Solid electrolyte with SEI (solid electrolyte interface) membrane, preparation method of solid electrolyte and solid lithium battery

Abstract

The invention belongs to the technical field of solid-state lithium batteries, and provides a solid-state electrolyte with an SEI membrane, a preparation method of the solid-state electrolyte and a solid-state lithium battery. The solid electrolyte with the SEI membrane comprises the SEI membrane, a solid electrolyte membrane and the SEI membrane which are sequentially stacked together, the SEI film comprises a polymer matrix, and a lithium salt and an additive which are dispersed in the polymer matrix, wherein the additive is one or more of a fluorine-containing additive, an oxygen-containing additive, a nitrogen-containing additive, a boron-containing additive, a phosphorus-containing additive, a sulfur-containing additive and a carbon-containing additive; the solid electrolyte membrane comprises a polymer matrix and lithium salt dispersed in the polymer matrix; and the molar mass ratio of the anions in the SEI membrane to the polymer matrix is greater than the molar mass ratio of the anions in the solid electrolyte membrane to the polymer matrix. The SEI film can resist puncture of lithium dendrites and improve the ionic conductivity and the interface stability, so that the charge-discharge efficiency and the cycle stability of the solid-state lithium battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium batteries, and particularly relates to a solid electrolyte with a SEI film, a preparation method thereof, and a solid-state lithium battery. Background Art

[0002] As an important part of the new energy technology architecture, the progress of solid-state lithium batteries plays a crucial role in promoting the global energy structure transformation and achieving sustainable development goals. During the charge and discharge cycles of solid-state lithium batteries, a solid electrolyte interface (SEI) film will naturally form on the surface of the negative electrode. This SEI film has an important impact on the comprehensive performance of solid-state lithium batteries. The SEI film can not only effectively suppress the further occurrence of side reactions and reduce the loss of negative electrode materials, but also profoundly affect key indicators such as the capacity, cycle durability, fast charge and discharge ability, and safety of solid-state lithium batteries. However, the naturally formed SEI film usually has significant defects in terms of ion conductivity, long-term stability, and uniformity. On the one hand, the naturally formed SEI film faces the problem of low ionic conductivity, which directly increases the internal resistance of solid-state lithium batteries and reduces the charge and discharge efficiency of solid-state lithium batteries. On the other hand, the naturally formed SEI film has a thick and uneven structure. The non-uniform distribution of the SEI film will induce non-uniform lithium ion deposition, which in turn leads to the generation of lithium dendrites, posing a threat to the safety performance and cycle life of solid-state lithium batteries. On the other hand, the volume change of the negative electrode material during the charge and discharge process poses a severe test to the mechanical stability of the SEI film.

[0003] Therefore, there is an urgent need to develop a new type of SEI film with excellent ionic conductivity, high uniformity, and long-term stability. Regarding the improvement strategies for SEI film technology, the current focus is mainly on the following directions: surface modification, controlling charging conditions, introducing artificial SEI films, and optimizing electrolyte / solid-state electrolyte formulations. Although the current SEI film improvement methods have improved the performance of solid-state lithium batteries to a certain extent, there are still some deficiencies. For example, the Chinese patent application with publication number CN119253037A proposes adding an artificial SEI film on a solid-state electrolyte (SSE), which includes two coating layers to improve the stability and ionic conductivity of solid-state lithium batteries. However, the interfacial contact between its SEI film and the solid-state electrolyte and electrode materials is not ideal, resulting in poor interfacial stability and cycle performance. The Chinese patent application with publication number CN119050358A proposes depositing a molten mixture on a lithium substrate to form an SEI film, and then cooling and solidifying it to make them combine; however, the process of constructing the SEI film is complex, and the SEI film has problems such as non-uniformity, low mechanical strength, and insufficient ability to resist the growth of lithium dendrites. The Chinese patent application with publication number CN117410490A proposes a conductive polymer artificial SEI film coated on the surface of a negative electrode material by an in-situ polymerization method; among them, the molecular chains of polyamide and polyphenylacetylene are intertwined and not easily broken, and the two form an interpenetrating conductive network structure, which is beneficial to lithium ion transmission and effectively improves the initial efficiency and rate performance of the negative electrode material; however, the artificial SEI film composed of pure polymers prepared does not significantly improve the ionic conductivity and cannot effectively resist the growth of lithium dendrites. Summary of the Invention

[0004] To solve the above problems of the prior art, the present invention provides a solid-state electrolyte with an SEI film, its preparation method, and a solid-state lithium battery, wherein the SEI film can resist the puncture of lithium dendrites, improve ionic conductivity and interfacial stability, thereby improving the charge-discharge efficiency and cycle stability of the solid-state lithium battery.

