Composite solid electrolyte membrane and preparation method thereof, and solid lithium battery

Abstract

The application discloses a kind of composite solid electrolyte membrane and preparation method thereof, solid lithium battery, the composite solid electrolyte membrane includes porous membrane matrix and solid polymer electrolyte body, the solid polymer electrolyte body includes alcoholysis of ethylene ester-acrylic ester block copolymer, polyethylene oxide, end epoxy polyoxyethylene, end amino polyoxyalkylene and lithium salt, and the solid polymer electrolyte body is arranged on the upper and lower surfaces of the porous membrane matrix and at least part of the solid polymer electrolyte body is embedded in the porosity of the porous membrane matrix.The composite solid electrolyte membrane has higher lithium ion migration number, electrical conductivity and mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a composite solid electrolyte membrane and its preparation method, and a solid lithium battery. Background Technology

[0002] Currently, with the urgent global demand for new energy materials, lithium-ion batteries have seen rapid application and development in recent years due to their advantages such as high voltage, high energy density, long cycle life, and wide electrochemical window. However, traditional lithium batteries, using liquid electrolytes, inevitably pose safety hazards. Therefore, developing solid-state lithium-ion batteries can fundamentally solve this problem. The structure of an all-solid-state lithium-ion battery includes a positive electrode, a solid electrolyte, and a negative electrode. The solid electrolyte, while conducting lithium ions, also acts as a separator, preventing electron transport. Compared to traditional lithium batteries, solid-state lithium batteries have the following main advantages: First, the risk of spontaneous combustion or explosion is significantly reduced, resulting in high safety. Second, the positive and negative electrode materials are optimized, reducing inactive components and increasing energy density. Third, the solid electrolyte does not dry out during long-term cycling, resulting in a long cycle life. Given the advantages and prospects of solid-state lithium-ion batteries, they have attracted the attention of research institutions, large electronics and automotive manufacturing companies worldwide. Governments around the world have successively introduced policies to encourage the research and development and industrialization of solid-state batteries. In this process, many types of solid electrolytes have emerged, such as inorganic, polymer, and organic / inorganic composite materials. Among them, if polymer systems can overcome a series of technical bottlenecks such as improving electrical performance, they will be the first to be put into practical industrial applications.

[0003] Solid polymer electrolytes are classified according to the molecular structure of the polymer matrix, such as polyethers, polyamines, and polyesters. These polymer electrolytes react with Li... + Complexation and decomplexation lead to the formation of materials with ionic conductivity. In polyether-based polymer electrolytes, polyethylene oxide (PEO) has been widely used as the host material for polymer electrolytes over the past few decades due to its high dielectric constant, which facilitates the dissociation of lithium salts. In polymer PEO, Li... + The conduction mainly relies on Li + It complexes with anions on PEO segments, and this conduction mainly occurs in the amorphous region. At room temperature, PEO has very high crystallinity; therefore, traditional PEO-Li... + The polymer electrolyte of the system has a low ionic conductivity (10). -7 ~10 -6 S cm -1 (25℃). In addition, PEO has low strength and cannot suppress lithium dendrite growth, which further hinders its application.

[0004] Therefore, existing solid electrolyte membranes need to be improved. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a composite solid-state electrolyte membrane and its preparation method, as well as a solid-state lithium battery. This composite solid-state electrolyte membrane possesses high lithium-ion transport number, conductivity, and mechanical strength, thereby significantly improving the discharge specific capacity, cycle capacity retention, and lifespan of solid-state lithium batteries.

[0006] In one aspect of the present invention, a composite solid electrolyte membrane is provided. According to an embodiment of the present invention, the composite solid electrolyte membrane comprises: a porous membrane substrate and a solid polymer electrolyte body. The solid polymer electrolyte body comprises an alcoholysis product of an ethylene ester-acrylate block copolymer, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyethylene oxide, and a lithium salt. The solid polymer electrolyte body is disposed on the upper and lower surfaces of the porous membrane substrate, and at least a portion of the solid polymer electrolyte body is embedded in the pores of the porous membrane substrate.

