All-solid-state battery

Abstract

The invention relates to the technical field of batteries, in particular to an all-solid-state battery which comprises a positive plate, a negative plate and a solid electrolyte layer positioned between the positive plate and the negative plate, in the thickness direction of the solid electrolyte layer, the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer which are stacked, the first solid electrolyte layer is close to the positive plate, and the second solid electrolyte layer is close to the negative plate; the first solid electrolyte layer comprises a first inorganic sulfide solid electrolyte; the second solid electrolyte layer comprises a second inorganic sulfide solid electrolyte and an organic binder, and the organic binder comprises polyurethane and lithium alginate. The all-solid-state battery provided by the invention can solve the problems of first-effect degradation of the positive electrode and cycle failure caused by expansion of the negative electrode, and improves the first-effect and cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to an all-solid-state battery. Background Technology

[0002] All-solid-state batteries are a core direction for next-generation energy storage due to their high intrinsic safety and high energy density potential. Among them, sulfide solid electrolytes have high room-temperature ionic conductivity (up to 10). -2 With its advantages of being on the order of S / cm and having good mechanical ductility, sulfide-based all-solid-state batteries have become the most promising technology route for industrialization. However, the commercialization of sulfide-based all-solid-state batteries still faces many problems: First, the first-efficiency degradation of the cathode: the sulfur content in the sulfide electrolyte... 2- It has strong reducing properties and is easily reacted with high oxidation state ions (such as Ni) in the positive electrode. 3+ / Ni 4+ Co 3+ Oxidation can lead to side reactions that generate high-resistivity products, causing irreversible consumption of lithium ions during the first cycle and resulting in low initial battery efficiency. Secondly, negative electrode expansion can cause cycle failure: when sulfide solid electrolytes are used with lithium metal, silicon-based, or other negative electrodes, the negative electrode undergoes drastic volume changes due to its own material properties (the expansion rate of silicon-based electrodes reaches 300%, and the volume of lithium metal electrodes is easily out of control). This not only disrupts the tight contact between the active material and the current collector but also compresses the brittle sulfide solid electrolyte layer, causing cracks and leading to solid-solid interface failure, which severely shortens the battery cycle life. Traditional porous current collector solutions have limited mitigation effects. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an all-solid-state battery that can solve the problems of positive electrode first-efficiency degradation and negative electrode expansion leading to cycle failure, thereby improving the battery's first-efficiency and cycle life.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides an all-solid-state battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer stacked thereon, the first solid electrolyte layer being close to the positive electrode and the second solid electrolyte layer being close to the negative electrode; The first solid electrolyte layer includes a first inorganic sulfide solid electrolyte, which includes Li x PS y M m N n M is selected from Cl or Br, N is selected from Cl and Br, which are different halogen elements from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0; The second solid electrolyte layer includes a second inorganic sulfide solid electrolyte and an organic binder. The second inorganic sulfide solid electrolyte includes Li6PS5Cl, and the organic binder includes polyurethane and lithium alginate.

[0005] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The all-solid-state battery of this invention utilizes a first solid-state electrolyte layer on the positive electrode side to improve initial efficiency and a second solid-state electrolyte layer on the negative electrode side to create a resilient double-layer solid-state electrolyte structure. This structure addresses the core technical bottlenecks of sulfide all-solid-state batteries: the degradation of initial efficiency at the positive electrode and the expansion of the negative electrode, thereby improving the battery's initial efficiency and cycle life. The specific mechanism of action is as follows: Firstly, from the perspective of the first solid electrolyte layer on the positive electrode side, its core advantage lies in optimizing interface compatibility and lithium-ion transport efficiency, thereby improving the battery's initial efficiency. The first solid electrolyte layer includes a first inorganic sulfide solid electrolyte, Li. x PS y M m N n The first inorganic sulfide solid electrolyte can be obtained by halogen site doping of Li6PS5Cl with LiBr. Li6PS5Cl has a well-defined crystal structure—part of the sulfur (S) acts as "backbone sulfur" to form [PS5] trigonal bipyramidal basic units with P, while the remaining S acts as "bridging sulfur" connecting these trigonal bipyramidal basic units; Li + Distributed in the lattice channels to maintain electroneutrality; Cl - As a free halide anion, it occupies a specific interstitial site (denoted as the X site) in the crystal lattice. This regular occupancy state leads to Li + With surrounding S² - Cl - The formation of a fixed coordination structure and a highly homogeneous coordination environment leads to Li + When migrating within lattice channels, the coordination energy barrier that needs to be overcome is relatively high; at the same time, the regular lattice is prone to forming local crystalline regions, hindering Li... + The rapid spread of [the virus / organization].

[0006] When LiBr is used for doping, the X sites located in the interstitial lattice are no longer affected by Cl. - Instead of single occupation, it forms Cl - With Br - The mixed occupation disrupts the original structural regularity, diversifying the coordination environment. For a large number of lattice points, some X sites are Cl. - , part of which is Br -The occupancy ratios m and n are determined by the atomic weight of Br atoms in the doping. Meanwhile, this localized structural modulation does not disrupt the overall structural integrity of the framework; the oxidation state of S remains -2; no redox reactions occur during doping; the bond length and bond energy of the PS covalent bond formed between S and P remain unchanged; and the trigonal bipyramidal geometry of [PS5] is not distorted.

[0007] The above doping mechanism synergistically improves the battery's first-cycle efficiency from two aspects: ion transport and interface stability. On the one hand, it can regulate the ion coordination environment of the electrolyte, reduce the lithium-ion migration barrier, promote its rapid transport at the electrolyte-cathode interface, and ensure efficient lithium-ion insertion into the positive electrode active site during the first charge. On the other hand, the doped Li6PS5Cl... 0.5 Br 0.5 For example, by replacing half of the Cl atom at position X with a Br atom, [PS5Cl] is formed. 0.5 Br 0.5 The triangular bipyramidal framework balances the repulsive forces between ligands, resulting in a regular framework structure with optimal stability. This effectively reduces the lithium-ion migration barrier, significantly suppresses irreversible side reactions with the cathode, and ultimately significantly improves the battery's first-stage efficiency. Secondly, from the perspective of the second solid electrolyte layer on the negative electrode side, its core advantages lie in buffering expansion stress and ensuring ion transport. The second solid electrolyte layer includes a second inorganic sulfide solid electrolyte, Li6PS5Cl, and an organic binder comprising polyurethane and lithium alginate, achieving a precise balance between mechanical toughness and ionic conductivity. Polyurethane, as an elastomer (elongation at break >300%), can absorb the volume expansion stress during negative electrode cycling through molecular chain stretching and slippage, preventing the solid electrolyte layer from cracking, solving stress-induced solid-solid interface contact failure, and significantly improving the battery's cycle life. Furthermore, the polar functional groups of lithium alginate (-OH, -COO) - It can form hydrogen bonds, ionic bonds, or coordination bonds with Li6PS5Cl particles to prevent organic-inorganic phase stripping. At the same time, its lithiophilic groups can provide low-barrier lithium-ion transport paths. Combined with polyurethane that provides mechanical stability, it ensures ionic conductivity. This achieves the synergy of mechanical stability and ionic conductivity in the second solid electrolyte layer. The combined effect of the first solid electrolyte layer further reduces lithium-ion loss and improves the battery's initial efficiency.

[0008] In summary, the two-layer solid electrolyte structure synergistically solves the core problems of positive electrode first-efficiency degradation and negative electrode expansion failure in sulfide all-solid-state batteries: the first solid electrolyte layer ensures excellent first-efficiency by optimizing interface compatibility and reducing irreversible lithium-ion consumption, while the second solid electrolyte layer avoids damage to the electrolyte caused by negative electrode expansion by buffering volume changes. Together, they maintain the structural integrity of the solid electrolyte layer and the smoothness of ion transport channels, ultimately enabling all-solid-state batteries to have excellent electrochemical performance with high first-efficiency and long cycle stability.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0010] Figure 1 The diagram shown is a structural schematic of an all-solid-state battery provided in an embodiment of the present invention.

