Silicon-carbon negative electrode sheet and preparation method therefor, and all-solid-state lithium-ion battery

Abstract

The present application provides a silicon-carbon negative electrode sheet and a preparation method therefor, and an all-solid-state lithium-ion battery. The silicon-carbon negative electrode sheet comprises an interface protection layer, which is arranged in contact with the surface of a negative electrode active layer away from a negative electrode current collector. The materials of the interface protection layer include a composite of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer is formed by means of an in-situ reaction of an inorganic silver salt and an excessive lithium strip on the surface of the negative electrode active layer. In the present application, the interface protection layer is formed on the negative electrode active layer by means of an in-situ displacement reaction of the inorganic silver salt and the lithium strip, thereby effectively improving the compatibility between a negative electrode material and an electrolyte, reducing the direct contact between the negative electrode material and the electrolyte during charging and discharging, and thus reducing the occurrence of side reactions. In addition, the lithium-silver alloy and the inorganic lithium salt in the interface protection layer can provide an additional lithium source, thereby improving the initial coulombic efficiency of a battery and prolonging the service life of the battery.

Description

Silicon-carbon anode sheet, its preparation method and all-solid-state lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 2024115160308, filed with the Chinese Patent Office on October 28, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion batteries, and more specifically, to a silicon-carbon negative electrode sheet, its preparation method, and an all-solid-state lithium-ion battery. Background Technology

[0003] Currently, all-solid-state batteries, which combine high safety and high energy density, have become the most sought-after battery system in the new energy field. Among them, sulfide electrolytes, due to their inherent characteristics of high ionic conductivity and good flexibility, are the most promising candidates for successful commercial application in all-solid-state battery products. Meanwhile, silicon-carbon anodes, with their advantages of high specific capacity and low redox potential, are the most promising anode materials for matching high-nickel ternary cathodes to achieve commercial sulfide all-solid-state battery products.

[0004] However, the low conductivity, low first-cycle coulombic efficiency, and poor solid-solid interface stability between silicon-carbon anodes and sulfide electrolytes severely affect the rate performance, energy density, and cycle life of all-solid-state batteries. Therefore, regulating the solid-solid interface compatibility between silicon-carbon anodes and sulfide electrolytes, reducing interfacial side reactions, and improving charge / ion transport behavior at the interface are crucial scientific problems that urgently need to be solved in the commercialization of all-solid-state lithium-ion batteries.

[0005] Therefore, how to provide a high-performance lithium-ion battery negative electrode to improve the interfacial stability between the negative electrode and the sulfide electrolyte, thereby improving the electrical performance of the all-solid-state lithium-ion battery, is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0006] The main objective of this application is to provide a silicon-carbon anode electrode, its preparation method, and an all-solid-state lithium-ion battery, so as to solve the problem of poor battery performance caused by the poor interface stability between the silicon-carbon anode electrode and the electrolyte in the existing all-solid-state lithium-ion batteries.

[0007] To achieve the above objectives, the first aspect of this application provides a silicon-carbon negative electrode sheet, comprising: a negative electrode current collector; a negative electrode active layer disposed on at least one side surface of the negative electrode current collector; the silicon-carbon negative electrode sheet further comprising: an interface protection layer disposed in contact with the surface of the negative electrode active layer away from the negative electrode current collector; the material of the interface protection layer comprises a composite of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer is formed by an in-situ reaction of an inorganic silver salt and an excess lithium strip on the surface of the negative electrode active layer.

[0008] This application effectively improves the stability and electrical performance of the silicon-carbon anode by forming an interface protective layer on the active layer of the anode, generated by an in-situ substitution reaction between inorganic silver salt and lithium strip. Specifically, the inorganic lithium salt and lithium-silver alloy in the interface protective layer are generated through an in-situ substitution reaction between the inorganic lithium salt and lithium strip. Compared to directly mixing the inorganic lithium salt and lithium-silver alloy as components to form a composite layer, this in-situ reaction system allows for more uniform dispersion of the inorganic lithium salt and lithium-silver alloy, and a tighter physical contact between the two phases. Ultimately, this more effectively optimizes the solid-solid interface and improves the performance of the electrode and the battery. Compared to the commonly used silicon-carbon anode electrode interface protection layer containing polymers such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and polymethyl methacrylate, the anode interface protection layer containing lithium-silver alloy and inorganic lithium salt provided in this application has higher lithium-ion conductivity, effectively reduces the interface resistance between the anode active layer and the solid electrolyte layer, and also has higher resistance to electrolyte corrosion and chemical stability, thereby significantly improving the electrical performance of the silicon-carbon anode electrode and the performance of the corresponding lithium-ion battery.

[0009] To ensure the in-situ substitution reaction proceeds more fully and to obtain silicon-carbon anode sheets with higher structural consistency and better electrical performance, the inorganic silver salt is further selected from one or more of silver oxide, silver carbonate, silver phosphate, and silver chloride; and / or, the inorganic lithium salt is selected from one or more of lithium oxide, lithium carbonate, lithium phosphate, and lithium chloride.

[0010] Furthermore, the thickness of the interface protective layer is 10μm to 15μm, so as to suppress the obstruction of electron transport caused by excessively thick protective layer, thereby more effectively improving the electrical performance of the negative electrode.

