A three-dimensional polymer composite solid electrolyte and a preparation method thereof

Abstract

The present invention discloses a three-dimensional polymer composite solid electrolyte and a preparation method thereof, relating to the field of solid electrolyte technology. The three-dimensional polymer composite solid electrolyte comprises a polymer matrix, a crosslinker, a photoinitiator, an inorganic filler, and a lithium salt. The polymer matrix is a mixture of PVDF, PEO, and PAA. The mass ratio of the PVDF, PEO, PAA, crosslinker, photoinitiator, inorganic filler, and lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7. Compared to simple PEO- or PVDF-based polymer composite solid electrolytes, the three-dimensional polymer composite solid electrolyte in this application can provide more lithium ion transmission channels, improve the room-temperature electrical conductivity and mechanical strength of the polymer solid electrolyte, and extend the battery cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to a three-dimensional polymer composite solid electrolyte and a preparation method thereof. Background Art

[0002] An all-solid-state lithium battery is a lithium secondary battery that uses solid electrodes and a solid electrolyte. Compared to conventional lithium-ion batteries with liquid organic electrolytes, all-solid-state lithium batteries are safer to use and have a higher energy density. Currently, all-solid-state lithium batteries are mainly divided into two categories based on the electrolyte: the first category is all-solid-state lithium batteries composed of organic polymer electrolytes, known as polymer all-solid-state lithium batteries; the second category is lithium-ion batteries composed of inorganic solid electrolytes, known as inorganic all-solid-state lithium batteries, which mainly include oxides and sulfides. During use, inorganic all-solid-state lithium batteries have high interfacial resistance, making them unstable to the lithium metal negative electrode. The critical current density at which lithium dendrites penetrate the solid electrolyte and cause a battery short circuit is low, thus limiting the application of inorganic solid electrolytes in all-solid-state lithium batteries. Furthermore, because inorganic solid electrolytes are fragile, their thickness is typically above 200μm, which significantly reduces the battery's rate performance and energy density. Compared with fragile inorganic solid electrolytes, polyoxyethylene (PEO) polymer solid electrolytes have better flexibility and good contact with the electrode interface, which can reduce the interface resistance of solid batteries. However, polymer solid electrolytes often have a thermal conductivity of about 10 -6 S cm -1 The low lithium ion conductivity increases the overpotential of the battery and limits the battery operating temperature to about 60°C.

[0003] With the continuous development of lithium battery technology, inorganic / polymer composite electrolytes have higher Li + Conductivity has become a research hotspot in recent years. For example, the Chinese patent application with the publication number CN111613833A and the application number CN202010415819.X discloses a polymer solid electrolyte and a preparation method thereof, which utilizes lithium salts and inorganic fillers containing large-volume anions to improve the conductivity and interfacial stability of PVDF and PVDF / PEO-based polymer electrolytes. However, this patent application improves the conductivity of the solid electrolyte by using large-volume anions to reduce the interaction with lithium ions, making it easy for lithium salts to dissociate. It only relies on increasing the volume of anions to increase the degree of negative charge delocalization, thereby having a limited effect on the dissociation of lithium salts, low conductivity at room temperature, poor mechanical properties of the solid electrolyte at high temperatures, and poor resistance to lithium dendrites. Summary of the Invention

[0004] 1. Technical problem to be solved by the invention

[0005] In response to the technical problems of low room-temperature electrical conductivity and poor high-temperature mechanical properties in existing polymer solid electrolytes, the present invention provides a three-dimensional polymer composite solid electrolyte and a preparation method thereof, which can significantly improve the lithium ion transport performance of the polymer solid electrolyte, enhance the room-temperature electrical conductivity and high-temperature mechanical strength of the polymer solid electrolyte, and extend the battery cycle life.

[0006] 2. Technical solution

[0007] In order to solve the above problems, the technical solution provided by the present invention is:

[0008] A three-dimensional polymer composite solid electrolyte comprises a polymer matrix, a crosslinker, a photoinitiator, an inorganic filler and a lithium salt, wherein the polymer matrix is a mixture of PVDF, PEO and PAA; wherein the mass ratio of the PVDF, the PEO, the PAA, the crosslinker, the photoinitiator, the inorganic filler and the lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7.