[0011] Explanation of reference numerals in the attached figures: Positive current collector 1, first positive electrode layer 2, second positive electrode layer 3, third positive electrode layer 4, first solid electrolyte layer 5, second solid electrolyte layer 6, first negative electrode layer 7, second negative electrode layer 8, negative current collector 9. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0013] The present invention provides an all-solid-state battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer stacked thereon, the first solid electrolyte layer being close to the positive electrode and the second solid electrolyte layer being close to the negative electrode.

[0014] The first solid electrolyte layer includes a first inorganic sulfide solid electrolyte, which includes Li x PS y M m N n M is selected from Cl or Br, N is selected from Cl and Br and is different from M. 0.5≤(m+n)≤1.5 (e.g. 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5), 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0.

[0015] The second solid electrolyte layer includes a second inorganic sulfide solid electrolyte and an organic binder. The second inorganic sulfide solid electrolyte includes Li6PS5Cl, and the organic binder includes polyurethane and lithium alginate.

[0016] This invention solves the core technical bottleneck of sulfide all-solid-state batteries by designing a first solid-state electrolyte layer on the positive electrode side to improve initial efficiency and a second solid-state electrolyte layer on the negative electrode side to provide toughness. Firstly, from the perspective of the first solid electrolyte layer on the positive electrode side, it includes the first inorganic sulfide solid electrolyte Li. x PS y M m N n The first inorganic sulfide solid electrolyte can be obtained by halogen site doping of Li6PS5Cl with LiBr. Li6PS5Cl has a well-defined crystal structure—part of the sulfur (S) acts as "backbone sulfur" to form [PS5] trigonal bipyramidal basic units with P, while the remaining S acts as "bridging sulfur" connecting these trigonal bipyramidal basic units; Li + Distributed in the lattice channels to maintain electroneutrality; Cl - As a free halide anion, it occupies a specific interstitial site (denoted as the X site) in the crystal lattice. This regular occupancy state leads to Li + With surrounding S² - Cl - The formation of a fixed coordination structure and a highly homogeneous coordination environment leads to Li + When migrating within lattice channels, the coordination energy barrier that needs to be overcome is relatively high; at the same time, the regular lattice is prone to forming local crystalline regions, hindering Li... + The rapid spread of [the virus / organization].

[0017] When LiBr is used for doping, the X sites located in the interstitial lattice are no longer affected by Cl. - Instead of single occupation, it forms Cl - With Br - The mixed occupation breaks the local lattice regularity formed by single occupation, diversifying the coordination environment. Among these, for a large number of lattice points, some X sites are Cl. - , part of which is Br - The occupancy ratios m and n are determined by the atomic weight of Br atoms in the doping. Meanwhile, this localized structural modulation does not disrupt the overall structural integrity of the framework; the oxidation state of S remains -2; no redox reactions occur during doping; the bond length and bond energy of the PS covalent bond formed between S and P remain unchanged; and the trigonal bipyramidal geometry of [PS5] is not distorted.

[0018] Based on the above, when Li x PS y M m N n(M is selected from Cl or Br, N is selected from Cl and Br, different from M; 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0) When (m+n)<0.5, it means that the doping amount of Br to Cl and the total halogen occupancy are both insufficient—the X site cannot form an effective Cl. - With Br - Mixed occupation, with some sites still retaining the original single Cl. - The lack of halogen occupancy at certain sites, and even at other sites, results in insufficient disruption of lattice regularity and a limited reduction in the lithium-ion migration barrier. + Low migration efficiency in lattice channels is detrimental to improving the initial efficiency of the battery. When (m+n)>1.5, it means that the doping amount of Br to Cl or the total halogen occupancy is excessive—excessive halogen cannot be fully integrated into the X site, and some is partially free or embedded in the [PS5] framework, causing distortion of the triangular bipyramidal geometry and destroying the integrity of the framework structure. This not only increases the resistance to lithium-ion migration but also triggers irreversible side reactions between halogen and the cathode, exacerbating lithium-ion loss and also affecting the initial efficiency of the battery. Therefore, limiting 0.5≤(m+n)≤1.5 ensures that the lattice regularity is broken through the appropriate halogen mixing and occupancy to reduce the migration barrier, while avoiding the interfacial side reactions and framework destruction caused by excessive or insufficient doping, ultimately ensuring the improvement of the initial efficiency of the battery.

[0019] The above doping mechanism synergistically improves the battery's first-cycle efficiency from two aspects: ion transport and interface stability. On the one hand, it can regulate the ion coordination environment of the electrolyte, reduce the lithium-ion migration barrier, promote its rapid transport at the electrolyte-cathode interface, and ensure efficient lithium-ion insertion into the positive electrode active site during the first charge. On the other hand, the doped Li6PS5Cl... 0.5 Br 0.5 For example, in this case, the mixed halogen doping amounts satisfy m=0.5 and n=0.5 (i.e., m+n=1.0). By replacing half of the Cl atoms at position X with Br atoms, [PS5Cl] is formed. 0.5 Br 0.5 The triangular bipyramidal framework balances the repulsive forces between ligands, resulting in a regular framework structure with optimal stability. This effectively reduces the lithium-ion migration barrier, avoids the generation of free halogens, significantly suppresses irreversible side reactions with the cathode, and ultimately significantly improves the battery's first-stage efficiency.

[0020] Secondly, regarding the second solid electrolyte layer on the negative electrode side, its core formulation uses Li6PS5Cl combined with an organic binder, achieving a precise balance between mechanical toughness and ionic conductivity. In terms of mechanical performance, the polyurethane in the organic binder, as an elastomer polymer with an elongation at break >300%, possesses excellent tensile, torsional, and slip properties in its molecular chain segments. It can directly absorb the drastic volume change stress during negative electrode cycling. This layer can dissipate concentrated stress through molecular chain deformation, preventing the traditional pure inorganic sulfide solid electrolyte layer from cracking due to excessive rigidity. This fundamentally solves the contact interruption problem caused by stress failure at the solid-solid interface, improving the battery's cycle life. Regarding interfacial bonding and ion transport, the polar functional groups (-OH, -COO) on the lithium alginate molecular chain... - It can react with S on the surface of Li6PS5Cl particles. 2- Li + The formation of strong interactions (hydrogen bonds, ionic bonds, and coordination bonds) effectively inhibits the peeling of the organic phase (binder) and inorganic phase (electrolyte particles) under cyclic stress, ensuring the structural integrity of the solid electrolyte layer. At the same time, lithium alginate itself is an excellent lithium-ion conductor, and its lithiophilic groups can construct low-barrier lithium-ion transport pathways. While the polyurethane improves toughness, it also ensures ion transport efficiency, achieving a synergy between mechanical stability and ionic conductivity in the second solid electrolyte layer. Combined with the technical effects of the first solid electrolyte layer, this further reduces lithium-ion loss and jointly improves the battery's initial efficiency.

[0021] In summary, the first solid electrolyte layer ensures excellent first-time efficiency by optimizing interfacial compatibility and reducing irreversible lithium-ion consumption, while the second solid electrolyte layer avoids damage to the electrolyte caused by negative electrode expansion by buffering volume changes. Together, they maintain the structural integrity of the solid electrolyte layer and the smoothness of ion transport channels, ultimately enabling the all-solid-state battery to have excellent electrochemical performance with high first-time efficiency and long cycle stability.

[0022] In one specific embodiment, based on the mass of the second solid electrolyte layer, the mass percentage of the second inorganic sulfide solid electrolyte is 90% to 99% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%), and the mass percentage of the organic binder is 1% to 10% (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%); and / or, the mass ratio of the polyurethane to the lithium alginate is (0.5 to 1.8):1 (e.g., 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, or 1.8:1).

