Polyoxometalate composite solid electrolyte membrane and preparation method thereof, and solid-state battery

Abstract

The application discloses a polyoxometalate composite solid electrolyte membrane and a preparation method thereof and a solid-state battery, and belongs to the technical field of solid-state lithium metal batteries. The polyoxometalate composite solid electrolyte membrane comprises a polyionic liquid and lithium silicotungstate; the polyionic liquid is composed of polydiallyl dimethyl ammonium cations and lithium salt anions; and the mass ratio of the lithium silicotungstate to the polyionic liquid is (4-25):(75-96). The application utilizes strong electrostatic coupling between polyoxometalate anions and polymer cation chains to construct an ion transmission network with ordered structure. The composite structure effectively promotes lithium salt dissociation and lithium ion directional migration, significantly improves the room temperature ionic conductivity, lithium ion transference number and mechanical strength of the electrolyte membrane, and simultaneously enhances the interface compatibility and electrochemical stability of the electrolyte membrane with a lithium metal negative electrode.

Description

Technical Field

[0001] This invention relates to the field of solid-state lithium metal battery technology, and in particular to a polyoxometalate composite solid electrolyte membrane and its preparation method, as well as a solid-state battery. Background Technology

[0002] Lithium metal batteries are considered a promising energy storage system due to the combination of high theoretical specific capacity and low redox potential in their anode materials. However, the industrialization of lithium metal batteries still faces significant challenges, primarily because conventional organic electrolytes readily undergo side reactions with highly reactive lithium metal, inducing uncontrolled lithium dendrite growth. This not only leads to a decline in battery cycle life and coulombic efficiency but can also cause safety issues such as internal short circuits and even thermal runaway. Therefore, developing intrinsically safe solid-state electrolytes is crucial for the practical application of lithium metal batteries.

[0003] Solid-state electrolytes, as a crucial functional layer between the positive and negative electrodes in a battery, not only isolate the electrodes and prevent short circuits but also serve as ion conduction channels, facilitating charge migration between the electrodes. Their ion conduction performance directly impacts the battery's energy conversion efficiency and cycle stability. Currently, the mainstream technologies include inorganic solid-state electrolytes and polymer solid-state electrolytes. While inorganic solid-state electrolytes possess high room-temperature ionic conductivity, their inherent brittleness makes processing difficult, and they suffer from poor solid-solid interface contact with the electrodes, resulting in significant interfacial impedance issues. Polymer solid-state electrolytes, on the other hand, offer good flexibility and processability, improving electrode contact; however, their room-temperature ionic conductivity is generally low, making it difficult to meet the requirements of high-power batteries.

[0004] To synergize the aforementioned advantages, organic-inorganic composite solid electrolyte systems have been extensively studied. These systems typically consist of a polymer matrix, lithium salt, and inorganic filler, aiming to combine high ionic conductivity with good interfacial adaptability. However, in such composite systems, polymer chain movement is often restricted by rigid fillers, and lithium-ion transport paths are often confined to amorphous regions of the polymer or discontinuous interfaces between the filler and the polymer, resulting in high ion migration barriers and limited overall conductivity improvement. While introducing liquid plasticizers or ionic liquids to form gel composite electrolytes can promote ion migration by enhancing chain movement, the residual liquid components easily trigger continuous side reactions at the lithium anode interface, forming a structurally and compositionally unstable solid electrolyte interfacial film. This not only fails to effectively suppress lithium dendrites but may also exacerbate interface deterioration and impair long-term cycling stability.

[0005] Existing composite solid-state electrolyte technologies still struggle to achieve long-term stable compatibility with lithium metal anodes while maintaining high ionic conductivity. Therefore, developing a composite electrolyte material that can synergistically improve bulk ion transport kinetics and electrode interface stability has become a pressing issue in this field. Summary of the Invention

[0006] In view of this, the present invention provides a polyoxometalate composite solid electrolyte membrane and its preparation method, as well as a solid battery. The present invention uses a specific polyoxometalate as a functional filler and combines it with a polyionic liquid to construct a solid electrolyte membrane that has both high room temperature ionic conductivity and excellent lithium metal interface stability.

[0007] In a first aspect, the present invention provides a polyoxometalate composite solid electrolyte membrane, comprising a polyionic liquid and lithium silicotungstate; wherein the polyionic liquid is composed of polydiallyldimethylammonium cations and lithium salt anions; and the mass ratio of lithium silicotungstate to the polyionic liquid is (4~25):(75~96).

[0008] Preferably, the mass ratio of the lithium silicotungsten to the polyionic liquid is (5~20): (80~95).

[0009] Preferably, the lithium salt anion is selected from at least one of bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, and hexafluorophosphate.

[0010] Preferably, the thickness of the polyoxometalate composite solid electrolyte membrane is 50~200μm.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned polyoxometalate composite solid electrolyte membrane, comprising the following steps:

[0012] A polyionic liquid was prepared by mixing and reacting an aqueous solution of polydiallyldimethylammonium chloride and an aqueous solution of lithium salt.