[0007] Therefore, a composite solid electrolyte membrane is obtained by mixing the alcoholysis product of ethylene ester-acrylate block copolymer, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyethylene oxide, and lithium salt to prepare a solid polymer electrolyte body. This solid polymer electrolyte body is formed on the upper and lower surfaces of a porous membrane substrate, with at least a portion embedded in the pores of the porous membrane substrate. The alcoholysis product of the ethylene ester-acrylate block copolymer reduces the crystallinity of the polyethylene oxide polymer system at room temperature, thereby increasing the lithium-ion transference number and conductivity of the composite solid electrolyte membrane, significantly improving its electrochemical performance. Furthermore, the epoxy-terminated polyethylene oxide and amino-terminated polyethylene oxide undergo cross-linking reactions of their active groups. Both contain amino and epoxy groups, respectively. Under heating conditions, the epoxy ring-opening reaction occurs, gradually polymerizing from the original low-molecular-weight monomer to a high-molecular-weight monomer. The material exhibits good film-forming properties. If a single substance is added without reacting groups, it cannot form a network framework. By adjusting the equivalent of the active groups of the two substances, a balance between the mechanical strength and electrical properties of the film can be achieved. In addition, after alcoholysis, the ethylene ester-acrylate block copolymer can facilitate the introduction of basic ions, such as sodium, potassium, or lithium, into the polymer chain segments, thus forming a single-ion conductor complex, which is particularly beneficial for the introduction of lithium ions, thereby improving the battery's discharge specific capacity and cycle capacity retention. The entire polymer system includes PEO (polyethylene oxide) as the main structure, epoxy-terminated polyethylene oxide and amino-terminated polyethylene oxide polymers forming a PEO-like structure, and branched ethylene ester-acrylate copolymer alcoholysis products. These three components work together to form an interpenetrating network structure. Most importantly, the synergistic effect of these three components results in a reduction in crystallinity, which promotes smoother lithium ion transport channels. Simultaneously, by employing a porous membrane substrate, the influence of the membrane material on lithium-ion conduction can be reduced, enabling the tensile strength of the composite solid electrolyte membrane to reach over 8 MPa. This improves the overall mechanical properties of the composite solid electrolyte membrane, effectively suppressing lithium dendrite growth and enhancing battery safety. Therefore, the composite solid electrolyte membrane of this invention possesses high lithium-ion transport number, conductivity, and mechanical strength, and its application in solid-state lithium batteries can significantly improve their discharge specific capacity, cycle capacity retention, and lifespan.

[0008] In addition, the composite solid electrolyte membrane according to the above embodiments of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, the solid polymer electrolyte body comprises: 10-70 parts by weight of polyethylene oxide, 1-20 parts by weight of epoxy-terminated polyethylene oxide, 2-30 parts by weight of amino-terminated polyoxyethylene, 3-55 parts by weight of the alcoholysis product of ethylene ester-acrylate block copolymer, and 10-50 parts by weight of lithium salt. This significantly improves the lithium-ion transport number and conductivity of the composite solid electrolyte membrane, thereby enhancing its electrochemical performance.

[0010] In some embodiments of the present invention, the degree of alcoholysis of the ethylene ester-acrylate block copolymer is 65% to 100%. This improves the lithium-ion transference number and conductivity of the composite solid electrolyte membrane, thereby enhancing its electrochemical performance.

[0011] In some embodiments of the present invention, the molar ratio of ethylene ester to acrylate monomers in the alcoholysis product of the ethylene ester-acrylate block copolymer is 1:5 to 4:1. This improves the lithium-ion transport number and conductivity of the composite solid electrolyte membrane.

[0012] In some embodiments of the present invention, the acrylate includes at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate. This can improve the lithium-ion transport number and conductivity of the composite solid electrolyte membrane.

[0013] In some embodiments of the present invention, the terminal epoxy group polyethylene oxide comprises at least one of cyclohexanediol diglycidyl ether, monoglycidyl ether of C12-C14 alcohols, butanediol diglycidyl ether, tert-butylphenol monoglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether. This can improve the lithium-ion transport number and conductivity of the composite solid electrolyte membrane.

[0014] In some embodiments of the present invention, the epoxy equivalent of the terminal epoxy group polyethylene oxide is 150–700 g / Eq. Therefore, the composite solid electrolyte membrane exhibits better film-forming properties, thereby improving the lithium-ion transference number and conductivity of the composite solid electrolyte membrane.

[0015] In some embodiments of the present invention, the terminal amino polyoxyethylene includes at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900, and T-5000.

[0016] In some embodiments of the present invention, the average AHEW of the terminal amino-terminated polyoxyethylene is 120–800 g / Eq. Therefore, the composite solid electrolyte membrane exhibits good film-forming properties, thereby improving the lithium-ion transference number and conductivity of the composite solid electrolyte membrane.

[0017] In some embodiments of the present invention, the molecular weight of the polyethylene oxide is 350,000 to 800,000. This increases the solubility of the polyethylene oxide, improves operability, and consequently enhances the lithium-ion transference number and conductivity of the composite solid electrolyte membrane.

[0018] In some embodiments of the present invention, the thickness of the porous membrane substrate is 6–16 μm, and the basis weight is 10–100 g / m³. 2 This improves the mechanical strength of the composite solid electrolyte membrane, provides a good channel for the electrolyte slurry, and enhances the overall mechanical properties of the composite solid electrolyte membrane.

[0019] In some embodiments of the present invention, the porous membrane substrate comprises at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, and nylon-10 / nylon-66. This improves the overall mechanical properties of the composite solid electrolyte membrane.

