Method for improving interface stability of efficient solid-state battery

Abstract

The invention relates to the technical field of solid-state batteries, and discloses an efficient solid-state battery interface stability improving method which comprises the following steps: firstly, forming a composite precursor layer consisting of copper fluoride and lithium fluoride on the surface of a sulfide solid-state electrolyte sheet body through a codeposition method; and then assembling the electrolyte sheet body with the layer and a lithium metal negative electrode. In the assembling process, the composite precursor layer and lithium metal are subjected to an in-situ chemical reaction, and a stable composite interface layer formed by uniformly dispersing nano metal copper particles in a lithium-rich fluoride matrix is generated. According to the invention, through the constructed interface layer, nano-copper particles are used as lithium-philic sites to induce uniform nucleation of lithium ions, and meanwhile, a lithium fluoride matrix is used as an electronic insulating layer to inhibit interface side reaction and lithium dendrite growth, and through the synergistic effect of the nano-copper particles and the lithium fluoride matrix, the problem of instability of an interface between a sulfide electrolyte and a lithium negative electrode is effectively solved; therefore, the critical current density, the cycle life and the rate capability of the solid-state battery are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, specifically to a method for improving the interface stability of high-efficiency solid-state batteries. Background Technology

[0002] Solid-state batteries, by using solid electrolytes instead of traditional organic liquid electrolytes, hold the promise of fundamentally solving battery safety issues and can be matched with high-energy-density electrode materials, making them an important development direction for next-generation energy storage technology. Among various inorganic solid electrolytes, sulfide solid electrolytes are considered one of the most promising material systems due to their room-temperature ionic conductivity comparable to liquid electrolytes and their good mechanical ductility. To maximize the energy density advantage of solid-state batteries, lithium metal, with its extremely high theoretical specific capacity, is typically used as the anode material.

[0003] There is an inherent thermodynamic and electrochemical incompatibility between sulfide solid electrolytes and lithium metal anodes. When the two come into direct contact, a spontaneous chemical or electrochemical reaction occurs, forming an interface layer with complex composition, unstable structure, and mixed ionic and electronic conductivity. This interface layer continues to grow during battery cycling, constantly consuming limited active lithium and electrolyte, leading to a rapid increase in interfacial impedance, which in turn causes rapid capacity decay and shortened cycle life.

[0004] During charging and discharging, the deposition and stripping of lithium ions at the solid electrolyte / anode interface are extremely uneven. The interface lacks effective lithium nucleation sites, leading to the localized enrichment of lithium deposits, forming needle-like or dendritic lithium dendrites. The growth of these dendrites continuously consumes active lithium; more seriously, they may puncture the solid electrolyte membrane, causing internal short circuits and posing a serious safety hazard. Simultaneously, the high and unstable interfacial impedance, combined with the uneven lithium deposition behavior, restricts the rapid transport of lithium ions, resulting in poor performance of solid-state batteries at high current densities, i.e., poor rate capability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for improving the interface stability of high-efficiency solid-state batteries. This method solves the problems of poor interfacial chemical / electrochemical stability when existing sulfide solid electrolytes are in direct contact with lithium metal anodes, which easily leads to the growth of lithium dendrites, resulting in short battery cycle life, poor rate performance, and safety hazards such as internal short circuits.

[0006] To achieve the above objectives, the present invention provides a method for improving the interface stability of high-efficiency solid-state batteries, comprising the following steps: S1: Provides sulfide solid electrolyte sheet; S2: A composite precursor layer composed of copper fluoride and lithium fluoride is formed on at least one side surface of the sulfide solid electrolyte sheet by a co-deposition method; S3: Assemble the sulfide solid electrolyte sheet with the composite precursor layer with the lithium metal anode, so that the composite precursor layer comes into contact with the lithium metal anode, thereby generating a composite interface layer containing nano-copper particles and lithium fluoride matrix in situ.

[0007] By employing the above technical solution, this invention constructs a composite interface layer composed of nano-sized copper particles and a lithium fluoride matrix between the sulfide solid electrolyte and the lithium metal anode. This interface layer enhances the stability of the interface and inhibits the growth of lithium dendrites. Its mechanism of action is as follows: In-situ interface reaction occurs: In step S3, when the composite precursor layer comes into contact with the lithium metal anode, due to the low chemical potential of lithium, it will spontaneously undergo a displacement reaction with copper fluoride. The reaction formula is: 2Li + CuF2 → 2LiF + Cu.

