Composite solid electrolyte membrane and method for manufacturing the same

Abstract

The present application relates to a composite solid-state electrolyte film and a preparation method thereof. The composite solid-state electrolyte film comprises two functional subregion layers L1 and L2 and a gradient transition zone at the interface between L1 and L2; L1 is a solid-state electrolyte A layer close to the lithium metal negative electrode side, which is made of Li 7‑x PS 6‑x Cl x material, 1.3≤x≤1.6; the thickness of the L1 layer is 10-40 μm; L2 is a solid-state electrolyte B layer close to the high-voltage positive electrode side, which is made of Li3MCl6 or a derivative material of Li3MCl6, M including In or Y; the thickness of the L2 layer is 1-10 μm; and the gradient transition zone is a chemical element gradient change transition zone, with a thickness of 1 nm≤T≤50 nm. The super-thin heterogeneous composite solid-state electrolyte film obtained by combining the functional subregion and the chemical element gradient transition zone realizes the oxidation protection of the high-voltage positive electrode side and the dendrite resistance / reduction resistance protection of the lithium metal negative electrode side, solves the high-impedance problem, and also realizes a key technical breakthrough of high-energy-density all-solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state lithium batteries, and in particular to a gradient composite solid electrolyte membrane for all-solid-state lithium batteries and its preparation method. Background Technology

[0002] Sulfide solid electrolytes (SSEs) are among the most competitive key materials in the field of all-solid-state lithium batteries (ASSBs), especially lithium-sulfur-silver-germanium ore electrolytes, due to their excellent room-temperature ionic conductivity (comparable to liquid electrolytes, ~10). - 3 S·cm -1 With its good processability, it is considered one of the most commercially promising inorganic solid electrolytes.

[0003] Despite the excellent performance of sulfide SSEs, their large-scale application still faces multiple interrelated challenges, mainly in terms of material stability, interfacial failure, and engineered preparation: (1) High interfacial impedance due to dual instability at the positive and negative electrode interfaces. The electrochemical stability window of sulfide SSEs is relatively narrow. On the lithium metal negative electrode side, sulfides are prone to reduction decomposition, forming a high-impedance solid electrolyte interface (SEI). At the same time, their anti-dendrying ability is insufficient, which easily leads to lithium dendrites penetrating the electrolyte along defects or grain boundaries. On the high-voltage positive electrode side, sulfide SSEs are prone to oxidation decomposition. When in direct contact with high-energy positive electrodes (such as NCM), harmful byproducts are generated and a space charge layer (SCL) is formed, which significantly increases the interfacial impedance and reduces cycle performance. To this end, researchers usually prefabricate a protective film on the surface of the sulfide solid electrolyte. The protective film helps to mitigate the chemical reaction between the electrolyte and high-energy-density negative electrodes such as lithium, thereby obtaining a long-cycle all-solid-state lithium (ion) battery. For example, the solid electrolyte composite material and lithium battery disclosed in invention patent CN116365017A uses a protective film with low electronic conductivity and high ionic conductivity and extremely high stability to form on the surface of the electrode material, thereby protecting the electrode material. However, it has the following problems: the electrolyte membrane is not functionally layered and the interface gradient is not designed. On the lithium anode side, its sulfide / oxide mixed system still has the risk of reduction and decomposition, and its anti-dendrying ability is insufficient; on the cathode side, it lacks a special high oxidation stability layer, which cannot effectively prevent the oxidation reaction between sulfides and high-voltage cathodes (such as NCM811), and the interface impedance continues to increase with cycling.

[0004] (2) High interfacial resistance caused by heterogeneous electrolyte integration. One of the strategies for addressing the defects of single SSEs in existing inventions is to use multilayer or composite electrolytes, such as combining high-conductivity sulfides and high-stability halides. However, simple contact between heterogeneous solid electrolyte materials often introduces new, high-resistivity solid-solid interfaces due to mismatches in crystal structure, chemical potential, or mechanical properties. This increase in interfacial impedance negates the advantage of the conductivity of such composite electrolytes.

[0005] (3) Difficulty in achieving ultrathin and large-scale preparation. To achieve the goal of high energy density, the thickness of sulfide electrolyte membranes needs to be reduced to <50μm. Traditional powder cold pressing or hot pressing methods are difficult to prepare ultrathin films with good mechanical strength and uniformity. At the same time, the high sensitivity of sulfide SSEs to commonly used polar organic solvents limits their application in existing lithium battery wet production lines, making the large-scale preparation of ultrathin films an engineering challenge.

[0006] Therefore, existing sulfide solid electrolytes are insufficient to meet the requirements of most consumers. Summary of the Invention

[0007] This invention aims to provide a gradient composite solid electrolyte membrane for all-solid-state lithium batteries and its preparation method, which overcomes the aforementioned problems of instability at the positive and negative electrode interfaces and high impedance at heterogeneous interfaces through an ingenious design of functional partitioning and continuous gradient transition regions. This invention offers a structurally innovative and engineering-feasible solid electrolyte solution that simultaneously achieves anti-oxidation protection for the high-voltage positive electrode side and anti-dendrying / anti-reduction protection for the lithium metal negative electrode side. It solves the high impedance problem caused by chemical incompatibility at heterogeneous solid-solid interfaces and achieves ultra-thin heterogeneous composite electrolyte membranes through precise structural design and integrated processes.

[0008] The technical solution of this invention is implemented as follows: The composite solid electrolyte membrane of the present invention is characterized by comprising at least two functional partition layers L1 and L2 and a gradient transition region located at the interface between L1 and L2; L1 is the solid electrolyte A layer near the lithium metal anode side, which uses a chloride-rich lithium-sulfur-silver-germanium ore electrolyte Li. 7-x PS 6-x Cl x The L1 layer, with a thickness of 1.3 ≤ x ≤ 1.6, utilizes the high shear modulus and lithium metal compatibility of high-chlorine-content sulfide materials to form a dense LiCl-rich interface phase in situ at the Li metal interface. This phase acts as an electronic insulator, effectively suppressing the formation and penetration of lithium dendrites and achieving a high critical current density (CCD). The thickness of the L1 layer ranges from 10 μm to 40 μm.

