Substituted polyoxometallate solid electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of solid-state batteries, in particular to a substituted polyoxometallate solid-state electrolyte as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing phosphotungstic acid hydrate with water, and adjusting the pH value to obtain an H3 [PW11O40] 2-solution; then mixing with soluble copper salt to adjust the pH (Potential of Hydrogen), so as to obtain an H3 [CuPW11O40] solution; and mixing with a lithium salt to adjust the pH value, and carrying out hydrothermal reaction to obtain the electrolyte. According to the method, metal ions are introduced through step-by-step acidification, crystallization is promoted hydrothermally, and a product with a nanorod structure is synthesized, so that the problems of uncertain product structure and low crystallinity of a traditional step-by-step acidification method are solved. The general chemical formula of the electrolyte is Li3CuPW11O40, the electrolyte has a three-dimensional continuous lithium ion transmission path, the ionic conductivity at room temperature reaches 0.9-1.0 mS / cm, and the activation energy is 0.1-0.2 eV. And a continuous lithium ion transmission network can be constructed in a solid-state battery, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, specifically to a substituted polyoxometalate solid electrolyte, its preparation method, and its application. Background Technology

[0002] With the rapid popularization of electrified transportation and the dramatic increase in demand for grid energy storage, new battery systems that combine high energy density and high safety have become a focus of research and industry. Compared to liquid batteries, which are prone to flammability and leakage, solid-state batteries often offer higher safety and a wider electrochemical stability window. Their solid electrolytes, due to their superior mechanical strength, chemical stability, electrochemical stability, and thermal stability, are considered a rational electrolyte form that effectively eliminates the potential safety issues associated with the high reactivity of liquid electrolytes.

[0003] Polyoxometalates, as a class of discrete molecular metal oxide anion clusters composed of transition metals, have shown broad application prospects in the field of solid-state batteries due to their unique structural and performance advantages. Their ion nuclei are composed of quasi-octahedral units sharing a common angle. This structure promotes the "jumping" transport of lithium ions, significantly reducing the lithium-ion diffusion barrier and providing the possibility of improving the ion conduction efficiency of solid-state electrolytes. The discrete anionic polynuclear metal oxide clusters endow polyoxometalates with excellent plasticity, enabling them to better adapt to complex stress changes within the battery, facilitating the construction of stable and adaptive interfaces, and enhancing battery stability during cycling. Polyoxometalates exhibit high stability against moisture and lithium metal, meeting the stringent requirements of solid-state batteries for solid-state electrolytes and effectively solving the problems of performance degradation and poor compatibility with lithium metal in traditional solid-state electrolytes under humid environments. By rationally selecting the structure and metal atoms, the chemical and physical properties of polyoxometalates can be easily tuned, and it is expected that materials with ideal properties can be obtained through techniques such as isomorphic substitution, providing rich design space for the development of novel solid-state electrolytes.

[0004] However, despite the numerous advantages of polyoxometalates, their application in the battery field is still in its early stages. Existing research has primarily focused on the modification of cathode and anode materials, for example, by modifying the material surface with polyoxometalates to improve the electronic conductivity and structural stability of the materials.

[0005] Currently, the stepwise acidification method is used to prepare polyoxometalates, which is one of the important methods for synthesizing or controlling the structure of polyoxometalates. Its core lies in controlling the degree of polymerization, structural type, and composition of metal oxoclusters by gradually adjusting the pH value of the system. However, it has the following problems: First, the accuracy of pH monitoring is crucial: a precision pH meter is needed for real-time monitoring to avoid human error (such as visual titration), especially when approaching the target pH, requiring slow addition of acid. Second, there is the risk of product stability: some polyoxometalates are easily decomposed under low pH conditions (e.g., copper-substituted polyoxometalates exist in different forms under different pH conditions), requiring preliminary experiments to determine the optimal acidification range. Third, the reaction cycle is long: stepwise acidification usually takes several days, which is longer than the one-step method. It is suitable for scenarios with high product purity requirements, while industrial-scale production may prefer the more efficient one-step method or template method. In summary, the stepwise acidification method for preparing polyoxometalate-based solid electrolytes suffers from uncertain product morphology and structure and low crystallinity. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a substituted polyoxometalate solid electrolyte, its preparation method, and its applications. This invention employs a stepwise acidification method to prepare a precursor solution, followed by a hydrothermal synthesis of the substituted polyoxometalate solid electrolyte. Specifically, stepwise acidification introduces vacancy-based metal ions, while the hydrothermal method promotes crystallization and synthesizes the product into a nanorod structure. This overcomes the problems of uncertain product morphology and low crystallinity inherent in traditional stepwise acidification methods for preparing polyoxometalate-based solid electrolytes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for preparing a substituted polyoxometalate solid electrolyte, comprising the following steps: S1. Using phosphotungstic acid hydrate as raw material and water as solvent, the pH is adjusted for the first time to form [PW]. 11 O 40 ] 5- The structure yields H3[PW] 11 O 40 ] 2- Solution.