[0011] The second aspect of this application provides a method for preparing the above-mentioned silicon-carbon negative electrode sheet, the method comprising: step S1, preparing a precursor dispersion containing inorganic silver salt; step S2, coating the precursor dispersion onto the negative electrode active layer and forming an inorganic silver salt layer on the negative electrode active layer; step S3, attaching an excess lithium strip to the surface of the inorganic silver salt layer in a direction away from the negative electrode active layer to obtain a composite layer comprising a lithium strip and an inorganic silver salt layer; step S4, heating the composite layer to allow the inorganic silver salt and lithium strip to react in situ on the surface of the negative electrode active layer to obtain an electrode interface protective layer, thereby obtaining a silicon-carbon negative electrode sheet.

[0012] In response to the aforementioned silicon-carbon anode sheet, this application provides a corresponding preparation method. The method involves uniformly coating a precursor dispersion containing inorganic silver salt onto the anode active layer of the silicon-carbon anode sheet. Then, by heating, the inorganic silver salt coated on the surface of the silicon-carbon anode undergoes an in-situ reaction with lithium metal, forming an interfacial protective layer primarily composed of a lithium-silver alloy and inorganic lithium salt.

[0013] Furthermore, the precursor dispersion was sprayed onto the negative electrode active layer in droplet form of 0.5 μm to 3.0 μm, with a spraying amount of 1.0 mL / cm². 2 ~1.5mL / cm 2 Under these spraying conditions, more suitable in-situ reaction conditions are created, ultimately forming an interface protective layer that provides effective protection and improves the electrical performance of the silicon-carbon anode electrode. Preferably, the thickness of the lithium strip is 5μm to 10μm to facilitate complete replacement reaction with the inorganic silver salt while more effectively suppressing passivation reactions caused by excess lithium metal residue on the surface, thereby more effectively improving the electrode's electrical performance.

[0014] Furthermore, the precursor dispersion also includes a binder, and the weight ratio of inorganic silver salt to binder is (9-19):1, thereby better balancing adhesion, stability, and conductivity, and more effectively improving the electrical performance of the silicon-carbon anode sheet and the lithium-ion battery in which it is located. Preferably, the binder is selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose to further improve the electrical performance of the resulting electrode sheet by utilizing its better compatibility.

[0015] Further, in step S1, the preparation process of the precursor dispersion includes: dissolving the binder in an organic solvent to obtain an organic solution, and then adding the inorganic silver salt to the organic solution to obtain the precursor dispersion. Under these preparation conditions, the system dispersion uniformity of the precursor dispersion is more effectively improved, and a silicon-carbon anode sheet with a more continuous and stable structure and higher electrical performance is finally obtained. Preferably, based on 100% of the total weight of the organic solution, the amount of inorganic silver salt added is 20% to 25%, thereby obtaining an inorganic silver salt layer with a better structure, forming a more effective interfacial protective layer, and the resulting silicon-carbon anode sheet has higher electrical performance. More preferably, the organic solvent is selected from one or more of N-methylpyrrolidone, acetonitrile, and N,N-dimethylformamide to improve the uniform dispersion of the inorganic silver salt and binder, improve the uniformity and density of the obtained interfacial protective layer, and the electrical performance of the silicon-carbon anode sheet in which it is located.

[0016] Furthermore, both steps S1 and S2 are performed in a dry environment; preferably, the temperature of the dry environment is 20℃~25℃ and the dew point is -60℃~-40℃. These conditions effectively reduce the water content of the inorganic silver salt layer, suppress the introduction of impurities, enhance the intrinsic protective effect of the final interface protective layer, optimize the bonding between the interface protective layer and the negative electrode active layer in the silicon-carbon negative electrode sheet, and ultimately obtain a silicon-carbon negative electrode sheet with superior electrical performance.

[0017] Furthermore, the heating treatment in step S4 is carried out at a temperature of 50℃ to 80℃ for a time of 0.5h to 2.0h; preferably, both steps S3 and S4 are carried out in an environment with an oxygen content of <1ppm and a water content of <1ppm. These conditions can significantly reduce the occurrence of side reactions during the in-situ reaction, thereby further improving the purity and stability of the obtained interface protective layer, and consequently resulting in superior performance of the corresponding silicon-carbon anode sheet and lithium-ion battery, especially exhibiting higher initial efficiency.

[0018] A third aspect of this application provides an all-solid-state lithium-ion battery, comprising a solid electrolyte layer. The all-solid-state lithium-ion battery is a full cell, comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive and negative electrode. The positive electrode comprises a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, and the positive active layer comprises a nickel-cobalt-manganese ternary layered oxide. The silicon-carbon negative electrode is the aforementioned silicon-carbon negative electrode, or a silicon-carbon negative electrode prepared by the aforementioned method. Alternatively, the all-solid-state lithium-ion battery is a half-cell, comprising a working electrode, a counter electrode, and a solid electrolyte layer disposed between the working electrode and the counter electrode. The counter electrode is a lithium-indium electrode. The working electrode is the aforementioned silicon-carbon negative electrode, or a silicon-carbon negative electrode prepared by the aforementioned method. More preferably, the solid electrolyte in the solid electrolyte layer is selected from Li7P3S. 11 Li 10 GeP2S 12 The silicon-carbon anode sheet provided in this application contains one or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I, with Li6PS5Cl being more preferred. This silicon-carbon anode sheet incorporates a high-performance interface protection layer, which improves compatibility and prevents direct contact between the anode active material and the solid electrolyte during charging and discharging, thereby reducing side reactions. It also provides an additional lithium source for the lithium-ion battery in which it is located. Therefore, all-solid-state lithium-ion full cells and half cells containing this silicon-carbon anode sheet exhibit excellent electrical performance, especially the first-cycle coulombic efficiency.

