Composite negative plate, preparation method thereof and lithium ion battery

Abstract

The invention provides a composite negative plate, a preparation method thereof and a lithium ion battery. The composite negative plate comprises a current collector and a composite coating located on at least one side surface of the current collector, wherein the composite coating comprises a first active layer, a second active layer and a lithium supplementing layer which are sequentially stacked in the direction away from the current collector; wherein the first active layer comprises a porous silicon carbon material, and the second active layer comprises a monatomic silicon material. The first active layer is beneficial to improving the overall stability of the electrode structure, thereby being beneficial to improving the cycle performance and being beneficial to exerting the capacity of monatomic silicon; the second active layer is beneficial to improving the energy density and the rate capability of the battery; and the lithium supplementing layer is beneficial to supplementing lithium loss. When the composite negative plate is applied to the lithium ion battery, especially the all-solid-state lithium ion battery, the rate capability and the capacity of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a composite negative electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] In recent years, all-solid-state batteries have developed rapidly. However, due to the higher energy density target (>350Wh / kg) of all-solid-state batteries, the 372mAh / g capacity of graphite anodes in traditional liquid batteries can no longer meet application requirements. Therefore, silicon anodes with higher capacities (~3750mAh / g) have become an important research direction. Previously, pure nano-silicon or a composite of nano-silicon and solid electrolyte was generally used as the anode in all-solid-state batteries. These electrodes had high capacity and excellent rate performance in the early stages of cycling. However, due to the inherently high volume expansion rate of silicon (~300%), silicon particles are prone to breakage and pulverization during cycling, leading to a sharp decline in battery performance. Subsequently, researchers developed porous silicon-carbon anodes for liquid battery systems, which greatly improved the volume expansion problem. However, when applied to all-solid-state battery systems, they still suffer from poor rate performance and relatively lower capacity compared to pure nano-silicon anodes. Therefore, neither nano-silicon nor porous silicon-carbon anodes can currently be widely used in all-solid-state batteries. Summary of the Invention

[0003] The main objective of this invention is to provide a composite negative electrode sheet, its preparation method, and a lithium-ion battery, in order to solve the problems of poor rate performance and low capacity of lithium-ion batteries in the prior art.

[0004] To achieve the above objectives, according to one aspect of the present invention, a composite negative electrode is provided, the composite negative electrode comprising a current collector and a composite coating located on at least one side surface of the current collector, the composite coating comprising a first active layer, a second active layer and a lithium replenishment layer stacked sequentially along a direction away from the current collector; wherein the first active layer comprises a porous silicon-carbon material and the second active layer comprises a elemental silicon material.

[0005] Furthermore, the mass content of porous silicon-carbon material in the first active layer is 60-90%; and / or, the mass content of elemental silicon material in the second active layer is 60-90%.

[0006] Furthermore, the porous silicon-carbon material contains 45-50% silicon by mass; and / or, the D50 of the porous silicon-carbon material is 1-10µm; and / or, the average pore size of the porous silicon-carbon material is 2-10nm; and / or, the porosity of the porous silicon-carbon material is 45-55%; and / or, the D50 of the elemental silicon material is 50-900nm.

[0007] Further, the lithium replenishment layer is a lithium foil or a lithium alloy foil; preferably, the lithium replenishment layer is a lithium alloy foil, and the lithium content in the lithium alloy foil is 2-10% by mass; more preferably, the lithium alloy foil is selected from any one of lithium indium alloy foil, lithium tin alloy foil, lithium aluminum alloy foil, and lithium zinc alloy foil.

[0008] Furthermore, the thickness of the first active layer is 30~60µm; and / or, the thickness of the second active layer is 10~30µm; and / or, the thickness of the lithium replenishment layer is 1~10µm.

[0009] Furthermore, the first active layer also includes 9-30% of a first solid electrolyte; and / or, the second active layer also includes 9-30% of a second solid electrolyte.

[0010] Furthermore, the D50 of the first solid electrolyte and the second solid electrolyte are each independently 1~10µm; preferably, the first solid electrolyte and the second solid electrolyte are each independently selected from Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 Li7P3S 11 Any one or more of the following.

[0011] Furthermore, the first active layer further includes 0.1-5% of a first conductive agent and 0.1-10% of a first binder; and / or, the second active layer further includes 0.1-5% of a second conductive agent and 0.1-10% of a second binder.

