Composite modification film, lithium metal negative electrode and preparation method of lithium metal negative electrode

Abstract

The invention discloses a composite modification film, a lithium metal negative electrode and a preparation method of the lithium metal negative electrode. The composite modified film comprises an organic polymer solid electrolyte, an inorganic solid electrolyte and a film-forming agent, and the mass ratio of the organic polymer solid electrolyte to the inorganic solid electrolyte to the film-forming agent is (10%-35%): (10%-35%): (30%-80%). The composite modified film effectively buffers cyclic stress, prevents early mechanical failure of the protective layer, and realizes mechanical durability of the interface protective layer; the immobilized film-forming agent can be slowly released, so that the continuous and stable repair of SEI is realized, the dynamic repair capability of the whole life cycle is provided, and the efficient cycle life of the battery is greatly prolonged; and the electrolyte does not need to depend on a high-concentration liquid additive, dramatic change of electrolyte components in circulation is avoided, the overall chemical stability of the battery is improved, and the stability of an electrolyte system is guaranteed.

Description

Technical Field

[0001] This application belongs to the field of lithium metal anode material technology, specifically relating to a composite modified film and a lithium metal anode and its preparation method. Background Technology

[0002] Lithium metal is known for its extremely high theoretical specific capacity (3860 mAh g). -1 With its extremely negative electrochemical potential (-3.04 V vs. SHE), lithium metal anodes are considered ideal anode materials for next-generation high-energy-density batteries. However, lithium metal anodes face significant challenges during cycling: firstly, uneven lithium deposition / stripping can form lithium dendrites, which may puncture the separator, causing a short circuit and posing a serious safety hazard; secondly, continuous side reactions between lithium metal and organic electrolytes lead to electrolyte consumption and loss of active lithium, resulting in a continuous increase in interfacial impedance, rapid capacity decay, and shortened cycle life.

[0003] To address these challenges, current research focuses on strategies such as interface engineering (e.g., constructing artificial modification layers on the surface of lithium metal anodes) and electrolyte optimization (developing novel lithium salts, solvents, and additives). These strategies aim to stabilize the electrode / electrolyte interface and guide uniform, dendrite-free lithium deposition, thereby extending the cycle life of the battery.

[0004] Interface engineering primarily involves coating the surface of a lithium metal anode with a polymer (such as PEO, PVDF) or inorganic solid electrolyte (such as LLZO, LATP) film to physically isolate the electrolyte and homogenize the lithium-ion flow. However, such rigid or single-component coatings struggle to adapt to the massive volumetric strain generated during lithium deposition / stripping, making them prone to cracking or peeling. This leads to increased side reactions between the lithium metal and the electrolyte, resulting in a failure of the protective function.

[0005] Electrolyte optimization involves developing and using novel lithium salts (such as lithium bis(fluorosulfonyl)imide (LiFSI)) or novel solvents (such as fluorinated solvents and ether solvents), as well as constructing high-concentration or locally high-concentration electrolyte systems. These methods aim to indirectly improve interfacial behavior by adjusting the lithium-ion solvation structure and enhancing the overall electrochemical stability of the electrolyte. However, such strategies have inherent limitations: First, their effect is essentially "bulk modification," and the optimization effect depends on changes to the entire electrolyte system, failing to construct a physical protective layer with specific mechanical properties locally at the electrode interface, thus making it difficult to effectively suppress lithium dendrite penetration. Second, macroscopic adjustments to the electrolyte composition often come with trade-offs in other properties, such as high viscosity, low wettability, and high cost associated with high-concentration systems. More importantly, these methods cannot respond to the microscopic demands of dynamic interfacial changes during battery cycling, especially the large volumetric strain caused by lithium deposition / stripping, resulting in insufficient long-term interfacial mechanical integrity.

[0006] Existing technologies have failed to fundamentally solve the problem of interface stability of lithium metal anodes under long-term, dynamic operation. Summary of the Invention

[0007] The purpose of this application is to provide a composite modified film and a lithium metal anode and a method for preparing the same.

[0008] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a composite modified membrane, which comprises an organic polymer solid electrolyte, an inorganic solid electrolyte, and a film-forming agent, wherein the mass ratio of the organic polymer solid electrolyte, the inorganic solid electrolyte, and the film-forming agent is (10%-35%):(10%-35%):(30%-80%).

[0009] Based on in-depth research into existing technologies, the inventors discovered that current lithium metal anode protection strategies have failed to reconcile the fundamental contradiction between the immediate mechanical stability of the interface layer and its long-term chemical repairability.