[0019] By applying the technical solution of this application, an interfacial protective layer formed by the in-situ exchange reaction of inorganic silver salt and lithium band is created on the negative electrode active layer. This effectively improves the compatibility between the negative electrode material and the electrolyte, reduces direct contact between the negative electrode material and the electrolyte during charging and discharging, and thus reduces the occurrence of side reactions. Simultaneously, the lithium-silver alloy and inorganic lithium salt in the interfacial protective layer can provide additional lithium sources, helping to improve the battery's initial coulombic efficiency and extend its lifespan. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0021] As described in the background section, existing all-solid-state lithium-ion batteries suffer from poor battery performance due to the poor interfacial stability between the silicon-carbon negative electrode and the electrolyte. To address this technical problem, a first aspect of this application provides a silicon-carbon negative electrode, comprising: a negative electrode current collector; a negative electrode active layer disposed on at least one side surface of the negative electrode current collector; the silicon-carbon negative electrode further comprising: an interface protection layer disposed in contact with the surface of the negative electrode active layer away from the negative electrode current collector, the interface protection layer being made of a composite material of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer being formed by an in-situ reaction of inorganic silver salt and excess lithium strip on the surface of the negative electrode active layer.

[0022] This application effectively improves the stability and electrical performance of the silicon-carbon anode sheet by forming an interface protective layer on the active layer of the anode, generated by the in-situ displacement reaction of inorganic silver salt and lithium band. Specifically, by setting an interface protective layer on the active layer of the silicon-carbon anode sheet, i.e., designing an interface protective layer between the anode and electrolyte, the excellent stability of the interface protective layer itself is utilized to avoid interface side reactions caused by direct contact between the two, while eliminating the high ion / electron transport impedance caused by interface voids. On the other hand, the lithium-silver alloy and the inorganic lithium salt component with high ionic conductivity contained in the interface protective layer promote the uniform and rapid transport of lithium ions at the interface. Among them, the uniformly dispersed lithium-silver alloy can regulate the uniform distribution of lithium ion concentration at the interface, avoiding electrode breakage caused by excessive local reaction, while the inorganic lithium salt component with high ionic conductivity is beneficial to the rapid transport of lithium ions, thus avoiding capacity decay and interface failure caused by lithium deposition on the surface of the silicon-carbon anode during high-rate charging. The two factors mentioned above synergistically and significantly improve the electrical performance of the resulting silicon-carbon anode sheet, ultimately enabling its corresponding all-solid-state lithium-ion battery to exhibit high first-cycle coulombic efficiency.

[0023] Compared to the commonly used silicon-carbon anode electrode interface protection layer containing polymers such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and polymethyl methacrylate, the anode interface protection layer containing lithium-silver alloy and inorganic lithium salt provided in this application has higher lithium-ion conductivity, effectively reduces the interface resistance between the anode active layer and the solid electrolyte layer, and also has higher resistance to electrolyte corrosion and chemical stability, thereby significantly improving the electrical performance of the silicon-carbon anode electrode and the performance of the corresponding lithium-ion battery.

[0024] In particular, in the interface protection layer on the silicon-carbon anode sheet provided in this application, both the inorganic lithium salt and the lithium-silver alloy are generated by in-situ substitution reaction between the inorganic silver salt and the lithium strip. Compared with directly mixing the inorganic lithium salt and the lithium-silver alloy as components to form a composite layer, the inorganic lithium salt and the lithium-silver alloy in this in-situ reaction system can be more uniformly dispersed and the physical contact between the two phases is tighter, which ultimately optimizes the solid-solid interface more effectively and improves the performance of the electrode sheet and the battery.

[0025] In several preferred embodiments, the inorganic silver salt is selected from one or more of silver oxide, silver carbonate, silver phosphate, and silver chloride; the inorganic lithium salt is selected from one or more of lithium oxide, lithium carbonate, lithium phosphate, and lithium chloride. To ensure a more complete in-situ substitution reaction and obtain a silicon-carbon anode electrode with higher structural consistency and better electrical performance, the inventors optimized the types of the aforementioned inorganic silver salts and the corresponding inorganic lithium salts through extensive experiments, thereby obtaining a silicon-carbon anode electrode with better overall performance. The lithium-ion battery containing this electrode also exhibits higher first-cycle coulombic efficiency. The preferred thickness of the interface protective layer is 10 μm to 15 μm.

[0026] The second aspect of this application provides a method for preparing the above-mentioned silicon-carbon negative electrode sheet, the method comprising: step S1, preparing a precursor dispersion containing inorganic silver salt; step S2, coating the precursor dispersion onto the negative electrode active layer and forming an inorganic silver salt layer on the negative electrode active layer; step S3, attaching an excess lithium strip to the surface of the inorganic silver salt layer in a direction away from the negative electrode active layer to obtain a composite layer comprising a lithium strip and an inorganic silver salt layer; step S4, heating the composite layer to allow the inorganic silver salt and lithium strip to react in situ on the surface of the negative electrode active layer to obtain an electrode interface protective layer, thereby obtaining a silicon-carbon negative electrode sheet.

[0027] In response to the aforementioned silicon-carbon anode sheet, this application provides a corresponding preparation method. The method involves uniformly coating a precursor dispersion containing inorganic silver salt onto the anode active layer of the silicon-carbon anode sheet. Then, by heating, the inorganic silver salt coated on the surface of the silicon-carbon anode undergoes an in-situ reaction with lithium metal, forming an interfacial protective layer primarily composed of a lithium-silver alloy and inorganic lithium salt.