[0020] In another aspect of the present invention, a method for preparing the above-mentioned composite solid electrolyte membrane is provided. According to an embodiment of the present invention, the preparation method includes:

[0021] (1) The alcoholysis product of ethylene ester-acrylate block copolymer, polyethylene oxide and solvent are mixed to obtain a first mixture;

[0022] (2) The first mixture is mixed with terminal epoxy polyethylene oxide, terminal amino polyethylene oxide and lithium salt to obtain a solid polymer electrolyte slurry;

[0023] (3) The solid polymer electrolyte slurry is coated on the upper and lower surfaces of the porous membrane substrate, and then placed in a heating device for step heating and constant temperature drying to obtain a composite solid electrolyte membrane.

[0024] Therefore, the preparation method of the present invention can be used to prepare the above-mentioned composite solid electrolyte membrane with high lithium-ion transport number, conductivity and mechanical strength, and its application in solid lithium batteries can significantly improve their discharge specific capacity, cycle capacity retention rate and service life.

[0025] In addition, the method for preparing composite solid electrolyte membranes according to the above embodiments of the present invention may also have the following additional technical features:

[0026] In some embodiments of the present invention, in step (3), the step heating includes a solvent evaporation section, a first polymerization stage and a second polymerization stage, wherein the temperature of the solvent evaporation section is 30-60°C, the temperature of the first polymerization stage is 50-70°C, the temperature of the second polymerization stage is 60-90°C, and the total temperature holding time of each stage of the step heating is 30 min to 2 h.

[0027] In another aspect, the present invention provides a solid-state lithium battery comprising a positive electrode, a negative electrode, and a solid electrolyte membrane, wherein the solid electrolyte membrane is the composite solid electrolyte membrane of the present invention. Thus, the solid-state lithium battery incorporates the aforementioned composite solid electrolyte membrane with high lithium-ion transport number, conductivity, and mechanical strength, thereby exhibiting high discharge specific capacity, cycle capacity retention, and service life.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0030] In one aspect of the present invention, a composite solid electrolyte membrane is provided. According to an embodiment of the present invention, the composite solid electrolyte membrane comprises: a porous membrane substrate and a solid polymer electrolyte body. The solid polymer electrolyte body comprises an alcoholysis product of an ethylene ester-acrylate block copolymer, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyethylene oxide, and lithium salt. The solid polymer electrolyte body is disposed on the upper and lower surfaces of the porous membrane substrate and at least a portion of the solid polymer electrolyte body is embedded in the pores of the porous membrane substrate.

[0031] The inventors discovered that a composite solid electrolyte membrane is obtained by mixing the alcoholysis product of ethylene ester-acrylate block copolymer, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyethylene oxide, and lithium salt to prepare a solid polymer electrolyte body that is formed on the upper and lower surfaces of a porous membrane substrate, with at least a portion of the solid polymer electrolyte body embedded in the pores of the porous membrane substrate. The alcoholysis product of the ethylene ester-acrylate block copolymer can reduce the crystallinity of the polyethylene oxide polymer system at room temperature, thereby increasing the lithium-ion transference number and conductivity of the composite solid electrolyte membrane, significantly improving its electrochemical performance. Furthermore, the active groups of the epoxy-terminated polyethylene oxide and amino-terminated polyethylene oxide undergo a cross-linking reaction; that is, both contain amino and epoxy groups respectively. Under heating conditions, the epoxy ring-opening reaction occurs, gradually polymerizing from the original low molecular weight monomer to a high molecular weight monomer, exhibiting good film-forming properties. If a single substance is added without reacting groups, a network framework cannot be formed. The composite solid electrolyte membrane is formed through the interaction of the active groups of these two substances. Equivalent adjustment can achieve a balance between the mechanical strength and electrical properties of the film. Furthermore, after alcoholysis, the ethylene-acrylate block copolymer can readily introduce alkaline ions, such as sodium, potassium, or lithium, into the polymer chain segments, forming single-ion conductor complexes, particularly beneficial for lithium ion introduction, thereby improving the battery's discharge specific capacity and cycle capacity retention. The entire polymer system comprises a PEO (polyethylene oxide) main structure, PEO-like structures formed by the polymerization of terminal epoxy-based polyethylene oxide and terminal amino-based polyethylene oxide, and branched ethylene-acrylate copolymer alcoholysis products. These three components synergistically form an interpenetrating network structure. Most importantly, their synergistic effect results in reduced crystallinity, promoting smoother lithium ion transport channels. Simultaneously, the use of a porous membrane substrate reduces the influence of the membrane material on lithium ion conduction, while simultaneously increasing the tensile strength of the composite solid electrolyte membrane to over 8 MPa, improving the overall mechanical properties of the composite solid electrolyte membrane. This effectively inhibits lithium dendrite growth and enhances battery safety. Therefore, the composite solid electrolyte membrane of the present invention has high lithium-ion transference number, electrical conductivity and mechanical strength, and its use in solid lithium batteries can significantly improve their discharge specific capacity, cycle capacity retention and service life.