[0023] Furthermore, this invention also controls the mass ratio of the second inorganic sulfide solid electrolyte to the organic binder within a suitable range, and controls the mass ratio of polyurethane to lithium alginate in the organic binder within a suitable range. This is beneficial for balancing the ionic conductivity, mechanical toughness, and interfacial bonding stability of the electrolyte layer, and can avoid the recurrence of technical bottlenecks due to imbalances in a single performance: First, the use of a second inorganic sulfide solid electrolyte with a relatively high proportion of organic binder in the second solid electrolyte layer can ensure that the ionic conductivity of the electrolyte layer meets the ion transport requirements of the positive electrode, avoiding ion transport bottlenecks caused by insufficient inorganic electrolyte content, and stabilizing the first-efficiency improvement effect brought by the first solid electrolyte layer. If the proportion of the second inorganic sulfide solid electrolyte is too high, it will lead to a decrease in the mechanical toughness of the second solid electrolyte layer, and a small amount of binder will not be able to form a continuous elastic network, and will not be able to absorb the volume change stress during negative electrode cycling. If the proportion of organic binder is too high, it will reduce the rigidity of the film layer, and will not be able to support the electrode stacking pressure. The interfacial contact will easily fail during cycling, which is also not conducive to improving the battery cycle performance. Secondly, by controlling the polyurethane-lithium alginate ratio in the organic binder to be roughly equal, polyurethane can fully exert its stress buffering effect, while ensuring lithium alginate assists in ion transport, so that the two can achieve a better synergistic effect. If the polyurethane ratio is too high (lithium alginate is insufficient), although it can enhance toughness and absorb more negative electrode expansion stress, it will weaken the interface bonding and ion transport, affecting the battery's first efficiency. If the lithium alginate ratio is too high (polyurethane is insufficient), the mechanical buffering ability will fail, and a small amount of polyurethane will not be able to absorb negative electrode expansion stress through molecular chain stretching and sliding, affecting the battery's cycle life. Therefore, it is necessary to accurately control the mass ratio of each material in the second solid electrolyte layer to achieve performance synergy.

[0024] In this invention, the mass content of polyurethane, lithium alginate, and the second inorganic sulfide solid electrolyte Li6PS5Cl in the second solid electrolyte layer of the finished all-solid-state battery can be measured using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The mass ratios of the second inorganic sulfide solid electrolyte to the organic binder and the polyurethane to lithium alginate can then be calculated. FTIR is primarily used for qualitative identification and semi-quantitative analysis of characteristic functional groups in the organic binder and their interactions with the inorganic electrolyte. The characteristic peak of polyurethane (PU) is the NH stretching vibration, which appears at ~3300 cm⁻¹. -1 Nearby (broad peak), C=O stretching vibration (amide I band): appears at ~1700 cm⁻¹ -1 Nearby, CN stretching vibrations and NH bending vibrations (amide II band): appear at ~1530 cm⁻¹ -1 Nearby, COC stretching vibrations occur at ~1220-1000 cm. -1Region; Characteristic peaks of lithium alginate: OH stretching vibration: appears at ~3400 cm⁻¹ -1 Nearby (broad peak, possibly overlapping with the NH peak), asymmetric COO - Stretching vibration: occurs at ~1590cm -1 Nearby, symmetrical COO - Stretching vibration: occurs at ~1400cm -1 Nearby; characteristic peaks of Li6PS5Cl: stretching vibrations of the PS bond: typically appearing at ~570 cm⁻¹ -1 and ~400cm -1 In the mid-to-far infrared region; FTIR has low sensitivity to sulfide lattice vibrations, but can still observe their presence. XPS is mainly used for quantitative elemental analysis, accurately determining the atomic percentage of each element and thus calculating the exact mass content of each component. Characteristic elements are selected as follows: Li6PS5Cl provides S (sulfur) and P (phosphorus), which are unique characteristic elements of the inorganic phase in the second electrolyte layer (the organic phase does not contain S and P); Polyurethane (PU) provides N (nitrogen), as the urethane groups in polyurethane contain N, while lithium alginate and Li6PS5Cl do not contain N; therefore, N is a unique identifier element for polyurethane; Lithium alginate (Li-Alginate) provides Na (sodium) or a specific C (carbon) environment. Commercial sodium alginate raw materials usually contain a small amount of residual Na; even after ion exchange to lithium alginate, trace amounts of Na can still be detected as its identifier. If Na is absent, the -COO in the C 1s spectrum can be analyzed. - The calculation is performed using the ratio of a specific carbon peak (~288.5 eV) of a functional group to the total C content.

[0025] In one specific embodiment, the negative electrode sheet further includes a negative electrode current collector, and a first negative electrode layer and a second negative electrode layer are stacked between at least one surface of the negative electrode current collector and the second solid electrolyte layer, the first negative electrode layer being close to the second solid electrolyte layer and the second negative electrode layer being close to the negative electrode current collector; the first negative electrode layer includes a first negative electrode active material, the first negative electrode active material including a lithium-containing silicon-carbon material; and / or, the second negative electrode layer includes a second negative electrode active material, the second negative electrode active material including lithium metal.

[0026] In one specific embodiment, the thickness of the first negative electrode layer is 20μm to 50μm, for example, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 32μm, 34μm, 36μm, 38μm, 40μm, 42μm, 44μm, 46μm, 48μm or 50μm.

[0027] In one specific embodiment, the thickness of the second negative electrode layer is 20μm to 50μm, for example, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 32μm, 34μm, 36μm, 38μm, 40μm, 42μm, 44μm, 46μm, 48μm or 50μm.

[0028] In the selection of anode materials for all-solid-state batteries, silicon-carbon materials, which combine porous structure and a certain degree of elasticity, and lithium metal anode materials, which have excellent electrical conductivity, have attracted much attention. In existing technologies, the design of combining these two to form a bilayer anode structure has been extensively studied: the silicon-carbon material layer faces the solid electrolyte layer, achieving good interface compatibility; the lithium metal layer faces the anode current collector, providing a low-impedance electron pathway, thereby improving battery cycle stability to some extent. This technical approach is a readily accepted and conventional solution in the field. However, this bilayer anode combination has technical drawbacks: during the first charge and discharge cycle, the silicon-carbon material needs to consume additional lithium metal to complete its own lithium intercalation and SEI film formation, resulting in a significant increase in irreversible lithium loss and poor initial efficiency.

[0029] Based on this, this application further proposes, on the basis of existing solutions, that the negative electrode active material in the first negative electrode layer is a lithium-containing silicon-carbon material. This lithium-containing silicon-carbon material can be prepared from silicon-carbon material through an electrochemical pre-lithiation process, which can reduce the consumption of the lithium metal foil in the second negative electrode layer and help improve the first efficiency of the all-solid-state battery. Specifically, this is reflected in: During the initial stage of battery charging, the lithium-containing silicon-carbon material in the first negative electrode layer can serve as an "internal lithium source." Lithium ions will preferentially embed into the three-dimensional structure surface and bulk phase of this silicon-carbon material, undergoing Si+xLi synthesis. + +xe - →Li x The Si reaction results in Li being uniformly distributed on the surface and in the bulk phase of silicon-carbon materials. x The Si alloy phases are excellent lithium-loving sites, eliminating the need for lithium metal in the second anode layer to provide the initial lithium source. Furthermore, the porous structure of silicon-carbon materials prevents lithium ions from concentrating on a single point on the lithium metal surface, dispersing the local current density and providing numerous uniform nucleation sites for lithium deposition. The low surface energy of the lithium-loving sites on this "built-in lithium source" substrate means that the nucleation overpotential required for lithium ion deposition is much lower than that on a smooth current collector or lithium metal substrate. This significantly reduces the diffusion barrier on the lithium atom surface, guiding subsequent lithium metal to grow laterally and uniformly on the second anode layer to suppress lithium dendrite formation. On the one hand, this reduces excessive SEI film growth and ineffective lithium consumption caused by localized high lithium ion concentrations; on the other hand, it suppresses lithium dendrite formation caused by the "tip effect," preventing lithium metal from being encased by dendrites and unable to participate in reversible reactions. By reducing these two types of irreversible lithium losses, the battery's initial efficiency is ultimately further improved.

[0030] In this invention, the first negative electrode active material further includes a negative electrode conductive agent and a negative electrode binder.

[0031] In one specific embodiment, the negative electrode conductive agent includes at least one of conductive carbon black (Super P), furnace black, acetylene black, Ketjen black, carbon nanotubes, and vapor-grown carbon fiber (VGCF).

[0032] In one specific embodiment, the negative electrode binder includes at least one of polyurethane, acrylic-acrylonitrile copolymer, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0033] In one specific embodiment, the positive electrode sheet further includes a positive electrode current collector, and a first positive electrode layer, a second positive electrode layer and a third positive electrode layer are stacked between at least one side surface of the positive electrode current collector and the first solid electrolyte layer. The first positive electrode layer is close to the positive electrode current collector, the third positive electrode layer is close to the first solid electrolyte layer, and the second positive electrode layer is located between the first positive electrode layer and the third positive electrode layer.

