and the second negative electrode material layer 12. It is understood that in some other embodiments of this application, the first negative electrode material layer 11 and the second negative electrode material layer 12 may be disposed on one surface of the negative electrode current collector 13, namely the first surface 131 or the second surface 132. By disposing of the second negative electrode material layer containing silicon-carbon material on the surface of the negative electrode 10 where the electrolyte is more easily transported, the electrolyte around the silicon-carbon material can be continuously replenished, thereby reducing the probability of the silicon-carbon material losing its reactivity due to local electrolyte deficiency, which would lead to a drop in capacity in the later stages of the electrochemical device cycle.

[0029] For example, the mass percentage of nano-metal oxides can be 0.01%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within any two of the above ranges. Adding nano-metal oxides to the second negative electrode material layer can improve the wettability of the second negative electrode material layer to the electrolyte, which is beneficial for the uniform distribution of the electrolyte within the pores of the second negative electrode material layer. If the mass percentage of nano-metal oxides is less than 0.01%, the content of nano-metal oxides in the second negative electrode material layer is too low, making it difficult for them to exert their function; if the mass percentage of nano-metal oxides is greater than 10%, the content of nano-metal oxides in the second negative electrode material layer is too high, which will correspondingly reduce the content of other components (such as the second negative electrode active material), thereby affecting the performance of the second negative electrode material layer, such as the processing reliability and capacity of the second negative electrode material layer, and thus affecting the performance of the electrochemical device.

[0030] Overall, the negative electrode sheet of this application simultaneously sets a first negative electrode material layer and a second negative electrode material layer on the surface of the negative electrode current collector. The second negative electrode material layer contains a mixture of silicon-carbon material and second graphite as the second negative electrode active material. The high capacity characteristics of silicon-carbon material are beneficial for improving the energy density of the electrochemical device. The high reactivity between silicon-carbon material and electrolyte means that silicon-carbon material requires a large amount of electrolyte during the electrochemical device cycle. This application addresses this by placing the second negative electrode material layer on the surface of the negative electrode sheet where electrolyte transport is easier, enabling continuous replenishment of electrolyte around the silicon-carbon material. Furthermore, the addition of nano-metal oxides within the scope of this application to the second negative electrode material layer improves the wettability of the negative electrode sheet to the electrolyte, facilitating uniform distribution of electrolyte within the pores of the second negative electrode material layer and reducing the probability of silicon-carbon material losing its reactivity due to localized electrolyte deficiency. Thus, applying this negative electrode sheet to an electrochemical device can alleviate the problem of capacity drop in the later stages of the electrochemical device cycle caused by rapid electrolyte consumption. This allows for improved cycle performance of the electrochemical device, and the electrochemical device also possesses a higher energy density.

[0031] In this application, the first graphite and the second graphite are each independently selected from natural graphite or artificial graphite.

[0032] In some embodiments of this application, the mass percentage of nano-metal oxide is between 0.5% and 3%, based on the mass of the second negative electrode material layer. For example, the mass percentage of nano-metal oxide is 0.5%, 1%, 1.2%, 1.6%, 2%, 2.3%, 2.6%, 3%, or any value within any two of the above ranges. Controlling the mass percentage of nano-metal oxide within the above range is beneficial for further improving the wettability of the second negative electrode material layer to the electrolyte, ensuring uniform distribution of the electrolyte within the pores of the second negative electrode material layer. This results in sufficient electrolyte around the silicon-carbon material during the electrochemical device's cycle, further reducing the probability of the silicon-carbon material losing its reactivity due to localized electrolyte deficiency, thus causing a significant capacity drop in the later stages of the electrochemical device's cycle. Therefore, the cycle performance of the electrochemical device is further improved.

[0033] In some embodiments of this application, the mass percentage of nano-metal oxide is 0.5% to 1.5% based on the mass of the second negative electrode material layer. For example, the mass percentage of nano-metal oxide is 0.5%, 1%, 1.2%, 1.4%, 1.5%, or any value between any two of the above ranges. Controlling the mass percentage of nano-metal oxide within the above range is beneficial for further improving the wettability of the negative electrode to the electrolyte, ensuring uniform distribution of the electrolyte within the pores of the second negative electrode material layer. This results in sufficient electrolyte around the silicon-carbon material during the electrochemical device's cycle, further reducing the probability of the silicon-carbon material losing its reactivity due to localized electrolyte deficiency, thus causing a significant capacity drop in the later stages of the electrochemical device's cycle. Consequently, the cycle performance of the electrochemical device is further improved.