[0012] According to another aspect of the present invention, a method for preparing the aforementioned composite negative electrode sheet is provided, the method comprising: step S1, coating a slurry containing porous silicon-carbon material onto at least one side surface of a current collector and drying it to form a first active layer; step S2, coating a slurry containing elemental silicon material onto the side surface of the first active layer away from the current collector and drying it to form a second active layer; and step S3, rolling a lithium supplement material onto the side surface of the second active layer away from the first active layer to form a lithium supplement layer, thereby obtaining a composite negative electrode sheet.

[0013] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a negative electrode, an electrolyte, and a positive electrode, wherein the negative electrode is the aforementioned composite negative electrode.

[0014] By applying the technical solution of this invention, the first active layer of this application includes a porous silicon-carbon material. This porous silicon-carbon material exhibits minimal volume expansion and stable bonding with the current collector, providing support for the second active layer containing elemental silicon material. This enhances the overall stability of the electrode structure, thereby improving cycle performance and maximizing the capacity of the elemental silicon. The elemental silicon material in the second active layer possesses relatively excellent ionic conductivity, high specific capacity, and a short ion transport path, which is beneficial for improving the battery's energy density and rate performance. The lithium replenishment layer has an ultra-high specific capacity, effectively replenishing lithium losses caused by low coulombic efficiency during the first charge-discharge cycle of the first and second active layers, as well as lithium losses due to side reactions in the early stages of cycling. Furthermore, the presence of the lithium replenishment layer helps to construct a low-expansion interface layer on the surface of the second active layer, buffering the volume expansion of the second active layer and improving lithium-ion interface transport efficiency, thus contributing to improved initial efficiency and cycle performance. Therefore, applying the composite negative electrode sheet of this application to lithium-ion batteries, especially all-solid-state lithium-ion batteries, helps improve the battery's rate performance and capacity. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0016] Figure 1 A schematic diagram of the structure of a composite negative electrode sheet in an embodiment of this application is shown.

[0017] The above figures include the following reference numerals:

[0018] 10. Current collector; 20. Composite coating; 21. First active layer; 22. Second active layer; 23. Lithium replenishment layer. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] As analyzed in the background section of this application, existing lithium-ion batteries suffer from poor rate performance and low capacity. To address these issues, this application provides a composite negative electrode sheet, its preparation method, and a lithium-ion battery.

[0021] In a typical embodiment of this application, a composite negative electrode is provided, such as Figure 1As shown, the composite negative electrode includes a current collector 10 and a composite coating 20 located on at least one side surface of the current collector. The composite coating 20 includes a first active layer 21, a second active layer 22 and a lithium replenishment layer 23 stacked sequentially along the direction away from the current collector. The first active layer includes a porous silicon-carbon material and the second active layer includes a single silicon material.

[0022] The first active layer of this application includes a porous silicon-carbon material. This porous silicon-carbon material exhibits minimal volume expansion and stable bonding with the current collector, providing support for the second active layer containing elemental silicon. This enhances the overall stability of the electrode structure, thereby improving cycle performance and maximizing the capacity of the elemental silicon. The elemental silicon material in the second active layer possesses relatively excellent ionic conductivity, high specific capacity, and a short ion transport path, which is beneficial for improving the battery's energy density and rate performance. The lithium replenishment layer has an ultra-high specific capacity, effectively compensating for lithium losses caused by low coulombic efficiency during the first charge-discharge cycle of the first and second active layers, as well as lithium losses due to side reactions in the early stages of cycling. Furthermore, the presence of the lithium replenishment layer helps to construct a low-expansion interface layer on the surface of the second active layer, buffering the volume expansion of the second active layer and improving lithium-ion interface transport efficiency, thus contributing to improved initial efficiency and cycle performance. Therefore, applying the composite negative electrode sheet of this application to lithium-ion batteries, especially all-solid-state lithium-ion batteries, helps improve the battery's rate performance and capacity.

[0023] It should be noted that the composite coating can be located on one side of the current collector or on both sides of the current collector.

[0024] In some embodiments of this application, the mass content of porous silicon-carbon material in the first active layer is 60-90%, specifically 60%, 65%, 70%, 75%, 80%, 85%, 95%, or any range between two values; and / or, the mass content of elemental silicon material in the second active layer is 60-90%, specifically 60%, 65%, 70%, 75%, 80%, 85%, 95%, or any range between two values.

