Gel with three-dimensional network structure, preparation method of gel and lithium battery

Abstract

The invention provides gel with a three-dimensional network structure, a preparation method of the gel and a lithium battery, and belongs to the technical field of lithium batteries. The gel provided by the invention comprises the following raw materials: polyethylene glycol dimethacrylate (PEGDMA) and / or a derivative thereof, a fluorine-containing carbonate compound, a cross-linking agent, a lithium salt, a flame retardant and an organic solvent. The PEGDMA and / or the derivative thereof and the fluorine-containing carbonic ester compound generate a three-dimensional network structure under the action of the cross-linking agent, the fluorine-containing carbonic ester compound can improve the interface stability between the gel and the electrode material, reduce the interface side reaction and improve the thermal stability of the gel, and the performance of the electrode material is improved. Meanwhile, the three-dimensional network structure has relatively high porosity and liquid absorption capacity, so that an ion transmission channel is improved, and the ionic conductivity of the gel is further improved. The room-temperature ionic conductivity of the gel with the three-dimensional network structure is larger than or equal to 3 mS / cm, and the thermal decomposition initial temperature is larger than or equal to 250 DEG C.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a gel with a three-dimensional network structure, a preparation method thereof, and a lithium battery. Background Art

[0002] In recent years, lithium batteries have made remarkable progress in terms of energy density and power density. According to the morphology of the electrolyte, lithium batteries mainly include liquid batteries, solid-state batteries, and gel-state batteries. Among them, liquid electrolytes have high ionic conductivity, but they are flammable and prone to leakage, with poor safety; although solid-state electrolytes have good safety, their ionic conductivity is low; gel-state electrolytes are a new type of electrolyte between liquid and solid states, with good safety. In the prior art, PEGDMA and / or its derivatives are usually used for cross-linking to obtain gel electrolytes, but their thermal stability and ionic conductivity still need to be further improved (the room-temperature ionic conductivity of existing PEGDMA-based gels is usually lower than 2 mS / cm, and the initial temperature of thermal decomposition is lower than 200 °C). At the same time, their flame retardancy is also low. Summary of the Invention

[0003] The purpose of the present invention is to provide a gel with a three-dimensional network structure, a preparation method thereof, and a lithium battery. The gel with a three-dimensional network structure provided by the present invention has excellent thermal stability, room-temperature ionic conductivity, and flame retardancy, with a room-temperature ionic conductivity ≥ 3 mS / cm, an initial temperature of thermal decomposition ≥ 250 °C, and a flame retardancy rating of UL-94 V-2 to V-0.

[0004] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a gel with a three-dimensional network structure, comprising the following raw materials: PEGDMA and / or its derivatives, fluorinated carbonate compounds, cross-linking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents.

[0006] Preferably, the fluorinated carbonate compounds include one or more of vinylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate.

[0007] Preferably, the mass ratio of the fluorinated carbonate compounds to PEGDMA and / or its derivatives is (1-10):(1-5).

[0008] Preferably, the lithium salts include one or more of LiPF6, LiClO4, LiBF4, and LiTFSi.

[0009] Preferably, the molar ratio of the lithium salt to the total volume of PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agent, and organic solvent is (0.5 - 1) mol: 1 L.

[0010] Preferably, the crosslinking agent includes one or more of a mixture of sodium bisulfite and an oxidizing agent, azobisisobutyronitrile, ammonium persulfate, and benzoyl peroxide.

[0011] Preferably, the phosphorus-containing flame retardant includes one or more of dimethyl methylphosphonate, diethyl ethylphosphonate, triphenyl phosphate, resorcinol bis(diphenyl phosphate), and bisphenol S bis(diphenyl phosphate).

[0012] Preferably, the organic solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile.

[0013] The present invention also provides a method for preparing the gel with a three-dimensional network structure described in the above technical solution, including:

[0014] Mix PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agent, lithium salt, phosphorus-containing flame retardant, and organic solvent, and successively carry out a polymerization reaction and curing to obtain a gel with a three-dimensional network structure.

[0015] The present invention also provides a lithium battery, and the electrolyte of the lithium battery is the gel with a three-dimensional network structure described in the above technical solution or the gel with a three-dimensional network structure prepared by the preparation method described in the above technical solution.