[0005] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a solid electrolyte with a SEI film, comprising a SEI film, a solid electrolyte film, and a SEI film stacked together in sequence; the SEI film comprises a polymer matrix and a lithium salt and an additive dispersed in the polymer matrix, and the additive is one or more of a fluorine-containing additive, an oxygen-containing additive, a nitrogen-containing additive, a boron-containing additive, a phosphorus-containing additive, a sulfur-containing additive, and a carbon-containing additive; the solid electrolyte film comprises a polymer matrix and a lithium salt dispersed in the polymer matrix; the molar mass ratio of anions to the polymer matrix in the SEI film is greater than the molar mass ratio of anions to the polymer matrix in the solid electrolyte film, wherein the anions in the SEI film refer to the anions in the lithium salt and the additive in the SEI film, and the anions in the solid electrolyte film refer to the anions in the lithium salt in the solid electrolyte film.

[0006] For the solid electrolyte with a SEI film of the present invention, SEI films are provided on both sides of the solid electrolyte film. The polymer matrix in the SEI film provides a soft interface contact and exhibits good compatibility and interface stability with the positive and negative electrodes of the solid-state lithium battery. An additive is added to the SEI film, and the molar mass ratio of anions to the polymer matrix in the SEI film is greater than the molar mass ratio of anions to the polymer matrix in the solid electrolyte film, so that an anion concentration gradient is formed from the outside to the inside of the solid electrolyte. The introduction of the additive in the SEI film and the higher anion concentration can improve the mechanical strength of the SEI film, enhance the lithium dendrite inhibition ability and interface stability, thereby extending the cycle service life of the solid-state lithium battery; on the other hand, the introduction of the additive and the higher anion concentration can also improve the ionic conductivity, enabling lithium ions to shuttle between the electrodes more efficiently and smoothly, accelerating the ion transport kinetics, and thus effectively enhancing the charge and discharge efficiency of the solid-state lithium battery. Adding a lithium salt to the SEI film can improve the ionic conductivity, optimize the composition of the SEI film, effectively enhance the mechanical strength, and at the same time can supplement the loss of lithium source.

[0007] In some preferred embodiments of the present invention, the polymer matrix and the lithium salt in the SEI film are respectively the same as the polymer matrix and the lithium salt in the solid electrolyte film, and the mass ratio of the polymer matrix and the lithium salt in the SEI film is the same as the mass ratio of the polymer matrix and the lithium salt in the solid electrolyte film.

[0008] In some preferred embodiments of the present invention, in the solid electrolyte film, the mass ratio of the polymer matrix to the lithium salt is (0.5 - 5):1, more preferably, the mass ratio of the polymer matrix to the lithium salt is 2:1; in the SEI film, the mass ratio of the polymer matrix, the lithium salt, and the additive is (0.5 - 5):1:(0.1 - 1), more preferably, the mass ratio of the polymer matrix, the lithium salt, and the additive is 4:2:1.

[0009] In some preferred embodiments of the present invention, the additive is a fluorine-containing additive, an oxygen-containing additive or a phosphorus-containing additive, and more preferably a phosphorus-containing additive.

[0010] In some preferred embodiments of the present invention, the fluorine-containing additive is one or more of LiF, NaF, KF, ZnF2, AlF3, LiPF6 and LiBF4; more preferably, the fluorine-containing additive is LiF or AlF3.

[0011] In some preferred embodiments of the present invention, the oxygen-containing additive is one or more of Li2O, SiO2, Al2O3, TiO2, CeO2, ZrO2, V2O5, La2O3 and Y2O3; more preferably, the oxygen-containing additive is ZrO2 or Li2O.

[0012] In some preferred embodiments of the present invention, the nitrogen-containing additive is one or more of Li3N, Si3N4, AlN and LiNO3; more preferably, the nitrogen-containing additive is Li3N.

[0013] In some preferred embodiments of the present invention, the boron-containing additive is one or more of LiBH4, TiB2, BN, H3BO3, LiFOB and LiBOB; more preferably, the boron-containing additive is LiBH4.

[0014] In some preferred embodiments of the present invention, the phosphorus-containing additive is one or more of LiPO2F2, Li3PO4, Zn3P2, FeP, Fe2P, CoP3, CoP, Co2P, Co3P, NiP, Ni2P and Ni3P. More preferably, the phosphorus-containing additive is LiPO2F2.

[0015] In some preferred embodiments of the present invention, the sulfur-containing additive is one or more of Li2S, Li2S2, CuS, CoS, CoS2, NiS, Ni3S2 and NiS2. More preferably, the sulfur-containing additive is Li2S.

[0016] In some preferred embodiments of the present invention, the carbon-containing additive is one or more of Li2CO3, TiC, SiC, B4C, WC, Mo2C, NbC, TaC; more preferably, the carbon-containing additive is Li2CO3.