[0008] S2, H3[PW 11 O 40 ] 2- The solution is mixed with a soluble copper salt solution, and the pH is adjusted a second time to form [CuPW] by introducing copper ions. 11 O 40 ] 3- The structure yields H3[CuPW] 11 O 40 Solution.

[0009] S3, with H3[CuPW 11 O 40 Using a solution and lithium salt as raw materials, the pH was adjusted a third time, and a hydrothermal reaction was carried out to promote the crystallization of the product into a nanorod structure, thus obtaining a substituted polyoxometalate solid electrolyte, namely Li3CuPW. 11 O 40 .

[0010] In a preferred embodiment of the present invention, the hydrothermal reaction temperature is 80°C to 90°C and the time is 5h to 7h.

[0011] In a preferred embodiment of the present invention, the pH is adjusted to 4.5-5 for the first adjustment, ≤2.0 for the second adjustment, and 6-7 for the third adjustment.

[0012] In a preferred embodiment of the present invention, the molar ratio of phosphotungstic acid hydrate to soluble copper salt is 1:1, and the soluble copper salt is copper chloride or copper sulfate.

[0013] In a preferred embodiment of the present invention, the molar volume ratio of phosphotungstic acid hydrate to water is 1 mol: 25 L to 50 L; in the soluble copper salt solution, the molar volume ratio of soluble copper salt to water is 1 mol: 50 L to 100 L.

[0014] In a preferred embodiment of the present invention, the molar ratio of soluble copper salt to lithium salt is 1:30, and the lithium salt is LiCl.

[0015] In a preferred embodiment of the present invention, after the second pH adjustment, copper ions are introduced at a temperature of 60°C to 80°C to form [CuPW]. 11 O 40 ] 3- structure.

[0016] A second objective of this invention is to provide a substituted polyoxometalate solid electrolyte prepared by the above method.

[0017] In a preferred embodiment of the present invention, the chemical formula of the substituted polyoxometalate solid electrolyte is Li3CuPW. 11 O 40 It has a three-dimensional continuous lithium-ion transport pathway, in which copper ions replace one tungsten ion, giving the substituted polyoxometalate solid electrolyte a directionality and forming a ternary substituted Keggin structure.

[0018] A third objective of this invention is to provide an application of the above-described substituted polyoxometalate solid electrolyte in solid-state batteries.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a method for preparing a substituted polyoxometalate solid electrolyte, which involves preparing a precursor solution via a stepwise acidification method followed by hydrothermal synthesis. Specifically, it includes: first adjusting the pH after mixing phosphotungstic acid hydrate with water to form [PW...] 11 O 40 ] 5- The structure yields H3[PW] 11 O 40 ] 2- Solution; then mixed with a soluble copper salt solution, pH adjusted a second time, to form [CuPW] by introducing copper ions. 11 O 40 ] 3- The structure yields H3[CuPW] 11 O 40 ] solution; with H3[CuPW 11 O 40 Using a solution and lithium salt as raw materials, a third pH adjustment is performed to initiate a hydrothermal reaction, promoting the crystallization of the product into a nanorod structure, thus obtaining a substituted polyoxometalate solid electrolyte. The stepwise acidification process introduces metal ions into the vacancy, and the hydrothermal method promotes crystallization and synthesizes the nanorod structure, thereby solving the problems of uncertain product morphology and low crystallinity in the stepwise acidification method for preparing polyoxometalate-based solid electrolytes. This preparation method is simple, operates under mild reaction conditions (87℃), requires no high temperature or high pressure, and offers strong process controllability, making it suitable for large-scale production.