[0016] The present invention provides a gel with a three-dimensional network structure, comprising the following raw materials: PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents. In the present invention, PEGDMA and / or its derivatives and fluorinated carbonate compounds generate a three-dimensional network structure under the action of a crosslinking agent. The fluorinated carbonate compounds can improve the interfacial stability between the gel and the electrode material, reduce interfacial side reactions, improve the thermal stability and ionic conductivity of the gel. At the same time, the three-dimensional network structure has a high porosity and liquid absorption capacity, improving the ion transport channels, and thus improving the ionic conductivity of the gel. As a result, the lithium battery assembled with the gel of the three-dimensional network structure of the present invention has excellent cycling performance. Adding a phosphorus-containing flame retardant and a fluorinated carbonate compound forms a 'fluorine-phosphorus synergistic effect'. The fluorine element captures combustion free radicals (-F + H· → HF) to inhibit gas-phase combustion, and the phosphorus element promotes the formation of a dense carbon layer on the gel surface to block the transfer of oxygen and heat, achieving efficient flame retardancy and improving the flame retardant performance of the gel with a three-dimensional network structure. The results of the examples show that the room-temperature ionic conductivity of the gel with a three-dimensional network structure provided by the present invention is ≥3 mS / cm, the initial thermal decomposition temperature is ≥250 °C, the flame retardant rating is UL-94 V-2 to V-0, and the lithium battery assembled can be stably cycled more than 5000 times at 5C / 5C. Description of the Drawings

[0017] Figure 1 It is a macroscopic view of the mixed solution obtained in step (1) of Example 1;

[0018] Figure 2 It is a macroscopic view of the gel with a three-dimensional network structure obtained in step (2) of Example 1;

[0019] Figure 3 It is a cycling performance diagram of a lithium battery assembled with the mixed solution obtained in step (1) of Example 1 as the liquid electrolyte and the gel with a three-dimensional network structure obtained in step (2) of Example 1 as the gel electrolyte. Detailed Description of the Invention

[0020] The present invention provides a gel with a three-dimensional network structure, comprising the following raw materials: PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents.

[0021] The raw materials for preparing the gel with a three-dimensional network structure of the present invention include PEGDMA (polyethylene glycol dimethacrylate) and / or its derivatives.

[0022] In the present invention, the derivatives of PEGDMA preferably include amino-polyethylene glycol dimethacrylate, sulfonic acid-polyethylene glycol dimethacrylate, fluorinated polyethylene glycol dimethacrylate, or phosphoric acid ester-polyethylene glycol dimethacrylate.

[0023] In the present invention, the molecular weight of the PEGDMA or its derivative is preferably 1,000 to 3,000, more preferably 2,000; the amino substitution degree of the amino-functionalized polyethylene glycol dimethacrylate is preferably 20 to 30 mol%; the sulfonic acid group substitution degree of the sulfonated polyethylene glycol dimethacrylate is preferably 20 to 30 mol%; the fluorine substitution degree of the fluorinated polyethylene glycol dimethacrylate is preferably 20 to 30 mol%; the phosphate group substitution degree of the phosphorylated polyethylene glycol dimethacrylate is preferably 20 to 30 mol%. In the present invention, the PEGDMA and / or its derivative is a gel matrix.

[0024] The raw materials for preparing the gel with the three-dimensional network structure of the present invention further include fluorinated carbonate compounds.

[0025] In the present invention, the fluorinated carbonate compounds preferably include one or more of vinyl fluoride carbonate (FEC), methyl (2,2,2-trifluoroethyl) carbonate (FEMC), bis(2,2,2-trifluoroethyl) carbonate (FDEC), and difluorodimethyl carbonate (FDMC). As an embodiment, the fluorinated carbonate compounds may specifically be vinyl fluoride carbonate, methyl (2,2,2-trifluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate with a mass ratio of 3:2:2:2, vinyl fluoride carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate with a mass ratio of 4:3:3, vinyl fluoride carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and bis(2,2,2-trifluoroethyl) carbonate with a mass ratio of 2:4:4, vinyl fluoride carbonate, bis(2,2,2-trifluoroethyl) carbonate, difluorodimethyl carbonate, and methyl (2,2,2-trifluoroethyl) carbonate with a mass ratio of 3.5:2.5:2:2, or vinyl fluoride carbonate, bis(2,2,2-trifluoroethyl) carbonate, and methyl (2,2,2-trifluoroethyl) carbonate with a mass ratio of 3.5:4:2.5.

[0026] In the present invention, the fluorinated carbonate compounds are added to crosslink with the PEGDMA and / or its derivative to form a three-dimensional network structure, and the fluorinated carbonate compounds can improve the interfacial stability between the gel and the electrode material, reduce interfacial side reactions, and improve the thermal stability and ionic conductivity of the gel. By controlling the types of the fluorinated carbonate compounds within the above range, the present invention can adjust the three-dimensional network structure of the gel, further improve the thermal stability, ionic conductivity of the gel, and the cycling performance of the assembled lithium battery.