[0017] In some preferred embodiments of the present invention, the polymer matrix is one or more of polypropylene carbonate (PPC), polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polydioxolane (PDOL), poly(malonamide) (PMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); more preferably, the polymer matrix is PPC. Compared with other polymers, the glass transition temperature (Tg) of PPC is much lower than room temperature, and its chain segments are active, enabling lithium ion migration through local relaxation at room temperature. In addition, the amorphous region of the polymer solid electrolyte serves as the main ion conduction channel, and PPC has a relatively high proportion of amorphous region, while the proportion of the amorphous region of PEO is usually less than 40%. Therefore, these advantages support PPC in maintaining efficient ion transport in the design of ultra-thin solid electrolytes.

[0018] In some preferred embodiments of the present invention, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), and lithium hexafluoroarsenate (LiAsF6); more preferably, the lithium salt is LiTFSI.

[0019] In some preferred embodiments of the present invention, the thickness of the SEI film is 1 - 900 nm, and the thickness of the solid electrolyte film is 1 - 100 μm.

[0020] Second, the present invention provides a method for preparing the solid electrolyte with an SEI film as Figure 1 shown, and the preparation method includes the following steps: S1, coating the SEI film solution on the surface of a substrate and drying to obtain the SEI film; wherein, the SEI film solution is obtained by adding a polymer, a lithium salt, and an additive to a solvent; S2, coating the polymer electrolyte solution on the SEI film obtained in S1 and drying to obtain the solid electrolyte film; wherein, the polymer electrolyte solution is obtained by adding a polymer and a lithium salt to a solvent; S3. Coat the SEI film solution on the solid electrolyte film obtained in S2 and dry it to obtain a solid electrolyte with an SEI film.

[0021] In some preferred embodiments of the present invention, the solvent in S1 and S2 is one or more of acetonitrile, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethanol, acetone, and ethylene glycol; more preferably, the solvent is DMF and NMP.

[0022] In some preferred embodiments of the present invention, the method for preparing the SEI film solution is: adding a polymer, a lithium salt, and an additive to a solvent and stirring to obtain the SEI film solution. Among them, the stirring temperature is 30-80°C, more preferably 50°C; the stirring time is 6-24 h, more preferably 12 h.

[0023] In some preferred embodiments of the present invention, the method for preparing the polymer electrolyte solution is: adding a polymer and a lithium salt to a solvent and stirring to obtain the polymer electrolyte solution. Among them, the stirring temperature is 30-80°C, more preferably 50°C; the stirring time is 6-24 h, more preferably 12 h.

[0024] In some preferred embodiments of the present invention, in S1 and S2, the drying temperature is 60-120°C and the drying time is 1-24 h. More preferably, the drying temperature is 80°C and the drying time is 3 h.

[0025] In some preferred embodiments of the present invention, in S3, the drying temperature is 60-120°C and the drying time is 1-24 h. More preferably, the drying temperature is 80°C and the drying time is 12 h.

[0026] In some preferred embodiments of the present invention, in S1, S2, and S3, the coating method used is blade coating or spin coating.

[0027] The above preparation method of the present invention has a simple process, controllable cost, and can form a micron-level uniform thin film (with controllable and relatively thin thickness).

[0028] In the third aspect, the present invention provides the application of the solid electrolyte with an SEI film in a solid-state lithium battery.

[0029] Specifically, the present invention provides a solid-state lithium battery, including a positive electrode, a solid electrolyte, and a negative electrode, wherein the solid electrolyte is the solid electrolyte with an SEI film as described above.

[0030] Compared with the prior art, the present invention has the following beneficial effects: On the one hand, the present invention adds an additive to the SEI film. The additive can form a protective layer, inhibit the side reaction between the solid electrolyte and the electrode, reduce the growth of lithium dendrites, and improve the interfacial stability. At the same time, the introduction of the additive makes the SEI film have higher mechanical strength, which can serve as a barrier against lithium dendrites and extend the cycle life of the solid-state lithium battery. Moreover, the introduction of the additive can also improve the ionic conductivity, enabling lithium ions to shuttle between the electrodes more efficiently and smoothly, accelerating the ionic transport kinetics, and thus effectively enhancing the charge-discharge efficiency of the solid-state lithium battery. On the other hand, the molar mass ratio of anions to the polymer matrix in the SEI film of the present invention is greater than that in the solid electrolyte film, so that an anion concentration gradient from the outside to the inside is formed in the solid electrolyte, and the anion concentration in the SEI film is higher than that in the solid electrolyte film. The higher anion concentration in the SEI film can further improve the mechanical strength of the SEI film, thereby enhancing the lithium dendrite inhibition ability and interfacial stability, and thus improving the cycle stability. At the same time, the higher anion concentration in the SEI film can also improve the ionic conductivity. In addition, the anion concentration in the solid electrolyte film is low, and the ion migration resistance is small, which can ensure the rapid migration of lithium ions. On the other hand, a lithium salt is added to the SEI film of the present invention, which can form a continuous lithium ion transport channel in the SEI film, improving the ionic conductivity. At the same time, the lithium salt can optimize the composition of the SEI film. The lithium salt participates in the reduction reaction and promotes the formation of inorganic components such as LiF. For example, the increase in the content of inorganic components such as LiF in the SEI film can effectively improve the mechanical strength; the increase in the content of inorganic components such as Li3N and Li3P in the SEI film can improve the ionic conductivity. In addition, the lithium salt continuously releases Li⁺ during the charge-discharge process to supplement the loss of lithium source. The polymer matrix introduced into the SEI film of the present invention provides a soft interface contact, having good compatibility and interfacial stability with the positive and negative electrodes. On the other hand, the present invention provides SEI films on both sides of the solid electrolyte film, which can prevent the active components in the solid electrolyte film from directly contacting the electrodes on both sides and inhibit the side reaction between the electrode and the electrolyte. At the same time, as a stress buffer layer, it can absorb part of the cyclic stress during the reaction process, effectively reducing the influence of the volume change of the positive and negative electrodes on the interface during the charge-discharge process and enhancing the structural stability.

