Composite solid electrolyte, method for preparing the same, and secondary battery including the same

Abstract

The application belongs to the field of batteries, and specifically discloses a composite solid electrolyte, a preparation method thereof and a secondary battery containing the same. In the composite electrolyte, fluoropropenoate compounds, styrene and derivatives thereof are used as in-situ polymerization monomers. The polymer obtained after polymerization can significantly improve the solid electrolyte interface contact and mechanical strength in the system, and is beneficial to reducing the side reaction between the monomer and the sulfide / halide solid electrolyte, significantly improving the conductivity of the composite electrolyte, the initial efficiency of the battery and the cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a composite solid electrolyte, its preparation method, and a secondary battery containing the same. Background Technology

[0002] Sulfide and halide solid electrolytes are considered key materials for realizing high-energy-density all-solid-state batteries due to their extremely high ionic conductivity or excellent voltage stability. To overcome their inherent defects of poor interfacial compatibility and poor mechanical properties leading to poor electrical performance, they are mixed with polymer monomers and then polymerized in situ. The polymer network phase formed after polymerization is used as a binder and buffer layer, which effectively improves the interfacial contact between the electrolyte and the electrode, enhances mechanical strength, and inhibits dendrite growth, showing great potential for synergistic effects.

[0003] However, the active monomers used to construct the polymer network exhibit severe chemical side reactions with the electrolyte. For example, sulfide ions are strong nucleophiles that attack electrophilic groups in commonly used monomers such as acrylates. This "nucleophilic attack" not only destroys the high-conductivity lithium backbone of the sulfide itself, leading to a permanent decrease in its ionic conductivity, but also consumes or modifies the monomers, resulting in incomplete and uneven polymerization reactions. Ultimately, these side reactions generate a high-resistivity impurity layer at the interface, increasing the battery's internal resistance, significantly shortening cycle life, and causing industrialization challenges due to its extreme sensitivity to process parameters and poor product consistency and repeatability. Summary of the Invention

[0004] In view of the problem that in the above-mentioned prior art, during the in-situ polymer-solid electrolyte composite process, the monomer is prone to side reactions with the solid electrolyte, which leads to a decrease in the conductivity of the obtained composite electrolyte and the performance of the assembled battery, the present invention will provide a composite solid electrolyte, a method for preparing the same, and a secondary battery containing the same.

[0005] To achieve the above objectives, the following technical solutions are specifically included: On one hand, the present invention provides a composite solid electrolyte, which is obtained by in-situ polymerization of raw materials comprising the following parts by weight: 1-50 parts of monomer, 30-80 parts of solid electrolyte, 0-10 parts of polymer, 1-60 parts of lithium salt, 0-1 part of initiator, and 0-30 parts of additive; wherein the monomer comprises at least one of fluorinated acrylate compounds, styrene and its derivatives; and wherein the solid electrolyte comprises at least one of sulfide solid electrolyte and halide solid electrolyte.

[0006] The composite solid electrolyte of the present invention uses monomers for in-situ polymerization including fluoroacrylate compounds, styrene and its derivatives. The polymer after in-situ polymerization can not only effectively improve the interfacial contact between the solid electrolyte and the electrode, enhance the mechanical strength of the composite electrolyte and suppress dendrites; but also, as a weakly polar monomer, it can reduce or even avoid chemical side reactions between itself and the solid electrolyte in the system. In particular, its relative inertness to sulfide and halide solid electrolytes is beneficial to improving the stability between the polymer and the solid electrolyte before and after polymerization, thereby improving the conductivity of the composite solid electrolyte, the first efficiency of the battery and the cycle performance.

[0007] Preferably, the composite solid electrolyte is obtained by in-situ polymerization of the following raw materials in parts by weight: 10-30 parts monomer, 40-75 parts solid electrolyte, 0-5 parts polymer, 10-30 parts lithium salt, 0.01-0.1 parts initiator, and 0-10 parts additives.

[0008] Preferably, the monomer content in the raw material is 1%-40% by mass, more preferably 9%-27%.

[0009] Preferably, the sulfide solid electrolyte has a mass percentage content of 0%-80% in the raw materials, more preferably 30%-70%, and even more preferably 36%-64%.