[0008] Formation of the complex interface structure: This in-situ reaction generates two key components: Nano-sized copper (Cu) particles: Since the reaction occurs in situ at the solid-phase interface, the generated metallic copper is uniformly dispersed in the interface region in the form of nanoparticles.

[0009] Lithium fluoride (LiF) matrix: This matrix consists of two parts: one part is the lithium fluoride directly deposited in step S2, and the other part is the newly generated lithium fluoride from the in-situ reaction in step 1. Together, these two parts constitute a continuous, lithium fluoride-rich matrix.

[0010] Functional collaboration of composite interface layers: Homogenized lithium-ion flow: The lithium-philic nanoparticles of copper act as distributed lithium nucleation sites, reducing the nucleation overpotential for lithium deposition. This guides the uniform deposition of lithium ions at the interface, avoiding the formation of lithium dendrites induced by excessive local current density.

[0011] Suppressing electron conduction: Lithium fluoride, acting as an electronic insulator and lithium-ion conductor, physically isolates dispersed copper nanoparticles, preventing them from agglomerating and forming continuous electronic pathways, thereby suppressing interfacial side reactions and micro-short circuits. Simultaneously, this matrix serves as a lithium-ion transport channel, enabling lithium ions to pass through and reach copper nucleation sites.

[0012] Therefore, this invention solves the problem of uneven lithium deposition by constructing a composite interface that combines lithium-affinity sites (nano-copper) and electronic insulation / ion conduction functions (lithium fluoride matrix), thereby suppressing the nucleation and growth of lithium dendrites and thus helping to obtain solid-state batteries with high critical current density, long cycle life and good rate performance.

[0013] Preferably, in step S2, the molar fraction of lithium fluoride in the composite precursor layer is controlled to be between 20 mol% and 60 mol%.

[0014] By adopting the above technical solution, a synergistic effect can be achieved between providing sufficient lithiophilic sites and ensuring interfacial electronic insulation. If the lithium fluoride content is less than 20 mol%, it may not be sufficient to completely encapsulate and isolate the generated copper nanoparticles, posing a risk of copper agglomeration and the formation of electronic pathways; if the lithium fluoride content is greater than 60 mol%, the density of lithiophilic copper nucleation sites will be relatively too low, which may lead to increased interfacial impedance and weaken its effect of homogenizing lithium ion flow.

[0015] Preferably, in step S2, the thickness of the composite precursor layer is controlled to be between 10 nm and 30 nm.

[0016] By adopting the above technical solution, an adjustment can be made between forming effective interface protection and controlling interface impedance. If the thickness is less than 10 nm, the composite precursor layer may be discontinuous or have defects, and cannot form complete protection; if the thickness is greater than 30 nm, it will increase the total interface impedance, especially the transport resistance of lithium ions through this layer, thereby affecting the rate performance and energy efficiency of the battery.

[0017] Preferably, the sulfide solid electrolyte sheet provided in step S1 is a Li6PS5Cl electrolyte sheet.

[0018] By adopting the above technical solution, Li6PS5Cl, as a sulfide solid electrolyte with high ionic conductivity, provides a good foundation for ion transport in solid-state batteries.

[0019] Preferably, in step S1, the sulfide solid electrolyte sheet is prepared by cold pressing sulfide solid electrolyte powder under a pressure of 400 MPa.

[0020] By adopting the above technical solution, a pressure of 400 MPa can ensure the preparation of a high-density solid electrolyte sheet, reduce internal porosity, improve its mechanical strength and ionic conductivity, and provide a flat substrate for subsequent thin film deposition.

[0021] Preferably, the co-deposition method in step S2 is magnetron co-sputtering, performed under an argon atmosphere of 0.5 Pa. The magnetron co-sputtering is performed by simultaneously activating both a copper fluoride target and a lithium fluoride target in the sputtering system, and the molar ratio of copper fluoride to lithium fluoride in the composite precursor layer is controlled by adjusting the respective radio frequency power of the copper fluoride target and the lithium fluoride target.

[0022] By employing the above-described technical solution, magnetron co-sputtering is a method capable of achieving atomic-level mixing and controlling film thickness and composition, which helps to obtain a composite precursor layer with uniform composition. Performing the process under an argon protective atmosphere prevents the raw materials from reacting with moisture or oxygen in the air. By adjusting the radio frequency power of different target materials, the stoichiometry of the composite precursor layer can be controlled.

[0023] Preferably, in order to obtain a lithium fluoride molar fraction of 20 mol% to 60 mol%, the radio frequency power of the copper fluoride target is set to 30 W, while the radio frequency power of the lithium fluoride target is set in the range of 45 W to 120 W.