[0031] Furthermore, the SEI film and the solid electrolyte film of the present invention adopt the same polymer matrix and lithium salt. On the one hand, it makes the solid electrolyte have interfacial chemical continuity. The same polymer matrix makes the interface transition smoother, can eliminate phase separation, maximize the interfacial compatibility, and make the contact between the SEI film and the solid electrolyte film more stable. On the other hand, the mechanical properties of the SEI film and the solid electrolyte film using the same polymer matrix and lithium salt are matched, and the elastic modulus can be kept stable in a wide temperature range. When drying and shrinking, the shrinkage rate difference between the solid electrolyte film and the SEI film is very small, which can avoid interface cracking or warping problems and improve the interfacial stability.

[0032] Furthermore, since the solid electrolyte membrane of the present invention uses a polymer matrix as the electrolyte, the polymer electrolyte has good flexibility, can adapt to the volume expansion of the electrode, and a thin layer can achieve a tight interfacial contact; in addition, the effective transport distance of the polymer electrolyte is short, and the movement of polymer chain segments promotes the hopping conduction of lithium ions, and a thin layer can meet the ion transport requirements; therefore, the solid electrolyte membrane of the present invention can be prepared with an ultra-thin thickness. The ultra-thin solid electrolyte membrane can efficiently transport lithium ions due to the short lithium ion transport path, reduce the diffusion time, and accelerate the ion transport kinetics. At the same time, the ultra-thin solid electrolyte membrane can also greatly improve the volumetric energy density of the solid-state lithium battery.

[0033] The present invention applies the solid electrolyte with the SEI film to a solid-state lithium battery, thereby improving the ion transport rate and stability of the solid-state lithium battery, and finally realizing the improvement of the charge and discharge efficiency and cycle life of the solid-state lithium battery.

[0034] The preparation method of the solid electrolyte with the SEI film of the present invention can evenly distribute the lithium salt by coating, solve the problem of the uniformity of the SEI film, ensure the uniformity and continuity of the SEI film, optimize the lithium ion transport path, and further improve the safety performance of the solid-state lithium battery. At the same time, the preparation method of the present invention is simple to operate and the cost is effectively controlled, providing a practical solution for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a flowchart of the preparation method of the solid electrolyte with the SEI film of the present invention.

[0037] Figure 2 It is a surface scanning electron microscope (SEM) image of the gradient layered structure sample prepared in Example 5.

[0038] Figure 3 It is an elemental distribution map of fluorine elements on the cross-section of the SEI film and the solid electrolyte membrane in the gradient layered structure sample prepared in Example 5.

[0039] Figure 4 It is the first charge and discharge curve graph of the gradient layered structure samples prepared in Example 1, Example 2, and Example 3.

[0040] Figure 5The first charge-discharge curves of the gradient laminated structure samples prepared in Example 4, Example 5, and Example 6.

[0041] Figure 6 The first charge-discharge curves of the gradient laminated structure samples prepared in Example 7, Example 8, and Example 9.

[0042] Figure 7 The first charge-discharge curves in the full-cell cycling performance of the samples prepared in Example 5 and Comparative Examples 1 to 3.

[0043] Figure 8 The overpotential bar chart of the first charge-discharge curves in the full-cell cycling performance of the samples prepared in Example 10 to Example 19.

[0044] Figure 9 The full-cell cycling performance diagrams of the samples prepared in Example 5 and Comparative Example 1. Detailed implementation manners

[0045] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] It should be noted that the process equipment or devices not specifically noted in the following examples all use conventional equipment or devices in the art.

[0047] It should be noted that the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the arrangement order of each method step or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantially changing the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0048] Example 1 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0049] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 1 g of LiF in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain the SEI film solution.

[0050] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0051] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the blade to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0052] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0053] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, cut it into a disc with a diameter of 14 mm with a cutting machine. The positive electrode material of the full cell is lithium iron phosphate (LiFePO4, LFP), and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0054] Example 2 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0055] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 1 g of Li2O in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain the SEI film solution.