[0032] Further, the aforementioned solid polymer electrolyte matrix comprises: 10-70 parts by weight of polyethylene oxide, 1-20 parts by weight of epoxy-terminated polyethylene oxide, 2-30 parts by weight of amino-terminated polyoxyethylene, 3-55 parts by weight of the alcoholysis product of ethylene ester-acrylate block copolymer, and 10-50 parts by weight of lithium salt. The inventors discovered that if the amount of polyethylene oxide is less than 10 parts by weight, the transport chain provided to lithium ions is too small, resulting in increased internal resistance. Conversely, if the amount of polyethylene oxide is greater than 70 parts by weight, it is difficult to control its crystallinity to a minimum. Because the amino and epoxy groups of the amino-terminated polyoxyethylene react with those of the epoxy-terminated polyethylene oxide under heating conditions, the amounts of both epoxy-terminated polyethylene oxide and amino-terminated polyoxyethylene need to be carefully defined. Exceeding these ranges prolongs the film-forming and curing cycle and introduces excessive amide inert groups into the entire molecular chain, hindering lithium ion migration. Conversely, if the amount is less than these ranges, it cannot provide support for the polymer network framework. Furthermore, the alcoholysis product of the ethylene ester-acrylate block copolymer... Below this range, the effect of inhibiting the crystallization of highly linear polymers decreases, failing to improve lithium-ion transport number and conductivity. If the alcoholysis product of the ethylene ester-acrylate block copolymer is above this range, the film rigidity increases, leading to tiny voids at the interface between the film and the positive and negative electrodes, increasing the interface size and causing increased internal resistance and capacity loss. Furthermore, if the lithium salt is below this range, the number of lithium ions in the electrolyte membrane system is insufficient, resulting in a capacity mismatch with the positive electrode and preventing full utilization of the theoretical capacity. If the lithium salt is above this range, it will reach saturation, wasting resources and increasing the difficulty of dispersion in the electrolyte membrane system. Uneven dispersion leads to more defects in the apparent and internal microstructure of the film. Therefore, this application controls the materials within the above-mentioned ranges to achieve optimal synergistic effects, significantly improving the lithium-ion transport number and conductivity of the composite solid electrolyte membrane and enhancing its electrochemical performance.

[0033] Furthermore, the molecular weight of the polyethylene oxide used above is 350,000 to 800,000. The inventors discovered that if the molecular weight of the polyethylene oxide is less than 350,000, it reduces the mechanical strength of the solid polymer electrolyte matrix and results in insufficient cross-linking networks, thereby reducing the conductivity of the ion-composite solid electrolyte membrane. Conversely, if the molecular weight of the polyethylene oxide is greater than 800,000, the dissolution efficiency of the polyethylene oxide is low, thus reducing operability and feasibility. Therefore, this application uses polyethylene oxide with a molecular weight of 350,000 to 800,000, which can increase the dissolution efficiency of the polyethylene oxide while improving the lithium-ion transference number, conductivity, and strength of the composite solid electrolyte membrane.

[0034] Furthermore, the degree of alcoholysis of the above-mentioned ethylene ester-acrylate block copolymer is 65%–100%. The inventors discovered that if the degree of alcoholysis of the ethylene ester-acrylate block copolymer is less than 65%, the content of inert ester bonds in the polymer segments is relatively high, while the ratio of lithium carboxylate to alcohol hydroxyl groups after alcoholysis is relatively low, resulting in a lower proportion of lithium-ion conductors and affecting the lithium-ion transference number and conductivity. Therefore, using an alcoholysis product of ethylene ester-acrylate block copolymer with a degree of alcoholysis of 65%–100% ensures that the lithium carboxylate content remains high, i.e., increasing the proportion of lithium-containing segments, increasing the content of lithium-ion conductors, further improving the lithium-ion transference number and conductivity of the composite solid electrolyte membrane, and improving the electrochemical performance of the composite solid electrolyte membrane. Simultaneously, the molar ratio of ethylene ester to acrylate monomers in the above-mentioned ethylene ester-acrylate block copolymer alcoholysis product is 1:5–4:1. The inventors discovered that when the molar ratio of vinyl ester to acrylate monomers is less than 1:5, the resulting slurry has a high viscosity, decreased dispersion characteristics, and poor permeability in porous membranes. Conversely, when the molar ratio is greater than 4:1, microbubbles are generated in the slurry, which are difficult to remove, resulting in a poor appearance after film formation, thus affecting conductivity and lithium-ion transport number. Therefore, this application uses a monomer molar ratio of vinyl ester to acrylate in the alcoholysis product of vinyl ester-acrylate block copolymer of 1:5 to 4:1 to further improve the lithium-ion transport number and conductivity of the composite solid electrolyte membrane. Furthermore, those skilled in the art can select the specific type of acrylate according to actual needs. For example, the acrylate may include at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate, thereby improving the lithium-ion transport number and conductivity of the composite solid electrolyte membrane.

