CN115020805A - Composite solid electrolyte membrane, preparation method thereof and solid lithium battery - Google Patents
Composite solid electrolyte membrane, preparation method thereof and solid lithium battery Download PDFInfo
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Abstract
The invention discloses a composite solid electrolyte membrane, a preparation method thereof and a solid lithium battery, wherein the composite solid electrolyte membrane comprises a porous membrane matrix and a solid polymer electrolyte body, the solid polymer electrolyte body comprises an alcoholysis product of a vinyl ester-acrylate block copolymer, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyoxyalkylene and lithium salt, the solid polymer electrolyte body is arranged on the upper surface and the lower surface of the porous membrane matrix, and at least part of the solid polymer electrolyte body is embedded into pores of the porous membrane matrix. The composite solid electrolyte membrane has higher lithium ion transference number, conductivity and mechanical strength.
Description
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a composite solid electrolyte membrane, a preparation method thereof and a solid lithium battery.
Background
At present, with the urgent need of new energy materials in the world, in recent years, lithium ion batteries have the advantages of high voltage, high energy density, long cycle life, wide electrochemical window and the like, and are rapidly applied and developed. However, the conventional lithium battery inevitably has potential safety hazards due to the adoption of liquid electrolyte, and therefore, the problem can be fundamentally solved by developing a solid lithium ion battery. The structure of the all-solid-state lithium ion battery comprises a positive electrode, a solid electrolyte and a negative electrode. The solid electrolyte can conduct lithium ions and also has the function of a diaphragm, so that electron transmission can be prevented. Compared with the traditional lithium battery, the solid-state lithium battery mainly has the following advantages: firstly, the risk of spontaneous combustion or explosion of the solid-state battery is obviously reduced, and the safety is high. And secondly, the anode and cathode materials are optimized, inactive ingredients are reduced, and the energy density is improved. Thirdly, the solid electrolyte can not dry up when being circulated for a long time, and the cycle life is long. In view of the advantages and prospects of solid-state lithium ion batteries, they are favored by various research institutions and large-scale electronics and automobile manufacturing companies. The governments of various countries have successively issued policies for encouraging the research and development and industrialization of solid-state batteries, and in the process, solid-state electrolytes come out of various materials such as inorganic materials, polymers, organic/inorganic composite materials and the like, wherein if a polymer system can break through a series of technical bottlenecks such as electrical property improvement and the like, the polymer system is first put into industrial practical application.
Among solid polymer electrolytes, there are polyethers, polyamines, polyesters, etc. according to the molecular structure of the polymer matrix, which are prepared by reacting with Li + The complex is decomplexed to form a material with ion-conducting properties. Among polyether-based polymer electrolytes, polyethylene oxide (PEO) has been widely used as a host of polymer electrolytes in the past several decades because of its high dielectric constant, facilitating the dissociation of lithium salts. In the Polymer PEO, Li + Conduction of (2) is mainly dependent on Li + Complexing with anions on the PEO segments, and this conduction occurs primarily in the amorphous region. At normal temperature, PEO has very strong crystallinity, and thus, conventional PEO-Li + The ionic conductivity of the polymer electrolyte of the system is low (10) -7 ～10 -6 S cm -1 At 25 ℃ C. In addition, PEO has low strength and fails to inhibit the growth of lithium dendrites, and these drawbacks further hinder its use.
Therefore, the existing solid electrolyte membrane is in need of improvement.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide a composite solid electrolyte membrane, a method for preparing the same, and a solid lithium battery, wherein the composite solid electrolyte membrane has high transference number, high conductivity, and high mechanical strength of lithium ions, so that the composite solid electrolyte membrane can significantly improve the specific discharge capacity, the retention rate of the cyclic capacity, and the service life when being applied to the solid lithium battery.
In one aspect thereof, the present invention provides a composite solid electrolyte membrane, which, according to an embodiment of the present invention, includes: the porous membrane comprises a porous membrane substrate and a solid polymer electrolyte body, wherein the solid polymer electrolyte body comprises alcoholysis products of vinyl ester-acrylate block copolymers, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyoxyalkylene and lithium salt, and the solid polymer electrolyte body is arranged on the upper surface and the lower surface of the porous membrane substrate, and at least part of the solid polymer electrolyte body is embedded in pores of the porous membrane substrate.
