Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering-based solid-state battery composite interface layer as well as preparation method and application thereof

Abstract

The invention relates to the technical field of energy storage, in particular to a solid-state battery composite interface layer based on Ag-Sn3N4-MgF2 quaternary co-sputtering and a preparation method and application of the solid-state battery composite interface layer. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is a buffer layer deposited on the surface of a solid-state electrolyte through magnetron sputtering, and the solid-state battery composite interface layer is a blended film containing Sn, Ag, Sn3N4 and MgF2. According to the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, in the first charging and discharging process, Sn3N4 reacts with lithium to generate Li3N and LixSn alloy, and MgF2 reacts with lithium to generate LiF and Mg. The invention provides the preparation method of the Ag-Sn-Sn3N4-MgF2 quaternary co-sputtered solid-state battery composite interface layer which is simple and convenient in process and simultaneously realizes low interface impedance, high cycling stability and excellent dendritic crystal inhibition capability.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, its preparation method, and its application. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is a composite interface layer formed on the surface of a solid electrolyte through quaternary co-sputtering, which can be used in all-solid-state lithium metal batteries. Background Technology

[0002] With the rapid development of renewable energy, electric transportation, and smart grids, higher demands are being placed on advanced energy storage systems with high specific energy, high security, and long lifespan. Lithium metal, as an anode material, possesses an extremely high theoretical capacity (3860 mAh g / g). -1 Solid-state batteries, with their lowest electrochemical potential (-3.04V vs. SHE), are key materials for achieving high-energy-density battery systems. While traditional lithium-ion batteries are widely used in consumer electronics and some electric vehicles, their energy density is nearing its theoretical limit, and the use of flammable liquid electrolytes poses potential safety hazards, making it difficult to meet the dual demands of next-generation energy storage technologies in terms of performance and reliability. Therefore, all-solid-state batteries, due to their high safety and high energy density, have become a research hotspot for next-generation energy storage technologies. However, the high interfacial impedance between solid-state electrolytes and electrode materials, and the problem of lithium dendrite growth, severely restrict their commercial application. Solid-state electrolytes (such as LAGP, LATP, and LLZO) have a large interfacial impedance with the lithium metal anode, mainly due to: 1) poor physical contact leading to interfacial resistance; 2) interfacial side reactions generating a high-resistivity interfacial layer; and 3) interfacial failure caused by lithium dendrite growth.

[0003] To address this issue, researchers have proposed various interface modification strategies, including introducing polymer interlayers, inert oxide or monometallic coatings, and in-situ construction of chemically stable interface layers on the solid electrolyte surface. In existing technologies, while single interface modification layers can improve interface performance to some extent, they struggle to simultaneously meet the multiple requirements of low interfacial impedance, high cycle stability, and dendrite suppression. Furthermore, the preparation of multi-component interface layers typically requires complex multi-step processes or atmosphere switching. For example, some techniques require depositing a metal layer in an argon atmosphere and then switching to a nitrogen atmosphere to deposit a nitride layer, a complex process prone to introducing interface contamination. This multi-step process not only increases manufacturing costs but also reduces the reproducibility and stability of the interface. Summary of the Invention

[0004] To address the interface problems between the solid electrolyte and lithium metal anode in existing all-solid-state batteries, this invention provides a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, its preparation method, and applications. The constructed Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering composite interface layer achieves synergistic regulation of interfacial ion / electron transport, thereby improving the critical current density, cycle life, and safety of lithium-ion batteries. Based on magnetron sputtering technology, this invention co-sputters a quaternary nanoscale interface modification layer on the surface of the solid electrolyte. Through an in-situ conversion mechanism, a controllable conversion reaction occurs between the quaternary component and lithium during the first charge-discharge process of the lithium-ion battery, dynamically generating an ideal interface phase. The four components complement each other, achieving synergistic effects, ultimately significantly improving the stability of the electrolyte-electrode interface, effectively reducing interfacial impedance, and thus improving the energy density and cycle life of the lithium-ion battery, endowing it with excellent comprehensive electrochemical performance. In summary, this invention provides a simple process (capable of preparation under a single atmosphere) for preparing a composite interface layer with low interfacial impedance, high cycle stability, and excellent dendrite suppression capability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention protects a solid-state battery composite interface layer (i.e., a composite interface layer or a quaternary nanoscale interface modification layer) based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering. The Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering composite interface layer is a buffer layer deposited on the surface of a solid electrolyte by magnetron sputtering. The magnetron sputtering method involves simultaneously sputtering an Ag target, a Sn target, a Sn3N4 target, and a MgF2 target onto the surface of the solid electrolyte. The obtained solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is a blend film containing Sn, Ag, Sn3N4, and MgF2, with a thickness of 10 nm to 500 nm. The sputtering power of the Sn target is 50 W to 100 W, the Ag target is 100 W to 150 W, the Sn3N4 target is 80 W to 120 W, and the MgF2 target is 120 W to 160 W. During the first charge-discharge process, the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering reacts with lithium to generate Li3N and Li. x Sn alloy, MgF2 reacts with lithium to form LiF and Mg, that is, after the first charge and discharge, the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering contains in-situ generated Li3N, LiF, and Li x Sn alloy and Mg nanoparticles.