[0020] 2. This invention provides a substituted polyoxometalate solid electrolyte with a ternary substituted Keggin structure and the general chemical formula Li3CuPW. 11 O 40 This invention provides a three-dimensional continuous lithium-ion transport pathway. The original structure is a Keggin, composed of a central heteroatom P tetrahedron and 12 surrounding metal-oxygen octahedra (W). This invention uses Cu metal substitution to create an octahedron on the periphery that differs from the other 11 metal-oxygen octahedra, making the structure more directional. The substitution mechanism involves polyoxometalates, which are primarily cationic in nature. Their large anions and high charge density typically do not participate in migration. The stable molecular structure of polyoxometalates, with their Keggin framework playing a key supporting role, and oxygen-rich structures (numerous bridging and terminal oxygens) forming hydrogen bonds or coordination with migrating ions, lowering the migration energy barrier. Simultaneously, the size and spatial configuration of the POMs restrict or guide the ion transport path. The solid electrolyte exhibits high ionic conductivity, low activation energy, and excellent plasticity. Specifically, the room temperature ionic conductivity is greater than 10. -3 The S / cm ratio is much higher than that of traditional inorganic solid electrolytes (such as Li3N, which has an ionic conductivity of 10). -3 S / cm~10 -4The overall activation energy is 0.1376688 eV, which is lower than that of most solid electrolytes (such as Li7La3Zr2O). 12 The activation energy is 0.3 eV to 0.4 eV, indicating that lithium ions have low migration resistance and excellent low-temperature performance in this electrolyte. In addition, the discrete Keggin structure endows the electrolyte with good plasticity, which can be prepared into various shapes under cold pressing conditions, facilitating battery assembly and reducing interfacial impedance.

[0021] 3. This invention provides the application of substituted polyoxometalate solid electrolytes, which utilize the three-dimensional channel characteristics of the Keggin structure to construct a continuous lithium-ion transport network, breaking through the bottleneck of ion conduction in traditional solid electrolytes. Attached Figure Description

[0022] Figure 1 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Li3PW and Comparative Example 1 12 O 40 XRD spectrum.

[0023] Figure 2 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Li3PW and Comparative Example 1 12 O 40 The FTIR spectrum.

[0024] Figure 3 The Li3CuPW of the present invention 11 O 40 Solid electrolytes and Li3PW 12 O 40 Impedance curve of solid electrolyte at room temperature.

[0025] Figure 4 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Scanning electron microscope image of the powder. Figure 4 (a) is a scanning electron microscope image at 10µm, and (b) is a scanning electron microscope image at 5µm.

[0026] Figure 5 The Li3CuPW of the present invention 11 O 40 Impedance curves of solid electrolytes at different temperatures. Figure 5 Figure (a) shows the impedance curve from 0℃ to 20℃, and Figure (b) shows the impedance curve from 30℃ to 60℃.

[0027] Figure 6 The Li3CuPW of the present invention11 O 40 Arrhenius diagram of solid electrolytes.

[0028] Figure 7 This is a SEM image of the solid electrolyte of Comparative Example 2 of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0031] Existing stepwise acidification methods for preparing polyoxometalate-based solid electrolytes suffer from uncertain product morphology and low crystallinity. Therefore, this invention provides a method for preparing novel element-substituted ternary polyoxometalates with high crystallinity and a three-dimensional continuous lithium-ion transport pathway. This method produces polyoxometalate-based solid electrolytes with high ionic conductivity, low activation energy, good chemical / electrochemical stability, and good plasticity.

[0032] First, this invention provides a method for preparing a substituted polyoxometalate solid electrolyte, comprising the following steps: S1, phosphotungstic acid hydrate H3[PW 12 O 40 ]·nH2O is dissolved in water and stirred. The pH is adjusted for the first time to obtain H3[PW 12 O 40 The nH2O solution is solution A.

[0033] S2. Dissolve the soluble copper salt in water, heat to 80°C, and then cool while stirring to obtain a soluble copper salt solution, i.e., solution B.