Thus, solid polymer electrolyte bodies prepared by mixing the alcoholysis product of the vinyl ester-acrylate block copolymer, the polyethylene oxide, the epoxy-terminated polyethylene oxide, the amino-terminated polyalkylene oxide and the lithium salt are formed on the upper and lower surfaces of the porous membrane matrix, and at least part of the solid polymer electrolyte bodies are embedded into pores of the porous membrane matrix to obtain the composite solid electrolyte membrane, wherein the alcoholysis product of the vinyl ester-acrylate block copolymer can reduce the crystallinity of the polyethylene oxide polymer system at normal temperature, thereby improving the lithium ion transference number and conductivity of the composite solid electrolyte membrane, greatly improving the electrochemical performance of the composite solid electrolyte membrane, and the active groups of the epoxy-terminated polyethylene oxide and the amino-terminated polyalkylene oxide are subjected to a crosslinking reaction, namely the two respectively contain amino and epoxy groups, the two groups react with each other through epoxy ring opening under the heating condition, the original low molecular weight monomer is gradually polymerized into high component, the macro expression has better film forming property, if a single substance is added, no group capable of reacting with the low molecular weight monomer exists, a network framework cannot be formed, and the balance of film forming mechanical strength and electrical property can be realized through the adjustment of the equivalent weight of the two active groups; in addition, after the vinyl ester-acrylate block copolymer is subjected to alcoholysis, alkaline ions such as sodium, potassium or lithium can be favorably introduced into a polymer chain segment, so that a single-ion conductor complex is formed, and particularly, the introduction of lithium ions is favorably realized, so that the discharge specific capacity and the cycle capacity retention rate of the battery are improved; the PEO (polyethylene oxide) is used as a main structure, the epoxy-terminated polyethylene oxide and the amino-terminated polyoxyalkylene are polymerized to form a PEO-like structure and an alcoholysis product of the vinyl ester-acrylate copolymer with a branched chain, and the PEO-like structure, the epoxy-terminated polyethylene oxide and the alcoholysis product are mutually cooperated to form an interpenetrating network structure. Meanwhile, by adopting the porous membrane substrate, the porous membrane can reduce the influence of the membrane material on the lithium ion conduction, so that the tensile strength of the composite solid electrolyte membrane reaches more than 8MPa, and the mechanical property of the whole composite solid electrolyte membrane is improved, thereby effectively inhibiting the growth of lithium dendrites and improving the safety performance of the battery. Therefore, the composite solid electrolyte membrane has higher lithium ion migration number, conductivity and mechanical strength, so that the composite solid electrolyte membrane can be used for a solid lithium battery to remarkably improve the discharge specific capacity, the cycle capacity retention rate and the service life of the solid lithium battery.
In addition, the composite solid electrolyte membrane according to the above-described embodiment of the invention may also have the following additional technical features:
in some embodiments of the invention, the solid polymer electrolyte body comprises: 10-70 parts of polyethylene oxide, 1-20 parts of epoxy-terminated polyethylene oxide, 2-30 parts of amino-terminated polyoxyalkylene, 3-55 parts of alcoholysis product of vinyl ester-acrylate block copolymer and 10-50 parts of lithium salt. Therefore, the transference number and the conductivity of lithium ions of the composite solid electrolyte membrane can be obviously improved, and the electrochemical performance of the composite solid electrolyte membrane is improved.
In some embodiments of the invention, the alcoholysis product of the vinyl ester-acrylate block copolymer has a degree of alcoholysis of from 65% to 100%. Therefore, the transference number and the conductivity of lithium ions of the composite solid electrolyte membrane can be improved, and the electrochemical performance of the composite solid electrolyte membrane is improved.
In some embodiments of the invention, the alcoholysis product of the vinyl ester-acrylate block copolymer has a monomer molar ratio of vinyl ester to acrylate of 1:5 to 4: 1. This can improve the lithium ion transport number and the electrical conductivity of the composite solid electrolyte membrane.
In some embodiments of the invention, the acrylate comprises 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 the electrical conductivity of the composite solid electrolyte membrane.
In some embodiments of the invention, the epoxy-terminated polyethylene oxide comprises at least one of cyclohexanedimethanol diglycidyl ether, monoglycidyl ethers 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 the electrical conductivity of the composite solid electrolyte membrane.
In some embodiments of the present invention, the epoxy-terminated polyethylene oxide has an epoxy equivalent weight of 150 to 700 g/Eq. Therefore, the composite solid electrolyte membrane has good film forming property, and further improves the lithium ion transference number and the conductivity of the composite solid electrolyte membrane.
In some embodiments of the invention, the amino-terminated polyoxyalkylene comprises at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900, and T-5000.
In some embodiments of the present invention, the amino-terminated polyoxyalkylene has an average AHEW of 120 to 800 g/Eq. Therefore, the composite solid electrolyte membrane has good film forming property, and further improves the lithium ion transference number and the conductivity of the composite solid electrolyte membrane.
In some embodiments of the invention, the polyethylene oxide has a molecular weight of 35 to 80 ten thousand. This increases the dissolution efficiency of polyethylene oxide, improves the operability, and further improves the lithium ion transport number and the electrical conductivity of the composite solid electrolyte membrane.
In some embodiments of the present invention, the porous membrane substrate has a thickness of 6 to 16 μm and a grammage of 10 to 100g/m 2 . Therefore, the mechanical strength of the composite solid electrolyte membrane is improved, a good channel is provided for electrolyte slurry, and the mechanical property of the whole composite solid electrolyte membrane is improved.
