Electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery electrolyte, in particular to electrolyte as well as a preparation method and application thereof. The electrolyte provided by the invention comprises a filler, an ionic liquid, a lithium salt and a film-forming additive. Under the combined action of the filler and the ionic liquid, the electrolyte has the shear thickening performance, and meanwhile has the non-combustible performance and the anti-impact performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery electrolyte, and in particular to an electrolyte and a preparation method and application thereof. Background Art

[0002] With the application of high-voltage and high-capacity electrode materials such as lithium-rich manganese-based positive electrodes and silicon-carbon negative electrodes, the energy density of lithium-ion batteries has been further improved. At the same time, the safety of lithium batteries has become one of the main development bottlenecks. Commercial lithium-ion batteries mainly use flammable and volatile carbonate-based electrolytes, which have serious thermal runaway risks. Once the battery is subjected to external impact and the diaphragm is broken, a thermal runaway reaction will be triggered. Therefore, the safety test of commercial lithium-ion batteries must include needle puncture or blunt nail tests to test the battery's ability to resist external force impact. It can be seen that one of the reasons for the risk of thermal runaway in lithium-ion batteries is that flammable commercial electrolytes lack the ability to resist mechanical impact. In the past, the improvement method for lithium batteries to resist mechanical impact was mainly based on the design of the external packaging of the battery, and did not focus on the electrolyte material itself. Therefore, it is necessary to design a new electrolyte with impact resistance to fundamentally improve the safety performance of lithium-ion batteries.

[0003] Shear thickening fluid is a non-Newtonian fluid, also known as dilatant fluid, which is usually a two-phase dispersion system formed by nano or micro particles dispersed in a medium fluid. Shear thickening fluid exhibits low viscosity at shear rates below the critical value, and when the applied shear stress reaches the critical value, the viscosity will increase significantly. This property of shear thickening fluid also has great application potential in improving the safety performance of lithium-ion batteries. If the electrolyte is endowed with shear thickening properties so that it maintains high ionic conductivity under normal conditions, and instantly increases viscosity when subjected to high shear force, presents solid properties and eliminates impact energy, a buffering effect can be achieved, helping lithium batteries to resist external shocks and prevent the risk of thermal runaway.

[0004] Applications with publication numbers CN 116387624 A and CN 117913364 A respectively disclose a method for preparing an impact-resistant electrolyte. The method uses porous silica, calcium carbonate, etc. as inorganic fillers, commercial electrolyte as a dispersion liquid, and obtains an electrolyte with shear thickening properties by a physical mixing method. However, the thickening range of the electrolyte prepared by this method is very limited, and the carbonate solvent component of the commercial electrolyte has a great risk of flammability, which cannot be fundamentally solved even with the use of flame retardant additives. Summary of the invention

[0005] In view of this, the object of the present invention is to provide an electrolyte and a preparation method and application thereof. The electrolyte of the present invention has shear thickening performance and is non-flammable and impact resistant.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The invention provides an electrolyte comprising a filler, an ionic liquid, a lithium salt and a film-forming additive.

[0007] Preferably, the mass percentage of the filler to the ionic liquid is 1.0-40%; The mass percentage of the lithium salt to the ionic liquid is 5-20%; The mass percentage of the film-forming additive to the ionic liquid is 0.1-10%.

[0008] Preferably, the filler comprises a modified or unmodified nanofiller; The nanofiller comprises silica and / or a metal organic framework; The metal organic framework includes one or more of MOF-5, MOF-525, HKUST-1, ZIF-7, ZIF-8, UiO-66, MIL-88, and UTSA-76.

[0009] Preferably, when the filler is a modified nanofiller, the modified nanofiller includes a nanofiller with surface chain segments grafted thereon or a nanofiller with surface functional groups modified thereon; The surface segments in the surface segment-grafted nanofiller include a linear structure, a V-shaped structure, a Y-shaped brush structure or a cross-linked structure; The surface functional groups in the surface functional group-modified nanofiller include isoelectrically neutral groups, anionic groups or cationic groups.

[0010] Preferably, the surface segments in the surface segment-grafted nanofiller include one or more of polyethylene glycol, polymethyl methacrylate, polyglycidyl methacrylate, polytert-butyl methacrylate, polyvinyl carbazole, polyoxyethylene methacrylate, polybutyl acrylate, polyisopropylacrylamide and polyvinyl pyridine; The surface functional groups in the surface functional group-modified nanofiller include one or more of halogen, hydroxyl, carboxyl, amino, sulfhydryl, thiol, quaternary ammonium ion, sulfonate ion, imidazole and pyridine.