[0006] The excessively thin composite interface layer (less than 10 nm) of the Ag-Sn-Sn3N4-MgF2 quaternary co-sputtered solid-state battery can lead to the following problems: 1. Insufficient interface protection: The thin composite interface layer cannot effectively prevent direct contact between the LAGP electrolyte and lithium metal, resulting in intensified interface side reactions. Ge elements in the LAGP solid-state electrolyte will react with lithium to generate an electronically conductive Ge phase, increasing the electrolyte's electronic conductivity and causing continuous self-discharge and capacity decay. 2. Insufficient dendrite suppression: The mechanical strength of the thin composite interface layer is insufficient to suppress lithium dendrite growth. During cycling, lithium dendrites can easily penetrate the composite interface layer, leading to battery short-circuit failure. 3. Poor interface stability: The thin composite interface layer is prone to localized damage during cycling, failing to form a continuous protective layer. This results in a rapid increase in interface impedance, shortened cycle life, and a decrease in first-cycle coulombic efficiency. 4. Uneven Distribution of Functional Components: In the ultrathin film layer, the four components Ag, Sn, Sn3N4, and MgF2 are difficult to form a uniform distribution, easily exhibiting local enrichment or deficiency. This leads to uneven interface performance, insufficient electronic conductivity in some areas, and hindered ion transport in others, resulting in severe overall performance degradation. Excessive thickness (over 500 nm) of the composite interface layer in solid-state batteries based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering can lead to: 1. Significantly increased interface impedance: An excessively thick composite interface layer hinders the rapid transport of lithium ions, resulting in increased interface impedance and severely affecting the battery's rate performance and power density. 2. Reduced critical current density: A thick film layer exacerbates stress concentration at the interface, making it easier for cracks and interface delamination to occur during charge and discharge, severely limiting the battery's high-rate performance. 3. Deteriorated cycle stability: An excessively thick composite interface layer generates greater volumetric stress during cycling, leading to microcracks and contact failure between the solid electrolyte and the composite interface layer. This accelerates interface side reactions and reduces cycle life. 4. Increased process costs: Excessive film thickness will significantly prolong sputtering time, increase target material consumption and equipment energy consumption, and reduce production efficiency. In addition, thick film layers are more prone to stress cracking and peeling, leading to a decrease in product yield.

[0007] Preferably, the thickness of the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is 10nm~100nm.

[0008] Preferably, the solid electrolyte is selected from inorganic solid electrolytes such as LAGP, LATP, and LLZO used in lithium-ion batteries.

[0009] Preferably, in the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, Ag, Sn, Sn3N4, and MgF2 exist in the form of nanoparticles with a particle size of 5nm~20nm. Nanoparticles in the quaternary co-sputtered composite interface layer have the following core advantages: 1. Maximized interface contact area: Nanoparticles have extremely high specific surface area, enabling them to form closer physical contact with the solid electrolyte and lithium metal, significantly reducing interface contact resistance. Simultaneously, the gaps between nanoparticles provide abundant three-dimensional diffusion channels for lithium-ion transport, facilitating the construction of a continuous ion transport network. 2. More complete in-situ conversion reaction: Nanoparticles of Sn3N4 and MgF2 can achieve faster and more complete in-situ conversion reactions during the first charge-discharge process. The small size effect lowers the reaction energy barrier, making Sn3N4 more easily converted into the superionic conductor Li3N and the lithium-loving alloy Li. x Sn and MgF2 are more readily converted into highly stable LiF and metallic Mg, thus forming a uniform and dense SEI protective layer at the interface. 3. Enhanced stress buffering capacity: Nanoparticles can better adapt to volume changes during charging and discharging, releasing stress through interparticle slippage and rearrangement, avoiding cracks and peeling of the interface layer. The plastic deformation capacity of Ag and Sn nanoparticles further enhances the mechanical stability of the composite interface layer, ensuring the integrity of the interface during long-term cycling. 4. More significant functional synergistic effect: Nanoscale Ag particles form a continuous electronic conductive network, homogenizing the interface electric field distribution. Nanoscale Sn particles provide abundant lithiophilic sites, reducing the lithium nucleation overpotential. The in-situ conversion products of nanoscale Sn3N4 and MgF2 particles synergistically construct high-speed ion channels and thermodynamically stable interfaces. 5. Enhanced self-healing ability: Unconverted nano-sized Sn3N4 and MgF2 particles can continuously participate in the interfacial reaction during the cycle, realizing the dynamic self-healing of the composite interfacial layer. The high reactivity of the nanoparticles enables them to respond quickly to interfacial damage, repair microcracks and defects in a timely manner, and ensure that the interfacial layer maintains stability and functionality during long-term cycling.