[0056] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, a SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0057] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0058] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient laminated structure sample. The gradient laminated structure sample is the solid electrolyte with a SEI film described in the present invention, wherein the intermediate layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0059] (6) Use the gradient laminated structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0060] Example 3 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0061] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of LiPO2F2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a SEI film solution.

[0062] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, a SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0063] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0064] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0065] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a circular piece with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0066] Example 4 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0067] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 0.6 g of LiPO2F2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0068] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0069] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0070] (5) Using the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0071] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a circular sheet with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0072] Example 5 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0073] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 1.2 g of LiPO2F2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0074] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0075] (4) Using the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0076] (5) Using the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0077] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a circular piece with a diameter of 14 mm using a cutting machine. The cathode material of the full cell is lithium iron phosphate, and the anode is metallic Li. Assemble it into a CR2025 coin cell according to the battery assembly process in a glove box, and conduct electrochemical performance tests.

[0078] Example 6 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0079] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 1.8 g of LiPO2F2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain the SEI film solution.

[0080] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0081] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the scraper to 50 μm, and evenly coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0082] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0083] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a circular piece with a diameter of 14 mm using a cutting machine. The cathode material of the full cell is lithium iron phosphate, and the anode is metallic Li. Assemble it into a CR2025 coin cell according to the battery assembly process in a glove box, and conduct electrochemical performance tests.

[0084] Example 7 (1)Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0085] (2)Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of LiBF4 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0086] (3)Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0087] (4)According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0088] (5)According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention, in which the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0089] (6)Use the gradient layered structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm with a punching machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0090] Example 8 (1)Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0091] (2)Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of AlF3 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0092] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0093] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0094] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0095] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0096] Example 9 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0097] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI, and 1 g of NaF in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0098] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0099] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0100] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0101] (6) Use the gradient layered structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box, and conduct electrochemical performance tests.

[0102] Example 10 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0103] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of ZrO2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0104] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0105] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0106] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0107] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a circular piece with a diameter of 14 mm with a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0108] Example 11 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0109] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of Li3N in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0110] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0111] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the scraper to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0112] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0113] (6) The gradient layer structure sample prepared in step (5) was used as the SSE, punched into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell was lithium iron phosphate, and the negative electrode was metallic Li. A CR2025 coin cell was assembled in a glove box according to the battery assembly process, and electrochemical performance tests were carried out.

[0114] Example 12 (1) Weigh 1.2 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0115] (2) Weigh 1.2 g of PPC, 2.4 g of LiTFSI and 0.24 g of Si3N4 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain the SEI film solution.

[0116] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven, dry it at 80 °C for 3 h, and after gravitational sedimentation, a SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0117] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0118] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0119] (6) The gradient layer structure sample prepared in step (5) was used as the SSE, punched into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell was lithium iron phosphate, and the negative electrode was metallic Li. A CR2025 coin cell was assembled in a glove box according to the battery assembly process, and electrochemical performance tests were carried out.

[0120] Example 13 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0121] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of LiBH4 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0122] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0123] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the blade to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0124] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0125] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, cut it into a disc with a diameter of 14 mm with a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0126] Example 14 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0127] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of BN in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0128] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0129] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0130] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Subsequently, transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0131] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0132] Example 15 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0133] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of CoP in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0134] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0135] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0136] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Subsequently, transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0137] (6) Take the gradient layered structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0138] Example 16 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0139] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of Li2S in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0140] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and uniformly scrape and coat it on the glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0141] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and uniformly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0142] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0143] (6) Use the gradient layered structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0144] Example 17 (1) Weigh 12 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0145] (2) Weigh 12 g of PPC, 2.4 g of LiTFSI and 2.4 g of CoS2 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0146] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0147] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the scraper to 50 μm, and evenly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0148] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0149] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine, use lithium iron phosphate as the positive electrode material of the full cell, and use metallic Li as the negative electrode. Assemble it into a CR2025 coin cell according to the battery assembly process in a glove box, and conduct electrochemical performance tests.

[0150] Example 18 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a uniform polymer electrolyte solution.

[0151] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of Li2CO3 in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0152] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and uniformly coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0153] (4) According to the method in step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the scraper to 50 μm, and uniformly coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0154] (5) According to the method in step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the scraper to 1 μm, and uniformly coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layer structure sample. The gradient layer structure sample is the solid electrolyte with an SEI film according to the present invention, wherein the middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0155] (6) Use the gradient layer structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm using a cutting machine, use lithium iron phosphate as the positive electrode material of the full cell, and use metallic Li as the negative electrode. Assemble it into a CR2025 coin cell according to the battery assembly process in a glove box, and conduct electrochemical performance tests.

[0156] Example 19 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0157] (2) Weigh 4.8 g of PPC, 2.4 g of LiTFSI and 1 g of SiC in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain an SEI film solution.