[0028] Specifically, the heating process can accelerate the substitution reaction between inorganic silver salt and lithium strip, and improve the reaction rate and uniformity of the alloying reaction between the silver metal obtained from the substitution and the lithium strip, thereby improving the process efficiency and the performance of the resulting silicon-carbon anode sheet.

[0029] Meanwhile, in practical applications, the bonding between the lithium strip and the inorganic silver salt layer can be achieved by rolling, or by applying a certain pressure to ensure that the two can be tightly bonded to guarantee the subsequent in-situ reaction.

[0030] Furthermore, through extensive experimentation, the inventors first transformed the precursor dispersion containing inorganic silver salts into droplet form using ultrasonic atomization. The preferred size of the droplet precursor dispersion was 0.5 μm to 3.0 μm, and the preferred spraying rate was 1.0 mL / cm³. 2 ~1.5mL / cm 2 This process creates uniformly dispersed reaction sites with suitable density, simultaneously avoiding incomplete reactions due to excessively large droplet size or spray volume, and poor results due to excessively small droplet size or spray volume. Under these spraying conditions, more suitable in-situ reaction conditions are constructed. Subsequently, by attaching a lithium strip larger than the silicon-carbon anode sheet and heating it, the generation of inorganic lithium salt and lithium-silver alloy was successfully achieved, ultimately forming an interface protective layer that provides effective protection and improves the electrical performance of the silicon-carbon anode sheet.

[0031] Meanwhile, the preferred thickness of the lithium strip is 5μm to 10μm, which promotes complete replacement reaction with inorganic silver salt while effectively suppressing excess lithium metal residue on the surface, preventing passivation reactions that generate a large number of byproducts and damage the interface structure. The electrode surface after the replacement and alloying reactions should have no obvious metallic luster.

[0032] In several typical embodiments, to obtain a more stable interfacial protective layer, the precursor dispersion preferably also includes a binder. Furthermore, through extensive experimentation, the inventors have optimized the weight ratio of inorganic silver salt to binder to be (9–19):1, thereby better balancing adhesion, stability, and conductivity, and more effectively improving the electrical performance of the silicon-carbon anode sheet and the lithium-ion battery. Additionally, for compatibility considerations, the binder is preferably selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose, thus obtaining a silicon-carbon anode sheet with better electrical performance.

[0033] Furthermore, in order to improve the uniformity of the precursor dispersion system, thereby improving the structural density and integrity of the inorganic silver salt layer formed by spraying, and ultimately obtaining a silicon-carbon anode sheet with a more continuous and stable structure and higher electrical performance, the preferred step S1 includes the following steps: dissolving the binder in an organic solvent to obtain an organic solution, and then adding the inorganic silver salt to the organic solution to obtain the precursor dispersion.

[0034] To better control droplet size and coating volume during the spraying process, the inventors, through extensive experimentation, optimized the addition of inorganic silver salt to 20%–25% of the total organic solution weight (100%). This resulted in a better-structured inorganic silver salt layer, leading to a more effective interfacial protective layer and higher electrical performance of the resulting silicon-carbon anode sheet. In several typical embodiments, the organic solvent is preferably selected from one or more of N-methylpyrrolidone, acetonitrile, and N,N-dimethylformamide to improve the uniform dispersion of the inorganic silver salt and binder, enhance the uniformity and density of the resulting interfacial protective layer, and improve the electrical performance of the silicon-carbon anode sheet in which it is located.

[0035] In several typical implementations, to form a more structurally stable inorganic silver salt layer, steps S1 and S2 are preferably performed in a dry environment. The inventors further prefer the dry environment to have a temperature of 20°C to 25°C and a dew point of -60°C to -40°C, thereby more effectively reducing the water content of the inorganic silver salt layer, suppressing the introduction of impurities, enhancing the intrinsic protective effect of the final interface protective layer, optimizing the bonding between the interface protective layer and the negative electrode active layer in the silicon-carbon negative electrode sheet, and ultimately obtaining a silicon-carbon negative electrode sheet with superior electrical performance.

[0036] In order to effectively promote the in-situ substitution reaction between inorganic silver salt and lithium strip while suppressing the material damage that may occur during the reaction, the inventors optimized the heating temperature in step S4 to be 50℃~80℃ and the time to be 0.5h~2.0h through a large number of experiments. Under these conditions, a more stable and superior negative electrode interface protective layer was obtained. The silicon-carbon negative electrode sheet and the lithium-ion battery containing it also showed higher electrical performance accordingly.

[0037] To better facilitate the in-situ substitution reaction, in several more typical implementations, steps S3 and S4 are carried out in a glove box with an oxygen content of <1 ppm and a water content of <1 ppm. Since the water and oxygen contents in the glove box change in real time, they only exhibit range values ​​rather than constant values ​​throughout the reaction. This ultra-low oxygen and low water environment, optimized through extensive experimentation, can significantly reduce the occurrence of side reactions during the in-situ reaction, thereby further improving the purity and stability of the resulting interface protective layer. This, in turn, leads to superior performance in the corresponding silicon-carbon anode electrode and lithium-ion battery, particularly exhibiting higher initial efficiency.

[0038] A third aspect of this application provides an all-solid-state lithium-ion battery, including a solid electrolyte layer.