[0009] In the present application, by setting the polymer matrix to a mixture of PVDF, PEO and PAA, under the irradiation of a photoinitiator and ultraviolet light, PEO, PAA and a cross-linking agent are cross-linked to form an amphiphilic block copolymer, and cross-linked with PVDF to form a polymer with an interpenetrating three-dimensional structure, a three-dimensional PVDF-PEO-PAA based polymer composite solid electrolyte, that is, a three-dimensional polymer composite solid electrolyte, is obtained, which improves the electrical conductivity and mechanical properties of the composite solid electrolyte. Since PEO has strong hydrophilicity and PAA has strong hydrophobicity, after cross-linking to form a copolymer, compared with other systems, on the one hand, it has good compatibility with organic solvents, which can improve the dispersion uniformity of raw materials in the preparation process; on the other hand, it enhances the affinity with lithium ions and enhances the lithium ion transport performance of the composite solid electrolyte. At the same time, the introduction of PVDF can enhance the surface smoothness, thermal stability and chemical stability of the composite solid electrolyte, and extend the service life of the solid electrolyte. In addition, by adding lithium salts and inorganic fillers, there is a strong adsorption effect between the inorganic filler and the lithium salt, which effectively promotes the dissociation of the lithium salt, thereby activating more mobile Li in the polymer solid electrolyte. + , thereby significantly improving the room-temperature conductivity of the polymer solid electrolyte, reducing the internal resistance of the solid battery and extending the cycle life. It can be seen that compared to simple PEO or PVDF-based polymer composite solid electrolytes, the three-dimensional polymer composite solid electrolyte in this application can provide more lithium ion transmission channels, improving the room-temperature conductivity and mechanical strength of the polymer solid electrolyte.

[0010] Optionally, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium hexafluoroborate, lithium perchlorate, lithium difluorobis(oxalatoborate), lithium triethylborohydride, lithium diisopropylamide, lithium acetoacetate, bis(trimethylsilyl)lithium, lithium pentamethylcyclopentadiene, 4,5-dicyano-2-trifluoromethylimidazole, lithium fluorosulfonic acid (perfluorobutylsulfonyl)imide, and tert-butyl lithium.

[0011] Optionally, the inorganic filler is any one of gadolinia-doped cerium oxide, cerium-stabilized scandium-doped zirconia, and yttria-stabilized zirconia.

[0012] Optionally, the crosslinking agent is selected from one or more of acrylate, trimethyl carbonate, divinylbenzene and diisocyanate, N,N-methylenebisacrylamide, polyalkyl acrylate, benzoyl peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, diethylenetriamine, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine.

[0013] Optionally, the photoinitiator is one or more of 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone.

[0014] At the same time, the present application also provides a method for preparing a three-dimensional polymer composite solid electrolyte, which is used to prepare the three-dimensional polymer composite solid electrolyte described above, and the preparation method comprises the following steps:

[0015] S1. Dissolving a polymer matrix, a cross-linking agent, a photoinitiator, an inorganic filler, and a lithium salt in acetonitrile, and stirring and mixing in a protective atmosphere to obtain a precursor mixed solution;

[0016] S2, coating the precursor mixed solution obtained in step S1 on a glass plate, and then curing it by ultraviolet light irradiation in a protective atmosphere to obtain a polymer solid electrolyte membrane;

[0017] S3. Peeling the polymer solid electrolyte membrane obtained in step S2 from the glass plate, washing it, and vacuum drying it to obtain a three-dimensional polymer composite solid electrolyte.

[0018] Optionally, step S1 is as follows: dissolving PVDF in acetonitrile at room temperature, then adding PEO, PAA, a crosslinker, a photoinitiator, an inorganic filler and a lithium salt, and stirring for 3-8 hours under an argon atmosphere or a nitrogen atmosphere to obtain a precursor mixed solution.

[0019] Optionally, the mass ratio of the PVDF, the PEO, the PAA, the crosslinker, the photoinitiator, the inorganic filler and the lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7; wherein the crosslinker is acrylate, the photoinitiator is 2-hydroxy-2-methylacetophenone, the inorganic filler is gadolinium oxide-doped cerium oxide, and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide. By setting the inorganic filler to gadolinium oxide-doped cerium oxide (Gd 0.1 Ce 0.9 O 1.95 , simplified as GDC), the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LITFSI), which makes GDC and LITFSI lithium salt anions have a strong adsorption effect, effectively promoting the dissociation of lithium salt and activating more mobile Li in the polymer solid electrolyte. + , significantly improving the room-temperature conductivity of polymer solid electrolytes, reducing the internal resistance of solid batteries and extending the cycle life.

