A fluorinated phase-separated polymer ion gel electrolyte, its preparation method and application, and lithium metal batteries.

Abstract

This invention belongs to the field of lithium metal battery technology, specifically relating to a fluorinated phase-separated polymer ion gel electrolyte, its preparation method and application, and lithium metal batteries. The fluorinated phase-separated polymer ion gel electrolyte provided by this invention comprises a solid phase and a liquid phase; the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds; the liquid phase comprises an ionic liquid and a lithium salt dissolved in the ionic liquid. Compared to liquid electrolytes and traditional SPEs, the fluorinated phase-separated polymer ion gel electrolyte provided by this invention has high ionic conductivity, mechanical strength, interfacial stability, and safety. It can effectively suppress the growth of lithium dendrites and adapt to large volume changes, avoiding short circuits and thermal runaway in lithium metal batteries under conditions of overcharging, over-discharging, or mechanical impact.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a fluorinated phase-separated polymer ion gel electrolyte, its preparation method and application, and lithium metal batteries. Background Technology

[0002] To meet the increasing demands of applications such as electric vehicles, low-altitude aerial vehicles (eVTOL), and energy storage systems, new battery technologies need to possess higher energy density to improve driving range or energy storage capacity on a single charge. Lithium metal batteries (LMBs) utilize high-capacity lithium metal (3860 mAh / g). -1 As a negative electrode, it can yield a yield of over 500 Wh·kg⁻¹. -1 Its high energy density makes it increasingly prominent in next-generation battery systems. However, how to solve the safety hazards caused by leakage, flammability, explosion, and lithium dendrite growth of liquid electrolytes has become a key issue troubling researchers.

[0003] Solid-state batteries, with their advantages of high safety and high energy density, are expected to eliminate the "drawbacks" faced by lithium metal batteries (LMBs). To meet the demand for solid polymer electrolytes (SPEs) in high-energy-density solid-state LMBs, a novel material—polymer ion gel (PIG)—can be prepared by embedding ionic liquids as plasticizers into the polymer backbone. However, PIGs constructed using polymer backbones, such as polyethylene oxide (PEO) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), typically exhibit a homogeneous structure with poor mechanical strength (Young's modulus ≤ 1 MPa), making it difficult to effectively suppress lithium dendrite growth (ideally, the Young's modulus should be at least 1 / 1000 of the 9 GPa Young's modulus of lithium metal) and accommodate large volume changes (expansion rate > 300%). This makes the battery highly susceptible to short circuits and thermal runaway under conditions such as overcharging, over-discharging, or mechanical shock. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a fluorinated phase-separated polymer ion gel electrolyte, its preparation method and application, and lithium metal batteries. Compared with liquid electrolytes and traditional SPEs, the fluorinated phase-separated polymer ion gel electrolyte provided by the present invention has high ionic conductivity, mechanical strength, interfacial stability and safety. It can effectively suppress the growth of lithium dendrites and adapt to large volume changes, avoiding short circuits and thermal runaway of lithium metal batteries under conditions such as overcharging, over-discharging or mechanical impact.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a fluorinated phase-separated polymer ion gel electrolyte, comprising a solid phase and a liquid phase; wherein the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds;

[0007] The liquid phase comprises an ionic liquid and a lithium salt dissolved in the ionic liquid.

[0008] Preferably, the fluorinated acrylate monomer includes one or more of fluoroethyl acrylate, trifluoroethyl acrylate, tetrafluoropropyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, and octafluoropentyl acrylate.

[0009] Preferably, the crosslinking agent containing carbon-carbon double bonds includes one or more of acrylamide, N,N-methylenebisacrylamide, methoxy polyethylene glycol acrylate, polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and trimethylolpropane triacrylate.

[0010] Preferably, the organic cation in the ionic liquid includes one or more of 1-vinyl-3-methylimidazolium, 1-methyl-1-allylpyrrolidine, 1-methyl-1-propylpyrrolidineonium, 1-ethyl-3-methylimidazolium, and 1-n-butyl-1-methylpyrrolidine, and the anion includes one or more of bis(trifluoromethanesulfonyl)imide ion, bis(trifluoromethanesulfonamide) ion, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, and dinitrileamine ion.