[0035] Furthermore, the epoxy equivalent of the aforementioned epoxy-terminated polyethylene oxide is 150–700 g / Eq. The inventors discovered that if the epoxy equivalent of the epoxy-terminated polyethylene oxide is less than 150 g / Eq, the crosslinking density decreases, leading to a reduction in the molecular weight of the polymer segments and thus decreasing the mechanical strength of the solid polymer electrolyte bulk. Conversely, if the epoxy equivalent of the solid polymer electrolyte bulk is greater than 700 g / Eq, the film-forming properties of the solid polymer electrolyte bulk are poor. Therefore, this application uses an epoxy equivalent of 150–700 g / Eq for the epoxy-terminated polyethylene oxide, which can improve both the mechanical strength and film-forming properties of the composite solid electrolyte membrane. It should be noted that those skilled in the art can select the specific type of the above-mentioned epoxy-terminated polyethylene oxide according to actual needs, as long as the above-mentioned epoxy equivalent is met. For example, the above-mentioned epoxy-terminated polyethylene oxide includes at least one of cyclohexanediethanol diglycidyl ether, monoglycidyl ether of C12-C14 alcohol, butanediol diglycidyl ether, tert-butylphenol monoglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether.

[0036] Furthermore, the average AHEW of the aforementioned terminal amino polyoxyethylene is 120–800 g / Eq. The inventors discovered that if the average AHEW of the terminal amino polyoxyethylene is less than 120 g / Eq, the crosslinking density will decrease, resulting in a decrease in the molecular weight of the polymer segments, thereby reducing the mechanical strength of the solid polymer electrolyte bulk; while if the average AHEW of the terminal amino polyoxyethylene is greater than 800 g / Eq, the film-forming properties of the solid polymer electrolyte bulk will be poor. Therefore, this application uses terminal amino polyoxyethylene with an average AHEW of 120-800 g / Eq, which results in better film-forming properties of the composite solid electrolyte membrane, thereby improving the lithium-ion transference number and conductivity of the composite solid electrolyte membrane. It should be noted that those skilled in the art can select the specific type of terminal amino polyoxyethylene according to actual needs, as long as it can meet the above average AHEW. For example, the terminal amino polyoxyethylene includes at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900 and T-5000.

[0037] Furthermore, the thickness of the porous membrane substrate is 6–16 μm, and the basis weight is 10–100 g / m³. 2 The inventors discovered that the basis weight of the porous membrane substrate is directly proportional to its thickness. If the porous membrane substrate used is below the aforementioned thickness and basis weight range, the mechanical strength of the composite solid electrolyte membrane will decrease. Conversely, if the porous membrane substrate used is above the aforementioned thickness and basis weight range, the number and size of pores will inevitably decrease, resulting in an inability to provide adequate channels for the electrolyte slurry. Therefore, this application uses a porous membrane substrate with a thickness of 6–16 μm and a basis weight of 10–100 g / m³. 2This can improve the mechanical strength of the composite solid electrolyte membrane, provide a good channel for the electrolyte slurry, and enhance the overall mechanical properties of the composite solid electrolyte membrane. It should be noted that those skilled in the art can select the specific type of porous membrane substrate according to actual needs, as long as the above conditions are met. For example, the porous membrane substrate can include at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, nylon-10, and nylon-66, thereby improving the overall mechanical properties of the composite solid electrolyte membrane.

[0038] In another aspect of the present invention, a method for preparing the above-mentioned composite solid electrolyte membrane is provided. According to an embodiment of the present invention, the preparation method includes:

[0039] S100: A mixture of alcoholysis product of ethylene ester-acrylate block copolymer, polyethylene oxide, and solvent.

[0040] In this step, the alcoholysis product of the ethylene ester-acrylate block copolymer, polyethylene oxide, and a solvent are mixed, dissolving the alcoholysis product and polyethylene oxide in the solvent to obtain a first mixture. The inventors have discovered that the alcoholysis product of the ethylene ester-acrylate block copolymer can reduce the crystallinity of the polyethylene oxide polymer system at room temperature, thereby increasing the lithium-ion transport number and conductivity of the composite solid electrolyte membrane, significantly improving its electrochemical performance. Preferably, the alcoholysis product of the ethylene ester-acrylate block copolymer and polyethylene oxide can be mixed separately with the solvent, and then the resulting solutions are mixed. It should be noted that those skilled in the art can select the specific type and amount of solvent according to actual needs, as long as it satisfies the above-mentioned dissolution of the alcoholysis product of the ethylene ester-acrylate block copolymer and polyethylene oxide; further details are omitted here.