[0034] In one specific embodiment, the first positive electrode layer includes a first positive electrode active material, the first positive electrode active material includes a third inorganic sulfide solid electrolyte, and based on the mass of the first positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the first positive electrode active material is 3% to 8%, for example, 3%, 4%, 5%, 6%, 7%, or 8%.

[0035] In one specific embodiment, the second positive electrode layer includes a second positive electrode active material, the second positive electrode active material includes a third inorganic sulfide solid electrolyte, and based on the mass of the second positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the second positive electrode active material is 8% to 13%, for example, 8%, 9%, 10%, 11%, 12%, or 13%.

[0036] In one specific embodiment, the third positive electrode layer includes a third positive electrode active material, the third positive electrode active material includes a third inorganic sulfide solid electrolyte, and based on the mass of the third positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the third positive electrode active material is 13% to 18%, for example, 13%, 14%, 15%, 16%, 17%, or 18%.

[0037] In one specific embodiment, the third inorganic sulfide solid electrolyte includes an LGPS-type solid electrolyte, a Li₂S-P₂S₅ system solid electrolyte, and a Li₂S-P₂S₅ system solid electrolyte. x PS y Mm N n At least one of the following, wherein M is selected from Cl or Br, N is selected from Cl and Br and is a halogen element different from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, m>0, n>0; the median particle size Dv50 of the third inorganic sulfide solid electrolyte is 0.3μm~5μm, for example, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0038] In one specific embodiment, the first positive electrode active material further includes a positive electrode active substance, and the thickness of the first positive electrode layer is 25μm to 60μm, for example, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm or 60μm; and / or, the second positive electrode active material further includes a positive electrode active substance, and the thickness of the second positive electrode layer is 30μm to 80μm, for example, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm or 80μm; and / or, the third positive electrode active material further includes a positive electrode active substance, and the thickness of the third positive electrode layer is 25μm to 60μm, for example, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm or 60μm.

[0039] In one specific embodiment, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, and lithium nickel oxide, and the median particle size Dv50 of the positive electrode active material is 1μm~25μm, for example, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, and 25μm.

[0040] In this invention, the first positive electrode active material, the second positive electrode active material and the third positive electrode active material further include a positive electrode conductive agent and a positive electrode binder.

[0041] This invention employs a dry process to prepare a three-layer positive electrode with different sulfide electrolyte contents. Specifically, the first positive electrode layer is close to the positive electrode current collector, the third positive electrode layer is close to the first solid electrolyte layer, and the second positive electrode layer is located between the first and third positive electrode layers. Based on the mass of the positive electrode active material corresponding to each positive electrode layer, the mass proportion of the third inorganic sulfide electrolyte in the third active material of the third positive electrode layer is greater than that in the second positive electrode layer, while the mass proportion of the third inorganic sulfide electrolyte in the second active material of the second positive electrode layer is greater than that in the first positive electrode layer. Correspondingly, based on the mass of the positive electrode active material corresponding to each positive electrode layer, the mass proportion of the positive active material and positive conductive agent in the third positive electrode layer is less than that in the second positive electrode layer, while the mass proportion of the positive active material and positive conductive agent in the second positive electrode layer is less than that in the first positive electrode layer.

[0042] This can be understood as follows: In the first cathode layer near the current collector, the inorganic sulfide solid electrolyte content is the lowest, while the conductive agent content is relatively the highest. The high conductive agent content can construct a well-developed electron network, ensuring that the electrons collected by the current collector are quickly dispersed throughout the electrode. The lower inorganic sulfide solid electrolyte content is suitable for the layer's low requirement for ion conductivity, while also highlighting its core role of high conductivity, giving the layer high electronic conductivity and low ion conductivity. In the intermediate second cathode layer, the inorganic sulfide solid electrolyte content increases while the conductive agent content relatively decreases, achieving a smooth transition between electronic and ion conductivity characteristics, avoiding abrupt changes in transport capacity, ensuring uniform distribution of the electrochemical reaction zone from the interface to the bulk phase, and reducing local stress concentration. In the third cathode layer near the solid electrolyte layer, the inorganic sulfide solid electrolyte content is the highest, while the conductive agent content is relatively the lowest. The high electrolyte content can construct an efficient ion transport channel, ensuring the lithium-ion transport efficiency at the cathode-electrolyte interface. Its lower electronic conductivity can be compensated by the sufficient electrons in the first cathode layer, avoiding interface reaction imbalance. The three-layer cathode is prepared by dry film preparation and then rolled composite, which precisely matches the transport law of ions and electrons in the cathode of all-solid-state battery, reduces the interface stress and failure risk caused by abrupt changes in the conductivity mechanism, optimizes the long-term stability of the interface between the cathode and the solid electrolyte layer, suppresses problems such as interface peeling and crack generation during cycling, and thus improves the battery cycle capacity retention rate and helps to improve the battery cycle life.

[0043] In one specific embodiment, the positive electrode conductive agent includes at least one of conductive carbon black (Super P), carbon nanotubes, conductive graphite, graphene, and vapor-grown carbon fiber (VGCF).

[0044] In one specific embodiment, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymers, acrylic polymers, polytetrafluoroethylene (PTFE), polyacrylonitrile, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0045] In one specific embodiment, based on the mass of the first positive electrode active material, the mass percentage of the positive electrode active substance in the first positive electrode active material is 85%~91%, the mass percentage of the positive electrode conductive agent is 4%~8%, and the mass percentage of the positive electrode binder is 1%~2%.

[0046] In one specific embodiment, based on the mass of the second positive electrode active material, the mass percentage of the positive electrode active substance in the second positive electrode active material is 81% to 87%, the mass percentage of the positive electrode conductive agent is 3% to 7%, and the mass percentage of the positive electrode binder is 1% to 2%.

[0047] In one specific embodiment, based on the mass of the third positive electrode active material, the mass percentage of the positive electrode active substance in the third positive electrode active material is 77% to 83%, the mass percentage of the positive electrode conductive agent is 2% to 6%, and the mass percentage of the positive electrode binder is 1% to 2%.

[0048] In one specific embodiment, the thickness of the first solid electrolyte layer is D1, 20μm≤D1≤35μm, for example, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm or 35μm.

[0049] In one specific embodiment, the thickness of the second solid electrolyte layer is D2, 10μm≤D2≤20μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0050] In one specific implementation, D1 and D2 satisfy the relationship: 1.2≤D1 / D2≤3, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.

[0051] Controlling the thicknesses of the first solid electrolyte layer (D1) and the second solid electrolyte layer (D2) to satisfy 1.2 ≤ D1 / D2 ≤ 3 further enables the synergistic effect of high initial efficiency and stress buffering, preventing imbalances in a single function from damaging battery stability. If D1 / D2 < 1.2, it means the first solid electrolyte layer is relatively too thin, resulting in insufficient interface regulation and lithium-ion transport optimization. This makes it difficult to fully suppress irreversible side reactions between the positive electrode and the electrolyte, easily generating a high-resistance interface layer, leading to irreversible lithium-ion consumption during the first cycle and affecting the battery's initial efficiency. If D1 / D2 > 3, it indicates the second solid electrolyte layer is relatively too thin, with insufficient stress buffering capacity. It cannot absorb the volume change stress during negative electrode cycling, easily causing electrolyte-negative electrode interface contact failure and interruption of ion transport channels, which is detrimental to improving battery cycle performance.

[0052] In one specific embodiment, the total thickness of the first negative electrode layer and the second negative electrode layer is D. 负 ,40μm≤D 负 ≤100μm; the total thickness of the first positive electrode layer, the second positive electrode layer, and the third positive electrode layer is D. 正 80μm≤D 正 ≤200μm.

[0053] In one specific embodiment, D1, D2, D 正 and D 负 The following relation is satisfied: 0.14≤(D1+D2) / (D 正 +D 负 )≤0.35, for example, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34 or 0.35.