[0010] This application abandons the single approach of "rigid coating" or "liquid consumables" and proposes a novel solid-supported slow-release composite modification film. A flexible organic polymer serves as the continuous phase, encapsulating and bonding rigid inorganic particles to form a composite substrate that combines rigidity and flexibility. This structure can adapt to volumetric strain through the relaxation of polymer segments, while utilizing high-modulus inorganic particles to resist lithium dendrite penetration, physically ensuring the structural integrity of the protective layer during cycling. The film-forming agent is pre-composite with the organic polymer solid electrolyte and the inorganic solid electrolyte and is "stored" in the aforementioned solid composite matrix. During cycling, it can be slowly released to the lithium metal interface in a controllable manner, undergoing a reduction reaction on the electrode surface to generate inorganic lithium compounds. These compounds then combine in situ with the modification film to form a uniform and dense SEI film, effectively reducing the problem of excessive local current density, providing a more uniform deposition environment for lithium ions, reducing the probability of lithium dendrite formation, and improving the safety performance of lithium metal batteries.

[0011] Although some electrolytes also contain film-forming additives (such as FEC, VC, and LiDFOB), these additives are preferentially reduced during the first charge to form an initial SEI film, which can suppress dendrites and reduce interfacial impedance to a certain extent. However, these film-forming additives are continuously consumed in subsequent cycles as they participate in the repair of the SEI. Their concentration decreases with each cycle until they are exhausted, and they cannot improve the performance of the lithium metal anode in a long-term and stable manner.

[0012] In this application, the film-forming agent in the modified film can be continuously released throughout the entire cycle life, continuously participating in the generation and repair of SEI, realizing the "immobilization" and "long-lasting" of the repair function. It can also be released into the electrolyte for a long time, avoiding the problem of additives in the electrolyte becoming ineffective due to depletion. At the same time, it maintains the stability of the bulk electrolyte composition, ensures the stability of the electrolyte, and allows lithium to be uniformly deposited on the negative electrode surface, thereby improving the cycle life of lithium metal batteries.

[0013] Through the synergistic effect of organic polymer solid electrolyte, inorganic solid electrolyte, and film-forming agent, this application not only avoids the failure problem of single-component modification layer under mechanical stress, but also overcomes the defects of easy depletion and unsustainable function of additives in electrolyte. It provides an interface protection layer for lithium metal anode with mechanical robustness, high ion conductivity and continuous self-healing ability, which significantly improves the cycle life and safety of battery.

[0014] Preferably, the organic polymer solid electrolyte comprises at least one of polyvinylidene fluoride (PVDF), polyethyleneimine (PEI), polyethylene oxide (PEO), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polypropylene carbonate (PPC), polyvinyl chloride (PVC), and polysiloxane (PSE).

[0015] Preferably, the inorganic solid electrolyte comprises perovskite-type electrolytes such as Li. 0.33 La 0.56 TiO3 (LLTO), NASICON type such as Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP), LISICON type such as Li2Zr2SiO7, garnet type such as Li7La3Zr2O 12 At least one of (LLZO).

[0016] Preferably, the film-forming agent comprises at least one of triethanolamine borate (TEB), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium fluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), lithium nitrate (LiNO3), and lithium phosphate (Li3PO4).

[0017] Preferably, the D50 (i.e., volume median diameter Dv50) of the inorganic solid electrolyte is 0.1-5 μm.

[0018] Secondly, this application provides a lithium metal anode, comprising a lithium metal anode body and the aforementioned composite modification film, wherein the composite modification film is coated on the surface of the lithium metal anode body.

[0019] Preferably, the thickness of the composite modified film is 0.5-5 μm.

[0020] Thirdly, this application provides a method for preparing a lithium metal anode, comprising the following steps: S1. Add the organic polymer solid electrolyte, the inorganic solid electrolyte, and the film-forming agent to the solvent, stir and disperse to obtain a slurry; S2. Apply the slurry onto the substrate and dry it to obtain the coating layer; S3. The coating layer is transferred to the surface of the lithium metal anode body to obtain a lithium metal anode containing a composite modification film.

[0021] Preferably, in step S1, the solvent comprises at least one of acetonitrile, ethyl acetate, ethylene carbonate, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and acetone.

[0022] Preferably, in step S1, the stirring speed is 500-2000 rpm and the stirring time is 2-12 h.

