Negative plate, preparation method thereof and solid-state battery

Abstract

The embodiment of the invention relates to a negative plate, a preparation method thereof and a solid-state battery. The negative plate comprises a current collector; the lithium metal layer is arranged on at least one surface of the current collector in the thickness direction; the first coating is arranged on the surface of one side, far away from the current collector, of the lithium metal layer; the first coating comprises graphite and a first sulfide solid electrolyte; the second coating is arranged on the surface of one side, far away from the lithium metal layer, of the first coating; the second coating includes a silicon carbon material and a second sulfide solid electrolyte. The first coating and the second coating which are sequentially stacked are arranged on the surface of the lithium metal layer, through the synergistic effect of the first coating and the second coating, the volume expansion of the negative electrode plate can be reduced while the growth of lithium dendrites can be inhibited, and the capacity of the negative electrode plate can be remarkably improved by the lithium metal and the carbon-silicon material with high specific capacity; therefore, the capacity, the rate capability and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet, its preparation method, and a solid-state battery. Background Technology

[0002] Solid-state batteries utilize solid electrolytes instead of traditional liquid electrolytes, fundamentally overcoming safety hazards such as electrolyte leakage and combustion, thus offering high safety. Among solid electrolytes, sulfide solid electrolytes possess extremely high room-temperature lithium-ion conductivity, a wide electrochemical window, and good mechanical ductility. They are compatible with higher-voltage cathode materials and higher-capacity anode materials, making them a potential material for constructing high-safety, high-energy-density, and high-power solid-state battery systems.

[0003] However, when a sulfide solid electrolyte is paired with a high-capacity lithium metal anode, electrochemical instability exists at the interface. During repeated charge-discharge cycles, lithium ions tend to deposit unevenly on the surface of the lithium metal anode, forming lithium dendrites. The growth of lithium dendrites severely affects the actual capacity and cycle life of the sulfide solid-state battery. Summary of the Invention

[0004] In view of this, the present application provides a negative electrode sheet, a method for preparing the same, and a solid-state battery to solve at least one problem existing in the prior art.

[0005] In a first aspect, embodiments of this application provide a negative electrode sheet, comprising: current collector; A lithium metal layer is disposed on at least one surface of the current collector along its thickness direction; A first coating is disposed on the surface of the lithium metal layer away from the current collector; the first coating comprises graphite and a first sulfide solid electrolyte. A second coating is disposed on the surface of the first coating away from the lithium metal layer; the second coating comprises a silicon-carbon material and a second sulfide solid electrolyte.

[0006] In conjunction with the first aspect of this application, in an optional embodiment, the first coating further includes a first conductive agent and a first binder; the mass ratio of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3).

[0007] In conjunction with the first aspect of this application, in an optional embodiment, the second coating further includes a second conductive agent and a second binder; the mass ratio of the silicon carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3).

[0008] In conjunction with the first aspect of this application, in an optional embodiment, the first coating further includes a first adhesive; the second coating further includes a second adhesive; the first adhesive and the second adhesive each independently include at least one selected from polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; and the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da.

[0009] In conjunction with the first aspect of this application, in an alternative embodiment, The thickness of the lithium metal layer is 5μm~70μm; and / or, The thickness of the first coating is 10 μm to 50 μm, preferably 20 μm to 40 μm; and / or, The thickness of the second coating is 10μm to 50μm, preferably 20μm to 40μm.

[0010] Secondly, embodiments of this application provide a method for preparing a negative electrode sheet, the method comprising the following steps: S1: Provide a substrate, the substrate comprising a current collector and a lithium metal layer disposed on at least one surface of the current collector in the thickness direction; S2: Graphite, a first sulfide solid electrolyte, a first conductive agent, and a first binder are dispersed in a first solvent and stirred evenly to obtain a first slurry; the first slurry is coated onto a first carrier film, and after a first drying process, a first coating is formed on the first carrier film; the first carrier film is composited with the substrate, with the first coating disposed opposite to the lithium metal layer; after a first rolling process, the first carrier film is removed, and the first coating is transferred to the surface of the lithium metal layer; S3: Disperse silicon-carbon material, second sulfide solid electrolyte, second conductive agent and second binder in a second solvent and stir evenly to obtain a second slurry; coat the second slurry onto a second carrier film, and after a second drying, form a second coating on the second carrier film; combine the second carrier film with the substrate, with the second coating and the first coating positioned opposite each other, and after a second rolling process, remove the second carrier film and transfer the second coating to the surface of the first coating to obtain the negative electrode sheet.

[0011] In conjunction with the second aspect of this application, in an optional embodiment, step S2 satisfies at least one of the following features: (1) The mass ratio of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3); (2) The ratio of the sum of the masses of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder to the mass of the first solvent is (4~7):(3~6), preferably (5~6):(5~6); (3) The first adhesive includes at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; (4) The first solvent includes at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane; (5) The first carrier film is a PET release film; (6) The temperature of the first drying is 50℃~100℃, preferably 70℃~90℃; (7) The pressure of the first roller is 10MPa~80MPa, preferably 40MPa~60MPa; the rolling speed of the first roller is 0.5m / min~3m / min, preferably 1m / min~2m / min.

[0012] In conjunction with the second aspect of this application, in an optional embodiment, step S3 satisfies at least one of the following features: (1) The mass ratio of the silicon-carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3); (2) The ratio of the sum of the masses of the silicon-carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder to the mass of the second solvent is (4~7):(3~6), preferably (5~6):(5~6); (3) The second adhesive includes at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; (4) The second solvent includes at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane; (5) The second carrier film is a PET release film; (6) The temperature of the second drying is 50℃~100℃, preferably 70℃~90℃; (7) The pressure of the second roller is 20MPa~60MPa, preferably 30MPa~50MPa; the rolling speed of the second roller is 0.3m / min~2m / min, preferably 0.8m / min~1.5m / min.

[0013] In conjunction with the second aspect of this application, in an optional embodiment, the resulting negative electrode sheet satisfies at least one of the following characteristics: (1) The thickness of the lithium metal layer is 5μm~70μm; (2) The thickness of the first coating is 10μm~50μm, preferably 20μm~40μm; (3) The thickness of the second coating is 10μm~50μm, preferably 20μm~40μm.

[0014] Thirdly, embodiments of this application provide a solid-state battery, including a negative electrode sheet as described in any of the first aspects or a negative electrode sheet prepared by a method including any of the second aspects.