[0034] S3. While stirring, add H3[PW] dropwise to the soluble copper salt solution. 12 O 40 In a solution of nH2O, a mixed solution is formed. The pH is adjusted a second time, and the solution is heated at 60℃~80℃ for 8~12 minutes to obtain a stable mixed solution, namely H3[CuPW]. 11 O 40 Solution.

[0035] S4. Add LiCl to the mixed solution, stir thoroughly, and store at 60℃ for 15 min. Adjust the pH for the third time and carry out a hydrothermal reaction to promote the crystallization of the product into nanorod structures. After cooling the mixed solution, centrifuge and dry to obtain the substituted polyoxometalate solid electrolyte, Li3CuPW. 11 O 40 .

[0036] It should be noted that the stepwise acidification method used in this invention can avoid the coexistence of multiple structures. Specifically, the purpose of the first acidification is to obtain [PW] 11 O 40 ] 5- The structure, the second acidification yields stable H3[CuPW] 11 O 40 The purpose of this solution is to form [CuPW] by introducing copper ions. 11 O 40 ] 3- Structure. The purpose of the third acidification is to react with the lithium salt to generate the substituted polymetallic hydrochloride final product Li3CuPW. 11 O 40 The preparation method of this invention is stepwise acidification followed by hydrothermal treatment. If hydrothermal treatment is used alone, a substituted structure cannot be formed. If stepwise acidification is used alone, the crystal structure of the ternary polyoxometalate is in an aggregated state, which is not conducive to improving the ionic conductivity.

[0037] The soluble copper salt is copper chloride or copper sulfate, preferably copper chloride CuCl2.

[0038] The hydrothermal reaction is carried out at a temperature of 80℃~90℃, preferably 87℃, for a time of 5h~7h.

[0039] The H3[PW] 12 O 40 The molar ratio of nH2O to CuCl2 is 1:1.

[0040] The H3[PW] 12 O 40 H3[PW] in nH2O solution 12 O 40 The molar volume ratio of nH2O to water is 1 mol: 25 L~50 L, and the molar volume ratio of CuCl2 to water in CuCl2 solution is 1 mol: 50 L~100 L.

[0041] The molar ratio of CuCl2 to LiCl is 0.01:0.3.

[0042] The pH value for the first adjustment is 4.5-5, preferably 4.8. The specific process involves adding Li2CO3 in small portions to bring the solution pH to 4.8.

[0043] The second adjustment aims to achieve a pH ≤ 2.0, preferably 2.0, specifically by using a solution with a concentration of 6 mol·L⁻¹. -1 The pH of the mixed solution was adjusted to 2.0 using an HCl solution.

[0044] The third pH adjustment is 6-7, preferably 6, and the specific process involves adding ammonia to adjust the pH to 6.

[0045] This invention employs a stepwise acidification method and a hydrothermal method to prepare the product at a temperature of 87°C. The stepwise acidification method can avoid the coexistence of multiple structures and is particularly suitable for synthesizing polyoxometalates (POMs) with specific degrees of polymerization or metal doping.

[0046] Secondly, this invention provides a substituted polyoxometalate solid electrolyte, wherein the substituted polyoxometalate solid electrolyte has a ternary substituted Keggin structure and the general chemical formula Li3CuPW. 11 O 40 It possesses a three-dimensional continuous lithium-ion transport pathway. Its original structure is Keggin, consisting of a central heteroatom P tetrahedron and 12 peripheral metal-oxygen octahedra W. Cu metal substitution preferentially occurs, resulting in an octahedron on the periphery that is different from the other 11 metal-oxygen octahedra, making this structure more directional.

[0047] It should be noted that the basic structural unit of polyoxometalates (POMs) is the MO6 (M being a transition metal) octahedron, with the metal ion located at the center of the octahedron and connected to the surrounding six oxygen atoms via coordinate bonds. These octahedrons can connect to each other by sharing vertices, edges, or faces, forming different structures. Polyoxometalates exhibit structural diversity and tunability. This invention achieves higher ion conductivity by replacing one transition metal element in the basic structural unit. The mechanism is that polyoxometalates are primarily cationic, and their numerous anions, with large volume and high charge density, typically do not participate in migration. The stable molecular structure of polyoxometalates, with their keggin framework playing a key supporting role, and oxygen-rich structures (numerous bridging oxygens and terminal oxygens) forming hydrogen bonds or coordination with migrating ions, lowering the migration energy barrier. Simultaneously, the size and spatial configuration of POMs restrict or guide ion transport paths. This invention, by replacing one transition metal, enriches the cation system in polyoxometalates, resulting in rod-shaped structures that are more conducive to ion conductivity, as revealed by SEM images.