[0023] Preferably, in step S1, the solid content of the slurry is 10%-50% (by mass), and the viscosity is 1000-4000 Pa·s.

[0024] Preferably, in step S2, the drying temperature is 40-60℃, the time is 10-30 min, and the air flow rate is 2-3 m / s.

[0025] Preferably, in step S2, the thickness of the coating layer is 1-10 μm.

[0026] Preferably, the transfer is achieved by hot rolling, with a rolling pressure of 0.1-100 MPa and a temperature of 25-100℃.

[0027] Compared with the prior art, the beneficial effects of this application are as follows: (1) The film-forming agent in the composite modified film of this application undergoes a reduction reaction on the electrode surface to generate inorganic lithium compounds, and then combines with the modified film in situ to form a uniform and dense SEI film. The SEI film formed in situ has excellent mechanical strength, flexibility, ionic conductivity and electronic insulation, which can effectively reduce the problem of excessive local current density and provide a more uniform deposition environment for lithium ions. It reduces the probability of lithium dendrite formation, inhibits lithium dendrites from piercing the battery separator and causing internal short circuits in the battery, and greatly improves the safety performance of lithium metal batteries. Furthermore, throughout the entire cycle life, the film-forming agent in the modified film can be continuously released and dynamically repaired, and can also be released into the electrolyte to prevent the electrolyte composition from changing, ensure the stability of the electrolyte, and make lithium uniformly deposited on the negative electrode surface, thereby improving the cycle life of lithium metal batteries.

[0028] (2) The composite modified film of this application effectively buffers cyclic stress, prevents early mechanical failure of the protective layer, achieves mechanical durability of the interface protective layer, and improves the continuous side reaction between lithium and electrolyte. In particular, the introduction of inorganic solid electrolyte as a key functional component into the composite system composed of organic polymer and film-forming agent significantly improves the mechanical modulus of the composite film, thereby physically inhibiting the penetration of lithium dendrites. Its high intrinsic lithium-ion conductivity optimizes the ion transport path in the film and promotes the uniform deposition of lithium ions. In addition, its stable rigid structure provides a carrier for the film-forming agent for immobilization and slow release, enabling the interface repair process to proceed continuously and controllably. The organic polymer solid electrolyte, inorganic solid electrolyte and film-forming agent work synergistically to achieve a unity of high mechanical stability, high ion conductivity and long-term dynamic repair. Attached Figure Description

[0029] Figure 1 This is an SEM image (magnification: 3k) of the composite modified film prepared in Example 1 of this application. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0031] The technical problem this application aims to solve is that current lithium metal anode protection strategies cannot simultaneously address both the instantaneous mechanical strength of the interface and the continuous self-healing capability throughout the entire lifecycle.

[0032] In view of this, in a first aspect, this application provides a composite modified film comprising an organic polymer solid electrolyte, an inorganic solid electrolyte, and a film-forming agent, wherein the mass ratio of the organic polymer solid electrolyte, the inorganic solid electrolyte, and the film-forming agent is (10%-35%):(10%-35%):(30%-80%). The film-forming agent undergoes a reduction reaction on the electrode surface to generate an inorganic lithium compound, which then combines in situ with the modified film to form a uniform and dense SEI film. This reduces the negative electrode interface impedance of the lithium metal battery, effectively reduces the problem of excessive local current density, provides a more uniform deposition environment for lithium ions, reduces the probability of lithium dendrite formation, and does not reduce the coulombic efficiency of the lithium metal battery. It also improves the migration ability of lithium ions on the negative electrode surface, the safety performance of the lithium metal battery, and its cycle life. Furthermore, the film-forming agent in the modified film can be continuously released slowly throughout the entire cycle life, without changing the electrolyte composition, ensuring electrolyte stability, and allowing lithium to be uniformly deposited on the negative electrode surface, thereby improving the cycle life of the lithium metal battery. Specifically, the mass ratio of organic polymer solid electrolyte, inorganic solid electrolyte, and film-forming agent can be, but is not limited to, 10%:10%:80%, 35%:35%:30%, 20%:20%:60%, or 25%:25%:50%, etc.

[0033] In some embodiments, the organic polymer solid electrolyte comprises at least one of polyvinylidene fluoride (PVDF), polyethyleneimine (PEI), polyethylene oxide (PEO), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polypropylene carbonate (PPC), polyvinyl chloride (PVC), and polysiloxane (PSE).