[0009] The L2 layer is a solid electrolyte B layer located near the high-voltage positive electrode. It is made of lithium metal halide electrolyte Li3MCl6 or its derivatives, which have a wide electrochemical window and high oxidation stability. M includes, but is not limited to, In or Y. This layer is in direct contact with the high-voltage positive electrode and, through physical isolation, effectively prevents the sulfide in the L1 layer from undergoing oxidative decomposition under high voltage, ensuring the safe and stable operation of the battery under high voltage. The thickness of the L2 layer ranges from 1 μm to 10 μm (preferably 2 μm to 6 μm).

[0010] The gradient transition region is a chemical element gradient transition region, which is a non-uniform chemical element gradient transition region formed by limited interdiffusion of elements at the heterogeneous interface between L1 and L2. The thickness range of this gradient transition region is 1 nm ≤ T ≤ 50 nm. The preferred thickness range of the gradient transition region is 3 nm ≤ T ≤ 30 nm. This transition region aims to effectively reduce the space charge layer effect (SCL) and interfacial reaction impedance at the heterogeneous phase interface through continuous changes in chemical potential or the formation of a stable buffer phase in situ, thereby ensuring rapid and low-barrier transport of Li+ between L1 and L2.

[0011] The present invention controls the thickness of the L1 and L2 layers within a specific range as follows: (1) The material of the L1 layer will form a dense interface phase rich in LiCl in situ. This thickness range can both block lithium dendrite penetration by its own structure and reduce the interface impedance with the lithium metal anode through the chlorine-rich characteristics, ensuring rapid lithium ion transport. At the same time, sufficient thickness can maintain mechanical integrity and avoid damage during subsequent heat treatment, rolling and other processes. (2) The material of the L2 layer has a wide electrochemical window and high oxidation stability. Its thickness is limited in order to reduce the impact of the high impedance layer on the overall ion conduction while blocking the oxidation reaction on the positive electrode side from eroding the L1 layer. If it is too thin, the protection will fail, and if it is too thick, it will drag down the overall conductivity of the battery.

[0012] The chemical composition gradient change sequence of the gradient transition region described in this invention is as follows: from the L1 side to the L2 side, the molar content of characteristic elements S and P in the L1 layer gradually decreases, while the molar content of characteristic elements Cl and M in the L2 layer gradually increases, and there is no obvious phase separation within the transition region, achieving a smooth transition in the concentration of S and P with Cl and M. Furthermore, in the gradient transition region, from the L1 side to the L2 side, the molar content of characteristic elements S and P in the L1 layer gradually decreases from 20-30 mol% in the bulk L1 layer to 0.1-5 mol% in the L2 transition region, while the molar content of characteristic elements Cl and M in the L2 layer gradually increases from 5-10 mol% in the L1 transition region to 40-50 mol% in the bulk L2 layer.

[0013] This invention also relates to a method for preparing a composite solid electrolyte membrane, comprising the following steps: S1: L1 layer slurry preparation: The L1 layer material is a chloride-rich sulfide electrolyte Li 7-x PS 6-x Cl x The powder is dispersed in an organic solvent to prepare a high-solids-content slurry; the organic solvent is a nonpolar protic solvent or a weakly polar aprotic solvent compatible with anhydrous ethanol (EtOH), tetrahydrofuran (THF), and ethyl acetate (EA) sulfides as the dispersion medium. The solid content of the slurry ranges from 10% to 40% to ensure the rheological properties of the subsequent coating; S2: L1 layer thin film preparation: The above slurry is coated by blade coating, casting or spraying, and then vacuum dried to obtain an L1 ultrathin film with a thickness of 10μm to 40μm (preferably 15μm to 30μm) after drying, so as to ensure the high energy density of the battery; S3: L2 layer solution preparation: Dissolve the L2 material Li3MCl6 or its derivative in a specific solvent and stir until completely dissolved to obtain an L2 precursor solution of the L2 layer high-pressure stable material (such as Li3InCl6); the specific solvent is selected from one or more anhydrous mixed solvents selected from ethyl acetate (EA), tetrahydrofuran (THF), anhydrous ethanol (EtOH), N-methylpyrrolidone (NMP) or dimethylformamide (DMF); S4: Construction of the integrated L1 / L2 layer membrane and gradient transition region: The precursor solution of the L2 layer is deposited on the surface of the L1 layer using a two-stage wet coating, atomic layer deposition (ALD), or molecular layer deposition (MLD) technology. The chemical composition and thickness of the interface are precisely controlled to obtain a composite membrane integrating the L1 and L2 layers. The heterogeneous interface between the L1 and L2 layers forms a transition region. The thickness of the L2 deposited layer is 1 μm to 10 μm (preferably 2 μm to 6 μm). During the deposition process, the chemical composition and initial thickness of the transition region between L1 and L2 are precisely controlled to form an initial gradient transition region with a gradient change in chemical composition between L1 and L2. The thickness range is 0.5 nm ≤ T0 ≤ 10 nm. S5: Gradient thermal treatment and densification: The film integrating L1 / L2 layers is subjected to subsequent gradient thermal treatment and densification treatment to induce limited interdiffusion of elements at the L1 / L2 heterostructure interface and control the thickness, so that the thickness range of the chemical element gradient transition region formed between the L1 and L2 heterophases is limited to 1nm to 50nm (preferably 3nm to 30nm), thereby realizing a continuous and gradual distribution of chemical composition in the transition region (i.e., chemical element gradient distribution).

[0014] It should be noted that gradient thermal treatment and densification increase the thickness of the transition region from the initial 0.5nm-10nm to 1nm-50nm. During this process, the thickness of the L1 and L2 layers will decrease slightly, but this is negligible. Since the maximum increase in the thickness of the transition region is only 50nm, and the thickness of the L1 and L2 layers is in μm (1μm=1000nm), the interdiffusion of elements in the transition region only occurs in the extremely thin interfacial area. The overall thickness impact on L1 (10-40μm) and L2 (1-10μm) is between 0.01% and 0.5%, which will not change the core function of the film and can therefore be ignored.

[0015] The present invention achieves a continuous and gradual distribution of the composition in the transition region by combining the initial thickness control in step S4 with the elemental interdiffusion in step S5.