[0054] In this invention, D1, D2, and D... 正 and D 负The thickness measurement method is scanning electron microscopy (SEM). This method is based on the general principles of the national standard GB / T 36401-2018 "Method for Measuring Transverse Dimensions by Scanning Electron Microscopy for Surface Chemical Analysis". Sample preparation: In a glove box filled with an inert atmosphere (e.g., argon, dew point < -40°C), a fresh, wrinkle-free cross-sectional sample is prepared from the positive and negative electrode sheets or solid electrolyte membrane using a sharp blade or punch. The cross-section should be as perpendicular as possible to the membrane surface. Image acquisition: The sample is transferred to the sample chamber of the scanning electron microscope (the transfer chamber can be protected with inert gas to avoid air contact). Under appropriate accelerating voltage and magnification, cross-sectional SEM images of the structure of each layer are acquired, allowing clear resolution. At least three representative images are acquired at different locations on each sample. Thickness measurement: Using image analysis software (e.g., ImageJ), the thickness is measured uniformly at at least five points along a direction perpendicular to the layer on each SEM image, and then the average thickness of the location represented by that image is calculated. Result Calculation: For D1 and D2, the final thickness value is the arithmetic mean of the average thickness values ​​of all valid measured images. For D... 正 The final thickness is the sum of the average thicknesses of the first, second, and third cathode layers. (D) 负 Similarly, we can obtain the following.

[0055] Furthermore, the solid electrolyte layer and the electrode satisfy 0.14 ≤ (D1 + D2) / (D 正 +D 负 )≤0.35, when (D1+D2) / (D 正 +D 负 When (D1+D2) / (D) < 0.14, it means the solid electrolyte layer is too thin or the electrode layer is too thick. 正 +D 负 When the solid electrolyte layer is greater than 0.35, it means that the solid electrolyte layer is too thick or the electrode layer is too thin. An excessively thin solid electrolyte layer or electrode layer indicates a decrease in mechanical strength, making it more susceptible to puncture or cracking when dealing with changes in the volume of the negative electrode during cycling, thus impairing the battery's cycle life. On the other hand, an excessively thick electrode layer or solid electrolyte layer means that lithium ions need to diffuse in the solid phase within longer and more tortuous electrode channels, increasing the transport impedance of ions inside the electrode and limiting the improvement in initial efficiency.

[0056] In summary, by further controlling the thickness relationship between the two solid electrolyte layers and the overall thickness relationship between the solid electrolyte layer and the positive and negative electrode layers, this invention achieves the optimal balance between the electrolyte and electrode ratios. This ensures that the first solid electrolyte layer improves the first-efficiency degradation problem of the positive electrode, while also ensuring that the second solid electrolyte layer effectively alleviates the volume change problem of the negative electrode. Ultimately, this achieves a synergistic improvement in the high first-efficiency and long-cycle performance of all-solid-state batteries.

[0057] In one specific implementation, such as Figure 1 As shown, the positive electrode includes a positive current collector 1 and a first positive electrode layer 2, a second positive electrode layer 3, and a third positive electrode layer 4 stacked on one side of the surface of the positive current collector 1; the first positive electrode layer 2 is close to the positive current collector 1, the third positive electrode layer 4 is close to the first solid electrolyte layer 5, and the second positive electrode layer 3 is located between the first positive electrode layer 2 and the third positive electrode layer 4; the first solid electrolyte layer 5 is located between the positive electrode and the second solid electrolyte layer 6, and the second solid electrolyte layer 6 is located between the negative electrode and the first solid electrolyte layer 5; the negative electrode includes a negative current collector 9 and a first negative electrode layer 7 and a second negative electrode layer 8 stacked on one side of the surface of the negative current collector 9; the first negative electrode layer 7 is close to the second solid electrolyte layer 6 and is located between the second negative electrode layer 8 and the second solid electrolyte layer 6; the second negative electrode layer 8 is close to the negative current collector 9 and is located between the negative current collector 9 and the first negative electrode layer 7.

[0058] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0059] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0060] Example 1 (1) Preparation of dry gradient cathode: 1. Raw material pretreatment and preparation: The positive electrode active material (LiNi with a Dv50 of 2μm) is prepared... 0.8 Co 0.1 Mn 0.1 O2) was vacuum dried at 120°C for 12 hours to remove residual moisture; the third inorganic sulfide solid electrolyte (Li6PS5Cl) was pretreated and sieved in a ball mill to control its Dv50=1μm; the conductive agent VGCF was vacuum dried at 150°C for 6 hours; the binder was PTFE powder obtained by emulsion polymerization.

[0061] 2. Separate mixing of the three electrode slurries (dry powder): Weigh the three dry powder mixtures separately. The first powder is the powder near the positive electrode current collector layer (first positive electrode layer), wherein the positive electrode active material: third inorganic sulfide solid electrolyte: VGCF:PTFE = 88%:5%:6%:1% (mass ratio); the second powder is the powder of the intermediate transition layer (second positive electrode layer), wherein the positive electrode active material: third inorganic sulfide solid electrolyte: VGCF:PTFE = 84%:10%:5%:1%; the third powder is the powder near the solid electrolyte layer side (third positive electrode layer), wherein the positive electrode active material: third inorganic sulfide solid electrolyte: VGCF:PTFE = 80%:15%:4%:1%. Each formulation of powder is separately loaded into a high-speed mixer (such as a three-dimensional mixer) and mixed for 6-12 hours under an inert atmosphere until it is uniformly mixed, thus obtaining three independent mixed cathode powders with different contents of the third inorganic sulfide solid electrolyte.

[0062] 3. Dry Film Formation and Fiberization: First, the mixed powder components are fed separately into an extruder. Under the combined action of a heating temperature of 60-80°C (below the melting point of PTFE) and shear force, the PTFE binder in the powder undergoes protofibrillation, interweaving to form a network structure, initially yielding three independent, self-supporting, loose electrode strips. Second, these three loose electrode strips are fed into a roller mill for multiple rolling processes. By precisely controlling the roller speed, pressure, and gap, the electrode strips are gradually rolled to the required thickness and density, ultimately forming a positive electrode film that combines density and a porous structure.

[0063] 4. Three-layer stacking and co-rolling. The three independently formed positive electrode films prepared above are precisely stacked in the order of "near-positive electrode current collector layer - intermediate layer - near-solid electrolyte layer"; the stacked three-layer positive electrode film is fed into a precision roller press for final rolling; under a suitable pressure of 400 MPa and 80℃, the three-layer interface is physically bonded into a whole under the action of PTFE fiber winding and mechanical interlocking, forming a multilayer structure with varying composition, and finally obtaining the positive electrode sheet; wherein, the thickness of the first positive electrode layer is 40μm, the thickness of the second positive electrode layer is 60μm, the thickness of the third positive electrode layer is 50μm, and the total thickness D of the first positive electrode layer, the second positive electrode layer and the third positive electrode layer is... 正 It is 150μm.

[0064] (2) Preparation of the double-layer solid electrolyte layer: 1. Synthesis and forming of the positive electrode side electrolyte membrane (first solid electrolyte layer): Li6PS5Cl was synthesized by mechanical ball milling. 0.5 Br 0.5The precursors, Li₂S, P₂S₅, LiCl, and LiBr powders, were precisely weighed in a molar ratio of 10:2:1:1. The precursors and grinding balls were placed together in the sealed grinding jar of a planetary ball mill and ball-milled at 500 rpm for 20-40 hours under an inert atmosphere. After ball milling, the product was heat-treated at an appropriate temperature (approximately 200-300°C) to crystallize, yielding a pure-phase, high-pressure resistant Li₆PS₅Cl. 0.5 Br 0.5 Powder. The synthesized electrolyte powder was used to form a thin film by solvent casting. The powder was mixed into a slurry using anhydrous p-xylene, which is inert to the electrolyte, and uniformly coated onto a substrate. After drying, it was peeled off to obtain a flexible electrolyte film.

[0065] 2. Preparation of the negative electrode side electrolyte membrane (second solid electrolyte layer): Polyurethane (PU) particles and lithium alginate (Li-Alginate) powder were weighed at a mass ratio of 1:1, mixed, and dissolved in anhydrous p-xylene solvent. The solid content of the system was 5%. This mixture was then thoroughly stirred until a homogeneous organic binder solution was formed. Li6PS5Cl electrolyte powder was mixed with the above organic binder solution at a mass ratio of 95%:5%, and stirred and degassed using a planetary vacuum mixer to form a homogeneous and stable electrolyte membrane slurry. The obtained slurry was coated onto the surface of a release film using a slot coating process. The release film coated with the slurry was then slowly dried at a low temperature (<80°C) to completely evaporate and remove the solvent, thus forming a flexible electrolyte membrane.