[0020] Optionally, in S2, the precursor mixed solution is coated on a glass plate by a doctor blade method, with a coating thickness of 20-80 μm; the protective atmosphere is an argon atmosphere or a nitrogen atmosphere; the light intensity is 1500-2500 W·cm -2 , the curing time is 60-120S. By setting the coating thickness to 20-80μm, the mechanical strength and conductivity of the polymer solid electrolyte membrane can be guaranteed; if the coating thickness is less than 20μm, it will reduce the mention and mass energy density of the solid battery, increase the battery cost, and is not conducive to large-scale application. In addition, too low a thickness will cause the mechanical strength of the electrolyte to weaken, reducing the safety of the solid battery; when the thickness is higher than 80μm, it will lead to an increase in the lithium ion transmission path, increase the internal resistance of the battery, and be detrimental to the battery power performance. At the same time, the light intensity is 1500-2500W·cm -2 The curing time is 60-120S, which can fully ensure the cross-linking between the components to form a polymer, avoiding long-term high-intensity radiation that may cause polymer grading and have an adverse effect on the electrochemical and mechanical properties of the polymer solid electrolyte.

[0021] Optionally, in S3, washing is performed 3-5 times with methanol or isopropanol, and the vacuum drying temperature is 30-70° C. for 10-24 hours. By washing the polymer solid electrolyte membrane 3-5 times with methanol or isopropanol, unpolymerized monomers, crosslinking agents, and excess photoinitiators can be removed, thereby improving the quality of the polymer solid electrolyte membrane.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0024] (1) A three-dimensional polymer composite solid electrolyte proposed in an embodiment of the present application is obtained by setting the polymer matrix to a mixture of PVDF, PEO and PAA. Under the irradiation of a photoinitiator and ultraviolet light, PEO, PAA and a cross-linking agent are cross-linked to form an amphiphilic block copolymer, and cross-linked with PVDF to form a polymer with an interpenetrating three-dimensional structure, thereby obtaining a three-dimensional PVDF-PEO-PAA-based polymer composite solid electrolyte, i.e., a three-dimensional polymer composite solid electrolyte, which improves the electrical conductivity and mechanical properties of the composite solid electrolyte. Since PEO has strong hydrophilicity and PAA has strong hydrophobicity, after cross-linking to form a copolymer, compared with other systems, on the one hand, it has good compatibility with organic solvents, which can improve the dispersion uniformity of raw materials in the preparation process; on the other hand, it enhances the affinity with lithium ions and enhances the lithium ion transport performance of the composite solid electrolyte. At the same time, the introduction of PVDF can enhance the surface smoothness, thermal stability and chemical stability of the composite solid electrolyte, thereby extending the service life of the solid electrolyte. In addition, by adding lithium salt and inorganic filler, there is a strong adsorption effect between the inorganic filler and the lithium salt, which effectively promotes the dissociation of lithium salt, thereby activating more mobile Li in the polymer solid electrolyte. + , thereby significantly improving the room-temperature conductivity of the polymer solid electrolyte, reducing the internal resistance of the solid battery and extending the cycle life. It can be seen that compared to simple PEO or PVDF-based polymer composite solid electrolytes, the three-dimensional polymer composite solid electrolyte in this application can provide more lithium ion transmission channels, improving the room-temperature conductivity and mechanical strength of the polymer solid electrolyte.

[0025] (2) A method for preparing a three-dimensional polymer composite solid electrolyte proposed in an embodiment of the present application can provide more lithium ion transmission channels and improve the room-temperature electrical conductivity and mechanical strength of the polymer solid electrolyte.

[0026] (3) A method for preparing a three-dimensional polymer composite solid electrolyte proposed in the embodiment of the present application is to set the inorganic filler to be gadolinium oxide-doped cerium oxide (Gd 0.1 Ce 0.9 O 1.95 , simplified as GDC), the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LITFSI), which makes GDC and LITFSI lithium salt anions have a strong adsorption effect, effectively promoting the dissociation of lithium salt and activating more mobile Li in the polymer solid electrolyte. + , significantly improving the room-temperature conductivity of polymer solid electrolytes, reducing the internal resistance of solid batteries and extending the cycle life.