[0016] The heat treatment conditions are limited to an inert gas environment (such as Ar or N2), and low-temperature heat treatment (150°C to 350°C) is performed to avoid sulfide decomposition, remove residual solvent, and induce limited interdiffusion of elements at the L1 / L2 heterostructure interface. The densification process employs low-pressure rolling or hot pressing integration, with a pressure range of 12 MPa to 50 MPa, thereby limiting the thickness of the chemical element gradient transition region formed between the L1 and L2 heterophases to within 1 nm to 50 nm.

[0017] The core innovation of the preparation method lies in the combination of steps S4 and S5 to form a functional nanoscale chemical element gradient transition region between the L1 and L2 heterophases, with the thickness of the chemical element gradient transition region between the L1 and L2 heterophases limited to 1 nm to 50 nm, more preferably 3 nm to 30 nm. Furthermore, the gradient transition region is formed through limited interdiffusion or in-situ reaction of the L1 and L2 components, thereby achieving a continuous change in the lithium-ion chemical potential at the nanoscale, effectively suppressing the space charge layer (SCL) effect and heterostructure interface reactions, and ensuring ultra-low interfacial impedance for Li+ transport.

[0018] The beneficial effects of the technical solution described in this invention compared with the prior art are: The composite solid-state electrolyte structure and its liquid-phase-assisted low-temperature integrated preparation method provided by this invention aim to solve bottleneck problems such as interface compatibility, poor solid-solid contact, and dendrite penetration in the core of sulfide-based all-solid-state lithium batteries. Its main technical effects are reflected in the following aspects: 1. Synergistically stabilizes the positive and negative electrode interfaces, significantly improving battery cycle stability: (1) Effective protection of the lithium metal anode: By using a chloride-rich silver-germanium sulfide electrolyte in the L1 layer, the chloride element promotes the in-situ formation of an electronically insulating and ionicly conductive chloride-rich interface phase at the lithium metal interface. This self-confined interface phase effectively blocks electron transport and inhibits sulfide decomposition. At the same time, the high mechanical strength of the L1 layer material helps resist the penetration of lithium dendrites, greatly improving the chemical stability and anti-dendrite ability of the Li / SSE interface.

[0019] (2) Ensuring electrochemical compatibility on the high-voltage cathode side: The L2 layer is made of a halide material with a wide electrochemical window and is placed on the cathode side through functional partitioning, effectively isolating the oxidation-sensitive L1 layer sulfide from direct contact with the high-voltage cathode active material. This significantly inhibits electrolyte oxidation and decomposition and element interdiffusion under high voltage, thereby reducing the interfacial impedance on the cathode side and ensuring long-term stable cycling of the all-solid-state battery at high cutoff voltage.

[0020] 2. Overcoming high impedance at heterogeneous interfaces and optimizing lithium-ion transport kinetics: (1) Constructing an ultra-low impedance solid-solid interface: This invention solves the problem of space charge layer (SCL) effect and interface impedance surge caused by chemical potential mismatch and crystal structure incompatibility when traditional heteroelectrolytes are simply stacked, by forming a nanoscale chemical element gradient transition region (thickness range of 1 nm to 50 nm) through precision integration process. This gradient transition region realizes continuous changes in composition and potential at the atomic or nanoscale, providing a fast and low-barrier transport channel for lithium ions and ensuring the overall high ionic conductivity inside the electrolyte.

[0021] (2) Enhance ion transference and interfacial conduction: By combining heterogeneous materials, especially by selecting halides with high oxidation stability in the L2 layer, the overall lithium ion transference of the electrolyte can be increased, concentration polarization can be reduced, and interfacial stability can be further promoted.

[0022] 3. Simplify the manufacturing process, improve battery energy density and engineering feasibility. (1) Achieving ultra-thin electrolyte membrane: Using liquid phase assisted integration method instead of traditional solid phase sintering, the thickness of L1 layer sulfide film and L2 layer protective coating can be precisely controlled, so that the total electrolyte membrane thickness can be controlled within the target range of ≤50μm, achieving a key technological breakthrough in high energy density all-solid-state batteries.

[0023] (2) Improve the environmental stability of sulfide materials: During the liquid phase preparation process, by strictly limiting the anhydrous, sulfide-compatible solvent system and inert gas environment, combined with low-temperature integrated process, the problem of sulfide electrolyte reacting with water vapor to generate harmful H2S during the preparation process is avoided to the greatest extent, which is conducive to the large-scale operation and storage of materials.

[0024] The invention will now be further described with reference to the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is an enlarged schematic diagram of the positive electrode material, lithium metal negative electrode, and composite electrolyte membrane structure in a preferred embodiment of the present invention.

[0026] Explanation of reference numerals in the attached figures: 1 represents the lithium metal anode, 2 represents the composite electrolyte membrane, and 3 represents the cathode material. 21 represents the solid electrolyte L1 layer near the lithium metal anode, 22 represents the gradient transition region, and 23 represents the solid electrolyte L2 layer near the high-voltage cathode.

[0027] Figure 2 This is an EDS diagram showing the distribution of elements on the L1 side of the gradient transition region in Example 1.

[0028] Figure 3 This is an EDS diagram showing the distribution of elements on the L2 side of the gradient transition region in Example 1. Detailed Implementation

[0029] The composite solid electrolyte membrane of the present invention comprises two functional partition layers L1 and L2 and a gradient transition region located at the interface between L1 and L2; L1 is the solid electrolyte A layer near the lithium metal anode side, which uses a chloride-rich lithium-sulfur-silver-germanium ore electrolyte Li. 7-x PS 6-x Cl x The material forms a dense interface phase rich in LiCl in situ at the lithium metal interface, with a thickness of 1.3 ≤ x ≤ 1.6; the thickness of the L1 layer ranges from 10 μm to 40 μm. The L2 layer is a solid electrolyte B layer close to the high-voltage positive electrode side. It is made of lithium metal halide electrolyte Li3MCl6 or its derivative material with a wide electrochemical window and high oxidation stability. M includes, but is not limited to, In or Y. The thickness of the L2 layer ranges from 1 μm to 10 μm. The gradient transition region is a chemical element gradient transition region, which is a non-uniform chemical element gradient transition region formed by limited interdiffusion of elements at the heterogeneous interface between L1 and L2, with a thickness range of 1 nm ≤ T ≤ 50 nm. Preferably, the thickness range is 3 nm ≤ T ≤ 30 nm.