[0015] Compared with the prior art, the embodiments of this application have the following beneficial effects: The negative electrode sheet, its preparation method, and solid-state battery provided in this application embodiment include: a current collector; a lithium metal layer disposed on at least one surface of the current collector along its thickness direction; a first coating disposed on the side surface of the lithium metal layer away from the current collector; the first coating includes graphite and a first sulfide solid electrolyte; a second coating disposed on the side surface of the first coating away from the lithium metal layer; the second coating includes silicon-carbon material and a second sulfide solid electrolyte. In this embodiment, the graphite in the first coating and the silicon-carbon material in the second coating can increase lithium-ion transport channels. The silicon-carbon material can form three-dimensional lithium-ion transport channels. Moreover, the second coating containing silicon-carbon material is located on the surface of the negative electrode, which is conducive to rapid lithium insertion and extraction. Combined with the first sulfide solid electrolyte and the second sulfide solid electrolyte with high lithium-ion conductivity, the lithium deposition flux on the surface of the lithium metal layer can be more uniform, thereby effectively suppressing the growth of lithium dendrites. In addition, the first coating includes low-expansion graphite, which has a small volume change during charging and discharging, and can buffer the large volume change of the lithium metal layer and the second coating during charging and discharging, reducing the overall volume expansion of the negative electrode. That is, in this embodiment, by setting the first coating and the second coating sequentially on the surface of the lithium metal layer, the synergistic effect of the first coating and the second coating can reduce the volume expansion of the negative electrode while suppressing the growth of lithium dendrites. Moreover, the lithium metal and silicon-carbon material with high specific capacity can significantly improve the capacity of the negative electrode, thereby improving the battery's capacity, rate performance and cycle performance.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A cross-sectional structural diagram of a negative electrode sheet provided in an embodiment of this application; Figure 2 This is a schematic flowchart illustrating a method for preparing a negative electrode sheet according to an embodiment of this application. Detailed Implementation

[0018] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0019] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0020] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0021] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0022] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0023] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0024] In related technologies, strategies such as lithium metal alloying and setting a protective layer on the surface of lithium metal anodes have been adopted to suppress the growth of lithium dendrites on the surface of lithium metal anodes. However, existing methods are still difficult to solve the problem of lithium dendrite growth well, and also face the challenge of large-scale production.

[0025] Based on this, embodiments of this application provide a negative electrode sheet, such as... Figure 1As shown, the negative electrode includes: a current collector 100; a lithium metal layer 200 disposed on at least one surface of the current collector 100 along its thickness direction; a first coating 300 disposed on the side surface of the lithium metal layer 200 away from the current collector 100; the first coating 300 includes graphite and a first sulfide solid electrolyte; a second coating 400 disposed on the side surface of the first coating 300 away from the lithium metal layer 200; the second coating 400 includes silicon carbide material and a second sulfide solid electrolyte.

[0026] Lithium ions typically have difficulty migrating on the surface of the lithium metal layer 200, making it challenging to achieve uniform deposition. In this embodiment, the graphite in the first coating 300 and the silicon-carbon material in the second coating 400 can increase lithium ion transport channels. The silicon-carbon material can also form three-dimensional lithium ion transport channels. Furthermore, the second coating 400, containing silicon-carbon material, is located on the surface of the negative electrode, facilitating rapid lithium insertion / extraction. Combined with the first and second sulfide solid electrolytes, which have high lithium ion conductivity, the lithium deposition flux on the surface of the lithium metal layer 200 can be made more uniform. In other words, the first coating 300 and the second coating 400 are equivalent to covering the surface of the lithium metal layer 200 with a sieve, promoting uniform lithium ion deposition and thus effectively suppressing lithium dendrite growth. In addition, the first... The first coating 300 includes low-expansion graphite, which has a small volume change during charging and discharging. It can buffer the large volume change of the lithium metal layer 200 and the second coating 400 during charging and discharging, thereby reducing the overall volume expansion of the negative electrode sheet. In other words, in this embodiment, by providing the first coating 300 and the second coating 400 sequentially stacked on the surface of the lithium metal layer 200, the synergistic effect of the first coating 300 and the second coating 400 can reduce the volume expansion of the negative electrode sheet while suppressing the growth of lithium dendrites. Moreover, the lithium metal and silicon carbide materials with high specific capacity can significantly improve the capacity of the negative electrode sheet, thereby improving the battery's capacity, rate performance, and cycle performance.

[0027] Understandable Figure 1 In this embodiment, the lithium metal layer 200, the first coating layer 300, and the second coating layer 400 are sequentially stacked on one surface of the current collector 100 along the thickness direction, which is only one example. In some other embodiments of this application, the lithium metal layer 200, the first coating layer 300, and the second coating layer 400 may be sequentially stacked on both surfaces of the current collector 100 along the thickness direction.

[0028] For example, the first sulfide solid electrolyte may include Li 10 GeP2S 12 Li 10 SnP2S 12 Li₂S-P₂S₅, Li 10 SiP2S 12At least one of Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. Specifically, the first sulfide solid electrolyte can be, for example, Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. 10 GeP2S 12 Li 10 SnP2S 12 Li₂S-P₂S₅, Li 10 SiP2S 12 At least one of Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. The second sulfide solid electrolyte may, for example, include Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. 5.5 PS 4.5 Cl 1.5 Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them. Specifically, the second sulfide solid electrolyte can be, for example, Li. 5.5 PS 4.5 Cl 1.5 Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them.

[0029] In some embodiments, the first coating 300 further includes a first conductive agent and a first binder; the mass ratio of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder can be (60~90):(5~35):(1~4):(0.5~4), for example, 60:5:1:0.5, 65:10:1.5:1, 70:15:2:1.5, 75:20:2.5:2, 80:25:3:2.5, 85:30:3.5:3, 90:35:4:4, or any other ratio within the above mass ratio range. This is beneficial for balancing the ionic and electronic conductivity of the first coating 300, thereby better promoting the uniform deposition of lithium ions on the surface of the lithium metal layer 200, and thus better suppressing the growth of lithium dendrites. Furthermore, by using an appropriate proportion of graphite, the large volume changes of the lithium metal layer 200 and the second coating 400 during charging and discharging can be better buffered, reducing the overall volume expansion of the negative electrode.

[0030] Furthermore, the preferred mass ratio of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder is (70~85):(15~25):(1~3):(1~3). This is beneficial for further improving the overall performance of the negative electrode.

[0031] In some embodiments, the second coating 400 further includes a second conductive agent and a second binder; the mass ratio of silicon-carbon material, second sulfide solid electrolyte, second conductive agent, and second binder can be (60~90):(5~35):(1~4):(0.5~4), for example, 60:5:1:0.5, 65:10:1.5:1, 70:15:2:1.5, 75:20:2.5:2, 80:25:3:2.5, 85:30:3.5:3, 90:35:4:4, or any other ratio within the above mass ratio range. This is beneficial for balancing the ionic and electronic conductivity of the second coating 400, thereby better promoting the uniform deposition of lithium ions on the surface of the lithium metal layer 200, and thus better suppressing the growth of lithium dendrites. Furthermore, an appropriate proportion of silicon-carbon material can also improve the ability of the negative electrode to rapidly insert and extract lithium and increase the capacity of the negative electrode. Furthermore, the preferred mass ratio of silicon-carbon material, second sulfide solid electrolyte, second conductive agent, and second binder is (70~85):(15~25):(1~3):(1~3). This is beneficial for further improving the overall performance of the negative electrode.