[0025] The porous structure of porous silicon-carbon materials helps alleviate expansion pressure. Controlling the mass content of porous silicon-carbon materials in the first active layer within the aforementioned range helps reduce the expansion of the composite negative electrode and improves the interfacial stability between the coating and the current collector. Elemental silicon materials have high theoretical specific capacity. Controlling the mass content of elemental silicon materials in the second active layer within the aforementioned range helps improve the energy density and rate performance of the battery.

[0026] In some embodiments of this application, the silicon content in the porous silicon-carbon material is 45-50% by mass; and / or, the D50 of the porous silicon-carbon material is 1-10µm; and / or, the average pore size of the porous silicon-carbon material is 2-10nm; and / or, the porosity of the porous silicon-carbon material is 45-55%; and / or, the D50 of the elemental silicon material is 50-900nm.

[0027] The mass content of silicon affects the specific capacity and cycle stability of porous silicon-carbon materials. Controlling the mass content of silicon in porous silicon-carbon materials within the aforementioned range helps to buffer silicon expansion while providing good capacity, maintaining the stability of the electrode structure. Controlling the D50 of porous silicon-carbon materials within the aforementioned range helps to shorten the lithium-ion transport path during charge and discharge, improving ion transport efficiency and thus improving the rate performance of the battery. Controlling the average pore size and porosity of porous silicon-carbon materials within the aforementioned range helps to reduce the mechanical stress of silicon materials during cycling, thereby further improving the cycle performance and overall energy density of the battery. Controlling the D50 of elemental silicon materials within the aforementioned range helps to improve ionic conductivity and enhance the rate performance of the battery.

[0028] In some embodiments of this application, the lithium replenishment layer is a lithium foil or a lithium alloy foil; preferably, the lithium replenishment layer is a lithium alloy foil, and the lithium mass content in the lithium alloy foil is 2-10%; more preferably, the lithium alloy foil is selected from any one of lithium indium alloy foil, lithium tin alloy foil, lithium aluminum alloy foil, and lithium zinc alloy foil.

[0029] Compared to plain lithium foil, lithium alloy foil exhibits better stability and plasticity, allowing for more uniform deposition and dissolution during charging and discharging. This helps reduce lithium dendrite formation, improving battery safety and cycle life. Controlling the lithium mass content in the lithium alloy foil within the aforementioned range helps improve lithium replenishment efficiency and the stability of the replenishment layer.

[0030] In some embodiments of this application, the thickness of the first active layer is 30~60µm; and / or, the thickness of the second active layer is 10~30µm; and / or, the thickness of the lithium replenishment layer is 1~10µm.

[0031] Controlling the thickness of the first active layer within the aforementioned range helps provide sufficient support to buffer the volume changes of the elemental silicon material in the second active layer during charge and discharge, reducing the risk of electrode pulverization and breakage. Controlling the thickness of the second active layer within the aforementioned range also helps improve the battery's energy density, charge / discharge efficiency, and rate performance. Controlling the thickness of the lithium replenishment layer within the aforementioned range helps replenish the lithium reserves lost by the negative electrode during the first charge and discharge process due to the formation of the SEI film and structural changes, thus improving initial efficiency.

[0032] In some embodiments of this application, the thickness ratio of the first active layer to the second active layer is (2~4):1.

[0033] The first active layer provides structural stability and high coulombic efficiency, while the second active layer contributes to high capacity. Controlling the thickness ratio of the first to the second active layer within the aforementioned range helps ensure that the silicon material of the second active layer, while exhibiting high capacity advantages, is effectively supported by the first active layer, thereby mitigating volume expansion, preventing electrode pulverization and breakage, and improving the cycle stability of the battery.

[0034] In some embodiments of this application, the first active layer further includes 9-30% of a first solid electrolyte; and / or, the second active layer further includes 9-30% of a second solid electrolyte.

[0035] In the first active layer, the presence of the first solid electrolyte helps improve the lithium-ion transport path and form a stable solid electrolyte interface film. Controlling the mass content of the first solid electrolyte in the first active layer within the aforementioned range helps improve ionic conductivity and reduce the occurrence of side reactions, thereby improving the battery's rate performance and initial charge / discharge efficiency. In the second active layer, the presence of the second solid electrolyte helps alleviate the volume expansion of silicon material during charge and discharge, improves lithium-ion transport efficiency, and controlling the mass content of the second solid electrolyte in the second active layer within the aforementioned range further helps improve the battery's rate performance and cycle stability.