[0011] Preferably, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

[0012] Preferably, the preparation method of the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds includes the following steps: mixing the fluorinated acrylate monomer, the crosslinking agent containing carbon-carbon double bonds and the photoinitiator, and carrying out a crosslinking polymerization reaction under light irradiation to obtain the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds.

[0013] Preferably, the photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0014] This invention also provides a method for preparing the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution, comprising the following steps:

[0015] Fluorinated acrylate monomers, carbon-carbon double bond crosslinking agents, ionic liquids, lithium salts, and photoinitiators are mixed, and the resulting precursor solution is coated onto a substrate. After crosslinking polymerization under light irradiation, the substrate is removed to obtain a fluorinated phase-separated polymer ion gel electrolyte.

[0016] The present invention also provides the application of the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method described in the above technical solution in lithium metal batteries.

[0017] The present invention also provides a lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method described in the above technical solution.

[0018] This invention provides a fluorinated phase-separated polymer ionogel electrolyte, comprising a solid phase and a liquid phase; the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds; the liquid phase comprises an ionic liquid and a lithium salt dissolved in the ionic liquid. The fluorinated phase-separated polymer ionogel electrolyte provided by this invention is a gel polymer electrolyte (GPE), which combines the high safety of solid polymer electrolytes (SPE) with the high ionic conductivity of liquid electrolytes. Furthermore, the introduction of a fluorinated acrylate monomer, which contains CF bonds with strong structural and electrochemical stability, makes it compatible with high-voltage (4.3V and above) cathode materials and provides excellent thermal stability and high safety. Fluorinated phase-separated polymer ion gel electrolytes can generate stable LiF-rich interfacial films at the positive and negative electrode interfaces, enabling efficient cycling of batteries assembled based on solid-state lithium metal and high-voltage cathode materials. The addition of ionic liquids allows the fluorinated phase-separated polymer ion gel electrolyte to form a composite phase structure of solid and liquid phases. This not only reduces the crystallinity of the polymer formed by cross-linking polymerization of fluorinated acrylate monomers and carbon-carbon double bond cross-linking agents, thus improving the overall ionic conductivity of the fluorinated phase-separated polymer ion gel electrolyte, but also simultaneously improves the oxidative stability, application safety, and mechanical flexibility of the fluorinated phase-separated polymer ion gel electrolyte. It effectively suppresses the growth of lithium dendrites (Young's modulus reaches 1 / 1000 of the Young's modulus of lithium metal 9 GPa) and adapts to large volume changes (expansion rate >300%), avoiding short circuits and thermal runaway in lithium metal batteries under conditions such as overcharging, over-discharging, or mechanical impact. This provides a new approach and solution for the practical application of solid-state lithium batteries. Attached Figure Description

[0019] Figure 1 SEM image of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1;

[0020] Figure 2 Temperature impedance diagram of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1;

[0021] Figure 3Linear sweep voltammetry curve of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1;

[0022] Figure 4 The It curves and impedance spectra before and after polarization of the Li / / Li symmetric cell prepared using the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1 are shown.

[0023] Figure 5 Rate cycling diagram of the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled in Application Example 1;

[0024] Figure 6 Cycling diagram of the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled in Application Example 1 at room temperature and 0.5C current density;

[0025] Figure 7 This is a folded diagram of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1. Detailed Implementation

[0026] This invention provides a fluorinated phase-separated polymer ion gel electrolyte, comprising a solid phase and a liquid phase; wherein the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds;

[0027] The liquid phase comprises an ionic liquid and a lithium salt dissolved in the ionic liquid.

[0028] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0029] The fluorinated phase-separated polymer ion gel electrolyte provided by the present invention comprises a solid phase; the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds.

[0030] In one embodiment, the fluorinated acrylate monomer has the structural formula CH2=CHCOO-R, where R=-CH2CH2F, -CH2CF3, -CH2-CF2-CF2H, -CH2-CHF-CF3, -CH2-CF2-CF3, -CH2-CF2H-CHF-CF3, and -CH2-CF2-CF2-CF2-CF2H, with -CH2-CF2H-CHF-CF3 being a specific embodiment. The fluorinated acrylate monomer includes one or more of fluoroethyl acrylate, trifluoroethyl acrylate, tetrafluoropropyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, and octafluoropentyl acrylate, with hexafluorobutyl acrylate being a specific embodiment. The fluorine content in the fluorinated acrylate monomer is 16-53% by mass, with 48% being a specific embodiment.