[0010] This invention also protects a method for preparing a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, comprising the following steps: In an argon atmosphere, a radio frequency magnetron sputtering coating system was used at a base vacuum of 0.1 × 10⁻⁶. -4 Pa ~ 9.9 × 10 -4 Under the conditions of Pa, working gas pressure 0.3Pa~0.6Pa, target distance 8cm~12cm, and room temperature, Ag target, Sn target, Sn3N4 target and MgF2 target are sputtered simultaneously on the surface of solid electrolyte for a sputtering time of 20s~1000s.

[0011] The sputtering power for Sn targets is 50W~100W, for Ag targets it is 100W~150W, for Sn3N4 targets it is 80W~120W, and for MgF2 targets it is 120W~160W. The range of RF sputtering power is closely related to the conductivity of the target material. Specifically, the better the conductivity of the target material, the higher the sputtering power can be set, because charge will not accumulate on the target surface, maintaining a stable plasma discharge. In addition, the melting point, thermal conductivity, and mechanical strength of the target material also affect the sputtering power setting. Targets with high melting points and high thermal conductivity can withstand higher power densities, while brittle ceramic targets require more careful power control to avoid fracture caused by thermal stress.

[0012] Preferably, the power supplies for Ag, Sn, Sn3N4 and MgF2 targets are turned on simultaneously, and co-sputtering is performed in an argon atmosphere for 20s to 200s.

[0013] Preferably, the purity of Ag target, Sn target, Sn3N4 target and MgF2 target is not less than 99.99%.

[0014] This invention also protects the application of a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering in the preparation of lithium-ion batteries.

[0015] When the lithium-ion battery is a solid-state lithium symmetric battery, it is prepared according to the following steps: Polished lithium metal sheets are placed on both sides of a solid electrolyte substrate with a composite interface layer deposited on both sides. The substrate is heated at 150°C for 1 hour to induce an interfacial reaction between lithium and the composite interface layer. After natural cooling to room temperature, the battery is installed in a standard CR2032 coin cell case, thus completing the assembly of the solid-state lithium symmetric battery.

[0016] When the lithium-ion battery is a solid-state lithium metal battery, it consists of a positive electrode, a solid electrolyte, a negative electrode, and a small amount of liquid electrolyte. The positive electrode is an aluminum foil current collector loaded with NCM811 active material, the negative electrode is a lithium metal sheet, and the electrolyte is a solution of lithium hexafluorophosphate (LiPF6) in a mixed solvent of dimethyl carbonate (DMC) and diethyl carbonate (DEC). The solid electrolyte uses a solid electrolyte substrate with a deposited composite interface layer, with the side containing the composite interface layer facing the lithium metal negative electrode to enhance interfacial wettability and ion conduction efficiency, thereby improving the cycle stability and interfacial compatibility of the lithium-ion battery.

[0017] Preferably, the preparation method of the positive electrode includes the following steps: adding the positive electrode active material NCM811, the conductive agent Super-P, and the binder polyvinylidene fluoride (PVDF) to the solvent N-methylpyrrolidone (NMP) in a predetermined ratio, stirring and dispersing evenly to obtain a uniform mixed slurry; subsequently, the obtained mixed slurry is ball-milled to form a stable NCM811 positive electrode slurry. The NCM811 positive electrode slurry is uniformly coated on the surface of an aluminum foil current collector, and then vacuum dried to obtain a dense and uniform positive electrode sheet for use in the assembly of solid-state lithium metal batteries.