[0034] In some embodiments, the inorganic solid electrolyte comprises perovskite-type electrolytes such as Li. 0.33 La 0.56 TiO3 (LLTO), NASICON type such as Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP), LISICON type such as Li2Zr2SiO7, garnet type such as Li7La3Zr2O 12 At least one of (LLZO).

[0035] In some embodiments, the film-forming agent comprises at least one of triethanolamine borate (TEB), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium fluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), lithium nitrate (LiNO3), and lithium phosphate (Li3PO4).

[0036] In some embodiments, the D50 (i.e., volume median diameter Dv50) of the inorganic solid electrolyte is 0.1-5 μm. A suitable D50 ensures that the inorganic particles can be uniformly dispersed in the polymer substrate, synergistically enhancing the mechanical strength of the film to physically inhibit lithium dendrite penetration, optimizing lithium-ion transport channels to achieve uniform ion flow distribution, and providing a stable and dense substrate for the sustained release and dynamic repair of the film-forming agent. These three factors synergistically significantly improve the interfacial stability, safety, and cycle life of the lithium metal battery. Specifically, the D50 of the inorganic solid electrolyte can be, but is not limited to, 0.1 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0037] Secondly, this application provides a lithium metal anode, including a lithium metal anode body and the aforementioned composite modification film, specifically, the composite modification film is coated on the surface of the lithium metal anode body.

[0038] In some embodiments, the thickness of the composite modification film on the surface of the lithium metal anode body is 0.5-5 μm. This thickness directly determines the critical balance in actual battery operation: sufficient thickness provides significant mechanical strength to persistently suppress lithium dendrite penetration and stores sufficient film-forming agents for long-term repair; while an excessively thick film disproportionately increases the overall interfacial impedance, exacerbates polarization, and impairs rate performance, and may also compromise interfacial stability due to stress concentration. Therefore, limiting the final thickness after transfer is a key measure to ensure an optimal balance between protective functions and electrochemical performance throughout the battery's entire lifespan. Specifically, the thickness of the composite modification film on the surface of the lithium metal anode body can be, but is not limited to, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

[0039] Thirdly, this application provides a method for preparing a lithium metal anode, comprising the following steps: S1. Add the organic polymer solid electrolyte, the inorganic solid electrolyte, and the film-forming agent to the solvent, stir and disperse to obtain a slurry; S2. Apply the slurry onto the PET substrate and dry it to obtain the coating layer; S3. The coating layer is transferred to the surface of the lithium metal anode body to obtain a lithium metal anode containing a composite modification film.

[0040] The transfer method can pre-prepare complete, dense and structurally optimized independent films of composite modified films in an inert environment, effectively avoiding side reactions and interface contamination that may be caused by direct coating on the highly active lithium metal surface. At the same time, this method can precisely control the final thickness and uniformity of the modified film after transfer, ensuring that it has sufficient mechanical strength and film-forming agent reserves, without excessively increasing the interface impedance. Thus, a stable, uniform and controllable artificial protective layer is constructed for the lithium metal anode before battery assembly.

[0041] In some embodiments, in step S1, the solvent comprises at least one of acetonitrile, ethyl acetate, ethylene carbonate, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and acetone. The key to selecting a specific solvent is that it must effectively dissolve the organic polymer solid electrolyte, forming a uniform and continuous matrix, while simultaneously dispersing the inorganic solid electrolyte particles well and being compatible with the film-forming agent. This ensures that all functional components are uniformly distributed in the slurry and provides suitable volatilization kinetics for subsequent drying and film formation, ultimately resulting in a dense, defect-free composite modified film.

[0042] In some embodiments, in step S1, the stirring speed is 1500-3000 rpm, and the stirring time is 4 hours. Controlling the stirring speed and time is to apply sufficient and appropriate shear force to the slurry, aiming to completely break up the agglomeration of inorganic particles, achieve uniform nanoscale dispersion in the polymer solution, and ensure thorough mixing of all components. This avoids localized defects within the membrane caused by slurry inhomogeneity from the source, ensuring the formation of a uniform and stable precursor slurry. Specifically, the stirring speed can be, but is not limited to, 1500 rpm, 2000 rpm, 2500 rpm, or 3000 rpm, etc.

