Gel electrolyte composition, liquid injection method thereof and lithium metal battery

Abstract

The invention provides a gel electrolyte composition, a liquid injection method thereof and a lithium metal battery. The gel electrolyte composition comprises a first component, a second component and a lithium salt, wherein the first component comprises a fluoroether compound, fluorocarbonate, a fluorine-free ether compound, a siloxane additive and an optional film-forming additive; and the second component comprises a cross-linking agent monomer and a free radical initiator. Under the synergistic effect of a first component, a second component and a lithium salt, the first component comprises a fluoroether compound, fluorocarbonate, a fluorine-free ether compound, a siloxane additive and an optional film-forming additive, the second component comprises a cross-linking agent monomer and a radical initiator, and the lithium salt, the formed gel electrolyte is more uniform and more stable in structure; the lithium dendrite problem and the interface side reaction problem in the lithium metal battery can be effectively improved, and the effect of improving the cycling stability and safety of the lithium metal battery is remarkable.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and more particularly, to a gel electrolyte composition, a method for injecting electrolyte, and a lithium metal battery. Background Art

[0002] With the rapid progress of technology and the popularization of electric vehicles, the market demand for rechargeable batteries with higher energy density is increasing. Lithium metal batteries, as a cutting-edge energy storage technology, have become a research hotspot due to their high theoretical specific capacity (3860 mAh / g), high theoretical energy density, no memory effect, and low self-discharge rate, especially in the field of pursuing high energy density of batteries. However, the high reactivity of lithium metal anodes and the formation of lithium dendrites have always been the key obstacles hindering their commercial applications, which not only affect the performance of the batteries but also may pose safety risks.

[0003] The electrolyte is a core component in the battery system, which is directly related to the capacity, internal resistance, cycle stability, and rate performance of the battery. To overcome the inherent challenges of lithium metal batteries, researchers have started to focus on the development of in-situ gel electrolytes. This type of electrolyte can form a stable interface inside the battery, effectively reducing the number of free solvent molecules, thus inhibiting the growth of lithium dendrites and enhancing the safety of the battery. At the same time, it can also maintain a high ionic conductivity comparable to that of traditional liquid electrolytes, which significantly promotes the cycle efficiency and safety performance of lithium metal batteries.

[0004] In the existing lithium-ion battery technology, although these batteries have made significant progress in terms of energy density, power density, and cycle life, for some high-demand application scenarios, especially in the fields of electric vehicles and aerospace that require higher energy density, traditional lithium-ion batteries still have limitations. Lithium metal, as a negative electrode material, is regarded as the key to breaking through the energy density ceiling of current lithium-ion batteries due to its excellent theoretical performance. However, the high activity of lithium metal makes it extremely prone to side reactions when contacting with traditional electrolytes, resulting in excessive consumption of the electrolyte, low Coulomb efficiency, and the formation of lithium dendrites, which seriously restrict the performance and safety of lithium metal batteries.

[0005] Therefore, combining the in-situ curing technology of liquid electrolytes to develop gel electrolytes has become an innovative solution to improve the performance of lithium metal batteries. In view of the above background, the present invention aims to provide a gel electrolyte component and a secondary electrolyte injection process to improve the cycle stability and safety of lithium metal batteries and promote their wide application in the fields with high power and high energy density requirements. For this reason, the present invention is specifically proposed. Summary of the Invention

[0006] The main object of the present invention is to provide a gel electrolyte composition, a method for injecting electrolyte, and a lithium metal battery, so as to solve the problems of lithium dendrites, interfacial side reactions in traditional liquid electrolyte lithium metal batteries, and the resulting structural stability problems of lithium metal batteries, aiming to comprehensively improve the cycle stability and safety of lithium metal batteries and promote their wide application in fields with high power and high energy density requirements.

[0007] The gel electrolyte composition provided by the present invention includes a first component, a second component, and a lithium salt; wherein, the first component includes a fluoroether compound, a fluorinated carbonate, a fluorine-free ether compound, a siloxane additive, and optionally a film-forming additive; the second component includes a crosslinking monomer and a radical initiator. Under the synergistic effect of each of the above components, the formed gel electrolyte is not only more uniform and stable, but also can effectively improve the problems of lithium dendrites and interfacial side reactions in lithium metal batteries, and has a significant effect on improving the cycle stability and safety of lithium metal batteries.

[0008] Further, by weight percentage, the first component includes: 1-60% of a fluoroether compound, 2-50% of a fluorinated carbonate, 1-60% of a fluorine-free ether compound; 0.01-10% of a siloxane additive, 0-10% of a film-forming additive; in the second component, the crosslinking monomer is 1-10% of the weight of the first component; the radical initiator is 0.01-5% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 0.5-3 mol / L; preferably, by weight percentage, the first component includes: 20-60% of a fluoroether compound, 20-40% of a fluorinated carbonate, 15-40% of a fluorine-free ether compound; 0.01-5% of a siloxane additive, 0.01-5% of a film-forming additive; in the second component, the crosslinking monomer is 1-5% of the weight of the first component; the radical initiator is 0.01-2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 0.5-3 mol / L. Controlling the content of each component of the gel electrolyte composition within the above range can better exert the synergistic effect between the components, which is beneficial to further improving the electrochemical performance of the gel electrolyte and the cycle stability performance of the lithium metal battery.

[0009] Further, the fluorinated carbonate is a cyclic fluorinated carbonate and / or a chain fluorinated carbonate; preferably, the fluorinated carbonate is a mixture of a cyclic fluorinated carbonate and a chain fluorinated carbonate; preferably, the weight ratio of the cyclic fluorinated carbonate to the chain fluorinated carbonate is 1:(0.5-5); more preferably, the weight ratio of the cyclic fluorinated carbonate to the chain fluorinated carbonate is 1:(1-3). When the cyclic fluorinated carbonate and the chain fluorinated carbonate are used in combination and the weight ratio of the two is controlled within the above preferred range, the improvement effect on the cycle stability performance of the lithium metal battery will be better.

[0010] Furthermore, the cyclic fluorinated carbonate has a compound with the structure shown in the following formula (I):

[0011]

[0012] In formula (I), R 3 , R 4 , R 5 and R 6 are each independently selected from H, F, an alkyl group of C 1 to C 10 , a fluoroalkyl group of C 1 to C 10 , an alkenyl group of C 2 to C 10 or a fluoroalkenyl group of C 2 to C 10 , and at least one of R 3 , R 4 , R 5 and R 6 contains a fluorine atom; preferably, R 3 , R 4 , R 5 and R 6 are each independently selected from H, F, an alkyl group of C 1 to C 5 or a fluoroalkyl group of C 1 to C 5 , and at least one of R 3 , R 4 , R 5 and R 6 contains a fluorine atom; more preferably, R 3 , R 4 , R 5 and R 6 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one of R 3 , R 4 , R 5 and R 6 contains a fluorine atom; most preferably, the cyclic fluorinated carbonate has the structure shown in the following formula (A):

[0013]

[0014] And / or, the linear fluorinated carbonate has a compound with the structure shown in the following formula (II):

[0015]

[0016] In formula (II), R 7 and R 8 are each independently selected from H, F, C1 ~C 10 alkyl group of, C 1 ~C 10 fluoroalkyl group of, C 2 ~C 10 alkenyl group of or C 2 ~C 10 fluoroalkenyl group of, and R 7 and R 8 contain at least one fluorine atom; preferably, R 7 and R 8 are each independently selected from H, F, C 1 ~C 5 alkyl group of or C 1 ~C 5 fluoroalkyl group of, and R 7 and R 8 contain at least one fluorine atom; more preferably, R 7 and R 8 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and R 7 and R 8 contain at least one fluorine atom; most preferably, the chain - like fluorinated carbonate has a structure shown in the following formula (B):