[0031] When fluorine is located on the side chain of a fluorinated acrylate monomer, the strongly electronegative fluorine atom on the side chain interacts electrostatically with the anions in the fluorinated phase-separated polymer ion gel electrolyte, capturing and passivating the anions, increasing the relative migration rate of lithium ions, and increasing the lithium ion transference number. When fluorine is in the main chain of a fluorinated acrylate monomer and is close to the ester group, it produces a stronger electron-withdrawing effect, leading to a devaluation of the binding energy between the carbonyl oxygen and lithium ions, which may reduce ionic conductivity. When fluorine is located in the side chain of a fluorinated acrylate monomer, if the position is appropriate, it can weaken the interaction between lithium ions and the solvent, making lithium ions easier to migrate and helping to improve lithium ion conductivity. When fluorine is in the main chain of a fluorinated acrylate monomer, it can make the copolymer main chain have high chemical stability and rigidity, which is conducive to the formation of a stable SEI film. When fluorine is in the side chain of a fluorinated acrylate monomer, it can react with the electrode surface to promote the formation of a uniform and stable fluorine-rich SEI film. The presence of fluorine atoms can enhance the oxidative stability of the fluorinated phase-separated polymer ion gel electrolyte. When the fluorination position is close to the ester group or highly fluorinated, it can enhance high-voltage stability by reducing the highest occupied molecular orbital (HOMO) level.

[0032] As one embodiment, the preparation method of the fluorinated acrylate monomer includes the following steps: mixing acrylic acid, fluorinated alcohol, polymerization inhibitor and solid acid catalyst, and carrying out esterification reaction to obtain fluorinated acrylate monomer.

[0033] In one embodiment, the acrylic acid includes substituted acrylic acid with substituents and / or unsubstituted acrylic acid (C3H4O2); the substituted acrylic acid with substituents is methacrylic acid (C4H6O2).

[0034] In one embodiment, the fluorinated alcohol includes one or more of fluoroethanol, trifluoroethanol, tetrafluoropropanol, pentafluoropropanol, hexafluorobutanol, and octafluoropentanol, with hexafluorobutanol being used in a specific embodiment; the molar ratio of acrylic acid to the fluorinated alcohol is >1:1, another embodiment is >1:1 and <1.5:1, with 1.2:1 being used in a specific embodiment.

[0035] In one embodiment, the polymerization inhibitor includes one or more of diphenylsulfide, phenothiazine, hydroquinone monomethyl ether, hydroquinone, phenol, 2,6-di-tert-butyl-4-methylphenol, 4-hydroxy-2,2,6,6-tetramethylpiperidine nitroxide radical, and 4-oxo-2,2,6,6-tetramethylpiperidine nitroxide radical, with hydroquinone being a specific example. The mass of the polymerization inhibitor is 1-3% of the total mass of the acrylic acid and the fluorinated alcohol, with 1%, 1.5%, 2%, 2.5%, or 3% being specific examples. This invention sets the amount of polymerization inhibitor within the above range, which avoids both insufficient polymerization inhibition due to too low an amount and increased costs due to too high an amount.

[0036] In one embodiment, the solid acid catalyst includes one or more of the following: metal salt solid acid catalysts, heteropolyacid catalysts, ion exchange resin catalysts, and supported acid catalysts. Specifically, in this embodiment, it is a metal salt solid acid catalyst. The metal salt solid acid catalyst is a sulfate. The sulfate includes one or more of MgSO4, Fe2(SO4)3, and ZnSO4, specifically MgSO4. The heteropolyacid catalyst includes phosphotungstic acid and / or silicotungstic acid, specifically phosphotungstic acid. The ion exchange resin catalyst is... The styrene-divinylbenzene copolymer sulfonic acid type resin; the supported acid catalyst comprises a porous support and a liquid acid supported on the surface and pores of the porous support; the porous support comprises activated carbon and / or silica, specifically activated carbon in the embodiment; the liquid acid comprises sulfuric acid and / or phosphoric acid, specifically phosphoric acid in the embodiment; the mass of the solid acid catalyst is 0.5% to 20% of the total mass of the acrylic acid and fluorinated alcohol, specifically 0.5%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20% in the embodiment.