[0027] In the present invention, the mass ratio of the fluorinated carbonate compound to PEGDMA and / or its derivative is preferably (1 to 10):(1 to 5). As an embodiment, the mass ratio of the fluorinated carbonate compound to PEGDMA and / or its derivative can be (2 to 8):(1 to 5), can also be (3 to 7):(1 to 5), and can also be (4 to 6):(1 to 5). By controlling the mass ratio of the fluorinated carbonate compound to PEGDMA and / or its derivative within the above range, the present invention can further improve the thermal stability of the gel, the ionic conductivity, and the cycling performance of the assembled lithium battery.

[0028] The raw materials for preparing the gel with a three-dimensional network structure of the present invention further include a crosslinking agent.

[0029] In the present invention, the crosslinking agent preferably includes one or more of a mixture of sodium bisulfite and an oxidizing agent, azobisisobutyronitrile (AIBN), ammonium persulfate (APS), and benzoyl peroxide (BPO).

[0030] The present invention has no special limitation on the oxidizing agent in the mixture of sodium bisulfite and the oxidizing agent, and any oxidizing agent well-known to those skilled in the art that can form a redox initiation system with sodium bisulfite can be used.

[0031] In the present invention, the mass ratio of the crosslinking agent to PEGDMA and / or its derivative is preferably (0.5 to 5):100. As an embodiment, the mass ratio of the crosslinking agent to PEGDMA and / or its derivative can specifically be 0.5:100, 1:100, 2:100, 3:100, 4:100, or 5:100. By controlling the mass ratio of the crosslinking agent to PEGDMA and / or its derivative within the above range, the present invention can enable the fluorinated carbonate compound to be fully crosslinked with PEGDMA and / or its derivative to form a three-dimensional network structure.

[0032] The raw materials for preparing the gel with a three-dimensional network structure of the present invention further include a lithium salt.

[0033] In the present invention, the lithium salt preferably includes one or more of LiPF6, LiClO4, LiBF4, and LiTFSi.

[0034] In the present invention, the molar ratio of the lithium salt to the total volume of PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents and organic solvents is preferably (0.5 - 1) mol : 1 L. As an embodiment, the molar ratio of the lithium salt to the total volume of PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents and organic solvents can specifically be 0.5 mol : 1 L, 0.6 mol : 1 L, 0.7 mol : 1 L, 0.8 mol : 1 L, 0.9 mol : 1 L or 1 mol : 1 L. By controlling the dosage of the lithium salt within the above range in the present invention, the ionic conductivity of the gel and the cycling performance of the assembled lithium battery can be further improved.

[0035] The raw materials for preparing the gel with a three-dimensional network structure of the present invention further include a phosphorus-containing flame retardant.

[0036] In the present invention, the phosphorus-containing flame retardant preferably includes one or more of dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP), triphenyl phosphate (TPP), resorcinol bisphosphate and bisphenol S bisphosphate.

[0037] In the present invention, the mass ratio of the phosphorus-containing flame retardant to PEGDMA and / or its derivatives is preferably (0.01 - 0.5) : 1. As an embodiment, the mass ratio of the phosphorus-containing flame retardant to PEGDMA and / or its derivatives can specifically be 0.01 : 1, 0.05 : 1, 0.1 : 1, 0.2 : 1, 0.3 : 1, 0.4 : 1 or 0.5 : 1. In the present invention, a phosphorus-containing flame retardant is compounded with a fluorinated carbonate compound. The fluorine group inhibits the generation of free radicals, and the phosphorus group forms a phosphoric acid ester carbon layer at high temperature, improving the flame retardancy level (such as UL-94 V-0 level) through the dual mechanisms of gas-phase dilution and condensed-phase isolation, thereby improving the safety of the lithium battery assembled with the gel.

[0038] The raw materials for preparing the gel with a three-dimensional network structure of the present invention further include an organic solvent.

[0039] In the present invention, the organic solvent preferably includes one or more of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and acetonitrile.

[0040] In the present invention, the mass ratio of PEGDMA and / or its derivatives to the organic solvent is preferably 3 : (2 - 7). As an embodiment, the mass ratio of PEGDMA and / or its derivatives to the organic solvent can specifically be 3 : 2, 3 : 3, 3 : 4, 3 : 5, 3 : 6 or 3 : 7. By controlling the dosage of the organic solvent within the above range in the present invention, the raw materials can be fully dissolved.

[0041] Adding fluorinated carbonate compounds in the present invention can improve the thermal stability, chemical stability, and interfacial stability between the gel and electrode materials of the gel. Meanwhile, the gel with a three-dimensional network structure has a high porosity and liquid absorption capacity, can absorb liquid electrolytes, improve the ion transport channels, and thus improve the ionic conductivity of the gel. Adding flame retardants can improve the flame retardant performance of the gel. The three-dimensional network structure effectively restricts the fluidity and volatility of the solvent, improves the safety of the lithium battery assembled with the gel, and the three-dimensional network structure has excellent mechanical flexibility, can better adapt to the deformation of electrode materials and battery casings, reduce damage caused by mechanical stress, and improve the safety of the battery.