[0017]

[0018] and / or, the fluoro - ether compound is a compound having a structure shown in the following formula (Ⅲ):

[0019]

[0020] In formula (Ⅲ), R 1 and R 2 are each independently selected from C 1 ~C 10 alkyl group of, C 1 ~C 10 fluoroalkyl group of, C 2 ~C 10 alkenyl group of or C 2 ~C 10 fluoroalkenyl group of, and R 1 and R 2 contain at least one fluorine atom; preferably, R 1 and R 2 are each independently selected from C 1 ~C 5 alkyl group of, and the alkyl group contains at least one fluorine atom; more preferably, R 1 and R 2Each independently selected from methyl, ethyl, monofluoromethyl, difluoromethyl, trifluoromethyl, 1,1,2,2 - tetrafluoroethyl, 1,1,2 - trifluoroethyl or trifluoromethylethyl; Most preferably, the fluoroether compound has the structure shown in the following formula (C):

[0021]

[0022]

[0023] And / or, the fluorine - free ether compound is a compound having the structure shown in the following formula (IV):

[0024]

[0025] In formula (IV), R 9 and R 10 Each independently selected from C 1 ~C 10 alkyl or C 2 ~C 10 alkoxyalkyl; More preferably, in formula (IV), R 9 and R 10 Each independently selected from C 1 ~C 5 alkyl; More preferably, R 9 and R 10 Each independently selected from methyl, ethyl, propyl, isopropyl or butyl; Most preferably, the fluorine - free ether compound has the structure shown in the following formula (D):

[0026]

[0027] Further, the lithium salt is one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium difluorophosphate; preferably, the siloxane additive is vinyltrimethoxysilane and / or allyltrimethoxysilane; preferably, the film-forming additive is at least one of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, methylene methanedisulfonate, 4-trifluoromethyl ethylene carbonate, 1,3,2-dioxathiolane-2,2-dioxide, ethylene sulfite, vinylene carbonate, succinic anhydride, propylene sulfite, allyl-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl, butylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt, N-methyl, propylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, fumarodinitrile, and 1,2,3-tris(2-cyanoethoxy)propane; preferably, the radical initiator is at least one of azobisisobutyronitrile, cyclohexanone peroxide, azobisisoheptonitrile, tert-butyl hydroperoxide, and dimethyl azobisisobutyrate; preferably, the crosslinking monomer is at least one of N,N-methylenebisacrylamide, methacrylamide, N-ethylacrylamide, and acrylamide with a cyclic structure. Using one or more of the above types of siloxane additives, film-forming additives, radical initiators, and crosslinking monomers as one of the components of the gel electrolyte composition has a better effect on improving the electrochemical performance of the gel electrolyte.

[0028] Further, the gel electrolyte composition comprises: by weight percentage, the first component includes: 49.5% of a fluoroether compound, 10% of a cyclic fluorocarbonate, 20% of a linear fluorocarbonate, 19.5% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, by weight percentage, the first component includes: 54% of a fluoroether compound, 8% of a cyclic fluorocarbonate, 22% of a linear fluorocarbonate, 15% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, by weight percentage, the first component includes: 49.5% of a fluoroether compound, 10% of a cyclic fluorocarbonate, 20% of a linear fluorocarbonate, 19.5% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 5% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L. The above solutions are exemplary. Controlling the content of each component in the gel electrolyte composition within the above proportion range is beneficial to making the gel electrolyte have better stability, thereby being beneficial to further improving the cycle stability and safety of the lithium metal battery.

[0029] According to the second aspect of the present invention, a method for injecting a gel electrolyte composition is further provided. The injection method includes the following steps: dividing the gel electrolyte composition into a first solution and a second solution. Among them, the first solution includes 80-92% of a fluoroether compound, 80-90% of a fluorinated carbonate, 80-90% of a fluorine-free ether compound, 100% of a siloxane additive, 0-90% of a film-forming additive, 100% of a crosslinking monomer, and 100% of a radical initiator; and the concentration of lithium salt in the first solution is 0.2-3 mol / L; the second solution includes: the remaining fluoroether compound, the remaining fluorinated carbonate, the remaining fluorine-free ether compound, the remaining film-forming additive, and the remaining lithium salt, and the concentration of lithium salt in the second solution is 0.5 mol / L-3.5 mol / L; the injection method includes the following steps: injecting the first solution into an electrochemical device for the first injection; subjecting the electrochemical device after the first injection to in-situ curing and formation to obtain a pretreated electrochemical device; injecting the second solution into the pretreated electrochemical device and performing vacuum sealing to complete the injection operation. The above secondary injection operation is beneficial to further improving the ionic conductivity of the gel electrolyte, improving the interfacial contact, and enhancing the interfacial stability of the lithium metal battery.

[0030] Further, the gel electrolyte composition is divided into a first solution and a second solution. Among them, the first solution includes 85-92% of the fluoroether compound in the gel electrolyte composition, 80-85% of the fluorinated carbonate, 80-85% of the fluorine-free ether compound, 100% of the siloxane additive, 0-90% of the film-forming additive, 100% of the crosslinking monomer, and 100% of the radical initiator; and the concentration of lithium salt in the first solution is 0.2-3 mol / L; the second solution includes: the remaining fluoroether compound, the remaining fluorinated carbonate, the remaining fluorine-free ether compound, the remaining film-forming additive, and the remaining lithium salt, and the concentration of lithium salt in the second solution is 0.5 mol / L-3.5 mol / L. The gel electrolyte formed after curing by the above injection method can further improve the interfacial contact, form a stable interface, and reduce the internal resistance of the lithium metal battery, thereby being beneficial to further enhancing the cycling performance of the lithium metal battery.

[0031] Further, the steps of in-situ curing and formation include: after the electrochemical device after the first injection is allowed to stand, it is charged at a constant current to 50-70% of the fully charged state to complete in-situ curing and formation; preferably, the standing time is 12-24 h; preferably, the constant current charging is carried out under the conditions of pressure P and temperature T, where 0.4 MPa ≤ P ≤ 1.2 MPa and 50 ≤ T ≤ 80 °C; preferably, the rate of constant current charging is 0.04C-0.2C. The above in-situ curing and formation conditions can further improve the interfacial stability of the gel electrolyte, increase the battery capacity and cycling stability.

[0032] According to the third aspect of the present invention, there is also provided a lithium metal battery, wherein the raw material of the electrolyte of the lithium metal battery is the above gel electrolyte composition; or, the electrolyte of the lithium metal battery is formed by the injection method of the above gel electrolyte composition.

[0033] Under the synergistic effect of the first component including a fluoroether compound, a fluorinated carbonate, a fluorine-free ether compound, a siloxane additive and optionally a film-forming additive, the second component including a crosslinking monomer and a radical initiator, and a lithium salt, the gel electrolyte formed not only has the advantages of being more uniform and more stable, but also can effectively improve the problems of lithium dendrites and interfacial side reactions in lithium metal batteries, and has a significant effect on improving the cycle stability and safety of lithium metal batteries. Detailed Embodiments

[0034] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0035] As described in the background art section, in the existing lithium-ion battery technology, although these batteries have made significant progress in terms of energy density, power density and cycle life, for some high-demand application scenarios, especially in the fields of electric vehicles and aerospace that require higher energy density, traditional lithium-ion batteries still have limitations. Lithium metal, as a negative electrode material, is regarded as the key to breaking through the energy density ceiling of current lithium-ion batteries due to its excellent theoretical performance. However, the high activity of lithium metal makes it extremely prone to side reactions when contacting with traditional electrolytes, resulting in excessive consumption of the electrolyte, low Coulomb efficiency, and the formation of lithium dendrites, which seriously restrict the performance and safety of lithium metal batteries.