[0037] In one embodiment, the temperature of the esterification reaction is 90–110°C, specifically 90°C, 95°C, 100°C, 105°C, or 110°C in specific embodiments; the heating rate to the esterification reaction is 5–20°C / min, specifically 5–10°C / min in specific embodiments. In this invention, the esterification reaction solution is sampled 10 minutes after the start of the esterification reaction, and the content of hexafluorobutanol in the esterification reaction solution is analyzed to track the progress of the esterification reaction. When the content of hexafluorobutanol in the esterification reaction solution is <1 wt%, the esterification reaction is terminated.

[0038] In one embodiment, the mixing and esterification reactions are carried out under stirring conditions; the present invention does not have a particular limitation on the stirring rate, as long as it is sufficient to mix the materials evenly.

[0039] In one embodiment, after the esterification reaction, the process further includes: sequentially filtering, washing, separating, and distilling the reaction solution after the esterification reaction to obtain fluorinated acrylate monomers; the washing reagent is a saturated aqueous solution of sodium bicarbonate; the washing continues until the residual amount of acrylic acid in the organic phase obtained from the separation is <0.1 wt%; the distillation equipment is a distillation column; the top temperature of the distillation column is 105-108°C, specifically 105-106°C in this embodiment, and the bottom temperature is 112-115°C, specifically 112-114°C in this embodiment; the reflux ratio is controlled to be 1-2 during the distillation process, specifically 2 in this embodiment; the preboiler produced during the distillation process is monitored, and after the purity of the fluorinated acrylate monomers in the preboiler reaches 96 wt%, all fractions are collected to obtain the fluorinated acrylate monomers.

[0040] In one embodiment, the carbon-carbon double bond-containing crosslinking agent includes one or more of acrylamide, N,N-methylenebisacrylamide, methoxy polyethylene glycol acrylate, polyethylene glycol diacrylate, pentaerythritol tetraacrylate, and trimethylolpropane triacrylate. In a specific embodiment, it is N,N-methylenebisacrylamide or polyethylene glycol diacrylate. The number average molecular weight of the polyethylene glycol diacrylate is 575 g / mol. The mass ratio of the fluorinated acrylate monomer to the carbon-carbon double bond-containing crosslinking agent is (5-50):(0.1-10). In another embodiment, it is (10-40):(0.1-6). In a specific embodiment, it is (15-30):(0.1-5).

[0041] As one embodiment, the preparation method of the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds includes the following steps: mixing the fluorinated acrylate monomer, the crosslinking agent containing carbon-carbon double bonds and the photoinitiator, and carrying out a crosslinking polymerization reaction under light irradiation to obtain the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds.

[0042] In one embodiment, the photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP), 1-hydroxycyclohexylphenyl ketone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, with 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) or 1-hydroxycyclohexylphenyl ketone in a specific embodiment; the mass ratio of the fluorinated acrylate monomer to the photoinitiator is (5-50):(0.1-5), another embodiment is (10-40):(0.1-3), and a specific embodiment is (15-30):(0.1-2).

[0043] In one embodiment, the light source for the irradiation is ultraviolet light; the wavelength of the ultraviolet light is 200–380 nm, specifically 365 nm in this embodiment; the irradiation time is 3–60 min, specifically 3 min, 5 min, 10 min, 20 min, 30 min, or 60 min in this embodiment; and the irradiation intensity is 50–200 mW / cm². 2 In a specific embodiment, it is 50mW / cm 2 100mW / cm 2 150mW / cm 2 Or 200mW / cm 2The carbon-carbon double bonds in the fluorinated acrylate monomer and the carbon-carbon double bonds in the crosslinking agent undergo a crosslinking polymerization reaction to form a long-chain polymer compound. This invention limits the light source, wavelength, time, and intensity of the light irradiation within the aforementioned ranges, enabling the crosslinking polymerization reaction to proceed more fully and further improving the electrochemical performance of the resulting product.

[0044] The fluorinated phase-separated polymer ion gel electrolyte provided by the present invention includes a liquid phase; the liquid phase includes an ionic liquid and a lithium salt dissolved in the ionic liquid.

[0045] In one embodiment, the organic cation in the ionic liquid includes one or more of 1-vinyl-3-methylimidazolium, 1-methyl-1-allylpyrrolidine, 1-methyl-1-propylpyrrolidineonium, 1-ethyl-3-methylimidazolium, and 1-n-butyl-1-methylpyrrolidine, and the anion includes one or more of bis(trifluoromethanesulfonyl)imide ion, bis(trifluoromethanesulfonamide) ion, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, and dinitrileamine ion.