[0034] In some embodiments of this application, the particle size Dv50 of the nano-metal oxide is... -1 The particle size is from 10 nm to 1000 nm, preferably from 100 nm to 600 nm. For example, the particle size Dv50 of the nano-metal oxide is... -1 The particle size Dv50 of the nano-metal oxide is 10nm, 70nm, 100nm, 200nm, 310nm, 390nm, 500nm, 600nm, 620nm, 700nm, 800nm, 900nm, 1000nm, or any value between any two of the above ranges. -1 Within the aforementioned range, the uniform distribution of nano-metal oxides in the second negative electrode material layer is beneficial, thereby improving the wettability of the negative electrode sheet to the electrolyte. This ensures the electrolyte is evenly distributed within the pores of the second negative electrode material layer, resulting in sufficient electrolyte around the silicon-carbon material during the electrochemical device's cycle. This reduces the probability of the silicon-carbon material losing its reactivity due to localized electrolyte deficiency, leading to a significant capacity drop in the later stages of the cycle. Consequently, the cycle performance of the electrochemical device is improved.

[0035] In some embodiments of this application, the particle size of the first graphite is Dv50. -2 The particle size ranges from 11.0 μm to 13.5 μm. For example, the first graphite has a particle size Dv50. -2 The particle size is 11.0 μm, 11.3 μm, 11.7 μm, 12.0 μm, 12.8 μm, 13.0 μm, 13.5 μm, or any value between any two of the above ranges. The particle size Dv50 of the first graphite is... -2Within the aforementioned range, the likelihood of agglomeration of the first graphite is low, allowing it to be uniformly distributed within the first negative electrode material layer. Furthermore, the surface area of ​​the first graphite ensures sufficient contact with the electrolyte, enabling it to fully exert its activity and resulting in a high capacity for the first negative electrode material layer. Consequently, the electrochemical device exhibits both good cycle performance and high energy density.

[0036] In some embodiments of this application, the particle size of the second graphite is Dv50. -3 The particle size ranges from 9 μm to 12 μm. For example, the particle size Dv50 of the second graphite is... -3 The particle size is 9 μm, 9.6 μm, 10.2 μm, 10.8 μm, 11.3 μm, 11.7 μm, 12 μm, or any value between any two of the above ranges. The particle size Dv50 of the second graphite is... -3 Within the aforementioned range, the second graphite has a shorter lithium intercalation path, resulting in a higher limiting lithium intercalation rate. This further enhances the kinetics of the second anode material layer and reduces anode electrode breakage.

[0037] In some embodiments of this application, the particle size of the silicon-carbon material is Dv10, Dv50. -4 Dv90 satisfies: 5μm≤Dv10≤6μm, 8μm≤Dv50 -4 ≤10.5μm, 13μm≤Dv90≤17μm. For example, the particle size Dv10 of silicon carbide materials is 5μm, 5.2μm, 5.4μm, 5.7μm, 5.8μm, 6μm, or any value between any two of the above ranges. For example, the particle size Dv50 of silicon carbide materials... -4 The particle size Dv90 of silicon carbide material is 8μm, 8.2μm, 8.7μm, 9.1μm, 9.8μm, 10.0μm, 10.5μm, or any value between any two of the above ranges. For example, the particle size Dv90 of silicon carbide material is 13μm, 13.6μm, 14.4μm, 14.7μm, 15.3μm, 16μm, 16.5μm, 17μm, or any value between any two of the above ranges. The particle size Dv10 and Dv50 of silicon carbide material are also considered. -4 When Dv90 is controlled within the aforementioned range, the silicon-carbon material has a suitable particle size with minimal inter-particle size differences. When distributed in the second negative electrode material layer, the probability of agglomeration is low, which is beneficial for uniform distribution within the second negative electrode material layer. This improves the wettability of the electrolyte on the negative electrode sheet, enhancing its wetting and liquid retention capabilities. Consequently, the utilization rate of the silicon-carbon material is improved, and the cycle performance and energy density of the electrochemical device are enhanced.

[0038] In some embodiments of this application, the particle sizes Dv10 and Dv90 of the silicon-carbon material satisfy the following condition: 7.5 μm ≤ Dv90 - Dv10 ≤ 11.5 μm. For example, the values ​​of Dv90 - Dv10 are 7.5 μm, 8.5 μm, 9.7 μm, 10.2 μm, 11.0 μm, 11.5 μm, or any value between any two of the above ranges. By controlling the values ​​of Dv90 - Dv10 within the above range, silicon-carbon materials of different particle sizes are distributed in a suitable gradient, which is beneficial for the close and uniform distribution of silicon-carbon materials in the second negative electrode material layer and reduces the consumption of electrolyte by silicon-carbon materials. This improves the cycle performance of the electrochemical device while maintaining a high energy density.