[0042] The present invention also provides a preparation method of the gel with the three-dimensional network structure described in the above technical solution, including:

[0043] Mix PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents, and carry out polymerization reaction and curing in sequence to obtain a gel with a three-dimensional network structure.

[0044] Unless otherwise specified, the present invention has no special limitation on the sources of each raw material, and commercially available products well-known to those skilled in the art can be used.

[0045] In the present invention, the mixing of PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents is preferably: mix PEGDMA and / or its derivatives with organic solvents, and then add crosslinking agents, fluorinated carbonate compounds, lithium salts, and phosphorus-containing flame retardants in sequence.

[0046] In the present invention, the mixing is preferably carried out under stirring conditions. The present invention has no special limitation on the way, rate, and time of the stirring, and it is only necessary to ensure that each raw material is mixed evenly.

[0047] In the present invention, the mixing is preferably carried out under anhydrous and light-proof conditions.

[0048] In the present invention, the temperature of the polymerization reaction is preferably 60 - 80 °C. As an implementation manner, the temperature of the polymerization reaction can specifically be 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C.

[0049] In the present invention, the heating rate to the polymerization reaction temperature is preferably 1 - 3 °C / min, more preferably 2 °C / min.

[0050] In the present invention, the time of the polymerization reaction is preferably 1 to 24 h. As an implementation manner, the time of the polymerization reaction may specifically be 1 h, 5 h, 10 h, 15 h, 20 h or 24 h. By controlling the temperature and time of the polymerization reaction within the above ranges in the present invention, the polymerization reaction can proceed sufficiently. In the present invention, the polymerization reaction process is mainly that monomers such as PEGDMA and / or its derivatives and fluorinated carbonate compounds polymerize under the action of a cross-linking agent to form long chains or network macromolecules. This process focuses on the growth of molecular chains and the construction of a preliminary network structure, and the reaction is mainly based on the chemical bonding between monomers.

[0051] In the present invention, the temperature of the curing is preferably room temperature; the time of the curing is preferably ≥10 h, more preferably 10 to 48 h. In the present invention, the curing process is to make the cross-linking reaction in the system proceed sufficiently on the basis of the polymerization reaction, and more and more stable cross-linking points are formed between molecular chains, and the gel system changes from a state with certain fluidity to a gel with a stable three-dimensional network structure, certain mechanical strength and shape retention ability. By controlling the temperature and time of the curing within the above ranges in the present invention, the curing can proceed sufficiently.

[0052] The present invention forms a gel with a three-dimensional network structure by in-situ polymerization cross-linking, and the preparation process is simple and suitable for industrial production.

[0053] The present invention also provides a lithium battery, and the electrolyte of the lithium battery is the gel with the three-dimensional network structure described in the above technical solution or the gel with the three-dimensional network structure prepared by the preparation method described in the above technical solution.

[0054] The present invention has no special limitation on the positive electrode and the negative electrode of the lithium battery, and the positive electrode and the negative electrode for lithium batteries well-known to those skilled in the art can be used.

[0055] Since the gel with the three-dimensional network structure of the present invention has good ionic conductivity, flame retardancy and thermal stability, the lithium battery assembled by the gel with the three-dimensional network structure has good electrochemical properties such as safety and cycle performance.

[0056] Next, the technical solutions in the present invention will be described clearly and completely in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0057] Example 1

[0058] A gel with a three-dimensional network structure is prepared from the following raw materials: PEGDMA (polyethylene glycol dimethacrylate, molecular weight 2000), fluorinated carbonate compounds (a mixture of vinyl fluorocarbonate, methyl (2,2,2-trifluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate in a mass ratio of 3:2:2:2), a crosslinking agent (azobisisobutyronitrile), a lithium salt (LiPF6), a flame retardant (dimethyl methylphosphonate), and an organic solvent (acetonitrile);

[0059] The mass ratio of polyethylene glycol dimethacrylate to acetonitrile is 3:7, the mass ratio of azobisisobutyronitrile to polyethylene glycol dimethacrylate is 2.5:100, the mass ratio of fluorinated carbonate compounds to polyethylene glycol dimethacrylate is 7:3, the molar amount of the lithium salt to the total volume of polyethylene glycol dimethacrylate, fluorinated carbonate compounds, crosslinking agent, and organic solvent is 0.75 mol:1 L, and the mass ratio of the flame retardant to polyethylene glycol dimethacrylate is 0.05:1;

[0060] The preparation method of the gel with the three-dimensional network structure is as follows: (1) Under anhydrous and light-shielded conditions, mix polyethylene glycol dimethacrylate and the organic solvent, and sequentially add the crosslinking agent, fluorinated carbonate compounds, lithium salt, and flame retardant, and stir evenly to obtain a mixed solution;

[0061] (2) Heat the mixed solution obtained in step (1) to 70 °C at a heating rate of 2 °C / min for a polymerization reaction for 3 h, and then cure at room temperature for 10 h to obtain a gel with a three-dimensional network structure.

