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

Abstract

The present invention provides a silicon-carbon negative electrode plate, a preparation method thereof, and an all-solid-state lithium-ion battery. The silicon-carbon negative electrode plate includes an interface protection layer, which is arranged 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 includes a composite of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer is formed by an inorganic silver salt and an excess lithium ribbon through an in-situ reaction on the surface of the negative electrode active layer. The present invention effectively improves the compatibility of the negative electrode material and the electrolyte by forming an interface protection layer generated by an in-situ substitution reaction of an inorganic silver salt and a lithium ribbon on the negative electrode active layer, reduces the direct contact between the negative electrode material and the electrolyte during the charge and discharge process, and thus reduces the occurrence of side reactions. At the same time, the lithium-silver alloy and the inorganic lithium salt in the interface protection layer can provide an additional lithium source, which helps to improve the first coulomb efficiency of the battery and extend the service life of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a silicon-carbon negative electrode sheet, a preparation method thereof, and an all-solid-state lithium-ion battery. Background Art

[0002] Currently, all-solid-state batteries, offering both high safety and high energy density, have become the most sought-after battery systems in the new energy sector. Sulfide electrolytes, with their inherent properties of high ionic conductivity and good flexibility, hold the greatest promise for successful commercial application in all-solid-state battery products. Silicon-carbon anodes, with their high specific capacity and low redox potential, are the most promising anode materials for commercial sulfide all-solid-state battery production, complementing high-nickel ternary cathodes.

[0003] However, the low conductivity, low first-cycle coulombic efficiency, and poor solid-solid interfacial stability of the silicon-carbon anode with the sulfide electrolyte have seriously affected the rate performance, energy density, and cycle life of all-solid-state batteries. Therefore, how to regulate the solid-solid interfacial compatibility between the silicon-carbon anode and the sulfide electrolyte, reduce interfacial side reactions, and improve the charge / ion transport behavior at the interface are important scientific issues that need to be addressed in the commercialization of all-solid-state lithium-ion batteries.

[0004] Based on this, how to provide a lithium-ion battery negative electrode sheet with excellent performance to improve the interface stability between the negative electrode sheet and the sulfide electrolyte, and thereby improve the electrical performance of the all-solid-state lithium-ion battery in which it is located, is one of the important technical problems that need to be solved in this field. Summary of the Invention

[0005] The main purpose of the present invention is to provide a silicon-carbon negative electrode plate, a preparation method thereof and an all-solid-state lithium-ion battery, so as to solve the problem of poor battery performance in the all-solid-state lithium-ion battery in the prior art due to poor interface stability between the silicon-carbon negative electrode plate and the electrolyte.

[0006] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a silicon-carbon negative electrode plate, comprising: a negative electrode current collector; a negative electrode active layer, arranged on at least one side surface of the negative electrode current collector, the silicon-carbon negative electrode plate also comprising: an interface protection layer, arranged 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 comprising 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 excess lithium strips on the surface of the negative electrode active layer.

[0007] The present invention effectively improves the stability and electrical performance of the silicon-carbon negative electrode plate by forming an interfacial protective layer on the negative electrode active layer, generated by an in-situ replacement reaction between an inorganic silver salt and a lithium ribbon. The inorganic lithium salt and lithium-silver alloy in the interfacial protective layer are both generated by an in-situ replacement reaction between the inorganic silver salt and the lithium ribbon. Compared to directly physically 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 the system generated by this in-situ reaction are more evenly dispersed and the physical contact between the two phases is closer, ultimately more effectively optimizing the solid-solid interface and improving the performance of the plate and battery. Compared with the silicon-carbon negative electrode interface protection layer commonly used in the art, which contains polymers such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and polymethyl methacrylate, the negative electrode interface protection layer provided by the present invention, which contains lithium-silver alloy and inorganic lithium salt, has higher lithium ion conductivity, effectively reduces the interface resistance between the negative electrode active layer and the solid electrolyte layer, and also has higher electrolyte corrosion resistance and chemical stability, thereby being able to more significantly improve the electrical properties of the silicon-carbon negative electrode sheet in which it is located, as well as the performance of the corresponding lithium-ion battery.

[0008] In order to make the in-situ replacement reaction proceed more fully and obtain a silicon-carbon negative electrode sheet with higher structural consistency and better electrical performance, further, 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.

[0009] Furthermore, the thickness of the interface protection layer is 10 μm to 15 μm, so as to suppress the obstruction of electron transmission caused by the excessive thickness of the protection layer, thereby more effectively improving the electrical performance of the negative electrode sheet.

[0010] The second aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon negative electrode plate, which comprises: step S1, preparing a precursor dispersion containing an 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, laminating an excess lithium ribbon on the surface of the inorganic silver salt layer in a direction away from the negative electrode active layer to obtain a composite layer including a lithium ribbon and an inorganic silver salt layer; step S4, heating the composite layer so that the inorganic silver salt and the lithium ribbon react in situ on the surface of the negative electrode active layer to obtain a plate interface protection layer, and thus obtain a silicon-carbon negative electrode plate.