[0024] By adopting the above technical solution, a process reference is provided for the preparation of specific component contents in the composite precursor layer.

[0025] Preferably, by controlling the co-sputtering deposition time to be 4 to 12 minutes, a composite precursor layer thickness of 10 nm to 30 nm can be obtained.

[0026] By adopting the above technical solution, a process reference is provided for the preparation of composite precursor layers with specific thicknesses.

[0027] Preferably, the powder used for the sulfide solid electrolyte sheet is prepared by the following steps: mixing raw materials in a molar ratio of Li2S:P2S5:LiCl=5:1:2 and then mechanically and chemically ball-milling them in a planetary ball mill at a speed of 500 rpm for 12 hours.

[0028] By adopting the above technical solution, this is an effective way to prepare Li6PS5Cl phase with high ionic conductivity, and provides an electrolyte material with high ionic conductivity for this method.

[0029] This invention provides a method for improving the interface stability of high-efficiency solid-state batteries. It has the following beneficial effects: 1. This invention forms a CuF2-LiF composite precursor layer on the surface of a sulfide solid electrolyte, and then generates a composite interface composed of nano-copper and lithium fluoride in situ upon contact with a lithium anode. The nano-copper particles in this interface provide uniform lithium deposition sites, while the lithium fluoride matrix serves as an ion channel and electronic insulating layer. This structure effectively homogenizes the current distribution at the interface, suppresses the nucleation and growth of lithium dendrites, and thus increases the critical current density of the interface.

[0030] 2. This invention physically isolates the direct contact between the sulfide electrolyte and the lithium metal anode through the formed in-situ composite interface layer, effectively suppressing persistent interfacial side reactions between the two. This reduces irreversible lithium loss and the increase in interfacial impedance during cycling, ensuring the long-term structural integrity of the electrode / electrolyte interface, thus improving the long-term cycle stability and capacity retention of the full cell.

[0031] 3. This invention utilizes a composite interface layer with low interfacial impedance. Lithophilic copper nanosites lower the charge transfer barrier during lithium deposition / stripping, while the lithium fluoride matrix with high ionic conductivity ensures rapid lithium-ion transport. This synergistic effect ensures that lithium ions can pass through the interface quickly and uniformly, even at high current densities, resulting in excellent rate performance in the solid-state battery. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the present invention; Figure 2 The attached figure shows the curve of leakage current changing over time according to the present invention. Figure 3 This is a voltage and time curve of the present invention; Figure 4 This is a graph showing the discharge specific capacity and cycle number of the present invention. Figure 5 This is a bar chart showing the relationship between discharge specific capacity and discharge rate of the present invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0035] Lithium sulfide (Li2S), CAS No.: 12136-58-2, purity 99.9%, battery-grade powder.

[0036] Phosphorus pentasulfide (P2S5), CAS No.: 1314-80-3, purity 99.9%, powder.

[0037] Lithium chloride (LiCl), CAS No.: 7447-41-8, purity 99.99%, anhydrous powder.

[0038] Copper fluoride (CuF2), CAS No.: 7789-19-7, purity 99.9%, is used as a raw material for molding targets.

[0039] Lithium fluoride (LiF), CAS No.: 7789-24-4, purity 99.95%, is used as a raw material for molding targets.

[0040] Alumina (Al2O3), CAS No.: 1344-28-1, purity 99.99%, is used as a raw material for molding targets.

[0041] Lithium metal (Li), CAS No.: 7439-93-2, purity 99.9%, thickness 0.45mm, in sheet form.

[0042] Lithium nickel cobalt manganese oxide (LiNi) 0.8 Co 0.1 Mn 0.1 O2), battery-grade positive electrode active material, D50 particle size 3.5μm.

[0043] Preparation example: This preparation example provides a method for preparing a sulfide solid electrolyte (Li6PS5Cl) powder, which is used in subsequent examples and comparative examples, including the following steps: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium sulfide, phosphorus pentasulfide, and lithium chloride powders were accurately weighed according to a molar ratio of Li2S:P2S5:LiCl = 5:1:2. The weighed mixed powder was transferred to a zirconia ball mill jar, and zirconia grinding balls (ball-to-powder ratio of 15:1) were added. Mechanochemical ball milling was performed on a planetary ball mill with a milling speed of 500 rpm and a cumulative milling time of 12 hours. After the ball milling was completed, the product was removed from the glove box to obtain Li6PS5Cl solid electrolyte powder for subsequent examples and comparative examples.