[0062] The macroscopic diagram of the mixed solution obtained in step (1) of Example 1 is as shown in Figure 1 shown, and the macroscopic diagram of the gel with a three-dimensional network structure obtained in step (2) of Example 1 is as shown in Figure 2 shown.

[0063] Using the alternating current impedance method, the room temperature conductivity of the gel with a three-dimensional network structure prepared in Example 1 is tested according to the ASTM E1858 standard, the test frequency range is 100 mHz to 1 MHz, and the temperature is 25 °C ± 0.5 °C. The room temperature ionic conductivity of the gel with a three-dimensional network structure prepared in Example 1 is 4 mS / cm.

[0064] The flame retardant grade of the gel with a three-dimensional network structure prepared in Example 1 is UL-94 V-2. It extinguishes within 10 s after leaving the fire, and there is no dripping to ignite the absorbent cotton. The fluorinated carbonate compounds and dimethyl methylphosphonate act synergistically. The fluorine element inhibits the free radical reaction, and the phosphorus element promotes the formation of a carbon layer.

[0065] The thermal decomposition onset temperature of the gel with a three-dimensional network structure prepared in Example 1 was determined by thermogravimetric analysis (TGA). The heating rate was 10 °C / min under a nitrogen atmosphere. The thermal decomposition onset temperature of the gel with a three-dimensional network structure prepared in Example 1 was 250 °C (mass loss < 5% below 250 °C), and the three-dimensional crosslinked network structure improved the high-temperature tolerance.

[0066] The mixed solution obtained in step (1) of Example 1 was used as the liquid electrolyte, and the gel with a three-dimensional network structure obtained in step (2) of Example 1 was used as the gel electrolyte to assemble a lithium battery with model M11390 and a system of LiFePO4 / graphite. Then, charge-discharge tests were carried out at 2.5 - 3.65 V / 5C / 25 °C, and the results are as Figure 3 shown. Among them, the liquid iron-lithium full battery used the mixed solution obtained in step (1) of Example 1 as the liquid electrolyte, and the gel iron-lithium battery used the gel with a three-dimensional network structure obtained in step (2) of Example 1 as the gel electrolyte. From Figure 3 this, it can be seen that the capacity of the liquid battery was unstable and gradually decreased during the cycling process, and the retention rate after 5000 cycles was only 75.7%. However, the capacity retention rate of the gel battery after 5000 cycles of 5C / 5C charge-discharge was 81.2%, showing better cycling performance.

[0067] Example 2

[0068] A gel with a three-dimensional network structure was prepared from the following raw materials: amino-terminated polyethylene glycol dimethacrylate (molecular weight 2000, amino substitution degree 25 mol%), fluorinated carbonate compounds (a mixture of vinylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate with a mass ratio of 4:3:3), crosslinking agent (azobisisobutyronitrile), lithium salt (LiClO4), flame retardant (diethyl ethylphosphonate), and organic solvent (N,N-dimethylformamide);

[0069] The mass ratio of amino-terminated polyethylene glycol dimethacrylate to N,N-dimethylformamide was 3:6, the mass ratio of azobisisobutyronitrile to amino-terminated polyethylene glycol dimethacrylate was 0.5:100, the mass ratio of fluorinated carbonate compounds to amino-terminated polyethylene glycol dimethacrylate was 6:3, the molar amount of lithium salt to the total volume of amino-terminated polyethylene glycol dimethacrylate, fluorinated carbonate compounds, crosslinking agent, and organic solvent was 0.5 mol:1 L, and the mass ratio of flame retardant to amino-terminated polyethylene glycol dimethacrylate was 0.1:1;

[0070] The preparation method of the gel with a three-dimensional network structure is as follows: (1) Under dry and light-proof conditions, mix amino-functionalized polyethylene glycol dimethacrylate and an organic solvent, and sequentially add a cross-linking agent, a fluorinated carbonate compound, a lithium salt, and a flame retardant, and stir evenly to obtain a mixed solution;

[0071] (2) Heat the mixed solution obtained in step (1) to 60 °C at a heating rate of 2 °C / min for a polymerization reaction for 4 h, and then cure at room temperature for 12 h to obtain a gel with a three-dimensional network structure.

[0072] The room-temperature ionic conductivity of the gel with a three-dimensional network structure prepared in Example 2 is 3.8 mS / cm.