[0010] Preferably, the mass percentage of the halide solid electrolyte in the raw materials is 0%-80%, more preferably 5%-45%, and even more preferably 15%-43%.

[0011] Preferably, the lithium salt has a mass percentage content of 5%-20% in the raw materials, and more preferably 7%-12%.

[0012] Preferably, the polymer in the raw materials has a mass percentage content of 0%-3.5%.

[0013] Preferably, the additive has a mass percentage content of 0%-10% in the raw materials.

[0014] Preferably, the solid electrolyte comprises a sulfide solid electrolyte and a halide solid electrolyte; the mass ratio of the sulfide solid electrolyte to the halide solid electrolyte is (35-70):(2-40), more preferably (35-60):(15-40).

[0015] Preferably, the derivatives of the styrene and its derivatives include styrene substituted with at least one of alkyl, alkoxy, olefinic, halogen, ether, ester, cyano, nitro or sulfur atoms.

[0016] More preferably, the alkyl group comprises a straight-chain or straight-chain alkyl group having 1-20 carbon atoms.

[0017] More preferably, the alkoxy group includes a straight-chain or straight-chain alkoxy group having 1-20 carbon atoms.

[0018] More preferably, the olefin group includes an olefin group having 2-20 carbon atoms.

[0019] More preferably, the styrene and its derivatives include at least one of 4-fluorostyrene, p-methylstyrene, m-methoxystyrene, methyl p-vinylbenzoate, p-cyanostrene, p-nitrostyrene, and p-mercaptostyrene.

[0020] Preferably, the fluorinated acrylate compound comprises at least one of the following: trifluoroethyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, 1H,1H,2H,2H-octafluoropentyl acrylate, 1H,1H,2H,2H-decafluorohexyl acrylate, 1H,1H,2H,2H-dodecylfluoroheptyl acrylate, 1H,1H,2H,2H-tetrafluorooctyl acrylate, perfluorooctyl acrylate, perfluorohexyl acrylate, perfluorobutyl acrylate, N-methylperfluorooctanesulfonamide ethyl acrylate, N-ethylperfluorooctanesulfonamide ethyl acrylate, 1H,1H,2H,2H-perfluorododecyl acrylate, 1H,1H,2H,2H-perfluorodecyl acrylate Esters, perfluorocyclohexyl methyl acrylate, 2-(perfluorooctyl)ethoxyethyl acrylate, 1H,1H,2H,2H-perfluoro-3,6-dioxanonyl acrylate, 1H,1H,2H,2H-perfluoro-3-oxahexyl acrylate, 2,2,3,3,4,4,5,5-octafluoropentoxyethyl acrylate, 1H,1H,2H,2H-perfluoro-6-thiazooctyl acrylate, 2-(perfluorohexyl)sulfonamide ethyl acrylate, 2-(1H,1H-perfluoroisopropoxy)ethyl acrylate, 1H,1H,2H,2H-perfluoro-4-vinylbutyl acrylate, trifluoroethyl methacrylate, pentafluoropropyl methacrylate, hexafluorobutyl methacrylate, 1H,1H-methacrylate H,2H,2H-octafluoropentyl ester, 1H,1H,2H,2H-decafluorohexyl methacrylate, 1H,1H,2H,2H-dodecylfluoroheptyl methacrylate, 1H,1H,2H,2H-tetrafluorooctyl methacrylate, perfluorohexylethyl methacrylate, perfluorohexyl ethyl methacrylate, perfluorobutyl ethyl methacrylate, N-methylperfluorooctane sulfonamide ethyl methacrylate, N-ethylperfluorooctane sulfonamide ethyl methacrylate, 1H,1H,2H,2H-perfluorododecyl methacrylate, 1H,1H,2H,2H-perfluorodecyl methacrylate, perfluorocyclohexyl methyl methacrylate, 2-(perfluorooctyl)ethoxyethyl methacrylate, methylpropionic acid Acrylic acid 1H,1H,2H,2H-perfluoro-3,6-dioxanonyl ester, methacrylate 1H,1H,2H,2H-perfluoro-3-oxahexyl ester, methacrylate 2,2,3,3,4,4,5,5-octafluoropentoxyethyl ester, methacrylate 1H,1H,2H,2H-perfluoro-6-thiaoctyl ester, methacrylate 2-(perfluorohexyl)sulfonamide ethyl ester, methacrylate α-trifluoromethacrylate, methacrylate α-fluoroacrylate, methacrylate 2-(1H,1H-perfluoroisopropoxy)ethyl ester, 1H,1H,2H,2H-perfluorooctane-1,8-diacrylate, 1H,1H,2H,2H-perfluorohexane-1,6-dimethylacrylate.