[0158] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and uniformly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0159] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the blade to 50 μm, and uniformly scrape and coat it on the SEI film. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0160] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the blade to 1 μm, and uniformly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a gradient layered structure sample. The gradient layered structure sample is the solid electrolyte with an SEI film described in the present invention. The middle layer is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0161] (6) Use the gradient layered structure sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm with a cutting machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell in a glove box according to the battery assembly process, and conduct electrochemical performance tests.

[0162] Comparative Example 1 (1) Weigh 4.8 g of PPC and 2.4 g of LiTFSI in a glove box, add them to 20 mL of DMF, and stir at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0163] (2) Take out 5 mL of the polymer electrolyte solution prepared in step 1, adjust the height of the blade to 50 μm, and uniformly scrape and coat it on a glass substrate. Then place the glass substrate in a vacuum drying oven and dry it at 80 °C for 12 h to obtain a solid electrolyte film with a thickness of 10 μm.

[0164] (3) The solid electrolyte membrane prepared in step (2) was used as the SSE and punched into a 14-mm-diameter wafer by a cutting machine. The cathode material of the full cell was lithium iron phosphate, and the anode was metallic Li. A CR2025 coin cell was assembled in a glove box according to the battery assembly process, and its electrochemical performance was tested.

[0165] Comparative Example 2 (1) 4.8 g of PPC and 2.4 g of LiTFSI were weighed in a glove box and added to 20 mL of DMF. The mixture was stirred at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0166] (2) 4.8 g of PPC, 2.4 g of LiTFSI, and 1.2 g of LiPO2F2 were weighed in a glove box and added to 20 mL of DMF. The mixture was stirred at 50 °C for 12 h to obtain an SEI film solution.

[0167] (3) 1 mL of the SEI film solution prepared in step (2) was taken out, the height of the scraper was adjusted to 1 μm, and it was evenly spin-coated on a glass substrate. The glass substrate was transferred to a vacuum drying oven and dried at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm was obtained on the glass substrate.

[0168] (4) According to the method of step (3), 5 mL of the polymer electrolyte solution prepared in step (1) was taken out, the height of the scraper was adjusted to 50 μm, and it was evenly spin-coated on the SEI film. Subsequently, the glass substrate was placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain a solid electrolyte membrane with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte membrane was the SEI film.

[0169] (5) The solid electrolyte membrane with an SEI film on one side prepared in step (4) was used as the SSE and punched into a 14-mm-diameter wafer by a cutting machine. The cathode material of the full cell was lithium iron phosphate, and the anode was metallic Li. A CR2025 coin cell was assembled in a glove box according to the battery assembly process, and its electrochemical performance was tested.

[0170] Comparative Example 3 (1) 4.8 g of PPC and 2.4 g of LiTFSI were weighed in a glove box and added to 20 mL of DMF. The mixture was stirred at 50 °C for 12 h to obtain a homogeneous polymer electrolyte solution.

[0171] (2) 1.2 g of LiPO2F2 was weighed in a glove box and added to 20 mL of DMF. The mixture was stirred at 50 °C for 12 h until completely dissolved to obtain an SEI film solution.

[0172] (3) Take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on a glass substrate. Transfer the glass substrate to a vacuum drying oven and dry it at 80 °C for 3 h. After gravitational sedimentation, an SEI film with a thickness of 500 nm is obtained on the glass substrate.

[0173] (4) According to the method of step (3), take out 5 mL of the polymer electrolyte solution prepared in step (1), adjust the height of the doctor blade to 50 μm, and evenly scrape and coat it on the SEI film. Subsequently, place the glass substrate in a vacuum drying oven and dry it at 80 °C for 3 h to obtain a solid electrolyte film with a thickness of 10 μm. At this time, the lower surface of the solid electrolyte film is the SEI film.

[0174] (5) According to the method of step (3), take out 1 mL of the SEI film solution prepared in step (2), adjust the height of the doctor blade to 1 μm, and evenly scrape and coat it on the solid electrolyte film. Then transfer it to a vacuum drying oven and dry it thoroughly at 80 °C for 12 h to obtain a solid electrolyte sample. The middle layer of the solid electrolyte sample is a solid electrolyte film with a thickness of 10 μm, and the upper and lower layers are SEI films with a thickness of 500 nm.

[0175] (6) Use the solid electrolyte sample prepared in step (5) as the SSE, punch it into a disc with a diameter of 14 mm with a punching machine. The positive electrode material of the full cell is lithium iron phosphate, and the negative electrode is metallic Li. Assemble it into a CR2025 type button cell according to the battery assembly process in a glove box and conduct electrochemical performance tests.

[0176] Figure 2 It is the surface scanning electron microscope (SEM) image of the gradient layered structure sample prepared in Example 5. It can be seen from the figure that the surface morphology of the sample prepared by the present invention is dense, uniform, and continuous, without cracks, holes, phase separation, etc. It can have a good contact interface with the electrode material, has excellent electrolyte-electrode interface stability, and reduces side reactions; at the same time, the uniform SEI film is beneficial to inhibiting the growth of lithium dendrites, thus having excellent cycle stability.