[0011] The present invention provides a method for preparing the aforementioned silicon-carbon negative electrode sheet. A precursor dispersion containing an inorganic silver salt is uniformly applied to the negative electrode active layer of the silicon-carbon negative electrode sheet. The inorganic silver salt coated on the surface of the silicon-carbon negative electrode reacts with lithium metal in situ by heating, forming an interfacial protective layer primarily composed of a lithium-silver alloy and an inorganic lithium salt.

[0012] Furthermore, the precursor dispersion was sprayed onto the negative electrode active layer in the form of droplets of 0.5 μm to 3.0 μm, with a spraying volume of 1.0 mL / cm 2 ~1.5mL / cm 2 Under these spraying conditions, more suitable in-situ reaction conditions were constructed, ultimately forming an interfacial protective layer that can provide effective protection, improving the electrical performance of the silicon-carbon negative electrode plate. Preferably, the thickness of the lithium ribbon is 5μm to 10μm, so as to promote the complete replacement reaction with the inorganic silver salt while more effectively suppressing the passivation reaction caused by excess lithium metal remaining on the surface, thereby more effectively improving the electrical performance of the electrode plate.

[0013] Furthermore, the precursor dispersion also includes a binder, with the weight ratio of the inorganic silver salt to the binder being (9-19):1, thereby better balancing adhesion, stability, and conductivity, and more effectively improving the electrical performance of the silicon-carbon negative electrode sheet and lithium-ion battery in which it is used. Preferably, the binder is selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose, as its greater compatibility further improves the electrical performance of the resulting electrode sheet.

[0014] Furthermore, 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 a precursor dispersion. Under this preparation condition, the system dispersion uniformity of the precursor dispersion is more effectively improved, and ultimately a silicon-carbon negative electrode sheet with a more continuous and stable structure and higher electrical performance is obtained. Preferably, based on the total weight of the organic solution as 100%, 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 interface protection layer, and the electrical performance of the resulting silicon-carbon negative electrode sheet is also higher. More preferably, the organic solvent is selected from one or more of N-methylpyrrolidone, acetonitrile and N,N-dimethylformamide, so as to improve the uniform dispersion of the inorganic silver salt and the binder, improve the uniformity and density of the resulting interface protection layer, and the electrical performance of the silicon-carbon negative electrode sheet in which it is located.

[0015] Furthermore, both step S1 and step S2 are performed in a dry room environment; preferably, the temperature of the dry room environment is 20°C to 25°C and the dew point is -60°C to -40°C. Such conditions can effectively reduce the water content of the inorganic silver salt layer, inhibit the introduction of impurities therein, enhance the intrinsic protective effect of the final interface protection layer, and optimize the bonding between the interface protection layer and the negative active layer in the silicon-carbon negative electrode sheet, ultimately obtaining a silicon-carbon negative electrode sheet with better electrical performance.

[0016] Furthermore, the heating treatment temperature in step S4 is 50°C to 80°C, and the time is 0.5h to 2.0h. Preferably, both steps S3 and S4 are performed in an environment with an oxygen content of less than 1ppm and a water content of less than 1ppm. Such conditions can greatly reduce the occurrence of side reactions during the in-situ reaction, thereby further improving the purity and stability of the resulting interface protective layer, thereby improving the performance of the corresponding silicon-carbon negative electrode sheet and lithium-ion battery, especially showing a higher first efficiency.

[0017] The third aspect of the present invention provides an all-solid-state lithium-ion battery, including a solid electrolyte layer, the all-solid-state lithium-ion battery is a full battery, the full battery includes a positive electrode sheet, a negative electrode sheet and a solid electrolyte layer arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode collector and a positive electrode active layer arranged on at least one side surface of the positive electrode collector, and the positive electrode active layer includes a nickel-cobalt-manganese ternary layered oxide; the silicon-carbon negative electrode sheet is the above-mentioned silicon-carbon negative electrode sheet, or the silicon-carbon negative electrode sheet prepared by the above-mentioned preparation method of the silicon-carbon negative electrode sheet; or, the all-solid-state lithium-ion battery is a half-cell, the half-cell includes a working electrode, a counter electrode and a solid electrolyte layer arranged between the working electrode and the counter electrode; the counter electrode is a lithium-indium electrode; the working electrode is the above-mentioned silicon-carbon negative electrode sheet, or the silicon-carbon negative electrode sheet prepared by the above-mentioned preparation method of the silicon-carbon negative electrode sheet; more preferably, the solid electrolyte in the solid electrolyte layer is selected from Li7P3S 11 、Li 10 GeP2S 12 , Li6PS5Cl, Li6PS5Br and Li6PS5I, more preferably Li6PS5Cl. The silicon-carbon negative electrode provided by the present invention contains an excellent interface protection layer, which can improve the compatibility and avoid direct contact between the negative electrode active material and the solid electrolyte during charging and discharging, thereby reducing the occurrence of side reactions. At the same time, it also provides an additional lithium source for the lithium-ion battery in which it is located. Therefore, the all-solid-state lithium-ion full battery and half-cell containing the silicon-carbon negative electrode plate exhibit excellent electrical performance, especially the first-cycle coulomb efficiency.