[0032] In this embodiment, the first conductive agent and the second conductive agent may, for example, include conductive carbon fiber. Specifically, both the first conductive agent and the second conductive agent can be conductive carbon fiber. The first adhesive and the second adhesive may each independently include at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers. Specifically, the first adhesive and the second adhesive are each independently at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers. The first adhesive and the second adhesive can be of the same type or different types.

[0033] Optionally, the molecular weight of polyisobutylene is between 2 million Da and 5 million Da, for example, it can be 2 million Da, 2.5 million Da, 3 million Da, 3.5 million Da, 4 million Da, 4.5 million Da, 5 million Da, or any value between any two of the above ranges. More preferably, the molecular weight of polyisobutylene can be between 3 million Da and 4 million Da.

[0034] Optionally, the molecular weight of styrene-butadiene rubber (SBR) is between 50,000 Da and 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of SBR can be between 100,000 Da and 400,000 Da.

[0035] Optionally, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 50,000 Da to 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 100,000 Da to 400,000 Da.

[0036] Polyisobutylene, styrene-butadiene rubber, or styrene-ethylene-butadiene-styrene block polymers with molecular weights within the above-mentioned range can ensure both strong adhesion and good solubility. In practical applications of slurry preparation, this not only facilitates the formation of a uniform slurry but also achieves the required bonding effect with relatively small addition amounts. This can increase the proportion of graphite and / or silicon carbide materials, thereby improving the electrochemical performance of the negative electrode.

[0037] In some embodiments, the thickness of the lithium metal layer 200 can be 5 μm to 70 μm, for example, 5 μm, 15 μm, 25 μm, 35 μm, 45 μm, 55 μm, 65 μm, 70 μm, or any value between any two of the above ranges. This helps to ensure the capacity of the negative electrode and control the overall volume expansion of the negative electrode, thereby improving the battery's capacity, rate performance, and cycle performance.

[0038] In some embodiments, the thickness of the first coating 300 can be 10 μm to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any value between any two of the above ranges. This is beneficial for better buffering of the large volume changes of the lithium metal layer 200 and the second coating 400 during charging and discharging, and for controlling the thickness of the negative electrode within a suitable range. This facilitates sufficient electrolyte wetting and promotes lithium-ion transport, thereby better suppressing lithium dendrite growth and ultimately improving the battery's capacity, rate performance, and cycle performance. Further, the thickness of the first coating 300 is preferably 20 μm to 40 μm.

[0039] In some embodiments, the thickness of the second coating 400 can be 10 μm to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any value between any two of the above ranges. This is beneficial for improving the ability and capacity of the negative electrode to rapidly insert and extract lithium, and for controlling the thickness of the negative electrode within a suitable range, which facilitates sufficient electrolyte wetting and promotes lithium-ion transport, thereby better suppressing lithium dendrite growth and ultimately improving the battery's capacity, rate performance, and cycle performance. Further, the thickness of the second coating 400 is preferably 20 μm to 40 μm.

[0040] This application also provides a method for preparing a negative electrode sheet. Please refer to... Figure 2 The method for preparing the negative electrode sheet provided in this application includes the following steps: S1: A substrate is provided, the substrate including a current collector and a lithium metal layer disposed on at least one surface of the current collector in the thickness direction; S2: Graphite, a first sulfide solid electrolyte, a first conductive agent, and a first binder are dispersed in a first solvent and stirred evenly to obtain a first slurry; the first slurry is coated onto a first carrier film, and after a first drying process, a first coating layer is formed on the first carrier film; the first carrier film is composited with a substrate, and the first coating layer is positioned opposite to the lithium metal layer; after a first rolling process, the first carrier film is removed, and the first coating layer is transferred to the surface of the lithium metal layer; S3: Disperse silicon-carbon material, second sulfide solid electrolyte, second conductive agent and second binder in second solvent, stir evenly to obtain second slurry; coat the second slurry onto the second carrier film, and after second drying, form a second coating on the second carrier film; composite the second carrier film with the substrate, with the second coating and the first coating positioned opposite each other, and after second rolling, remove the second carrier film and transfer the second coating to the surface of the first coating to obtain the negative electrode sheet.

[0041] In this embodiment, a first slurry is coated onto a first carrier film to form a first coating layer, a second slurry is coated onto a second carrier film to form a second coating layer, and then the first coating layer and the second coating layer are sequentially transferred to the surface of the lithium metal layer. This avoids the problem of the solvent easily reacting with lithium metal when the slurry is directly coated onto the surface of the lithium metal layer. The preparation method is highly feasible and practical, and is easy to scale up for production. The graphite in the first coating and the silicon-carbon material in the second coating can increase lithium-ion transport channels. The silicon-carbon material can form three-dimensional lithium-ion transport channels. Moreover, the second coating containing silicon-carbon material is located on the surface of the negative electrode, which is conducive to rapid lithium insertion and extraction. Combined with the first sulfide solid electrolyte and the second sulfide solid electrolyte with high lithium-ion conductivity, the lithium deposition flux on the surface of the lithium metal layer can be more uniform, thereby effectively suppressing the growth of lithium dendrites. In addition, the first coating includes low-expansion graphite, which has small volume change during charging and discharging, and can buffer the large volume change of the lithium metal layer and the second coating during charging and discharging, reducing the overall volume expansion of the negative electrode. That is, in the embodiments of this application, by forming the first coating and the second coating sequentially stacked on the lithium metal layer, the synergistic effect of the first coating and the second coating can reduce the volume expansion of the negative electrode while suppressing the growth of lithium dendrites. Moreover, the lithium metal and silicon-carbon material with high specific capacity can significantly improve the capacity of the negative electrode, thereby improving the battery's capacity, rate performance and cycle performance.

[0042] In step S1, a substrate is provided, the substrate including a current collector and a lithium metal layer disposed on at least one surface of the current collector in the thickness direction.

[0043] In actual fabrication processes, the substrate fabrication step may include laminating a lithium metal foil onto a current collector (specifically, a copper foil), ensuring a tight bond between the two. The lithium metal layer may be laminated onto one surface of the current collector along its thickness direction, or onto both surfaces along its thickness direction.

[0044] In some embodiments, the thickness of the lithium metal layer can be 5 μm to 70 μm, for example, 5 μm, 15 μm, 25 μm, 35 μm, 45 μm, 55 μm, 65 μm, 70 μm, or any value between any two of the above ranges. This helps to ensure the capacity of the negative electrode and control the overall volume expansion of the negative electrode, thereby improving the battery's capacity, rate performance, and cycle performance.