[0036] To solve the above problems, the present invention provides a gel electrolyte composition, which includes a first component, a second component and a lithium salt; wherein, the first component includes a fluoroether compound, a fluorinated carbonate, a fluorine-free ether compound, a siloxane additive and optionally a film-forming additive; the second component includes a crosslinking monomer and a radical initiator.

[0037] The gel electrolyte composition provided by the present invention uses a fluoroether compound, a fluorinated carbonate, a fluorine-free ether compound, a siloxane additive and optionally a film-forming additive as the first component, and a crosslinking monomer and a radical initiator as the second component. In addition, it also includes a lithium salt. Under the synergistic effect of the above various components, the formed gel electrolyte is not only more uniform and more stable, but also can effectively improve the problems of lithium dendrites and interfacial side reactions in lithium metal batteries, and has a significant effect on improving the cycle stability and safety of lithium metal batteries.

[0038] Among them, the fluoroether compound in the gel electrolyte composition is not only not easily reactive with active lithium metal, but also can form a dense protective film on the positive electrode, improving the interfacial stability of the lithium metal battery. At the same time, the fluoroether compound structure contains groups with a large dipole moment, which can enhance the miscibility between the components in the gel electrolyte composition, facilitating the better formation of a uniform and stable gel electrolyte composition solution. In addition, the fluoroether compound in the gel electrolyte composition can also act as a "diluent", diluting the lithium salt concentration in the gel electrolyte composition, reducing free solvent molecules, inhibiting side reactions, and improving the transport of lithium ions in the gel electrolyte.

[0039] The fluorinated carbonate in the gel electrolyte composition can make the formed gel electrolyte have good oxidation resistance on the positive electrode side. In addition, the presence of fluorinated carbonate in the gel electrolyte will also form an organic polymer solid electrolyte interface layer (SEI) containing carbon and oxygen elements and a fluorine-containing inorganic solid electrolyte interface layer (SEI) on the surface of the lithium metal negative electrode. Under the synergistic effect of the above two types of SEI layers, the stability and protection of the negative electrode surface are further enhanced, effectively inhibiting the growth of lithium dendrites and reducing the occurrence of side reactions at the interface layer, which has a good promoting effect on improving the interfacial stability between the gel electrolyte and the negative electrode of the lithium metal battery.

[0040] The fluorine-free ether compound in the gel electrolyte composition has good miscibility with each component in the gel electrolyte composition and good stability to the lithium metal negative electrode. As one of the components of the gel electrolyte composition, it can interact better with each component to form a more uniform and stable gel electrolyte composition solution. In addition, the presence of the fluorine-free ether compound can further reduce the decomposition and side reactions of the fluorinated carbonate solution in the lithium metal battery, which is beneficial to further improving the stability of the gel electrolyte.

[0041] Furthermore, the lithium salt in the gel electrolyte composition is fully mixed with other components in the composition, providing lithium ions in the electrolyte, and the components work together to promote electron migration during the operation of the lithium metal battery. In addition, the lithium salt can also form a negative electrode protective film on the negative electrode, thereby further improving the cycling performance of the lithium metal battery.

[0042] The gel electrolyte composition further comprises: siloxane additives and optionally film-forming additives. The siloxane additives can directionally scavenge harmful by-products generated by the violent decomposition of lithium salts and other components during the in-situ curing of the gel electrolyte composition solution, improve the stability of the system during the in-situ curing and formation of the gel electrolyte composition, and better form a uniform and stable gel electrolyte. In addition, the siloxane additives can also form a silicon-containing inorganic cathode electrolyte interface (CEI) on the positive electrode of the lithium metal battery. Under the synergistic effect of this and the organic polymer solid electrolyte interface layer (SEI) containing carbon and oxygen elements and the fluorine-containing inorganic solid electrolyte interface layer (SEI) formed on the surface of the lithium metal negative electrode by fluorinated carbonate, the stability between the gel electrolyte and the interface of the lithium metal battery can be further improved.

[0043] The crosslinking monomer and free radical initiator in the gel electrolyte composition are compatible with fluorinated ether compounds, fluorinated carbonates, and non-fluorinated ether compounds. After thorough mixing, a uniform mixed solution can be formed. The mixed solution undergoes a polymerization reaction at high temperature to form a gel electrolyte with uniform composition. The presence of the crosslinking monomer and free radical initiator can further improve the stability of the positive and negative electrode interfaces and improve the cycling performance of the lithium metal battery.

[0044] In summary, the fluorinated ether compounds, fluorinated carbonates, non-fluorinated ether compounds, siloxane additives, film-forming additives, crosslinking monomers, free radical initiators, and lithium salts in the gel electrolyte composition of the present invention have different properties. Under the synergistic effect of each component in the above gel electrolyte composition, the formed gel electrolyte not only has the advantages of being more uniform and more stable, but also can effectively improve the problems of lithium dendrites and interfacial side reactions in the lithium metal battery. The gel electrolyte composition with the above formula has a good effect on improving the cycling stability and safety of the lithium metal battery.

[0045] In a preferred embodiment, by weight percentage, the first component comprises: 1-60% of a fluoroether compound, 2-50% of a fluorinated carbonate, 1-60% of a fluorine-free ether compound; 0.01-10% of a siloxane additive, 0-10% of a film-forming additive; in the second component, the crosslinking agent monomer is 1-10% of the weight of the first component; the free radical initiator is 0.01-5% of the weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 0.5-3 mol / L. In the gel electrolyte composition, the fluoroether compound is beneficial to forming a protective film, enhancing miscibility and diluting the lithium salt, and improving the interfacial stability; the fluorinated carbonate improves the oxidation resistance and synergistically forms a SEI layer to inhibit lithium dendrites and stabilize the anode interface; the fluorine-free ether compound improves the solubility of the lithium salt, reduces side reactions, and enhances the stability; the siloxane and the film-forming additive scavenge curing by-products and improve the interfacial performance; the lithium salt promotes electron migration and forms a protective film on the anode; the crosslinking agent and the initiator ensure uniform and sufficient curing, jointly improving the battery energy density and cycle safety. The effects of each component complement each other and work together to improve the cycle stability and safety of the lithium metal battery. Controlling the contents of the components of the gel electrolyte composition within the above ranges can better exert the synergistic effects among the components, which is beneficial to further improving the electrochemical performance of the gel electrolyte and the cycle stability performance of the lithium metal battery.

[0046] Preferably, by weight percentage, the first component comprises: 20-60% of a fluoroether compound, 20-50% of a fluorinated carbonate, 10-60% of a fluorine-free ether compound; 0.01-10% of a siloxane additive, 0-10% of a film-forming additive; in the second component, the crosslinking agent monomer is 1-10% of the weight of the first component; the free radical initiator is 0.01-5% of the weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 0.5-3 mol / L. Controlling the contents of the components of the gel electrolyte composition within the above preferred ranges, the synergistic effects among the components are better, which is beneficial to better improving the electrochemical performance of the gel electrolyte and the cycle stability performance of the lithium metal battery.

[0047] More preferably, by weight percentage, the first component comprises: 20-60% of a fluoroether compound, 20-40% of a fluorinated carbonate, 15-40% of a fluorine-free ether compound; 0.01-5% of a siloxane additive, 0.01-5% of a film-forming additive; in the second component, the crosslinking agent monomer is 1-5% of the weight of the first component; the free radical initiator is 0.01-2% of the weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 0.5-3 mol / L. Controlling the contents of the components of the gel electrolyte composition within the above ranges, the comprehensive improvement effect is better, and the cycle stability performance of the lithium metal battery is better.