[0043] In some embodiments, in step S1, the solid content of the slurry is 10%-50% (mass percentage), and the viscosity is 1000-4000 Pa·s. Limiting the solid content and viscosity of the slurry aims to ensure it possesses suitable rheological properties, thereby enabling the formation of a uniform thickness, smooth surface, and defect-free wet film in subsequent coating processes. This guarantees the acquisition of a dense, uniformly composed, and consistent-thickness composite modified film after drying, and is a key precursor control step for achieving excellent and repeatable electrochemical performance. Specifically, the solid content of the slurry can be, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the viscosity can be, but is not limited to, 1000 Pa·s, 1500 Pa·s, 2000 Pa·s, 2500 Pa·s, 3000 Pa·s, 3500 Pa·s, or 4000 Pa·s.

[0044] In some embodiments, the thickness of the resulting coating layer in step S2 is 1-10 μm. The purpose of limiting the coating layer thickness here is to precisely balance interface protection and electrochemical performance: if the film is too thin, the mechanical strength is insufficient, making it difficult to effectively suppress lithium dendrite penetration; if the film is too thick, it will significantly increase ion transport impedance and reduce battery energy density. By optimizing the thickness, sufficient mechanical strength can be ensured to physically block dendrites while minimizing the obstruction to ion transport and providing a uniform lateral migration channel for lithium ions. This, in conjunction with the film-forming agent, constructs a stable interface, ultimately achieving a balance between high safety and long cycle life. Specifically, the thickness of the resulting coating layer is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc.

[0045] In some embodiments, in step S2, the drying temperature is 40-60°C, the time is 10-30 min, and the air velocity is 2-3 m / s. Specific drying temperature, time, and air velocity are designed to precisely control the solvent evaporation rate, ensuring that the polymer chains can fully and orderly rearrange and tightly encapsulate the inorganic particles and film-forming agent. This avoids stress cracks, pores, or uneven component distribution within the film due to excessively rapid solvent evaporation, ultimately resulting in a dense, smooth, and structurally uniform composite modified film. Specifically, the drying temperature can be, but is not limited to, 40°C, 50°C, 55°C, or 60°C, the drying time can be, but is not limited to, 10 min, 15 min, 20 min, 25 min, or 30 min, and the air velocity can be, but is not limited to, 2 m / s, 2.5 m / s, or 3 m / s.

[0046] In some embodiments, the transfer is achieved using hot rolling, with a pressure of 0.1-100 MPa and a temperature of 25-100°C. The specific pressure and temperature of the hot rolling are designed to achieve maximum adhesion between the composite modified film and the lithium metal surface through softening and pressurization, thereby eliminating interfacial voids, reducing interfacial impedance, and ensuring the structural integrity of the film and the stability of its functional components (such as inorganic particles and film-forming agents) during the transfer process. Ultimately, this results in a low-impedance, highly stable, and uniform electrode-modified film interface. Specifically, the hot rolling pressure can be, but is not limited to, 0.1 MPa, 1 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, or 100 MPa, and the hot rolling temperature can be, but is not limited to, 25°C, 30°C, 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0047] The following describes specific embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0048] Example 1 A method for preparing a lithium metal anode includes the following steps: S1. PVDF, LATP (D50=0.8μm) and TEB were added to tetrahydrofuran organic solvent at mass ratios of 10%, 10% and 80%, respectively. The mixture was stirred at 1500 rpm for 4 h to obtain a uniformly mixed slurry with a solid content of 25% and a viscosity of 1800 Pa·s. S2. The slurry obtained in step S1 is coated on a PET substrate, and then baked in an oven at 55°C and an air flow rate of 3m / s for 15 min to obtain a coating layer with a thickness of 6μm on the PET surface. S3. The coating layer obtained in step S2 is applied to both sides of the lithium metal anode strip and hot-rolled. The rolling pressure is 20 MPa and the temperature is 45°C. The coating layer is transferred to the surface of the lithium metal anode under the action of hot roller pressure to obtain the lithium metal anode. The thickness of the composite modified film after transfer is 3 μm.

[0049] Example 2 A method for preparing a lithium metal anode includes the following steps: S1. PVDF, LATP (D50=0.8μm) and LiDFOB were added to N,N-dimethylformamide (DMF) organic solvent at mass ratios of 35%, 35% and 30%, respectively. The mixture was stirred at 3000 rpm for 4 h to obtain a uniformly mixed slurry with a solid content of 15% and a viscosity of 3500 Pa·s. S2. The slurry obtained in step S1 is coated on a PET substrate, and then baked in an oven at 60°C and an air flow rate of 3m / s for 15 min to obtain a coating layer on the PET surface with a thickness of 6μm. S3. The coating layer obtained in step S2 is applied to both sides of the lithium metal anode strip and hot-rolled. The rolling pressure is 40 MPa and the temperature is 45°C. The coating layer is transferred to the surface of the lithium metal anode under the action of hot roller pressure to obtain the lithium metal anode. The thickness of the composite modified film after transfer is 3 μm.