[0046] In another embodiment, the ionic liquid comprises 1-vinyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-methyl-1-allylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, 1-methyl-1-propylpyrrolidineonium bis(fluorosulfonyl)imide, 1-methyl-1-propylpyrrolidineonium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-3-methylimidazolium dinitrileamine salt, and 1-n-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide At least one of the following, specifically in the embodiments, is one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-propylpyrrolidineonium bis(fluorosulfonyl)imide and 1-n-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide; the mass ratio of the fluorinated acrylate monomer to the ionic liquid is (5-50):(20-70), another embodiment is (10-40):(20-60), and in the specific embodiment it is (15-30):(15-40).

[0047] In one embodiment, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium tetrafluoroborate, and lithium difluorooxalate borate. In a specific embodiment, it is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, and lithium nitrate. The mass ratio of the ionic liquid to the lithium salt is (20-70):(10-45), another embodiment is (20-60):(10-40), and in a specific embodiment, it is (20-50):(15-40).

[0048] In one embodiment, the thickness of the fluorinated phase-separated polymer ion gel electrolyte is 100-150 μm, and in a specific embodiment it is 108 μm.

[0049] This invention also provides a method for preparing the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution, comprising the following steps:

[0050] Fluorinated acrylate monomers, carbon-carbon double bond crosslinking agents, ionic liquids, lithium salts, and photoinitiators are mixed, and the resulting precursor solution is coated onto a substrate. After crosslinking polymerization under light irradiation, the substrate is removed to obtain a fluorinated phase-separated polymer ion gel electrolyte.

[0051] In one embodiment, the fluorinated acrylate monomer, the carbon-carbon double bond crosslinking agent, the ionic liquid, the lithium salt, and the photoinitiator are mixed as follows: the fluorinated acrylate monomer and the carbon-carbon double bond crosslinking agent are mixed and stirred for a first time to obtain a monomer solution; the ionic liquid and the lithium salt are mixed and stirred for a second time to obtain an ionic liquid solution; the monomer solution, the ionic liquid solution, and the photoinitiator are mixed and ultrasonically dispersed to obtain a precursor solution; the first and second stirring are mechanical stirring; the temperature of the first and second stirring is independently 25-30°C, specifically 25°C in this embodiment; the rotation speed is independently 300-500 rpm, specifically 300 rpm, 400 rpm, or 500 rpm in this embodiment; the time is independently 6-24 h, specifically 6 h, 12 h, 18 h, or 24 h in this embodiment; the ultrasonic dispersion temperature is 25-30°C, specifically 25°C in this embodiment; the time is 30-120 min, specifically 30-60 min in this embodiment; and the power is 10-100 W, specifically 50 W in this embodiment.

[0052] This invention enables the components to be mixed more evenly by controlling the rotation speed, temperature, and time of the first and second stirring.

[0053] In one embodiment, the substrate is a glass substrate; the glass substrate is prepared by sandwiching three spacers between two glass substrates to obtain the glass substrate; the thickness of each spacer is 40 μm; the size of the glass substrate is 10 × 10 cm. 2 .

[0054] As one implementation method, the specific parameters for the crosslinking polymerization reaction under light irradiation are as described above and will not be repeated here.

[0055] The present invention does not have any particular limitation on the method of removing the substrate; any method known in the art may be used.

[0056] This invention synthesizes elastomer monomers (fluorinated acrylate monomers) with different degrees of fluorination and fluorination sites, and constructs a fluorinated phase-separated polymer ion gel electrolyte with high ionic conductivity, high mechanical strength and stable interfacial performance by using polymerization-induced phase separation technology. Solid-state lithium metal batteries (LMBs) assembled with this electrolyte surpass the level of existing liquid lithium metal batteries in terms of high rate, low temperature, long cycle stability and safety.

[0057] The present invention also provides the application of the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method described in the above technical solution in lithium metal batteries.

[0058] The present invention also provides a lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte; wherein the electrolyte is the fluorinated phase-separated polymer ion gel electrolyte described in the above technical solution or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method described in the above technical solution.