[0030] The chemical composition gradient change sequence of the gradient transition zone is as follows: from L1 to L2, the molar content of characteristic elements S and P in layer L1 gradually decreases, while the molar content of characteristic elements Cl and M in layer L2 gradually increases. Furthermore, there is no significant phase separation within the transition zone, achieving a smooth transition in the concentrations of S and P with Cl and M. Specifically, in the gradient transition zone, from L1 to L2, the molar content of characteristic elements S and P in layer L1 gradually decreases from 20-30 mol% in the bulk of layer L1 to 0.1-5 mol% in the transition zone L2, while the molar content of characteristic elements Cl and M in layer L2 gradually increases from 5-10 mol% in the transition zone L1 to 40-50 mol% in the bulk of layer L2.

[0031] The preparation method of the gradient composite solid electrolyte membrane for all-solid-state lithium batteries (hereinafter referred to as gradient membrane) of the present invention includes the following steps: S1: Preparation of L1 layer slurry: The L1 material Li 7-x PS 6-x Cl x A high-solids-content slurry is prepared by dispersing powder in an organic solvent; the organic solvent is a nonpolar protic solvent or a weakly polar aprotic solvent compatible with anhydrous ethanol, tetrahydrofuran, and ethyl acetate sulfide as the dispersion medium; the solid content of the slurry ranges from 10% to 40%. S2: Preparation of L1 layer film: The slurry is coated onto a polytetrafluoroethylene plate by means of blade coating, casting or spraying, and then vacuum dried to obtain an L1 ultrathin film with a thickness of 10μm to 40μm after drying; S3: L2 layer solution preparation: The L2 material Li3MCl6 or its derivatives are dissolved in a specific solvent, M including but not limited to In or Y, and stirred until completely dissolved to obtain an L2 precursor solution with a concentration of 5wt%-20wt%; the specific solvent is selected from one or more anhydrous mixed solvents selected from ethyl acetate, tetrahydrofuran, anhydrous ethanol, N-methylpyrrolidone or dimethylformamide; S4: Construction of the integrated L1 / L2 layer film and gradient transition region: Using a two-stage wet coating and ALD / MLD technology, the precursor solution of the L2 layer is deposited on the surface of the L1 layer to form an integrated L1 / L2 layer film. The heterogeneous interface between the L1 and L2 layers forms a transition region. The thickness of the L2 layer is controlled between 1 μm and 10 μm. During the deposition process, the chemical composition and initial thickness of the transition region between L1 and L2 need to be precisely controlled so that an initial gradient transition region with a gradient change in chemical composition is formed between L1 and L2, and its thickness range is 0.5 nm ≤ T0 ≤ 10 nm. S5: Gradient thermal treatment and densification: The film integrating L1 / L2 layers is subjected to subsequent gradient thermal treatment and densification treatment to induce limited interdiffusion of elements at the L1 / L2 heterostructure interface and control the thickness, so that the thickness range of the chemical element gradient transition region formed between the L1 and L2 heterophases is limited to 1nm to 50nm, realizing a continuous and gradual distribution of chemical composition in the transition region.

[0032] The heat treatment conditions are limited to an inert gas (such as Ar or N2) environment, and low-temperature heat treatment (150°C to 350°C) is performed to avoid sulfide decomposition, remove residual solvent, and induce limited interdiffusion of elements at the L1 / L2 heterostructure interface; the densification treatment is performed by low-pressure rolling or hot pressing integration, with a pressure range of 12MPa to 50MPa, thereby limiting the thickness range of the chemical element gradient transition region formed between the L1 and L2 heterophases to 1nm to 50nm.

[0033] The methods for precisely controlling the interfacial chemical composition and the initial thickness of the transition zone are as follows: If using ALD / MLD technology: adjust the deposition cycle number (1-20 cycles) to control the amount of single-atom layer deposition of the L2 precursor, making the L2 layer thickness 1μm to 10μm. At this point, an initial gradient transition zone is formed between L1 and L2, with a thickness range of 0.5nm ≤ T0 ≤ 10nm. If using a two-stage wet coating: adjust the L2 precursor solution concentration to 5wt%-20wt% and the coating speed to 5-20mm / s to control the penetration depth of the L2 precursor into the L1 layer surface, making the L2 layer thickness 2μm to 6μm, with an initial gradient transition zone thickness of 0.8nm ≤ T0 ≤ 8nm.

[0034] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0035] 1.1 Test Method All embodiments and comparative examples used the same all-solid-state battery assembly structure (Li metal anode / electrolyte membrane / LiCoO2 cathode) and underwent electrochemical performance testing at 25°C. Cyclic performance testing was performed by charging and discharging at a rate of 0.1C, and the data for the first 50 cycles were recorded. Interfacial impedance was measured by electrochemical impedance spectroscopy (EIS), and ionic conductivity was calculated using the electrochemical impedance method combined with the blocked electrode structure.

[0036] 1.2 Implementation Example Design Example 1: Li 7-1.3 PS 6-1.3 Cl 1.3 / Li3InCl6 gradient film (transition region 3nm)