[0048] In a preferred embodiment, the fluorinated carbonate is a cyclic fluorinated carbonate and / or a linear fluorinated carbonate. Preferably, the fluorinated carbonate is a combination of a cyclic fluorinated carbonate and a linear fluorinated carbonate. The cyclic fluorinated carbonate or the linear fluorinated carbonate in the fluorinated carbonate can form an organic polymer SEI layer containing carbon and oxygen elements and a fluorine-containing inorganic SEI layer on the surface of the lithium metal anode to inhibit the growth of lithium dendrites and reduce the occurrence of side reactions. When the cyclic fluorinated carbonate and the linear fluorinated carbonate are used in combination, they act synergistically to improve the kinetic performance of the gel electrolyte, thereby further improving the cycle stability of the lithium metal battery. Preferably, the weight ratio of the cyclic fluorinated carbonate to the linear fluorinated carbonate is 1:(0.5 to 5), specifically, for example: 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or any weight ratio between any of the above ratios; controlling the mixing ratio of the cyclic fluorinated carbonate and the linear fluorinated carbonate within the above range is beneficial to further improving the kinetic performance in the gel electrolyte. More preferably, the weight ratio of the cyclic fluorinated carbonate to the linear fluorinated carbonate is 1:(1 to 3), specifically, for example: 1:1, 1:1.3, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3 or any weight ratio between any of the above ratios. When the weight ratio of the cyclic fluorinated carbonate to the linear fluorinated carbonate is within the above preferred range, the above effects are better, and the improvement effect on the cycle stability performance of the lithium metal battery will also be better.

[0049] In a preferred embodiment, the cyclic fluorinated carbonate is a compound having the structure shown in the following formula (I):

[0050]

[0051] In formula (I), R 3 , R 4 , R 5 and R 6 are each independently selected from H, F, an alkyl group of C 1 to C 10 , a fluoroalkyl group of C 1 to C 10 , an alkenyl group of C 2 to C 10 or a fluoroalkenyl group of C 2 to C 10 , and R 3 , R 4 , R 5 and R 6contains at least one fluorine atom. The cyclic fluorinated carbonate with the above structure has better compatibility with the lithium salt in the gel electrolyte composition, and can better form an organic polymer solid electrolyte interface layer (SEI) containing carbon and oxygen elements and a fluorine-containing inorganic solid electrolyte interface layer (SEI) on the surface of the lithium metal anode, improving the interface stability between the gel electrolyte and the anode of the lithium metal battery. Preferably, R 3 、R 4 、R 5 and R 6 are each independently selected from H, F, an alkyl group of C 1 ~C 5 or a fluoroalkyl group of C 1 ~C 5 , and at least one of R 3 、R 4 、R 5 and R 6 contains a fluorine atom; more preferably, R 3 、R 4 、R 5 and R 6 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one of R 3 、R 4 、R 5 and R 6 contains a fluorine atom. For the cyclic fluorinated carbonate structure within the preferred range, the above effects are better. Most preferably, the cyclic fluorinated carbonate has the structure shown in the following formula (A):

[0052]

[0053] and / or, the chain fluorinated carbonate has a compound with the structure shown in the following formula (Ⅱ):

[0054]

[0055] In formula (Ⅱ), R 7 and R 8 are each independently selected from H, F, an alkyl group of C 1 ~C 10 , a fluoroalkyl group of C 1 ~C 10 , an alkenyl group of C 2 ~C 10 or a fluoroalkenyl group of C 2 ~C 10 , and R 7 and R 8contains at least one fluorine atom. The chain fluorinated carbonate with the above structure has a lower viscosity and can synergistically act with the cyclic fluorinated carbonate to improve the kinetic performance of the gel electrolyte and the cycle stability of the lithium metal battery. Preferably, R 7 and R 8 are each independently selected from H, F, C 1 to C 5 alkyl or C 1 to C 5 fluoroalkyl, and at least one of R 7 and R 8 contains a fluorine atom; more preferably, R 7 and R 8 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one of R 7 and R 8 contains a fluorine atom; the chain fluorinated carbonate structure within the preferred range has better above effects. Most preferably, the chain fluorinated carbonate has the structure shown in the following formula (B):

[0056]

[0057] and / or, the fluoroether compound is a compound having the structure shown in the following formula (Ⅲ):

[0058]

[0059] In formula (Ⅲ), R 1 and R 2 are each independently selected from C 1 to C 10 alkyl, C 1 to C 10 fluoroalkyl, C 2 to C 10 alkenyl or C 2 to C 10 fluoroalkenyl, and at least one of R 1 and R 2 contains a fluorine atom; the fluoroether compound with the above structure has better solubility with the composition and can better form a dense protective film on the positive electrode, effectively improving the interfacial stability of the lithium metal battery and the transport effect of lithium ions in the gel electrolyte. Preferably, R 1 and R 2 are each independently selected from C 1 to C 5 alkyl, and the alkyl contains at least one fluorine atom; more preferably, R 1 and R 2Each independently selected from methyl, ethyl, monofluoromethyl, difluoromethyl, trifluoromethyl, 1,1,2,2 - tetrafluoroethyl, 1,1,2 - trifluoroethyl or trifluoromethyl ethyl; for the structure of the fluoroether compound within the preferred range, the above effects are better. Most preferably, the fluoroether compound has the structure shown in the following formula (C):

[0060]

[0061] And / or, the fluorine - free ether compound is a compound having the structure shown in the following formula (IV):

[0062]

[0063] In formula (IV), R 9 and R 10 Each independently selected from C 1 ~C 10 alkyl or C 2 ~C 10 alkoxyalkyl; more preferably, in formula (IV), R 9 and R 10 Each independently selected from C 1 ~C 5 alkyl. The fluorine - free ether compound having the above structure can better dissolve the lithium salt, can improve the decomposition and side reactions of the fluorocarbonate solution in the lithium metal battery, and further improve the stability of the gel electrolyte. More preferably, R 9 and R 10 Each independently selected from methyl, ethyl, propyl, isopropyl or butyl; for the structure of the fluorine - free ether compound within the preferred range, the above effects are better. Most preferably, the fluorine - free ether compound has the structure shown in the following formula (D):

[0064]

[0065] By way of example but not limitation, the lithium salt is one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium difluorophosphate; the present application does not strictly limit the type of lithium salt, and the use of the above lithium salts has a better effect on improving the electrochemical performance of the gel electrolyte and is more suitable for the gel electrolyte system of the present application. Preferably, the siloxane additive is vinyltrimethoxysilane and / or allyltrimethoxysilane; preferably, the film-forming additive is one or more of lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, methylene methanedisulfonate, 4-trifluoromethyl ethylene carbonate, 1,3,2-dioxathiolane-2,2-dioxide, ethylene sulfite, vinylene carbonate, succinic anhydride, propylene sulfite, allyl-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl, butylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-methyl, propylpiperidinium bis(trifluoromethylsulfonyl)imide, 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, fumarodinitrile, and 1,2,3-tris(2-cyanoethoxy)propane; preferably, the radical initiator is at least one of azobisisobutyronitrile, cyclohexanone peroxide, azobisisoheptonitrile, tert-butyl hydroperoxide, and dimethyl azobisisobutyrate; preferably, the crosslinking monomer is at least one of N,N-methylenebisacrylamide, methacrylamide, N-ethylacrylamide, and acrylamide with a cyclic structure. Using one or more of the above types of siloxane additives, film-forming additives, radical initiators, and crosslinking monomers as one of the components of the gel electrolyte composition has a better effect on improving the electrochemical performance of the gel electrolyte.

[0066] In a preferred embodiment, the gel electrolyte composition comprises: by weight percentage, the first component includes: 49.5% of a fluoroether compound, 10% of a cyclic fluorocarbonate, 20% of a linear fluorocarbonate, 19.5% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, by weight percentage, the first component includes: 54% of a fluoroether compound, 8% of a cyclic fluorocarbonate, 22% of a linear fluorocarbonate, 15% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, by weight percentage, the first component includes: 49.5% of a fluoroether compound, 10% of a cyclic fluorocarbonate, 20% of a linear fluorocarbonate, 19.5% of a fluorine-free ether compound; 0.5% of a siloxane additive, 0.5% of a film-forming additive; in the second component, the crosslinking monomer is 5% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L. The above solutions are exemplary. Controlling the content of each component in the gel electrolyte composition within the above proportional range is beneficial to making the gel electrolyte have better stability, thereby being beneficial to further improving the cycle stability and safety of the lithium metal battery.