[0044] Example 1: This embodiment provides a solid electrolyte with a [CuF2+LiF] composite precursor layer and its preparation method, including the following steps: Take 200 mg of Li6PS5Cl powder prepared in Preparation Example 1, put it into a mold with a diameter of 13 mm, and cold press it under a pressure of 400 MPa to prepare a solid electrolyte sheet.

[0045] The solid electrolyte sheet was placed in a magnetron co-sputtering system. Under an argon atmosphere of 0.5 Pa, CuF2 target (RF power 30 W) and LiF target (RF power 80 W) were simultaneously turned on for co-sputtering deposition for 8 minutes to form a composite precursor layer on one side of the electrolyte sheet. The total thickness of the composite layer was 20 nm, and the molar fraction of LiF was 40 mol.

[0046] In the glove box, a solid electrolyte sheet with a composite precursor layer (composite layer facing the negative electrode) and NCM are placed... 811 The composite positive electrode and lithium metal negative electrode are assembled into a coin cell.

[0047] Example 2: This embodiment provides a solid electrolyte with a [CuF2+LiF] composite precursor layer and its preparation method. The difference between this embodiment and Example 1 is that the molar fraction of LiF in the composite precursor layer is lower. The method includes the following steps: Take 200 mg of Li6PS5Cl powder prepared in Preparation Example 1, put it into a mold with a diameter of 13 mm, and cold press it under a pressure of 400 MPa to prepare a solid electrolyte sheet.

[0048] The solid electrolyte sheet was placed in a magnetron co-sputtering system. Under an argon atmosphere of 0.5 Pa, CuF2 target (RF power 30 W) and LiF target (RF power 45 W) were simultaneously turned on for co-sputtering deposition for 8 minutes to form a composite precursor layer on one side of the electrolyte sheet. The total thickness of the composite layer was 20 nm, and the molar fraction of LiF was 20 mol.

[0049] In the glove box, a solid electrolyte sheet with a composite precursor layer (composite layer facing the negative electrode) and NCM are placed... 811 The composite positive electrode and lithium metal negative electrode are assembled into a coin cell.

[0050] Example 3: This embodiment provides a solid electrolyte with a [CuF2+LiF] composite precursor layer and its preparation method. The difference between this embodiment and Example 1 is that the molar fraction of LiF in the composite precursor layer is higher. The method includes the following steps: Take 200 mg of Li6PS5Cl powder prepared in Preparation Example 1, put it into a mold with a diameter of 13 mm, and cold press it under a pressure of 400 MPa to prepare a solid electrolyte sheet.

[0051] The solid electrolyte sheet was placed in a magnetron co-sputtering system. Under an argon atmosphere of 0.5 Pa, CuF2 target (RF power 30 W) and LiF target (RF power 120 W) were simultaneously turned on for co-sputtering deposition for 8 minutes to form a composite precursor layer on one side of the electrolyte sheet. The total thickness of the composite layer was 20 nm, and the molar fraction of LiF was 60 mol.

[0052] In the glove box, a solid electrolyte sheet with a composite precursor layer (composite layer facing the negative electrode) and NCM are placed... 811 The composite positive electrode and lithium metal negative electrode are assembled into a coin cell.

[0053] Example 4: This embodiment provides a solid electrolyte with a [CuF2+LiF] composite precursor layer and its preparation method. The difference between this embodiment and Embodiment 1 is that the composite precursor layer is thinner. The method includes the following steps: Take 200 mg of Li6PS5Cl powder prepared in Preparation Example 1, put it into a mold with a diameter of 13 mm, and cold press it under a pressure of 400 MPa to prepare a solid electrolyte sheet.

[0054] The solid electrolyte sheet was placed in a magnetron co-sputtering system. Under an argon atmosphere of 0.5 Pa, CuF2 target (RF power 30 W) and LiF target (RF power 80 W) were simultaneously turned on for co-sputtering deposition for 4 minutes to form a composite precursor layer on one side of the electrolyte sheet. The total thickness of the composite layer was 10 nm, and the molar fraction of LiF was 40 mol.

[0055] In the glove box, a solid electrolyte sheet with a composite precursor layer (composite layer facing the negative electrode) and NCM are placed... 811 The composite positive electrode and lithium metal negative electrode are assembled into a coin cell.

[0056] Example 5: This embodiment provides a solid electrolyte with a [CuF2+LiF] composite precursor layer and its preparation method. The difference between this embodiment and Embodiment 1 is that the composite precursor layer is thicker, and the method includes the following steps: Take 200 mg of Li6PS5Cl powder prepared in Preparation Example 1, put it into a mold with a diameter of 13 mm, and cold press it under a pressure of 400 MPa to prepare a solid electrolyte sheet.