[0011] Preferably, the cation of the ionic liquid includes one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, pyrrolidine, piperidine, functionalized olefinic group, functionalized hydroxyl group, functionalized carboxyl group, functionalized ether group, functionalized ester group, functionalized benzyl group and functionalized nitrile group; The anions of the ionic liquid include one or more of hexafluorophosphoric acid, tetrafluoroboric acid, bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide and perchlorate anions.

[0012] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium perchlorate.

[0013] Preferably, the film-forming additive includes one or more of ethylene carbonate, vinyl acetate, fluoroethylene carbonate, lithium bis(oxalatoborate) and lithium difluorooxalatoborate.

[0014] The present invention also provides a method for preparing the electrolyte described in the above technical solution, comprising the following steps: The filler, ionic liquid, lithium salt, film-forming additive and organic solvent are mixed, and the solvent is evaporated to obtain the electrolyte.

[0015] The present invention also provides the use of the electrolyte described in the above technical solution or the electrolyte prepared by the preparation method described in the above technical solution in a lithium ion battery.

[0016] The present invention provides an electrolyte, comprising a filler, an ionic liquid, a lithium salt and a film-forming additive. In the present invention, the filler is added to the electrolyte to form a shear thickening system, which can react sensitively to shear stress. When encountering a rapid impact from the outside, the filler (having thickening properties) contained in the system will agglomerate under the action of the shear force, so that the overall viscosity of the system will increase rapidly, showing solid-state properties, thereby realizing the ability to resist external impact; at the same time, collisions and relative friction occur between the fillers, thereby dissipating the impact energy. After the shear force disappears, the viscosity and ion conductivity of the electrolyte can be immediately restored to the initial state to ensure the normal operation of the battery. At the same time, the filler can interact with the ionic liquid based on ionic bonds, covalent bonds or hydrogen bonds, and form a solvation layer on the surface of the filler, further stabilizing the filler clusters generated by the shear stress, and improving the thickening performance of the electrolyte. The ionic liquid in the electrolyte of the present invention can ensure that the electrolyte has high-efficiency ion conductivity, and has the characteristics of non-combustion and non-volatility, which can effectively avoid the combustion risk of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The cycle performance curve of the lithium ion battery described in Example 1; Figure 2 This is the thickening performance of the electrolyte described in Example 1. DETAILED DESCRIPTION

[0018] The invention provides an electrolyte comprising a filler, an ionic liquid, a lithium salt and a film-forming additive.

[0019] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0020] In the present invention, the mass percentage of the filler in the ionic liquid is preferably 1.0-40%, more preferably 10-30%, and most preferably 15-25%; the mass percentage of the lithium salt in the ionic liquid is preferably 5-20%, more preferably 10-15%; the mass percentage of the film-forming additive in the ionic liquid is preferably 0.1-10%, more preferably 2-8%, and most preferably 4-6%. In an embodiment of the present invention, the mass percentage of the filler in the ionic liquid may be 10%, 20%, 30% or 15%; the mass percentage of the lithium salt in the ionic liquid may be 10%, 15%, 16% or 20%; the mass percentage of the film-forming additive in the ionic liquid may be 0.5%, 1% or 0.2%.

[0021] In the present invention, the average particle size of the filler is preferably 10 to 500 nm. The filler preferably includes a modified or unmodified nanofiller; the nanofiller preferably includes silica and / or a metal organic framework. The metal organic framework in the modified or unmodified metal organic framework preferably includes one or more of MOF-5, MOF-525, HKUST-1, ZIF-7, ZIF-8, UiO-66, MIL-88, and UTSA-76. When the metal organic framework is two or more of the above specific selections, the present invention does not have any special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. In the present invention, the modified nanofiller preferably includes a nanofiller grafted with a surface segment or a nanofiller modified with a surface functional group; the surface segment in the nanofiller grafted with a surface segment preferably includes a linear structure, a V-shaped structure, a Y-shaped brush structure or a cross-linked structure; the surface functional group in the nanofiller modified with a surface functional group preferably includes an isoelectrically neutral group, an anionic group or a cationic group; the surface segment in the nanofiller grafted with a surface segment includes one or more of polyethylene glycol, polymethyl methacrylate, polyglycidyl methacrylate, polytert-butyl methacrylate, polyvinyl carbazole, polyoxyethylene methacrylate, polybutyl acrylate, polyisopropylacrylamide and polyvinyl pyridine; the surface functional group in the nanofiller modified with a surface functional group includes one or more of halogen, hydroxyl, carboxyl, amino, sulfhydryl, thiol, quaternary ammonium ion, sulfonate ion, imidazole and pyridine. In the present invention, the source of the modified nanofiller is preferably commercially available or prepared by conventional modification. In an embodiment of the present invention, the filler can be a silica nanofiller with a surface modified with polyethylene glycol linear chain (average particle size of 20 nm), a sulfonic acid group-modified metal organic framework (HKUST-1) nanofiller (average particle size of 100 nm), a quaternary ammonium group-modified metal organic framework (UiO-66) nanofiller (average particle size of 100 nm), an imidazole-modified metal organic framework (ZIF-8) nanofiller (average particle size of 180 nm) or a pyridine-modified metal organic framework (UTSA-76) nanofiller (average particle size of 210 nm).