[0039] In this application, Dv10 refers to the particle size that, in a volumetric particle size distribution of silicon-carbon material, reaches 10% of the cumulative volume from the smallest particle size side. Dv90 refers to the particle size that, in a volumetric particle size distribution of silicon-carbon material, reaches 90% of the cumulative volume from the smallest particle size side. Dv50 refers to the particle size that, in a volumetric particle size distribution of silicon-carbon material, reaches 50% of the cumulative volume from the smallest particle size side. Here, "particles" can be silicon-carbon material, first graphite, second graphite, or nano-metal oxides.

[0040] This application does not impose any particular restrictions on the method of controlling the particle size of nano-metal oxides, silicon-carbon materials, first graphite, and second graphite, as long as the purpose of this application can be achieved. For example, it can be achieved through crushing or sieving. Alternatively, commercially available nano-metal oxides, silicon-carbon materials, first graphite, and second graphite can be purchased, and the particle sizes Dv50 of the nano-metal oxides, first graphite, and second graphite, and the particle sizes Dv10, Dv50, and Dv90 of the silicon-carbon materials can be determined by combining the test method for "particle size testing" in this application.

[0041] In some embodiments of this application, the overall mass percentage of silicon-carbon material in the negative electrode sheet is 10% to 30%, the mass percentage of silicon-carbon material in the second negative electrode active material is 20% to 80%, and the mass percentage of silicon in the silicon-carbon material is 30% to 60%. For example, the overall mass percentage of silicon-carbon material in the negative electrode sheet is 10%, 15%, 20%, 25%, 30%, 35%, 30%, or any value between any two of the above ranges. For example, the mass percentage of silicon-carbon material in the second negative electrode active material is 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any value between any two of the above ranges. For example, the mass percentage of silicon in the silicon-carbon material is 30%, 34%, 39%, 42%, 50%, 53%, 60%, or any value between any two of the above ranges. By controlling the silicon-carbon material content and the silicon element content within the silicon-carbon material to be within the aforementioned range in the second negative electrode active material, the silicon-carbon material can achieve a high capacity while exhibiting a low probability of volume expansion. Thus, applying silicon-carbon material to the second negative electrode material layer results in a second negative electrode material layer with high capacity and high reactivity. Applying this negative electrode to an electrochemical device enables the device to possess excellent cycle performance and high energy density.

[0042] In this application, "the overall mass percentage of silicon-carbon material in the negative electrode sheet" refers to the percentage of the mass of silicon-carbon material in the second negative electrode material layer relative to the sum of the mass of the first negative electrode active material in the first negative electrode material layer and the mass of the second negative electrode active material in the second negative electrode material layer.

[0043] In some embodiments of this application, the mass percentage of the second graphite in the second negative electrode active material is 20% to 80%.

[0044] This application does not impose any particular restrictions on the method of controlling the mass percentage of silicon in silicon-carbon materials, as long as the purpose of this application can be achieved. For example, when preparing silicon-carbon materials by depositing silicon in porous carbon, the mass percentage of silicon in the silicon-carbon material can be changed by controlling the amount of silicon deposited during the preparation process. Alternatively, silicon-carbon materials with different silicon contents can be purchased directly, and the desired silicon content can be selected by referring to the "testing of the mass percentage of silicon in silicon-carbon materials" provided in this application.

[0045] This application does not impose any particular limitation on the coating weight of the second negative electrode material layer, as long as it achieves the purpose of this application. For example, the coating weight of the second negative electrode material layer is 20mg / 1540.25mm. 2 Up to 80mg / 1540.25mm 2 .

[0046] This application does not impose any particular limitation on the total coating weight of the negative electrode sheet, as long as the purpose of this application is achieved. For example, the total coating weight of the negative electrode sheet is 80mg / 1540.25mm. 2 Up to 160mg / 1540.25mm 2 .

[0047] In some embodiments of this application, the specific surface area of ​​the silicon-carbon material is 0.5 m². 2 / g to 3.5m 2 / g. For example, the specific surface area of ​​silicon-carbon materials is 0.5m². 2 / g, 0.7m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.5m 2 / g or any value between any two of the above ranges. By controlling the specific surface area of ​​the silicon-carbon material within the above range, the surface of the silicon-carbon material can fully contact the electrolyte, allowing the silicon-carbon material to exert its high capacity characteristics, resulting in a high capacity negative electrode. When the negative electrode is applied in an electrochemical device, the electrochemical device exhibits good cycle performance and high energy density.