[0018] The technical solution of the present invention forms an interfacial protective layer on the negative electrode active layer, generated by an in-situ substitution reaction between an inorganic silver salt and a lithium ribbon. 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 the charge and discharge process, and thus reduces the occurrence of side reactions. Furthermore, the lithium-silver alloy and inorganic lithium salt in the interfacial protective layer provide an additional lithium source, helping to improve the battery's initial coulombic efficiency and extend its service life. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0020] As described in the background art, existing all-solid-state lithium-ion batteries have the problem of poor battery performance due to poor interface stability between the silicon-carbon negative electrode plate and the electrolyte. In order to solve the above technical problems, the first aspect of the present invention provides a silicon-carbon negative electrode plate, comprising: a negative electrode current collector; a negative electrode active layer disposed on at least one side of the negative electrode current collector; the silicon-carbon negative electrode plate also includes: 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 comprising a composite of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer is formed by an in-situ reaction between an inorganic silver salt and excess lithium strips on the surface of the negative electrode active layer.

[0021] The present invention effectively improves the stability and electrical performance of the silicon-carbon negative electrode plate by forming an interface protection layer generated by an in-situ replacement reaction between an inorganic silver salt and a lithium strip on the negative electrode active layer. Specifically, by arranging an interface protection layer on the negative electrode active layer of the silicon-carbon negative electrode plate, that is, designing an interface protection layer between the negative electrode and the electrolyte, on the one hand, the excellent stability of the interface protection layer itself is utilized to avoid the interface side reactions caused by the direct contact between the two, and at the same time eliminate the high ion / electron transmission impedance caused by the interface gap. On the other hand, the lithium-silver alloy and the inorganic lithium salt component with high ionic conductivity contained in the interface protection layer promote the uniform and rapid transmission of lithium ions on the interface; wherein, the uniformly dispersed lithium-silver alloy can regulate the uniform distribution of lithium ion concentration on the interface, avoiding electrode rupture caused by local excessive reaction, and the inorganic lithium salt component with high ionic conductivity is beneficial to the rapid transmission of lithium ions, thereby avoiding the capacity decay and interface failure problems caused by lithium precipitation on the surface of the silicon-carbon negative electrode during high-rate charging. The above two reasons synergistically significantly improve the electrical performance of the obtained silicon-carbon negative electrode sheet, and ultimately make its corresponding all-solid-state lithium-ion battery exhibit high first-cycle coulombic efficiency.

[0022] Compared with the silicon-carbon negative electrode interface protection layer commonly used in the art, which contains polymers such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, and polymethyl methacrylate, the negative electrode interface protection layer provided by the present invention, which contains lithium-silver alloy and inorganic lithium salt, has higher lithium ion conductivity, effectively reduces the interface resistance between the negative electrode active layer and the solid electrolyte layer, and also has higher electrolyte corrosion resistance and chemical stability, thereby being able to more significantly improve the electrical performance of the silicon-carbon negative electrode sheet in which it is located, as well as the performance of the corresponding lithium-ion battery.

[0023] In particular, in the interface protection layer provided by the present invention and present on the silicon-carbon negative electrode plate, the inorganic lithium salt and the lithium-silver alloy are both generated by an in-situ replacement reaction between the inorganic silver salt and the lithium ribbon. Compared with directly physically 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 the system generated by this in-situ reaction can be dispersed more evenly and the physical contact between the two phases is closer, ultimately more effectively optimizing the solid-solid interface and improving the performance of the plate and the battery.

[0024] 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. In order to make the in-situ replacement reaction proceed more fully and obtain a silicon-carbon negative electrode with higher structural consistency and better electrical performance, the inventors have optimized the types of the above-mentioned inorganic silver salts and the corresponding types of inorganic lithium salts through a large number of experiments, and thus obtained a silicon-carbon negative electrode with better comprehensive performance. The lithium-ion battery in which it is located also shows a higher first-cycle coulomb efficiency. The thickness of the preferred interface protection layer is 10μm to 15μm.

[0025] The second aspect of the present invention provides a method for preparing the above-mentioned silicon-carbon negative electrode plate, which comprises: step S1, preparing a precursor dispersion containing an 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, laminating an excess lithium ribbon on the surface of the inorganic silver salt layer in a direction away from the negative electrode active layer to obtain a composite layer including a lithium ribbon and an inorganic silver salt layer; step S4, heating the composite layer so that the inorganic silver salt and the lithium ribbon react in situ on the surface of the negative electrode active layer to obtain a plate interface protection layer, and thus obtain a silicon-carbon negative electrode plate.