[0022] In the present invention, the surface chain segment grafted nanofiller can increase the relative friction resistance between filler particles, making them easier to agglomerate under the action of shear force, thereby greatly improving the thickening performance of the electrolyte and consuming shear energy; the surface functional group-modified nanofiller can regulate the interaction mode between the particles and the electrolyte, prevent the precipitation and precipitation of the filler particles in the dispersed system, and improve the dispersion stability; it can improve the filler particles' ability to transmit lithium ions and improve the overall ionic conductivity of the electrolyte.

[0023] In the present invention, the cation of the ionic liquid preferably includes one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, pyrrolidine, piperidine, functionalized alkenyl, functionalized hydroxyl, functionalized carboxyl, functionalized ether, functionalized ester, functionalized benzyl and functionalized nitrile; when the cation of the ionic liquid is two or more of the above-mentioned specific selections, the present invention has no special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. The anion of the ionic liquid preferably includes one or more of hexafluorophosphoric acid, tetrafluoroboric acid, bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide and perchlorate anion. When the anion is two or more of the above-mentioned specific selections, the present invention has no special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the ionic liquid may be 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide salt ionic liquid or N-methoxyethyl-N-methyldiethylammonium bis(fluorosulfonyl)imide salt ionic liquid. In an embodiment of the present invention, the ionic liquid may be 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide salt ionic liquid, N-methoxyethyl-N-methyldiethylammonium bis(fluorosulfonyl)imide salt ionic liquid or 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid.

[0024] In the present invention, the nanofiller can interact with the ionic liquid based on ionic bonds, covalent bonds or hydrogen bonds, forming a solvation layer on the surface of the nanofiller, further stabilizing the filler clusters generated by shear stress and improving the thickening performance of the electrolyte.

[0025] In the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium perchlorate. When the lithium salt is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the lithium salt can be lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide.

[0026] In the present invention, the film-forming additive preferably includes one or more of ethylene carbonate, vinyl acetate, fluoroethylene carbonate, lithium bis(oxalatoborate) and lithium difluorooxalatoborate. When the film-forming additive is two or more of the above-mentioned specific selections, the present invention has no special restrictions on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the film-forming additive can be ethylene carbonate, fluoroethylene carbonate, lithium bis(oxalatoborate) or lithium difluorooxalatoborate.

[0027] The present invention also provides a method for preparing the electrolyte described in the above technical solution, comprising the following steps: The filler, ionic liquid, lithium salt, film-forming additive and organic solvent are mixed, and the solvent is evaporated to obtain the electrolyte.

[0028] In the present invention, the organic solvent preferably includes one or more of methanol, ethanol, acetonitrile, toluene, acetone, N,N-dimethylformamide and dimethyl sulfoxide. When the organic solvent is two or more of the above specific selections, the present invention has no special restrictions on the ratio of the above specific substances, and they can be mixed in any ratio. In an embodiment of the present invention, the organic solvent can be ethanol, acetone or N,N-dimethylformamide.

[0029] In the present invention, the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the mixed solution obtained after mixing is preferably 0.5-20%, more preferably 5-15%, and most preferably 8-12%. In an embodiment of the present invention, the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the mixed solution obtained after mixing can be 5% or 3%.