In some embodiments of the invention, the porous membrane substrate comprises at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, nylon-10/nylon-66. Thereby, the mechanical properties of the entire composite solid electrolyte membrane are improved.
In still another aspect of the present invention, the present invention provides a method of producing the above composite solid electrolyte membrane, according to an embodiment of the present invention, the method comprising:
(1) mixing an alcoholysis product of a vinyl ester-acrylate block copolymer, polyethylene oxide and a solvent to obtain a first mixed solution;
(2) mixing the first mixed solution with epoxy-terminated polyethylene oxide, amino-terminated polyalkylene oxide and lithium salt to obtain solid polymer electrolyte slurry;
(3) and coating the solid polymer electrolyte slurry on the upper surface and the lower surface of the porous membrane substrate, then placing the porous membrane substrate into a heating device for stepwise heating, and drying at constant temperature to obtain the composite solid electrolyte membrane.
Therefore, the composite solid electrolyte membrane with higher lithium ion migration number, conductivity and mechanical strength can be prepared by adopting the preparation method disclosed by the invention, so that the discharge specific capacity, the cycle capacity retention rate and the service life of the composite solid electrolyte membrane can be obviously improved when the composite solid electrolyte membrane is used for a solid lithium battery.
In addition, the method of manufacturing a composite solid electrolyte membrane according to the above-described embodiment of the invention may also have the following additional technical features:
in some embodiments of the present invention, in the step (3), the step temperature rise comprises a solvent evaporation section, a first polymerization stage and a second polymerization stage, wherein the temperature of the solvent evaporation section is 30 to 60 ℃, the temperature of the first polymerization stage is 50 to 70 ℃, the temperature of the second polymerization stage is 60 to 90 ℃, and the sum of the temperature holding time of each step temperature rise stage is 30min to 2 h.
In another aspect of the present invention, the present invention provides a solid 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. Therefore, the solid lithium battery is loaded with the composite solid electrolyte membrane with higher lithium ion migration number, conductivity and mechanical strength, so that the solid lithium battery has higher specific discharge capacity, cycle capacity retention rate and service life.
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 Description
The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention.
In one aspect of the present invention, the present invention provides a composite solid electrolyte membrane including, according to an embodiment of the present invention: the porous membrane comprises a porous membrane substrate and solid polymer electrolyte bodies, wherein the solid polymer electrolyte bodies comprise alcoholysis products of vinyl ester-acrylate block copolymers, polyethylene oxide, epoxy-terminated polyethylene oxide, amino-terminated polyalkylene oxide and lithium salt, and the solid polymer electrolyte bodies are arranged on the upper surface and the lower surface of the porous membrane substrate and at least part of the solid polymer electrolyte bodies are embedded in pores of the porous membrane substrate.
The inventors found that a composite solid electrolyte membrane is obtained by mixing an alcoholysate of a vinyl ester-acrylate block copolymer, polyethylene oxide, an epoxy-terminated polyethylene oxide, an amino-terminated polyoxyalkylene, and a lithium salt to prepare a solid polymer electrolyte body formed on the upper and lower surfaces of a porous membrane substrate and at least a part of the solid polymer electrolyte body is embedded in the pores of the porous membrane substrate, wherein the alcoholysate of the vinyl ester-acrylate block copolymer can reduce the crystallinity of a polyethylene oxide polymer system at normal temperature, thereby increasing the lithium ion transference number and conductivity of the composite solid electrolyte membrane, greatly improving the electrochemical performance of the composite solid electrolyte membrane, and the active groups of the epoxy-terminated polyethylene oxide and the amino-terminated polyoxyalkylene undergo a crosslinking reaction, i.e. both contain an amino group and an epoxy group, the two groups react with each other through epoxy ring opening under the heating condition, the original low molecular weight monomer is gradually polymerized into high component, the macro expression has better film forming property, if a single substance is added, no group capable of reacting with the low molecular weight monomer exists, a network framework cannot be formed, and the balance of film forming mechanical strength and electrical property can be realized through the adjustment of the equivalent weight of the two active groups; in addition, after the vinyl ester-acrylate block copolymer is subjected to alcoholysis, alkaline ions such as sodium, potassium or lithium can be favorably introduced into a polymer chain segment, so that a single-ion conductor complex is formed, and particularly, the introduction of lithium ions is favorably realized, so that the discharge specific capacity and the cycle capacity retention rate of the battery are improved; the PEO (polyethylene oxide) is used as a main structure, the epoxy-terminated polyethylene oxide and the amino-terminated polyoxyalkylene are polymerized to form a PEO-like structure and a vinyl ester-acrylate copolymer alcoholysis product with a branched chain, and the PEO-like structure and the vinyl ester-acrylate copolymer alcoholysis product are mutually cooperated to form an interpenetrating network structure, and most importantly, the cooperation of the PEO-like structure, the epoxy-terminated polyethylene oxide and the vinyl ester-acrylate copolymer alcoholysis product reflects the reduction of crystallinity, so that a lithium ion transmission channel is more smooth; meanwhile, by adopting the porous membrane substrate, the porous membrane can reduce the influence of the membrane material on the lithium ion conduction, simultaneously the tensile strength of the composite solid electrolyte membrane reaches more than 8MPa, and the mechanical property of the whole composite solid electrolyte membrane is improved, so that the growth of lithium dendrite can be effectively inhibited, and the safety performance of the battery is improved. Therefore, the composite solid electrolyte membrane has higher lithium ion migration number, conductivity and mechanical strength, so that the composite solid electrolyte membrane can be used for a solid lithium battery to remarkably improve the discharge specific capacity, the cycle capacity retention rate and the service life of the solid lithium battery.