[0050] Example 3 A method for preparing a lithium metal anode includes the following steps: S1. PVDF, LATP (D50=0.8μm) and LiBOB were added to N-methylpyrrolidone (NMP) organic solvent at mass ratios of 25%, 25% and 50%, respectively. The mixture was stirred at 2000 rpm for 4 h to obtain a uniformly mixed slurry with a solid content of 20% and a viscosity of 2000 Pa·s. S2. The slurry obtained in step S1 is coated on a PET substrate, and then baked in an oven at 55°C and an air flow rate of 3m / s for 15 min to obtain a coating layer with a thickness of 6μm on the PET surface. S3. The coating layer obtained in step S2 is applied to both sides of the lithium metal anode strip and hot-rolled. The rolling pressure is 20 MPa and the temperature is 45°C. The coating layer is transferred to the surface of the lithium metal anode under the action of hot roller pressure to obtain the lithium metal anode. The thickness of the composite modified film after transfer is 3 μm.

[0051] Comparative Example 1 The lithium metal anode surface is not modified, and the maximum amount of TEB is added directly to the electrolyte.

[0052] Comparative Example 2 It is basically the same as Example 1, except that the composite modified film does not contain a film-forming agent.

[0053] Comparative Example 3 The process is basically the same as in Example 1, except that the composite modified film does not contain a film-forming agent, and the maximum amount of TEB is added to the electrolyte.

[0054] Comparative Example 4 The process is basically the same as in Example 1, except that the composite modified membrane does not contain inorganic solid electrolytes and film-forming agents, and the maximum amount of TEB is added to the electrolyte.

[0055] Comparative Example 5 The process is basically the same as in Example 1, except that the composite modified membrane does not contain organic solid electrolytes and film-forming agents, and the maximum amount of TEB is added to the electrolyte.

[0056] Comparative Example 6 It is basically the same as Example 1, except that the composite modified film does not contain organic solid electrolytes and inorganic solid electrolytes.

[0057] Performance testing: 1. Battery assembly (1) Preparation of electrode plates and diaphragms Commercial high-nickel ternary cathode plates (LiNi) 0.8 Co 0.1 Mn 0.1O2, surface capacity ≥3.0 mAh / cm³ 2 Cut to the designed dimensions.

[0058] Take a separator (Celgard 2320), slightly larger than the positive electrode sheet.

[0059] Take the lithium metal anode sheet (thickness 50–100 μm) prepared by each embodiment and comparative example, cut it to size, with its modified layer facing the separator.

[0060] (2) Stacking bare cells In a drying room (dew point ≤ -40℃) or an argon glove box (H2O / O2 ≤ 0.1 ppm), Z-type stacking is performed in the order of "positive electrode - separator - negative electrode".

[0061] Repeat stacking until the designed number of layers (e.g., 2-10 layers) is reached, ensuring that each layer is aligned and that there are no wrinkles between the electrode and the separator.

[0062] The outermost layer is the positive electrode, meaning the battery structure begins and ends with the positive electrode.

[0063] (3) Welding the electrode tabs to the leads Ultrasonic welding is used to weld the aluminum tabs to the pre-set solder joints of the positive current collector (aluminum foil).

[0064] Ultrasonic welding is used to weld the nickel tab to the pre-set solder joint of the current collector (copper foil) of the lithium metal anode.

[0065] After welding, check the weld strength and for any burrs.

[0066] (4) Battery cell casing Using a hard case (aluminum case): After the bare cell is wrapped in the insulating film, it is placed inside the case. The tabs are bent to the corresponding terminal positions, and insulating gaskets are used to prevent short circuits.

[0067] (5) Liquid injection and packaging A measured amount of electrolyte is injected into the drying chamber, the cover is placed on top, and the chamber is sealed using laser welding to ensure airtightness.

[0068] (6) Settling and transformation After encapsulation, the battery should be left to stand at 25°C for 12-24 hours to ensure that the electrolyte is fully impregnated.

[0069] Formation process: Use a small current (such as 0.02C-0.05C) for the first charge and discharge cycle for 1-3 weeks to allow the film-forming agent in the composite modification film on the negative electrode surface to participate in the formation of a stable SEI.