[0018] Preferably, the NCM811 positive electrode slurry is ball-milled during the preparation process for 1.5 hours; the NCM811 positive electrode slurry coated on the aluminum foil is vacuum-dried at 100°C for 24 hours to obtain a uniform, dense and firmly adhered positive electrode sheet.

[0019] Preferably, the concentration of lithium hexafluorophosphate (LiPF6) in the liquid electrolyte is 1 mol / L to ensure good ionic conductivity and electrochemical stability.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention discloses a solid electrolyte with a quaternary nanoscale interface modification layer on its surface. The modification layer consists of silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) co-deposited on one side of the solid electrolyte surface, forming a continuous and uniform nanocomposite thin layer. Metallic silver exhibits excellent electronic conductivity and good wettability to lithium metal, and can form a stable Ag-Li alloy with lithium, thereby significantly reducing the solid electrolyte / lithium interface resistance and improving the interface electrochemical stability. Metallic tin can form various reversible lithium compounds with lithium, and its excellent flexibility helps alleviate the volume changes and mechanical stress caused by lithium metal deposition and stripping at the interface, thereby enhancing interface contact stability and improving cycle performance. Tin nitride and magnesium fluoride undergo in-situ conversion reactions during the first charge-discharge process, generating Li3N (a superionic conductor) and LiF (a stable SEI component), respectively. Li3N has a room temperature ionic conductivity as high as 10⁻⁶. -3 S / cm provides a high-speed channel for lithium-ion transport; LiF has extremely high thermodynamic stability and electronic insulation, which can effectively suppress lithium dendrite growth. This in-situ conversion mechanism realizes the dynamic construction and optimization of the interface layer.

[0021] Ag provides an electronically conductive network, Sn provides lithiophilic sites, Sn3N4 provides high-speed ion channels, and MgF2 provides mechanical strength and chemical stability; their synergistic effect significantly reduces interfacial impedance. Ag nanoparticles form a continuous electronically conductive network, homogenizing the interfacial electric field distribution; Sn nanoparticles provide abundant lithiophilic sites, reducing the lithium nucleation overpotential; Li3N converted from Sn3N4 constructs high-speed ion channels; and LiF converted from MgF2 provides mechanical barriers and chemical protection. During cycling, unconverted Sn3N4 and MgF2 can continue to transform, achieving self-repair and dynamic optimization of the interfacial layer. This structurally adaptive mechanism can adapt to volume changes and interfacial evolution during cycling, ensuring the long-term stability of the interfacial layer.

[0022] The introduction of the aforementioned quaternary nanoscale interface modification layer effectively optimizes the interfacial compatibility between the solid electrolyte and lithium metal, improves interfacial ion transport efficiency, and suppresses lithium dendrite growth to a certain extent. Furthermore, this quaternary nanoscale interface modification layer allows for controllable composition and structure by adjusting the target sputtering power, sputtering time, and film thickness, thus providing a highly operable and reproducible technical solution for preparing high-performance solid-state lithium metal batteries.

[0023] 2. Compared to existing technologies, based on thermodynamic and kinetic principles, this invention achieves uniform and controllable lithium deposition on the surface of a solid electrolyte with a quaternary nanoscale interface modification layer by co-sputtering tin (Sn), silver (Ag), tin nitride (Sn3N4), and magnesium fluoride (MgF2) onto the solid electrolyte surface to form a buffer layer. This buffer layer forms continuous electron and ion conduction channels at the interface, significantly improving the physical contact between the solid electrolyte and the lithium metal anode, reducing interfacial impedance, and suppressing irreversible side reactions between lithium and the solid electrolyte, thereby enhancing interfacial chemical stability. In summary, this invention provides a solid-state lithium metal battery technology solution that regulates interfacial properties and lithium deposition behavior through a quaternary nanoscale Sn-Ag-Sn3N4-MgF2 composite modification layer, achieving multiple optimizations in interfacial stability, cycle performance, and safety, and providing an effective solution for the design and application of high-performance solid-state lithium-ion batteries. Attached Figure Description

[0024] Figure 1 The lithium-ion symmetric battery assembled using a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 and a bare solid electrolyte substrate was tested at 30°C and 0.1 mA cm⁻¹. -2 Constant current cycling curve at current density.

[0025] Figure 2 The graph shows the cycling performance of the NCM811 all-solid-state lithium battery assembled on a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 at 30°C and 0.2C rate.