[0027] (4) The preparation method of a three-dimensional polymer composite solid electrolyte proposed in the embodiment of the present application can ensure the mechanical strength and electrical conductivity of the polymer solid electrolyte membrane by setting the coating thickness to 20-80 μm; if the coating thickness is less than 20 μm, it will reduce the mention and mass energy density of the solid battery, increase the battery cost, and be unfavorable for large-scale application. Moreover, too low a thickness will cause the mechanical strength of the electrolyte to weaken, reducing the safety of the solid battery; when the thickness is higher than 80 μm, it will lead to an increase in the lithium ion transmission path, increase the internal resistance of the battery, and be unfavorable for the battery power performance. At the same time, the light intensity is 1500-2500 W·cm -2 The curing time is 60-120S, which can fully ensure the cross-linking between the components to form a polymer, avoiding long-term high-intensity radiation that may cause polymer grading and have an adverse effect on the electrochemical and mechanical properties of the polymer solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic flow chart of a method for preparing a three-dimensional polymer composite solid electrolyte proposed in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments.

[0030] The present application will be further described below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended solely to illustrate the relevant inventions and are not intended to limit the inventions. It should also be noted that, for ease of description, only portions relevant to the invention are shown in the drawings. Terms such as "first" and "second" in the present application are provided for the convenience of describing the technical solutions of the present invention and do not have a specific limiting effect. They are general references and do not constitute a limitation on the technical solutions of the present invention. It should be noted that the embodiments and features therein in the present application may be combined with each other unless there is a conflict. In the description of the present invention, it should be noted that terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed, removable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0031] In this application, it should be noted that all reagent components involved in this application are existing reagents and can be purchased. Among them, PVDF is polyvinylidene fluoride, PEO is polyethylene oxide, PAA is polyacrylic acid, LITFSI is lithium bis(trifluoromethanesulfonyl)imide, GDC is gadolinium oxide doped cerium oxide Gd 0.1 Ce 0.9 O 1.95 .

[0032] The present application provides a three-dimensional polymer composite solid electrolyte, comprising a polymer matrix, a crosslinker, a photoinitiator, an inorganic filler, and a lithium salt. The polymer matrix is a mixture of PVDF, PEO, and PAA. The mass ratio of the PVDF, PEO, PAA, crosslinker, photoinitiator, inorganic filler, and lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7. Under irradiation with a photoinitiator and ultraviolet light, the PEO, PAA, and crosslinker crosslink to form an amphiphilic block copolymer, which then crosslinks with PVDF to form an interpenetrating three-dimensional polymer structure, resulting in a three-dimensional PVDF-PEO-PAA-based polymer composite solid electrolyte, i.e., a three-dimensional polymer composite solid electrolyte, which improves the electrical conductivity and mechanical properties of the composite solid electrolyte. Since PEO has strong hydrophilicity and PAA has strong hydrophobicity, after cross-linking to form a copolymer, compared with other systems, on the one hand, it has good compatibility with organic solvents, which can improve the dispersion uniformity of raw materials in the preparation process; on the other hand, it enhances the affinity with lithium ions and enhances the lithium ion transport performance of the composite solid electrolyte. At the same time, the introduction of PVDF can enhance the surface flatness, thermal stability and chemical stability of the composite solid electrolyte and extend the service life of the solid electrolyte. In addition, by adding lithium salts and inorganic fillers, there is a strong adsorption effect between the inorganic fillers and the lithium salts, which effectively promotes the dissociation of lithium salts, thereby activating more mobile Li in the polymer solid electrolyte. + , thereby significantly improving the room-temperature conductivity of the polymer solid electrolyte, reducing the internal resistance of the solid battery and extending the cycle life. It can be seen that compared to simple PEO or PVDF-based polymer composite solid electrolytes, the three-dimensional polymer composite solid electrolyte in this application can provide more lithium ion transmission channels, improving the room-temperature conductivity and mechanical strength of the polymer solid electrolyte.

[0033] Specifically, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium hexafluoroborate, lithium perchlorate, lithium difluorobis(oxalatoborate), lithium triethylborohydride, lithium diisopropylamide, lithium acetoacetate, lithium bis(trimethylsilyl)lithium, lithium pentamethylcyclopentadienyl, 4,5-dicyano-2-trifluoromethylimidazole, lithium fluorosulfonic acid (perfluorobutylsulfonyl)imide, and tert-butyl lithium; the inorganic filler is any one of gadolinium oxide-doped cerium oxide, cerium-stabilized scandium-doped zirconia, and yttrium oxide-stabilized zirconia; the crosslinking agent is selected from acrylate, trimethyl carbonate, divinylbenzene, diisocyanate, N,N-methylenediamine, benzophenone ... One or more of bisacrylamide, polyalkyl acrylate, benzoyl peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, diethylenetriamine, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine; the photoinitiator is one or more of 2-hydroxy-2-methylacetophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone.