[0048] In some embodiments of this application, the specific surface area of ​​the silicon-carbon material is 1.0 m². 2 / g to 2.0m 2 / g. For example, the specific surface area of ​​silicon-carbon materials is 1.0 m². 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 2.0m 2 / g or any value between any two of the above ranges. Adjusting the specific surface area of ​​silicon-carbon materials within the above range is beneficial for further improving the cycle performance of electrochemical devices while maintaining high energy density.

[0049] This application does not impose any particular restrictions on the method of controlling the specific surface area of ​​silicon-carbon materials, as long as it achieves the purpose of this application. For example, it can be achieved by controlling the particle size of silicon-carbon materials or by controlling the pore size distribution of porous carbon when preparing silicon-carbon materials using a deposition method. Alternatively, it can be achieved by directly purchasing silicon-carbon materials with a specific surface area within the range of this application and combining it with the test method for "testing the specific surface area of ​​silicon-carbon materials" in this application to determine the specific surface area of ​​the silicon-carbon materials and select silicon-carbon materials with the desired specific surface area.

[0050] In some embodiments of this application, the tap density of the silicon carbide material is 0.8 g / cm³. 3 Up to 1.05 g / cm 3 For example, the tap density of silicon carbide materials is 0.8 g / cm³. 3 0.85g / cm 3 0.87g / cm 3 0.91g / cm 3 0.96g / cm 3 1.00g / cm 3 1.05g / cm 3 Or any value between any two of the above ranges. Controlling the tap density of silicon-carbon materials within the above range is beneficial for the presence of suitable porosity within the silicon-carbon materials, enabling electrochemical devices to achieve both high energy density and low volume expansion rate.

[0051] In some embodiments of this application, the mass percentage of the first negative electrode active material is 95% to 98.5% based on the mass of the first negative electrode material layer. Optionally, the first negative electrode material layer further includes a conductive agent, a thickener, and a binder. This application does not impose any particular limitation on the mass percentage of the conductive agent, thickener, and binder in the first negative electrode material layer, as long as the purpose of this application can be achieved. For example, based on the mass of the first negative electrode material layer, the mass percentage of the conductive agent is 0.1% to 0.5%, the mass percentage of the thickener is 0.1% to 0.5%, and the mass percentage of the binder is 1% to 4%.

[0052] In some embodiments of this application, the mass percentage of the second negative electrode active material is 90% to 98.5% based on the mass of the second negative electrode material layer. Optionally, the second negative electrode material layer further includes a conductive agent, a thickener, and a binder. This application does not impose any particular limitation on the mass percentage of the conductive agent, thickener, and binder in the second negative electrode material layer, as long as the purpose of this application is achieved. For example, based on the mass of the second negative electrode material layer, the mass percentage of the conductive agent is 0.1% to 0.5%, the mass percentage of the thickener is 0.1% to 0.5%, and the mass percentage of the binder is 1% to 9%.

[0053] This application does not impose any particular restrictions on the types of conductive agents, thickeners, and binders. Conductive agents, thickeners, and binders known in the art can be selected, as long as they can achieve the purpose of this application.

[0054] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector includes, but is not limited to, copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 20 μm. This application also does not impose any particular limitation on the thickness of the negative electrode sheet, the first negative electrode material layer, and the second negative electrode material layer, as long as they achieve the purpose of this application.

[0055] This application does not impose any particular restrictions on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of this application. For example, in some embodiments, the preparation method of the negative electrode sheet includes, but is not limited to, the following steps: (1) after mixing the first negative electrode active material, conductive agent, thickener and binder evenly, add solvent and stir evenly to obtain the first negative electrode slurry; (2) after mixing the second negative electrode active material, conductive agent, thickener, binder and nano metal oxide evenly, add solvent and stir evenly to obtain the second negative electrode slurry; (3) after coating the first negative electrode slurry on the two surfaces of the negative electrode current collector, after drying, a first negative electrode material layer is formed, and then, the second negative electrode slurry is coated on the surfaces of the two first negative electrode material layers away from the negative electrode current collector, after drying, a second negative electrode material layer is formed, and after cold pressing and cutting, a negative electrode sheet with a first negative electrode material layer and a second negative electrode material layer on both sides is obtained. In other embodiments, the preparation method of the negative electrode sheet includes, but is not limited to, the following steps: (1) mixing the first negative electrode active material, conductive agent, thickener, and binder evenly, adding solvent, and stirring evenly to obtain a first negative electrode slurry; (2) mixing the second negative electrode active material, conductive agent, thickener, binder, and nano-metal oxide evenly, adding solvent, and stirring evenly to obtain a second negative electrode slurry; (3) coating the first negative electrode slurry on one surface of the negative electrode current collector, drying it, forming a first negative electrode material layer on the surface of the negative electrode current collector, coating the second negative electrode slurry on the surface of the first negative electrode material layer away from the negative electrode current collector, drying it, and then cold pressing and slitting to obtain a negative electrode sheet with a first negative electrode material layer and a second negative electrode material layer on one side. This application does not have any particular restrictions on the type of solvent in steps (1) and (2) above, as long as it can achieve the purpose of this application. This application does not have any particular restrictions on the solid content of the first and second negative electrode slurries above, as long as it can achieve the purpose of this application. This application does not impose any particular restrictions on the drying temperature and time in step (3) above. Those skilled in the art can choose according to the actual situation, as long as the purpose of this application can be achieved.