[0057] The solid electrolyte sheet was placed in a magnetron co-sputtering system. Under an argon atmosphere of 0.5 Pa, CuF2 target (RF power 30 W) and LiF target (RF power 80 W) were simultaneously turned on for co-sputtering deposition for 12 minutes, forming a composite precursor layer on one side of the electrolyte sheet. The total thickness of the composite layer was 30 nm, and the molar fraction of LiF was 40 mol.

[0058] In the glove box, a solid electrolyte sheet with a composite precursor layer (composite layer facing the negative electrode) and NCM are placed... 811 The composite positive electrode and lithium metal negative electrode are assembled into a coin cell.

[0059] Comparative Example 1: The difference compared to Example 1 is that after the solid electrolyte sheet is prepared, no interface layer is deposited, and it is directly used to assemble coin cells.

[0060] Comparative Example 2: Compared with Example 1, the difference is that: a magnetron sputtering method is used, only the Al2O3 target is turned on, and a 10nm thick Al2O3 physical isolation layer is deposited on the surface of the solid electrolyte sheet; all other aspects are the same.

[0061] Comparative Example 3: Compared with Example 1, the difference is that: a magnetron sputtering method is used, only the CuF2 target is turned on, and a pure CuF2 precursor layer with a thickness of 12nm is deposited on the surface of the solid electrolyte sheet to ensure that the total molar amount of Cu element is equivalent to that in Example 1, and all other aspects are the same.

[0062] Comparative Example 4: Compared with Example 1, the difference is that: a magnetron sputtering method is used, only the LiF target is turned on, and a pure LiF physical isolation layer with a thickness of 20nm is deposited on the surface of the solid electrolyte sheet; the rest are the same.

[0063] Test Example 1: Evaluation of Interface Electronic Insulation Reference Appendix Figure 2 Experimental steps: Solid electrolyte sheets with interface layers from Example 1 and Comparative Example 3 were respectively assembled into symmetrical coin cells with a Li / interface / SE / interface / Li structure in an argon atmosphere glove box.

[0064] The assembled symmetrical cell was placed in a constant temperature environment of 25°C and connected to an electrochemical workstation.

[0065] A constant DC voltage of 50mV was applied to the battery, and the current flowing through the battery was continuously recorded from 0 to 7200 seconds (2 hours).

[0066] Experimental data: Table 1. Leakage current of symmetrical cells under constant voltage of 50mV over time in conclusion: The experimental data in Table 1 show a fundamental difference between the symmetrical cells of Example 1 and Comparative Example 3 in the DC polarization test. The current of the Example 1 cell dropped rapidly at the beginning of the test and stabilized at an extremely low level below 0.1 μA after approximately 1800 seconds. This exponential decay of current over time is typical capacitive behavior, demonstrating effective electronic insulation at its interface. In contrast, the current of the Comparative Example 3 cell remained consistently above 15 μA throughout the test, exhibiting ohmic resistance characteristics, indicating the formation of a stable electronic conduction pathway within its interface.

[0067] This result verifies the mechanism of the present invention. In Example 1, the [CuF2+LiF] composite precursor reacts in situ with lithium metal to generate Cu and LiF. The simultaneously generated LiF acts as an ionic conductor matrix, physically separating the nano-sized Cu particles, inhibiting their aggregation and growth, and thus preventing the formation of an electronically conductive network penetrating the interface.

[0068] In Comparative Example 3, since the precursor was only pure CuF2, the metallic Cu formed by its reaction with lithium lacked the physical constraint of the LiF matrix, resulting in uncontrolled migration and aggregation, ultimately forming a micro-short-circuit path connecting the lithium anode and the solid electrolyte. The existence of this path led to the high steady-state leakage current observed in the test.

[0069] Therefore, this test case confirms that by introducing LiF as a necessary component of the composite precursor, the present invention successfully solves the problem of interfacial electronic short circuit caused by product (Cu) agglomeration after the in-situ reaction of a single reactant (CuF2), ensuring the electronic insulation of the interface, which is the basis for constructing a stable solid-state battery.

[0070] Test Example 2: Electrochemical Evaluation of Interfacial Lithophilicity Reference Appendix Figure 3 Experimental steps: Solid electrolyte sheets with interface layers from Examples 1, 2, and 4 were assembled into symmetrical coin cells with a Li / interface / SE / interface / Li structure in an argon atmosphere glove box.

[0071] The assembled symmetrical cell was placed in a constant temperature environment of 25°C and connected to an electrochemical workstation.