[0067] According to another aspect of the present invention, there is also provided a method for injecting a liquid into the above gel electrolyte composition, which divides the gel electrolyte composition into a first solution and a second solution. Among them, the first solution includes 80-92% of the fluoroether compound, 80-90% of the fluorocarbonate, 80-90% of the fluorine-free ether compound, 100% of the siloxane additive, 0-90% of the film-forming additive, 100% of the crosslinking monomer, 100% of the radical initiator in the gel electrolyte composition; and the concentration of the lithium salt in the first solution is 0.2-3 mol / L; the second solution includes: the remaining fluoroether compound, the remaining fluorocarbonate, the remaining fluorine-free ether compound, the remaining film-forming additive, and the remaining lithium salt, and the concentration of the lithium salt in the second solution is 0.5 mol / L - 3.5 mol / L; the liquid injection method includes the following steps: injecting the first solution into the electrochemical device for the first liquid injection; subjecting the electrochemical device after the first liquid injection to in-situ curing and formation to obtain a pretreated electrochemical device; injecting the second solution into the pretreated electrochemical device and performing vacuum sealing to complete the liquid injection operation.

[0068] The liquid injection method for the gel electrolyte composition provided by the present invention performs two liquid injection operations successively. First, the gel electrolyte composition provided by the present invention is distributed in the above specific manner to obtain a first solution and a second solution. Then, the first solution is first injected into the electrochemical device. After in-situ curing and formation, the second liquid injection is carried out. After the two liquid injections are completed, it is sealed under vacuum to complete the liquid injection operation.

[0069] Among them, the first solution in the liquid injection method proposed in this application includes in the gel electrolyte composition: 80-92% of a fluoroether compound, 80-90% of a fluorinated carbonate, 80-90% of a fluorine-free ether compound, 100% of a siloxane additive, 0-90% of a film-forming additive, 100% of a crosslinking monomer, and 100% of a radical initiator; and the concentration of the lithium salt in the first solution is 0.2-3 mol / L. The above components can undergo a crosslinking polymerization reaction, and then a gel electrolyte layer is formed during the subsequent in-situ curing and formation processes. The second solution in the liquid injection method proposed in this application includes: the remaining fluoroether compound, the remaining fluorinated carbonate, the remaining fluorine-free ether compound, the remaining film-forming additive, and the remaining lithium salt, and the concentration of the lithium salt in the second solution is 0.5 mol / L - 3.5 mol / L. After the in-situ curing and formation of the first solution, each component in the first solution undergoes a polymerization reaction to form a crosslinked semi-solid gel electrolyte, and on this basis, the second solution is injected into it. The second liquid injection exists in the electrolyte region of the lithium metal in a liquid state, which plays a role in further filling the interface voids and improving the interface contact.

[0070] Specifically, the proportion of the fluoroether compound, etc. in the first solution is relatively high. Under the synergistic effect of the various compounds in the above proportions, the first solution has the characteristic of low viscosity. The gel electrolyte formed by the first solution with this characteristic has better wettability for the separator, the positive electrode plate, and the negative electrode plate in the lithium metal battery, and the formed gel electrolyte has a flatter and more stable interface, which is beneficial to reducing the internal resistance of the gel electrolyte. In addition, the presence of the siloxane additive in the first solution can absorb by-products generated by the decomposition of solvents, lithium salts, etc. during the electrolyte curing process, reducing the damage to the positive and negative electrode plates during the gel electrolyte curing and formation processes, and further improving the cycle stability and safety performance of the battery. Further, the second solution contains the remaining fluoroether compound, the remaining fluorinated carbonate, the remaining fluorine-free ether compound, the remaining film-forming additive, and the remaining lithium salt. Under the synergistic effect of the various compounds in the above proportions, it can not only ensure the oxidation resistance of the electrolyte on the positive electrode side and reduce the presence of free solvents, but also further improve the interface stability between the gel electrolyte and the lithium metal negative electrode. The presence of the film-forming additive in the second solution can further stabilize the electrolyte interface.

[0071] In the above two liquid injection operations, on the basis of the gel electrolyte formed by in-situ curing and forming of the first solution, the second solution is added. The second solution can fill the interfacial voids and improve the interfacial contact, avoiding the problem of too high local current density caused by uneven contact during the curing process. Furthermore, it is beneficial to enhance the ion transport path, reduce the polarization phenomenon, and improve the cycle stability of the lithium metal battery. At the same time, after the second solution is injected into the electrochemical device, it can also infiltrate to make up for the unreacted regions in the cross-linked network, further improving the interfacial uniformity of the electrolyte and enhancing the battery cycle performance. Controlling the content of each component in the first solution and the second solution within the above ranges is beneficial for the lithium metal battery to achieve better internal resistance and interfacial state. At the same time, it can also avoid the damage to the gel structure part caused by too much amount of the liquid electrolyte part. Moreover, controlling the concentrations of the first solution and the second solution within the above ranges during the liquid injection process can further improve the conductivity and wettability of the first solution and the second solution. The secondary liquid injection operation in the above manner is beneficial to further improve the ionic conductivity of the gel electrolyte, improve the interfacial contact, and enhance the interfacial stability of the lithium metal battery.

[0072] Preferably, the lithium salt concentration in the first solution is less than that in the second solution. Controlling the lithium salt concentration ratio in the first solution and the second solution within the above preferred ranges and controlling their relative concentrations can enable the first solution and the second solution to have good conductivity and wettability, while further avoiding the adverse effect on the interfacial stability of the gel electrolyte formed by the first solution caused by too much free solvent in the second solution, which is beneficial to further improve the interfacial uniformity of the gel electrolyte, thereby better enhancing the cycle performance of the lithium metal battery.

[0073] In a preferred embodiment, the gel electrolyte composition is divided into a first solution and a second solution. Among them, the first solution includes 85-92% of fluoroether compounds, 80-85% of fluorinated carbonates, 80-85% of fluorine-free ether compounds, 100% of siloxane additives, 0-90% of film-forming additives, 100% of cross-linking monomer, and 100% of radical initiator in the gel electrolyte composition; and the lithium salt concentration in the first solution is 0.2-3 mol / L; the second solution includes the remaining fluoroether compounds, the remaining fluorinated carbonates, the remaining fluorine-free ether compounds, the remaining film-forming additives, and the remaining lithium salt, and the lithium salt concentration in the second solution is 0.5 mol / L-3.5 mol / L.

[0074] After a large number of experiments, the inventor creatively found that increasing the proportion of the fluoroether compound in the first solution and correspondingly decreasing the proportion of the fluorinated carbonate or the fluorine-free ether compound in the first solution can result in better liquid injection effect. This may be because the first solution under the above proportion conditions has better wettability for the separator, the positive electrode sheet and the negative electrode sheet in the lithium metal battery. The gel electrolyte formed after curing can further improve the interface contact, form a stable interface, reduce the internal resistance of the lithium metal battery, and thus is beneficial to further improving the cycle performance of the lithium metal battery.

[0075] In a preferred embodiment, the steps of in-situ curing and formation include: after the electrochemical device after the first liquid injection is left standing, it is charged at a constant current to 50-70% of the full charge state, and then the in-situ curing and formation can be completed. Due to the high reaction activity and low density of the lithium metal negative electrode, large volume expansion will occur during high-temperature and high-rate charge and discharge, resulting in the repeated generation and rupture of the SEI at the negative electrode interface and the formation of lithium dendrites, threatening the safety performance of the battery. In the above in-situ curing and formation operation, the curing of the gel electrolyte and the formation of the battery are carried out simultaneously, which is beneficial to improving the flatness and uniformity of the in-situ curing and forming a more stable and uniform lithium metal deposition.