[0013] The polyionic liquid is mixed with lithium silicotungsten in an organic solvent to form a membrane, which is a polyoxometalate composite solid electrolyte membrane.

[0014] Preferably, the concentration of the polydiallyldimethylammonium chloride aqueous solution is 20-38 wt%; the concentration of the lithium salt aqueous solution is 0.1-0.5 mol / L; and the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

[0015] Furthermore, the molar ratio of the polydiallyldimethylammonium chloride to the lithium salt is 1:(0.9~1.1).

[0016] Preferably, the organic solvent is selected from N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), acetonitrile, or dimethyl sulfoxide (DMSO).

[0017] Thirdly, the present invention provides a solid-state battery, comprising a polyoxometalate composite solid electrolyte membrane as described in the first aspect or a polyoxometalate composite solid electrolyte membrane prepared by the preparation method described in the second aspect.

[0018] Preferably, the solid-state battery is a solid-state lithium metal battery.

[0019] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0020] (1) This invention constructs an ordered ion transport network by compositing lithium silicotungstate with polydiallyldimethylammonium polyionic liquid in a specific mass ratio, utilizing the strong electrostatic coupling between polyoxometalate anions and polymer cation chains. This composite structure effectively promotes lithium salt dissociation and directional lithium ion migration, significantly improving the ionic conductivity and lithium ion transference number of the electrolyte at room temperature, while also enhancing its interfacial compatibility and electrochemical stability with the lithium metal anode.

[0021] (2) The solid-state lithium metal battery assembled based on the composite electrolyte membrane provided by this invention exhibits excellent electrochemical performance. The lithium symmetric battery can achieve [results] at 0.3 mA·cm⁻¹. -2 It can cycle stably for more than 2,500 hours at a current density; after 600 cycles at 0.5C rate, the full cell matched with lithium iron phosphate or lithium cobalt oxide cathode still retains a capacity of more than 95%, demonstrating excellent long cycle life and interface stability.

[0022] (3) The preparation method of the present invention uses readily available raw materials, mild process conditions and does not require complex equipment. It can be completed through simple solution mixing and conventional film-making process, with low production cost and good process repeatability, and has broad prospects for industrial application. Attached Figure Description

[0023] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] Figure 1 These are the X-ray diffraction (XRD) patterns of lithium silicotungstic acid (referred to as "SiWLi") and silicotungstic acid (referred to as "SiWA") in Example 1 of this invention;

[0025] Figure 2These are scanning electron microscope (SEM) images, infrared spectra, and solid-state nuclear magnetic resonance (NMR) images of the solid electrolyte membranes of Comparative Example 1 and Example 1 of the present invention. In this image, A is the SEM image of the solid electrolyte membrane of Comparative Example 1, B is the SEM image of the composite solid electrolyte membrane of Example 1, and C is the SEM image of the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1 at 1000-600 cm⁻¹. -1 The infrared spectra of the range, where D represents the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1. 7 Li solid-state nuclear magnetic resonance spectrum;

[0026] Figure 3 These are Raman spectra of the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1.

[0027] Figure 4 This is a comparison of the electrochemical impedance spectra of the composite solid electrolyte membranes prepared in Examples 1-4 of this invention and the solid electrolyte membranes prepared in Comparative Example 1, which are assembled into stainless steel symmetric batteries.

[0028] Figure 5 The figure shows the polarization curve of the lithium symmetric battery assembled with the solid electrolyte membrane prepared in Comparative Example 1 of this invention. The inset shows the impedance spectrum before and after polarization.

[0029] Figure 6 These are the polarization curves of lithium symmetric batteries assembled with composite solid electrolyte membranes prepared in Examples 1-4 of this invention. The inset shows the impedance spectra before and after polarization; where A: Example 2, B: Example 1, C: Example 3, D: Example 4.

[0030] Figure 7 The critical current density test graphs are of the lithium symmetric batteries assembled with solid electrolyte membranes prepared in Embodiment 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0031] Figure 8 The lithium-ion symmetric battery assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1 operates at a constant current density (0.3 mA·cm⁻¹). -2 The results of long-term cycling stability tests are shown in the figure.

[0032] Figure 9 The images are scanning electron microscope (SEM) images of the lithium anode surface of a lithium symmetric battery assembled with the composite solid electrolyte membrane prepared in Example 1 of the present invention and the solid electrolyte membrane prepared in Comparative Example 1 after 100 hours of cycling. In the images, A: Comparative Example 1, B: Example 1.

[0033] Figure 10The image shows the X-ray photoelectron spectrum of the negative electrode surface of a lithium symmetric battery assembled with the composite solid electrolyte membrane prepared in Example 1 of this invention after 100 hours of cycling; where A is the F 1s spectrum and B is the Li 1s spectrum.

[0034] Figure 11 This is a comparison chart of the coulombic efficiency of the long-cycle performance of lithium-to-copper batteries assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1.