[0039] The all-solid-state lithium-ion battery is a full cell, comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, and the positive active layer includes a nickel-cobalt-manganese ternary layered oxide. The negative electrode is the aforementioned silicon-carbon negative electrode, or a silicon-carbon negative electrode prepared by the aforementioned method for preparing silicon-carbon negative electrodes. Alternatively, the all-solid-state lithium-ion battery is a half cell, comprising a working electrode, a counter electrode, and a solid electrolyte layer disposed between the working electrode and the counter electrode. The counter electrode is a lithium-indium electrode; the working electrode is the aforementioned silicon-carbon negative electrode, or a silicon-carbon negative electrode prepared by the aforementioned method for preparing silicon-carbon negative electrodes.

[0040] Because the silicon-carbon anode electrode provided in this application contains a high-performance interface protection layer, which can improve compatibility and avoid direct contact between the anode active material and the solid electrolyte during charging and discharging, thereby reducing the occurrence of side reactions, and also providing an additional lithium source for the lithium-ion battery in which it is located, the all-solid-state lithium-ion full cell and half cell containing the silicon-carbon anode electrode exhibit excellent electrical performance, especially the first-cycle coulombic efficiency.

[0041] Specifically, the solid electrolyte layer has a thickness of 100μm to 200μm, which serves to provide ion transport channels and prevent short circuits between the positive and negative electrodes.

[0042] In several preferred embodiments, the solid electrolyte in the solid electrolyte layer includes, but is not limited to, Li7P3S. 11 Li 10 GeP2S 12 One or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I are preferred. Li6PS5Cl is preferred because the inventors discovered through extensive experimentation that this sulfide solid electrolyte can better cooperate with the aforementioned interface protective layer, thereby obtaining an all-solid-state lithium-ion battery with higher initial efficiency.

[0043] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0044] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.

[0045] Example 1

[0046] A method for preparing a silicon-carbon negative electrode sheet:

[0047] In this embodiment, a silicon-carbon anode sheet prepared by wet coating is used as the original silicon-carbon anode sheet, wherein the mass ratio of silicon-carbon active material, sulfide electrolyte LPS5Cl, and polyacrylic acid binder is 16:4:1. The precursor materials selected for preparing the interface protective layer include silver carbonate (Ag2CO3) as the inorganic silver salt, polyvinylidene fluoride (PvDF) as the binder, N-methylpyrrolidone (NMP) as the organic solvent, and an ultrathin lithium strip with a thickness of 5 μm. The specific implementation process is as follows:

[0048] S1. In a dry room environment with a temperature of 25℃ and a dew point of -50℃, weigh 2 parts by mass of PvDF binder and add it to 98 parts by mass of NMP organic solvent. Stir for 6 hours until the organic solution is clear and free of obvious particles. Then add 25 parts by mass of Ag2CO3 inorganic silver salt and stir thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2CO3 inorganic silver salt to PvDF binder is 12.5:1, and the amount of Ag2CO3 inorganic silver salt added relative to the organic solution is 25wt%).

[0049] S2. Also in a dry environment with a temperature of 25℃ and a dew point of -50℃, the precursor prepared in S1 was dispersed into 0.5μm droplets by an ultrasonic atomizer and then sprayed onto the surface of a silicon-carbon anode sheet. The amount of precursor solution sprayed per unit area of ​​the silicon-carbon anode sheet was 1.5mL / cm². 2 After the coating is applied, the electrode is transferred to a vacuum oven at 60°C and placed for 12 hours. After drying, a silicon-carbon electrode with an Ag2CO3 coating on the surface is obtained.

[0050] S3. In a glove box with oxygen content <1ppm and water content <1ppm, the electrode sheet prepared in S2 is transferred to the glove box, and an ultra-thin lithium strip with a thickness of 5μm and a flexible non-woven fabric are sequentially bonded to the surface of the silicon-carbon electrode sheet. The lithium strip and the Ag2CO3 coating on the silicon-carbon electrode sheet are tightly bonded by a roller press to obtain a composite electrode sheet containing a composite layer.

[0051] S4. Similarly, in a glove box with oxygen content <1ppm and water content <1ppm, the composite electrode prepared in S3 is transferred to a heating stage at 60℃ and reacted for 0.5h. Then, the elemental lithium in the lithium strip undergoes an in-situ exchange reaction with the silver in Ag2CO3. After the lithium strip loses its obvious metallic luster, the flexible nonwoven fabric and the reacted lithium strip are removed to obtain a silicon-carbon electrode with the main components of the interface protective layer being lithium-silver alloy and lithium carbonate (Li2CO3). The thickness of this interface protective layer is 10μm.

[0052] Example 2

[0053] A method for preparing a silicon-carbon negative electrode sheet:

[0054] In this embodiment, a silicon-carbon anode sheet prepared by wet coating is used as the original silicon-carbon anode sheet, wherein the mass ratio of silicon-carbon active material, sulfide electrolyte LPS5Cl, and polyacrylic acid binder is 16:4:1. The precursor materials selected for preparing the interface protective layer include silver oxide (Ag2O) as the inorganic silver salt, polyvinylidene fluoride (PvDF) as the binder, N-methylpyrrolidone (NMP) as the organic solvent, and an ultrathin lithium strip with a thickness of 5 μm. The specific implementation process is as follows:

[0055] S1. In a dry room environment with a temperature of 20℃ and a dew point of -60℃, weigh 2 parts by mass of PvDF binder and add it to 98 parts by mass of NMP organic solvent. Stir for 6 hours until the organic solution is clear and free of obvious particulate matter. Then add 20 parts by mass of Ag2O inorganic silver salt and stir thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2O inorganic silver salt to PvDF binder is 10:1, and the amount of Ag2O inorganic silver salt added relative to the organic solution is 20wt%).