[0036] In some embodiments of this application, the mass ratio of porous silicon-carbon material to the first solid electrolyte is (6~7):1; and / or, the mass ratio of elemental silicon material to the second solid electrolyte is (6~7):1.

[0037] Controlling the mass ratio of porous silicon-carbon material to the first solid electrolyte within the aforementioned range helps to promote interfacial compatibility and optimize ion transport. Controlling the mass ratio of elemental silicon material to the second solid electrolyte within the aforementioned range helps to enhance structural stability and improve rate performance.

[0038] To further improve the ionic conductivity of the composite negative electrode, thereby enhancing the rate performance and cycle stability of the battery, in some embodiments of this application, the D50 of the first solid electrolyte and the second solid electrolyte are each independently 1~10µm; preferably, the first solid electrolyte and the second solid electrolyte are each independently selected from Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 Li7P3S 11 Any one or more of the following.

[0039] In order to improve the structural stability and conductivity of the composite negative electrode, thereby further improving the battery capacity, rate performance and cycle stability, in some embodiments of this application, the first active layer further includes 0.1-5% of a first conductive agent and 0.1-10% of a first binder; and / or, the second active layer further includes 0.1-5% of a second conductive agent and 0.1-10% of a second binder.

[0040] Including but not limited to, the first conductive agent and the second conductive agent are each independently selected from any one or more of conductive carbon black, VGCF (vapor-grown carbon fiber), carbon nanotubes, conductive graphite and conductive graphene; the first binder and the second binder are each independently selected from any one or more of PVDF (polyvinylidene fluoride), PAA (polyacrylic acid), SEBS (styrene-ethylene-butene-styrene block copolymer), and NBR (nitrile rubber).

[0041] In another typical embodiment of this application, a method for preparing the aforementioned composite negative electrode is provided. The method includes: step S1, coating a slurry containing porous silicon-carbon material onto at least one side surface of a current collector and drying it to form a first active layer; step S2, coating a slurry containing elemental silicon material onto the side surface of the first active layer away from the current collector and drying it to form a second active layer; and step S3, rolling a lithium supplement material onto the side surface of the second active layer away from the first active layer to form a lithium supplement layer, thereby obtaining a composite negative electrode.

[0042] The method for preparing the composite negative electrode in this application is simple and low in cost.

[0043] Including but not limited to, the current collector is a copper foil with a thickness of 4~12μm; the solvent in the slurry is selected from any one or more of p-xylene, methanol and ethanol.

[0044] In another typical embodiment of this application, a lithium-ion battery is provided, including a negative electrode, an electrolyte, and a positive electrode, wherein the negative electrode is the aforementioned composite negative electrode.

[0045] Because the aforementioned lithium-ion battery contains the composite negative electrode of this application, the lithium-ion battery has high rate performance and capacity.

[0046] In some embodiments of this application, the positive electrode sheet includes a current collector and a positive electrode active layer located on at least one side of the current collector. The positive electrode active layer, by mass percentage, comprises 70-90% positive electrode active material, 9-20% solid electrolyte, 0.1-5% conductive agent, and 0.1-5% binder. Preferably, the positive electrode active material is LiNi oxide coated with an oxide layer. x Co y Mn zO2, x+y+z=1, x≥0.8, y>0, z>0, the oxide layer material is selected from any one or more of LiNbO3, ZrO2, Li2ZrO3, Li2TiO3 and Al2O3, and the thickness of the oxide layer is 5~15nm; and / or, the solid electrolyte is selected from Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 Li7P3S 11 Any one or more of the following; and / or, the conductive agent is selected from any one or more of conductive carbon black, VGCF (vapor-grown carbon fiber), carbon nanotubes, conductive graphite and conductive graphene; and / or, the binder is selected from any one or more of PVDF (polyvinylidene fluoride), PAA (polyacrylic acid), SEBS (styrene-ethylene-butene-styrene block copolymer), and NBR (nitrile rubber).

[0047] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0048] Example 1

[0049] A copper foil with a thickness of 6 μm was selected as the current collector 10. 82% porous silicon-carbon material (silicon content 50%, D50 5µm, average pore size 6nm, porosity 50%), 12% solid electrolyte Li6PS5Cl (D50 5µm), 3% conductive agent conductive carbon black, and 3% binder polyvinylidene fluoride were added to p-xylene for mixing and dispersion to obtain the first active slurry. Subsequently, the first active slurry was coated onto one side of the copper foil using a scraper. The coated electrode was placed in a vacuum drying oven and dried at 100℃ under vacuum for 12 hours to form the first active layer 21 (thickness 45µm).