[0035] Figure 12 This is a comparison of the cycle performance of full cells assembled from the composite solid electrolyte membrane prepared in Example 1 of the present invention and the solid electrolyte membrane prepared in Comparative Example 1 at different rates; wherein, A is the rate performance curve of the lithium iron phosphate full cell; B is the rate performance curve of the lithium cobalt oxide full cell.

[0036] Figure 13 These are the cycle performance curves of lithium iron phosphate full batteries assembled from solid electrolyte membranes prepared in Examples 1, 1, and 2 of this invention.

[0037] Figure 14 The figures show the cycle performance curves of a lithium cobalt oxide full battery assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] This invention provides a polyoxometalate composite solid electrolyte membrane, comprising a polyionic liquid and lithium silicotungstate; wherein the polyionic liquid is composed of polydiallyldimethylammonium cations and lithium salt anions; and the mass ratio of lithium silicotungstate to the polyionic liquid is (4~25):(75~96).

[0040] This invention achieves synergistic optimization of the microstructure ordering and ion transport kinetics enhancement of solid-state electrolytes by introducing lithium silicotungstenate into a polyionic liquid matrix. Lithium silicotungstenate, as a polyoxometalate, has an anion composed of high-valence transition metal ions and oxygen atoms, forming a typical metal-oxygen cluster structure. This structure possesses significant characteristics: firstly, a large anion volume; and secondly, a high density of negative charge (tetravalent). This enables it to serve as an additional lithium-ion source and makes it a key structural and functional unit in composite materials.

[0041] When lithium silicotungsten oxide is composited with polyionic liquids, a strong electrostatic interaction occurs between its polyoxometalate anions and the regularly distributed quaternary ammonium cations (polydiallyldimethylammonium cations) on the polyionic liquid backbone. This interaction drives molecular rearrangement at the phase interface: multi-charged inorganic anions, acting as multifunctional crosslinking sites, are effectively anchored to the cationic sites of the polymer backbone. This anchoring effect simultaneously induces locally ordered arrangement of adjacent polymer chain segments, thereby constructing a continuous and stable three-dimensional network structure within the composite system.

[0042] This unique composite structure enhances the overall performance of the electrolyte from multiple dimensions: First, the anchored, highly negatively charged silicotungstenate anions strongly bind the quaternary ammonium salt cations on the polymer chain through electrostatic interactions. This indirectly restricts the migration freedom of the paired mobile anions, thereby significantly increasing the lithium-ion transport number and achieving selective and rapid lithium-ion conduction. Second, the locally ordered microstructure induced by the above interactions creates continuous transport channels with low energy barriers for lithium ions. Simultaneously, the large rigid anion volume of lithium silicotungstenate generates a steric hindrance effect in the polymer matrix, effectively suppressing the local aggregation and crystallization tendency of lithium salts. This helps maintain the system in an amorphous state with high ionic conductivity, ensuring high room-temperature ionic conductivity. Furthermore, the stable inorganic metal-oxygen cluster framework of the silicotungstenate itself also endows the composite material with superior thermal stability and a broadened electrochemical stability window, helping to reduce decomposition side reactions under high-voltage conditions.

[0043] This invention improves the ion conductivity (including ion conductivity and lithium-ion transference number) and interface stability of the electrolyte simultaneously through the electrostatic interaction between lithium silicotungstate and polyionic liquid, which is beneficial for the preparation of high-performance solid-state lithium metal batteries.

[0044] In an optional embodiment of the present invention, the mass ratio of the lithium silicotungstenate to the polyionic liquid is (5~20):(80~95), more preferably (5~15):(85~95). A suitable mass ratio ensures sufficient polyanions to generate effective electrostatic interactions with the polycation chains, breaking the random entanglement of the polymer chains, inducing the formation of ordered channels conducive to ion transport, and significantly increasing the lithium-ion transference number; simultaneously, it avoids the loss of film flexibility, increased brittleness, and deterioration of interfacial contact caused by excessive lithium silicotungstenate.

[0045] In an optional embodiment of the present invention, the lithium salt anion is selected from bis(trifluoromethanesulfonyl)imide (TFSI) - ), difluorosulfonyl imide (FSI) - ), hexafluorophosphate (PF6) - At least one of the following, more preferably TFSI -It possesses excellent chemical / electrochemical stability, the ability to promote lithium salt dissociation, and weak coordination with polymer cations.

[0046] In an optional embodiment of the present invention, the thickness of the polyoxometalate composite solid electrolyte membrane is 50~200μm, more preferably 100~200μm. The thinner the membrane, the lower the bulk ion transport resistance, which is beneficial to improving the rate performance of the battery; however, excessively thin membranes have poor mechanical strength, are prone to short circuits, and have weak buffering capacity against interfacial side reactions.