[0037] S1: L1 layer slurry preparation: Li 6.7 PS 4.7 Cl 1.3 The powder (10g) was dispersed in anhydrous ethanol (30mL), magnetically stirred for 2h, and ultrasonically dispersed for 30min to prepare a slurry with a solid content of 33%. S2: L1 layer film formation: The slurry was coated onto a polytetrafluoroethylene sheet using a doctor blade coater (gap 20μm), and vacuum dried at 60℃ for 2h to obtain an L1 film with a thickness of 15μm after drying; S3: L2 layer solution preparation: Li3InCl6 powder (2g) was dissolved in EA / THF mixed solvent (volume ratio 1:1, 10mL) and stirred for 1h until completely dissolved to obtain L2 precursor solution; S4: Construction of integrated L1 / L2 layer membrane and gradient transition region: L2 layer was deposited on the surface of L1 membrane using ALD technology. The specific control methods are as follows: (1) Precursor selection: Li source is bis(trimethylsilyl)aminolithium (LiN(SiMe3)2), In source is indium trichloride (InCl3), and Cl source is hydrogen chloride (HCl) to ensure matching with the composition of Li3InCl6; (2) Deposition cycle number control: 15 cycles were set. The deposition process of each cycle is Li source pulse 10ms → Ar purge 30ms → In source pulse 12ms → Ar purge 40ms → Cl source pulse 8ms → Ar purge 35ms; (3) Chemical composition control: By using the Li / In / Cl precursor pulse time ratio (10:12:8), the stoichiometric ratio of Li / In / Cl in Li3InCl6 is accurately matched to 3:1:6. XRD verification showed no LiCl or InCl3 impurity phases; (4) Thickness control: ALD was used to control the thickness of the Li source membrane. With self-limiting growth characteristics, the growth rate is stable at 0.2 μm / cycle per cycle, and 15 cycles correspond to a L2 layer thickness of 3 μm (2.95 μm measured by a step meter); (5) Initial transition zone control: By controlling the Ar purging time (30-45 ms), the L2 precursor is slightly penetrated into the L1 layer surface to form an initial transition zone thickness T0=0.8 nm; S5: Post-treatment (gradient heat treatment and densification): Under an argon atmosphere, heat treatment at 180℃ for 2 hours thickened the initial transition region to 3±0.2 nm through interdiffusion of interfacial elements; densification was achieved by roll pressing at 25 MPa to obtain a GCSE film (Li) with a total thickness of 18 μm. 7-1.3 PS 6-1.3 Cl 1.3 / Li3InCl6 gradient film), with a transition region thickness of 3nm.

[0038] Example 2: Li 7-1.4 PS 6-1.4 Cl 1.4 / Li3InCl6 gradient film (transition region 10nm) Different from Example 1: S1: The L1 layer uses Li 6.6 PS 4.6 Cl 1.4 Powder, otherwise the same as in Example 1, with a thickness of 15 μm after drying; S3: L2 layer solution preparation: Li3InCl6 powder (3.3 g) was dissolved in EA / THF mixed solvent (volume ratio 1:1, 10 mL) to prepare a solution with a concentration of 25 wt%; S4: Gradient transition zone construction: The L2 layer was deposited by a two-stage spraying method. The specific control methods are as follows: (1) Spraying parameter control: the nozzle distance from the L1 film surface is 5cm, the atomization pressure is 0.12MPa, and the coating speed is 10mm / s; (2) Thickness control: the number of spraying times (5 times) is precisely controlled. After each spraying, the material is vacuum dried at 60℃ for 15min. The thickness of a single spray is approximately 1μm. After 5 sprayings, the total thickness of the L2 layer is 5μm (measured 4.9μm); (3) Chemical composition control: Li3InCl6 in the solution is completely dissolved without precipitation. The molar ratio of Li / In / Cl is 3.02:1:5.98; (4) Initial transition zone control: the spraying speed is controlled at 10mm / s so that the contact time between the precursor and the L1 layer is 2.5s and the penetration depth is 3nm, forming an initial transition zone T0=3nm; S5: Post-treatment: Heat treatment at 220℃ for 2 hours under argon atmosphere, interdiffusion of interfacial elements thickens the transition region to 10nm; densification by roll pressing at 25MPa yields Li with a total thickness of 20μm. 7-1.4 PS 6-1.4 Cl 1.4 / Li3InCl6 gradient film, with a transition region thickness of 10nm.

[0039] The main purpose of "25MPa roll forming densification" is to eliminate porosity within the membrane layer (such as ethanol evaporation pores remaining after drying the L1 layer and loose gaps after deposition / spraying of the L2 layer), thereby improving the membrane's density and mechanical strength. Roll forming essentially compresses the membrane's "total thickness" through mechanical pressure, inevitably leading to synchronous changes in the thickness of each component region (L1 layer, transition zone, L2 layer). However, since densification is achieved solely by eliminating porosity through roll forming, the total thickness does not change significantly and can be considered within the margin of error. Therefore, in this embodiment, the thickness before and after roll forming is essentially the same.

[0040] Example 3: Li 7-1.5 PS 6-1.5Cl 1.5 / Li3YCl6 gradient film (transition region 20nm) Different from Example 1: S1: The L1 layer uses Li 6.5 PS 4.5 Cl 1.5 The powder was dispersed in anhydrous ethanol (35 mL) to prepare a slurry with a solid content of 25%, which was dried to a thickness of 20 μm. S3: L2 layer solution preparation: Li3YCl6 powder (3.6g) was dissolved in NMP solvent (10mL) to prepare a 15wt% solution; S4: Gradient transition region construction: The L2 layer was deposited using a two-stage coating method, with the specific control method as follows: (1) Coating parameter control: doctor blade gap 10μm, coating speed 8mm / s; (2) Thickness control: A 10μm gap between the scrapers corresponds to a wet film thickness of 10μm. After vacuum drying at 60℃ for 2h, the thickness of the L2 layer is 6μm (actual measurement 5.8μm). (3) Chemical composition control: NMP solvent was selected to avoid hydrolysis of Li3YCl6; (4) Initial transition zone control: The coating speed of 8 mm / s allows the precursor to penetrate 2.5 nm into the surface of the L1 layer, forming an initial transition zone T0 = 2.5 nm; S5: Post-treatment: Heat treatment at 250℃ for 2 hours under argon atmosphere, element interdiffusion thickens the transition region to 20nm; densification by roll pressing at 30MPa yields Li with a total thickness of 26μm. 7-1.5 PS 6-1.5 Cl 1.5 The Li3YCl6 gradient film has a transition region thickness of 20 nm.

[0041] Example 4: Li 7-1.6 PS 6-1.6 Cl 1.6 / Li3InCl6 gradient film (transition region 30nm) Different from Example 1: S1: The L1 layer uses Li 6.4 PS 4.4 Cl 1.6 Powder, 25 μm thick after drying; S3: L2 layer solution preparation: Li3InCl6 powder (4.4g) was dissolved in EA / THF mixed solvent (10mL) to prepare a 30wt% solution; S4: Gradient transition region construction: The L2 layer is deposited using the ALD technique, and the specific control method is as follows: (1) Precursor parameters: Li source pulse 12ms, In source pulse 15ms, Cl source pulse 10ms, Ar purge time 40ms / cycle; (2) Cycle number control: Set to 20 cycles, with a growth rate of 0.4 μm / cycle per cycle. 20 cycles correspond to an L2 layer thickness of 8 μm (actual measurement 7.9 μm). (3) Chemical composition control: Ensure Li / In / Cl = 3:1:6 by adjusting the pulse time ratio of Li / In / Cl (12:15:10); (4) Initial transition region control: Extend the pulse time of In source and Cl source (15ms, 10ms) to promote precursor penetration, and the initial transition region T0=10nm; S5: Post-treatment: Heat treatment at 300℃ for 2 hours under argon atmosphere to thicken the transition zone to 30nm; densification by roll pressing at 35MPa to obtain Li with a total thickness of 33μm. 7-1.6 PS 6-1.6 Cl 1.6 / Li3InCl6 gradient film (transition region 30nm).