[0177] Figure 3 It is the elemental distribution map of fluorine elements on the cross-section of the SEI film and the solid electrolyte film in the gradient layered structure sample prepared in Example 5. It can be seen that the fluorine element concentration in the upper and lower layers of the SEI film in the gradient layered structure sample prepared in Example 5 is higher than that in the middle layer solid electrolyte film, indicating that the gradient layered structure sample has a layered structure with a concentration gradient.

[0178] Figure 4The first charge-discharge curves of the gradient layered structure samples prepared in Example 1, Example 2, and Example 3 are shown. The discharge specific capacities are 146.3 mAh / g, 145.8 mAh / g, and 152.7 mAh / g respectively, and the overpotentials are 193.1 mV, 158.2 mV, and 98.2 mV respectively. It can be seen that under the condition of different additives, the gradient layered structure sample prepared in Example 3 has a lower overpotential and a higher discharge specific capacity for the SEI film. This result indicates that compared with the additives LiF and Li2O, the solid-state lithium battery assembled with the gradient layered structure sample prepared by introducing the additive LiPO2F2 in Example 3 has faster reaction kinetics, good electrode-electrolyte interface stability, and is beneficial to improving the cycle stability.

[0179] Figure 5 The first charge-discharge curves of the gradient layered structure samples prepared in Example 4, Example 5, and Example 6 are shown. The discharge specific capacities are 149.8 mAh / g, 154.3 mAh / g, and 141.9 mAh / g respectively, and the overpotentials are 117.3 mV, 87.1 mV, and 228.5 mV respectively. It can be seen that under the condition of the SEI film with different additive concentrations, the gradient layered structure sample prepared in Example 5 has a lower overpotential and a higher discharge specific capacity for the SEI film. This result indicates that compared with other examples of the SEI film, the solid-state lithium battery assembled with the sample prepared with a mass ratio of 4:2:1 of the polymer matrix, lithium salt, and additive in Example 5 has higher ionic conductivity and a more stable electrode-electrolyte interface phase, which can greatly reduce the occurrence of side reactions and improve the cycle stability.

[0180] Figure 6 The first charge-discharge curves of the gradient layered structure samples prepared in Example 7, Example 8, and Example 9 are shown. The discharge specific capacities are 130.3 mAh / g, 145.1 mAh / g, and 136.5 mAh / g respectively, and the overpotentials are 238.8 mV, 167.1 mV, and 247.6 mV respectively. It can be seen that compared with LiBF4 and NaF, the solid-state lithium battery assembled with the gradient layered structure sample prepared using AlF3 as an additive has faster reaction kinetics, good electrode-electrolyte interface stability, and is beneficial to improving the cycle stability.

[0181] Figure 7Figure 1 is the first charge-discharge curve of the full battery cycling performance of the samples prepared in Example 5 and Comparative Examples 1-3. The discharge specific capacities of Example 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are 154.3 mAh / g, 125.3 mAh / g, 129.6 mAh / g, and 126.8 mAh / g, respectively, and the overpotentials are 87.1 mV, 496.5 mV, 317.2 mV, and 409.9 mV, respectively. It can be seen that compared with Comparative Examples 1-3, Example 5 can release the highest capacity. This result shows that the electrode-electrolyte interface stability of the solid-state lithium battery assembled with the gradient layered structure sample in Example 5 is better, and the electrode material realizes more sufficient lithium ion insertion / extraction, improving the utilization rate of the active material. The overpotential of the SEI film of the gradient layered structure sample prepared in Example 5 is the lowest, which is beneficial to the ion transport process; Comparative Example 1 without an SEI film has the highest overpotential. In Comparative Example 2, the SEI film is deposited only on one side of the solid electrolyte film. Although the overpotential is lower than that of Comparative Example 1, it is still higher than that of Example 5. In Comparative Example 3, the SEI film does not introduce a polymer matrix and a lithium salt, and its overpotential is lower than that of Comparative Example 1 but still higher than that of Example 5. This result shows that compared with Comparative Example 1 without an SEI film, the solid-state lithium battery assembled with the gradient layered structure sample with an SEI film formed by adding an additive in Example 5 has a higher ionic conductivity, the electrode-electrolyte interface phase is more stable, and the cycle stability can be improved. In addition, depositing SEI films on both sides of the solid electrolyte film and introducing a polymer matrix and a lithium salt into the SEI film can both improve the ionic conductivity and interface stability.

[0182] Figure 8 Figure 2 is a bar chart of the overpotentials of the first charge-discharge curves of the full battery cycling performance of the samples prepared in Examples 10-19. Combining Figures 4 - 7 Analysis shows that compared with Comparative Examples 1-3, the overpotentials of the samples prepared in Examples 10-19 are lower, indicating that the solid electrolyte with an SEI film in the present invention can improve the ionic conductivity and interface stability. By comparing and analyzing with Examples 1-9, it is found that adding fluorine-containing additives, oxygen-containing additives, and phosphorus-containing additives has better effects.