[0056] A second aspect of this application provides an electrochemical device comprising the negative electrode as described in any of the foregoing embodiments. Therefore, the electrochemical device exhibits good cycle performance.

[0057] The electrochemical device of this application includes a positive electrode. This application does not impose any particular limitation on the positive electrode, as long as it achieves the purpose of this application. In some embodiments, the positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is disposed on one or both surfaces of the positive current collector. The aforementioned "surface" can be a portion of the surface of the positive current collector or the entire surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may contain aluminum foil or aluminum alloy foil. The positive active material layer of this application contains a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material may contain at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. In this application, the positive electrode active material may further include non-metallic elements, which may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive electrode active material. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness of the single-layer positive electrode active material layer is 30 μm to 120 μm. Optionally, the positive electrode active material layer may further include at least one of a conductive agent or a binder. This application does not particularly limit the types of conductive agents and binders in the positive electrode active material layer, as long as the purpose of this application is achieved. This application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved.

[0058] The electrochemical device of this application also includes a diaphragm disposed between the positive electrode and the negative electrode to separate them. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane. This application does not impose any particular limitation on the thickness of the diaphragm, as long as it achieves the purpose of this application.

[0059] The electrochemical device of this application also includes an electrolyte. This application does not impose any particular limitation on the electrolyte, as long as it achieves the purpose of this application. For example, in some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiNO3, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinylene carbonate. Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1,2-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester 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, decanolactone, valproic acid lactone, or caprolactone. The aforementioned 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 aforementioned 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-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0060] The electrochemical device of this application also includes a housing for accommodating the positive electrode, the negative electrode, the separator, and the electrolyte, as well as other components known in electrochemical devices in the art. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be any housing known in the art, as long as it achieves the purpose of this application.

[0061] This application does not impose any particular limitation on the type of electrochemical device, which may include any device in which an electrochemical reaction occurs. For example, electrochemical devices may include, but are not limited to, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0062] The preparation process of the electrochemical device in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the diaphragm, positive electrode, diaphragm and negative electrode in sequence, and winding, folding or other operations as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and obtaining the electrochemical device through processes such as formation, degassing and shaping. Alternatively, stacking the diaphragm, positive electrode, diaphragm and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it; and obtaining the electrochemical device through processes such as formation, degassing and shaping.

[0063] A third aspect of this application provides an electronic device comprising the electrochemical device described in any of the foregoing embodiments. Therefore, the electronic device exhibits excellent performance.

[0064] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0065] Example

[0066] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0067] Test methods and equipment:

[0068] Particle size testing:

[0069] The particle sizes Dv10 and Dv50 of silicon-carbon materials were measured using a MasterSizer 2000 laser particle size analyzer. -4 Dv90, the particle size of nano-metal oxides is Dv50. -1 The first graphite has a particle size of Dv50. -2 The particle size of the second graphite is Dv50. -3 .

[0070] Test of the mass percentage of silicon in silicon-carbon materials:

[0071] The silicon-carbon material is dissolved in nitric acid, and the volume is adjusted to a final volume using a volumetric flask. A portion of the diluted solution is then taken out and tested using an inductively coupled plasma atomic emission spectrometer (ICP) to obtain the mass percentage of silicon in the silicon-carbon material.

[0072] Test of the overall mass percentage of silicon-carbon material in the negative electrode:

[0073] The lithium-ion battery was disassembled, and the negative electrode sheet was removed. The negative electrode sheet was cleaned in dimethyl carbonate (DMC) and dried. A certain area of ​​the negative electrode sheet was cut off, and the first and second negative electrode material layers were completely scraped off. The sheet was then sintered in a fluoropolymer furnace at 500°C for 6 hours, and the powders of the first and second negative electrode active materials were collected. The collected first and second negative electrode active materials were measured using inductively coupled plasma atomic emission spectrometry (ICP) to obtain the silicon content. Based on the mass percentage of silicon in the silicon-carbon material, the overall mass percentage of the silicon-carbon material can be calculated.