[0070] After formation, the pouch cell is evacuated and resealed to remove the generated gas.

[0071] (7) Separation and screening Capacity testing was conducted at 25°C using standard charge and discharge regimes (e.g., constant current charging at 0.33C to the upper limit voltage, constant voltage charging to the current ≤0.05C cutoff, and constant current discharging at 0.33C).

[0072] Record the discharge capacity and screen batteries whose capacity, internal resistance, and open-circuit voltage meet the design requirements.

[0073] (8) Post-processing and warehousing The selected batteries undergo visual inspection and are then labeled.

[0074] Store in a dry environment or conduct subsequent aging and performance tests.

[0075] 2. Lithium metal battery impedance test: Impedance testing was performed using a Solartron 1260+1287 electrochemical workstation.

[0076] (1) Place the battery to be tested on the test clip of the electrochemical workstation and start the test after the open circuit voltage of the battery stabilizes.

[0077] (2) The test conditions are: AC disturbance amplitude of 5 mV and frequency range of 10 mV. 5 -0.1 Hz, sampling frequency is 5 points per second.

[0078] (3) After the test, the Nyquist plot was obtained, and the relaxation time distribution (DRT) analysis was performed on it to obtain the negative electrode interface impedance. The results are shown in Table 1.

[0079] Table 1: Negative interface impedance of each embodiment and comparative example

[0080] As shown in Table 1: Examples 1-3 demonstrate how the three materials work together to create a dense, low-impedance interface.

[0081] Comparative Example 1: Bare lithium anode with only electrolyte additive (TEB) has the most unstable interface and the highest impedance.

[0082] Comparative Example 2 lacked a film-forming agent and relied solely on a polymer / inorganic framework, resulting in poor interfacial mechanical stability and increased impedance. This demonstrates that while the initial interfacial quality is acceptable without a dynamic repair source, it is unsustainable.

[0083] Comparative Example 3 lacked a film-forming agent but contained TEB in its electrolyte. Compared to Comparative Example 2, its interfacial impedance was reduced, demonstrating that liquid additives can improve the initial interface. However, compared to Example 1, the effect was still inferior to the immobilized sustained-release mode.

[0084] Comparative Example 4 lacked an inorganic framework and a film-forming agent, and its electrolyte contained TEB, resulting in a higher impedance than Comparative Example 3. This demonstrates that even with a liquid repair agent, the interfacial mechanical stability remains poor and the impedance increases when a rigid reinforcing phase is absent.

[0085] Comparative Example 5 lacks polymer binders and film-forming agents, and its electrolyte contains TEB, resulting in extremely high interfacial impedance. This demonstrates that the lack of a flexible film-forming matrix prevents the formation of a continuous, dense protective layer.

[0086] Comparative Example 6 contains only film-forming agents, without polymers and inorganic frameworks, and cannot form an effective physical barrier. The film-forming agents cannot be "immobilized" or "slowly released", resulting in the worst interface.

[0087] 3. Lithium metal battery electrical performance testing Long-cycle testing was conducted using the Xinwei charge-discharge testing system.

[0088] (1) Connect the battery to be tested to the corresponding channel of the Xinwei test cabinet.

[0089] (2) The test conditions are: under normal temperature environment, voltage range 2.8 V-4.3 V, constant current charging at 1C to 4.3 V, then constant voltage charging until the current drops to 0.05C cutoff, and then constant current discharge at 0.33C to 2.8 V.

[0090] (3) After the test is completed, export the loop data table.

[0091] (4) Calculate the capacity retention rate: The discharge capacity of the first cycle is used as the baseline capacity (C0).

[0092] The capacity retention rate of the Nth cycle = (discharge capacity of the Nth cycle / C0) × 100%.

[0093] (5) Calculate the capacity retention rate at the 500th, 1000th and 2100th laps. The results are shown in Table 2.

[0094] Table 2: Full-cell cycle capacity retention of each embodiment and comparative example

[0095] As shown in Table 2: Examples 1-3 demonstrate the synergistic effect of the three materials, resulting in optimal sustained-release performance and outstanding long cycle life.

[0096] Comparative Example 1 only had liquid additives, which could not form a stable interface, leading to early battery failure.

[0097] Comparative Example 2 lacked film-forming agents, had no dynamic repair, and experienced continuous interface deterioration, leading to mid-term battery failure.

[0098] Comparative Example 3 lacked a film-forming agent. The addition of liquid additives had a certain repair effect, but the effect was limited and unsustainable, and it still failed earlier than the examples.