[0042] Example 5: Li 7-1.3 PS 6-1.3 Cl 1.3 / Li3YCl6 gradient film (5nm transition region) Different from Example 1: S3: L2 layer solution preparation: Li3YCl6 powder (1.3g) was dissolved in THF solvent (10mL) to prepare a 10wt% solution; S4: Gradient transition region construction: The L2 layer is deposited using the ALD technique, and the specific control method is as follows: (1) Precursor selection: Li source is Li(thd), Y source is tris(dimethylamino)yttrium (Y(NMe2)3), and Cl source is trichloromethylsilane (CH3SiCl3); (2) Cycle number control: Set to 10 cycles, the deposition process in each cycle is as follows: Li source pulse 8ms → Ar purge 30ms → Y source pulse 10ms → Ar purge 35ms → Cl source pulse 6ms → Ar purge 30ms; (3) Thickness control: The growth rate per cycle is 0.2 μm / cycle, and 10 cycles correspond to a layer thickness of 2 μm (actual measurement 1.95 μm); (4) Chemical composition control: By using the Y / Cl pulse time ratio (10:6), ensure that Y / Cl = 1:6 in Li3YCl6; (5) Initial transition zone control: control the purge time to 30-35ms to reduce precursor penetration, and the initial transition zone T0=1.5nm; S5: Post-treatment: Heat treatment at 200℃ for 2 hours under argon atmosphere to thicken the transition zone to 5nm; densification by roll pressing at 15MPa to obtain Li with a total thickness of 17μm. 7-1.3 PS 6-1.3 Cl 1.3 / Li3YCl6 gradient film (transition region 5nm).

[0043] Example 6: Li 7-1.4 PS 6-1.4 Cl 1.4 / Li3YCl6 gradient film (transition region 15nm) Different from Example 1: S1: L1 layer slurry solid content 30% (Li 6.6 PS 4.6 Cl 1.4 10g of powder, 23mL of anhydrous ethanol), after drying, the thickness is 18μm; S3: L2 layer solution preparation: Li3YCl6 powder (2.2g) was dissolved in a THF / EA mixed solvent (volume ratio 1:1, 10mL), concentration 10wt%; S4: Gradient transition region construction: The L2 layer is deposited using a two-stage spraying method, with the specific control method as follows: (1) Spraying parameters: nozzle distance 6cm, atomization pressure 0.1MPa, coating speed 12mm / s; (2) Thickness control: The thickness is controlled by the number of spraying times (3 times). After each spraying and drying, the thickness is approximately 1.3 μm, and the total thickness after 3 sprays is 4 μm (actual measurement 3.9 μm). (3) Chemical composition control: Mixed solvents improve the solubility of Li3YCl6, Li / Y / Cl=3.01:1:5.97; (4) Initial transition zone control: High-speed spraying at 12mm / s reduces precursor penetration, and the initial transition zone T0=1.2nm; S5: Post-treatment: Heat treatment at 240℃ for 2 hours under argon atmosphere to thicken the transition zone to 15nm; densification by roll pressing at 28MPa to obtain Li with a total thickness of 22μm. 7-1.4 PS 6-1.4 Cl 1.4 / Li3YCl6 gradient film (transition region 15nm).

[0044] Example 7: Li 7-1.5 PS 6-1.5 Cl 1.5 / Li3InCl6 gradient film (transition region 25nm) Different from Example 1: S1: The thickness of L1 layer after drying is 22μm; S3: L2 layer solution preparation: Li3InCl6 powder (4.0 g) was dissolved in EA / THF mixed solvent (10 mL) to prepare a solution with a concentration of 28 wt%; S4: Gradient transition region construction: The L2 layer was deposited using a two-stage coating method, with the specific control method as follows: (1) Coating parameters: doctor blade gap 14μm, coating speed 6mm / s; (2) Thickness control: The doctor blade gap of 14μm corresponds to a wet film thickness of 14μm, and the thickness of L2 layer after drying is 7μm (actual measurement 6.8μm). (3) Chemical composition control: The solution concentration is 28wt% to ensure uniform composition after film formation; (4) Initial transition zone control: Low-speed coating at 6mm / s extends the contact time, the precursor penetration depth is 4nm, and the initial transition zone T0=4nm; S5: Post-treatment: Heat treatment at 280℃ for 2 hours under argon atmosphere to thicken the transition zone to 25nm; densification by roll pressing at 32MPa to obtain Li with a total thickness of 29μm. 7-1.5 PS 6-1.5 Cl 1.5 / Li3InCl6 gradient film (transition region 25nm).

[0045] Example 8: Li 7-1.6 PS 6-1.6 Cl 1.6 / Li3YCl6 gradient film (transition region 40nm) Different from Example 1: S1: L1 layer solid content 35% (Li 6.4 PS 4.4 Cl 1.6 10g of powder, 18mL of anhydrous ethanol), after drying, the thickness is 28μm; S3: L2 layer solution preparation: Li3YCl6 powder (5.0 g) was dissolved in NMP solvent (10 mL) to prepare a solution with a concentration of 33 wt%; S4: Gradient transition region construction: The L2 layer is deposited using the ALD technique, and the specific control method is as follows: (1) The deposition cycle number is 20 cycles, and the pulse time per cycle is: Li source 15ms → purge 40ms → Y source 18ms → purge 50ms → Cl source 12ms → purge 45ms; (2) Chemical composition control: By using the Y / Cl pulse time ratio (18:12), ensure that Y / Cl = 1:6 in Li3YCl6; (3) Thickness control: The growth rate per cycle is 0.45 μm / cycle, and 20 cycles correspond to a layer thickness of 9 μm (actual measurement 8.9 μm); (4) Initial transition region control: Extend the pulse time of Y source and Cl source (18ms, 12ms) to promote the adsorption and penetration of precursor into L1 layer, and the initial transition region thickness T0=8nm; S5: Post-treatment: Heat treatment at 320℃ for 2 hours under argon atmosphere to thicken the transition zone to 40nm; densification by roll pressing at 40MPa to obtain Li with a total thickness of 37μm. 7-1.6 PS 6-1.6 Cl 1.6 / Li3YCl6 gradient film (transition region 40nm).