[0072] At 0.1mA / cm 2 Lithium deposition (electroplation) was performed on the battery using a constant current density, and the battery voltage was recorded as a function of time during this process.

[0073] The highest voltage value (nucleation peak voltage) at the moment of lithium nucleation and the plateau voltage value during the subsequent steady-state deposition were obtained using voltage-time curves. The nucleation overpotential was calculated as the difference between the nucleation peak voltage and the plateau voltage.

[0074] Experimental data: Table 2. Overpotential data for lithium deposition nucleation at different interfaces in conclusion: Table 2 provides a quantitative overview of the differences in lithium metal deposition behavior at different interfaces. The symmetric cells of Comparative Example 2 (Al₂O₃ interface) and Comparative Example 4 (LiF interface) both exhibit high nucleation overpotentials of 52.4 mV and 64.8 mV, respectively. This phenomenon indicates that the Al₂O₃ and LiF surfaces have a low chemical affinity for lithium metal, and lithium atoms need to overcome a high energy barrier to nucleate on these inert surfaces, thus manifesting as a significant initial voltage spike in electrochemistry.

[0075] The nucleation overpotential of the battery in Example 1 was only 6.8 mV, far lower than that of the two comparative examples. This result verifies the design mechanism of the present invention. In Example 1, the [CuF2+LiF] composite precursor, upon contact with lithium, generates in-situ nano-sized Cu particles with excellent lithiophilicity, enabling them to alloy with lithium and serve as preferential nucleation sites for lithium deposition. These highly affinity sites significantly lower the lithium nucleation energy barrier, allowing the lithium deposition process to proceed smoothly without requiring a high initial driving voltage.

[0076] Therefore, the results of this test case confirm that the present invention successfully constructs a lithiophilic interface by introducing CuF2 into the interface precursor and forming Cu nanoparticles in situ. Compared with conventional Al2O3 or LiF inert isolation layers, this lithiophilic interface can effectively guide the uniform deposition of lithium, which is a prerequisite for suppressing lithium dendrite growth and improving battery cycle stability.

[0077] Test Example 3: Long-term Cycle Stability Evaluation of Full-Battery Experimental steps: The coin cells assembled in Examples 1-5 and Comparative Examples 1-4 were left to stand for 2 hours to ensure that the electrolyte fully wetted the electrode materials.

[0078] Place the battery in a constant temperature test chamber at 25°C and connect it to the battery test system.

[0079] First, the battery was activated twice at a current density of 0.1C, with the voltage range set from 3.0V to 4.3V.

[0080] After activation, a long charge-discharge cycle test was conducted at a constant current density of 0.2C. The discharge capacity and coulombic efficiency for each cycle were recorded, and the number of cycles was set to 100. The capacity retention rate was calculated as the ratio of the discharge capacity of the 100th cycle to the discharge capacity of the 1st cycle.

[0081] Experimental data: Table 3. Long-cycle performance data of the full cell at 0.2C in conclusion: Table 3 shows the cycling performance data, indicating that the batteries in Examples 1-5 all exhibited excellent cycling stability, with capacity retention exceeding 91% after 100 cycles and an average coulombic efficiency approaching 99.9%. Examples 1 and 4 showed particularly outstanding performance. In contrast, all comparative batteries exhibited severe capacity decay.

[0082] The battery in Comparative Example 1 (without an interface layer) failed rapidly within 20 cycles, demonstrating that there are serious interfacial side reactions between the Li6PS5Cl electrolyte and the lithium anode, making stable cycling impossible.

[0083] While Comparative Example 2 (Al2O3 layer) and Comparative Example 4 (LiF layer) provided some physical isolation in the initial stage, their capacity retention remained at only around 50% after 100 cycles. Combined with the results of Test Example 2, their failure was attributed to the low lithiophilicity of the Al2O3-LiF interface. This low lithiophilicity leads to a high nucleation energy barrier during lithium deposition, causing lithium ions to tend to deposit unevenly at a few dominant sites, forming dendrites that pierce the electrolyte or consume active lithium, resulting in continuous capacity decay and low coulombic efficiency.

[0084] Comparative Example 3 (pure CuF2 layer) exhibited a faster degradation rate than Comparative Examples 2 and 4, with a capacity retention of only 35.8% and a low average coulombic efficiency. This aligns with the conclusion of Test Example 1, which indicates that the metallic Cu generated from the reaction of pure CuF2 agglomerates, forming electronic pathways at the interface. This leads to continuous electrolyte decomposition and loss of active lithium at the interface, manifesting as a rapid decline in battery capacity.