[0073] The flame retardancy rating of the gel with a three-dimensional network structure prepared in Example 2 is UL-94V-1. It extinguishes within 5 s after leaving the fire, and there are no dripping objects to ignite absorbent cotton. Diethyl ethylphosphonate is compounded with the fluorinated carbonate compound, with dual effects of gas-phase dilution and condensed-phase carbon layer.

[0074] The initial thermal decomposition temperature of the gel with a three-dimensional network structure prepared in Example 2 is 280 °C. Amino substitution enhances the intermolecular force, and the structure is more stable at high temperatures.

[0075] Using the same method to test the cycling performance of a lithium battery assembled with the gel with a three-dimensional network structure prepared in Example 2 as a gel-state electrolyte, the capacity retention rate of the gel battery assembled in Example 2 after 5000 cycles of 5C / 5C charge and discharge is 78-80%, and the initial Coulomb efficiency is 97-98% (multiple tests).

[0076] Example 3

[0077] A gel with a three-dimensional network structure is prepared from the following raw materials: sulfonated polyethylene glycol dimethacrylate (molecular weight 2000, sulfonic acid group substitution degree 20 mol%), fluorinated carbonate compound (a mass ratio of 2:4:4 of vinylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and methyl(2,2,2-trifluoroethyl) carbonate), cross-linking agent (ammonium persulfate), lithium salt (LiBF4), flame retardant (triphenyl phosphate), and organic solvent (dimethyl sulfoxide);

[0078] The mass ratio of sulfonated polyethylene glycol dimethacrylate to dimethyl sulfoxide is 3:5, the mass ratio of ammonium persulfate to sulfonated polyethylene glycol dimethacrylate is 5:100, the mass ratio of the fluorinated carbonate compound to sulfonated polyethylene glycol dimethacrylate is 8:3, the molar amount of the lithium salt to the total volume of sulfonated polyethylene glycol dimethacrylate, fluorinated carbonate compound, cross-linking agent, and organic solvent is 1 mol:1 L, and the mass ratio of the flame retardant to sulfonated polyethylene glycol dimethacrylate is 0.08:1;

[0079] The preparation method of the gel with a three-dimensional network structure is as follows: (1) Under dry and light-proof conditions, sulfonated polyethylene glycol dimethacrylate and an organic solvent are mixed, and a cross-linking agent, a fluorinated carbonate compound, a lithium salt, and a flame retardant are sequentially added, and stirred evenly to obtain a mixed solution;

[0080] (2) The mixed solution obtained in step (1) is heated to 80 °C at a heating rate of 2 °C / min for a polymerization reaction for 5 h, and then cured at room temperature for 15 h to obtain a gel with a three-dimensional network structure.

[0081] The room temperature ionic conductivity of the gel with a three-dimensional network structure prepared in Example 3 is 3.5 mS / cm.

[0082] The flame retardant grade of the gel with a three-dimensional network structure prepared in Example 3 is UL-94V-1. It extinguishes within 5 s after leaving the fire, and there is no dripping to ignite absorbent cotton. Triphenyl phosphate and the fluorinated carbonate compound cooperate to isolate oxygen and heat through a carbon layer.

[0083] The initial thermal decomposition temperature of the gel with a three-dimensional network structure prepared in Example 3 is >300 °C. The sulfonic acid group substitution and the strong cross-linking effect of ammonium persulfate improve the heat resistance.

[0084] Using the same method to test the cycle performance of a lithium battery assembled with the gel with a three-dimensional network structure prepared in Example 3 as a gel electrolyte, the capacity retention rate of the gel battery assembled in Example 3 after 5000 cycles of 5C / 5C charge and discharge is 75-77%, and the initial Coulomb efficiency is 96-97% (multiple tests).

[0085] Example 4

[0086] A gel with a three-dimensional network structure is prepared from the following raw materials: fluorinated polyethylene glycol dimethacrylate (molecular weight 2000, fluorine substitution degree 30 mol%), fluorinated carbonate compounds (fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, difluorodimethyl carbonate, and methyl(2,2,2-trifluoroethyl) carbonate with a mass ratio of 3.5:2.5:2:2), cross-linking agent (azobisisobutyronitrile), lithium salt (LiTFSi), flame retardant (resorcinol bisphosphate), and organic solvent (acetonitrile);

[0087] The mass ratio of fluorinated polyethylene glycol dimethacrylate to acetonitrile is 3:4, the mass ratio of azobisisobutyronitrile to fluorinated polyethylene glycol dimethacrylate is 1:100, the mass ratio of fluorinated carbonate compound to fluorinated polyethylene glycol dimethacrylate is 7:3, the molar amount of lithium salt to the total volume of fluorinated polyethylene glycol dimethacrylate, fluorinated carbonate compound, crosslinking agent and organic solvent is 0.8 mol:1 L, and the mass ratio of flame retardant to fluorinated polyethylene glycol dimethacrylate is 0.12:1;

[0088] The preparation method of the gel with a three-dimensional network structure is as follows: (1) Under dry and light-proof conditions, mix fluorinated polyethylene glycol dimethacrylate and an organic solvent, and successively add a crosslinking agent, a fluorinated carbonate compound, a lithium salt and a flame retardant, and stir evenly to obtain a mixed solution;

[0089] (3) Heat the mixed solution obtained in step (1) to 75 °C at a heating rate of 2 °C / min for a polymerization reaction for 3.5 h, and then cure at room temperature for 10 h to obtain a gel with a three-dimensional network structure.