[0047] The present invention also provides a method for preparing the above-mentioned polyoxometalate composite solid electrolyte membrane, comprising the following steps:

[0048] A polyionic liquid was prepared by mixing and reacting an aqueous solution of polydiallyldimethylammonium chloride and an aqueous solution of lithium salt.

[0049] The polyionic liquid is mixed with lithium silicotungsten in an organic solvent to form a membrane, which is a polyoxometalate composite solid electrolyte membrane.

[0050] In an optional embodiment of the present invention, the concentration of the polydiallyldimethylammonium chloride aqueous solution is 20-38 wt%; the concentration of the lithium salt aqueous solution is 0.1-0.5 mol / L; the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate. Further, the molar ratio of the polydiallyldimethylammonium chloride to the lithium salt is 1:(0.9-1.1). This step is an anion exchange reaction, the goal of which is to remove the Cl- from the polydiallyldimethylammonium chloride. - The lithium salt is completely replaced by the target lithium salt anion to form a homogeneous polyionic liquid. In this invention, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium hexafluorophosphate (LiPF6).

[0051] To ensure a complete reaction between polydiallyldimethylammonium chloride and lithium salt, the reaction temperature is 15–40°C, more preferably 20–30°C, and preferably carried out at room temperature for 2–8 hours. After the reaction, the precipitate is collected by centrifugation or filtration and washed at least three times each with water and a low-boiling-point organic solvent (such as ethanol or acetone). The washing aims to remove residual chloride ions and free lithium salt. After washing, the precipitate is dried, either by vacuum drying or freeze-drying.

[0052] In optional embodiments of the present invention, the organic solvent is selected from N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), acetonitrile, or dimethyl sulfoxide (DMSO). The use of strongly polar aprotic solvents such as DMF, NMP, and DMSO is to simultaneously and fully dissolve the polyionic liquid and disperse lithium silicotungsticate, forming a molecular / nanoscale homogeneous blend solution, which is beneficial for obtaining a uniform composite film. NMP is more preferably selected as the organic solvent.

[0053] In the step of film formation after mixing the polyionic liquid with lithium silicotungstenate in an organic solvent, the mixing is carried out by magnetic stirring or ultrasonic dispersion for 4 to 24 hours to ensure uniform dispersion and the formation of a pre-assembled structure. The mixing temperature is 15 to 40°C, more preferably 20 to 30°C, and preferably at room temperature.

[0054] This invention does not impose special limitations on the film-forming method; for example, conventional film-forming methods such as casting, blade coating, or casting can be used. After film formation, a drying step is also included. The preferred drying method is: first, drying at 40-70°C under normal pressure for 1-5 hours to initially remove the solvent, followed by drying in a vacuum oven at 60-90°C for 8-24 hours to completely remove residual solvent, thereby obtaining a dense, crack-free composite solid electrolyte membrane.

[0055] This invention does not impose special restrictions on the source of lithium silicotungsten oxide; it can be obtained commercially or synthesized in-house. Preferably, it is obtained by reacting silicotungstenic acid with an alkaline lithium source in an aqueous solution. The alkaline lithium source includes lithium hydroxide, lithium carbonate, or lithium oxide. The molar ratio of silicotungstenic acid to the alkaline lithium source is 1:(2~5). The specific reaction temperature can be 15~60℃, the reaction time is 1~10h, and the reaction is carried out under an inert atmosphere to prevent the influence of moisture or carbon dioxide in the air on the purity of the product. After the reaction, drying is performed, which can be done by vacuum drying or forced-air drying, preferably under vacuum at 50~80℃ for 5~15 hours to remove residual moisture and obtain a product with high crystallinity and excellent chemical stability.

[0056] The present invention also provides a solid-state battery, comprising the above-described polyoxometalate composite solid electrolyte membrane or the polyoxometalate composite solid electrolyte membrane prepared by the above-described preparation method.

[0057] In an optional embodiment of the present invention, the solid-state battery is a solid-state lithium metal battery, specifically comprising a negative electrode, a positive electrode, a solid electrolyte, and a liquid electrolyte. The negative electrode is a lithium sheet.

[0058] In an optional embodiment of the present invention, the negative electrode is a lithium sheet. The positive electrode can be a lithium iron phosphate positive electrode or a lithium cobalt oxide positive electrode, etc., and the active material in the positive electrode accounts for more than 80% of the total mass of the positive electrode coating.

[0059] In an optional embodiment of the present invention, the electrolyte can be an electrolyte suitable for lithium-sulfur batteries, such as: 1M LiTFSI dissolved in ethylene glycol dimethyl ether (DME) and 1,3-dioxane (DOL), with a volume ratio of DME to DOL of 1:1; or, 1M LiTFSI and 2wt% LiNO3 dissolved in DME and DOL, with a volume ratio of DME to DOL of 1:1.

[0060] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not have any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used. In the following embodiments, room temperature refers to 25±3℃.

[0061] Example 1

[0062] This embodiment provides a method for preparing a composite solid electrolyte membrane.