[0056] S2. Similarly, in a dry environment with a temperature of 20℃ and a dew point of -60℃, the precursor prepared in S1 was dispersed into 3.0μm droplets using an ultrasonic atomizer and then sprayed onto the surface of a silicon-carbon anode sheet. The amount of precursor solution sprayed per unit area of ​​the silicon-carbon anode sheet was 1.0mL / cm². 2 After the coating is applied, the electrode is transferred to a vacuum oven at 60°C and placed for 12 hours. After drying, a silicon-carbon electrode with an Ag2C coating on the surface is obtained.

[0057] S3. In a glove box with oxygen content <1ppm and water content <1ppm, the electrode sheet prepared in S2 is transferred to the glove box, and an ultra-thin lithium strip with a thickness of 5μm and a flexible non-woven fabric are sequentially bonded to the surface of the silicon-carbon electrode sheet. The lithium strip and the Ag2CO3 coating on the silicon-carbon electrode sheet are tightly bonded by a roller press to obtain a composite electrode sheet containing a composite layer.

[0058] S4. Similarly, in a glove box with an oxygen content of <1ppm and a water content of <1ppm, the composite electrode prepared in S3 is transferred to a heating stage at 60°C and reacted for 0.5h. Then, the elemental lithium in the lithium strip undergoes an in-situ exchange reaction with the silver in Ag2O. After the lithium strip loses its obvious metallic luster, the flexible nonwoven fabric is removed to obtain a silicon-carbon electrode with the main components of the interface protective layer being lithium-silver alloy and lithium oxide (Li2O). The thickness of this interface protective layer is 15μm.

[0059] Example 3

[0060] A method for preparing a silicon-carbon negative electrode sheet:

[0061] The only difference between this embodiment and Example 1 is the precursor material used to prepare the interface protective layer. Specifically, the inorganic silver salt is silver phosphate (Ag3PO4), the binder is polyacrylic acid (PAA), the organic solvent is acetonitrile (ACN), and the thickness is an ultrathin lithium strip of 10 μm. The amount of each component and the parameter settings in the specific experimental conditions are the same.

[0062] Example 4

[0063] A method for preparing a silicon-carbon negative electrode sheet:

[0064] The only difference between this embodiment and Example 1 is the precursor material used to prepare the interface protective layer. Specifically, the inorganic silver salt is silver chloride (AgCl), the binder is carboxymethyl cellulose (CMC), the organic solvent is N,N-dimethylformamide, and the thickness is an ultrathin lithium strip of 10 μm. The amounts of each component and the parameter settings in the specific experimental conditions are the same.

[0065] Example 5

[0066] A method for preparing a silicon-carbon negative electrode sheet:

[0067] The difference between this embodiment and Embodiment 1 lies only in step S1. Specifically, 2 parts by mass of PvDF binder are weighed and added to 98 parts by mass of NMP organic solvent. The mixture is stirred for 6 hours until the organic solution is clear and free of obvious particulate matter. Then, 16 parts by mass of Ag2CO3 inorganic silver salt are added and stirred thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2CO3 inorganic silver salt to PvDF binder is 8:1, and the amount of Ag2CO3 inorganic silver salt added relative to the organic solution is 16 wt%).

[0068] Example 6

[0069] A method for preparing a silicon-carbon negative electrode sheet:

[0070] The difference between this embodiment and Embodiment 1 lies only in step S1. Specifically, 2 parts by mass of PvDF binder are weighed and added to 98 parts by mass of NMP organic solvent. The mixture is stirred for 6 hours until the organic solution is clear and free of obvious particulate matter. Then, 40 parts by mass of Ag2CO3 inorganic silver salt are added and stirred thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2CO3 inorganic silver salt to PvDF binder is 20:1, and the amount of Ag2CO3 inorganic silver salt added relative to the organic solution is 40 wt%).

[0071] Example 7

[0072] A method for preparing a silicon-carbon negative electrode sheet:

[0073] The only difference between this embodiment and Embodiment 1 is that the precursor dispersion was not ultrasonically atomized in step S2; instead, it was directly coated at a concentration of 1.5 mL / cm³. 2 The coating amount was applied to the surface of the silicon-carbon negative electrode, and then transferred to a vacuum oven at 60°C for 12 hours. After drying, a silicon-carbon electrode with an Ag2CO3 coating on the surface was obtained.

[0074] Comparative Example 1

[0075] The untreated raw silicon-carbon electrode sheet used in Example 1 was directly used as the silicon-carbon negative electrode sheet sample.

[0076] Comparative Example 2

[0077] A method for preparing a silicon-carbon negative electrode sheet:

[0078] The only difference between this embodiment and Embodiment 1 is that: in step S4, the composite electrode is not heated, that is, the degree of in-situ reaction between elemental lithium in the lithium strip and Ag2CO3 is low, and the interface protective layer of the resulting silicon-carbon electrode contains less inorganic lithium salt and lithium-silver alloy components and a large amount of precursor reactant components.

[0079] Comparative Example 3

[0080] A method for preparing a silicon-carbon negative electrode sheet:

[0081] In a dry room environment with a temperature of 25℃ and a dew point of -50℃, metallic silver particles were spread on the surface of a lithium strip to carry out an alloying reaction. After 2 hours of reaction, a lithium-silver alloy strip was obtained.