[0046] 1.3 Comparative Design Comparative Example 1: Single Li 6.5 PS 4.5 Cl 1.5 Sulfide film Preparation steps: Only the L1 layer (same as the L1 layer in Example 3, with a thickness of 20 μm) is prepared, without the L2 layer and transition region, and directly heat-treated at 250℃ + rolled at 30 MPa.

[0047] Comparative Example 2: Single Li3InCl6 halide film Preparation steps: Only the L2 layer (same as the L2 layer in Example 1, with a thickness of 3 μm) is prepared, without the L1 layer and transition region, and then heat-treated at 180℃ and rolled at 20MPa.

[0048] Comparative Example 3: Li 6.5 PS 4.5 Cl 1.5 / Li3InCl6 simple stacked film Preparation steps: L1 layer (20μm) and L2 layer (3μm) were prepared separately. There was no transition region construction step. The two layers were directly stacked and then heat-treated at 250℃ + rolled at 30MPa, with a total thickness of 23μm.

[0049] Comparative Example 4: Li 6.5 PS 4.5 Cl 1.5 / Li3InCl6 high-temperature sintered stacked film Unlike Comparative Example 3: After stacking, traditional high-temperature sintering (600℃, 2h) + 500MPa high-pressure densification was used, with a total thickness of 22μm.

[0050] Comparative Example 5: The steps S1-S4 of Example 3 were followed exactly, and the battery was directly assembled after deposition without the heat treatment and densification in step S5.

[0051] Comparative Example 6: Steps S1-S4 are the same as in Example 3. In step S5, only 250°C argon atmosphere heat treatment was performed for 2 hours (to remove solvent and induce a small amount of element interdiffusion). Rolling densification was not performed, and the final transition region thickness was 8 nm.

[0052] 1.4 Performance Test Data and Comparison

[0053]

[0054] 1.5 Conclusion Analysis

[0055] The following conclusions can be drawn from the analysis of the results of the examples and comparative examples in the table above: (1) Improvement of interface stability by gradient structure: The 50-cycle capacity retention (89.5%-95.0%) and coulombic efficiency (98.7%-99.5%) of Examples 1-8 were significantly higher than those of Comparative Examples 1-4 (58.8%-72.5%, 95.3%-97.5%), proving that the high shear modulus of the L1 layer (chloride-rich sulfide) and the LiCl-rich interface phase can effectively suppress lithium dendrites, and the L2 layer (halide) can block the oxidation decomposition on the positive electrode side. The two work together to solve the problem of instability at the positive and negative electrode interfaces. However, Comparative Example 1 (single sulfide) suffered from oxidation decomposition on the positive electrode side, and Comparative Example 2 (single halide) suffered from low ionic conductivity, both of which resulted in severe degradation of cycle performance.

[0056] (2) The effect of the gradient transition region on impedance optimization: The interface impedance (75-112 Ω·cm²) of the examples is much lower than that of Comparative Example 3 (no transition region, 420 Ω·cm²) and Comparative Example 4 (high temperature sintering, 380 Ω·cm²), indicating that the nanoscale gradient transition region (1-50 nm) suppresses the space charge layer effect through continuous change of chemical potential, realizing low-barrier Li⁺ transport. In Comparative Example 3, due to direct contact between heterogeneous interfaces, the space charge layer effect is significant, and the impedance increases sharply; although the high temperature sintering of Comparative Example 4 can reduce some contact impedance, it leads to the growth of electrolyte grains, which in turn reduces ionic conductivity.

[0057] (3) Influence of process parameters on performance: Example 6 (transition zone 15nm, rolling pressure 28MPa) has the best overall performance (capacity retention 95.0%, impedance 75Ω·cm²), indicating that the thickness of the transition zone is not necessarily better the thicker it is (Examples 4 and 8 have increased impedance due to excessively thick transition zones); low-pressure and low-temperature processes (150-350℃, 12-50MPa) are superior to traditional high-temperature and high-pressure processes (Comparative Example 4), which can avoid sulfide decomposition, achieve densification, and reduce preparation costs. Comparing Example 3 and Comparative Example 5 (without step S5), Example 3 shows an increase of 73.9% in ionic conductivity (2.0 vs 0.9mS / cm), a decrease of 84.1% in interfacial impedance (92 vs 580Ω·cm²), and an increase of 75.5% in capacity retention (91.8 vs 52.3%). The reasons are: lack of heat treatment leads to solvent residue and ineffective interdiffusion of interfacial elements, preventing the formation of a continuous gradient transition region; lack of densification results in poor L1 / L2 interlayer contact, with porosity defects hindering Li... + Transmission; Compared with Comparative Example 6 (heat treatment only) and Example 3, the interfacial impedance of Comparative Example 6 is still as high as 320 Ω·cm² (3.5 times that of Example 3), and the capacity retention is 13.2% lower (78.6% vs 91.8%). This proves that heat treatment alone can remove solvent and induce a small amount of interdiffusion of elements, but cannot eliminate interlayer porosity. Only by combining densification treatment can tight interlayer contact be achieved, while fixing the thickness and composition gradient of the gradient transition region, ensuring Li + Low-barrier transmission.

[0058] In summary, the gradient composite solid electrolyte membrane of the present invention, through functional partitioning and gradient transition region design, combined with liquid-phase assisted low-temperature integration process, can simultaneously solve the problems of unstable positive and negative electrode interfaces, high impedance of heterogeneous interfaces and ultrathinness of sulfide SSEs, and has excellent electrochemical performance and engineering application potential.