[0076] Preferably, the standing time is 12-24 h; preferably, the constant current charging is carried out under the conditions of pressure P and temperature T, where 0.4 MPa ≤ P ≤ 1.2 MPa and 50 ≤ T ≤ 80 °C. When controlling the in-situ curing and formation operation, controlling the pressure during the constant current charging within the above range can further improve the wettability of the gel electrolyte and reduce its internal resistance, and can also effectively shorten the contact distance between the gel electrolyte and the positive and negative electrodes, forming a more uniform interface contact. In addition, when controlling the in-situ curing and formation operation, controlling the pressure during the constant current charging within the above range can further avoid the volume expansion of lithium metal during the formation process caused by too low pressure, which affects the safety performance of the battery; and the damage of the battery structure caused by too high pressure, making it difficult to form a uniform electrolyte interface. Further, controlling the temperature during the constant current charging within the above range can further improve the curing effect of the gel electrolyte, which is beneficial to the full curing of the electrolyte and the formation of a more stable interface. At the same time, it is also beneficial to avoid the decomposition of substances easily caused by too high temperature, so as to further prevent problems such as battery capacity attenuation caused by the generation of corrosive by-products and a large amount of gas. Preferably, the rate of the constant current charging is 0.04C-0.2C. During the above in-situ curing and formation process, lithium metal is deposited on the negative electrode. Controlling the rate of the constant current charging within the above range can further improve the lithium dendrite phenomenon, is beneficial to the formation of a uniform lithium metal deposition layer, further improve the interface stability of the gel electrolyte, and also can achieve the purpose of increasing the battery capacity.

[0077] According to the fourth aspect of the present invention, a lithium metal battery is further provided. The raw material of the electrolyte of the lithium metal battery is the above gel electrolyte composition; or, the electrolyte of the lithium metal battery is formed by the liquid injection method of the above gel electrolyte composition.

[0078] The following further describes the present application in detail with specific examples, and these examples should not be construed as limiting the scope claimed by the present application.

[0079] It should be further noted here that in the examples and comparative examples described in the present application, the fluoroether compound used has the structure shown in formula (C); the cyclic fluorinated carbonate has the structure shown in formula (A); the linear fluorinated carbonate has the structure shown in formula (B); the fluorine-free ether compound has the structure shown in formula (D); the lithium salt has the structure shown in formula (E); the siloxane additive is: vinyltrimethoxysilane; the film-forming additive is LiNO 3 ; the crosslinking monomer is N,N-methylenebisacrylamide; the radical initiator is azobisisobutyronitrile. The specific structures are as follows:

[0080]

[0081] Example 1

[0082] (I) Solution preparation

[0083] The gel electrolyte composition includes: fluoroether compound, cyclic fluorinated carbonate, linear fluorinated carbonate, fluorine-free ether compound, siloxane additive, and film-forming additive as the first component. Among them, by weight percentage, the cyclic fluorinated carbonate accounts for 10%, the linear fluorinated carbonate accounts for 20%, the fluorinated carbonate accounts for 49.5%, the fluorine-free ether compound accounts for 19.5%, the siloxane additive accounts for 0.5%, and the film-forming additive accounts for 0.5%; the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L.

[0084] The gel electrolyte composition of the above components is used as Gel Electrolyte Composition 1 and is divided into a first solution and a second solution. Among them, the first solution and the second solution are divided by using the first liquid injection method. Specifically:

[0085] The first solution includes 88% of the fluoroether compound, 80% of the cyclic fluorinated carbonate, 80% of the linear fluorinated carbonate, 85% of the fluorine-free ether compound, 100% of the siloxane additive, 100% of the crosslinking monomer, and 100% of the radical initiator in the gel electrolyte composition; and the concentration of the lithium salt in the first solution is 1.3 mol / L.

[0086] The second solution includes: the balance of fluoroether compound, the balance of cyclic fluorocarbonate, the balance of linear fluorocarbonate, the balance of fluorine-free ether compound, the balance of film-forming additive, and the balance of lithium salt; the concentration of the lithium salt in the second solution is 2 mol / L.

[0087] (II) Preparation of lithium metal battery

[0088] Preparation of the positive electrode sheet: The positive electrode active material single crystal lithium nickel cobalt manganate (LiNi 0.88 Co 0.07 Mn 0.05 O 2 ), a conductive agent (Super P conductive carbon), and a binder (polyvinylidene fluoride) are mixed according to a weight ratio of approximately 97.9:1.1:1, NMP (N-methylpyrrolidone) is added, and the mixture is stirred in a vacuum mixer until the system is homogeneous to obtain a positive electrode slurry with a solid content of 73%; the positive electrode slurry is uniformly coated on a positive electrode current collector aluminum foil (aluminum foil thickness is 15 μm) with a thickness of 56 μm, dried, cold-pressed, cut, and then dried under vacuum conditions at 90 °C for about 6 h to obtain the positive electrode sheet.

[0089] Preparation of the negative electrode sheet: By means of physical roll pressing, metallic lithium is compounded onto a negative electrode current collector copper foil with a thickness of 8 μm. By adjusting the pressure of the roller, the copper current collector is coated with lithium on one side, and the thickness of the lithium layer is controlled to be 50 μm. After cutting and slitting, the negative electrode sheet is obtained and stored in a dry argon atmosphere glove box for standby.

[0090] Lithium metal separator: Polyethylene (PE) with a thickness of 25 μm is used as the separator.

[0091] Liquid injection in batches:

[0092] The obtained positive electrode sheet, lithium metal separator, and negative electrode sheet are stacked in sequence. After welding the tabs, they are placed in an outer packaging aluminum-plastic film, and the top side is sealed to obtain an electrochemical device for liquid injection;

[0093] The first solution is injected into the electrochemical device for the first liquid injection;

[0094] The electrochemical device after the first liquid injection is subjected to in-situ curing and formation to obtain a pretreated electrochemical device; among them, the following in-situ curing and formation method is used for the in-situ curing and formation operation, and this in-situ curing and formation method is named in-situ curing and formation method one. Specifically, the specific operation of the in-situ curing and formation method one includes: after the electrochemical device after the first liquid injection is left standing for 12 h, it is charged at a constant current to 50% of the full charge state under the conditions of pressure P and temperature T, and the in-situ curing and formation can be completed; among them, P is 1 MPa, T is 70 °C, and the constant current charging rate is 0.1C;

[0095] Inject the second solution into the pre-treated electrochemical device, seal it under vacuum to complete the liquid injection operation; the obtained electrochemical device can be aged and capacitanced to obtain a lithium metal battery.

[0096] It should be particularly noted here that in the process of preparing the lithium metal battery in the examples and comparative examples of this application, the differences from Example 1 are reflected in the gel electrolyte composition, liquid injection method, in-situ curing, and forming method. In order to more clearly compare their effects, the differences in the lithium metal battery preparation process from Example 1 are listed in Table 4. Among them, the specific compositions of each component in Gel Electrolyte Composition 1, Gel Electrolyte Composition 2, Gel Electrolyte Composition 3, Gel Electrolyte Composition 4, Gel Electrolyte Composition 5, Gel Electrolyte Composition 6, Gel Electrolyte Composition 7, Gel Electrolyte Composition 8, Gel Electrolyte Composition 9, Gel Electrolyte Composition 10, Gel Electrolyte Composition 11, Gel Electrolyte Composition 12, and Gel Electrolyte Composition 13 in Table 4 are shown in Table 1; the liquid injection methods 1, 2, and 3 in Table 4 are shown in Table 2; the specific operation methods of in-situ curing, forming method 1, forming method 2, and forming method 3 in Table 4 are shown in Table 3.