[0026] Figure 3 The images show SEM images of an NCM811 all-solid-state lithium battery assembled on a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 after 24 hours of cycling. (a) is an SEM image of the cross-section of the quaternary nanoscale interface modification layer, and (b) is an SEM image of the surface of the quaternary nanoscale interface modification layer. Detailed Implementation

[0027] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0028] This invention discloses a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering and its preparation method. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is obtained by co-depositing silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) on the surface of a solid electrolyte substrate.

[0029] In this invention, a quaternary nanoscale interface modification layer formed on the surface of a solid electrolyte by silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) acts as a buffer layer. Its advantages are multifaceted, specifically: First, the quaternary co-sputtering technology uses a single argon atmosphere, allowing simultaneous sputtering of four targets (Ag, Sn, Sn3N4, and MgF2) without atmosphere switching (such as switching from argon to nitrogen or reactive gases) or multi-step deposition processes. This design simplifies complex multi-step interface modification into a single step, significantly reducing equipment configuration requirements, process control difficulty, and manufacturing costs, while improving process repeatability and interface quality consistency, thus facilitating industrial application. Second, intelligent self-adaptation of the composite interface layer is achieved through a dual mechanism of "in-situ conversion + stable protection." During the first charge-discharge process, Sn3N4 reacts with lithium to generate the superionic conductor Li3N (room temperature ionic conductivity >10⁻³ S / cm) and the lithium-loving alloy Li. xSn and MgF2 are transformed into highly stable LiF and metallic Mg. This in-situ transformation dynamically constructs high-speed ion channels and a thermodynamically stable interface. Ag and Sn nanoparticles maintain a stable structure. Ag forms a continuous electronic conductivity network to homogenize the interfacial electric field, while Sn provides abundant lithiophilic sites to reduce the lithium nucleation overpotential. Together, they construct a stable electron transport and lithiophilic interface. Simultaneously, the four components achieve synergistic effects through functional complementarity: Ag provides electronic conductivity, Sn provides lithiophilicity and volume buffering, Sn3N4 in-situ generates Li3N to provide ultra-high-speed ion transport, and MgF2 in-situ generates LiF to provide mechanical strength and chemical stability. This synergistic effect enables the composite interface layer to simultaneously possess low interfacial impedance, high critical current density, excellent dendrite suppression capability, and long-term cycling stability. Finally, during cycling, unconverted Sn3N4 and MgF2 can continue to transform, achieving self-repair and dynamic optimization of the composite interface layer. This structural adaptive mechanism can adapt to volume changes and interface evolution during cycling. x The reversible reaction of Sn alloy and the high mechanical strength of LiF work synergistically to ensure the integrity and stability of the composite interface layer during long-term cycling. In summary, the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, through the synergistic effects of physical buffering, chemical stabilization, deposition regulation, and electronic conduction, not only optimizes the interface environment between the solid electrolyte and lithium metal, but also significantly improves the cycle stability, coulombic efficiency, and safety of solid-state lithium metal batteries, while enhancing the mechanical and chemical durability of the interface during charge and discharge processes.

[0030] The solid electrolyte substrate used in this invention is a NASICON-type Li 1.4 Al 0.4 Ge 1.6 (PO4)3, the electrolyte powder used is a commercially available product of Hefei Kejing Company.

[0031] The lithium battery constructed based on the quaternary nanoscale interface modification layer comprises a positive electrode, a negative electrode, and a small amount of liquid electrolyte. The positive electrode is an aluminum foil current collector loaded with NCM811 active material, the negative electrode is a polished lithium metal sheet, and the liquid electrolyte is a mixed solution of dimethyl carbonate (DMC) and diethyl carbonate (DEC) containing lithium hexafluorophosphate (LiPF6). Notably, the quaternary co-sputtered solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 attached to the solid electrolyte substrate faces the lithium metal negative electrode, thereby optimizing interfacial contact, improving lithium-ion transport efficiency, alleviating local volume expansion and mechanical stress caused by lithium deposition, suppressing irreversible side reactions, enhancing interfacial chemical stability, guiding uniform lithium deposition, and improving the cycle performance and safety of the lithium battery.