Further, the above solid polymer electrolyte body includes: 10-70 parts of polyethylene oxide, 1-20 parts of epoxy-terminated polyethylene oxide, 2-30 parts of amino-terminated polyoxyalkylene, 3-55 parts of alcoholysis product of vinyl ester-acrylate block copolymer and 10-50 parts of lithium salt. The inventors found that if the polyethylene oxide is less than 10 parts by weight, the transport chains provided to lithium ions are too small, so that the internal resistance increases, while if the polyethylene oxide is more than 70 parts by weight, it is difficult to control the crystallinity thereof to a minimum value; because the amino and epoxy groups of the amino-terminated polyoxyalkylene and the epoxy-terminated polyoxyalkylene react with each other under the heating condition, the addition amount of the epoxy-terminated polyoxyalkylene and the epoxy-terminated polyoxyalkylene needs to be defined together, if the addition amount exceeds the range, the film-forming curing period is prolonged, and meanwhile, excessive amide inert groups are introduced into the whole molecular chain segment, so that the lithium ion migration is hindered, and if the addition amount is lower than the range, the support effect of a polymer network skeleton cannot be achieved; if the alcoholysate of the vinyl ester-acrylate block copolymer is higher than the range, the film forming rigidity is increased, so that a tiny gap is generated between the diaphragm and the interface of the positive electrode and the negative electrode, the interface is increased, and the internal resistance of the battery is increased, so that the capacity loss is increased; if the lithium salt is higher than the range, the lithium salt is more than a saturated state, resources are wasted, the difficulty of dispersion in the electrolyte membrane system is increased, and once the lithium salt is not uniformly dispersed, the appearance and the internal microstructure of a formed membrane present more defects. Therefore, the materials are controlled in the range, the mutual synergistic effect is best, the transference number and the conductivity of lithium ions of the composite solid electrolyte membrane can be obviously improved, and the electrochemical performance of the composite solid electrolyte membrane is improved.
Further, the molecular weight of the polyethylene oxide used is 35 to 80 ten thousand. The inventors found that if the molecular weight of polyethylene oxide is less than 35 ten thousand, the mechanical strength of the solid polymer electrolyte bulk is reduced and a crosslinked network is generated insufficiently, thereby lowering the ion composite solid electrolyte membrane conduction efficiency, whereas if the molecular weight of polyethylene oxide is more than 80 ten thousand, the dissolution efficiency of polyethylene oxide is low, thereby lowering the operability and realizability. Therefore, the molecular weight of polyethylene oxide adopted by the composite solid electrolyte membrane is 35-80 ten thousand, and the lithium ion transference number, the conductivity and the strength of the composite solid electrolyte membrane can be improved while the dissolving efficiency of the polyethylene oxide is increased.
Further, the alcoholysis degree of the alcoholysate of the vinyl ester-acrylic ester block copolymer is 65 to 100 percent. The inventors found that if the alcoholysis degree of the alcoholysis product of the vinyl ester-acrylate block copolymer is less than 65%, the content of the inert ester bonds in the polymer chain segment is relatively high, and the content ratio of the lithium carboxylate after alcoholysis to the alcoholic hydroxyl group is relatively low, so that the content ratio of the lithium ion conductor is reduced, and the exertion of the transference number and the conductivity of the lithium ions is influenced. Therefore, by adopting the alcoholysis product of the vinyl ester-acrylate block copolymer with the alcoholysis degree of 65-100%, the lithium carboxylate can be kept at a higher proportion, namely the proportion of the lithium-containing chain segment is increased, the content of the lithium ion conductor is increased, the lithium ion migration number and the conductivity of the composite solid electrolyte membrane are further improved, and the electrochemical performance of the composite solid electrolyte membrane is improved. Meanwhile, the molar ratio of the vinyl ester to the acrylate in the alcoholysis product of the vinyl ester-acrylate block copolymer is 1: 5-4: 1. The inventors found that when the molar ratio of the vinyl ester to the acrylic ester monomer is less than 1:5, the resulting slurry has a large viscosity, and the dispersion characteristics are deteriorated, and the permeability of the porous membrane is deteriorated, whereas when the molar ratio of the vinyl ester to the acrylic ester monomer is more than 4:1, the resulting slurry generates microbubbles, is difficult to remove, has a poor appearance after film formation, and further affects the conductivity and the lithium ion transport number. Therefore, the molar ratio of the vinyl ester in the alcoholysis product of the vinyl ester-acrylic ester block copolymer to the monomer of the acrylic ester is 1: 5-4: 1, so that the transference number and the conductivity of lithium ions of the composite solid electrolyte membrane can be further improved. And those skilled in the art can select the specific type of the above-mentioned acrylate according to actual needs, for example, the acrylate includes 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 the electrical conductivity of the composite solid electrolyte membrane.