[0066] 3. Bilayer Composite. The high-voltage resistant electrolyte membrane on the positive electrode side and the tough electrolyte membrane on the negative electrode side prepared above are composited by hot pressing. Hot pressing is carried out at a temperature of 80-100°C (slightly higher than the glass transition temperature of polyurethane) and a pressure of 10-50 MPa. Hot pressing causes the polymer segments at the interface of the two layers to diffuse and entangle with each other, forming a strong chemical bond, thereby obtaining an integrated bilayer solid electrolyte membrane. The thickness of the first solid electrolyte layer is D1=30μm, the thickness of the second solid electrolyte layer is D2=15μm, D1 / D2=2, and the total thickness is 45μm.

[0067] (3) Preparation of double negative electrode layer negative electrode: 1. Preparation of the first negative electrode layer (silicon-carbon layer containing lithium): Porous silicon-carbon negative electrode material (uniformly dispersed or embedded in a porous carbon framework with a single particle size of 100nm, Dv50=3μm, specific surface area=2000 m² / g, pore volume=1 cm³ / g, reversible specific capacity up to 2500mAh / g), conductive agent VGCF, binder polyacrylic acid PAA are mixed with heptane at a mass ratio of 90:5:5 and stirred into a uniform slurry. The slurry is coated onto a copper foil current collector, dried, and then rolled to obtain a dense silicon-carbon negative electrode sheet. Using an electrochemical pre-lithiation process, in a half-cell, the silicon-carbon negative electrode sheet is used as the positive electrode and a lithium metal sheet is used as the negative electrode, allowing lithium ions to be embedded in the silicon-carbon material, resulting in a 30μm thick pre-lithiated silicon-carbon negative electrode sheet, i.e., the first negative electrode layer includes silicon-carbon material containing lithium.

[0068] 2. Preparation of the second negative electrode layer (lithium metal foil layer): In the drying room, a large roll of lithium metal ingots is rolled into an ultra-thin lithium foil with a thickness of 20μm using a precision roller press.

[0069] 3. Integration of the dual negative electrode layer negative electrode sheet: The first negative electrode layer and the second negative electrode layer prepared above are laminated by room temperature rolling at a pressure of 10-30 MPa, finally obtaining a total thickness D. 负 It is a 50μm double negative electrode layer negative electrode sheet.

[0070] (4) Integration and packaging of the entire battery: 1. The stacking adopts a "sandwich" stacking structure: The positive electrode sheet (with pre-welded tabs) from step (1) is cut to the required size. The double-layer solid electrolyte layer from step (2) is cut to a size slightly larger than the positive electrode sheet. The double-layer negative electrode sheet from step (3) is cut to the required size. Then, the positive electrode sheet, solid electrolyte layer, and negative electrode sheet are stacked according to... Figure 1 The stacked components are arranged in the order shown. Where D1 = 30 μm, D2 = 15 μm, and D... 正 150μm, D 负 50μm, (D1+D2) / (D 正 +D 负 =0.225.

[0071] 2. Hot pressing and encapsulation: The stacked cells are placed into aluminum-plastic film encapsulation bags, and top and side sealing is performed under vacuum conditions to form a soft-pack battery. The encapsulated cells are then placed in a warm isostatic press and hot-pressed at appropriate temperature (60-80°C) and pressure (300-500 MPa). This step is crucial, as it greatly enhances the interfacial contact between the positive electrode / electrolyte and the electrolyte / negative electrode, reduces interfacial impedance, and makes the bonding between layers tighter, forming an integrated structure. After hot pressing, the all-solid-state battery finally undergoes formation treatment to obtain the all-solid-state battery of this invention.

[0072] Example 2 group This set of embodiments is based on Embodiment 1, except that the first inorganic sulfide solid electrolyte Li in the first solid electrolyte layer is changed. x PS y M m N n (M is selected from Cl or Br, N is selected from Cl and Br, which are halogen elements different from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0) The value of (m+n) is as follows: In Example 2-1, the precursors Li₂S, P₂S₅, LiCl, and LiBr powders were precisely weighed in a molar ratio of 12:2:1:1, meaning the first inorganic sulfide solid electrolyte in the first solid electrolyte layer was Li₂S. 6.5 PS 5.5 Cl 0.25 Br 0.25 , where m+n=0.5; In Example 2-2, the precursors Li₂S, P₂S₅, LiCl, and LiBr powders were precisely weighed in a molar ratio of 8:2:3:3, meaning the first inorganic sulfide solid electrolyte in the first solid electrolyte layer was Li₂S / P₂S₅. 5.5 PS 4.5 Cl 0.75 Br 0.75 , where m+n=1.5.

[0073] Example 3 Group This set of embodiments is based on Embodiment 1, except that the mass ratio of the sulfide electrolyte Li6PS5Cl to the organic binder in the second solid electrolyte layer is changed. Specifically: Example 3-1: Li6PS5Cl electrolyte powder and the above organic binder solution were mixed at a mass ratio of 90%:10%; In Example 3-2, Li6PS5Cl electrolyte powder was mixed with the above-mentioned organic binder solution at a mass ratio of 99%:1%. In Example 3-3, Li6PS5Cl electrolyte powder and the above organic binder solution were mixed at a mass ratio of 89%:11%; In Examples 3-4, Li6PS5Cl electrolyte powder and the above-mentioned organic binder solution were mixed at a mass ratio of 99.5%:0.5%.

[0074] Example 4 group This set of embodiments is based on Embodiment 1, except that the mass ratio of polyurethane to lithium alginate in the organic binder of the second solid electrolyte layer is changed. Specifically: Example 4-1: Polyurethane particles and lithium alginate powder were weighed at a mass ratio of 0.5:1; Example 4-2: Polyurethane particles and lithium alginate powder were weighed at a mass ratio of 1.8:1; In Examples 4-3, polyurethane particles and lithium alginate powder were weighed at a mass ratio of 0.45:1; In Examples 4-4, polyurethane particles and lithium alginate powder were weighed at a mass ratio of 1.85:1.

[0075] Example 5 group This set of embodiments is based on Embodiment 1, except that the composition of the negative electrode is changed, specifically: Example 6-1: In the preparation of the first negative electrode layer, the silicon-carbon negative electrode sheet is not pre-lithiated, that is, the silicon-carbon material of the first negative electrode layer does not contain lithium. Example 6-2 uses a single layer of lithium metal as the negative electrode layer, without setting a first negative electrode layer.

[0076] Example 6 This embodiment is based on Embodiment 1, except that the mass percentage of the third inorganic sulfide solid electrolyte in the first active material of the first positive electrode layer (based on the mass of the first positive electrode active material) and the mass percentage of the third inorganic sulfide solid electrolyte in the third active material of the third positive electrode layer (based on the mass of the third positive electrode active material) are changed. Specifically: Based on the mass of the first positive electrode active material, the mass ratio of the third inorganic sulfide solid electrolyte in the first active material of the first positive electrode layer is 10%; based on the mass of the third positive electrode active material, the mass ratio of the third inorganic sulfide solid electrolyte in the third active material of the third positive electrode layer is 10%; this is equivalent to only needing to obtain one type of positive electrode layer powder in the process of preparing the positive electrode sheet, wherein the positive electrode active material: third inorganic sulfide solid electrolyte: VGCF:PTFE = 84%:10%:5%:1% (equal to the mass ratio of the four substances in the second active material of the second positive electrode layer in Example 1), and the final thickness of the prepared positive electrode layer is 150μm, which is equal to the total thickness of the first, second, and third positive electrode layers in Example 1.