[0050] By mass percentage, 80% of elemental silicon material (D50 of 500 nm, purity greater than 99%), 12% of solid electrolyte Li6PS5Cl (D50 of 5 µm), 3% of conductive agent conductive carbon black, and 5% of binder polyvinylidene fluoride were added to p-xylene for mixing and stirring to obtain a second active slurry. Then, the second active slurry was coated onto the surface of the first active layer away from the copper foil using a doctor blade. The coated electrode was placed in a vacuum drying oven and dried at 100 °C under vacuum for 12 h to form the second active layer 22 (thickness of 20 µm).

[0051] Lithium and indium foils were stacked and pressed flat. Then, a lithium-indium alloy foil (lithium content 3.6% by mass) was rolled onto the surface of the second active layer, away from the first active layer, to form a lithium supplement layer 23 (2µm thick). Finally, the electrode was placed in a dry environment with an ambient dew point < -45℃ and left to stand for 12 hours to obtain a composite negative electrode. A schematic diagram of the structure is shown below. Figure 1 As shown.

[0052] Example 2

[0053] The difference from Example 1 is that the thickness of the first active layer is 30µm and the thickness of the second active layer is 30µm, resulting in a composite negative electrode sheet.

[0054] Example 3

[0055] The difference from Example 1 is that the thickness of the first active layer is 60µm and the thickness of the second active layer is 10µm, resulting in a composite negative electrode sheet.

[0056] Example 4

[0057] The difference from Example 1 is that the thickness of the first active layer is 20µm and the thickness of the second active layer is 35µm, resulting in a composite negative electrode sheet.

[0058] Example 5

[0059] The difference from Example 1 is that the thickness of the lithium replenishment layer is 10µm, resulting in a composite negative electrode.

[0060] Example 6

[0061] The difference from Example 1 is that the thickness of the lithium replenishment layer is 12µm, resulting in a composite negative electrode.

[0062] Example 7

[0063] The difference from Example 1 is that the mass content of porous silicon-carbon material in the first active layer is 90%, and the mass content of elemental silicon material in the second active layer is 60%, ultimately resulting in a composite negative electrode.

[0064] Example 8

[0065] The difference from Example 1 is that the mass content of porous silicon-carbon material in the first active layer is 95%, and the mass content of elemental silicon material in the second active layer is 55%, ultimately resulting in a composite negative electrode.

[0066] Example 9

[0067] The difference from Example 1 is that the silicon content in the porous silicon-carbon material is 45% by mass, resulting in a composite negative electrode.

[0068] Example 10

[0069] The difference from Example 1 is that the silicon content in the porous silicon-carbon material is 55% by mass, resulting in a composite negative electrode.

[0070] Example 11

[0071] The difference from Example 1 is that the D50 of the porous silicon-carbon material is 10µm, the average pore size of the porous silicon-carbon material is 10nm, the porosity of the porous silicon-carbon material is 45%, and the D50 of the elemental silicon material is 900nm, ultimately resulting in a composite negative electrode.

[0072] Example 12

[0073] The difference from Example 1 is that the D50 of the porous silicon-carbon material is 12µm, the average pore size of the porous silicon-carbon material is 12nm, the porosity of the porous silicon-carbon material is 40%, and the D50 of the elemental silicon material is 1000nm, ultimately resulting in a composite negative electrode.

[0074] Example 13

[0075] The difference from Example 1 is that the lithium content in the lithium replenishment layer is 10%, resulting in a composite negative electrode.

[0076] Example 14

[0077] The difference from Example 1 is that the lithium content in the lithium replenishment layer is 12%, resulting in a composite negative electrode.

[0078] Example 15

[0079] The difference from Example 1 is that a copper foil with a thickness of 12 μm was selected as the current collector, and 82% porous silicon-carbon material (silicon content of 50%, D50 of 5 µm, average pore size of 2 nm, and porosity of 55%) and 9% solid electrolyte Li were added by mass percentage. 10 GeP2S 12 (D50 is 5µm), 5% conductive carbon nanotubes, and 4% binder polyacrylic acid are added to p-xylene for mixing and stirring to obtain the first active slurry. Then, the first active slurry is coated on one side of the copper foil using a doctor blade. The coated electrode is placed in a vacuum drying oven and dried at 100℃ in a vacuum environment for 12 hours to form the first active layer (thickness is 45µm).