[0090] The room temperature ionic conductivity of the gel with a three-dimensional network structure prepared in Example 4 is 3.2 mS / cm.

[0091] The flame retardant grade of the gel with a three-dimensional network structure prepared in Example 4 is UL-94V-0 grade. It extinguishes immediately when removed from the fire, and there are no dripping objects to ignite absorbent cotton (the highest flame retardant standard). Resorcinol bis(diphenyl phosphate) (a macromolecular phosphorus-based flame retardant) and the fluorinated carbonate compound have a 'fluorine-phosphorus synergistic effect'. Fluorine elements capture combustion free radicals (-F + H· → HF), and phosphorus elements catalyze the formation of a glassy carbon layer on the gel surface to block heat conduction, making the flame retardant grade reach UL-94V-0 grade (extinguishing immediately when removed from the fire).

[0092] The initial thermal decomposition temperature of the gel with a three-dimensional network structure prepared in Example 4 is 320 °C. The high bond energy of the C-F bond and the fluorinated crosslinked network significantly increase the thermal decomposition temperature.

[0093] Using the same method to test the cycle performance of a lithium battery assembled with the gel with a three-dimensional network structure prepared in Example 4 as a gel electrolyte, the capacity retention rate of the gel battery assembled in Example 4 after 5000 cycles of 5C / 5C charge and discharge is 79-81%, and the initial Coulomb efficiency is 98-99% (multiple tests).

[0094] Example 5

[0095] A gel with a three-dimensional network structure is prepared from the following raw materials: phosphoric acid esterified polyethylene glycol dimethacrylate (molecular weight 2000, degree of substitution of phosphate ester groups is 28 mol%), fluorinated carbonate compounds (a mass ratio of 3.5:4:2.5 of fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate and methyl(2,2,2-trifluoroethyl) carbonate), crosslinking agent (benzoyl peroxide), lithium salt (LiTFSi), flame retardant (bisphenol S bisphosphate) and organic solvents (acetonitrile and dimethyl sulfoxide with a volume ratio of 1:1);

[0096] The mass ratio of phosphoric acid esterified polyethylene glycol dimethacrylate to organic solvents is 3:2, the mass ratio of benzoyl peroxide to phosphoric acid esterified polyethylene glycol dimethacrylate is 4:100, the mass ratio of fluorinated carbonate compounds to phosphoric acid esterified polyethylene glycol dimethacrylate is 6:3, the molar amount of lithium salt to the total volume of phosphoric acid esterified polyethylene glycol dimethacrylate, fluorinated carbonate compounds, crosslinking agent and organic solvents is 1 mol:1 L, and the mass ratio of flame retardant to phosphoric acid esterified polyethylene glycol dimethacrylate is 0.15:1;

[0097] The preparation method of the gel with the three-dimensional network structure is as follows: (1) Under dry and light-shielded conditions, mix phosphoric acid esterified polyethylene glycol dimethacrylate and organic solvents, and sequentially add a crosslinking agent, fluorinated carbonate compounds, lithium salt and flame retardant, and stir evenly to obtain a mixed solution;

[0098] (2) Heat the mixed solution obtained in step (1) to 80 °C at a heating rate of 1.5 °C / min for a polymerization reaction for 10 h, and then cure at room temperature for 12 h to obtain a gel with a three-dimensional network structure.

[0099] The room temperature ionic conductivity of the gel with the three-dimensional network structure prepared in Example 5 is 4.1 mS / cm.

[0100] The flame retardant grade of the gel with the three-dimensional network structure prepared in Example 5 is UL-94V-0 grade. It extinguishes immediately when removed from the fire, and no dripping ignites absorbent cotton. Bisphenol S bisphosphate and phosphoric acid esterified polymer form a "phosphorus-carbon" synergistic flame retardant system with high flame retardant efficiency.

[0101] The initial thermal decomposition temperature of the gel with the three-dimensional network structure prepared in Example 5 is >350 °C. The phosphate ester groups and long curing time form the densest three-dimensional network with the best thermal stability.