[0097] Table 1

[0098]

[0099]

[0100] Regarding the description of the data in Table 1: Taking Gel Electrolyte Composition 1 in Table 1 as an example, the fluoroether compound, cyclic fluorinated carbonate, linear fluorinated carbonate, fluorine-free ether compound, siloxane additive, and film-forming additive are used as the first component. Among them, by weight percentage, in the first component, the cyclic fluorinated carbonate accounts for 10%, the linear fluorinated carbonate accounts for 20%, the fluorinated carbonate accounts for 49.5%, the fluorine-free ether compound accounts for 19.5%, the siloxane additive accounts for 0.5%, and the film-forming additive accounts for 0.5%; in the second component, the crosslinking monomer is 3% of the weight of the first component; the radical initiator is 2% of the weight of the crosslinking monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L.

[0101] Table 2

[0102]

[0103]

[0104] Regarding the data description in Table 2, taking one example of the liquid injection method in Table 2: The first solution includes 88% of fluoroether compounds, 80% of cyclic fluorocarbonates, 80% of linear fluorocarbonates, 85% of fluorine-free ether compounds, 100% of silicone additives, 100% of crosslinking monomer, and 100% of radical initiator in the gel electrolyte composition; and the concentration of lithium salt in the first solution is 1.3 mol / L.

[0105] The second solution includes: the balance of fluoroether compounds, the balance of cyclic fluorocarbonates, the balance of linear fluorocarbonates, the balance of fluorine-free ether compounds, the balance of film-forming additives, and the balance of lithium salt; the concentration of lithium salt in the second solution is 2 mol / L.

[0106] Table 3

[0107]

[0108] Table 4

[0109]

[0110]

[0111] The lithium metal batteries prepared in the above examples and comparative examples were respectively tested for their cycling performance at room temperature (25 °C) and high temperature (45 °C), and the results are shown in Table 5. Among them, the test method is as follows.

[0112] Test method for cycling performance at room temperature (25 °C): Place the lithium metal battery in an incubator at 25 °C and let it stand for 30 minutes to reach a constant temperature. Charge the lithium metal battery at a constant current and constant voltage of 0.2C, with a cut-off voltage of 4.3V and a cut-off current of 0.04C, and then discharge it at a constant current of 1C until the voltage reaches 3V. This is one charge-discharge cycle. Taking the capacity of the first discharge as 100%, repeat the charge-discharge cycle until the discharge capacity decays to 80%, then stop the test and record the number of cycles. This parameter can be used as an index to evaluate the cycling stability of the lithium metal battery.

[0113] Test method for cycling performance at high temperature (45 °C): Place the lithium metal battery in an incubator at 45 °C and let it stand for 30 minutes to reach a constant temperature. Charge the lithium metal battery at a constant current and constant voltage of 0.2C, with a cut-off voltage of 4.3V and a cut-off current of 0.04C, and then discharge it at a constant current of 1C until the voltage reaches 3V. This is one charge-discharge cycle. Taking the capacity of the first discharge as 100%, repeat the charge-discharge cycle until the discharge capacity decays to 80%, then stop the test and record the number of cycles. This parameter can be used as an index to evaluate the cycling stability of the lithium metal battery at a higher temperature, and can also reflect the safety performance of the lithium metal battery.

[0114] Table 5

[0115]

[0116]

[0117] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0118] The lithium metal batteries prepared in the examples and comparative examples were cycled at 25 °C and 45 °C until the discharge capacity decayed to 80%, and the number of cycles was tested. Among them, Examples 1 to 12 are lithium metal batteries prepared by using the gel electrolyte composition provided in the present application and using the liquid injection method, curing method, and forming method provided in the present application. As can be seen from the results in Table 5, the cycle stabilities of the corresponding lithium metal batteries are all within a good range. In particular, in Examples 1 to 8 and Examples 11 to 12, the proportions of the various components in the gel electrolyte composition, as well as the liquid injection method, curing method, and forming method, are all within the preferred range, and the cycle stability and safety of the lithium metal batteries prepared in the corresponding examples are better. Example 13 uses the gel electrolyte composition provided in the present application. Although the liquid injection method in the present application is not used, the effect is acceptable.

[0119] On the contrary, in Comparative Examples 1 to 3, although the liquid injection method, curing method, and forming method are the same as those in Examples 1 to 10, since the components of the gel electrolyte composition are not within the technical solutions provided in the present application, the cycle stability and safety of the lithium metal batteries are quite different from those in Examples 1 to 10. In Comparative Example 4, the gel electrolyte composition, liquid injection method, curing method, and forming method are not within the scope provided in the present application, and the cycle stability and safety of the corresponding lithium metal batteries are far from the technical effects that can be obtained by the technical solutions provided in the present application.

[0120] In summary, using the gel electrolyte composition provided in the present application has a good effect on improving the cycle stability and safety of lithium metal batteries. It can be seen that, under the synergistic effect of the various components in the gel electrolyte composition formula provided in the present application, the formed gel electrolyte not only has the advantages of uniformity and stability, but also can effectively improve the problems of lithium dendrites and interfacial side reactions in lithium metal batteries. In addition, by combining the gel electrolyte composition provided in the present application with the liquid injection method, curing method, and forming method provided in the present application, the cycle stability and safety of the prepared lithium metal batteries can be further effectively improved.

[0121] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A gel electrolyte composition, characterized in that: The gel electrolyte composition comprises a first component, a second component and a lithium salt; wherein, The first component includes a fluorinated ether compound, a fluorinated carbonate, a fluorine-free ether compound, a siloxane additive, and optionally a film-forming additive; The second component includes a crosslinker monomer and a free radical initiator.

2. The gel electrolyte composition according to claim 1, characterized in that In terms of weight percentage, the first component includes: 1 to 60% of the fluorinated ether compound, 2 to 50% of the fluorinated carbonate, 1 to 60% of the fluorine-free ether compound; 0.01 to 10% of the siloxane additive, and 0 to 10% of the film-forming additive; In the second component, the crosslinking agent monomer is 1 to 10% by weight of the first component; the free radical initiator is 0.01 to 5% by weight of the crosslinking agent monomer; In the gel electrolyte composition, the concentration of the lithium salt is 0.5 to 3 mol / L; Preferably, the first component comprises, by weight percentage: 20-60% of the fluoroether compound, 20-40% of the fluorocarbonate, 15-40% of the fluorine-free ether compound; 0.01-5% of the siloxane additive, and 0.01-5% of the film-forming additive; In the second component, the crosslinking agent monomer is 1 to 5% by weight of the first component; the free radical initiator is 0.01 to 2% by weight of the crosslinking agent monomer; In the gel electrolyte composition, the concentration of the lithium salt is 0.5 to 3 mol / L.

3. The gel electrolyte composition according to claim 1 or 2, characterized in that: The fluorinated carbonate is a cyclic fluorinated carbonate and / or a chain fluorinated carbonate; Preferably, the fluorocarbonate is a compound of the cyclic fluorocarbonate and the chain fluorocarbonate; Preferably, the weight ratio of the cyclic fluorocarbonate to the chain fluorocarbonate is 1:(0.5-5); more preferably, the weight ratio of the cyclic fluorocarbonate to the chain fluorocarbonate is 1:(1-3).