[0063] (1) Dissolve 1 mol of silicotungstic acid in 20 mL of deionized water to obtain an aqueous solution of silicotungstic acid; dissolve 4 mol of lithium hydroxide in 100 mL of deionized water to obtain an aqueous solution of lithium hydroxide. Then slowly add the aqueous solution of lithium hydroxide to the aqueous solution of silicotungstic acid, stir for 2 h, and then dry under vacuum at 60 °C for 12 h to obtain lithium silicotungstate.

[0064] (2) Polydiallyldimethylammonium chloride was dissolved in deionized water to obtain a 25 wt% aqueous solution of polydiallyldimethylammonium chloride. A 0.3 mol / L aqueous solution of lithium bis(trifluoromethanesulfonyl)imide was added dropwise to the aqueous solution of polydiallyldimethylammonium chloride, controlling the molar ratio of polydiallyldimethylammonium chloride to lithium bis(trifluoromethanesulfonyl)imide to be 1:1. The reaction was stirred at room temperature for 4 h, and then the precipitate was collected by centrifugation, washed alternately with deionized water and ethanol, and finally freeze-dried to obtain a polyionic liquid powder, denoted as PDADMATFSI.

[0065] (3) Dissolve 0.1 g of lithium silicotungsten obtained in step (1) in 1 g of NMP to obtain an NMP solution of lithium silicotungsten; dissolve 0.9 g of PDADMATFSI obtained in step (2) in 3 g of NMP to obtain an NMP solution of PDADMATFSI. Stir and mix the NMP solution of lithium silicotungsten and the NMP solution of PDADMATFSI at room temperature for 5 h, i.e., the mass ratio of lithium silicotungsten to PDADMATFSI is 10:90 to obtain a casting solution. Cast the casting solution onto a flat polytetrafluoroethylene plate, then pre-dry it at 60 °C for 2 h, and then dry it in a vacuum oven at 80 °C for 10 h to obtain a composite solid electrolyte membrane with a thickness of about 150 μm.

[0066] Figure 1 The X-ray diffraction (XRD) patterns of lithium silicotungstenate (denoted as "SiWLi") and silicotungstic acid (denoted as "SiWA") in this embodiment are shown. It can be seen that the SiWA sample exhibits multiple diffraction peaks in the 10–40° range, indicating its certain crystallinity. The SiWLi sample shows more obvious and sharper diffraction peaks in the same angular range, with significantly enhanced intensity, indicating the formation of a more structurally complete and more crystalline compound during lithiation. Furthermore, the diffraction peak positions of SiWLi are slightly shifted compared to SiWA, indicating that lithium ions successfully intercalated into the metal-oxygen cluster structure of the polyoxometalate during the reaction, causing a slight change in the lattice constant. This result demonstrates the formation of SiWLi and the stability of its crystal structure, indicating that the lithiation method used in this embodiment can effectively achieve the conversion of silicotungsten acid to lithium silicotungstenate, providing a structural basis for the subsequent preparation of composite solid electrolytes.

[0067] Example 2

[0068] The difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, the mass ratio of lithium silicotungstate and PDADMATFSI is 5:95.

[0069] Example 3

[0070] The difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, the mass ratio of lithium silicotungstate and PDADMATFSI is 15:85.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 1 is that in step (3) of this embodiment, the mass ratio of lithium silicotungstate and PDADMATFSI is 20:80.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that lithium silicotungstate is not added in this comparative example. The specific preparation method is as follows:

[0075] (1) Polydiallyldimethylammonium chloride was dissolved in deionized water to obtain a 25 wt% aqueous solution of polydiallyldimethylammonium chloride. A 0.3 mol / L aqueous solution of lithium bis(trifluoromethanesulfonyl)imide was added dropwise to the aqueous solution of polydiallyldimethylammonium chloride, and the molar ratio of polydiallyldimethylammonium chloride to lithium bis(trifluoromethanesulfonyl)imide was controlled to be 1:1. The reaction was stirred at 25 °C for 12 h, and then the precipitate was collected by centrifugation, washed alternately with deionized water and ethanol, and finally freeze-dried to obtain polyionic liquid powder, denoted as PDADMATFSI.

[0076] (2) Dissolve 1 g of PDADMATFSI in 4 g of NMP to obtain an NMP solution of PDADMATFSI. Cast the solution onto a flat polytetrafluoroethylene plate and pre-dry it at 60°C for 2 hours. Then dry it in a vacuum oven at 80°C for 10 hours to obtain a solid electrolyte membrane with a thickness of about 150 μm.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that polyvinylidene fluoride (PVDF) is used instead of PDADMATFSI in this comparative example.