[0048] The substituted polyoxometalate solid electrolyte has a room temperature ionic conductivity of 0.9 mS / cm to 1.0 mS / cm, preferably 0.94 mS / cm, and an activation energy of 0.1 eV to 0.2 eV, preferably 0.137 eV.

[0049] Finally, this invention provides an application of the above-mentioned substituted polyoxometalate solid electrolyte in solid-state batteries.

[0050] The following specific examples will provide further explanation.

[0051] Example 1 A substituted polyoxometalate solid electrolyte Li3CuPW 11 O 40 The preparation method includes the following steps: S1. Preparation of solution A: Add 0.01 mol of H3[PW] 12 O 40 Dissolve nH2O in 25mL of deionized water and stir for 10min. Then add Li2CO3 in small portions (0.5g each) to bring the pH of the solution to 4.8, thus obtaining solution A.

[0052] S2. Preparation of solution B: Dissolve 0.01 mol of CuCl2 in 50 mL of deionized water, heat to 80 °C, and then cool while stirring to obtain solution B.

[0053] S3, Preparation of Li3CuPW 11 O 40 Powder: While stirring, add solution B dropwise to solution A to form a mixed solution, and use a 6 mol·L⁻¹ powder. -1 The pH of the mixed solution was adjusted to 2.0 using HCl solution, heated at 60℃ for 10 min, and 0.3 mol of LiCl was added. After thorough stirring, the mixture was kept at 60℃ for 15 min. Ammonia was added to the mixed solution to adjust the pH to 6. The mixed solution was transferred to a reaction vessel and kept at 87℃ for 6 h. After cooling, the mixed solution was centrifuged at 8000 rpm for 10 min, and then dried in a vacuum oven at 87℃ for 12 h to obtain the substituted polyoxometalate solid electrolyte, namely Li3CuPW. 11 O 40 powder.

[0054] Comparative Example 1 A polyoxometalate solid electrolyte Li3PW 12 O 40 The preparation method includes the following steps: 0.01 mol of H3[PW 12 O 40·nH2O and 0.04 mol LiCl were added to deionized water and stirred for 10 min. Then, ammonia was added to adjust the pH to 6. The mixture was transferred to a reaction vessel and kept at 87 °C for 6 h. After cooling, the mixture was centrifuged and dried to obtain Li3PW. 12 O 40 powder.

[0055] Comparative Example 2 A substituted polyoxometalate solid electrolyte Li3CuPW 11 O 40 The preparation method includes the following steps: S1. Preparation of solution A: Add 0.01 mol of H3[PW] 12 O 40 Dissolve nH2O in 25mL of deionized water and stir for 10min. Then add Li2CO3 in small portions (0.5g each) to bring the pH of the solution to 4.8, thus obtaining solution A.

[0056] S2. Preparation of solution B: Dissolve 0.01 mol of CuCl2 in 50 mL of deionized water, heat to 80 °C, and then cool while stirring to obtain solution B.

[0057] S3, Preparation of Li3CuPW 11 O 40 Powder: While stirring, add solution B dropwise to solution A to form a mixed solution, and use a 6 mol·L⁻¹ powder. -1 The pH of the mixed solution was adjusted to 2.0 with HCl solution, and 0.3 mol of LiCl was added. After thorough stirring, the mixture was kept at 60°C for 15 min. Ammonia was added to the mixed solution to adjust the pH to 6. The mixed solution was then transferred to a reaction vessel and reacted for 6 h. After cooling, the mixed solution was centrifuged at 8000 rpm for 10 min, and then dried in a vacuum oven at 87°C for 12 h to obtain the substituted polyoxometalate solid electrolyte, namely Li3CuPW. 11 O 40 powder.