[0183] Figure 9Figure of the full-cell cycling performance of the samples prepared in Example 5 and Comparative Example 1. Compared with Comparative Example 1, the full-cell cycling performance of the gradient layered structure sample prepared in Example 5 is better, with higher specific capacity and cycling stability. After 100 cycles, the solid-state lithium battery assembled with the gradient layered structure sample prepared in Example 5 still has a capacity retention rate of 86.7%, while the solid-state lithium battery assembled with the sample prepared in Comparative Example 1 only has a capacity retention rate of 55.4% after 100 cycles. It shows that the SEI film of the gradient layered structure sample prepared in Example 5 is beneficial to promoting the formation of a stable electrode-electrolyte interface, which can realize a stable lithium deposition and stripping process, thereby improving the cycling stability.

Claims

1. A solid electrolyte with a SEI film, characterized in that, It includes an SEI film, a solid electrolyte film, and an SEI film stacked together in sequence; the SEI film includes a polymer matrix and lithium salts and additives dispersed in the polymer matrix, and the additives are one or more of fluorine-containing additives, oxygen-containing additives, nitrogen-containing additives, boron-containing additives, phosphorus-containing additives, sulfur-containing additives, and carbon-containing additives; the solid electrolyte film includes a polymer matrix and lithium salts dispersed in the polymer matrix; the molar mass ratio of anions to the polymer matrix in the SEI film is greater than that in the solid electrolyte film, where the anions in the SEI film refer to the anions in the lithium salts and additives in the SEI film, and the anions in the solid electrolyte film refer to the anions in the lithium salts in the solid electrolyte film.

2. The solid electrolyte with an SEI film according to claim 1, characterized in that, The polymer matrix and lithium salts in the SEI film correspond to the polymer matrix and lithium salts in the solid electrolyte film respectively and are the same, and the mass ratio of the polymer matrix and lithium salts in the SEI film is the same as that in the solid electrolyte film.

3. The solid electrolyte with an SEI film according to claim 2, wherein, In the solid electrolyte film, the mass ratio of the polymer matrix to the lithium salt is (0.5~5):1; in the SEI film, the mass ratio of the polymer matrix, lithium salt, and additive is (0.5~5):1:(0.1~1).

4. The solid electrolyte with an SEI film according to claim 1, characterized in that, The fluorine-containing additive is one or more of LiF, NaF, KF, ZnF2, AlF3, LiPF6, and LiBF4; the oxygen-containing additive is one or more of Li2O, SiO2, Al2O3, TiO2, CeO2, ZrO2, V2O5, La2O3, and Y2O3; the nitrogen-containing additive is one or more of Li3N, Si3N4, AlN, and LiNO3; the boron-containing additive is one or more of LiBH4, TiB2, BN, H3BO3, LiFOB, and LiBOB.

5. The solid electrolyte with an SEI film according to claim 1, characterized in that, The phosphorus-containing additive is one or more of LiPO2F2, Li3PO4, Zn3P2, FeP, Fe2P, CoP3, CoP, Co2P, Co3P, NiP, Ni2P, and Ni3P; the sulfur-containing additive is one or more of Li2S, Li2S2, CuS, CoS, CoS2, NiS, Ni3S2, and NiS2; the carbon-containing additive is one or more of Li2CO3, TiC, SiC, B4C, WC, Mo2C, NbC, and TaC.

6. The solid electrolyte with an SEI film according to claim 1, characterized in that, The thickness of the SEI film is 1~900 nm, and the thickness of the solid electrolyte film is 1~100 μm.

7. The solid electrolyte with an SEI film according to claim 1, characterized in that, The polymer matrix is one or more of poly(propylene carbonate), polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, poly(dioxolane), polypropylene diamide, poly(vinylidene fluoride), and poly(vinylidene fluoride-hexafluoropropylene) copolymer.

8. The solid electrolyte with an SEI film according to claim 1, characterized in that, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium hexafluorophosphate, lithium perchlorate, and lithium hexafluoroarsenate.

9. The preparation method of the solid electrolyte with an SEI film according to any one of claims 1 to 8, characterized in that, It includes the following steps: S1. Coat the surface of the substrate with the SEI film solution and dry it to obtain the SEI film. Among them, the SEI film solution is obtained by adding a polymer, a lithium salt, and an additive to a solvent. S2. Coat the SEI film obtained in S1 with the polymer electrolyte solution and dry it to obtain the solid electrolyte film. Among them, the polymer electrolyte solution is obtained by adding a polymer and a lithium salt to a solvent. S3. Coat the solid electrolyte film obtained in S2 with the SEI film solution and dry it to obtain the solid electrolyte with the SEI film.

10. A solid-state lithium battery, characterized in that, It includes a positive electrode, a solid electrolyte, and a negative electrode. The solid electrolyte is the solid electrolyte with the SEI film according to any one of claims 1 to 8.

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