[0074] Testing the specific surface area of ​​silicon-carbon materials:

[0075] The specific surface area of ​​the silicon-carbon materials in each embodiment and comparative example was measured using a Tristar II 3020M surface area analyzer via nitrogen adsorption. The specific testing was conducted in accordance with the national standard GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0076] Cyclic performance testing:

[0077] The lithium-ion battery was left to stand at 25±3℃ for 30 minutes, then charged at a constant current rate of 2C to 4.5V. Charging was then stopped at a constant voltage of 4.5V to 0.05C. The battery was left to stand for 30 minutes. It was then discharged at a current of 0.5C to 3.0V and left to stand for 30 minutes. This charge-discharge cycle was repeated 300 times, and the discharge capacity on the 300th cycle was recorded as C. 300Using the discharge capacity of the second cycle as the 100% capacity baseline, the discharge capacity of the second cycle is recorded as C2. Capacity retention rate (%) = C 300 / C2×100%.

[0078] Cycle performance is characterized by capacity retention rate; the higher the capacity retention rate, the better the cycle performance of the lithium-ion battery.

[0079] Example 1-1

[0080] <Preparation of Negative Electrode Sheets>

[0081] The first negative electrode active material, first graphite (artificial graphite, graphitization degree 97%), binder polyacrylic acid (weight average molecular weight Mw = 3000), and conductive agent single-walled carbon nanotubes were mixed in a mass ratio of 97:2.8:0.2. Deionized water was added as a solvent and stirred to prepare a first negative electrode slurry with a solid content of 45wt%. The first negative electrode slurry was coated on both surfaces of a 6μm thick copper foil for negative electrode current collector and dried at 100℃ to form the first negative electrode material layer. The second negative electrode active material, second graphite (artificial graphite, graphitization degree 97%), silicon carbon material, binder polyacrylic acid (Mw=3000), conductive agent single-walled carbon nanotubes, and nano-metal oxide copper oxide were thoroughly mixed in a mass ratio of 67.9:29.1:2.6:0.2:0.2. Deionized water was added and stirred to prepare a second negative electrode slurry with a solid content of 45wt%. This slurry was coated onto the surfaces of the two first negative electrode material layers away from the copper foil. After drying at 100℃, the second negative electrode material layers were formed. Cold pressing and slitting were then performed to obtain negative electrode sheets with a size of 800mm×50mm.

[0082] The silicon-carbon material comprises 10% by mass in the negative electrode, 30% by mass in the second negative electrode active material, and 50% by mass of silicon in the silicon-carbon material. The silicon-carbon material has a particle size of Dv10 = 5.5 μm and Dv50. -4 =9.1μm, Dv90=15μm. The specific surface area of ​​silicon-carbon materials is 1.3m². 2 / g, the tap density of silicon carbide material is 1.0 g / cm³. 3 The particle size Dv50 of nano-metal oxides -1 =500nm, the particle size of the first graphite is Dv50 -2 =11.5μm, the particle size Dv50 of the second graphite -2 =10.5μm. The coating weight of the first negative electrode material layer, CW1, is 80mg / 1540.25mm. 2 The coating weight of the second negative electrode material layer, CW2, is 40 mg / 1540.25 mm. 2 CW1:CW2 = 2:1, the coating weight of the negative electrode is CW12 =120mg / 1540.25mm 2 .

[0083] <Preparation of the positive electrode>

[0084] Lithium cobalt oxide (CCO) as the positive electrode active material, conductive carbon black (Super P) as the conductive agent, and polyvinylidene fluoride (PVDF, Mw = 600000) as the binder were mixed in a mass ratio of 97.8:1.4:0.8. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 72 wt% was obtained. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil for the positive electrode current collector and dried at 85°C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material (90 μm thick). The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active material. After cold pressing, cutting, and welding of positive electrode tabs, a positive electrode sheet with a size of 792 mm × 49.5 mm was obtained for use.

[0085] <Preparation of the diaphragm>

[0086] A porous polyethylene (PE) membrane with a thickness of 8 μm was used as the diaphragm.

[0087] <Preparation of Electrolyte>

[0088] In a dry argon atmosphere, non-aqueous solvents ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 1:1, and lithium salt lithium hexafluorophosphate was added and stirred until homogeneous to obtain the electrolyte. The lithium salt concentration was 1 mol / L.

[0089] <Preparation of Lithium-ion Batteries>

[0090] The separator, positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and after dehydration at 80°C, electrolyte is injected and the battery is sealed. After processes such as formation, degassing, and shaping, a lithium-ion battery is obtained.