[0041] S200: Mix the first mixture with terminal epoxy-based polyethylene oxide, terminal amino-based polyethylene oxide, and lithium salt.

[0042] In this step, the first mixture obtained above is mixed with terminal epoxy-based polyethylene oxide, terminal amino-based polyoxyethylene oxide, and lithium salt to obtain a solid polymer electrolyte slurry. The inventors discovered that in this process, the entire polymer system comprises PEO (polyethylene oxide) as the main structure, terminal epoxy-based polyethylene oxide and terminal amino-based polyoxyethylene oxide forming a PEO-like structure after polymerization, and branched ethylene ester-acrylate copolymer alcoholysis products. These three components synergistically form an interpenetrating network structure. Most importantly, the synergistic effect of these three components manifests as a reduction in crystallinity, which facilitates smoother lithium-ion transport channels, introduces lithium ions at the polymer molecular chain ends, and forms ion-conducting complexes, thereby improving the battery's discharge specific capacity and cycle capacity retention. Preferably, the first mixture obtained above is mixed with terminal epoxy-based polyethylene oxide and terminal amino-based polyoxyethylene oxide and stirred evenly, and then lithium salt is added and stirred evenly to obtain the solid polymer electrolyte slurry.

[0043] S300: A solid polymer electrolyte slurry is coated onto the upper and lower surfaces of a porous membrane substrate, and then placed in a heating device for stepwise heating.

[0044] In this step, the solid polymer electrolyte slurry obtained above is coated on the upper and lower surfaces of a porous membrane substrate, and then placed in a heating device for stepwise heating and constant-temperature drying to obtain a composite solid electrolyte membrane. The inventors discovered that by using a porous membrane substrate, the porous membrane can reduce the influence of the membrane material on lithium-ion conduction, while simultaneously achieving a tensile strength of over 8 MPa in the composite solid electrolyte membrane, thus improving the overall mechanical properties of the composite solid electrolyte membrane. This effectively inhibits the growth of lithium dendrites and improves the safety performance of the battery. According to one embodiment of the present invention, the stepped heating includes a solvent evaporation stage, a first polymerization stage, and a second polymerization stage. The solvent evaporation stage has a temperature of 30–60°C, during which a portion of the solvent is evaporated. The first polymerization stage has a temperature of 50–70°C, during which the remaining solvent is evaporated while the amino and epoxy groups in the terminal epoxy group polyethylene oxide and the terminal amino group polyethylene oxide react, with the epoxy ring opening to generate hydroxyl groups. The two substances gradually polymerize, forming a polymer network backbone in situ. The second polymerization stage has a temperature of 60–90°C, during which the remaining solvent continues to evaporate, and unreacted groups are further polymerized, reducing the residual amount of small molecules. The total temperature holding time for each stage of the stepped heating is 30 min–2 h.

[0045] Therefore, the preparation method of the present invention can be used to prepare the above-mentioned composite solid electrolyte membrane with high lithium-ion transport number, conductivity and mechanical strength, and its application in solid lithium batteries can significantly improve their discharge specific capacity, cycle capacity retention rate and service life.

[0046] It should be noted that the features and advantages described above for composite solid electrolyte membranes also apply to the method for preparing composite solid electrolyte membranes, and will not be repeated here.

[0047] In another aspect, the present invention provides a solid-state lithium battery. According to an embodiment of the invention, the solid-state lithium battery includes a positive electrode, a negative electrode, and a solid electrolyte membrane, wherein the solid electrolyte membrane is the aforementioned composite solid electrolyte membrane or a composite solid electrolyte membrane obtained by the aforementioned method. Thus, the solid-state lithium battery incorporates the aforementioned composite solid electrolyte membrane with high lithium-ion transport number, conductivity, and mechanical strength, thereby exhibiting high discharge specific capacity, cycle capacity retention, and lifespan.

[0048] It should be noted that the materials used in the positive and negative electrodes of the above-mentioned solid-state lithium battery are all conventional materials in the field, and will not be described in detail here. At the same time, the features and advantages described above for the composite solid-state electrolyte membrane also apply to this solid-state lithium battery, and will not be described in detail here.