[0082] In a dry room environment with a temperature of 25°C and a dew point of -50°C, 2 parts by mass of PvDF binder were weighed and added to 98 parts by mass of NMP organic solvent. The mixture was stirred for 6 hours until the organic solution was clear and free of obvious particulate matter. Then, 12.5 parts by mass of Li2CO3 inorganic lithium salt was added and stirred thoroughly to obtain a mixed slurry. The mixed slurry was sprayed onto a silicon-carbon electrode sheet as described in Example 1. After the electrode sheet was coated, 12.5 parts by mass of lithium-silver alloy strip was laid on the surface. The electrode sheet was then transferred to a vacuum oven at 60°C and placed for 12 hours. After drying, a silicon-carbon negative electrode sheet sample was obtained directly.

[0083] In this comparative example, Li2CO3 inorganic lithium salt and lithium silver alloy are used as components of the interface protective layer, which directly forms an interface protective layer on the surface of the original silicon-carbon anode without undergoing an in-situ exchange reaction.

[0084] Test methods

[0085] 1. Preparation of half-cell samples:

[0086] Taking Example 1 as an example, the silicon-carbon negative electrode sheet prepared therefrom was used as the working electrode, Li6PS5Cl was used as the solid electrolyte, and a lithium-indium alloy sheet with a thickness of 100μm was used as the counter electrode to prepare a half-cell sample. The specific steps are as follows:

[0087] (1) In the glove box, slowly pour 0.1g of Li6PS5Cl powder into and spread it in the Φ10mm mold sleeve, assemble the gasket and the upper pressure head, put the mold into the work table of the tablet press, apply a pressure of 2t at a uniform speed, hold the pressure for 3min, and then use the demolding sleeve to push out the tablet in the mold to obtain a solid electrolyte membrane with a thickness of 200μm.

[0088] (2) In the glove box, the silicon-carbon negative electrode sheet and lithium-indium alloy prepared in Example 1 are cut into circular pieces with a diameter of Φ10mm, and the cut silicon-carbon negative electrode sheet, solid electrolyte membrane and cut lithium-indium circular pieces are slowly placed into the mold sleeve and flattened in sequence. The gasket and pressure head are then assembled.

[0089] (3) Apply pressure to the assembled test device using a torque wrench until the test pressure of the mold battery is 80 MPa to obtain the corresponding half-cell sample of Example 1, and perform subsequent electrochemical tests.

[0090] The preparation of the corresponding half-cell samples in the other embodiments and comparative examples were carried out in the same manner as described above.

[0091] 2. Preparation of full-cell samples:

[0092] Taking Example 1 as an example, the silicon-carbon negative electrode sheet prepared therefrom was used as the working electrode, Li6PS5Cl was used as the solid electrolyte, and the nickel-cobalt-manganese ternary layered oxide LiNi was used as the electrolyte. 0.8 Co 0.1 Mn 0.1 The specific steps for preparing full-cell samples using O2 as the positive electrode active material are as follows:

[0093] (1) A solid electrolyte membrane with a thickness of 200 μm was obtained by following the above method for preparing half-cell samples;

[0094] (2) Using nickel-cobalt-manganese ternary layered oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the active material to obtain the positive electrode sheet by wet coating, wherein the mass ratio of active material, LPS5Cl sulfide electrolyte, carbon nanotube conductive agent and PvDF binder is 20:7:2:1;

[0095] (3) In the glove box, the silicon-carbon negative electrode sheet prepared in Example 1 and the positive electrode sheet obtained in (2) are cut into circular pieces with a diameter of Φ10mm respectively. The cut silicon-carbon negative electrode sheet, solid electrolyte membrane and cut positive electrode sheet are slowly placed into the mold sleeve and flattened in sequence. The gasket and pressure head are assembled.

[0096] (4) Apply pressure to the assembled test device using a torque wrench until the test pressure of the mold battery is 80 MPa to obtain the full battery sample corresponding to Example 1, and perform subsequent electrochemical tests.

[0097] The preparation of the full-cell samples in the other embodiments and comparative examples were carried out in the same manner as described above.

[0098] 3. First-cycle coulombic efficiency of the battery: The silicon-carbon anode sheets prepared in Examples 1-7 and Comparative Examples 1-3 were assembled into half-cells and full cells respectively according to the above method. The first-cycle charge-discharge cycle was carried out at a rate of 0.1C in a voltage range of 2V to 4.25V (full cell) or -0.61V to 0.90V (half cell). The first-cycle coulombic efficiency of the half-cell samples and full-cell samples corresponding to each example and comparative example was obtained, as detailed in Table 1.

[0099] Table 1

[0100] As can be seen from the above description, the above embodiments of this application realize the preparation of silicon-carbon anode sheets containing an interface protective layer. The resulting silicon-carbon anode sheets have excellent performance and higher interface stability with the solid electrolyte layer. Both the all-solid-state lithium-ion half-cell and the full cell in which they are located exhibit excellent first-cycle coulombic efficiency.

[0101] Specifically, Example 3 is a silicon-carbon anode sheet with an interface composition of inorganic lithium salt Li3PO4 and lithium silver alloy. It exhibits the highest first-cycle coulombic efficiency of half-cell and full-cell, indicating that Li3PO4 performs best in this interface system compared to inorganic lithium salts such as Li2CO3, Li2O and LiCl.