[0034] At the same time, the present application also provides a method for preparing a three-dimensional polymer composite solid electrolyte, comprising the following steps:

[0035] S1. Dissolve the polymer matrix, cross-linking agent, photoinitiator, inorganic filler and lithium salt in acetonitrile, and stir and mix them in a protective atmosphere to obtain a precursor mixed solution.

[0036] Specifically, PVDF is dissolved in acetonitrile at room temperature, and then PEO, PAA, a cross-linking agent, a photoinitiator, an inorganic filler and a lithium salt are added, wherein the mass ratio of the PVDF, the PEO, the PAA, the cross-linking agent, the photoinitiator, the inorganic filler and the lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7, the cross-linking agent is acrylate, the photoinitiator is 2-hydroxy-2-methylpropiophenone, the inorganic filler is gadolinium oxide doped cerium oxide, and the lithium salt is lithium bistrifluoromethanesulfonyl imide; then, the mixture is stirred for 3-8 hours under an argon atmosphere or a nitrogen atmosphere to obtain a precursor mixed solution. By setting the lithium salt to lithium bistrifluoromethanesulfonyl imide (LITFSI) and the inorganic filler to gadolinium oxide doped cerium oxide (Gd 0.1 Ce 0.9 O 1.95 , simplified as GDC), which makes GDC have a strong adsorption effect with LITFSI lithium salt anions, effectively promoting the dissociation of lithium salts and activating more mobile Li in the polymer solid electrolyte.+ , significantly improving the room-temperature conductivity of polymer solid electrolytes, reducing the internal resistance of solid batteries and extending cycle life. At the same time, in an argon or nitrogen atmosphere, it can prevent other pollutants from interfering with the reaction.

[0037] S2. The precursor mixed solution obtained in step S1 is coated on a glass plate, and then cured by ultraviolet light irradiation in a protective atmosphere to obtain a polymer solid electrolyte membrane.

[0038] Specifically, the precursor mixed solution is coated on a glass plate by a doctor blade method with a coating thickness of 20-80 μm; and then cured by ultraviolet light irradiation in an argon or nitrogen atmosphere with a light intensity of 1500-2500 W·cm -2 , the curing time is 60-120S. By setting the coating thickness to 20-80μm, the mechanical strength and conductivity of the polymer solid electrolyte membrane can be guaranteed; if the coating thickness is less than 20μm, it will reduce the mention and mass energy density of the solid battery, increase the battery cost, and is not conducive to large-scale application. In addition, too low a thickness will cause the mechanical strength of the electrolyte to weaken, reducing the safety of the solid battery; when the thickness is higher than 80μm, it will lead to an increase in the lithium ion transmission path, increase the internal resistance of the battery, and be detrimental to the battery power performance. At the same time, the light intensity is 1500-2500W·cm -2 The curing time is 60-120S, which can fully ensure the cross-linking between the components to form a polymer, avoiding long-term high-intensity radiation that may cause polymer grading and have an adverse effect on the electrochemical and mechanical properties of the polymer solid electrolyte.

[0039] S3. Peeling the polymer solid electrolyte membrane obtained in step S2 from the glass plate, washing it, and vacuum drying it to obtain a three-dimensional polymer composite solid electrolyte.

[0040] Specifically, the polymer solid electrolyte membrane is peeled from the glass plate, washed 3-5 times with methanol or isopropyl alcohol, and vacuum dried at 30-70°C for 10-24 hours to obtain a three-dimensional polymer composite solid electrolyte. Washing with methanol or isopropyl alcohol 3-5 times can remove unpolymerized monomers, crosslinkers, and excess photoinitiators from the polymer solid electrolyte membrane, thereby improving the quality of the polymer solid electrolyte membrane.

[0041] In practical application, when the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LITFSI) and the inorganic filler is gadolinium oxide-doped cerium oxide (Gd 0.1 Ce 0.9 O 1.95, simplified as GDC), the PVDF, the PEO, and the PAA are prepared under the action of a crosslinking agent and a photoinitiator to prepare a three-dimensional polymer composite solid electrolyte. The process diagram of the three-dimensional polymer composite solid electrolyte is as follows Figure 1 As shown, the value range of n is 80000-200000, the value range of m is 20000-500000, and the value range of p is 50000-300000.