[0032] The specific preparation method of the above-mentioned solid electrolyte and lithium battery includes the following steps: Step 1, Preparation of solid electrolyte substrate: Weigh 10g of Li 1.4 Al 0.4 Ge 1.6 (PO4)3 powder was mixed with acetone as a dispersant and placed in a zirconia ball mill jar with a ball-to-powder ratio of 10:1. The grinding balls were also made of zirconia. The mixture was ball-milled at 500 rpm for 1.5 hours in a planetary ball mill to obtain a uniformly dispersed slurry. After ball milling, the slurry was passed through a 250-mesh sieve and then allowed to dry in air. 200 mg of the dried powder was weighed out and pressed into tablets under 120 MPa pressure. These tablets were then sintered in a muffle furnace at 850°C for 6 hours at a heating rate of 2°C / min. After sintering and natural cooling, both sides of the solid electrolyte tablets were polished to obtain the product with the chemical formula Li. 1.4 Al 0.4 Ge 1.6 (PO4)3 NASICON type solid electrolyte substrate.

[0033] Step 2: Preparation of the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering: The solid electrolyte substrate obtained in Step 1 is fixed in the magnetron sputtering cavity and covered with a baffle. The appropriate metal target is selected according to the predetermined deposition elements. The target surface is first polished with sandpaper, then cleaned with acetone and dried to remove impurities and ensure the purity of subsequent deposition (target purity ≥ 99.99%). Before the formal sputtering, the target is pre-sputtered for 10 minutes to remove surface oxides and other impurities. Then, the baffle is opened and RF magnetron sputtering is performed. The process parameters are set as follows: base vacuum 0.1 × 10⁻⁶. -4 Pa ~ 9.9 × 10 -4 The sputtering parameters are as follows: working pressure 0.3Pa~0.6Pa, target distance 8cm~12cm, sputtering temperature 20℃~30℃, sample disk rotation speed 15rpm, and sputtering time 30s~1800s; sputtering power for Sn target is 50W~100W, for Ag target is 100W~150W, for Sn3N4 target is 80W~120W, and for MgF2 target is 120W~160W. The optimal sputtering power is selected based on the characteristics of different target materials to obtain the best deposition effect. Tin has a lower melting point, so the sputtering power should be correspondingly lower. After sputtering, a uniformly adhered quaternary nanoscale interface modification layer is formed on the surface of the solid electrolyte substrate. The thickness of the quaternary nanoscale interface modification layer formed by tin (Sn), silver (Ag), tin nitride (Sn3N4), and magnesium fluoride (MgF2) is 10nm~500nm.

[0034] Step 3: Preparation of the NCM811 cathode: NCM811, Super-P, and polyvinylidene fluoride (PVDF) were weighed at a weight ratio of 8:1:1 and dispersed in N-methylpyrrolidone (NMP) solvent. The mixture was stirred thoroughly to obtain a homogeneous mixture. Subsequently, the mixture was ball-milled for 1.5 hours using the same method as in Step 1 to ensure thorough dispersion of the components and the formation of a homogeneous slurry, i.e., the NCM811 cathode slurry. The NCM811 cathode slurry was uniformly drop-coated onto the surface of an aluminum foil current collector and smoothed using a scraper to form a continuous film. Finally, the coated aluminum foil was placed in a vacuum drying oven and dried at 100°C for 24 hours to completely solidify the NCM811 cathode slurry, thus obtaining a stable NCM811 cathode.

[0035] Step 4: Preparation of liquid electrolyte: Mix equal volumes of dimethyl carbonate (DMC) and diethyl carbonate (DEC) to obtain mixed solution A; dissolve lithium hexafluorophosphate (LiPF6) in mixed solution A and adjust the concentration to 1 mol / L to obtain the desired electrolyte solution, i.e., liquid electrolyte.

[0036] Step 5: Assembly of the all-solid-state lithium battery: The polished lithium metal anode, the solid electrolyte substrate with a deposited quaternary nanoscale interface modification layer, and the NCM811 cathode are sequentially assembled into a standard CR2032 coin cell case. 3μL~8μL of liquid electrolyte is added at the interface between the cathode and the solid electrolyte to improve interfacial ion transport. During assembly, the side of the solid electrolyte substrate with the quaternary nanoscale interface modification layer faces the lithium metal anode, thereby optimizing interfacial contact, alleviating lithium deposition stress, and guiding uniform lithium deposition. After assembly, a stable NCM811 all-solid-state lithium battery is obtained.

[0037] In the above operation, steps 4 and 5 must be carried out in a glove box with argon protection, and the oxygen and moisture content in the protective atmosphere must be controlled below 0.01 ppm.

[0038] The prepared all-solid-state lithium battery was subjected to charge-discharge performance testing at 30°C with a cycle rate of 0.2C and a voltage range of 3.0V~4.5V for each cycle.