[0102] Using the same method to test the cycle performance of a lithium battery assembled with the gel with the three-dimensional network structure prepared in Example 5 as a gel electrolyte, the capacity retention rate of the gel battery assembled in Example 5 after 5000 cycles of 5C / 5C charge and discharge is 82-84%, and the initial Coulomb efficiency is 98-99% (multiple tests).

[0103] Example 6

[0104] A gel with a three-dimensional network structure is prepared from the following raw materials: PEGDMA (molecular weight 2000), difluorodimethyl carbonate (FDMC), azobisisobutyronitrile (AIBN), LiPF6, dimethyl methylphosphonate (DMMP), and acetonitrile;

[0105] The mass ratio of difluorodimethyl carbonate (FDMC) to PEGDMA is 5:3, the mass ratio of azobisisobutyronitrile to PEGDMA is 2.5:100, the molar amount of the lithium salt to the total volume of PEGDMA, FDMC, cross-linking agent, and organic solvent is 0.75 mol:1 L, the mass ratio of the flame retardant to PEGDMA is 0.05:1, and the mass ratio of PEGDMA to acetonitrile is 3:7;

[0106] The preparation method is the same as that of Example 1.

[0107] Test results: The room temperature ionic conductivity is 3.3 mS / cm, the initial thermal decomposition temperature is 260 °C, the flame retardant grade is UL-94V-1, and the capacity retention rate of the assembled lithium battery after 5000 cycles at 5C / 5C is 79%.

[0108] Example 7

[0109] A gel with a three-dimensional network structure is prepared from the following raw materials: PEGDMA (molecular weight 2000), fluoroethylene carbonate (FEC), azobisisobutyronitrile (AIBN), LiPF6, triphenyl phosphate (TPP), and acetonitrile;

[0110] The mass ratio of fluoroethylene carbonate (FEC) to PEGDMA is 7:3, the mass ratio of azobisisobutyronitrile to PEGDMA is 2.5:100, the molar amount of the lithium salt to the total volume of PEGDMA, FEC, cross-linking agent, and organic solvent is 0.75 mol:1 L, the mass ratio of the flame retardant (TPP) to PEGDMA is 0.2:1, and the mass ratio of PEGDMA to acetonitrile is 3:7;

[0111] The preparation method is the same as that of Example 1.

[0112] Test results: The room temperature ionic conductivity is 3.5 mS / cm, the initial thermal decomposition temperature is 255 °C, the flame retardant grade is UL-94V-1, it extinguishes 8 s after leaving the fire, there is no dripping to ignite the absorbent cotton, and the capacity retention rate of the assembled lithium battery after 5000 cycles at 5C / 5C is 78%.

[0113] In summary, the gel with a three-dimensional network structure provided by the present invention has excellent flame retardancy, thermal stability and room temperature ionic conductivity, and the lithium battery assembled therefrom has excellent cycle performance.

[0114] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements can be made without departing from the principle of the present invention, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A gel with a three-dimensional network structure, comprising the following raw materials: PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents.

2. The gel according to claim 1, characterized in that, The fluorinated carbonate compounds include one or more of vinylene carbonate, methyl (2,2,2-trifluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, and difluorodimethyl carbonate.

3. The gel according to claim 1 or 2, characterized in that, The mass ratio of the fluorinated carbonate compounds to PEGDMA and / or its derivatives is (1 - 10):(1 - 5).

4. The gel according to claim 1, wherein The lithium salts include one or more of LiPF6, LiClO4, LiBF4, and LiTFSi.

5. The gel according to claim 1 or 4, characterized in that, The molar amount of the lithium salts to the total volume of PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, and organic solvents is (0.5 - 1) mol:1 L.

6. The gel according to claim 1, wherein The crosslinking agents include one or more of a mixture of sodium bisulfite and oxidants, azobisisobutyronitrile, ammonium persulfate, and benzoyl peroxide.

7. The gel according to claim 1, characterized in that, The phosphorus-containing flame retardants include one or more of dimethyl methylphosphonate, diethyl ethylphosphonate, triphenyl phosphate, resorcinol bis(diphenyl phosphate), and bisphenol S bis(diphenyl phosphate).

8. The gel according to claim 1, characterized in that, The organic solvents include one or more of dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile.

9. A method for preparing the gel with a three-dimensional network structure according to any one of claims 1 - 8, comprising: Mixing PEGDMA and / or its derivatives, fluorinated carbonate compounds, crosslinking agents, lithium salts, phosphorus-containing flame retardants, and organic solvents, and successively performing a polymerization reaction and curing to obtain a gel with a three-dimensional network structure.

10. A lithium battery, wherein the electrolyte of the lithium battery is the gel with a three-dimensional network structure according to any one of claims 1 - 8 or the gel with a three-dimensional network structure prepared by the preparation method according to claim 9.

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