[0042] Depend on Figure 1 It can be seen that under the irradiation of photoinitiator and ultraviolet light, PEO, PAA and crosslinking agent crosslink to form amphiphilic block copolymer, and crosslink with PVDF to form interpenetrating three-dimensional polymer, namely three-dimensional polymer composite solid electrolyte, which improves the electrical conductivity and mechanical properties of the composite solid electrolyte. At the same time, the lithium salt is lithium bistrifluoromethanesulfonyl imide (LITFSI), and the inorganic filler is gadolinium oxide doped cerium oxide (Gd 0.1 Ce 0.9 O 1.95 , simplified as GDC), which makes GDC have a strong adsorption effect with LITFSI lithium salt anions, effectively promoting the dissociation of lithium salts, activating more mobile Li+ in the polymer solid electrolyte, significantly improving the room temperature conductivity of the polymer solid electrolyte, reducing the internal resistance of the solid battery and extending the cycle life. In addition, because PEO has strong hydrophilicity and PAA has strong hydrophobicity, after cross-linking to form a copolymer, compared with other systems, on the one hand, it has good compatibility with organic solvents, which can improve the dispersion uniformity of raw materials in the preparation process; on the other hand, it enhances the affinity with lithium ions and enhances the lithium ion transport performance of the composite solid electrolyte; and the introduction of PVDF can enhance the surface flatness, thermal stability and chemical stability of the composite solid electrolyte, extending the service life of the solid electrolyte. It can be seen that compared with simple PEO or PVDF-based polymer composite solid electrolytes, the three-dimensional polymer composite solid electrolyte prepared by the above method can provide more lithium ion transmission channels, improve the room temperature conductivity and mechanical strength of the polymer solid electrolyte.

[0043] In addition, in order to determine the polymer formed by cross-linking between PEO, PAA and PVDF to form an interpenetrating three-dimensional structure after ultraviolet light irradiation, this application uses acetone or acetonitrile as an etching solution to remove the principle of PVDF, PEO and PAA. The three-dimensional composite polymer solid electrolyte prepared above was immersed in an acetone or acetonitrile solution at room temperature for 15-30 hours, then taken out and washed with methanol 3-5 times, and finally, vacuum dried at 30-70°C for 10-15 hours and weighed. The results showed that the three-dimensional composite polymer solid electrolyte prepared in Example 1 did not change significantly before and after immersion, and the three-dimensional composite polymer solid electrolyte remained intact. It can be seen that after ultraviolet light curing, photocuring polymerization occurred between PEO, PAA and PVDF, and it was an insoluble cross-link.

[0044] Example 1

[0045] PVDF was dissolved in acetonitrile at room temperature to form a transparent solution, and then PEO, PAA, acrylate, 2-hydroxy-2-methylpropiophenone, GDC powder, and LITFSI were added. The mass ratio of PVDF, PEO, PAA, acrylate, 2-hydroxy-2-methylpropiophenone, GDC, and LITFSI was 14:15:14:8:0.4:4:6. The mixture was stirred continuously for 5 hours under an argon atmosphere to obtain a uniformly dispersed precursor mixed solution. The precursor mixed solution was then evenly coated on a glass plate using a doctor blade method to a coating thickness of 60 μm and cured by UV irradiation in an argon atmosphere for 90 seconds at an illumination intensity of 2200 W·cm -2 Then, the cured polymer solid electrolyte membrane was peeled off from the glass, washed with methanol four times, and vacuum dried at 55°C for 16 hours to obtain a three-dimensional polymer composite solid electrolyte.

[0046] Example 2

[0047] PVDF was dissolved in acetonitrile at room temperature to form a transparent solution, and then PEO, PAA, acrylate, 2-hydroxy-2-methylpropiophenone, GDC powder, and LITFSI were added. The mass ratio of PVDF, PEO, PAA, acrylate, 2-hydroxy-2-methylpropiophenone, GDC, and LITFSI was 10:20:10:5:0.5:2:3. The mixture was stirred continuously for 8 hours under an argon atmosphere to obtain a uniformly dispersed precursor mixed solution. The precursor mixed solution was then evenly coated on a glass plate using a doctor blade method to a coating thickness of 80 μm and cured by UV irradiation in an argon atmosphere for 120 seconds at an illumination intensity of 1500 W·cm -2Then, the cured polymer solid electrolyte membrane was peeled off from the glass, washed five times with isopropyl alcohol, and dried under vacuum at 70°C for 24 hours to obtain a three-dimensional polymer composite solid electrolyte.