[0102] Comparing Examples 1, 5, and 6, it is easy to analyze and determine the optimal ratio of inorganic lithium salt in the precursor solution (as in Example 1). This yields a silicon-carbon anode sheet with the best interface protection layer performance, and both the assembled half-cell and full-cell exhibit higher first-cycle coulombic efficiency.

[0103] Based on Comparative Examples 1-3, it is easy to conclude that neither the method of not using a heating step to promote the complete in-situ reaction between the lithium strip and the inorganic silver salt, nor the method of directly coating the interface protective layer with inorganic lithium salt and lithium-silver alloy without using an in-situ reaction method, can achieve excellent first-cycle coulombic efficiency. The main reasons are incomplete reaction, resulting in a small amount of the expected products (inorganic lithium salt and lithium-silver alloy), and a large amount of residual precursor leading to complex interface composition, affecting interface ion transport efficiency; and the direct coating method resulting in uneven dispersion of the two components and poor interface contact, severely impacting interface ion transport efficiency.

[0104] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0105] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A silicon-carbon negative electrode sheet, comprising: Negative electrode current collector; A negative electrode active layer is disposed on at least one surface of the negative electrode current collector; The silicon-carbon negative electrode sheet is characterized in that it further includes: An interface protective layer is disposed in contact with the surface of the negative electrode active layer away from the negative electrode current collector. The material of the interface protective layer includes a composite of inorganic lithium salt and lithium-silver alloy, and the interface protective layer is formed by an in-situ reaction of inorganic silver salt and excess lithium strip on the surface of the negative electrode active layer.

2. The silicon-carbon negative electrode sheet according to claim 1, characterized in that, The inorganic silver salt is selected from one or more of silver oxide, silver carbonate, silver phosphate, and silver chloride; and / or, the inorganic lithium salt is selected from one or more of lithium oxide, lithium carbonate, lithium phosphate, and lithium chloride.

3. The silicon-carbon negative electrode sheet according to claim 1 or 2, characterized in that, The thickness of the interface protective layer is 10μm to 15μm.

4. A method for preparing a silicon-carbon negative electrode sheet according to any one of claims 1 to 3, characterized in that, The preparation method includes: Step S1: Prepare a precursor dispersion containing inorganic silver salt; Step S2: The precursor dispersion is coated onto the negative electrode active layer, and an inorganic silver salt layer is formed on the negative electrode active layer. Step S3: Along the direction away from the negative electrode active layer, apply excess lithium strip to the surface of the inorganic silver salt layer to obtain a composite layer including the lithium strip and the inorganic silver salt layer. Step S4: The composite layer is heated to allow the inorganic silver salt and the lithium strip to react in situ on the surface of the negative electrode active layer, thereby obtaining the electrode interface protection layer and the silicon-carbon negative electrode.

5. The preparation method according to claim 4, characterized in that, The precursor dispersion was sprayed onto the negative electrode active layer in droplet form of 0.5 μm to 3.0 μm, with a spraying rate of 1.0 mL / cm³. 2 ~1.5mL / cm 2 ; Preferably, the thickness of the lithium strip is 5μm to 10μm.

6. The preparation method according to claim 4 or 5, characterized in that, The precursor dispersion also includes a binder, and the weight ratio of the inorganic silver salt to the binder is (9-19):1; Preferably, the adhesive is selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose.

7. The preparation method according to claim 6, characterized in that, In step S1, the preparation process of the precursor dispersion includes: dissolving the binder in an organic solvent to obtain an organic solution, and then adding the inorganic silver salt to the organic solution to obtain the precursor dispersion; Preferably, the amount of inorganic silver salt added is 20% to 25% based on the total weight of the organic solution as 100%; More preferably, the organic solvent is selected from one or more of N-methylpyrrolidone, acetonitrile, and N,N-dimethylformamide.

8. The preparation method according to any one of claims 4 to 7, characterized in that, Both steps S1 and S2 are performed in a dry room environment; Preferably, the temperature of the drying room environment is 20℃~25℃ and the dew point is -60℃~-40℃.

9. The preparation method according to any one of claims 4 to 8, characterized in that, The heating treatment in step S4 is performed at a temperature of 50℃ to 80℃ for a time of 0.5h to 2.0h. Preferably, both step S3 and step S4 are carried out in an environment where the oxygen content is <1 ppm and the water content is <1 ppm.

10. An all-solid-state lithium-ion battery, comprising a solid electrolyte layer, characterized in that, The all-solid-state lithium-ion battery is a full cell, comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive and negative electrode; the positive electrode comprises a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, and the positive active layer comprises a nickel-cobalt-manganese ternary layered oxide; the negative electrode is a silicon-carbon negative electrode as described in any one of claims 1 to 3, or a silicon-carbon negative electrode prepared by the method for preparing a silicon-carbon negative electrode as described in any one of claims 4 to 9; or, The all-solid-state lithium-ion battery is a half-cell, which includes a working electrode, a counter electrode, and a solid electrolyte layer disposed between the working electrode and the counter electrode; the counter electrode is a lithium-indium electrode; the working electrode is a silicon-carbon negative electrode sheet according to any one of claims 1 to 3, or a silicon-carbon negative electrode sheet prepared by the method of preparing silicon-carbon negative electrode sheet according to any one of claims 4 to 9. More preferably, the solid electrolyte in the solid electrolyte layer is selected from Li7P3S. 11 Li 10 GeP2S 12 One or more of Li6PS5Cl, Li6PS5Br and Li6PS5I, more preferably Li6PS5Cl.

Images