[0077] Example 7 group This set of embodiments is based on Embodiment 1, except that the thickness D1 of the first solid electrolyte layer and the thickness D2 of the second solid electrolyte layer are changed. Specifically: Example 5-1: The thickness of the first solid electrolyte layer is D1 = 22 μm, the thickness of the second solid electrolyte layer is D2 = 18 μm, D1 / D2 = 1.22, (D1+D2) / (D 正 +D 负=0.2; Example 5-2: The thickness of the first solid electrolyte layer is D1 = 32 μm, the thickness of the second solid electrolyte layer is D2 = 11 μm, D1 / D2 = 2.91, (D1+D2) / (D 正 +D 负 ) = 0.215; Example 5-3: The thickness of the first solid electrolyte layer D1 = 20 μm, the thickness of the second solid electrolyte layer D2 = 18 μm, D1 / D2 = 1.11, (D1+D2) / (D 正 +D 负 ) = 0.19; In Examples 5-4, the thickness of the first solid electrolyte layer is D1 = 34 μm, the thickness of the second solid electrolyte layer is D2 = 11 μm, D1 / D2 = 3.09, and (D1+D2) / (D 正 +D 负 =0.225.

[0078] Example 8 group This set of embodiments refers to Embodiment 1, except that the thickness D1 of the first solid electrolyte layer and the thickness D2 of the second solid electrolyte layer are changed, or the total thickness D of the first negative electrode layer and the second negative electrode layer is changed. 负 Alternatively, the total thickness D of the first, second, and third cathode layers can be changed. 正 , specifically: Example 8-1: The thickness of the first solid electrolyte layer is D1 = 22 μm, the thickness of the second solid electrolyte layer is D2 = 13 μm, D1 / D2 = 1.69, the thickness of the first positive electrode layer is 50 μm, the thickness of the second positive electrode layer is 60 μm, and the thickness of the third positive electrode layer is 50 μm. 正 =160μm, the thickness of the first negative electrode layer is 45μm, the thickness of the second negative electrode layer is 45μm, D 负 =90μm, (D1+D2) / (D 正 +D 负 ) = 0.14; Example 8-2: The thickness of the first solid electrolyte layer is D1 = 34 μm, the thickness of the second solid electrolyte layer is D2 = 19 μm, D1 / D2 = 1.79, the thickness of the first positive electrode layer is 30 μm, the thickness of the second positive electrode layer is 40 μm, and the thickness of the third positive electrode layer is 32 μm. 正 =102μm, the thickness of the first negative electrode layer is 25μm, the thickness of the second negative electrode layer is 25μm, D 负 =50μm, (D1+D2) / (D 正 +D 负 ) = 0.349; In Example 8-3, the thickness of the first solid electrolyte layer is D1 = 20 μm, the thickness of the second solid electrolyte layer is D2 = 10 μm, D1 / D2 = 2, the thickness of the first positive electrode layer is 53 μm, the thickness of the second positive electrode layer is 65 μm, and the thickness of the third positive electrode layer is 52 μm. 正 =170μm, the thickness of the first negative electrode layer is 50μm, the thickness of the second negative electrode layer is 50μm, D 负 =100μm, (D1+D2) / (D 正 +D 负 ) = 0.111; In Examples 8-4, the thickness of the first solid electrolyte layer is D1 = 35 μm, the thickness of the second solid electrolyte layer is D2 = 20 μm, D1 / D2 = 1.75, the thickness of the first positive electrode layer is 29 μm, the thickness of the second positive electrode layer is 39 μm, and the thickness of the third positive electrode layer is 31 μm. 正 =170μm, the thickness of the first negative electrode layer is 20μm, the thickness of the second negative electrode layer is 20μm, D 负 =40μm, (D1+D2) / (D 正 +D 负 =0.396.

[0079] Comparative Example 1 This comparative study was conducted with reference to Example 1, except that the first inorganic sulfide solid electrolyte Li in the first solid electrolyte layer was changed. x PS y M m N n (M is selected from Cl or Br, N is selected from Cl and Br, which are halogen elements different from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0) The value of (m+n) is as follows: Comparative Example 1-1: The precursors Li₂S, P₂S₅, LiCl, and LiBr powders were precisely weighed in a molar ratio of 28:5:2:2, meaning the first inorganic sulfide solid electrolyte in the first solid electrolyte layer was Li₂S / P₂S₅. 6.6 PS 5.6 Cl 0.2 Br 0.2 , where m+n=0.4; Comparative Examples 1-2: The precursors Li₂S, P₂S₅, LiCl, and LiBr powders were precisely weighed in a molar ratio of 17:5:8:8, meaning the first inorganic sulfide solid electrolyte in the first solid electrolyte layer was Li₂S / P₂S₅. 5.4 PS 4.4 Cl 0.8 Br 0.8 , where m+n=1.6.

[0080] Comparative Example 2 This comparative study was conducted with reference to Example 1, except that the material selection of the organic binder in the second solid electrolyte layer was changed. Specifically: Comparative Example 2-1: The only organic binder was polyurethane; In Comparative Example 2-2, the only organic binder was lithium alginate.

[0081] Comparative Example 3 This comparative example is based on Example 1, except that a first solid electrolyte layer is not provided.

[0082] Comparative Example 4 This comparative example is based on Example 1, except that a second solid electrolyte layer is not provided.

[0083] Test case The following tests were performed on the all-solid-state batteries obtained in the above embodiments and comparative examples.

[0084] (1) Initial coulombic efficiency and long-cycle performance test: The above solid electrolyte battery was charged at a rate of 0.1C to the upper limit voltage of 4.25V, and discharged at the same rate of 0.1C to the cutoff voltage of 2.5V. The initial charge capacity (Q_charge) and initial discharge capacity (Q_discharge) were accurately recorded, and the initial coulombic efficiency (ICE) was calculated as (Q_discharge / Q_charge) × 100%. The test results are recorded in Table 1.

[0085] (2) Charge the above solid electrolyte battery at a rate of 0.2C to the upper limit voltage of 4.25V, and discharge it at a rate of 0.5C to the cutoff voltage of 2.5V. Repeat this charge and discharge process 1000 times and record the discharge capacity (Q1000) of 1000T. The capacity retention rate of 1000T cycles is (Q1000 / Q_discharge)×100%. The test results are recorded in Table 1.

[0086] Table 1 Based on the data in Table 1 above: By analyzing Examples 1, 2, 1, and 3, it can be found that when a first solid electrolyte layer including a first inorganic sulfide solid electrolyte is present, and the solid electrolyte Li x PS y M m N n When 0.5 ≤ (m + n) ≤ 1.5 is satisfied, especially when Li6PS5Cl is selected. 0.5 Br 0.5(When the mixed halogen doping amounts satisfy m=0.5, n=0.5, m+n=1.0), the [PS5Cl] formed... 0.5 Br 0.5 The triangular bipyramidal framework structure is the most regular and stable, which can significantly suppress the side reactions between the positive electrode and the electrolyte, effectively reduce the irreversible consumption of lithium ions, and thus significantly improve the first efficiency of the battery.

[0087] By analyzing Examples 1, 2, and 4, it can be found that when the organic binder in the second solid electrolyte layer is only polyurethane, polyurethane can absorb the stress of negative electrode volume change. Although it does not significantly affect the cycle performance of the battery, the battery's first efficiency is slightly reduced due to the lack of ion transport optimization effect of lithium alginate. When the organic binder is only lithium alginate, its mechanical toughness is insufficient and it cannot buffer the stress of negative electrode volume change, resulting in a low cycle capacity retention rate of the battery. When the second solid electrolyte layer is absent, there is no elastic component to buffer the expansion stress, resulting in the lowest battery cycle retention rate and a significantly damaged battery cycle life. Furthermore, there is no ion transport channel or interface protection to ensure the technical effect brought by the first inorganic sulfide solid electrolyte in the first solid electrolyte layer, and the battery's first efficiency performance is also not ideal.

[0088] Analysis of Examples 1, 3, and 4 reveals that in the second solid electrolyte layer, the proportion of the second inorganic sulfide solid electrolyte should not be too low. Too low a proportion leads to insufficient ion conductivity to meet transport requirements, creating an ion transport bottleneck and hindering the initial efficiency improvement brought by the first solid electrolyte layer. Similarly, the proportion of the organic binder should not be too low; insufficient binder dosage prevents effective absorption of volume change stress during negative electrode cycling, making the electrolyte layer prone to cracking and causing solid-solid interface contact failure, thus reducing battery cycle life. Furthermore, in the organic binder, the proportion of polyurethane should not be too low; insufficient polyurethane dosage makes the electrolyte layer prone to cracking due to decreased interface contact stability, affecting battery cycle life. The proportion of lithium alginate should also not be too low; too low a proportion lacks sufficient lithiophilic groups to construct a low-resistance ion transport path, increasing lithium-ion transport impedance and affecting the battery's initial efficiency. Overall, in the second solid electrolyte layer, the imbalance in the amount of core materials (second inorganic sulfide solid electrolyte and organic binder) has a greater impact on the battery's initial efficiency and cycle performance than the imbalance in the amount of internal components (lithium alginate and polyurethane) in the organic binder.