[0079] 0.1 g of lithium silicotungstenate was dissolved in 1 g of NMP to obtain an NMP solution of lithium silicotungstenate; 0.9 g of PVDF was dissolved in 3 g of NMP to obtain an NMP solution of PVDF. The NMP solutions of lithium silicotungstenate and PVDF were stirred and mixed at room temperature for 5 h, i.e., the mass ratio of lithium silicotungstenate to PVDF was 10:90, to obtain a casting solution. The casting solution was cast onto a flat polytetrafluoroethylene plate, and then pre-dried at 60 °C for 2 h, followed by drying in a vacuum oven at 80 °C for 10 h to obtain a composite solid electrolyte membrane with a thickness of approximately 150 μm.

[0080] Test case

[0081] 1. Surface morphology test

[0082] Figure 2 In the figure, A is a scanning electron microscope (SEM) image of the surface of the solid electrolyte membrane in Comparative Example 1 of the present invention. Figure 2 B in the image is a SEM image of the composite solid electrolyte membrane of Example 1 of this invention. It can be seen that... Figure 2 The surface of the A membrane in Example 1 is relatively flat. Compared with the solid electrolyte membrane of Comparative Example 1, the surface of the composite solid electrolyte membrane in Example 1 shows obvious wrinkles and stacked structures, indicating that the inorganic filler of lithium silicotungstate is uniformly dispersed in the polymer matrix and forms a three-dimensional lithium conduction channel.

[0083] 2. Infrared testing

[0084] Figure 2 In this context, C represents the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1 at a depth of 1000-600 cm⁻¹. -1 Fourier transform infrared (FTIR) spectra of the range, with the composite solid electrolyte membrane of Example 1 at 970 cm⁻¹. -1 (WO) d -W), 921 cm -1 (Si-O) a -W), 885 cm -1 (WO) b-W) and 806 cm -1 (WO) c Four new peaks appeared at -W), corresponding to SiW. 12 O 40 4- The characteristic stretching peaks correspond to the Keggin structure of polyoxometalates.

[0085] 3. Solid-state nuclear magnetic resonance testing

[0086] Figure 2 In this context, D represents the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1. 7 The solid-state nuclear magnetic resonance (NMR) spectrum of Li, as shown in the figure, indicates that, compared to Example 1, 7 The chemical shift of Li is approximately -0.361 ppm, while that of Example 1 is approximately -0.318 ppm with a significantly narrower spectral width. This shift indicates a change in the chemical environment of lithium ions in the composite system, suggesting that the introduction of inorganic components enhances the interaction between lithium ions and the matrix, thereby contributing to improved lithium ion migration rate and conductivity.

[0087] 4. Raman spectroscopy analysis

[0088] Figure 3 Raman spectral analysis of the composite solid electrolyte membrane of Example 1 and the solid electrolyte membrane of Comparative Example 1. As can be seen from the figure, after the introduction of lithium silicotungsticate (SiWLi), the free ions (740 cm⁻¹)... -1 The proportion increased from 8.2% to 58.2%, and the ion pairs (744 cm⁻¹) -1 ) and ion clusters (749 cm -1 The percentages decreased to 11% and 30.8%, respectively. The large, multi-electrolyte anions in SiWLi can weaken the Li... + With TFSI - The constraints, while providing additional Li + It forms a multi-point coordination structure with the polymer chain, thereby constructing a continuous ion conduction channel.

[0089] 5. Electrochemical performance testing and analysis

[0090] (1) Battery assembly

[0091] To comprehensively evaluate the performance of the composite solid electrolyte membrane of Example 1 of this invention, four types of standard test batteries were constructed, and their assembly methods are as follows:

[0092] i. Stainless steel symmetric cell: A composite membrane or control membrane is placed between two stainless steel (SS) blocking electrodes to assemble an SS|electrolyte membrane|SS structure. This is used to test the bulk ionic conductivity of the electrolyte membrane itself.

[0093] ii. Lithium-ion symmetric battery: An electrolyte membrane is placed between two lithium wafers, assembled into a Li|electrolyte membrane|Li structure. Used to evaluate the interfacial stability between the electrolyte membrane and lithium metal, lithium-ion transference number, and dendrite resistance (through critical current density and long-cycle testing).

[0094] iii. Lithium-to-copper battery: A Li|electrolyte membrane|Cu structure is assembled using a lithium foil as both the counter and reference electrode, and a copper foil as the working electrode. It is used for quantitative analysis of the reversible deposition / stripping efficiency (coulombic efficiency) of lithium on the negative electrode side.

[0095] iv. Full cell: Using commercial lithium iron phosphate (LFP) or lithium cobalt oxide (LCO) as the active material as the positive electrode and a lithium sheet as the negative electrode, assembled into a Li|electrolyte membrane|positive electrode structure. Used to evaluate the overall electrochemical performance (rate capability, cycle life) of the electrolyte membrane in a real battery.

[0096] All electrolyte membranes were dried and then punched into 16mm diameter discs. Before battery assembly, they were soaked in an electrolyte solution for 6 hours. The electrolyte solution consisted of 1M LiTFSI dissolved in dimethyl ethylene glycol (DME) and 1,3-dioxane (DOL), with a DME to DOL volume ratio of 1:1. All batteries were assembled in an argon-protected glove box and sealed using standard pressure using CR2025 and CR2032 type button cell casings.