[0048] Example 3

[0049] PVDF was dissolved in acetonitrile at room temperature to form a transparent solution. PEO, PAA, divinylbenzene and diisocyanate, 2-hydroxy-2-methylpropiophenone, GDC powder, and lithium bis(oxalatoborate) were then added. The mass ratio of PVDF, PEO, PAA, divinylbenzene and diisocyanate, 2-hydroxy-2-methylpropiophenone, GDC, and lithium bis(oxalatoborate) was 14:15:14:8:0.4:4:6. The mixture was stirred continuously for 5 hours under an argon atmosphere to obtain a uniformly dispersed precursor mixed solution. The precursor mixed solution was then evenly coated on a glass plate using a doctor blade method to a coating thickness of 60 μm. The solution was then cured by UV irradiation in an argon atmosphere for 90 seconds at an illumination intensity of 2200 W·cm. -2 Then, the cured polymer solid electrolyte membrane was peeled off from the glass, washed with methanol four times, and vacuum dried at 55°C for 16 hours to obtain a three-dimensional polymer composite solid electrolyte.

[0050] Comparative Example 1

[0051] Compared with Example 1, the difference is that the polymer matrix in Comparative Example 1 does not contain the PVDF component, and the other conditions are the same as those in Example 1.

[0052] Comparative Example 2

[0053] Compared with Example 1, the difference is that the polymer matrix in Comparative Example 2 does not contain the component PEO, and the other conditions are the same as those in Example 1.

[0054] Comparative Example 3

[0055] Compared with Example 1, the difference is that the polymer matrix in Comparative Example 3 does not contain the component PAA, and the other conditions are the same as those in Example 1.

[0056] Comparative Example 4

[0057] Compared with Example 1, the difference is that the polymer matrix in Comparative Example 4 is only pure PEO, and the other conditions are the same as those in Example 1.

[0058] Comparative Example 5

[0059] Compared with Example 1, the difference is that the inorganic filler GDC is not added to the components in Comparative Example 5, and the other conditions are the same as those in Example 1.

[0060] Comparative Example 6

[0061] Compared with Example 1, the difference is that the curing time in Comparative Example 6 is 180S and the light intensity is 3000W·cm -2 , the remaining conditions are the same as in Example 1.

[0062] Various performance test evaluations

[0063] The three-dimensional polymer composite solid electrolytes prepared in Examples 1-3 and the solid electrolytes prepared in Comparative Examples 1-6 were subjected to tensile tests at 10 mm / min in accordance with GB1040-92 "Test Method for Tensile Properties of Plastics". The test temperatures were 30°C and 60°C, respectively. Each sample was tested 5 times, and the average of the three middle values was taken. At the same time, the pressed solid electrolytes were subjected to AC internal resistance tests at 30°C and 60°C using a double probe method. The frequency range was 1-106 Hz. The AC impedance directly reflects the lithium ion transmission resistivity. To reduce the measurement error, the bottom and top of the sample were sprayed with gold before the test. In addition, a composite positive electrode sheet was prepared using the ternary material NCM, and a lithium-indium alloy sheet (lithium atomic ratio of 55%) was used as the negative electrode. The three-dimensional polymer composite solid electrolytes prepared in Examples 1-3 and the solid electrolytes prepared in Comparative Examples 1-6 were pressed at 35 standard atmospheres to prepare the corresponding solid full batteries. The solid-state full batteries prepared above were then subjected to charge-discharge cycle life tests at 30°C and 60°C, within the voltage range of 2.8-4.1V, and at a 0.1C rate. Table 1 shows the performance test results for the three-dimensional polymer composite solid electrolytes prepared in Examples 1-3 and the solid electrolytes prepared in Comparative Examples 1-6.

[0064] Table 1.

[0065]

[0066] As shown in Table 1, the three-dimensional polymer composite solid electrolytes prepared in Examples 1-3, compared to Comparative Examples 1-6, significantly reduced AC impedance, significantly enhanced tensile strength, and increased battery cycle life at both 30°C (room temperature) and 60°C (high temperature). This shows that the three-dimensional polymer composite solid electrolytes prepared in this application can significantly improve solid electrolyte performance, reduce solid battery internal resistance, increase room-temperature conductivity, and extend cycle life.

[0067] Specifically, in combination with Example 1 and Comparative Examples 1-4, it can be seen that compared with pure PEO, the three-dimensional polymer composite solid electrolyte prepared by the present invention has better mechanical properties and electrochemical properties. The main mechanism is that the polymer matrix is a mixture of PVDF, PEO and PAA, so that after the PVDF-PEO-PAA is composited, it provides more lithium ion transmission channels, mechanical strength and chemical stability.