[0059] Although the present invention has been described with reference to specific embodiments, such description is not intended to limit the invention. Other variations of the disclosed embodiments, based on the description of the invention, will be foreseeable to those skilled in the art, and such variations should fall within the scope defined by the appended claims.

Claims

1. A composite solid electrolyte membrane, characterized in that... It consists of two functional partition layers, L1 and L2, and a gradient transition region located at the interface between L1 and L2; L1 is the solid electrolyte A layer near the lithium metal anode side, which uses a chloride-rich lithium-sulfur-silver-germanium ore electrolyte Li. 7- x PS 6-x Cl x The material forms a dense interface phase rich in LiCl in situ at the lithium metal interface, with a thickness of 1.3 ≤ x ≤ 1.6; the thickness of the L1 layer ranges from 10 μm to 40 μm. The L2 layer is a solid electrolyte B layer close to the high-voltage positive electrode side. It is made of lithium metal halide electrolyte Li3MCl6 or its derivative material with a wide electrochemical window and high oxidation stability. M includes, but is not limited to, In or Y. The thickness of the L2 layer ranges from 1 μm to 10 μm. The gradient transition region is a chemical element gradient change transition region, which is a non-uniform gradient transition region of chemical elements formed by limited interdiffusion of elements at the heterogeneous interface between L1 and L2, with a thickness range of 1nm≤T≤50nm.

2. The composite solid electrolyte membrane according to claim 1, characterized in that... The chemical composition gradient change order of the gradient transition region is as follows: from L1 side to L2 side, the molar content of characteristic elements S and P in L1 layer gradually decreases, and the molar content of characteristic elements Cl and M in L2 layer gradually increases. Moreover, there is no obvious phase separation in the transition region, so as to achieve a smooth transition of the concentration of S and P with Cl and M.

3. The composite solid electrolyte membrane according to claim 2, characterized in that... In the gradient transition region, from the L1 side to the L2 side, the molar content of characteristic elements S and P in the L1 layer gradually decreases from 20-30 mol% in the bulk of the L1 layer to 0.1-5 mol% in the L2 transition region, while the molar content of characteristic elements Cl and M in the L2 layer gradually increases from 5-10 mol% in the L1 transition region to 40-50 mol% in the bulk of the L2 layer.

4. The composite solid electrolyte membrane according to claim 1, characterized in that... The thickness range of the gradient transition region is 3nm≤T≤30nm.

5. A method for preparing a composite solid electrolyte membrane as described in any one of claims 1-4, characterized in that... Includes the following steps: S1: Preparation of L1 layer slurry: The L1 material Li 7-x PS 6-x Cl x A high-solids-content slurry is prepared by dispersing powder in an organic solvent; the organic solvent is a nonpolar protic solvent or a weakly polar aprotic solvent compatible with anhydrous ethanol, tetrahydrofuran, and ethyl acetate sulfide as the dispersion medium; the solid content of the slurry ranges from 10% to 40%. S2: Preparation of L1 layer film: The slurry is coated onto a polytetrafluoroethylene plate by means of blade coating, casting or spraying, and then vacuum dried to obtain an L1 ultrathin film with a thickness of 10μm to 40μm after drying; S3: L2 layer solution preparation: The L2 material Li3MCl6 or its derivatives are dissolved in a specific solvent, M including but not limited to In or Y, and stirred until completely dissolved to obtain an L2 precursor solution with a concentration of 5wt%-20wt%; the specific solvent is selected from one or more anhydrous mixed solvents selected from ethyl acetate, tetrahydrofuran, anhydrous ethanol, N-methylpyrrolidone or dimethylformamide; S4: Construction of the integrated L1 / L2 layer film and gradient transition region: Using a two-stage wet coating and ALD / MLD technology, the precursor solution of the L2 layer is deposited on the surface of the L1 layer to form an integrated L1 / L2 layer film. The heterogeneous interface between the L1 and L2 layers forms a transition region. The thickness of the L2 layer is controlled between 1 μm and 10 μm. During the deposition process, the chemical composition and initial thickness of the transition region between L1 and L2 need to be precisely controlled so that an initial gradient transition region with a gradient change in chemical composition is formed between L1 and L2, and its thickness range is 0.5 nm ≤ T0 ≤ 10 nm. S5: Gradient thermal treatment and densification: The film integrating L1 / L2 layers is subjected to subsequent gradient thermal treatment and densification treatment to induce limited interdiffusion of elements at the L1 / L2 heterostructure interface and control the thickness, so that the thickness range of the chemical element gradient transition region formed between the L1 and L2 heterophases is limited to 1nm to 50nm, realizing a continuous and gradual distribution of chemical composition in the transition region.

6. The preparation method according to claim 5 is characterized in that... The heat treatment conditions are limited to an inert gas environment, and low-temperature heat treatment (150°C to 350°C) is performed to avoid sulfide decomposition, remove residual solvent, and induce limited interdiffusion of elements at the L1 / L2 heterojunction.

7. The preparation method according to claim 5 is characterized in that... The densification process employs low-pressure roller pressing or hot pressing integration, with a pressure range of 12MPa to 50MPa, thereby limiting the thickness range of the chemical element gradient transition region formed between the L1 and L2 heterophases to 1nm to 50nm.

8. The preparation method according to claim 5 is characterized in that... The method for precisely controlling the chemical composition of the interface and the initial thickness of the transition zone is as follows: using ALD / MLD technology: adjusting the number of deposition cycles to control the amount of single-atom layer deposition of the L2 precursor, so that the thickness of the L2 layer is 1μm to 10μm. At this time, an initial gradient transition zone is formed between L1 and L2, with a thickness range of 0.5nm≤T0≤10nm.

9. The preparation method according to claim 5 is characterized in that... The method for precisely controlling the chemical composition of the interface and the initial thickness of the transition zone is as follows: a two-stage wet coating process is used: the concentration of the L2 precursor solution is adjusted to 5wt%-20wt% and the coating speed is adjusted to 5-20mm / s to control the penetration depth of the L2 precursor into the surface of the L1 layer, so that the thickness of the L2 layer is 2μm to 6μm and the initial gradient transition zone thickness is 0.8nm≤T0≤8nm.

10. The preparation method according to claim 7 is characterized in that... The thickness range of the chemical element gradient transition region is limited to 3 nm to 30 nm.

Images