Further, the epoxy equivalent of the epoxy-terminated polyethylene oxide is 150 to 700 g/Eq. The inventors found that if the epoxy equivalent of the epoxy-terminated polyethylene oxide is less than 150g/Eq, the crosslinking density is lowered, so that the molecular weight of the polymer segment is lowered, thereby lowering the mechanical strength of the solid polymer electrolyte bulk; if the epoxy equivalent of the solid polymer electrolyte is larger than 700g/Eq, the film forming property of the solid polymer electrolyte is poor. Therefore, the epoxy equivalent of the epoxy-terminated polyethylene oxide is 150-700 g/Eq, so that the mechanical strength of the composite solid electrolyte membrane can be improved, and the film forming property of the composite solid electrolyte membrane can be improved. The epoxy-terminated polyethylene oxide may be selected by those skilled in the art according to the actual requirements, as long as the epoxy equivalent weight is satisfied, and for example, the epoxy-terminated polyethylene oxide includes at least one of cyclohexanedimethanol 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.
Further, the average AHEW of the amino-terminated polyoxyalkylene is 120 to 800 g/Eq. The inventors found that, if the average AHEW of the amino-terminated polyoxyalkylene is less than 120g/Eq, the crosslinking density is lowered, so that the molecular weight of the polymer segment is lowered, thereby lowering the mechanical strength of the solid polymer electrolyte bulk; if the average AHEW of the amino-terminated polyoxyalkylene is more than 800g/Eq, the film-forming property of the solid polymer electrolyte body is poor. Therefore, the average AHEW of the amino-terminated polyoxyalkylene is 120-800 g/Eq, the composite solid electrolyte membrane has good membrane forming property, and further the lithium ion migration number and the conductivity of the composite solid electrolyte membrane are improved, and it is noted that a person skilled in the art can select the specific type of the amino-terminated polyoxyalkylene according to actual needs as long as the average AHEW can be met, for example, the amino-terminated polyoxyalkylene comprises at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900 and T-5000.
Further, the porous membrane substrate has a thickness of 6 to 16 μm and a basis weight of 10 to 100g/m 2 . The inventors found that the grammage of the porous membrane substrate is proportional to the thickness thereof, and if the porous membrane substrate is used below the above-mentioned range of thickness and grammage, the mechanical strength of the composite solid electrolyte membrane is lowered, whereas if the porous membrane substrate is used above the above-mentioned range of thickness and grammage, the number and size of pores are inevitably reduced, resulting in failure to provide good channels for the electrolyte slurry. Therefore, the porous membrane substrate adopted by the application has the thickness of 6-16 mu m and the gram weight of 10-100 g/m 2 The mechanical strength of the composite solid electrolyte membrane can be improved, a good channel is provided for electrolyte slurry, and the mechanical property of the whole composite solid electrolyte membrane is improved. It should be noted that the specific type of the porous membrane substrate, for example, at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, nylon-10, and nylon-66, may be selected by those skilled in the art according to actual needs as long as the above conditions are satisfied, thereby improving the mechanical properties of the entire composite solid electrolyte membrane.
In still another aspect of the present invention, the present invention provides a method of producing the above composite solid electrolyte membrane, according to an embodiment of the present invention, the production method including:
s100: mixing an alcoholysis product of a vinyl ester-acrylate block copolymer, polyethylene oxide and a solvent
In the step, an alcoholysis product of the vinyl ester-acrylate block copolymer, polyethylene oxide and a solvent are mixed, so that the alcoholysis product of the vinyl ester-acrylate block copolymer and the polyethylene oxide are dissolved in the solvent to obtain a first mixed solution. The inventor finds that the alcoholysis product of the vinyl ester-acrylate block copolymer can reduce the crystallinity of a polyethylene oxide polymer system at normal temperature, thereby improving the transference number and the conductivity of lithium ions of the composite solid electrolyte membrane and greatly improving the electrochemical performance of the composite solid electrolyte membrane. Preferably, the alcoholysis product of the vinyl ester-acrylate block copolymer and the polyethylene oxide are separately mixed with the solvent, and the mixed solution is then mixed. It should be noted that, the specific type and addition amount of the solvent can be selected by those skilled in the art according to the actual needs, as long as the above-mentioned dissolution of the alcoholysis product of the vinyl ester-acrylate block copolymer and the polyethylene oxide can be satisfied, and the details are not repeated herein.