[0045] In step S2, graphite, a first sulfide solid electrolyte, a first conductive agent, and a first binder are dispersed in a first solvent and stirred evenly to obtain a first slurry; the first slurry is coated onto a first carrier film, and after a first drying process, a first coating is formed on the first carrier film; the first carrier film is composited with a substrate, and the first coating is positioned opposite to the lithium metal layer; after a first rolling process, the first carrier film is removed, and the first coating is transferred to the surface of the lithium metal layer.

[0046] In the actual preparation process, step S2 above may include the following steps: S21: Graphite, a first sulfide solid electrolyte, and a first conductive agent are mixed, and a first binder and a first solvent are added. After stirring into a uniform first slurry, the first slurry is coated onto a first carrier film and dried first to form a first coating on the first carrier film. This coating can also be called a graphite / electrolyte layer.

[0047] In step S21, the mass ratio of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder can be (60~90):(5~35):(1~4):(0.5~4), for example, 60:5:1:0.5, 65:10:1.5:1, 70:15:2:1.5, 75:20:2.5:2, 80:25:3:2.5, 85:30:3.5:3, 90:35:4:4, or any other ratio within the above range. This helps to balance the ionic and electronic conductivity of the first coating, thereby promoting the uniform deposition of lithium ions on the surface of the lithium metal layer and effectively suppressing the growth of lithium dendrites. Furthermore, the appropriate proportion of graphite can effectively buffer the large volume changes of the lithium metal layer and the second coating during charging and discharging, reducing the overall volume expansion of the negative electrode. Furthermore, the preferred mass ratio of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder is (70~85):(15~25):(1~3):(1~3). This is beneficial for further improving the overall performance of the negative electrode.

[0048] In step S21, the ratio of the sum of the masses of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder to the mass of the first solvent can be (4~7):(3~6), for example, it can be 4:3, 4:4, 4:5, 4:6, 5:3, 5:4, 6:4, 6:5, 7:3, 7:4, 7:5, 7:6, or any other ratio within the above range. This helps to ensure sufficient dispersion of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder, forming a relatively uniform first slurry, and can control the solid content and viscosity of the first slurry within a suitable range, thereby facilitating subsequent coating to form a higher quality first coating. Further, the ratio of the sum of the masses of graphite, the first sulfide solid electrolyte, the first conductive agent, and the first binder to the mass of the first solvent can be (5~6):(5~6).

[0049] For example, the first sulfide solid electrolyte may include Li 10 GeP2S 12 Li 10 SnP2S 12 Li₂S-P₂S₅, Li 10 SiP2S 12 At least one of Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. Specifically, the first sulfide solid electrolyte can be, for example, Li₂S-Si₂S₂, Li₂S-B₂S₃, and Li₆PS₅Cl. 10 GeP2S 12 Li 10 SnP2S 12 Li₂S-P₂S₅, Li 10SiP2S 12 At least one of Li2S-Si2S2, Li2S-B2S3, and Li6PS5Cl.

[0050] For example, the first adhesive may include at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers. Specifically, the first adhesive may be at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers.

[0051] Optionally, the molecular weight of polyisobutylene is between 2 million Da and 5 million Da, for example, it can be 2 million Da, 2.5 million Da, 3 million Da, 3.5 million Da, 4 million Da, 4.5 million Da, 5 million Da, or any value between any two of the above ranges. More preferably, the molecular weight of polyisobutylene can be between 3 million Da and 4 million Da.

[0052] Optionally, the molecular weight of styrene-butadiene rubber (SBR) is between 50,000 Da and 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of SBR can be between 100,000 Da and 400,000 Da.

[0053] Optionally, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 50,000 Da to 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 100,000 Da to 400,000 Da.

[0054] Polyisobutylene, styrene-butadiene rubber, or styrene-ethylene-butadiene-styrene block polymers with molecular weights within the above-mentioned range can ensure both strong adhesion and good solubility. In practical applications of slurry preparation, this not only facilitates the formation of a uniform slurry but also achieves the required bonding effect with relatively small addition amounts. This can increase the proportion of graphite and / or silicon carbide materials, thereby improving the electrochemical performance of the negative electrode.

[0055] For example, the first conductive agent may include conductive carbon fiber. Specifically, the first conductive agent may be conductive carbon fiber. The first solvent may include at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane. Specifically, the first solvent may be at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane. The first carrier film may be a PET release film.

[0056] In step S21, the temperature of the first drying step can be 50°C to 100°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or any value between any two of the above ranges. Further, the temperature of the first drying step is preferably 70°C to 90°C.

[0057] S22: The first carrier film loaded with the first coating is laminated with the substrate, and the lithium metal layer with the first coating facing the substrate is disposed. After a first rolling process, the first coating loaded on the first carrier film is transferred to the surface of the lithium metal layer. Here, the coating after the lithium metal layer and the graphite / electrolyte layer are laminated can also be called a lithium metal / graphite composite coating.

[0058] The pressure of the first roller can be from 10 MPa to 80 MPa, for example, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, or any value within any two of the above ranges; the rolling speed of the first roller can be from 0.5 m / min to 3 m / min, for example, 0.5 m / min, 1 m / min, 1.5 m / min, 2 m / min, 2.5 m / min, 3 m / min, or any value within any two of the above ranges. This helps to ensure that the first coating is transferred to the surface of the lithium metal layer more effectively and completely.

[0059] Furthermore, the pressure of the first roller is preferably 40MPa to 60MPa; the rolling speed of the first roller is preferably 1m / min to 2m / min.

[0060] In step S3, silicon-carbon material, second sulfide solid electrolyte, second conductive agent and second binder are dispersed in a second solvent and stirred evenly to obtain a second slurry; the second slurry is coated on a second carrier film, and after a second drying, a second coating is formed on the second carrier film; the second carrier film is composited with a substrate, the second coating is positioned opposite to the first coating, and after a second rolling process, the second carrier film is removed, and the second coating is transferred to the surface of the first coating to obtain a negative electrode sheet.

[0061] In the actual preparation process, step S3 above may include the following steps: S31: Silicon-carbon material, second sulfide solid electrolyte, and second conductive agent are mixed, and a second binder and a second solvent are added. After stirring to form a uniform second slurry, the second slurry is coated onto a second carrier film and then dried to form a second coating on the second carrier film. This coating can also be called a silicon-carbon / electrolyte layer.

[0062] In step S31, the mass ratio of silicon-carbon material, second sulfide solid electrolyte, second conductive agent, and second binder can be (60~90):(5~35):(1~4):(0.5~4), for example, 60:5:1:0.5, 65:10:1.5:1, 70:15:2:1.5, 75:20:2.5:2, 80:25:3:2.5, 85:30:3.5:3, 90:35:4:4, or any other ratio within the above range. This helps to balance the ionic and electronic conductivity of the second coating, thereby better promoting the uniform deposition of lithium ions on the surface of the lithium metal layer and thus better suppressing the growth of lithium dendrites. Furthermore, an appropriate proportion of silicon-carbon material can also improve the ability of the negative electrode to rapidly insert and extract lithium, as well as increase the capacity of the negative electrode. Furthermore, the preferred mass ratio of silicon-carbon material, second sulfide solid electrolyte, second conductive agent and second binder is (70~85):(15~25):(1~3):(1~3).