4. The gel electrolyte composition according to claim 3, characterized in that: The cyclic fluorinated carbonate has a compound having a structure shown in the following formula (I): In the formula (I), R3, R4, R5 and R6 are each independently selected from H, F, Cl~C 10 Alkyl, C1~C 10 Fluorinated alkyl, C2~C 10 Alkenyl or C2~C 10 fluoroalkenyl, and at least one fluorine atom is contained in R3, R4, R5 and R6; preferably, R3, R4, R5 and R6 are each independently selected from H, F, C1-C5 alkyl or C1-C5 fluoroalkyl, and at least one fluorine atom is contained in R3, R4, R5 and R6; more preferably, R3, R4, R5 and R6 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one fluorine atom is contained in R3, R4, R5 and R6; most preferably, the cyclic fluorinated carbonate has a structure shown in the following formula (A): And / or, the chain fluorinated carbonate has a compound having a structure shown in the following formula (II): In the formula (II), R7 and R8 are each independently selected from H, F, Cl~C 10 Alkyl, C1~C 10 Fluorinated alkyl, C2~C 10 Alkenyl or C2~C 10 fluoroalkenyl, and at least one fluorine atom is contained in R7 and R8; preferably, R7 and R8 are each independently selected from H, F, C1-C5 alkyl or C1-C5 fluoroalkyl, and at least one fluorine atom is contained in R7 and R8; more preferably, R7 and R8 are each independently selected from H, F, methyl, ethyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one fluorine atom is contained in R7 and R8; most preferably, the chain fluorinated carbonate has a structure shown in the following formula (B): And / or, the fluoroether compound is a compound having a structure represented by the following formula (III): In the formula (III), R1 and R2 are each independently selected from C1 to C 10 Alkyl, C1~C 10 Fluorinated alkyl, C2~C 10 Alkenyl or C2~C 10 fluoroalkenyl, and at least one fluorine atom is contained in R1 and R2; preferably, R1 and R2 are each independently selected from C1 to C5 alkyl, and at least one fluorine atom is contained in the alkyl; more preferably, R1 and R2 are each independently selected from methyl, ethyl, monofluoromethyl, difluoromethyl, trifluoromethyl, 1,1,2,2-tetrafluoroethyl, 1,1,2-trifluoroethyl or trifluoromethylethyl; most preferably, the fluoroether compound has a structure shown in the following formula (C): And / or, the fluorine-free ether compound is a compound having a structure shown in the following formula (IV): In the formula (IV), R9 and R 10 Each independently selected from C1 to C 10 Alkyl or C2~C 10 More preferably, in the formula (IV), the R9 and the R 10 are independently selected from C1 to C5 alkyl groups; more preferably, the R9 and R 10 Each is independently selected from methyl, ethyl, propyl, isopropyl or butyl; most preferably, the fluorine-free ether compound has a structure as shown in the following formula (D):

5. The gel electrolyte composition according to any one of claims 1 to 4, characterized in that The lithium salt is one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium trifluoromethylsulfonate and lithium difluorophosphate; Preferably, the siloxane additive is vinyltrimethoxysilane and / or acryltrimethoxysilane; Preferably, the film-forming additive is at least one of lithium dioxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, methylene disulfonate, 4-trifluoromethylethylene carbonate, 1,3,2-dioxazolidinone-2,2-dioxide, ethylene sulfite, vinyl carbonate, succinic anhydride, propylene sulfite, propylene-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl, butylpyrrolidine bis(trifluoromethanesulfonyl imide), N-methyl, propylpiperidinium bis(trifluoromethanesulfonyl imide), 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, trans-butylene dinitrile and 1,2,3-tris(2-cyanoethoxy)propane; Preferably, the free radical initiator is at least one of azobisisobutyronitrile, cyclohexanone peroxide, azobisisoheptanenitrile, tert-butyl hydroperoxide and dimethyl azobisisobutyrate; Preferably, the cross-linking agent monomer is at least one of N,N-methylenebisacrylamide, methacrylamide, N-ethylacrylamide and cyclic structure acrylamide.

6. The gel electrolyte composition according to any one of claims 3 to 5, characterized in that The gel electrolyte composition comprises: By weight percentage, the first component includes: 49.5% of the fluorinated ether compound, 10% of the cyclic fluorinated carbonate, 20% of the chain fluorinated carbonate, 19.5% of the fluorine-free ether compound; 0.5% of the siloxane additive, 0.5% of the film-forming additive; in the second component, the crosslinking agent monomer is 3% by weight of the first component; the free radical initiator is 2% by weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, By weight percentage, the first component includes: 54% of the fluorinated ether compound, 8% of the cyclic fluorinated carbonate, 22% of the chain fluorinated carbonate, 15% of the fluorine-free ether compound; 0.5% of the siloxane additive, 0.5% of the film-forming additive; in the second component, the crosslinking agent monomer is 3% of the weight of the first component; the free radical initiator is 2% of the weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L; or, In terms of weight percentage, the first component includes: 49.5% of the fluoroether compound, 10% of the cyclic fluorocarbonate, 20% of the chain fluorocarbonate, and 19.5% of the fluorine-free ether compound; 0.5% of the siloxane additive, and 0.5% of the film-forming additive; in the second component, the crosslinking agent monomer is 5% of the weight of the first component; the free radical initiator is 2% of the weight of the crosslinking agent monomer; in the gel electrolyte composition, the concentration of the lithium salt is 1.5 mol / L.

7. The method for injecting a gel electrolyte composition according to any one of claims 1 to 6, characterized in that: The gel electrolyte composition is divided into a first solution and a second solution, wherein The first solution includes 80-92% of the fluoroether compound, 80-90% of the fluorocarbonate, 80-90% of the fluorine-free ether compound, 100% of the siloxane additive, 0-90% of the film-forming additive, 100% of the crosslinking agent monomer, and 100% of the free radical initiator; and the concentration of the lithium salt in the first solution is 0.2-3 mol / L; The second solution comprises: the balance of the fluorinated ether compound, the balance of the fluorinated carbonate, the balance of the fluorine-free ether compound, the balance of the film-forming additive and the balance of the lithium salt, and the concentration of the lithium salt in the second solution is 0.5 mol / L to 3.5 mol / L; The liquid injection method comprises the following steps: injecting the first solution into an electrochemical device for a first injection; In-situ solidification and chemical formation of the electrochemical device after the first injection to obtain a pretreated electrochemical device; The second solution is injected into the pretreatment electrochemical device and sealed by vacuum to complete the injection operation.

8. The method for injecting a gel electrolyte composition according to claim 7, characterized in that: The gel electrolyte composition is divided into a first solution and a second solution, wherein The first solution includes 85-92% of the fluorinated ether compound, 80-85% of the fluorinated carbonate, 80-85% of the fluorine-free ether compound, 100% of the siloxane additive, 0-90% of the film-forming additive, 100% of the crosslinking agent monomer, and 100% of the free radical initiator in the gel electrolyte composition; and the concentration of the lithium salt in the first solution is 0.2-3 mol / L; The second solution includes: the remainder of the fluoroether compound, the remainder of the fluorocarbonate, the remainder of the fluorine-free ether compound, the remainder of the film-forming additive and the remainder of the lithium salt, and the concentration of the lithium salt in the second solution is 0.5 mol / L to 3.5 mol / L.

9. The liquid injection method according to claim 7 or 8, characterized in that: The in-situ solidification and formation step comprises: after the electrochemical device is left to stand after the first injection, charging it with a constant current to 50-70% of the full charge state, thereby completing the in-situ solidification and formation; Preferably, the standing time is 12 to 24 hours; Preferably, the constant current charging is carried out under the conditions of pressure P and temperature T, wherein 0.4MPa≤P≤1.2MPa, 50≤T≤80°C; Preferably, the constant current charging rate is 0.04C to 0.2C.

10. A lithium metal battery, characterized in that: The raw material of the electrolyte of the lithium metal battery is the gel electrolyte composition according to any one of claims 1 to 6; or, the electrolyte of the lithium metal battery is formed by the injection method of the gel electrolyte composition according to any one of claims 7 to 9.

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