[0080] By mass percentage, the mixture consists of 80% elemental silicon material (D50 of 500 nm, purity greater than 99%) and 9% solid electrolyte Li. 10 GeP2S 12(D50 is 5µm), 5% conductive carbon nanotubes and 6% binder polyacrylic acid are added to p-xylene for mixing and stirring to obtain a second active slurry. Then, the second active slurry is coated on the surface of the first active layer away from the copper foil using a doctor blade. The coated electrode is placed in a vacuum drying oven and dried at 100℃ in a vacuum environment for 12 hours to form the second active layer (thickness is 20µm).

[0081] The lithium foil and tin foil are stacked and pressed flat. Then, the lithium-tin alloy foil (lithium content of 3.6%) is rolled onto the surface of the second active layer away from the first active layer to form a lithium supplement layer (thickness of 2µm). Finally, the electrode is placed in a dry environment with an ambient dew point of <-45℃ and left to stand for 12 hours to obtain the composite negative electrode.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that the coating of the first active layer is omitted. Instead, by mass percentage, 80% of elemental silicon material (D50 of 500 nm, purity greater than 99%), 12% of solid electrolyte Li6PS5Cl (D50 of 5 µm), 3% of conductive agent conductive carbon black, and 5% of binder polyvinylidene fluoride are added to p-xylene for mixing and stirring to obtain a second active slurry. The second active slurry is then coated onto one side of a copper foil using a doctor blade. The coated electrode is placed in a vacuum drying oven and dried at 100°C under vacuum for 12 hours to form a second active layer (thickness of 20 µm).

[0084] The lithium foil and indium foil are stacked and pressed flat. Then, the lithium-indium alloy foil (lithium content of 3.6% by mass) is rolled onto the surface of the second active layer away from the copper foil to form a lithium replenishment layer (thickness of 2µm). Finally, the electrode is placed in a dry environment with an ambient dew point of <-45℃ and left to stand for 12 hours to obtain a composite negative electrode.

[0085] Comparative Example 2

[0086] The difference from Example 1 is that the coating of the second active layer is omitted, and a copper foil with a thickness of 6 μm is selected as the current collector. By mass percentage, 82% of porous silicon-carbon material (silicon content of 50%, D50 of 5 µm, average pore size of 6 nm, and porosity of 50%), 12% of solid electrolyte Li6PS5Cl (D50 of 5 µm), 3% of conductive agent conductive carbon black, and 3% of binder polyvinylidene fluoride are added to p-xylene for mixing and stirring to obtain the first active slurry. Then, the first active slurry is coated on one side of the copper foil using a doctor blade. The coated electrode is placed in a vacuum drying oven and dried at a temperature of 100°C under vacuum for 12 hours to form the first active layer (thickness of 45 µm).

[0087] The lithium foil and indium foil are stacked and pressed flat. Then, the lithium-indium alloy foil (lithium content of 3.6% by mass) is rolled onto the surface of the first active layer away from the copper foil to form a lithium supplement layer (thickness of 2µm). Finally, the electrode is placed in a dry environment with an ambient dew point of <-45℃ and left to stand for 12 hours to obtain a composite negative electrode.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that the rolling of the lithium replenishment layer is omitted, and a copper foil with a thickness of 6μm is selected as the current collector. By mass percentage, 82% of porous silicon-carbon material (silicon mass content of 50%, D50 of 5µm, average pore size of 6nm, and porosity of 50%), 12% of solid electrolyte Li6PS5Cl (D50 of 5µm), 3% of conductive agent conductive carbon black, and 3% of binder polyvinylidene fluoride are added to p-xylene for mixing and stirring to obtain a first active slurry. Then, the first active slurry is coated on one side of the copper foil using a doctor blade. The coated electrode is placed in a vacuum drying oven and dried at a temperature of 100°C in a vacuum environment for 12 hours to form a first active layer (thickness of 45µm).