[0068] At the same time, in combination with Example 1 and Comparative Example 6, it can be seen that if the ultraviolet light irradiation time is too long or the intensity is too high, it will cause the polymer material to age, which in turn leads to a decrease in battery performance.

[0069] In addition, it can be seen from Example 1 and Comparative Example 5 that the anion TFSI of GDC and LITFSI is added - There is a strong bonding force between them, TFSI - With cation Li + The interaction between them is weakened, releasing more Li + , increasing the Li + transfer number, reduce the internal resistance of the battery, and improve the cycle life of the solid battery.

[0070] It can be seen from this that the three-dimensional polymer composite solid electrolyte prepared in this application can significantly improve the lithium ion transport performance and mechanical strength of the polymer solid electrolyte, providing a reference for the development of high-performance polymer solid electrolytes.

[0071] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A three-dimensional polymer composite solid electrolyte, characterized in that: Including polymer matrix, crosslinker, photoinitiator, Inorganic filler and lithium salt, the polymer matrix is a mixture of PVDF, PEO and PAA; Wherein, the mass ratio of the PVDF, the PEO, the PAA, the crosslinking agent, the photoinitiator, the inorganic filler and the lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7; The inorganic filler is any one of gadolinia-doped cerium oxide, cerium-stabilized scandium-doped zirconia, and yttria-stabilized zirconia; The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium perchlorate, lithium difluorobis(oxalatoborate), lithium triethylborohydride, lithium diisopropylamide, lithium acetoacetate, lithium bis(trimethylsilyl)lithium, lithium pentamethylcyclopentadiene, 4,5-dicyano-2-trifluoromethylimidazole, lithium fluorosulfonic acid (perfluorobutylsulfonyl)imide, and tert-butyl lithium.

2. The three-dimensional polymer composite solid electrolyte according to claim 1, characterized in that The cross-linking agent is selected from the group consisting of One or more of acrylate, trimethyl carbonate, divinylbenzene, diisocyanate, N,N-methylenebisacrylamide, polyalkyl acrylate, benzoyl peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, diethylenetriamine, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine.

3. The three-dimensional polymer composite solid electrolyte according to claim 1, characterized in that The photoinitiator is one or more of 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone.

4. A method for preparing a three-dimensional polymer composite solid electrolyte, characterized in that: For preparing the three-dimensional polymer composite solid electrolyte according to any one of claims 1 to 3, the preparation method comprises the following steps: S1. Dissolving a polymer matrix, a cross-linking agent, a photoinitiator, an inorganic filler, and a lithium salt in acetonitrile, and stirring and mixing in a protective atmosphere to obtain a precursor mixed solution; S2, coating the precursor mixed solution obtained in step S1 on a glass plate, and then Curing by light irradiation to obtain a polymer solid electrolyte membrane; S3, peeling the polymer solid electrolyte membrane obtained in step S2 from the glass plate, washing it, and vacuum drying it to obtain three dimensional polymer composite solid electrolyte.

5. The method for preparing a three-dimensional polymer composite solid electrolyte according to claim 4, characterized in that: S1 step Specifically, PVDF is dissolved in acetonitrile at room temperature, and then PEO, PAA, a crosslinker, a photoinitiator, an inorganic filler and a lithium salt are added, and stirred for 3-8 hours under an argon atmosphere or a nitrogen atmosphere to obtain a precursor mixed solution.

6. The method for preparing a three-dimensional polymer composite solid electrolyte according to claim 5, characterized in that: described The mass ratio of PVDF, the PEO, the PAA, the crosslinker, the photoinitiator, the inorganic filler and the lithium salt is 10-20:10-20:10-20:5-10:0.3-0.5:2-5:3-7; wherein the crosslinker is acrylate, the photoinitiator is 2-hydroxy-2-methylacetophenone, the inorganic filler is gadolinium oxide-doped cerium oxide, and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

7. The method for preparing a three-dimensional polymer composite solid electrolyte according to claim 4, characterized in that: In S2, The precursor mixed solution is coated on a glass plate by a scraper method with a coating thickness of 20-80 μm; the protective atmosphere is an argon atmosphere or a nitrogen atmosphere; the light intensity is 1500-2500 W·cm-2, and the curing time is 60-120 seconds.

8. The method for preparing a three-dimensional polymer composite solid electrolyte according to claim 4, characterized in that: In S3, Wash with methanol or isopropanol 3-5 times, vacuum dry at 30-70°C, and dry for 10-24 hours.

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