[0026] The present invention provides a method for preparing the aforementioned silicon-carbon negative electrode sheet. A precursor dispersion containing an inorganic silver salt is uniformly applied to the negative electrode active layer of the silicon-carbon negative electrode sheet. The inorganic silver salt coated on the surface of the silicon-carbon negative electrode reacts with lithium metal in situ by heating, forming an interfacial protective layer primarily composed of a lithium-silver alloy and an inorganic lithium salt.

[0027] Specifically, the heating process can accelerate the replacement reaction between the inorganic silver salt and the lithium strip, and improve the reaction rate and uniformity of the alloying reaction between the silver metal obtained by replacement and the lithium strip, thereby improving the process efficiency and the performance of the resulting silicon-carbon negative electrode sheet.

[0028] At the same time, in practical applications, the bonding between the lithium ribbon and the inorganic silver salt layer can be achieved by rolling, or by providing a certain pressure so that the two can be tightly bonded to ensure that the subsequent in-situ reaction occurs.

[0029] Furthermore, after a large number of experiments, the inventors first transformed the precursor dispersion containing the inorganic silver salt into a droplet form by ultrasonic atomization, and the size of the precursor dispersion in the droplet form was preferably 0.5 μm to 3.0 μm, and the spraying amount was preferably 1.0 mL / cm 2 ~1.5mL / cm 2 , thereby forming evenly dispersed reaction sites with an appropriate density, while simultaneously avoiding inadequate reaction due to excessive droplet size or spray volume, and poor results due to excessive droplet size or spray volume. Under these spraying conditions, more suitable in-situ reaction conditions were constructed. Subsequently, by laminating a lithium ribbon larger than the silicon-carbon negative electrode and heating it, the inorganic lithium salt and lithium-silver alloy were successfully generated, ultimately forming an interfacial protective layer that provided effective protection, improving the electrical performance of the silicon-carbon negative electrode.

[0030] The lithium ribbon is preferably 5μm to 10μm thick to facilitate a complete replacement reaction with the inorganic silver salt while effectively preventing excess lithium metal from remaining on the surface, which could lead to a passivation reaction and generate a large amount of byproducts, damaging the interface structure. After the replacement and alloying reactions are complete, the electrode surface should have no noticeable metallic luster.

[0031] In several typical embodiments, in order to obtain a more structurally stable interface protective layer, it is preferred that the precursor dispersion also includes a binder. At the same time, after a large number of experiments, the inventors preferably selected the weight ratio of inorganic silver salt to binder to be (9-19):1, so as to better balance the adhesion, stability and conductivity, and more effectively improve the electrical performance of the silicon-carbon negative electrode sheet and the lithium-ion battery in which it is located. In addition, for the sake of coordination and compatibility, the binder is preferably selected from one or more of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose, thereby obtaining a silicon-carbon negative electrode sheet with better electrical performance.

[0032] Furthermore, in order to improve the system dispersion uniformity of the precursor dispersion, and thereby improve the structural density and integrity of the inorganic silver salt layer obtained during spraying and formation, and ultimately obtain a silicon-carbon negative electrode sheet with a more continuous and stable structure and higher electrical performance, preferably 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 a precursor dispersion.

[0033] In order to better coordinate the droplet size and spraying amount during the spraying process, the inventors, after extensive experiments, preferably added 20% to 25% of the inorganic silver salt based on the total weight of the organic solution as 100%. This resulted in a better-structured inorganic silver salt layer, which in turn formed a more effective interface protection layer, and the resulting silicon-carbon negative electrode sheet had higher electrical performance. In several typical embodiments, the organic solvent is preferably selected from one or more of N-methylpyrrolidone, acetonitrile, and N,N-dimethylformamide, in order to improve the uniform dispersion of the inorganic silver salt and the binder, improve the uniformity and density of the resulting interface protection layer, and improve the electrical performance of the silicon-carbon negative electrode sheet in which it is located.

[0034] In several typical embodiments, in order to form a more structurally stable inorganic silver salt layer, both step S1 and step S2 are preferably performed in a dry room environment. The inventors further preferably select a dry room environment with 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, inhibiting the introduction of impurities therein, enhancing the intrinsic protective effect of the final interface protective layer, and optimizing the bonding between the interface protective layer and the negative electrode active layer in the silicon-carbon negative electrode sheet, ultimately obtaining a silicon-carbon negative electrode sheet with superior electrical performance.

[0035] Regarding the in situ substitution reaction between inorganic silver salt and lithium ribbon, in order to effectively promote the in situ substitution reaction while inhibiting the material damage that may be caused during the reaction process, the inventors have optimized the heating treatment temperature in step S4 to 50°C~80°C and the time to 0.5h~2.0h after a large number of experiments. Under these conditions, a negative electrode interface protection layer with a more stable structure and better performance was obtained, and the silicon-carbon negative electrode sheet and lithium-ion battery in which it is located also exhibited higher electrical performance accordingly.