[0063] In step S31, the ratio of the total mass of the silicon carbide material, the second sulfide solid electrolyte, the second conductive agent, and the second binder to the mass of the second solvent can be (4~7):(3~6), for example, 4:3, 4:4, 4:5, 4:6, 5:3, 5:4, 6:4, 6:5, 7:3, 7:4, 7:5, 7:6, or any other ratio within the above range. This helps to ensure sufficient dispersion of the silicon carbide material, the second sulfide solid electrolyte, the second conductive agent, and the second binder, forming a more uniform second slurry, and allows the solid content and viscosity of the second slurry to be controlled within a suitable range, thereby facilitating subsequent coating to form a higher quality second coating. Further, the preferred ratio of the total mass of the silicon carbide material, the second sulfide solid electrolyte, the second conductive agent, and the second binder to the mass of the second solvent is (5~6):(5~6).

[0064] For example, the second sulfide solid electrolyte may include Li 5.5 PS 4.5 Cl 1.5 Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them. Specifically, the second sulfide solid electrolyte can be, for example, Li. 5.5 PS 4.5 Cl 1.5 Li 10 GeP2S 12 Li 10 SnP2S 12 At least one of them.

[0065] For example, the second adhesive may include at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers. Specifically, the second adhesive may be at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymers.

[0066] Optionally, the molecular weight of polyisobutylene is between 2 million Da and 5 million Da, for example, it can be 2 million Da, 2.5 million Da, 3 million Da, 3.5 million Da, 4 million Da, 4.5 million Da, 5 million Da, or any value between any two of the above ranges. More preferably, the molecular weight of polyisobutylene can be between 3 million Da and 4 million Da.

[0067] Optionally, the molecular weight of styrene-butadiene rubber (SBR) is between 50,000 Da and 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of SBR can be between 100,000 Da and 400,000 Da.

[0068] Optionally, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 50,000 Da to 500,000 Da, for example, it can be 50,000 Da, 150,000 Da, 200,000 Da, 250,000 Da, 300,000 Da, 350,000 Da, 400,000 Da, 450,000 Da, 500,000 Da, or any value between any two of the above ranges. More preferably, the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is from 100,000 Da to 400,000 Da.

[0069] Polyisobutylene, styrene-butadiene rubber, or styrene-ethylene-butadiene-styrene block polymers with molecular weights within the above-mentioned range can ensure both strong adhesion and good solubility. In practical applications of slurry preparation, this not only facilitates the formation of a uniform slurry but also achieves the required bonding effect with relatively small addition amounts. This can increase the proportion of graphite and / or silicon carbide materials, thereby improving the electrochemical performance of the negative electrode.

[0070] For example, the second conductive agent may include conductive carbon fiber. Specifically, the second conductive agent may be conductive carbon fiber. The second solvent may include at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane. Specifically, the second solvent may be at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane. The second carrier film may be a PET release film.

[0071] In step S31, the temperature for the second drying can be 50°C to 100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or any value between any two of the above ranges. Further, the temperature for the second drying is preferably 70°C to 90°C.

[0072] S32: The second carrier film loaded with the second coating is composited with the substrate loaded with the first coating, and the second coating is positioned facing the first coating. After a second rolling process, the second coating loaded on the second carrier film is transferred to the surface of the first coating to obtain the negative electrode sheet. Here, the coating resulting from the composite of the silicon-carbon / electrolyte layer and the lithium metal / graphite composite coating can also be called a lithium metal / graphite / silicon-carbon coating, and the composite of the lithium metal / graphite / silicon-carbon coating loaded on the current collector can be called a lithium metal / graphite / silicon-carbon composite negative electrode.

[0073] The pressure of the second roller can be between 20 MPa and 60 MPa, for example, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, or any value within any two of the above ranges; the rolling speed of the second roller is between 0.3 m / min and 2 m / min, for example, 0.3 m / min, 0.5 m / min, 1 m / min, 1.5 m / min, 2 m / min, or any value within any two of the above ranges. This facilitates a better and more complete transfer of the second coating to the surface of the lithium metal layer.

[0074] Furthermore, the pressure of the second roller is preferably 30MPa~50MPa; the rolling speed of the second roller is preferably 0.8m / min~1.5m / min.

[0075] In step S3, the thickness of the first coating in the final negative electrode sheet can be 10 μm to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any value between any two of the above ranges. This is beneficial for better buffering the large volume changes of the lithium metal layer and the second coating during charging and discharging, and for controlling the thickness of the negative electrode sheet within a suitable range. This facilitates sufficient electrolyte wetting and promotes lithium ion transport, thereby better suppressing lithium dendrite growth and ultimately improving the battery's capacity, rate performance, and cycle performance. Furthermore, the thickness of the first coating formed on the surface of the lithium metal layer is preferably 20 μm to 40 μm.

[0076] In step S3, the thickness of the second coating in the final negative electrode sheet can be 10 μm to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any value between any two of the above ranges. This is beneficial for improving the ability of the negative electrode sheet to rapidly insert and extract lithium and its capacity through the second coating, and it allows the thickness of the negative electrode sheet to be controlled within a suitable range, facilitating sufficient wetting of the electrolyte and promoting lithium ion transport, thereby better suppressing lithium dendrite growth, and ultimately improving the battery's capacity, rate performance, and cycle performance. Further, the thickness of the second coating is preferably 20 μm to 40 μm.

[0077] This application also provides a solid-state battery, which includes the negative electrode sheet described in any of the above embodiments or the negative electrode sheet prepared by the method described in any of the above embodiments.

[0078] It is understood that the beneficial effects of the negative electrode sheet described in any of the above embodiments are also applicable to this solid-state battery. The solid-state battery in the embodiments of this application has high capacity, high rate performance, and high cycle performance.

[0079] Typically, solid-state batteries also include a positive electrode and a solid electrolyte located between the positive and negative electrodes. The solid electrolyte not only facilitates the transport of lithium ions between the positive and negative electrodes but also serves as an insulator. These types of batteries are also known as all-solid-state batteries.