S200: mixing the first mixed solution with epoxy-terminated polyethylene oxide, amino-terminated polyethylene oxide and lithium salt
In this step, the first mixed solution obtained above is mixed with an epoxy-terminated polyethylene oxide, an amino-terminated polyalkylene oxide, and a lithium salt to obtain a solid polymer electrolyte slurry. The inventor finds that in the process, PEO (polyethylene oxide) is taken as a main structure, epoxy-terminated polyethylene oxide and amino-terminated polyoxyalkylene are polymerized to form a PEO-like structure and a vinyl ester-acrylate copolymer alcoholysis product with a branched chain in the whole polymer system, and the PEO-like structure and the vinyl ester-acrylate copolymer alcoholysis product are mutually cooperated to form an interpenetrating network structure, and what is most important is represented by the synergistic effect of the PEO-like structure, the PEO-like structure and the vinyl ester-acrylate copolymer alcoholysis product is that the crystallinity is reduced, so that a lithium ion transmission channel is smooth, lithium ions are introduced into the chain end of a polymer molecule, and an ion conductor complex is formed, so that the specific discharge capacity and the cycle capacity retention rate of a battery are improved. Preferably, the first mixed solution obtained above is mixed with the epoxy-terminated polyethylene oxide and the amino-terminated polyoxyalkylene, and then stirred uniformly, and then the lithium salt is added and stirred uniformly, thereby obtaining the solid polymer electrolyte slurry.
S300: coating the solid polymer electrolyte slurry on the upper and lower surfaces of the porous membrane substrate, and heating in a heating device
In the step, the obtained solid polymer electrolyte slurry is coated on the upper surface and the lower surface of a porous membrane matrix, and then the porous membrane matrix is placed into a heating device for stepwise heating, and is dried at constant temperature to obtain the composite solid electrolyte membrane. The inventor finds that by adopting the porous membrane substrate, the porous membrane can reduce the influence of the membrane material on the lithium ion conduction, simultaneously the tensile strength of the composite solid electrolyte membrane reaches more than 8MPa, and the mechanical property of the whole composite solid electrolyte membrane is improved, so that the growth of lithium dendrite can be effectively inhibited, and the safety performance of the battery is improved. According to one embodiment of the invention, the step temperature rise comprises a solvent volatilization section, a first polymerization stage and a second polymerization stage, wherein the temperature of the solvent volatilization section is 30-60 ℃, and the temperature section is mainly a process of volatilizing part of the solvent; the temperature of the first polymerization stage is 50-70 ℃, in the first polymerization stage, while the residual solvent is volatilized, the reaction of amino and epoxy in the epoxy-terminated polyoxyethylene and the amino-terminated polyoxyalkylene occurs, the epoxy ring is opened to generate hydroxyl, and the two substances are gradually polymerized to form a polymer network skeleton in situ; the temperature of the second polymerization stage is 60-90 ℃, residual solvent is continuously volatilized in the second polymerization stage, unreacted groups are further polymerized, and the residual quantity of micromolecular substances is reduced; the sum of the temperature keeping time of each stage of the stepped temperature rise is 30 min-2 h.
Therefore, the composite solid electrolyte membrane with higher lithium ion migration number, conductivity and mechanical strength can be prepared by adopting the preparation method disclosed by the invention, so that the discharge specific capacity, the cycle capacity retention rate and the service life of the composite solid electrolyte membrane can be obviously improved when the composite solid electrolyte membrane is used for a solid lithium battery.
It is to be noted that the features and advantages described above for the composite solid electrolyte membrane apply equally to the method of producing a composite solid electrolyte membrane, and are not described here in detail.
In another aspect of the invention, a solid state lithium battery is provided. According to an embodiment of the present invention, the solid lithium battery includes a positive electrode, a negative electrode, and a solid electrolyte membrane, wherein the solid electrolyte membrane is the composite solid electrolyte membrane described above or the composite solid electrolyte membrane obtained by the method described above. Therefore, the solid lithium battery is loaded with the composite solid electrolyte membrane with higher lithium ion migration number, conductivity and mechanical strength, so that the solid lithium battery has higher specific discharge capacity, cycle capacity retention rate and service life.
It should be noted that the materials used for the positive electrode and the negative electrode of the solid-state lithium battery are conventional materials in the art, and are not described herein again, and the features and advantages described above for the composite solid-state electrolyte membrane are also applicable to the solid-state lithium battery, and are not described herein again.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Preparation of the composite solid electrolyte membrane:
comparative example 1 (alcoholysate without addition of vinyl ester-acrylate Block copolymer)
(1) Dissolving 50 parts by weight of polyethylene oxide with the molecular weight of 40 ten thousand in acetonitrile solvent to obtain a first mixed solution;
(2) adding 2 parts by weight of cyclohexanedimethanol diglycidyl ether and ED-90025 parts by weight of amino-terminated polyoxyalkylene into the first mixed solution, and uniformly stirring to obtain a second mixed solution;
(3) adding 15 parts by weight of lithium sulfonimide salt into the second mixed solution, and uniformly stirring to obtain solid polymer electrolyte slurry;
(4) coating the solid polymer electrolyte slurry on a porous membrane substrate of a 12-micron meta-aramid system, then placing the porous membrane substrate into a heating device for step heating, wherein the step heating comprises a solvent volatilization section, a first polymerization stage and a second polymerization stage, the temperature of the solvent volatilization section is 40 ℃ and is kept for 30min, the temperature of the first polymerization stage is 60 ℃ and is kept for 30min, the temperature of the second polymerization stage is 80 ℃ and is kept for 1h, and after complete drying, a composite solid electrolyte membrane with the total thickness of 35 microns is obtained and is placed in a glove box for later use.