[0036] In order to better promote the smooth progress of the in-situ exchange reaction, in several more typical embodiments, steps S3 and S4 are both carried out in a glove box with an oxygen content of less than 1ppm and a water content of less than 1ppm. At the same time, because the water and oxygen contents in the glove box change in real time, they can only present a range of values ​​rather than a fixed value throughout the reaction process. This ultra-low oxygen and low water environment, which the inventors have optimized through extensive experiments, can greatly reduce the occurrence of side reactions during the in-situ reaction, thereby further improving the purity and stability of the resulting interface protective layer, thereby making the corresponding silicon-carbon negative electrode sheet and lithium-ion battery performance better, especially showing a higher first efficiency.

[0037] A third aspect of the present invention provides an all-solid-state lithium-ion battery comprising a solid electrolyte layer.

[0038] The all-solid-state lithium-ion battery is a full cell, comprising a positive electrode sheet, a negative electrode sheet, and a solid electrolyte layer disposed between the positive and negative electrode sheets; the positive electrode sheet comprises a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, wherein the positive active layer comprises a nickel-cobalt-manganese ternary layered oxide; the negative electrode sheet is the aforementioned silicon-carbon negative electrode sheet, or a silicon-carbon negative electrode sheet prepared by the aforementioned method for preparing a silicon-carbon negative electrode sheet. 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 and counter electrodes; the counter electrode is a lithium-indium electrode; and the working electrode is the aforementioned silicon-carbon negative electrode sheet, or a silicon-carbon negative electrode sheet prepared by the aforementioned method for preparing a silicon-carbon negative electrode sheet.

[0039] Because the silicon-carbon negative electrode provided by the present invention contains an interface protection layer with excellent performance, it can improve compatibility and avoid direct contact between the negative electrode active material and the solid electrolyte during charging and discharging, thereby reducing the occurrence of side reactions. At the same time, it also provides an additional lithium source for the lithium-ion battery in which it is located. Therefore, the all-solid-state lithium-ion full battery and half-cell containing the silicon-carbon negative electrode sheet both exhibit excellent electrical performance, especially the first-cycle coulomb efficiency.

[0040] Specifically, the solid electrolyte layer has a thickness of 100 μm to 200 μm, which provides an ion transmission channel and prevents short circuit between the positive and negative electrodes.

[0041] In several preferred embodiments, the solid electrolyte in the solid electrolyte layer includes but is not limited to Li7P3S 11 、Li 10 GeP2S 12 On this basis, Li6PS5Cl is more preferred because the inventors have found through extensive experiments that this sulfide solid electrolyte can better cooperate with the above-mentioned interface protection layer, thereby obtaining an all-solid-state lithium-ion battery with higher initial efficiency.

[0042] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0043] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0044] Example 1

[0045] A method for preparing a silicon-carbon negative electrode sheet:

[0046] In this example, a silicon-carbon negative electrode sheet prepared by wet coating was used as the original silicon-carbon negative electrode sheet, wherein the mass ratio of the silicon-carbon active material, the sulfide electrolyte LPS5Cl, and the polyacrylic acid binder was 16:4:1. The precursor materials selected for preparing the interface protection layer included silver carbonate (Ag2CO3) as an inorganic silver salt, polyvinylidene fluoride (PVDF) as a binder, N-methylpyrrolidone (NMP) as an organic solvent, and an ultra-thin lithium ribbon with a thickness of 5μm. The specific implementation process is as follows:

[0047] S1. In a dry room environment at 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, 25 parts by mass of Ag2CO3 inorganic silver salt were added and stirred thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2CO3 inorganic silver salt to PvDF binder was 12.5:1, and the amount of Ag2CO3 inorganic silver salt added relative to the organic solution was 25 wt%).

[0048] S2: Also in a dry room environment with a temperature of 25°C and a dew point of -50°C, the precursor prepared in S1 was dispersed through an ultrasonic atomizer to form 0.5 μm droplets, which were then sprayed on the surface of the silicon-carbon negative electrode sheet. The amount of precursor solution sprayed per unit area of ​​the silicon-carbon negative electrode sheet was 1.5 mL / cm 2 The sprayed electrode was transferred to a vacuum oven at 60°C for 12 hours and dried to obtain a silicon-carbon electrode with an Ag2CO3 coating on the surface.

[0049] S3. In a glove box with an oxygen content of <1 ppm and a water content of <1 ppm, the electrode prepared in S2 is transferred to the glove box, and an ultra-thin lithium strip and a flexible non-woven fabric with a thickness of 5 μm are sequentially attached to the surface of the silicon-carbon electrode. The lithium strip and the Ag2CO3 coating on the silicon-carbon electrode are tightly attached by a roller press to obtain a composite electrode containing a composite layer;

[0050] S4. Similarly, in a glove box with an oxygen content of <1ppm and a water content of <1ppm, the composite electrode prepared in S3 was transferred to a heating table at 60°C for reaction for 0.5h, so that the elemental lithium in the lithium strip and the silver in Ag2CO3 underwent an in-situ substitution reaction. After the surface of the lithium strip lost its obvious metallic luster, the flexible non-woven fabric and the reacted lithium strip were removed to obtain a silicon-carbon electrode whose main components of the interface protective layer were lithium-silver alloy and lithium carbonate (Li2CO3). The thickness of the interface protective layer was 10μm.