[0030] In the present invention, the mixing is preferably carried out under heating and stirring conditions, the heating temperature is preferably 40-180°C, more preferably 80-120°C; the stirring speed is preferably 10-120rpm, more preferably 30-100rpm, most preferably 50-70rpm; the stirring time is preferably 1-10h, more preferably 3-6h. In an embodiment of the present invention, the heating temperature may be 50°C, 60°C or 80°C; the stirring speed may be 60rpm or 100rpm; the stirring time may be 8h, 5h or 4h.

[0031] In the present invention, the temperature for evaporating the solvent is preferably 60-250°C, more preferably 100-200°C.

[0032] The present invention also provides the use of the electrolyte described in the above technical solution or the electrolyte prepared by the preparation method described in the above technical solution in a lithium ion battery. The present invention does not have any special limitation on the method of the application, and the method well known to those skilled in the art can be used.

[0033] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1 The electrolyte consists of filler (silica nanofiller with surface modified polyethylene glycol straight chain, with an average particle size of 20 nm), ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid), lithium salt (lithium tetrafluoroborate) and film-forming additive (ethylene carbonate), among which the mass of filler accounts for 10% of the mass of ionic liquid, the mass of lithium salt accounts for 10% of the mass of ionic liquid, and the mass of ethylene carbonate accounts for 0.5% of the mass of ionic liquid.

[0035] Preparation of electrolyte: filler, ionic liquid, lithium salt and film-forming additive are dispersed in ethanol (the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the obtained mixed solution is 5%), heated and stirred (temperature is 60°C, stirring speed is 60 rpm, time is 4h), and then the solvent is evaporated (temperature is 80°C) to obtain electrolyte; Performance test: using silicon-carbon negative electrode (MA-EN-AN-0034) and lithium-rich manganese-based positive electrode (model MA-EN-CA-0071, purchased from Canrd) as electrodes, taking 80 μL of the electrolyte to soak the glass fiber separator, placing it between the positive electrode and the negative electrode, using CR2032 battery shell to assemble button batteries, completing the sealing under a pressure of 60 MPa, using aluminum-plastic film to assemble single-layer soft-pack batteries, using a sealing machine to complete the sealing, and preparing a lithium-ion battery; the lithium-ion battery was subjected to charge and discharge tests: the voltage range was 2.0~4.0V, the charge and discharge rate was 0.1C, and the number of cycles was 200 times; wherein, Figure 1 is the cycle performance curve of the lithium ion battery described in Example 1, Figure 1 It can be seen that the first reversible specific capacity of the lithium-ion battery is 2074 mA·h / g, and the capacity retention rate after 200 cycles is 92.1%; The thickening performance of the electrolyte is tested using a rotational rheometer; wherein Figure 2 is the thickening property of the electrolyte, Figure 2 It can be seen that the critical shear rate of the electrolyte is 10.3s -1 , the thickening amplitude (the ratio of the maximum viscosity of the liquid after thickening under high shear force to the normal viscosity under low shear force) is 83 times; The electrolyte is placed in a battery shell of a 2032 button battery, ignited with a blowtorch and the burning time is recorded to test the flammability of the electrolyte; the test result is: the electrolyte cannot be ignited; The soft-pack battery assembled as above is fixed, and a weight of a specific mass is used to fall freely to control the impact energy on the soft-pack battery. The open circuit voltage of the battery is monitored in real time to determine the impact resistance of the battery. The test result is: the maximum impact energy that the soft-pack battery can withstand while maintaining the open circuit voltage is 2.2J.

[0036] Example 2 The electrolyte consists of filler (sulfonic acid modified metal organic framework (HKUST-1) nanofiller with an average particle size of 100 nm), ionic liquid (1-butyl-3-methylimidazole-bis(trifluoromethylsulfonyl)imide salt ionic liquid), lithium salt (lithium bis(trifluoromethylsulfonyl)imide) and film-forming additive (fluoroethylene carbonate), among which the filler mass accounts for 20% of the ionic liquid mass, the lithium salt mass accounts for 16% of the ionic liquid mass, and the ethylene carbonate mass accounts for 0.5% of the ionic liquid mass.

[0037] Preparation of electrolyte: filler, ionic liquid, lithium salt and film-forming additive are dispersed in acetone (the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the obtained mixed solution is 3%), heated and stirred (temperature is 50°C, stirring speed is 60rpm, time is 5h), and then the solvent is evaporated (temperature is 80°C) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 1958 mA·h / g, and the capacity retention rate after 200 cycles was 96.5%; the critical shear rate of the electrolyte was 61.6 s -1 The thickening range is 55 times; the electrolyte cannot be ignited; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open circuit voltage is 1.8J.