[0021] Preferably, the polymer includes at least one of a binder and a polymer electrolyte material.

[0022] More preferably, the polymer includes at least one of styrene-ethylene-butene-styrene copolymer, butadiene-styrene copolymer, polyvinylidene fluoride and its derivatives, polytetrafluoroethylene, cellulose, polystyrene, polyvinyl chloride, polyamide, polyimide, polyethylene, polypropylene, polyethylene oxide, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, styrene-butadiene rubber, nitrile rubber, sodium carboxymethyl cellulose, polyphenylene sulfide, and polyetheretherketone.

[0023] Preferably, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium tetrachloroaluminate, 4,5-dicyano-2-trifluoromethylimidazolium, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, and lithium nitrate.

[0024] Preferably, the solid electrolyte comprises Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li 11 Sn2PS 12 At least one of Li6PS5Cl, Na3PS4, Li3InCl6, Li3YCl6, Li2ZrCl4, and LiSc3Br6.

[0025] Preferably, the additive comprises at least one of ionic liquids, organic nitrile compounds, and crown ethers. The additive functions to improve the solid-solid interface contact and reduce interfacial impedance in the composite solid electrolyte. A mixture of organic nitrile compounds and / or crown ethers with lithium salts can constitute an organic eutectic electrolyte. An organic eutectic electrolyte is a eutectic mixture composed of lithium salts and small molecule ligands; for example, a mixture of LiDFOB and succinic acid can constitute an organic eutectic, which can improve the solid-solid interface contact and reduce interfacial impedance in the composite solid electrolyte.

[0026] More preferably, the ionic liquid includes imidazole, pyridine, quaternary ammonium, quaternary phosphorus, pyrrolidine, and piperidine ionic liquids.

[0027] More preferably, the ionic liquid comprises 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0028] Preferably, the initiator includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, potassium persulfate, ammonium persulfate, 2-hydroxy-2-methyl-1-phenylpropanone, methyl benzoylformate, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone.

[0029] On the other hand, the present invention provides a method for preparing the composite solid electrolyte, comprising the following steps: S1. Mix the raw materials with the organic solvent evenly to obtain an electrolyte slurry; S2. The electrolyte slurry is coated onto the substrate, and then subjected to photo-initiated and / or thermally initiated polymerization, followed by hot pressing to obtain a composite solid electrolyte.

[0030] Preferably, in step S1, the organic solvent includes n-hexane.

[0031] Preferably, in step S2, the thermal initiation temperature is 70-100℃ during the thermal initiation process.

[0032] Preferably, in step S2, the hot pressing temperature is 100-150℃, and the hot pressing time is 6-24h.

[0033] In addition, the present invention also provides a secondary battery comprising the aforementioned composite solid electrolyte.

[0034] Specifically, the composite solid electrolyte is disposed between the positive electrode and the negative electrode of the secondary battery.

[0035] Compared with the prior art, the present invention has the following beneficial effects: In the composite electrolyte of the present invention, fluoroacrylate compounds, styrene and its derivatives are used as monomers for in-situ polymerization. The polymer network obtained by in-situ polymerization can not only significantly improve the contact and mechanical strength of the solid electrolyte and electrode interface in the system, but also help reduce the side reactions between the monomer and the sulfide / halide solid electrolyte, and significantly improve the conductivity of the composite electrolyte and the first efficiency and cycle performance of the battery. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further explain the invention below. Unless otherwise specified, the test methods used in the embodiments and / or comparative examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0037] Examples 1-29 and Comparative Examples 1-2 A method for preparing a composite solid electrolyte includes the following steps: S1. Under anhydrous and oxygen-free conditions, monomers, sulfide solid electrolytes, halide solid electrolytes, lithium salts, initiators, and other optional polymers and additives are added to n-hexane solvent by weight and mixed evenly to form an electrolyte slurry. S2. Under anhydrous and oxygen-free conditions, the electrolyte slurry is coated onto the substrate material with a coating thickness of about 50 μm. It is heated to 80°C and held for 2 hours to remove the solvent and initiate polymerization. Then, it is hot-pressed at 130°C for 12 hours to obtain a dense composite solid electrolyte membrane. The detailed raw material usage is shown in Table 1.