[0091] Examples 1-2 to Examples 1-19

[0092] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0093] When the mass percentage of nano-metal oxides changes, the mass percentage of the second negative electrode active material changes accordingly. The mass percentages of the second graphite and silicon carbide materials in the second negative electrode active material remain unchanged, as do the mass percentages of the conductive agent and binder. The sum of the mass percentages of the second negative electrode active material, binder, conductive agent, and nano-metal oxides is 100%.

[0094] Examples 2-1 to 2-20

[0095] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-6.

[0096] Examples 3-1 to 3-5

[0097] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-6.

[0098] Among them, the comprehensive mass percentage of silicon-carbon materials W 12 The change is achieved by adjusting the ratio CW1:CW2 between the coating weights of the first and second negative electrode material layers, where CW1 is the total coating weight of the first and second negative electrode material layers. 12 constant.

[0099] Examples 3-6 to 3-9

[0100] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-6.

[0101] When the mass percentage W2 of silicon-carbon material in the second negative electrode active material changes, the mass percentage of second graphite in the second negative electrode active material changes accordingly, while the mass percentage of the second negative electrode active material in the second negative electrode material layer remains unchanged. The overall mass percentage W of silicon-carbon material in the negative electrode sheet is controlled by adjusting the coating weight ratio CW1:CW2 between the first and second negative electrode material layers. 12 constant.

[0102] Examples 3-10 to 3-13

[0103] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 1-6.

[0104] The change in the mass percentage of silicon can be achieved by adjusting the type of silicon-carbon material.

[0105] Comparative Example 1 and Comparative Example 2

[0106] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0107] When the mass percentage of nano-metal oxides changes, the mass percentage of the second negative electrode active material changes accordingly. The mass percentages of the second graphite and silicon carbide materials in the second negative electrode active material remain unchanged, as do the mass percentages of the conductive agent and binder. The sum of the mass percentages of the second negative electrode active material, binder, conductive agent, and nano-metal oxides is 100%.

[0108] Comparative Example 3

[0109] <Preparation of Negative Electrode Sheets>

[0110] Artificial graphite (97% graphitization), silicon carbon material, polyacrylic acid binder (weight average molecular weight Mw = 3000), and single-walled carbon nanotubes conductive agent were mixed in a mass ratio of 87.3:9.7:2.8:0.2. Deionized water was added as a solvent, and the mixture was stirred to prepare a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was coated onto both surfaces of the copper foil current collector and dried at 100℃ to form the negative electrode material layer. Cold pressing and slitting were then performed to obtain negative electrode sheets with a size of 800 mm × 50 mm. The coating weight of the negative electrode material layer was 120 mg / 1540.25 mm. 2 .

[0111] The preparation of the positive electrode, the separator, the electrolyte, and the lithium-ion battery are the same as in Examples 1-1.

[0112] The preparation parameters and performance data of each embodiment and comparative example are shown in Tables 1 to 3.

[0113] Table 1

[0114]

[0115] Note: In Table 1, "\" indicates that there is no corresponding parameter.

[0116] As can be seen from Examples 1-1 to 1-12 and Comparative Examples 1 to 3, the negative electrode sheet of this application, by setting a second negative electrode material layer on its surface and controlling the content and type of nano-metal oxides added to the second negative electrode material layer within the scope of this application, results in a higher capacity retention rate when the negative electrode sheet is applied to a lithium-ion battery, indicating that the cycle performance of the lithium-ion battery has been improved. In contrast, the lithium-ion batteries of the comparative examples, where the content of nano-metal oxides in the second negative electrode material layer is not within the scope of this application, or where the negative electrode sheet does not have a second negative electrode material layer on its surface, exhibit a lower capacity retention rate, indicating that the cycle performance of the comparative lithium-ion batteries is poor.

[0117] The mass percentage of nano-metal oxides typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-9, Comparative Examples 1 and 2, lithium-ion batteries with a mass percentage of nano-metal oxides within the scope of this application exhibit higher capacity retention, indicating that the lithium-ion batteries have good cycle performance.

[0118] The type of nano-metal oxide typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-6, 1-10 to 1-12, lithium-ion batteries using nano-metal oxides within the scope of this application exhibit high capacity retention, indicating that the lithium-ion batteries have good cycle performance.

[0119] The particle size Dv50 of nano-metal oxides -1 This typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-6, 1-13 to 1-19, the selected nano-metal oxide with a particle size Dv50... -1 The lithium-ion batteries within the scope of this application have a high capacity retention rate, indicating that the lithium-ion batteries have good cycle performance.