[0049] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0050] Preparation of composite solid electrolyte membranes:

[0051] Comparative Example 1 (Alcohololysis product without ethylene-acrylate block copolymer)

[0052] (1) Dissolve 50 parts by weight of polyethylene oxide with a molecular weight of 400,000 in acetonitrile solvent to obtain the first mixture;

[0053] (2) Add 2 parts by weight of cyclohexanediol diglycidyl ether and 25 parts by weight of amino-terminated polyoxyethylene ED-900 to the first mixture, stir evenly to obtain the second mixture;

[0054] (3) Add 15 parts by weight of lithium sulfonamide to the second mixture and stir evenly to obtain a solid polymer electrolyte slurry;

[0055] (4) The solid polymer electrolyte slurry is coated on a porous membrane substrate of 12 μm meta-aramid system, and then placed in a heating device for step heating. The step heating includes a solvent evaporation section, a first polymerization stage and a second polymerization stage. The temperature of the solvent evaporation section is 40℃ and held for 30 min, the temperature of the first polymerization stage is 60℃ and held for 30 min, and the temperature of the second polymerization stage is 80℃ and held for 1 h. After complete drying, a composite solid electrolyte membrane with a total thickness of 35 μm is obtained and placed in a glove box for later use.

[0056] Comparative Example 2 (without using a porous membrane substrate)

[0057] (1) The alcoholysis product of ethylene ester-methyl acrylate block copolymer is dissolved in acetonitrile solvent to obtain the first mixture;

[0058] (2) Dissolve 50 parts by weight of polyethylene oxide with a molecular weight of 400,000 in acetonitrile solvent to obtain a second mixture;

[0059] (3) After mixing the first mixture and the second mixture, add 15 parts by weight of cyclohexanediol diglycidyl ether and 5 parts by weight of amino-terminated polyoxyethylene ED-900, stir evenly, and obtain the third mixture.

[0060] (4) Add 40 parts by weight of lithium sulfonamide to the third mixture and stir until uniform to obtain a solid polymer electrolyte slurry;

[0061] (5) The solid polymer electrolyte slurry is directly coated onto the release membrane substrate and then placed in a heating device for step heating. The step heating includes a solvent evaporation section, a first polymerization stage and a second polymerization stage. The temperature of the solvent evaporation section is 30°C and held for 30 min, the temperature of the first polymerization stage is 60°C and held for 1 h, and the temperature of the second polymerization stage is 85°C and held for 1 h. After complete drying, a composite solid electrolyte membrane with a total thickness of 20 μm is obtained and placed in a glove box for later use.

[0062] Table 1 shows some of the specific parameters used in the preparation process of Comparative Example 1 and Comparative Example 2.

[0063] General methods

[0064] (1) The alcoholysis product of ethylene ester-acrylate block copolymer is dissolved in acetonitrile solvent to obtain the first mixture;

[0065] (2) Dissolve polyethylene oxide in a solvent to obtain a second mixture;

[0066] (3) After mixing the first mixture and the second mixture, add terminal epoxy polyethylene oxide and terminal amino polyethylene oxide, stir evenly to obtain the third mixture;

[0067] (4) Add lithium salt to the third mixture and stir until homogeneous to obtain solid polymer electrolyte slurry;

[0068] (5) The solid polymer electrolyte slurry is coated on the porous membrane substrate and then placed in a heating device for step heating. The step heating includes a solvent evaporation stage, a first polymerization stage and a second polymerization stage. After constant temperature drying, a composite solid electrolyte membrane is obtained.

[0069] The preparation methods of Examples 1-6 adopt the general methods described above, and the specific process parameters are shown in Table 1.

[0070] Tensile strength determination of composite solid electrolyte membrane:

[0071] Referring to the standard GB / T13022-1991 Test Method for Tensile Properties of Plastic Films, with a speed of 50 mm / min, the electrolyte membrane is first cut into samples with a width of 15 mm and a length of >18 cm for later use. The thickness of the samples is measured with a thickness gauge, and then the average thickness of the samples is calculated.

[0072] The formula for calculating tensile strength is: Tensile strength = Maximum force / Cross-sectional area

[0073]

[0074] Solid-state lithium battery fabrication:

[0075] This solid-state lithium battery comprises a positive electrode, a lithium metal negative electrode, and a solid polymer electrolyte membrane prepared in Comparative Examples 1-2 and Examples 1-6, with the composite solid polymer electrolyte membrane positioned between the positive and negative electrodes. The positive electrode active material is lithium iron phosphate, the conductive agent is Super P, and the binder is polyvinylidene fluoride. A positive electrode slurry is prepared by mixing lithium iron phosphate:Super P:polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The positive electrode slurry is coated onto aluminum foil and vacuum dried at 110°C for 24 hours to obtain the positive electrode sheet. The solid polymer electrolyte membranes prepared in Comparative Examples 1-2 and Examples 1-6 are then assembled with lithium metal to form button cells under an argon atmosphere.

[0076] Solid-state lithium battery performance testing:

[0077] (1) Lithium-ion conductivity test

[0078] A blocking battery consisting of a stainless steel sheet and a solid polymer electrolyte (thickness l, area S) was constructed. An EIS spectrum was obtained by testing the battery with a 5mV perturbation voltage and a frequency range of 0.1 to 1000kHz. The bulk resistance Rb of the solid polymer electrolyte was obtained. The lithium-ion conductivity σ of the solid polymer electrolyte was obtained by using the formula σ = l / (Rb × S).