[0038] Comparative Example 3 Compared with Example 1, this comparative example does not involve in-situ polymerization and includes the following steps: S1. Under anhydrous and oxygen-free conditions, add 10 parts by weight of commercially available polystyrene (Mw~200,000), 60 parts by weight of sulfide solid electrolyte, 15 parts by weight of halide solid electrolyte, 10 parts by weight of lithium salt and 3 parts by weight of nitrile rubber to hexane solvent, mix them evenly to form an electrolyte slurry. S2. Under anhydrous and oxygen-free conditions, the electrolyte slurry is coated onto the substrate material with a coating thickness of about 50 μm, and then hot-pressed at 130°C for 12 hours to obtain a dense composite solid electrolyte membrane.

[0039] Performance testing: (1) The composite solid electrolyte membranes obtained in the examples and comparative examples were subjected to room temperature impedance testing at 25°C using an electrochemical workstation, and the ionic conductivity of the solid electrolyte membranes was calculated using the following formula: Ionic conductivity = L / (R×S); Where L is the thickness of the composite solid electrolyte membrane, in cm; R is the room temperature impedance of the composite solid electrolyte membrane, in Ω; and S is the effective ion conduction area of ​​the composite solid electrolyte membrane, in cm². 2 .

[0040] (2) The composite solid electrolyte membranes obtained in the examples and comparative examples were respectively set between the positive electrode and the negative electrode to form an all-solid-state battery. The only difference between the all-solid-state batteries prepared in the examples and comparative examples is the raw material of their respective composite solid electrolyte membranes. The size of the composite solid electrolyte membrane, the size and model of the all-solid-state battery and the corresponding test conditions are the same. Among them, ternary nickel cobalt manganese oxide (NCM811) was selected as the positive electrode active material and lithium indium alloy was selected as the negative electrode to assemble a lithium half-cell. The coulombic efficiency of the half-cell at 25°C, voltage test range of 2.8V-4.3V and 0.1C rate and the capacity retention rate after 100 cycles were tested.

[0041] The test results are shown in Table 2.