[0038] Example 3 The electrolyte consists of filler (quaternary ammonium-modified metal organic framework (UiO-66) nanofiller with an average particle size of 100 nm), ionic liquid (N-methoxyethyl-N-methyldiethylammonium bisfluorosulfonyl imide salt ionic liquid), lithium salt (lithium bisfluorosulfonyl imide) and film-forming additive (lithium difluorooxalatoborate), among which the filler mass accounts for 20% of the ionic liquid mass, the lithium salt mass accounts for 20% of the ionic liquid mass, and ethylene carbonate accounts for 0.5% of the ionic liquid mass.

[0039] Preparation of electrolyte: filler, ionic liquid, lithium salt and film-forming additive are dispersed in N,N-dimethylformamide (the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the obtained mixed solution is 5%), heated and stirred (temperature is 80°C, stirring speed is 100 rpm, time is 8h), and then the solvent is evaporated (temperature is 120°C) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 1933 mA·h / g, and the capacity retention rate after 200 cycles was 95.7%; the critical shear rate of the electrolyte was 75.2 s -1 , the thickening range is 62 times; the electrolyte cannot be ignited; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open circuit voltage is 1.8J.

[0040] Example 4 The electrolyte consists of filler (imidazole-modified metal organic framework (ZIF-8) nanofiller with an average particle size of 180 nm), ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid), lithium salt (lithium tetrafluoroborate) and film-forming additive (lithium bis(oxalatoborate)). The filler mass accounts for 30% of the ionic liquid mass, the lithium salt mass accounts for 15% of the ionic liquid mass, and the lithium bis(oxalatoborate) mass accounts for 1.0% of the ionic liquid mass.

[0041] Preparation of electrolyte: filler, ionic liquid, lithium salt and film-forming additive are dispersed in toluene (the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the obtained mixed solution is 5%), heated and stirred (temperature is 60°C, stirring speed is 80 rpm, time is 6h), and then the solvent is evaporated (temperature is 80°C) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 1943 mA·h / g, and the capacity retention rate after 200 cycles was 94.2%; the critical shear rate of the electrolyte was 42.2 s -1 The thickening range is 71 times; the electrolyte cannot be ignited; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open circuit voltage is 2.2J.

[0042] Example 5 The electrolyte consists of filler (pyridine-modified metal-organic framework (UTSA-76) nanofiller with an average particle size of 210 nm), ionic liquid (N-methoxyethyl-N-methyldiethylammonium bis(fluorosulfonyl)imide ionic liquid), lithium salt (lithium bis(fluorosulfonyl)imide) and film-forming additive (fluoroethylene carbonate), among which the filler mass accounts for 15% of the ionic liquid mass, the lithium salt mass accounts for 10% of the ionic liquid mass, and the ethylene carbonate mass accounts for 0.2% of the ionic liquid mass.

[0043] Preparation of electrolyte: filler, ionic liquid, lithium salt and film-forming additive are dispersed in ethanol (the total mass percentage of filler, ionic liquid, lithium salt and film-forming additive in the obtained mixed solution is 5%), heated and stirred (temperature is 50°C, stirring speed is 100 rpm, time is 6h), and then the solvent is evaporated (temperature is 80°C) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 1994 mA·h / g, and the capacity retention rate after 200 cycles was 94.5%; the critical shear rate of the electrolyte was 43.9 s -1, the thickening range is 65 times; the electrolyte cannot be ignited; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open circuit voltage is 2.1J.

[0044] Comparative Example 1 The electrolyte consists of filler (silicon dioxide nanofiller with surface modified polyethylene glycol branches, with an average particle size of 20 nm), lithium salt (lithium tetrafluoroborate) and film-forming additive (ethylene carbonate), wherein the mass ratio of filler, lithium salt and ethylene carbonate is 10:10:0.5.

[0045] Preparation of electrolyte: Disperse filler, lithium salt and film-forming additive into 1 mol / L LiPF6 solution of commercial electrolyte (solvent is EC and DEC with a volume ratio of 1:1) (the mass of filler in the obtained mixed solution is 10% of the mass of commercial electrolyte) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 2182 mA·h / g, and the capacity retention rate after 200 cycles was 92.4%; the critical shear rate of the electrolyte was 286.1 s -1 The thickening range is 12 times; the self-extinguishing time of the electrolyte is 41s; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open-circuit voltage is 0.6J.