[0085] The success of Examples 1-5 demonstrates the core mechanism of this invention. The interface generated by the in-situ reaction of the composite precursor possesses both electronic insulation and lithiophilicity. Specifically, the nano-Cu particles, acting as lithiophilic sites, significantly reduce the lithium nucleation overpotential, guiding uniform lithium deposition; simultaneously, the in-situ generated LiF matrix effectively separates the Cu particles, constructing a stable interface that is ion-conducting yet electronically insulating, suppressing side reactions. The results of Examples 2 and 3 show that effective protection can be achieved with a LiF molar fraction ranging from 20 mol% to 60 mol%. The results of Examples 4 and 5 indicate that the expected effect can be achieved with a composite layer thickness ranging from 10 nm to 30 nm.

[0086] In summary, this test case systematically verifies, from the perspective of the macroscopic performance of the full cell, that the composite interface constructed by the present invention can simultaneously solve the three core problems of interface chemical stability, electronic insulation and lithium affinity, thereby achieving stable long-cycle performance of solid-state batteries.

[0087] Test Example 4: Full Battery Rate Performance Evaluation Reference Appendix Figure 5 Experimental steps: Take the button cells assembled in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 and let them stand for 2 hours.

[0088] Place the battery in a constant temperature test chamber at 25°C and connect it to the battery test system.

[0089] Charge the battery to 4.3V with a constant current of 0.1C, and then charge it with a constant voltage until the current is less than 0.02C.

[0090] The cells were discharged to 3.0V at constant current densities of 0.1C, 0.2C, 0.5C, 1.0C, and 2.0C, respectively, and the discharge specific capacity at each rate was recorded.

[0091] Experimental data: Table 4. Specific capacity data of full cells at different discharge rates in conclusion: The rate performance data in Table 4 show that the battery of Example 1 exhibits significantly better rate performance than the comparative examples. At a high rate of 2.0C, Example 1 can still release a capacity of 151.3 mAh / g, which is 78.9% of the capacity at 0.1C, while all the comparative batteries showed severe polarization or rapid failure at this current density.

[0092] The capacity of the battery in Comparative Example 1 (without an interface layer) drops precipitously at current densities above 0.2C, indicating that the unstable negative electrode interface will undergo catastrophic degradation at high currents and cannot support the rapid transport of lithium ions.

[0093] The rate performance of Comparative Example 2 (Al2O3 layer) is inferior to that of Example 1, with its capacity decreasing sharply with increasing current density. This is mainly attributed to the high interfacial impedance of the Al2O3 layer. This impedance has little effect at low currents, but at high currents it leads to a huge polarization voltage, causing the effective discharge voltage plateau of the battery to drop rapidly below the cutoff voltage, resulting in a severe loss of discharge capacity.

[0094] Comparative Example 3 (pure CuF2 layer) also exhibited poor rate performance, and its capacity decay at high rates was more severe than that of Comparative Example 2. Its failure mechanism differed from Comparative Example 2, primarily stemming from interfacial electronic short circuits. High current density exacerbated side reactions and Joule heating along this short-circuit path, not only consuming active lithium but also potentially further damaging the interfacial structure, leading to a sharp increase in polarization.

[0095] The success of Example 1 systematically verifies the advantages of the present invention. The interface generated in situ by this method is a functional interface integrating lithium-ion conductor, electronic insulator, and lithiophilic site. The lithiophilicity of the nano-Cu particles ensures that lithium ions can be rapidly and uniformly inserted and extracted, avoiding local current concentration under high current; the ion conduction characteristics of the LiF matrix provide a low-impedance transport path for this process; at the same time, the electronic insulation of the interface suppresses parasitic side reactions at high rates. The three work synergistically to form a low-impedance and stable solid electrolyte-anode interface.

[0096] Test Example 5: Critical Current Density (CCD) Evaluation Experimental steps: The sheets (with or without an interface layer) from Examples 1, 1, 2 and 3 were assembled into symmetrical coin cells with a Li / interface / SE / interface / Li structure in an argon atmosphere glove box.

[0097] The assembled symmetrical battery was placed in a constant temperature environment of 25°C and connected to the battery testing system.

[0098] The battery was subjected to constant current charge-discharge testing, with a capacity of 0.5 mAh / cm³ per half-cycle. 2 Current density from 0.1 mA / cm 2 Initially, the value increases by one every 10 cycles, set sequentially as follows: 0.1, 0.2, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 1.8, 2.0 mA / cm. 2 .

[0099] Record the voltage-time curve for each cycle. When the voltage curve suddenly drops to near 0V or oscillates violently, it is determined that an internal short circuit has occurred in the battery. The current density of the last stable cycle before the battery short circuit is the critical current density at that interface.