[0080] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0081] Example 1

[0082] The preparation of the negative electrode in this embodiment includes the following steps: Step S101: Mix graphite, sulfide solid electrolyte Li6PS5Cl, and conductive carbon fiber (first conductive agent), add polyisobutylene (first binder) and xylene (first solvent), and stir to form a uniform first slurry; wherein, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is 60:35:1:4, the mass ratio of the added xylene to the total mass of the above solid substances (graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene) is 6:4, and the molecular weight of polyisobutylene is 2 million Da; coat the first slurry onto a PET release film (first carrier film), and dry it at 100°C to form a film (first drying), forming a first coating on the PET release film, which can be called a graphite / electrolyte layer; Step S102: Add silicon-carbon material and sulfide solid electrolyte Li 10 SnP2S 12Conductive carbon fiber (second conductive agent) is mixed with polyisobutylene (second binder) and xylene (second solvent), and stirred to form a uniform second slurry; wherein, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber and polyisobutylene is 60:35:2:3, the mass ratio of the added xylene to the total mass of the above solid substances (silicon carbon material, sulfide solid electrolyte, conductive carbon fiber and polyisobutylene) is 6:4, and the molecular weight of polyisobutylene is 2 million Da; the second slurry is coated on PET release film (second carrier film), and dried at 100°C to form a film (second drying), forming a second coating on PET release film, which can be called silicon carbon / electrolyte layer; Step S103: The PET release film loaded with graphite / electrolyte layer is rolled together with a 5μm thick lithium metal layer loaded on one surface of copper foil (current collector) (first rolling process). The graphite / electrolyte layer and the lithium metal layer are arranged opposite each other. The rolling pressure is 10MPa and the rolling speed is 0.5m / min. After rolling, the graphite / electrolyte layer is transferred to the surface of the lithium metal layer. The coating after the lithium metal layer and the graphite / electrolyte layer are combined can be called lithium metal / graphite composite coating. Step S104: The PET release film loaded with the silicon-carbon / electrolyte layer is rolled together with the lithium metal / graphite composite coating (second rolling process). The silicon-carbon / electrolyte layer and the graphite / electrolyte layer are positioned opposite each other. The rolling pressure is 20 MPa, and the rolling speed is 0.5 m / min. After rolling, the silicon-carbon / electrolyte layer is transferred to the surface of the lithium metal / graphite composite coating, resulting in a negative electrode sheet. The thickness of the first coating in the negative electrode sheet is 10 μm, and the thickness of the second coating is 50 μm. The coating resulting from the combination of the silicon-carbon / electrolyte layer and the lithium metal / graphite composite coating can be called a lithium metal / graphite / silicon-carbon coating. The composite of the lithium metal / graphite / silicon-carbon coating loaded on copper foil can be called a lithium metal / graphite / silicon-carbon composite negative electrode.

[0083] Example 2

[0084] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 90:5:4:1; the mass ratio of xylene to the total mass of the solid phase is adjusted to 3:7; the molecular weight of polyisobutylene is adjusted to 5 million Da; and the temperature of the first drying is adjusted to 50°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber and polyisobutylene is adjusted to 90:5:4:1; the mass ratio of xylene to the total mass of solid phase material is adjusted to 3:7; the molecular weight of polyisobutylene is adjusted to 5 million Da; and the temperature of the second drying is adjusted to 50°C. 3) In step S103, the thickness of the lithium metal layer is adjusted to 70 μm; the pressure of the first rolling process is adjusted to 80 MPa, and the rolling speed is adjusted to 3 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 60MPa and the rolling speed is adjusted to 2m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 50μm and the thickness of the second coating is adjusted to 10μm.

[0085] Example 3

[0086] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 75:20:2:3; the mass ratio of xylene to the total mass of the solid phase is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3.5 million Da; and the temperature of the first drying is adjusted to 75°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 75:20:2:3; the mass ratio of xylene to the total mass of solid phase material is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3.5 million Da; and the temperature of the second drying is adjusted to 75°C. 3) In step S103, the thickness of the lithium metal layer is adjusted to 40 μm; the pressure of the first rolling process is adjusted to 45 MPa, and the rolling speed is adjusted to 1.8 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 40MPa and the rolling speed is adjusted to 1.2m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 30μm and the thickness of the second coating is adjusted to 30μm.

[0087] Example 4

[0088] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 65:30:1.5:3.5; the mass ratio of xylene to the total mass of the solid phase is adjusted to 4:6; the molecular weight of polyisobutylene is adjusted to 2.5 million Da; and the temperature of the first drying is adjusted to 90°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 65:30:1.5:3.5; the mass ratio of xylene to the total mass of solid phase material is adjusted to 4:6; the molecular weight of polyisobutylene is adjusted to 2.5 million Da; and the temperature of the second drying is adjusted to 90°C. 3) In step S103, the thickness of the lithium metal layer is adjusted to 10 μm; the pressure of the first rolling process is adjusted to 20 MPa, and the rolling speed is adjusted to 1.0 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 25MPa and the rolling speed is adjusted to 0.7m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 20μm and the thickness of the second coating is adjusted to 40μm.

[0089] Example 5

[0090] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 70:25:2.5:2.5; the mass ratio of xylene to the total mass of the solid phase is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3 million Da; and the temperature of the first drying is adjusted to 80°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 70:25:2.5:2.5; the mass ratio of xylene to the total mass of solid phase material is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3 million Da; and the temperature of the second drying is adjusted to 80℃. 3) In step S103, the thickness of the lithium metal layer is adjusted to 20 μm; the pressure of the first rolling process is adjusted to 30 MPa, and the rolling speed is adjusted to 1.5 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 30MPa and the rolling speed is adjusted to 0.9m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 40μm and the thickness of the second coating is adjusted to 20μm.

[0091] Example 6

[0092] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 80:15:3:2; the mass ratio of xylene to the total mass of the solid phase is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 4 million Da; and the temperature of the first drying is adjusted to 70°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber and polyisobutylene is adjusted to 80:15:3:2; the mass ratio of xylene to the total mass of solid phase material is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 4 million Da; and the temperature of the second drying is adjusted to 70℃. 3) In step S103, the thickness of the lithium metal layer is adjusted to 30 μm; the pressure of the first rolling process is adjusted to 40 MPa, and the rolling speed is adjusted to 2 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 35MPa and the rolling speed is adjusted to 1.4m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 30μm and the thickness of the second coating is adjusted to 30μm.

[0093] Example 7

[0094] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 85:10:3.5:1.5; the mass ratio of xylene to the total mass of the solid phase is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 4.5 million Da; and the temperature of the first drying is adjusted to 60°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 85:10:3.5:1.5; the mass ratio of xylene to the total mass of solid phase material is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 4.5 million Da; and the temperature of the second drying is adjusted to 60°C. 3) In step S103, the thickness of the lithium metal layer is adjusted to 50 μm; the pressure of the first rolling process is adjusted to 50 MPa, and the rolling speed is adjusted to 2.5 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 45MPa and the rolling speed is adjusted to 1.6m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 30μm and the thickness of the second coating is adjusted to 30μm.