[0046] It can be seen that directly adding nanofillers to commercial electrolytes without using ionic liquids can also give the electrolyte shear thickening properties, but compared with ionic liquids, the critical shear rate of the electrolyte is higher, indicating that it is less sensitive to impact, and the thickening amplitude is lower than the maximum impact energy that the battery can withstand. The impact resistance of the surface electrolyte is lower, and the electrolyte can be ignited, indicating that its flame retardancy is lower.

[0047] Comparative Example 2 The electrolyte consists of filler (silica nanofiller with surface modified polyethylene glycol branches, with an average particle size of 20 nm), ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid) and lithium salt (lithium tetrafluoroborate), among which the filler accounts for 10% of the mass of the ionic liquid and the lithium salt accounts for 10% of the mass of the ionic liquid.

[0048] Preparation of electrolyte: dispersing filler, ionic liquid and lithium salt in ethanol (the total mass percentage of filler, ionic liquid and lithium salt in the obtained mixed solution is 5%) to obtain electrolyte; The performance test was performed with reference to Example 1. The test results were as follows: the first reversible specific capacity of the prepared lithium-ion battery was 1647 mA·h / g, and the capacity retention rate after 200 cycles was 31.1%; the critical shear rate of the electrolyte was 60.3 s -1, the thickening range is 62 times; the electrolyte cannot be ignited; the maximum impact energy that the prepared soft-pack battery can withstand to maintain the open circuit voltage is 1.8J.

[0049] It can be seen that not adding film-forming additives to the electrolyte has little effect on the rheological properties, but it will make it difficult to form a stable SEI film, which will significantly reduce the cycle stability of the battery.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that: Including fillers, ionic liquids, lithium salts and film-forming additives.

2. The electrolyte according to claim 1, characterized in that The mass percentage of the filler to the ionic liquid is 1.0-40%; The mass percentage of the lithium salt to the ionic liquid is 5-20%; The mass percentage of the film-forming additive to the ionic liquid is 0.1-10%.

3. The electrolyte according to claim 1, characterized in that The filler includes modified or unmodified nanofillers; The nanofiller comprises silica and / or a metal organic framework; The metal organic framework includes one or more of MOF-5, MOF-525, HKUST-1, ZIF-7, ZIF-8, UiO-66, MIL-88, and UTSA-76.

4. The electrolyte according to claim 1, characterized in that When the filler is a modified nanofiller, the modified nanofiller includes a nanofiller with surface chain segments grafted or a nanofiller with surface functional groups modified; The surface segments in the surface segment-grafted nanofiller include a linear structure, a V-shaped structure, a Y-shaped brush structure or a cross-linked structure; The surface functional groups in the surface functional group-modified nanofiller include isoelectrically neutral groups, anionic groups or cationic groups.

5. The electrolyte according to claim 4, characterized in that The surface segments in the surface segment-grafted nanofiller include one or more of polyethylene glycol, polymethyl methacrylate, polyglycidyl methacrylate, polytert-butyl methacrylate, polyvinyl carbazole, polyoxyethylene methacrylate, polybutyl acrylate, polyisopropylacrylamide and polyvinyl pyridine; The surface functional groups in the surface functional group-modified nanofiller include one or more of halogen, hydroxyl, carboxyl, amino, sulfhydryl, thiol, quaternary ammonium ion, sulfonate ion, imidazole and pyridine.

6. The electrolyte according to claim 1, characterized in that The cation of the ionic liquid includes one or more of imidazole, pyridine, quaternary ammonium, quaternary phosphonium, pyrrolidine, piperidine, functionalized olefinic group, functionalized hydroxyl group, functionalized carboxyl group, functionalized ether group, functionalized ester group, functionalized benzyl group and functionalized nitrile group; The anions of the ionic liquid include one or more of hexafluorophosphoric acid, tetrafluoroboric acid, bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide and perchlorate anions.

7. The electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium perchlorate.

8. The electrolyte according to claim 1, characterized in that The film-forming additive includes one or more of ethylene carbonate, vinyl acetate, fluoroethylene carbonate, lithium bis(oxalatoborate) and lithium difluorooxalatoborate.

9. The method for preparing the electrolyte according to any one of claims 1 to 8, characterized in that: The following steps are involved: The filler, ionic liquid, lithium salt, film-forming additive and organic solvent are mixed, and the solvent is evaporated to obtain the electrolyte.

10. Use of the electrolyte according to any one of claims 1 to 8 or the electrolyte prepared by the preparation method according to claim 9 in a lithium ion battery.

Images