[0097] (2) Performance test results

[0098] Figure 4 This is a comparison of the electrochemical impedance spectroscopy (EIS) spectra of stainless steel symmetrical batteries assembled from the composite solid electrolyte membranes prepared in Examples 1-4 of this invention and the solid electrolyte membrane prepared in Comparative Example 1. It can be seen that the impedance of the example samples is significantly lower than that of Comparative Example 1, indicating that both the interfacial impedance and bulk impedance are significantly reduced. Among them, Example 1 has the lowest impedance, indicating that it has the highest ionic conductivity and more unobstructed ion transport channels in the electrolyte. The calculated ionic conductivity of the solid electrolyte membrane in Comparative Example 1 is 0.53 mS·cm. -1 The ionic conductivity of the composite solid electrolyte membranes in Examples 1-4 is 2.57 mS·cm, respectively. -1 1.87 mS·cm -1 1.46 mS·cm -1 and 1.05 mS·cm -1 .

[0099] Figure 5 This is the polarization curve of a lithium-symmetric battery assembled from the solid electrolyte membrane prepared in Comparative Example 1 of this invention. The inset shows the impedance spectra before and after polarization. Figure 5The lithium-ion transference number (LTF) of Comparative Example 1 can be calculated from this. The value is 0.26.

[0100] Figure 6 The figures show the polarization curves of lithium-ion symmetric batteries assembled using the composite solid electrolyte membranes prepared in Examples 1-4 of this invention. The inset shows the impedance spectra before and after polarization. The lithium-ion transference numbers for Examples 1, 2, 3, and 4 are 0.82, 0.87, 0.71, and 0.65, respectively. The lithium-ion transference number decreases with increasing SiWLi content, mainly due to the difference in SiW... 12 O 40 4- Larger volume and higher content can, to some extent, hinder Li + The migration.

[0101] Figure 7 This describes the critical current density (CCD) test of lithium-ion symmetric batteries assembled using the solid electrolyte membranes prepared in Examples 1, 1, and 2 of this invention. During CCD testing at room temperature, the critical current density increased to 0.3 mA·cm⁻¹. -2 At that time, the lithium symmetric battery assembled in Comparative Example 2 experienced a soft short circuit. The polarization voltage of the lithium symmetric battery assembled in Comparative Example 1 was generally higher than that of the lithium symmetric battery assembled in Example 1, when the current density increased to 0.5 mA·cm⁻¹. -2 In contrast, the lithium-ion symmetric battery assembled in Example 1 exhibited drastic overpotential fluctuations and failed due to excessively high overpotential. Conversely, the lithium-ion symmetric battery assembled in Example 1 had a critical current density as high as 0.5 mA·cm⁻¹. -2 The polarization voltage increases gradually within a small range, with minimal voltage fluctuations. The higher critical current density is mainly due to the high ionic conductivity and high Li content of the solid electrolyte membrane in Example 1. + The high transfer rate gives the assembled solid-state lithium metal batteries significant advantages in terms of energy density, safety, and cycle life.

[0102] Figure 8 The lithium-ion symmetric battery assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1 operates at a constant current density (0.3 mA·cm⁻¹). -2 The results of long-term cycle stability tests are as follows. Comparative Example 1 experienced a short circuit in less than 100 hours, exhibiting interface instability and lithium dendrite growth. In contrast, Example 1 maintained relatively stable voltage during cycling for more than 2500 hours, further demonstrating that the composite solid electrolyte membrane of Example 1 has good interface stability and excellent mechanical strength during lithium deposition / stripping, ensuring excellent long-term cycle stability of the battery.

[0103] Figure 9In the diagram, A is a scanning electron microscope image of the lithium anode surface of the lithium symmetric battery assembled with the solid electrolyte membrane prepared in Comparative Example 1 of this invention after 100 hours of cycling. Figure 9 In Figure B, the lithium anode surface of the lithium symmetric battery assembled with the composite solid electrolyte membrane prepared in Example 1 of this invention is a scanning electron microscope image after 100 hours of cycling. It can be seen that the lithium deposition on the anode surface of the lithium symmetric battery assembled in Comparative Example 1 is very uneven, forming dendritic crystals, which corresponds to the failure of its lithium symmetric battery in less than 100 hours. In contrast, the anode surface of the lithium symmetric battery assembled in Example 1 shows a uniform and flat blocky deposition, indicating that its anode side has uniform lithium deposition sites.

[0104] Figure 10 This is the X-ray photoelectron spectroscopy (XPS) of the negative electrode surface of a lithium symmetric battery assembled with the composite solid electrolyte membrane prepared in Example 1 of this invention after 100 hours of cycling. + The surface of the lithium metal anode is etched to reflect the composition information of the solid electrolyte interphase (SEI) film at different depths. Figure 10 In the spectrum, A represents F 1s, and a distinct LiF characteristic peak is formed after 60s. Figure 10 B in the diagram represents the Li 1s spectrum, revealing the LiF and Li-CO2 products formed at the interface. The results indicate that the LiF-rich interface layer formed in Example 1 helps improve interface stability and ion migration efficiency.