[0039] The technical solution of the present invention will be further studied using the following embodiments, as detailed below: Example 1 The preparation of a solid electrolyte substrate with a deposited quaternary nanoscale interface modification layer includes the following steps: The pre-prepared NASICON-type solid electrolyte substrate was fixed in the magnetron sputtering chamber and covered with a baffle. Silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) targets with a purity of 99.99% were polished with 800-grit sandpaper, cleaned with acetone, and dried before being pre-sputtered for 10 minutes to remove oxides and impurities from the target surfaces, ensuring sufficient purity for the subsequent deposition of the quaternary nanoscale interface modification layer on the NASICON-type solid electrolyte substrate surface. The process parameters for RF magnetron sputtering were set as follows: base vacuum 5.0 × 10⁻⁶. -4 The process involved introducing 99.99% pure argon gas at a working pressure of 0.45 Pa, a target distance of 10 cm, and sputtering powers of 90 W for tin, 120 W for silver, 100 W for tin nitride, and 150 W for magnesium fluoride. The sputtering temperature was 25 °C, and the sputtering time was 120 s. The study showed that the deposition rate was 28 nm / min, resulting in a solid electrolyte substrate with a quaternary nanoscale interface modification layer, which had a thickness of 56 nm.

[0040] Example 2 The preparation of a solid electrolyte substrate with a deposited quaternary nanoscale interface modification layer includes the following steps: The pre-prepared NASICON-type solid electrolyte substrate was fixed in the magnetron sputtering chamber and covered with a baffle. Silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) targets with a purity of 99.99% were polished with 800-grit sandpaper, cleaned with acetone, and dried before being pre-sputtered for 10 minutes to remove oxides and impurities from the target surfaces, ensuring sufficient purity for the subsequent deposition of the quaternary nanoscale interface modification layer on the NASICON-type solid electrolyte substrate surface. The process parameters for RF magnetron sputtering were set as follows: base vacuum 9.9 × 10⁻⁶. -4 Argon gas with a purity of 99.99% was introduced at a working pressure of 0.6 Pa, a target distance of 8 cm, a sputtering power of 50 W for tin, 100 W for silver, 80 W for tin nitride, and 120 W for magnesium fluoride, a sputtering temperature of 25 °C, and a sputtering time of 1000 s, to obtain a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited.

[0041] Example 3 The preparation of a solid electrolyte substrate with a deposited quaternary nanoscale interface modification layer includes the following steps: The pre-prepared NASICON-type solid electrolyte substrate was fixed in the magnetron sputtering chamber and covered with a baffle. Silver (Ag), tin (Sn), tin nitride (Sn3N4), and magnesium fluoride (MgF2) targets with a purity of 99.99% were polished with 800-grit sandpaper, cleaned with acetone, and dried before being pre-sputtered for 10 minutes to remove oxides and impurities from the target surfaces, ensuring sufficient purity for the subsequent deposition of the quaternary nanoscale interface modification layer on the NASICON-type solid electrolyte substrate surface. The process parameters for RF magnetron sputtering were set as follows: base vacuum 0.1 × 10⁻⁶. -4 Argon gas with a purity of 99.99% was introduced at a working pressure of 0.3 Pa, a target distance of 12 cm, a sputtering power of 100 W for tin, 150 W for silver, 120 W for tin nitride, and 160 W for magnesium fluoride, a sputtering temperature of 25 °C, and a sputtering time of 20 s, to obtain a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited.

[0042] In Examples 1 to 3 of this invention, composite interface layers with low interfacial impedance, high cycling stability, and excellent dendrite suppression were prepared. The composite interface layer of Example 1 is used as an example for further study, with a bare solid electrolyte substrate (i.e., a bare solid electrolyte substrate) without a deposited quaternary nanoscale interface modification layer serving as a control group. Specific research methods and results are shown below: The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering from Example 1 was applied to an NCM811 all-solid-state battery. The NASICON-type solid electrolyte substrate was prepared using a conventional solid-state reaction method, as described above. Subsequently, the NCM811 cathode and liquid electrolyte were prepared using the above method, and then the NCM811 all-solid-state lithium battery was assembled using the above method. In the NCM811 all-solid-state lithium battery, the amount of liquid electrolyte added was 3 μL.

[0043] Following the steps above, the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering in Example 1 was applied to a solid-state lithium symmetric battery.

[0044] A lithium-ion symmetric battery assembled using a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 was tested at 30°C and 0.1 mA cm⁻¹. -2 The potential under current density remained stable at around 200mV throughout the entire test cycle (e.g. Figure 1 As shown in the figure, it exhibits excellent electrochemical stability. In contrast, the potential of the bare solid electrolyte substrate control group fluctuated significantly during the test and remained in the negative potential range of -1V to -2V for a long time. This indicates that the interfacial impedance was significantly reduced and the interfacial ion and electron transport efficiency was improved after depositing the quaternary nanoscale interface modification layer.