[0090] By mass percentage, 80% of elemental silicon material (D50 of 500 nm, purity greater than 99%), 12% of solid electrolyte Li6PS5Cl (D50 of 5 µm), 3% of conductive agent conductive carbon black, and 5% of binder polyvinylidene fluoride were added to p-xylene for mixing and stirring to obtain a second active slurry. Then, the second active slurry was coated onto the surface of the first active layer away from the copper foil using a scraper. The coated electrode was placed in a vacuum drying oven and dried at 100 °C under vacuum for 12 h to form a second active layer (thickness of 20 µm), thus obtaining a composite negative electrode.

[0091] Comparative Example 4

[0092] The difference from Example 1 is that the first active slurry and the second active slurry are mixed and coated on one side of the copper foil. The coated electrode is then placed in a vacuum drying oven and dried at 100°C in a vacuum environment for 12 hours to form an active layer (65µm thick).

[0093] Lithium foil and indium foil are stacked and pressed flat. Then, lithium-indium alloy foil (lithium content of 3.6% by mass) is rolled onto the surface of the active layer away from the copper foil to form a lithium replenishment layer (thickness of 2µm). Finally, the electrode is placed in a dry environment with an ambient dew point of <-45℃ and left to stand for 12 hours to obtain a composite negative electrode.

[0094] Cathode preparation: 88% of LiNi was coated with Al2O3 by mass percentage. 0.8 Co 0.1 Mn 0.1 O2 (D50 is 3μm, Al2O3 thickness is 10nm), 10% solid electrolyte Li6PS5Cl (D50 is 5µm), 1% conductive agent conductive carbon black, and 1% binder polyvinylidene fluoride are added to p-xylene for mixing and stirring to obtain a positive electrode active slurry. Then, the positive electrode active slurry is coated on one side of an aluminum foil (thickness is 10µm) using a scraper. The coated electrode is placed in a vacuum drying oven and dried at 100℃ in a vacuum environment for 12h to form a positive electrode active layer (thickness is 160µm), thus obtaining the positive electrode sheet.

[0095] Electrolyte membrane preparation: 99% of solid electrolyte Li6PS5Cl and 1% of binder polyvinylidene fluoride were added to p-xylene for mixing and stirring to obtain an electrolyte slurry. The electrolyte slurry was then coated onto one side of the release film using a doctor blade. Finally, the coated electrolyte membrane was placed in a vacuum drying oven and dried at 100℃ under vacuum for 12 hours to obtain an electrolyte membrane with a thickness of 60µm.

[0096] Battery fabrication: First, the prepared positive electrode sheet and the composite negative electrode sheet prepared in the examples and comparative examples are die-cut into small positive and negative electrode pieces containing coating areas and tab areas using positive and negative electrode die-cutting molds. The coating area of ​​the positive electrode piece is 4cm×4cm and the tab area is 2cm×0.5cm. The coating area of ​​the negative electrode piece is 4.2cm×4.2cm and the tab area is 2cm×0.5cm. Then, the electrolyte membrane is peeled off from the release film and cut into small electrolyte membrane pieces with a size of 4.5cm×4.5cm. Finally, the small negative electrode pieces, electrolyte membrane pieces and positive electrode pieces are stacked together in sequence and encapsulated with aluminum-plastic film to obtain an all-solid-state lithium-ion battery.

[0097] Performance testing

[0098] The all-solid-state lithium-ion batteries prepared in the examples and comparative examples were subjected to performance testing. Specifically, the packaged all-solid-state lithium-ion batteries were pressurized using an isostatic pressurization device, specifically held at 300 MPa for 10 minutes. Then, the all-solid-state lithium-ion batteries were placed in a flat pressurization mold, and electrochemical performance testing was conducted while maintaining an initial preload of 50 MPa. The test conditions were: ① constant current and constant voltage charging at 0.1C to obtain the charging capacity C1; ② resting for 10 minutes; ③ constant current and constant voltage charging at 0.1C. ④ Discharge with current to obtain discharge capacity C2; ⑤ Let stand for 10 minutes; ⑥ Repeat the above steps with 0.5C current to obtain 0.5C discharge capacity C3; ⑦ Continue to repeat the above steps with 0.5C current 50 times to obtain 50th discharge capacity C4; ⑧ Initial efficiency = (C2 / C1) × 100%; Capacity retention rate = (C4 / C3) × 100%. Record the discharge specific capacity C2 at 0.1C, the discharge specific capacity C3 at 0.5C, the capacity retention rate and initial efficiency after 50 cycles at 0.5C. The results are shown in Table 1.