[0105] Figure 11 This is a comparison of the coulombic efficiency of lithium-to-copper batteries assembled with the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1. The results show that the coulombic efficiency of Example 1 is consistently maintained at 99.01%, which is significantly higher than that of Comparative Example 1, effectively reducing side reactions and improving cycle stability.

[0106] Figure 12 This is a comparison chart of the cycling performance of full cells assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1 at different rates, wherein: Figure 12 In the figure, A represents the rate performance curve of a lithium iron phosphate (LFP) full cell. Figure 12 B in the figure represents the rate performance curve of the lithium cobalt oxide (LCO) full cell. All of them show that Example 1 has higher specific capacity and stability at rates from 0.1C to 2C, and has excellent reversibility and rate performance.

[0107] Figure 13These are the cycle performance curves of lithium iron phosphate (LFP) full batteries assembled from the solid electrolyte membranes prepared in Examples 1, 1, and 2 of this invention. The batteries were charged and discharged at a 0.5C rate. Compared to Comparative Examples 1 and 2, Example 1 exhibited better cycle stability, providing 145.67 mAh·g after stable cycling. -1 High initial discharge specific capacity and 145.03 mAh·g after 600 cycles. -1 The specific capacity is 99.9%, the average coulombic efficiency is 99.9%, and the capacity retention is 99.5%. Comparative Example 2 provides 141.83 mAh·g. -1 The initial discharge specific capacity and 111.56 mAh·g after 600 cycles -1 The specific capacity is 99.8%, the average coulombic efficiency is 99.8%, and the capacity retention rate is 78.7%.

[0108] Figure 14 This is a cycle performance curve of a lithium cobalt oxide (LCO) full battery assembled from the composite solid electrolyte membrane prepared in Example 1 of this invention and the solid electrolyte membrane prepared in Comparative Example 1. The battery was charged and discharged at a rate of 0.5C. Example 1 provided 132.1 mAh·g after stable cycling. -1 It exhibits a high initial discharge capacity, with a specific capacity of 125.8 mAh·g after 600 cycles. -1 The capacity retention rate was 95.2%, and the average coulombic efficiency was 99.9%. The initial discharge specific capacity of Comparative Example 1 was only 97.39 mAh·g. -1 After 600 cycles, it decreased to 57.17 mAh·g. -1 The capacity retention rate was 58.7%. This shows that the long-cycle performance of Example 1 is far superior to that of Comparative Example 1, and it can be perfectly adapted to LCO (high voltage) cathode.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polyoxometalate composite solid electrolyte membrane, characterized in that, It includes a polyionic liquid and lithium silicotungstenate; wherein the polyionic liquid is composed of polydiallyldimethylammonium cations and lithium salt anions; the mass ratio of lithium silicotungstenate to the polyionic liquid is (5~20): (80~95); The lithium salt anion is bis(trifluoromethanesulfonyl)imide; The lithium silicotungsten oxide is Li4SiW 12 O 40 ; The combination of lithium silicotungstate and polydiallyldimethylammonium polyionic liquid utilizes the strong electrostatic coupling between polyoxometalate anions and polymer cationic chains to construct a structurally ordered ion transport network.

2. The polyoxometalate composite solid electrolyte membrane as described in claim 1, characterized in that, The thickness of the polyoxometalate composite solid electrolyte membrane is 50~200μm.

3. The method for preparing the polyoxometalate composite solid electrolyte membrane according to any one of claims 1 to 2, characterized in that, Includes the following steps: A polyionic liquid was prepared by mixing and reacting an aqueous solution of polydiallyldimethylammonium chloride and an aqueous solution of lithium salt. The polyionic liquid is mixed with lithium silicotungsten in an organic solvent to form a membrane, which is a polyoxometalate composite solid electrolyte membrane.

4. The preparation method according to claim 3, characterized in that, The concentration of the polydiallyldimethylammonium chloride aqueous solution is 20~38 wt%; the concentration of the lithium salt aqueous solution is 0.1~0.5 mol / L; the lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide.

5. The preparation method according to claim 4, characterized in that, The molar ratio of polydiallyldimethylammonium chloride to lithium salt is 1:(0.9~1.1).

6. The preparation method according to claim 3, characterized in that, The organic solvent is selected from N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, or dimethyl sulfoxide.

7. A solid-state battery, characterized in that, The polyoxometalate composite solid electrolyte membrane includes the polyoxometalate composite solid electrolyte membrane as described in any one of claims 1 to 2 or the polyoxometalate composite solid electrolyte membrane prepared by the preparation method described in any one of claims 3 to 6.

8. The solid-state battery as described in claim 7, characterized in that, The solid-state battery is a solid-state lithium metal battery.

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