[0089] Analysis of Examples 1 and 5 reveals that in Example 5-1, the first negative electrode layer uses lithium-free silicon-carbon material, paired with lithium metal foil in the second negative electrode layer. While its porous structure slightly disperses the local stress during lithium metal expansion (resulting in a cycle capacity retention rate similar to Example 1), the silicon-carbon material requires additional lithium metal to complete the initial lithium intercalation and SEI film formation, leading to increased irreversible lithium loss. Therefore, without a pre-lithiation process for the silicon-carbon material, the lithium atom surface diffusion barrier is high, resulting in low suppression of lithium dendrite formation in the second negative electrode layer. This causes lithium metal to be encased by dendrites and unable to participate in the reversible reaction, affecting the battery's initial efficiency. In Example 5-2, the negative electrode active material uses only pure lithium metal foil, and its irreversible lithium loss mainly originates from the formation of the surface SEI film. The amount is relatively controllable, so the initial efficiency is acceptable. However, this scheme does not introduce a pre-lithiation design and lacks the buffering and stress dispersion effect provided by the porous structure of silicon-carbon materials. Not only is the initial efficiency not further optimized, but the interface failure is also caused by drastic changes in lithium metal volume and lithium dendrite growth during cycling. Therefore, the cycle stability is slightly worse than that of Example 1 and Example 5-1 with silicon-carbon materials. Therefore, in this invention, the significant improvement in battery cycle performance still depends on the core function of toughening and stress buffering provided by the polyurethane organic binder in the second solid electrolyte layer. In addition, the porous structure of silicon-carbon materials has a relatively limited effect on improving battery cycle performance. Therefore, it is proposed to improve the initial efficiency of this double-layer negative electrode structure by performing a pre-lithiation process on the silicon-carbon material of the first negative electrode layer, so as to further ensure the technical effect brought by the first solid electrolyte layer.

[0090] Analysis of Examples 1 and 6 reveals that if the positive electrode lacks a smooth transition structure between electronic and ionic conduction, abrupt changes in transport characteristics can lead to interfacial stress concentration, uneven distribution of the electrochemical reaction zone, and problems such as interfacial peeling and cracking during cycling. This results in long-term deterioration of interfacial stability, a decrease in battery cycle capacity retention, and poor cycle life.

[0091] Finally, through analysis of Examples 1, 7, and 8, it can be found that: in the solid electrolyte layer, if the first solid electrolyte layer is too thin, it cannot sufficiently suppress the irreversible side reaction between the positive electrode and the electrolyte, resulting in damage to the battery's first efficiency; if the second solid electrolyte layer is too thin, it cannot absorb the volume change stress during negative electrode cycling, and the battery's cycle performance is also impaired; in the battery, if the solid electrolyte layer or electrode layer is too thin, it is more likely to be punctured or cracked when dealing with the volume change of the negative electrode during cycling, resulting in damage to the battery's cycle life; correspondingly, if the solid electrolyte layer or electrode layer is too thick, the transport impedance of ions inside the electrode increases, and the improvement in the first efficiency is limited.

[0092] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. An all-solid-state battery, characterized in that, It includes a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode; the solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer stacked together, the first solid electrolyte layer being close to the positive electrode and the second solid electrolyte layer being close to the negative electrode; The first solid electrolyte layer includes a first inorganic sulfide solid electrolyte, which includes Li x PS y M m N n M is selected from Cl or Br, N is selected from Cl and Br and is different from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m> 0, n> 0; The second solid electrolyte layer includes a second inorganic sulfide solid electrolyte and an organic binder. The second inorganic sulfide solid electrolyte includes Li6PS5Cl, and the organic binder includes polyurethane and lithium alginate.

2. The all-solid-state battery according to claim 1, characterized in that, Based on the mass of the second solid electrolyte layer, the mass percentage of the second inorganic sulfide solid electrolyte is 90%~99%, and the mass percentage of the organic binder is 1%~10%. And / or, the mass ratio of the polyurethane to the lithium alginate is (0.5~1.8):

1.

3. The all-solid-state battery according to claim 1, characterized in that, The negative electrode sheet further includes a negative electrode current collector, and a first negative electrode layer and a second negative electrode layer are stacked between at least one surface of the negative electrode current collector and the second solid electrolyte layer, wherein the first negative electrode layer is close to the second solid electrolyte layer and the second negative electrode layer is close to the negative electrode current collector. The first negative electrode layer includes a first negative electrode active material, which includes a lithium-containing silicon-carbon material. And / or, the second negative electrode layer includes a second negative electrode active material, which includes lithium metal.

4. The all-solid-state battery according to claim 3, characterized in that, The thickness of the first negative electrode layer is 20μm~50μm; And / or, the thickness of the second negative electrode layer is 20μm~50μm.

5. The all-solid-state battery according to claim 1 or 3, characterized in that, The positive electrode sheet further includes a positive electrode current collector. Between at least one side surface of the positive electrode current collector and the first solid electrolyte layer, there are stacked first positive electrode layer, second positive electrode layer and third positive electrode layer. The first positive electrode layer is close to the positive electrode current collector, the third positive electrode layer is close to the first solid electrolyte layer, and the second positive electrode layer is located between the first positive electrode layer and the third positive electrode layer. The first positive electrode layer includes a first positive electrode active material, and the first positive electrode active material includes a third inorganic sulfide solid electrolyte. Based on the mass of the first positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the first positive electrode active material is 3% to 8%. The second positive electrode layer includes a second positive electrode active material, and the second positive electrode active material includes a third inorganic sulfide solid electrolyte. Based on the mass of the second positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the second positive electrode active material is 8% to 13%. The third positive electrode layer includes a third positive electrode active material, which includes a third inorganic sulfide solid electrolyte. Based on the mass of the third positive electrode active material, the mass percentage of the third inorganic sulfide solid electrolyte in the third positive electrode active material is 13% to 18%. The third inorganic sulfide solid electrolyte includes LGPS-type solid electrolyte, Li2S-P2S5 system solid electrolyte, and Li... x PS y M m N n At least one of the following, wherein M is selected from Cl or Br, N is selected from Cl and Br and is a halogen element different from M, 0.5≤(m+n)≤1.5, 5.5≤x≤6.5, 4.5≤y≤5.5, and m>0, n>0; The median particle size Dv50 of the third inorganic sulfide solid electrolyte is 0.3 μm to 5 μm.

6. The all-solid-state battery according to claim 5, characterized in that, The first positive electrode active material further includes a positive electrode active substance, and the thickness of the first positive electrode layer is 25μm~60μm; And / or, the second positive electrode active material further includes a positive electrode active substance, and the thickness of the second positive electrode layer is 30 μm to 80 μm; And / or, the third positive electrode active material further includes a positive electrode active substance, and the thickness of the third positive electrode layer is 25μm~60μm; The positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, and lithium nickel oxide, and the median particle size Dv50 of the positive electrode active material is 1μm~25μm.

7. The all-solid-state battery according to claim 1, characterized in that, The thickness of the first solid electrolyte layer is D1, where 20μm≤D1≤35μm; And / or, the thickness of the second solid electrolyte layer is D2, 10μm≤D2≤20μm.

8. The all-solid-state battery according to claim 7, characterized in that, The relationship between D1 and D2 is: 1.2≤D1 / D2≤3.

9. The all-solid-state battery according to claim 5, characterized in that, The total thickness of the first negative electrode layer and the second negative electrode layer is D. 负 ,40μm≤D 负 ≤100μm; the total thickness of the first positive electrode layer, the second positive electrode layer, and the third positive electrode layer is D. 正 80μm≤D 正 ≤200μm.

10. The all-solid-state battery according to claims 7 and 9, characterized in that, The D1, D2, D 正 and D 负 The following relation is satisfied: 0.14≤(D1+D2) / (D 正 +D 负 )≤0.35.

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