Comparative example 2 (without porous film substrate)
(1) Dissolving an alcoholysis product of the vinyl ester-methyl acrylate block copolymer in an acetonitrile solvent to obtain a first mixed solution;
(2) dissolving 50 parts by weight of polyethylene oxide with the molecular weight of 40 ten thousand in acetonitrile solvent to obtain a second mixed solution;
(3) mixing the first mixed solution and the second mixed solution, adding 15 parts by weight of cyclohexanedimethanol diglycidyl ether and 15 parts by weight of amino-terminated polyoxyalkylene ED-9005, and uniformly stirring to obtain a third mixed solution;
(4) adding 40 parts by weight of lithium sulfimide salt into the third mixed solution, and uniformly stirring to obtain solid polymer electrolyte slurry;
(5) directly coating the solid polymer electrolyte slurry on a release film substrate, then placing the release film substrate into a heating device for step heating, wherein the step heating comprises a solvent volatilization section, a first polymerization stage and a second polymerization stage, the temperature of the solvent volatilization section is 30 ℃ and is kept for 30min, the temperature of the first polymerization stage is 60 ℃ and is kept for 1h, the temperature of the second polymerization stage is 85 ℃ and is kept for 1h, and after complete drying, a composite solid electrolyte film with the total thickness of 20 mu m is obtained and is placed in a glove box for later use.
Some specific parameters used in the preparation process in comparative examples 1 and 2 are shown in table 1.
General procedure
(1) Dissolving an alcoholysis product of the vinyl ester-acrylate block copolymer in an acetonitrile solvent to obtain a first mixed solution;
(2) dissolving polyethylene oxide in a solvent to obtain a second mixed solution;
(3) after mixing the first mixed solution and the second mixed solution, adding epoxy-terminated polyoxyethylene and amino-terminated polyoxyalkylene, and uniformly stirring to obtain a third mixed solution;
(4) adding lithium salt into the third mixed solution, and uniformly stirring to obtain solid polymer electrolyte slurry;
(5) and coating the solid polymer electrolyte slurry on a porous membrane substrate, then placing the porous membrane substrate into a heating device for step heating, wherein the step heating comprises a solvent volatilization section, a first polymerization stage and a second polymerization stage, and drying at constant temperature to obtain the composite solid electrolyte membrane.
The preparation of examples 1-6 was carried out using the general procedure described above and the specific process parameters are given in table 1.
And (3) measuring the tensile strength of the composite solid electrolyte membrane:
referring to the test method of the tensile property of the plastic film in the standard GB/T13022-1991, the speed is 50mm/min, the electrolyte film is cut into sample pieces with the width of 15mm and the length of more than 18cm for standby, the thickness of the sample pieces is measured by a thickness gauge, and then the average thickness of the sample pieces is calculated.
Calculation formula of tensile strength: tensile strength-maximum force/cross-sectional area
Preparing a solid lithium battery:
the solid lithium battery comprises a positive electrode, a lithium metal negative electrode and the solid polymer electrolyte membrane prepared in comparative examples 1-2 and examples 1-6, wherein the composite solid polymer electrolyte membrane is arranged between the positive electrode and the negative electrode. The positive electrode active material is lithium iron phosphate, the conductive agent is Super P, the binder is polyvinylidene fluoride, the lithium iron phosphate, the Super P and the polyvinylidene fluoride are mixed in N-methyl pyrrolidone (NMP) according to the mass ratio of 8:1:1 to obtain positive electrode slurry, the positive electrode slurry is coated on aluminum foil, and vacuum drying is carried out at 110 ℃ for 24 hours to obtain the positive electrode piece. Button cells were assembled with lithium metal under an argon atmosphere using the solid polymer electrolyte membranes prepared in comparative examples 1-2 and examples 1-6, respectively.
And (3) testing the performance of the solid lithium battery:
(1) lithium ion conductivity test
Forming an ss/solid polymer electrolyte/ss blocked battery by using a stainless steel sheet and a solid polymer electrolyte (thickness l, area S), testing at a frequency range of 0.1-1000 kHz by using a disturbance voltage of 5mV to obtain an EIS map, obtaining a bulk resistance Rb of the solid polymer electrolyte, and obtaining a lithium ion conductivity sigma of the solid polymer electrolyte according to a formula sigma l/(Rb multiplied by S).