[0100] Experimental data: Table 5. Critical Current Density (CCD) and Cycle Life Data for Symmetrical Cells in conclusion: The data in Table 5 clearly show the critical current density (1.8 mA / cm²) that the symmetrical cell of Example 1 can withstand. 2 The result is significantly higher than all comparative examples. This result directly reflects the effectiveness of the present invention in suppressing lithium dendrite growth.

[0101] Comparative Example 1 (without interface layer) at only 0.1 mA / cm 2 The fact that a short circuit occurs at a current density of 0.0 ...

[0102] Comparative Example 2 (Al2O3 layer) improved the CCD to 0.5 mA / cm. 2 This indicates that a dense physical insulating layer can provide limited protection. However, due to the poor lithium affinity of the Al2O3 surface, the uneven distribution of lithium-ion flux is exacerbated at high current densities, causing lithium to preferentially deposit at weak points and eventually penetrate the insulating layer, thus limiting the current density it can withstand.

[0103] The CCD of Comparative Example 3 (pure CuF2 layer) has an A / cm² reading of only 0.3 mA / cm². 2The performance was inferior to that of Comparative Example 2. Combining the conclusions of Test Examples 1 and 3, the failure mechanism lies in the agglomeration of in-situ generated Cu particles, forming electronic pathways. Under high current, this micro-short circuit not only exacerbates interfacial side reactions, but the resulting local Joule heating may also induce the formation of lithium dendrites, leading to battery failure at even lower current densities.

[0104] The interface in Example 1 is able to withstand up to 1.8 mA / cm 2 The high current density is due to its unique interface structure, which effectively regulates lithium deposition behavior. First, the in-situ generated nano-Cu particles, acting as uniformly distributed lithiophilic sites, significantly lower the lithium nucleation energy barrier, guiding lithium ions to deposit uniformly across the entire interface and preventing dendrite "hot spots" caused by current concentration from the outset. Second, the LiF matrix possesses electronic insulation properties, which not only suppresses interfacial side reactions but, more importantly, ensures the uniformity of lithium deposition, preventing uncontrolled dendrite growth caused by Cu particle agglomeration.

Claims

1. A method for improving the interface stability of high-efficiency solid-state batteries, characterized in that, Includes the following steps: S1: Provides sulfide solid electrolyte sheet; S2: A composite precursor layer composed of copper fluoride and lithium fluoride is formed on at least one side surface of the sulfide solid electrolyte sheet by a co-deposition method; S3: Assemble the sulfide solid electrolyte sheet with the composite precursor layer with the lithium metal anode, so that the composite precursor layer comes into contact with the lithium metal anode, thereby generating a composite interface layer containing nano-copper particles and lithium fluoride matrix in situ.

2. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, In step S2, the molar fraction of lithium fluoride in the composite precursor layer is controlled to be between 20 mol% and 60 mol%.

3. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, In step S2, the thickness of the composite precursor layer is controlled to be between 10 nm and 30 nm.

4. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, The sulfide solid electrolyte sheet provided in step S1 is a Li6PS5Cl electrolyte sheet.

5. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, In step S1, the sulfide solid electrolyte sheet is prepared by cold pressing sulfide solid electrolyte powder under a pressure of 400 MPa.

6. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, The co-deposition method in step S2 is magnetron co-sputtering, and it is carried out under an argon atmosphere of 0.5 Pa.

7. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 6, characterized in that, The magnetron co-sputtering is performed by simultaneously activating both copper fluoride and lithium fluoride targets in the sputtering system, and the molar ratio of copper fluoride and lithium fluoride in the composite precursor layer is controlled by adjusting the radio frequency power of each of the copper fluoride and lithium fluoride targets.

8. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 7, characterized in that, To obtain a lithium fluoride molar fraction of 20 mol% to 60 mol%, the radio frequency power of the copper fluoride target is set to 30 W, while the radio frequency power of the lithium fluoride target is set in the range of 45 W to 120 W.

9. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 7, characterized in that, By controlling the co-sputtering deposition time to 4 to 12 minutes, a composite precursor layer thickness of 10 nm to 30 nm can be obtained.

10. The method for improving the interface stability of high-efficiency solid-state batteries according to claim 1, characterized in that, The powder used for the sulfide solid electrolyte sheet is prepared by the following steps: mixing raw materials in a molar ratio of Li2S:P2S5:LiCl=5:1:2 and then mechanically and chemically ball-milling them in a planetary ball mill at a speed of 500 rpm for 12 hours.

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