[0042] Table 1 Continued from Table 1 Table 2 Continued from Table 2 In Comparative Example 1, polystyrene was used, resulting in low conductivity of the composite electrolyte and a sharp decline in capacity retention, leading to poor cycle performance. Comparative Example 2, using conventional acrylate monomers, experienced a sharp drop in conductivity due to side reactions with the sulfide electrolyte, resulting in low first-cycle efficiency and early short circuits, failing to complete 100 cycles. As shown in the examples and comparative examples, the composite solid electrolyte membrane in the examples comprehensively outperforms the comparative examples in terms of ionic conductivity, first-cycle efficiency, and 100-cycle capacity retention. This demonstrates that the polymer network phase formed by in-situ polymerization of fluorinated acrylates and / or fluorinated acrylate monomers in this invention serves as a binder and buffer layer, effectively improving the interfacial contact between the electrolyte and electrode. It significantly suppresses side reactions in the system, particularly those with the sulfide electrolyte, and constructs continuous ion channels. By improving the interfacial contact between the solid electrolyte and the electrode, it significantly enhances the conductivity of the composite solid electrolyte, the first-cycle efficiency, and the capacity retention of the battery, significantly extending the battery cycle life and demonstrating a significant advantage in improving the long-term reliability of all-solid-state batteries.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite solid electrolyte, characterized in that, The preparation method of the composite solid electrolyte includes the following steps: S1. Mix the raw materials with an organic solvent until homogeneous to obtain an electrolyte slurry; the organic solvent includes n-hexane; S2. The electrolyte slurry is coated onto a substrate, and then subjected to photo-initiated and / or thermally initiated polymerization, followed by hot pressing to obtain a composite solid electrolyte; the hot pressing temperature is 100-150℃, and the hot pressing time is 6-24h. In step S1, the raw material is composed of the following components in parts by weight: 1-50 parts monomer, 30-80 parts solid electrolyte, 0-10 parts polymer, 1-60 parts lithium salt, 0.01-0.1 parts initiator, and 0-30 parts additive; the monomer includes at least one of fluorinated acrylate compounds and styrene derivatives; the solid electrolyte includes at least one of sulfide solid electrolyte and halide solid electrolyte; the styrene derivative includes at least one of 4-fluorostyrene, p-methylstyrene, m-methoxystyrene, methyl p-vinylbenzoate, p-cyanostyrene, p-nitrostyrene, and p-mercaptostyrene. The fluorinated acrylate compounds include at least one of the following: trifluoroethyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, perfluorooctyl ethyl acrylate, perfluorohexyl ethyl acrylate, perfluorobutyl ethyl acrylate, N-methylperfluorooctane sulfonamide ethyl acrylate, N-ethylperfluorooctane sulfonamide ethyl acrylate, 1H,1H,2H,2H-perfluorododecyl acrylate, perfluorocyclohexyl methyl acrylate, 2-(perfluorooctyl)ethoxyethyl acrylate, 2-(perfluorohexyl)sulfonamide ethyl acrylate, pentafluoropropyl methacrylate, hexafluorobutyl methacrylate, methyl acrylate. Perfluorooctyl ethyl methacrylate, perfluorohexyl ethyl methacrylate, perfluorobutyl ethyl methacrylate, N-methylperfluorooctane sulfonamide ethyl methacrylate, N-ethylperfluorooctane sulfonamide ethyl methacrylate, 1H,1H,2H,2H-perfluorododecyl methacrylate, perfluorocyclohexyl methyl methacrylate, 2-(perfluorooctyl)ethoxyethyl methacrylate, 2-(perfluorohexyl)sulfonamide ethyl methacrylate, 1H,1H,2H,2H-perfluorooctane-1,8-diacrylate, 1H,1H,2H,2H-perfluorohexane-1,6-dimethyl methacrylate; The polymer includes at least one of binders and polymer electrolyte materials; The additives include at least one of ionic liquids, organic nitrile compounds, and crown ethers.

2. The composite solid electrolyte as described in claim 1, characterized in that, The polymer includes at least one of the following: styrene-ethylene-butene-styrene copolymer, butadiene-styrene copolymer, polyvinylidene fluoride and its derivatives, polytetrafluoroethylene, cellulose, polystyrene, polyvinyl chloride, polyamide, polyimide, polyethylene, polypropylene, polyethylene oxide, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, styrene-butadiene rubber, nitrile rubber, sodium carboxymethyl cellulose, polyphenylene sulfide, and polyetheretherketone.

3. The composite solid electrolyte as described in claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium dioxalate borate, lithium trifluoromethanesulfonate, lithium tetrachloroaluminate, lithium 4,5-dicyano-2-trifluoromethylimidazolium, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate, and lithium nitrate.

4. The composite solid electrolyte as described in claim 1, characterized in that, The solid electrolyte includes Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li 11 Sn2PS 12 At least one of Li6PS5Cl, Na3PS4, Li3InCl6, Li3YCl6, Li2ZrCl4, and LiSc3Br6.

5. The composite solid electrolyte as described in claim 1, characterized in that, The solid electrolyte includes sulfide solid electrolyte and halide solid electrolyte; the mass ratio of the sulfide solid electrolyte to the halide solid electrolyte is (35-70):(2-40).

6. The composite solid electrolyte as described in claim 1, characterized in that, The initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, potassium persulfate, ammonium persulfate, 2-hydroxy-2-methyl-1-phenylpropanone, methyl benzoylformate, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone.

7. A method for preparing the composite solid electrolyte according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Mix the raw materials with an organic solvent until homogeneous to obtain an electrolyte slurry; the organic solvent includes n-hexane; S2. The electrolyte slurry is coated onto a substrate, and then subjected to photo-initiated and / or thermally initiated polymerization, followed by hot pressing to obtain a composite solid electrolyte; the hot pressing temperature is 100-150℃, and the hot pressing time is 6-24h.

8. A secondary battery, characterized in that, Includes the composite solid electrolyte as described in any one of claims 1-6.

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