[0051] Example 2

[0052] A method for preparing a silicon-carbon negative electrode sheet:

[0053] In this example, a silicon-carbon negative electrode sheet prepared by wet coating was used as the original silicon-carbon negative electrode sheet, wherein the mass ratio of the silicon-carbon active material, the sulfide electrolyte LPS5Cl, and the polyacrylic acid binder was 16:4:1. The precursor materials selected for preparing the interface protective layer included silver oxide (Ag2O) as an inorganic silver salt, polyvinylidene fluoride (PVDF) as a binder, N-methylpyrrolidone (NMP) as an organic solvent, and an ultra-thin lithium ribbon with a thickness of 5μm. The specific implementation process is as follows:

[0054] S1. In a dry room environment at a temperature of 20°C and a dew point of -60°C, 2 parts by mass of PvDF binder was added to 98 parts by mass of NMP organic solvent and stirred for 6 hours until the organic solution was clear and free of obvious particulate matter. Then, 20 parts by mass of Ag2O inorganic silver salt was added and stirred thoroughly to obtain a precursor dispersion (wherein the weight ratio of Ag2O inorganic silver salt to PvDF binder was 10:1, and the amount of Ag2O inorganic silver salt added relative to the organic solution was 20 wt%).

[0055] S2: Also in a dry room environment with a temperature of 20°C and a dew point of -60°C, the precursor prepared in S1 was dispersed through an ultrasonic atomizer to form 3.0 μm droplets, which were then sprayed on the surface of the silicon-carbon negative electrode sheet. The amount of precursor solution sprayed per unit area of ​​the silicon-carbon negative electrode sheet was 1.0 mL / cm 2 The sprayed electrode was transferred to a vacuum oven at 60°C for 12 hours and dried to obtain a silicon carbon electrode with an Ag2C coating on the surface.

[0056] S3. In a glove box with an oxygen content of <1 ppm and a water content of <1 ppm, the electrode prepared in S2 is transferred to the glove box, and an ultra-thin lithium strip and a flexible non-woven fabric with a thickness of 5 μm are sequentially attached to the surface of the silicon-carbon electrode. The lithium strip and the Ag2CO3 coating on the silicon-carbon electrode are tightly attached by a roller press to obtain a composite electrode containing a composite layer;

[0057] S4. Similarly, in a glove box with an oxygen content of <1ppm and a water content of <1ppm, the composite electrode prepared in S3 was transferred to a heating table at 60°C for reaction for 0.5h, so that the elemental lithium in the lithium strip and the silver in Ag2O underwent an in-situ substitution reaction. After the surface of the lithium strip lost its obvious metallic luster, the flexible non-woven fabric was removed to obtain a silicon-carbon electrode whose main components of the interface protective layer were lithium-silver alloy and lithium oxide (Li2O). The thickness of the interface protective layer was 15μm.

[0058] Example 3

[0059] A method for preparing a silicon-carbon negative electrode sheet:

[0060] This example differs from Example 1 only in the precursor materials used to prepare the interface protective layer: silver phosphate (Ag3PO4), polyacrylic acid (PAA), and acetonitrile (ACN) as the binder. The experimental conditions and parameters remain the same.

[0061] Example 4

[0062] A method for preparing a silicon-carbon negative electrode sheet:

[0063] This example differs from Example 1 only in the precursor materials used to prepare the interface protective layer: silver chloride (AgCl), carboxymethyl cellulose (CMC), N,N-dimethylformamide, and a 10 μm-thick ultrathin lithium ribbon. The experimental conditions and parameters remain the same.

[0064] Example 5

[0065] A method for preparing a silicon-carbon negative electrode sheet:

[0066] The difference between this embodiment and embodiment 1 is 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, and stirred for 6 hours until the organic solution is clear and free of obvious particulate matter, and 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%).

[0067] Example 6

[0068] A method for preparing a silicon-carbon negative electrode sheet:

[0069] The difference between this embodiment and embodiment 1 is 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, and stirred for 6 hours until the organic solution is clear and free of obvious particulate matter, and 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%).

[0070] Example 7

[0071] A method for preparing a silicon-carbon negative electrode sheet:

[0072] The only difference between this embodiment and embodiment 1 is that in step S2, the precursor dispersion is not subjected to ultrasonic atomization treatment, but is directly sprayed at 1.5 mL / cm 2 The coating amount was applied to the surface of the silicon-carbon negative electrode sheet, and then transferred to a vacuum oven at 60°C for 12 hours. After drying, a silicon-carbon electrode sheet with a surface coated with Ag2CO3 was obtained.

[0073] Comparative Example 1

[0074] The original silicon-carbon electrode piece used in Example 1 without any treatment was directly used as the silicon-carbon negative electrode piece sample.

[0075] Comparative Example 2

[0076] A method for preparing a silicon-carbon negative electrode sheet:

[0077] 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 the elemental lithium in the lithium strip and Ag2CO3 is low, and the interface protection layer of the resulting silicon-carbon electrode correspondingly contains less inorganic lithium salt and lithium-silver alloy components and a large amount of precursor reactant components.