[0095] Example 8

[0096] The preparation method of the negative electrode in this embodiment is basically the same as that in Example 1, except that: 1) In step S101, the mass ratio of graphite, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 75:20:2:3; the mass ratio of xylene to the total mass of the solid phase is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3.5 million Da; and the temperature of the first drying is adjusted to 75°C. 2) In step S102, the mass ratio of silicon carbon material, sulfide solid electrolyte, conductive carbon fiber, and polyisobutylene is adjusted to 75:20:2:3; the mass ratio of xylene to the total mass of solid phase material is adjusted to 5:5; the molecular weight of polyisobutylene is adjusted to 3.5 million Da; and the temperature of the second drying is adjusted to 75°C. 3) In step S103, the thickness of the lithium metal layer is adjusted to 60 μm; the pressure of the first rolling process is adjusted to 60 MPa, and the rolling speed is adjusted to 3 m / min; 4) In step S104, the pressure of the second rolling process is adjusted to 50MPa and the rolling speed is adjusted to 1.8m / min; in the obtained negative electrode sheet, the thickness of the first coating is adjusted to 30μm and the thickness of the second coating is adjusted to 30μm.

[0097] Comparative Example 1 The preparation of the negative electrode in this comparative example includes the following steps: A lithium metal layer is loaded onto the surface of a copper foil to obtain a negative electrode, wherein the thickness of the lithium metal layer in the negative electrode is 50 μm.

[0098] Comparative Example 2 The preparation method of the negative electrode in this comparative example is basically the same as that in Example 3, except that: Steps S102 and S104 were omitted; in step S103, the pressure of the first rolling process was adjusted to 50 MPa and the rolling speed was adjusted to 2 m / min; that is, Comparative Example 2 omitted the second coating compared to Example 3, and only the first coating was formed on the surface of the lithium metal layer.

[0099] Comparative Example 3 The preparation method of the negative electrode in this comparative example is basically the same as that in Example 3, except that: Steps S101 and S103 were omitted; correspondingly, in step S104, the second coating was directly transferred to the surface of the lithium metal layer; that is, Comparative Example 3 omitted the first coating compared to Example 3, and the second coating was formed only on the surface of the lithium metal layer.

[0100] Comparative Example 4 The preparation method of the negative electrode in this comparative example is basically the same as that in Example 3, except that: The order of steps S103 and S104 is reversed, that is, the second coating is transferred to the surface of the lithium metal layer first, and then the first coating is transferred to the surface of the second coating; at the same time, the thickness of the lithium metal layer is adjusted to 60 μm; the pressure of the first rolling process in step S103 is adjusted to 50 MPa; the pressure of the second rolling process in step S104 is adjusted to 60 MPa, and the rolling speed is adjusted to 3.0 m / min.

[0101] The negative electrode sheets prepared in the above embodiments and comparative examples were used to prepare batteries, and the electrochemical performance of the batteries was tested.

[0102] The battery preparation steps are as follows: First, nickel-cobalt-manganese ternary cathode material (NCM811) is mixed with sulfide solid electrolyte and conductive carbon fiber, polyisobutylene and xylene are added, and stirred to form a uniform cathode slurry. This slurry is then coated onto aluminum foil, dried, and cut into 10mm diameter discs as cathode sheets. The cathode sheets prepared in the above embodiments and comparative examples are cut into 10mm diameter discs as cathode sheets. The cathode discs are placed in a 10mm diameter polyetheretherketone (PEEK) cylindrical mold. Both pressure rods of the mold are made of stainless steel. The side of the cathode disc loaded with the cathode active material is away from the pressure rods. Then, sulfide solid electrolyte powder is added to the mold and spread evenly on the surface of the cathode disc. A pressure of 300MPa is applied and held for 3 minutes to form a powder cake. Then, the cathode disc is placed in the mold, with the side loaded with the cathode active material facing the sulfide solid electrolyte powder cake, and a pressure of 100MPa is applied to obtain a solid-state battery.

[0103] The performance of the prepared battery was tested as follows: Cycling performance testing at different rates: In a 25℃ constant temperature chamber, the charging current value Ic was set on the battery tester. Ic = (weight of positive electrode sheet - weight of current collector) × proportion of positive electrode active material × 190 × rate. In the above formula, the unit of weight is grams (g), and the unit of current is milliamperes (mA). The discharge current is the same as the charging current, and the rate current is calculated based on the nominal capacity of the positive electrode active material of 190mAh / g. During the test, a constant current charge-discharge method was used. The battery cycle performance was tested according to the following procedure: charge-rest-discharge-rest-charge, and so on, until the capacity was 50% lower than the first discharge capacity. The rest time was 10 minutes. Among them, the 0.5C rate capacity is based on the discharge capacity of the second cycle in the 0.5C charge and 0.5C discharge cycle. The 1C rate capacity is based on the discharge capacity of the second cycle in the 1C charge and 1C discharge cycle. 0.1C first efficiency = first 0.1C discharge capacity / first 0.1C charge capacity.

[0104] Capacity retention rate after 100 cycles at 0.3C: The calculation method is based on the industry-standard method of 100 cycles at 0.3C. The discharge capacity of the first cycle and the discharge capacity of the 100th cycle are recorded. The capacity retention rate after 100 cycles at 0.3C = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100%.

[0105] The test results are shown in Table 1.

[0106] Table 1

[0107] As can be seen from the data in Table 1, in Comparative Example 1, the lithium metal layer is loaded onto the copper foil surface of the negative electrode, and no coating is applied to the surface of the lithium metal layer. This leads to uneven deposition of lithium ions on the surface of the lithium metal layer, forming lithium dendrites, which ultimately causes a short circuit in the battery, and the battery tester cannot detect any performance data. In Comparative Example 2, compared to Comparative Example 1, a first coating containing graphite and sulfide solid electrolyte is applied to the lithium metal layer. This first coating can, to some extent, ensure the battery's rate capacity at low rates (0.5C) and its first-time efficiency at low rates (0.1C). However, at a high rate of 1C, the battery still experienced a short circuit. Therefore, it can be concluded that the first coating alone has a limited effect on suppressing lithium dendrite growth. In Comparative Example 3, compared to Comparative Example 1, a second coating comprising silicon-carbon material and a sulfide solid electrolyte was applied to the lithium metal layer. Based on the high specific capacity and three-dimensional lithium-ion transport channels of the silicon-carbon material, the rate capacity and initial efficiency of the battery were somewhat guaranteed under the action of the second coating. However, because both the lithium metal layer and the silicon-carbon material undergo significant volume changes during charge and discharge, the capacity retention rate after 100 cycles at 0.3C is low, meaning the battery's cycle performance is poor. Therefore, it can be concluded that a second coating alone is insufficient to simultaneously improve the battery's cycle performance.

[0108] As can be seen from the data in Table 1, in Examples 1 to 8, the corresponding batteries exhibited high rate capacity and initial efficiency at different rates, while the capacity retention rate after 100 cycles at 0.3C all exceeded 90%. This indicates that, in this application, by sequentially stacking a first coating layer and a second coating layer on the surface of the lithium metal layer, the synergistic effect of the first and second coating layers can suppress lithium dendrite growth while reducing the volume expansion of the negative electrode. Furthermore, the high specific capacity of lithium metal and silicon carbide materials can significantly improve the capacity of the negative electrode, thereby enhancing the battery's capacity, rate performance, and cycle performance.