[0120] Table 2

[0121]

[0122] The first graphite has a particle size of Dv50. -2 This typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-6 and Examples 2-1 to 2-5, the selected first graphite with a particle size Dv50... -2 The lithium-ion batteries within the scope of this application have a high capacity retention rate, indicating that the lithium-ion batteries have good cycle performance.

[0123] The second graphite has a particle size of Dv50. -3 This typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 2-2, 2-6 to 2-9, the particle size Dv50 of the selected second graphite is... -3 The lithium-ion batteries within the scope of this application have a high capacity retention rate, indicating that the lithium-ion batteries have good cycle performance.

[0124] Silicon-carbon materials with particle sizes Dv10 and Dv50 -3 The values ​​of Dv90 and Dv90-Dv10 typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 2-2, 2-10 to 2-13, the particle sizes Dv10 and Dv50 of the selected silicon-carbon material... -3 Lithium-ion batteries with values ​​of Dv90 and Dv90-Dv10 within the scope of this application have high capacity retention, indicating that the lithium-ion batteries have good cycle performance.

[0125] The specific surface area of ​​silicon-carbon materials typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 2-2, 2-14 to 2-20, lithium-ion batteries using silicon-carbon materials with a specific surface area within the range of this application exhibit high capacity retention, indicating good cycle performance.

[0126] Table 3

[0127]

[0128] The overall mass percentage of silicon-carbon material in the negative electrode and the mass percentage of silicon-carbon material in the second negative electrode active material typically affect the cycle performance of lithium-ion batteries. As can be seen from Examples 1-6 and Examples 3-1 to 3-9, lithium-ion batteries with silicon-carbon material content in both the negative electrode and the second negative electrode active material falling within the scope of this application exhibit higher capacity retention, indicating that the lithium-ion batteries have good cycle performance.

[0129] The mass percentage of silicon in silicon-carbon materials typically affects the cycle performance of lithium-ion batteries. As can be seen from Examples 1-6 and Examples 3-10 to 3-13, lithium-ion batteries using silicon-carbon materials with a silicon content within the range of this application exhibit high capacity retention, indicating good cycle performance.

[0130] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0131] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0132] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the first negative electrode material layer is disposed between the negative electrode current collector and the second negative electrode material layer; The first negative electrode material layer includes a first negative electrode active material, and the first negative electrode active material includes a first graphite; The second negative electrode material layer comprises a second negative electrode active material and nano-metal oxides. The second negative electrode active material comprises silicon-carbon material and second graphite. The nano-metal oxides comprise at least one of aluminum oxide, zinc oxide, magnesium oxide, tin oxide, indium oxide, zirconium oxide, copper oxide, or silver oxide. Based on the mass of the second negative electrode material layer, the mass percentage of the nano-metal oxides is 0.5% to 3%.

2. The negative electrode sheet according to claim 1, wherein, The particle size Dv50 of the nano-metal oxide -1 The range is from 10nm to 1000nm.

3. The negative electrode sheet according to claim 1, wherein, The particle size Dv50 of the nano-metal oxide -1 The range is from 100nm to 600nm.

4. The negative electrode sheet according to claim 1, wherein, The particle size of the first graphite is Dv50 -2 The particle size Dv50 of the second graphite is 11.0 μm to 13.5 μm. -3 The size ranges from 9μm to 12μm.

5. The negative electrode sheet according to claim 1, wherein, The silicon-carbon material has particle sizes Dv10 and Dv50. -4 Dv90 satisfies: 5μm≤Dv10≤6μm, 8μm≤Dv50 -4 ≤10.5μm, 13μm≤Dv90≤17μm.

6. The negative electrode sheet according to claim 5, wherein, The particle sizes Dv10 and Dv90 of the silicon-carbon material satisfy the following: 7.5μm≤Dv90-Dv10≤11.5μm.

7. The negative electrode sheet according to claim 1, wherein, The silicon-carbon material in the negative electrode sheet has a total mass percentage content of 10% to 30%, the silicon-carbon material in the second negative electrode active material has a mass percentage content of 20% to 80%, and the silicon-carbon material has a mass percentage content of 30% to 60%.

8. The negative electrode sheet according to claim 1, wherein, The specific surface area of ​​the silicon-carbon material is 0.5 m². 2 / g to 3.5m 2 / g.

9. The negative electrode sheet according to claim 1, wherein, The specific surface area of ​​the silicon-carbon material is 1.0 m². 2 / g to 2.0m 2 / g.

10. An electrochemical device, wherein, The electrochemical device includes the negative electrode sheet according to any one of claims 1 to 9.

11. An electronic device, wherein, The electronic device includes the electrochemical device of claim 10.

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