[0078] Comparative Example 3

[0079] A method for preparing a silicon-carbon negative electrode sheet:

[0080] In a dry room environment with a temperature of 25°C and a dew point of -50°C, metallic silver particles are spread on the surface of a lithium strip for alloying reaction. After 2 hours of reaction, a lithium-silver alloy strip is obtained.

[0081] 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, and 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 were added and stirred thoroughly to obtain a mixed slurry; the mixed slurry was sprayed onto the silicon-carbon electrode in the manner of Example 1, and 12.5 parts by mass of lithium-silver alloy strips were spread on the surface of the sprayed electrode, and then transferred to a vacuum oven at 60°C for 12 hours. After drying, the silicon-carbon negative electrode sample was directly obtained.

[0082] That is, this comparative example uses Li2CO3 inorganic lithium salt and lithium silver alloy as components of the interface protection layer, and directly forms the interface protection layer on the surface of the original silicon-carbon negative electrode without undergoing an in-situ replacement reaction.

[0083] Test Method

[0084] 1. Preparation of half-cell samples:

[0085] Taking Example 1 as an example, the prepared silicon-carbon negative electrode sheet was used as the working electrode, Li6PS5Cl was used as the solid electrolyte, and a lithium-indium alloy sheet with a thickness of 100 μm was used as the counter electrode to prepare a half-cell sample. The specific steps are as follows:

[0086] (1) In a glove box, 0.1 g of Li6PS5Cl powder was slowly poured into and flattened in a Φ10 mm mold sleeve. The gasket and upper pressure head were assembled, and the mold was placed on the tablet press workbench. A pressure of 2 t was applied at a uniform speed. After holding the pressure for 3 min, the tablet in the mold was ejected using a mold ejector sleeve to obtain a solid electrolyte membrane with a thickness of 200 μm.

[0087] (2) In a glove box, the silicon-carbon negative electrode sheet and lithium-indium alloy prepared in Example 1 were cut into Φ10 mm diameter discs, and the cut silicon-carbon negative electrode sheet, solid electrolyte membrane, and cut lithium-indium disc were slowly placed and flattened in the mold sleeve in sequence, and the gasket and upper pressure head were assembled;

[0088] (3) Use a torque wrench to apply pressure to the assembled test device until the test pressure of the mold battery reaches 80 MPa, obtain the corresponding half-cell sample of Example 1, and perform subsequent electrochemical tests.

[0089] The preparation of the corresponding half-cell samples of the remaining embodiments and comparative examples was carried out in the same manner as above.

[0090] 2. Preparation of full battery samples:

[0091] Taking Example 1 as an example, the silicon-carbon negative electrode sheet prepared therefrom is used as the working electrode, Li6PS5Cl is used as the solid electrolyte, and the nickel-cobalt-manganese ternary layered oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode active material to prepare the full battery sample. The specific steps are as follows:

[0092] (1) A solid electrolyte membrane with a thickness of 200 μm was obtained according to the preparation method of the half-cell sample described above;

[0093] (2) Nickel-cobalt-manganese ternary layered oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 was used as the active material for wet coating to obtain the positive electrode sheet, wherein the mass ratio of the active material, LPS5Cl sulfide electrolyte, carbon nanotube conductive agent and PvDF binder was 20:7:2:1;

[0094] (3) In a glove box, the silicon-carbon negative electrode sheet prepared in Example 1 and the positive electrode sheet obtained in (2) were cut into circular pieces with a diameter of 10 mm, and the cut silicon-carbon negative electrode sheet, solid electrolyte membrane, and cut positive electrode sheet were slowly placed and flattened in the mold sleeve in sequence, and the gasket and upper pressure head were assembled;

[0095] (4) Use a torque wrench to apply pressure to the assembled test device until the test pressure of the mold battery reaches 80 MPa, obtain the corresponding full battery sample of Example 1, and perform subsequent electrochemical tests.

[0096] The preparation of the corresponding full battery samples of the remaining embodiments and comparative examples was carried out in the same manner as above.

[0097] 3. First-cycle coulombic efficiency of the battery: The silicon-carbon negative electrode sheets prepared in Examples 1-7 and Comparative Examples 1-3 were assembled into half-cells and full-cells according to the above method, and then subjected to the first cycle of charge-discharge at a rate of 0.1C to obtain the first-cycle coulombic efficiency of the half-cell samples and full-cell samples corresponding to each embodiment and comparative example. See Table 1 for details.

[0098] Table 1

[0099]

[0100]

[0101] From the above description, it can be seen that the above-mentioned embodiment of the present invention realizes the preparation of a silicon-carbon negative electrode plate containing an interface protection layer. The obtained silicon-carbon negative electrode plate has excellent performance and higher interface stability with the solid electrolyte layer. The all-solid-state lithium-ion half-cell and full battery in which it is located both show excellent first-cycle coulombic efficiency.