[0079] (2) Electrochemical stability window

[0080] An SS / / solid polymer electrolyte / / Li semi-blocking battery was constructed using stainless steel sheets, solid polymer electrolyte, and lithium sheets. The sample was treated at 80℃ and a certain pressure for 2 hours before use. The linear sweep voltammetry was used for testing, with a scan rate of 2mV / s and a voltage scan range from open circuit voltage of 0V to reference voltage of 6V.

[0081] (3) Lithium-ion transference number

[0082] The test method adopts the steady-state polarization method and uses a non-blocking battery system. When a constant voltage is applied to the two ends of the battery, a large initial current Ii will be generated. Then the current gradually decreases and tends to a stable value Is. The ratio of Is to Ii is the lithium-ion transference number.

[0083] (4) Solid-state lithium battery cycling

[0084] The assembled solid-state lithium battery was subjected to charge-discharge tests at 60°C within a range of 2.5–3.7V.

[0085] The results of the above performance tests are shown in Table 2.

[0086] Table 2

[0087]

[0088]

[0089] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A composite solid electrolyte membrane, characterized in that, include: Porous membrane substrate; A solid polymer electrolyte body, comprising an alcoholysis product of an ethylene ester-acrylate block copolymer, polyethylene oxide, terminal epoxy-terminated polyethylene oxide, terminal amino-terminated polyoxyethylene oxide, and a lithium salt, wherein the solid polymer electrolyte body is disposed on the upper and lower surfaces of the porous membrane substrate and at least a portion of the solid polymer electrolyte body is embedded in the pores of the porous membrane substrate. The solid polymer electrolyte body comprises: 10-70 parts by weight of polyethylene oxide, 1-20 parts by weight of epoxy-terminated polyethylene oxide, 2-30 parts by weight of amino-terminated polyoxyethylene, 3-55 parts by weight of alcoholysis product of ethylene ester-acrylate block copolymer, and 10-50 parts by weight of lithium salt. The degree of alcoholysis of the ethylene ester-acrylate block copolymer is 65%~100%; The monomer molar ratio of ethylene ester to acrylate in the alcoholysis product of the ethylene ester-acrylate block copolymer is 1:5 to 4:

1.

2. The composite solid electrolyte membrane according to claim 1, characterized in that, The acrylates include at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate.

3. The composite solid electrolyte membrane according to claim 1, characterized in that, The terminal epoxy-based polyethylene oxide comprises at least one of cyclohexanediol diglycidyl ether, monoglycidyl ether of C12-C14 alcohols, butanediol diglycidyl ether, tert-butylphenol monoglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether. Optionally, the epoxy equivalent of the terminally epoxy-terminated polyethylene oxide is 150~700 g / Eq.

4. The composite solid electrolyte membrane according to claim 1, characterized in that, The terminal amino polyoxyethylene includes at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900 and T-5000; Optionally, the average AHEW of the terminal amino polyoxyethylene is 120~800 g / Eq.

5. The composite solid electrolyte membrane according to claim 1, characterized in that, The molecular weight of the polyoxyethylene is 350,000 to 800,000; Optionally, the thickness of the porous membrane substrate is 6~16 μm, and the basis weight is 10~100 g / m³. 2 ; Optionally, the porous membrane substrate comprises at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, nylon-10, and nylon-66.

6. A method for preparing the composite solid electrolyte membrane according to any one of claims 1 to 5, characterized in that, include: (1) The alcoholysis product of ethylene ester-acrylate block copolymer, polyethylene oxide and solvent are mixed to obtain a first mixture; (2) The first mixture is mixed with terminal epoxy polyethylene oxide, terminal amino polyethylene oxide and lithium salt to obtain a solid polymer electrolyte slurry; (3) The solid polymer electrolyte slurry is coated on the upper and lower surfaces of the porous membrane substrate, and then placed in a heating device for step heating and constant temperature drying to obtain a composite solid electrolyte membrane.

7. The method for preparing the composite solid electrolyte membrane according to claim 6, characterized in that, In step (3), the stepped temperature increase includes a solvent evaporation stage, a first polymerization stage, and a second polymerization stage. The solvent evaporation stage has a temperature of 30-60°C, the first polymerization stage has a temperature of 50-70°C, the second polymerization stage has a temperature of 60-90°C, and the total holding time for each stage of the stepped heating is 30 min to 2 h.

8. A solid-state lithium battery, characterized in that, include: A positive electrode, a negative electrode, and a solid electrolyte membrane, wherein the solid electrolyte membrane is a composite solid electrolyte membrane according to any one of claims 1-5 or a composite solid electrolyte membrane obtained by the method according to claim 6 or 7.

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