(2) Electrochemically stable window
The ss/solid polymer electrolyte/Li semi-blocking battery is formed by a stainless steel sheet, a solid polymer electrolyte and a lithium sheet, a sample is processed for 2 hours at 80 ℃ and under certain pressure for standby, and the sample is tested by linear sweep voltammetry, wherein the sweep rate is 2mV/S, and the open-circuit voltage in the voltage sweep range is 0V to 6V.
(3) Transference number of lithium ion
The testing method adopts a steady state polarization method and a non-blocking battery system, a larger initial current Ii Is generated at the moment of applying a constant voltage to two ends of the battery, then the current Is gradually reduced and tends to a stable value Is, and the ratio of Is to Ii Is the transference number of lithium ions.
(4) Solid state lithium battery cycling
And carrying out a charge-discharge test on the assembled solid lithium battery within the range of 2.5-3.7V in the environment of 60 ℃.
The results of the above performance tests are shown in table 2.
TABLE 2
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
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, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A composite solid electrolyte membrane, comprising:
a porous membrane substrate;
a solid polymer electrolyte body comprising an alcoholysis of a vinyl ester-acrylate block copolymer, polyethylene oxide, an epoxy-terminated polyethylene oxide, an amino-terminated polyalkylene oxide, and a lithium salt, and 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.
2. The composite solid electrolyte membrane according to claim 1, wherein the solid polymer electrolyte body comprises: 10-70 parts of polyethylene oxide, 1-20 parts of epoxy-terminated polyethylene oxide, 2-30 parts of amino-terminated polyoxyalkylene, 3-55 parts of alcoholysis product of vinyl ester-acrylate block copolymer and 10-50 parts of lithium salt.
3. The composite solid electrolyte membrane according to claim 1, wherein the alcoholysis degree of the alcoholysate of the vinyl ester-acrylate block copolymer is from 65% to 100%.
4. The composite solid electrolyte membrane according to claim 1 or 2, wherein the molar ratio of the vinyl ester to the acrylate monomer in the alcoholysate of the vinyl ester-acrylate block copolymer is from 1:5 to 4: 1;
optionally, the acrylate comprises at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, and butyl methacrylate.
5. The composite solid electrolyte membrane according to claim 1, wherein the epoxy-terminated polyethylene oxide comprises at least one of cyclohexanedimethanol diglycidyl ether, a monoglycidyl ether of a C12-C14 alcohol, butanediol diglycidyl ether, tert-butylphenol monoglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol diglycidyl ether, and 1, 6-hexanediol diglycidyl ether;
optionally, the epoxy-terminated polyethylene oxide has an epoxy equivalent weight of 150 to 700 g/Eq.
6. The composite solid electrolyte membrane according to claim 1, wherein the amino-terminated polyoxyalkylene comprises at least one of D-205, D-400, D-230, EDR-148, T-430, SD-401, ED-900, and T-5000;
optionally, the amino-terminated polyoxyalkylene has an average AHEW of 120 to 800 g/Eq.
7. The composite solid electrolyte membrane according to claim 1, wherein the polyethylene oxide has a molecular weight of 35 to 80 ten thousand;
optionally, the porous membrane substrate has a thickness of 6 to 16 μm and a gram weight of 10 to 100g/m 2 ；
Optionally, the porous membrane substrate comprises at least one of polyethylene terephthalate, polypropylene, polyethylene, polyvinylidene fluoride, aramid, nylon-10, and nylon-66.
8. A method for producing the composite solid electrolyte membrane according to any one of claims 1 to 7, comprising:
(1) mixing an alcoholysis product of a vinyl ester-acrylate block copolymer, polyethylene oxide and a solvent to obtain a first mixed solution;
(2) mixing the first mixed solution with epoxy-terminated polyethylene oxide, amino-terminated polyalkylene oxide and lithium salt to obtain solid polymer electrolyte slurry;
(3) and coating the solid polymer electrolyte slurry on the upper surface and the lower surface of the porous membrane substrate, then placing the porous membrane substrate into a heating device for stepwise heating, and drying at constant temperature to obtain the composite solid electrolyte membrane.
9. The production method of a composite solid electrolyte membrane according to claim 8, characterized in that, in step (3), the stepwise temperature rise includes a solvent evaporation stage, a first polymerization stage, and a second polymerization stage,
wherein the temperature of the solvent volatilization section is 30-60 ℃, the temperature of the first polymerization stage is 50-70 ℃, the temperature of the second polymerization stage is 60-90 ℃, and the total time of the temperature of each stage of the step temperature rise is 30 min-2 h.
10. A solid state lithium battery, comprising: a cathode, an anode and a solid electrolyte membrane, wherein the solid electrolyte membrane is the composite solid electrolyte membrane according to any one of claims 1 to 7 or obtained by the method according to claim 8 or 9.
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