[0058] The structure and performance of the polyoxometalate solid electrolytes of Example 1 and Comparative Examples 1 to 2 were characterized.

[0059] Figure 1 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Li3PW and Comparative Example 1 12 O 40 The XRD spectrum. (Example) Figure 1 As shown, Li3CuPW 11 O 40The diffraction peaks of the two powders broadened due to decreased crystallinity, but in the low-angle range, the positions of the diffraction peaks of the two powders were consistent, indicating that the two powders have the same structure; however, Li3CuPW 11 O 40 The peak positions of the powder compared to Li3PW 12 O 40 The powder peaks shifted to higher angles, indicating that copper successfully replaced tungsten.

[0060] Figure 2 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Li3PW and Comparative Example 1 12 O 40 The FTIR spectrum. (Example) Figure 2 As shown, at 700cm -1 ~1100cm -1 The presence of four characteristic vibrational absorptions belonging to the Keggin structure within the range indicates that both powders possess a keggin structure. The difference lies in the PO (1081 cm⁻¹) composition. -1 The splitting of the WO3 bond due to vibrational absorption indicates a change in the skeletal symmetry of the substituted product due to the introduction of copper. This splitting can serve as one of the criteria for the introduction of a substituent element into a polyoxometalate. Secondly, the terminal oxygen bond WO3... t (O) t (for end oxygen) (960cm) -1 The vibration absorption shifts to lower wavenumbers, indicating that the introduction of copper metal can absorb the vibrations of WO3. t Provide electrons to weaken WO t The intensity.

[0061] Next, the Li3CuPW of Example 1 was analyzed. 11 O 40 Solid electrolyte and Li3PW of Comparative Example 1 12 O 40 The solid electrolyte was subjected to performance testing. The specific process involved preparing Li3CuPW... 11 O 40 Powder and Li3PW 12 O 40 The powder was pressed into solid electrolyte tablets with a diameter of 10 mm and a thickness of 1 mm using cold pressing equipment (automatic tablet press and tableting mold). The electrolyte tablets were placed between stainless steel blocking electrodes of the pressure mold for ionic conductivity testing. The test data were analyzed using an equivalent circuit consisting of a parallel connection of resistive elements (R1), a resistor (R2), and a phase-constant element (CPE1), and a series connection of the Warburg impedance (W1). The results are shown in [reference needed]. Figure 3 .

[0062] Figure 3The Li3CuPW of the present invention 11 O 40 Solid electrolytes and Li3PW 12 O 40 Impedance curve of a solid electrolyte at room temperature. Figure 3 It can be seen that Li3CuPW 11 O 40 The impedance of the solid electrolyte is 135Ω, Li3PW 12 O 40 The impedance of the solid electrolyte is 546 Ω. Li3CuPW 11 O 40 The ionic conductivity of the solid electrolyte is 0.94 mS·cm. -1 Li3PW 12 O 40 The ionic conductivity of the solid electrolyte is 0.23 mS·cm. -1 Therefore, Li3CuPW 11 O 40 Solid electrolytes compared to Li3PW 12 O 40 Solid electrolytes have better ionic conductivity.

[0063] Figure 4 The Li3CuPW of Embodiment 1 of the present invention 11 O 40 Scanning electron microscope image of the powder. Figure 4 Image (a) is a scanning electron microscope (SEM) image at 10 μm, and image (b) is a scanning electron microscope (SEM) image at 5 μm. Figure 4 It can be seen that the Li3CuPW prepared in this invention 11 O 40 The powder has a rod-shaped particle structure. The extension direction of this structure is consistent with the ion transport direction, which is conducive to unidirectional ion conduction, thereby effectively reducing the resistance caused by misalignment and voids at the grain interface.

[0064] Next, the Li3CuPW prepared in Example 1 of this invention will be analyzed. 11 O 40 The solid electrolyte underwent temperature-dependent performance testing. The specific process involved preparing Li3CuPW... 11 O 40 The powder was pressed into solid electrolyte sheets with a diameter of 10 mm and a thickness of 1 mm using a cold pressing device. The electrolyte sheets were placed between stainless steel blocking electrodes in a pressure mold, which was then placed in an electrically heated forced-air drying oven to achieve variable temperature conditions for ionic conductivity testing. The test data were analyzed using an equivalent circuit consisting of a parallel connection of resistive elements (R1), a resistor (R2), and a phase-constant element (CPE1), and a series connection of the Warburg impedance (W1). The results are shown in [reference needed]. Figure 5 .