[0102] Specifically, Example 3 is a silicon-carbon negative electrode sheet whose interface components are inorganic lithium salt Li3PO4 and lithium-silver alloy. It shows the highest first-cycle coulombic efficiency of half-cell and full-cell, indicating that compared with inorganic lithium salts such as Li2CO3, Li2O and LiCl, Li3PO4 performs best in this interface system.

[0103] By comparing Examples 1, 5, and 6, it is not difficult to analyze that by regulating the optimal ratio of inorganic lithium salt in the precursor solution (such as Example 1), a silicon-carbon negative electrode sheet with optimal interface protection layer performance can be obtained, and the assembled half-cell and full cell both show higher first-cycle coulombic efficiency.

[0104] Combining Comparative Examples 1-3, it is easy to analyze that the failure to adopt a heating step to promote the complete in-situ reaction between the lithium ribbon and the inorganic silver salt, as well as the direct coating of the inorganic lithium salt and lithium-silver alloy without the in-situ reaction method to prepare the interface protective layer, failed to achieve excellent first-cycle coulombic efficiency performance. The main reasons for this are incomplete reaction, resulting in a small amount of expected products (inorganic lithium salt and lithium-silver alloy), a large amount of residual precursors leading to complex interface components, affecting the interfacial ion transmission efficiency; and the direct coating method resulting in uneven dispersion of the two and poor interfacial contact, which seriously affects the interfacial ion transmission efficiency.

[0105] It should be noted that the terms "first," "second," and the like 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 precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

[0106] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A silicon-carbon negative electrode plate, comprising: negative electrode current collector; A negative electrode active layer is provided on at least one side of the negative electrode current collector; Characterized in that, the silicon-carbon negative electrode plate further comprises: An interface protection layer is provided in contact with the surface of the negative electrode active layer away from the negative electrode current collector, wherein the material of the interface protection layer includes a composite of an inorganic lithium salt and a lithium-silver alloy, and the interface protection layer is formed by an inorganic silver salt and excess lithium strips through an in-situ reaction 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 protection layer is 10 μm to 15 μm.

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 comprises: Step S1, preparing a precursor dispersion containing an 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, laminating an excess lithium ribbon onto the surface of the inorganic silver salt layer in a direction away from the negative electrode active layer to obtain a composite layer including the lithium ribbon and the inorganic silver salt layer; Step S4, heating the composite layer to allow the inorganic silver salt and the lithium ribbon to react in situ on the surface of the negative electrode active layer to obtain the electrode interface protection layer, and then obtain 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 the form of droplets of 0.5 μm to 3.0 μm, with a spraying volume of 1.0 mL / cm 2 ~1.5 mL / cm 2 .

6. The preparation method according to claim 5, characterized in that The thickness of the lithium strip is 5 μm to 10 μm.

7. The preparation method according to claim 4, 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.

8. The preparation method according to claim 7, characterized in that The binder is selected from one or more of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose.

9. The preparation method according to claim 7, 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.

10. The preparation method according to claim 9, characterized in that Based on the total weight of the organic solution being 100%, the added amount of the inorganic silver salt is 20% to 25%.

11. The preparation method according to claim 9, characterized in that The organic solvent is selected from one or more of N-methylpyrrolidone, acetonitrile and N,N-dimethylformamide.

12. The preparation method according to any one of claims 4 to 11, characterized in that Both step S1 and step S2 are performed in a dry room environment.

13. The preparation method according to claim 12, characterized in that The temperature of the dry room environment is 20°C~25°C and the dew point is -60°C~-40°C.

14. The preparation method according to any one of claims 4 to 11, characterized in that The temperature of the heating treatment in step S4 is 50° C. to 80° C., and the time is 0.5 h to 2.0 h.

15. The preparation method according to claim 14, characterized in that Both step S3 and step S4 are performed in an environment where the oxygen content is less than 1 ppm and the water content is less than 1 ppm.

16. 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 battery, comprising a positive electrode sheet, a negative electrode sheet, and the solid electrolyte layer disposed between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode collector and a positive electrode active layer disposed on at least one side surface of the positive electrode collector, and the positive electrode active layer comprises a nickel-cobalt-manganese ternary layered oxide; the negative electrode sheet 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 for preparing a silicon-carbon negative electrode sheet according to any one of claims 4 to 15; or, The all-solid-state lithium-ion battery is a half-cell, which includes a working electrode, a counter electrode, and the solid electrolyte layer arranged between the working electrode and the counter electrode; the counter electrode is a lithium-indium electrode; the working electrode is the silicon-carbon negative electrode sheet according to any one of claims 1 to 3, or a silicon-carbon negative electrode sheet prepared by the preparation method of the silicon-carbon negative electrode sheet according to any one of claims 4 to 15.

17. The all-solid-state lithium-ion battery according to claim 16, characterized in that: 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.

18. The all-solid-state lithium-ion battery according to claim 16, wherein: The solid electrolyte in the solid electrolyte layer is Li6PS5Cl.

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