[0099] Comparative Example 4 lacks an inorganic framework, resulting in insufficient interfacial mechanical strength, which cannot be compensated for by liquid additives, leading to mid-term battery failure.

[0100] Comparative Example 5 lacked a polymer binder, making film formation impossible and resulting in very early battery failure (within approximately 500 cycles).

[0101] Comparative Example 6 contained only film-forming agents and had no physical protection or load-bearing capacity, resulting in rapid battery failure.

[0102] In summary, the direct comparison between Comparative Examples 2 and 3 and Example 1 demonstrates that immobilizing the film-forming agent within a composite framework to achieve sustained release (Example 1) results in significantly better interfacial stability and longer cycle life compared to schemes that do not contain any film-forming agent (Comparative Example 2) or rely solely on liquid-based film-forming agents (Comparative Example 3). This addresses the fundamental drawback of the unsustainable consumption of traditional liquid additives.

[0103] Comparative Example 5 (lacking polymer) exhibited extremely poor performance, demonstrating its indispensable role as a flexible binder in forming a continuous and dense protective layer; Comparative Example 4 (lacking inorganic phase) showed significantly inferior performance compared to Example 1, proving its crucial role in providing rigid support and dendrite suppression for the composite film; The complete failure of Comparative Example 6 (containing only film-forming agent) conversely confirms that film-forming agents must rely on a polymer / inorganic composite framework to achieve their "immobilization" and "slow-release" functions.

[0104] The superior performance of Examples 1-3 is the best manifestation of the synergistic effect of organic polymer (flexible matrix), inorganic solid electrolyte (rigid framework) and film-forming agent (dynamic repair source).

[0105] This application successfully constructs a lithium metal anode interface that combines excellent mechanical stability, high ionic conductivity, and full-lifecycle self-healing capability through an original integrated design of a "rigid-flexible composite framework" and a "fixed-load slow-release repair unit." This design fundamentally overcomes the two major pain points of existing technologies: easy mechanical failure of the protective layer and unsustainable repair function, providing an effective solution for the development of high-safety, long-life lithium metal batteries.

[0106] The technical means disclosed in this application are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A composite modified film characterized in that: The composite modification film comprises an organic polymer solid electrolyte, an inorganic solid electrolyte, and a film-forming agent, and the mass ratio of the organic polymer solid electrolyte, the inorganic solid electrolyte, and the film-forming agent is (10%-35%):(10%-35%):(30%-80%).

2. The composite finished film of claim 1 wherein: The organic polymer solid electrolyte comprises at least one of polyvinylidene fluoride, polyethyleneimine, polyethylene oxide, polyvinylidene fluoride hexafluoropropylene, polyacrylonitrile, polymethyl methacrylate, polypropylene carbonate, polyvinyl chloride, and polysiloxane.

3. The composite finished film of claim 1 wherein: The inorganic solid electrolyte comprises at least one of perovskite type, NASICON type, LISICON type, and garnet type inorganic solid electrolyte.

4. The composite finished film of claim 1 wherein: The film-forming agent comprises at least one of triethanolamine borate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, fluorinated lithium phosphate, lithium triflate, lithium nitrate, and lithium phosphate.

5. The composite modified film according to claim 1 or 3, wherein: The D50 of the inorganic solid electrolyte is 0.1-5 μm.

6. A lithium metal anode, characterized by: The lithium metal negative electrode body comprises a lithium metal negative electrode body and the composite modification film according to any one of claims 1-6, and the composite modification film is coated on the surface of the lithium metal negative electrode body.

7. The lithium metal anode of claim 6, wherein: The thickness of the composite modification film is 0.5-5 μm.

8. A method of producing a lithium metal anode as claimed in claim 6 or 7, characterized in that, The method comprises the following steps: S1, adding an organic polymer solid electrolyte, an inorganic solid electrolyte, and a film-forming agent into a solvent, stirring and dispersing to obtain a slurry; S2, coating the slurry on a substrate and drying to obtain a coating layer; S3, transferring the coating layer to the surface of a lithium metal negative electrode body to obtain a lithium metal negative electrode comprising a composite modification film.

9. The production method according to claim 8, characterized by: In step S1, the solid content of the slurry is 10%-50%, and the viscosity is 1000-4000 Pa·s.

10. The production method according to claim 8, characterized by: In step S3, the transfer is realized by hot roller pressing, the roller pressing pressure is 0.1-100 MPa, and the temperature is 25-100℃.

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