[0065] Figure 5 The Li3CuPW of the present invention 11 O 40 Impedance curves of solid electrolytes at different temperatures. Figure 5 Figure (a) shows the impedance curves from 0℃ to 20℃, and Figure (b) shows the impedance curves from 30℃ to 60℃. Figure 5 It can be seen that the Li3CuPW prepared in this invention 11 O 40 The impedance of solid electrolytes decreases with increasing temperature, meaning that their ionic conductivity increases with increasing temperature.

[0066] To conduct in-depth research on Li3CuPW 11 O 40 The intrinsic mechanism of ion conduction in solid electrolytes is explored in this invention. By establishing the Arrhenius equation through the linear relationship between temperature and ion conductivity, and fitting the activation energy value, the results are described in [reference needed]. Figure 6 .

[0067] Figure 6 The Li3CuPW of the present invention 11 O 40 Arrhenius diagram of solid electrolytes. (By...) Figure 6 It can be seen that the Li3CuPW prepared in this invention 11 O 40 Solid electrolytes can achieve lower activation energies, i.e., E a =0.137eV.

[0068] Figure 7 This is a SEM image of the solid electrolyte of Comparative Example 2 of the present invention. Figure 7 It can be seen that the crystal structure of Comparative Example 2 is in an aggregated state. Compared with the directional rod-shaped structure of Example 1, this aggregated structure is not conducive to improving ionic conductivity.

[0069] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0070] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a substituted polyoxometalate solid electrolyte, characterized in that, Includes the following steps: Using phosphotungstic acid hydrate as a raw material and water as a solvent, the pH was adjusted for the first time to form [PW]. 11 O 40 ] 5- The structure yields H3[PW] 11 O 40 ] 2- Solution; H3[PW 11 O 40 ] 2- The solution is mixed with a soluble copper salt solution, and the pH is adjusted a second time to form [CuPW] by introducing copper ions. 11 O 40 ] 3- The structure yields H3[CuPW] 11 O 40 Solution; With H3[CuPW 11 O 40 Using a solution and lithium salt as raw materials, the pH was adjusted a third time, and a hydrothermal reaction was carried out to promote the crystallization of the product into a nanorod structure, thus obtaining a substituted polyoxometalate solid electrolyte, namely Li3CuPW. 11 O 40 .

2. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, The hydrothermal reaction temperature is 80℃~90℃, and the time is 5h~7h.

3. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, The pH should be adjusted to 4.5-5 for the first adjustment, ≤2.0 for the second adjustment, and 6-7 for the third adjustment.

4. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, The molar ratio of phosphotungstic acid hydrate to soluble copper salt is 1:1, and the soluble copper salt is copper chloride or copper sulfate.

5. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, The molar volume ratio of phosphotungstic acid hydrate to water is 1 mol: 25 L~50 L; in the soluble copper salt solution, the molar volume ratio of soluble copper salt to water is 1 mol: 50 L~100 L.

6. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, The molar ratio of soluble copper salt to lithium salt is 1:30, and the lithium salt is LiCl.

7. The method for preparing the substituted polyoxometalate solid electrolyte according to claim 1, characterized in that, After the second pH adjustment, copper ions were introduced at a temperature of 60℃~80℃ to form [CuPW]. 11 O 40 ] 3- structure.

8. A substituted polyoxometalate solid electrolyte, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The substituted polyoxometalate solid electrolyte according to claim 8, characterized in that, The chemical formula of the substituted polyoxometalate solid electrolyte is Li3CuPW. 11 O 40 It has a three-dimensional continuous lithium-ion transport pathway, in which copper ions replace one tungsten ion, giving the substituted polyoxometalate solid electrolyte a directionality and forming a ternary substituted Keggin structure.

10. The application of the substituted polyoxometalate solid electrolyte of claim 8 or claim 9 in a solid-state battery.

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