[0045] The NCM811 / Li all-solid-state lithium battery assembled using a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 underwent cycling tests at 30°C and 0.2C rate (e.g., Figure 2 As shown in the figure, the battery capacity remains stable as the number of cycles increases, and even after 60 cycles, the battery capacity and coulombic efficiency remain at a high level.

[0046] The NCM811 / Li all-solid-state lithium battery assembled using a solid electrolyte substrate with a quaternary nanoscale interface modification layer deposited in Example 1 was cycled at 0.2C for 24 hours, and the results are as follows: Figure 3 As shown. Figure 3 The results in Figure (a) show that the quaternary nanoscale interface modification layer has an inhibitory effect on the penetration of lithium dendrites, effectively suppresses interface side reactions, improves battery performance, and enhances the cycle stability of the battery. Figure 3 The results in Figure (b) show that the lithium dendrites grow laterally on the surface and do not penetrate the quaternary nanoscale interface modification layer and enter the solid electrolyte.

[0047] In this invention, the core mechanism for improving solid-state battery performance lies in the synergistic effect of a dual mechanism of "in-situ conversion + stability protection" achieved through a composite interface layer constructed by quaternary co-sputtering. Specifically, Sn3N4 undergoes a conversion reaction with lithium during the first charge-discharge process, generating the superionic conductor Li3N (ionic conductivity > 10). -3 (S / cm) and lithium-loving Li x Sn alloys construct high-speed ion transport channels, while MgF2 is converted into highly stable LiF and metallic Mg, forming a thermodynamically stable interface. Meanwhile, Ag and Sn nanoparticles provide a continuous electronic conductivity network and abundant lithiophilic sites, respectively, homogenizing the interfacial electric field distribution and reducing the lithium nucleation overpotential. The synergistic effect of the four components reduces interfacial impedance and increases critical current density, resulting in a comprehensive improvement in battery performance.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, characterized in that, The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is a buffer layer deposited on the surface of a solid electrolyte by magnetron sputtering. The magnetron sputtering method is to simultaneously sputter Ag target, Sn target, Sn3N4 target and MgF2 target on the surface of the solid electrolyte. The resulting solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is a blend film containing Sn, Ag, Sn3N4 and MgF2 with a thickness of 10nm~500nm. The sputtering power of the Sn target is 50W~100W, the sputtering power of the Ag target is 100W~150W, the sputtering power of the Sn3N4 target is 80W~120W, and the sputtering power of the MgF2 target is 120W~160W.

2. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 1, characterized in that, The thickness of the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is 10nm~100nm.

3. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 1, characterized in that, The solid electrolyte is selected from inorganic solid electrolytes used in lithium-ion batteries.

4. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 3, characterized in that, The solid electrolyte is selected from LAGP, LATP or LLZO.

5. The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 1, characterized in that, In the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering, Ag, Sn, Sn3N4 and MgF2 exist in the form of nanoparticles with a particle size of 5nm~20nm.

6. A method for preparing a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering as described in claim 1, characterized in that, Includes the following steps: In an argon atmosphere, using a radio frequency magnetron sputtering film coating system, in the base vacuum degree 0.1×10 -4 Pa~9.9×10 -4 Pa, working pressure 0.3Pa~0.6Pa, target distance 8cm~12cm, room temperature conditions, on the surface of solid electrolyte, sputtering Ag target, Sn target, Sn3N4 target and MgF2 target at the same time, the sputtering time is 20s~1000s; The sputtering power of the Sn target is 50W~100W, the sputtering power of the Ag target is 100W~150W, the sputtering power of the Sn3N4 target is 80W~120W, and the sputtering power of the MgF2 target is 120W~160W.

7. The method for preparing a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 6, characterized in that, Sputtering time is 20s~200s.

8. The method for preparing a solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering according to claim 6, characterized in that, The purity of Ag target, Sn target, Sn3N4 target and MgF2 target is not less than 99.99%.

9. The application of the solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering as described in claim 1 in the preparation of lithium-ion batteries.

10. The application according to claim 9, characterized in that, The solid-state battery composite interface layer based on Ag-Sn-Sn3N4-MgF2 quaternary co-sputtering is bonded to the lithium sheet.

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