[0109] A comparison of the data from Examples 1 to 8 in Table 1 shows that as the content of sulfide solid electrolyte in the first and second coatings increases, the rate capacity of the battery at different rates generally shows a gradual increasing trend. This indicates that the high lithium-ion conductivity of the sulfide solid electrolyte is beneficial to improving the rate performance of the battery. Furthermore, with the total thickness of the first and second coatings remaining constant, as the thickness of the second coating increases and the thickness of the first coating decreases, the rate capacity of the battery generally shows a gradual increasing trend. However, the initial efficiency and capacity retention rate after 100 cycles at 0.3C show a gradual decreasing trend. This further demonstrates that only through the synergistic effect of the first and second coatings can the improvement of battery capacity, rate performance, and cycle performance be achieved.

[0110] As can be seen from the data in Comparative Example 4 of Table 1, if the positions of the first and second coatings are interchanged—that is, the second coating is placed on the surface of the lithium metal layer and the first coating is placed on the surface of the second coating—the volume expansion of the second coating, which includes silicon-carbon materials, is much greater than that of the first coating, which includes graphite. This causes the intermediate layer structure of the negative electrode sheet to collapse and be destroyed more quickly due to the volume expansion and contraction. Therefore, the cycle stability and rate performance of the corresponding battery deteriorate. Thus, in this application, the first and second coatings must be sequentially placed on the lithium metal layer to achieve a synergistic effect, thereby improving the battery's capacity, rate performance, and cycle performance.

[0111] It should be noted that the negative electrode sheet embodiments, negative electrode sheet preparation method embodiments and solid-state battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0112] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations of this application. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A negative electrode sheet, characterized in that, include: current collector; A lithium metal layer is disposed on at least one surface of the current collector along its thickness direction; A first coating is disposed on the surface of the lithium metal layer away from the current collector; the first coating comprises graphite and a first sulfide solid electrolyte. A second coating is disposed on the surface of the first coating away from the lithium metal layer; the second coating comprises a silicon-carbon material and a second sulfide solid electrolyte.

2. The negative electrode sheet according to claim 1, characterized in that, The first coating further includes a first conductive agent and a first binder; the mass ratio of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3).

3. The negative electrode sheet according to claim 1, characterized in that, The second coating further includes a second conductive agent and a second binder; the mass ratio of the silicon carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3).

4. The negative electrode sheet according to claim 1, characterized in that, The first coating further includes a first adhesive; the second coating further includes a second adhesive; the first adhesive and the second adhesive each independently include at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The thickness of the lithium metal layer is 5μm~70μm; and / or, The thickness of the first coating is 10μm~50μm, preferably 20μm~40μm; And / or, The thickness of the second coating is 10μm to 50μm, preferably 20μm to 40μm.

6. A method for preparing a negative electrode sheet, characterized in that, The method includes the following steps: S1: Provide a substrate, the substrate comprising a current collector and a lithium metal layer disposed on at least one surface of the current collector in the thickness direction; S2: Graphite, a first sulfide solid electrolyte, a first conductive agent, and a first binder are dispersed in a first solvent and stirred evenly to obtain a first slurry; the first slurry is coated onto a first carrier film, and after a first drying process, a first coating is formed on the first carrier film; the first carrier film is composited with the substrate, with the first coating disposed opposite to the lithium metal layer; after a first rolling process, the first carrier film is removed, and the first coating is transferred to the surface of the lithium metal layer; S3: Disperse silicon-carbon material, second sulfide solid electrolyte, second conductive agent and second binder in a second solvent and stir evenly to obtain a second slurry; coat the second slurry onto a second carrier film, and after a second drying, form a second coating on the second carrier film; combine the second carrier film with the substrate, with the second coating and the first coating positioned opposite each other, and after a second rolling process, remove the second carrier film and transfer the second coating to the surface of the first coating to obtain the negative electrode sheet.

7. The method for preparing the negative electrode sheet according to claim 6, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The mass ratio of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3); (2) The ratio of the sum of the masses of the graphite, the first sulfide solid electrolyte, the first conductive agent and the first binder to the mass of the first solvent is (4~7):(3~6), preferably (5~6):(5~6); (3) The first adhesive includes at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; (4) The first solvent includes at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane; (5) The first carrier film is a PET release film; (6) The temperature of the first drying is 50℃~100℃, preferably 70℃~90℃; (7) The pressure of the first roller is 10MPa~80MPa, preferably 40MPa~60MPa; the rolling speed of the first roller is 0.5m / min~3m / min, preferably 1m / min~2m / min.

8. The method for preparing the negative electrode sheet according to claim 6, characterized in that, Step S3 satisfies at least one of the following characteristics: (1) The mass ratio of the silicon-carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder is (60~90):(5~35):(1~4):(0.5~4), preferably (70~85):(15~25):(1~3):(1~3); (2) The ratio of the sum of the masses of the silicon-carbon material, the second sulfide solid electrolyte, the second conductive agent and the second binder to the mass of the second solvent is (4~7):(3~6), preferably (5~6):(5~6); (3) The second adhesive includes at least one of polyisobutylene, styrene-butadiene rubber, and styrene-ethylene-butadiene-styrene block polymer; optionally, the molecular weight of the polyisobutylene is 2 million Da to 5 million Da, preferably 3 million Da to 4 million Da; the molecular weight of the styrene-butadiene rubber is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; the molecular weight of the styrene-ethylene-butadiene-styrene block polymer is 50,000 Da to 500,000 Da, preferably 100,000 Da to 400,000 Da; (4) The second solvent includes at least one of xylene, trimethylbenzene, n-heptane, n-decane, and dodecane; (5) The second carrier film is a PET release film; (6) The temperature of the second drying is 50℃~100℃, preferably 70℃~90℃; (7) The pressure of the second roller is 20MPa~60MPa, preferably 30MPa~50MPa; the rolling speed of the second roller is 0.3m / min~2m / min, preferably 0.8m / min~1.5m / min.

9. The method for preparing the negative electrode sheet according to any one of claims 6 to 8, characterized in that, The prepared negative electrode sheet satisfies at least one of the following characteristics: (1) The thickness of the lithium metal layer is 5μm~70μm; (2) The thickness of the first coating is 10μm~50μm, preferably 20μm~40μm; (3) The thickness of the second coating is 10μm~50μm, preferably 20μm~40μm.

10. A solid-state battery, characterized in that, The negative electrode sheet includes the negative electrode sheet according to any one of claims 1 to 5, or the negative electrode sheet prepared by any one of claims 6 to 9.

Images