[0099] Table 1

[0100]

[0101] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0102] The first active layer of this application includes a porous silicon-carbon material. This porous silicon-carbon material exhibits minimal volume expansion and stable bonding with the current collector, providing support for the second active layer containing elemental silicon. This enhances the overall stability of the electrode structure, thereby improving cycle performance and maximizing the capacity of the elemental silicon. The elemental silicon material in the second active layer possesses relatively excellent ionic conductivity, high specific capacity, and a short ion transport path, which is beneficial for improving the battery's energy density and rate performance. The lithium replenishment layer has an ultra-high specific capacity, effectively compensating for lithium losses caused by low coulombic efficiency during the first charge-discharge cycle of the first and second active layers, as well as lithium losses due to side reactions in the early stages of cycling. Furthermore, the presence of the lithium replenishment layer helps to construct a low-expansion interface layer on the surface of the second active layer, buffering the volume expansion of the second active layer and improving lithium-ion interface transport efficiency, thus contributing to improved initial efficiency and cycle performance. Therefore, applying the composite negative electrode sheet of this application to lithium-ion batteries, especially all-solid-state lithium-ion batteries, helps improve the battery's rate performance and capacity.

[0103] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite negative electrode sheet, characterized by comprising: The composite negative electrode sheet comprises a current collector and a composite coating layer located on at least one side surface of the current collector, the composite coating layer comprises a first active layer, a second active layer and a lithium supplementing layer in sequence from the current collector; 2. The composite negative electrode sheet according to claim 1, characterized by The mass content of the porous silicon-carbon material in the first active layer is 60-90%; and / or the mass content of the elemental silicon material in the second active layer is 60-90%.

3. The composite negative electrode sheet according to claim 1 or 2, characterized by, The mass content of silicon in the porous silicon-carbon material is 45-50%; and / or the D50 of the porous silicon-carbon material is 1-10 µm; and / or the average pore size of the porous silicon-carbon material is 2-10 nm; and / or the porosity of the porous silicon-carbon material is 45-55%; And / or the D50 of the elemental silicon material is 50-900 nm.

4. The composite negative electrode sheet according to any one of claims 1 to 3, characterized by, The lithium supplementing layer is a lithium foil or a lithium alloy foil; preferably, the lithium supplementing layer is a lithium alloy foil, the mass content of lithium in the lithium alloy foil is 2-10%; further preferably, the lithium alloy foil is selected from any one of a lithium-indium alloy foil, a lithium-tin alloy foil, a lithium-aluminum alloy foil and a lithium-zinc alloy foil.

5. The composite negative electrode sheet according to any one of claims 1 to 4, characterized by, The thickness of the first active layer is 30-60 µm; and / or the thickness of the second active layer is 10-30 µm; and / or the thickness of the lithium supplementing layer is 1-10 µm.

6. The composite negative electrode sheet according to any one of claims 1 to 5, characterized by, The first active layer further comprises 9-30% of a first solid-state electrolyte; and / or the second active layer further comprises 9-30% of a second solid-state electrolyte.

7. The composite negative electrode sheet according to claim 6, characterized by The D50 of the first solid-state electrolyte and the second solid-state electrolyte is independently 1-10 µm; Preferably, the first solid-state electrolyte and the second solid-state electrolyte are each independently selected from any one or more of Li6PS5CI, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 , Li7P3S 11 .

8. The composite negative electrode sheet according to any one of claims 1 to 7, characterized by, The first active layer further comprises 0.1-5% of a first conductive agent and 0.1-10% of a first binder; and / or the second active layer further comprises 0.1-5% of a second conductive agent and 0.1-10% of a second binder.

9. A method for producing the composite negative electrode sheet according to any one of claims 1 to 8, characterized by, The preparation method comprises: Step S1, coating a slurry containing a porous silicon-carbon material on at least one side surface of a current collector to form a first active layer; Step S2, coating a slurry containing an elemental silicon material on one side surface of the first active layer away from the current collector to form a second active layer; Step S3, calendering a lithium supplementing material to one side surface of the second active layer away from the first active layer to form a lithium supplementing layer, thereby obtaining the composite negative electrode sheet.

10. A lithium-ion battery comprising a negative electrode sheet, an electrolyte, and a positive electrode sheet, characterized by, The negative electrode sheet is the composite negative electrode sheet according to any one of claims 1-8.

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