[0059] In one embodiment, the fluorinated phase-separated polymer ion gel electrolyte is located between the positive and negative electrodes; the positive electrode includes a substrate and a positive electrode coating coated on the substrate; the components of the positive electrode coating include a positive electrode active material, a conductive agent, and a binder; the positive electrode active material is lithium iron phosphate (LFP) or a nickel-cobalt-manganese ternary material, specifically a nickel-cobalt-manganese ternary material; the nickel-cobalt-manganese ternary material is NCM811 or NCM622, specifically NCM811; the conductive agent is carbon black; the binder is polyvinylidene fluoride; the substrate is aluminum, specifically aluminum foil; the mass ratio of the positive electrode active material, conductive agent, and binder is 80:10:10; the thickness of the aluminum material is 20–60 μm, specifically 23 μm; the thickness of the positive electrode coating is 30–120 μm, specifically 60 μm.

[0060] As one embodiment, the preparation method of the positive electrode includes the following steps: mixing positive electrode active material, conductive agent, binder and organic solvent, stirring to obtain a slurry; coating the slurry onto a substrate, drying to obtain the positive electrode; the organic solvent includes N-methylpyrrolidone; the mass of the organic solvent is 2 to 3 times the total mass of the positive electrode active material, conductive agent and binder, specifically 2.6 times; the stirring is magnetic stirring; the stirring speed is 100 to 500 rpm, specifically 200 rpm, and the time is 12 to 24 hours, specifically 24 hours; the drying temperature is 80 to 120°C, specifically 120°C, and the time is 12 to 24 hours, specifically 24 hours; the drying is vacuum drying; the vacuum degree of the vacuum drying is 0 to 0.1 MPa, specifically 0.016 MPa; the positive electrode is a circular electrode sheet with a diameter of 12 to 16 mm, specifically 13 mm.

[0061] In one embodiment, the negative electrode includes a metal material, a graphite material, or a silicon-based material; the metal material is a lithium sheet; the thickness of the negative electrode is 400–600 μm, and in a specific embodiment it is 500–600 μm.

[0062] In one embodiment, the lithium metal battery is a button cell battery; the button cell battery is a 2025 type button cell battery. The present invention does not impose any particular limitation on the preparation method of the lithium metal battery; any preparation method well known to those skilled in the art can be used.

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0064] Example 1

[0065] (1) Preparation of hexafluorobutyl acrylate:

[0066] Hexafluorobutanol, acrylic acid, polymerization inhibitor (hydroquinone), and solid acid catalyst (magnesium sulfate) were added to a 1.5L three-necked flask equipped with a mechanical stirrer, reflux condenser, exhaust gas absorption and emission device, and thermometer. Stirring was started. The molar ratio of acrylic acid to hexafluorobutanol was 1.2:1. The amount of solid acid catalyst was 10 wt% of the total mass of hexafluorobutanol and acrylic acid, and the amount of polymerization inhibitor was 2 wt% of the total mass of hexafluorobutanol and acrylic acid. Microwave heating was initiated, and the temperature was increased to 100℃ at a rate of 5℃ / min to initiate the esterification reaction. Sampling and analysis were started 10 minutes after the reaction to monitor the reaction. When the sampled reaction solution showed... When the content of hexafluorobutanol is <1wt%, the esterification reaction is terminated to obtain a reaction solution containing hexafluorobutyl acrylate. The filtrate obtained by filtration is washed and separated into layers with a saturated aqueous solution of sodium bicarbonate at a volume ratio of 1:1 until the residual amount of acrylic acid in the organic phase of hexafluorobutyl acrylate obtained by separation is <0.1wt%. The washing process is then terminated. Then, the solution is distilled in a distillation column with a top temperature of 105℃ and a bottom temperature of 112℃. The reflux ratio is controlled at 2. The foreboiling fraction is tracked. When the purity of hexafluorobutyl acrylate in the foreboiling fraction reaches 96wt%, all fractions are collected to obtain hexafluorobutyl acrylate with a yield of 80% and a purity of 96%.

[0067] (2) Preparation of fluorinated phase-separated polymer ion gel electrolyte:

[0068] 0.16 g of the above-mentioned hexafluorobutyl acrylate and 0.04 g of polyethylene glycol diacrylate (Mn = 575 g / mol) were mixed at 25 °C and stirred at 300 rpm for 6 h to obtain a monomer solution; 0.33 g of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 0.32 g of lithium bis(trifluoromethanesulfonyl)imide were mixed at 25 °C and stirred at 300 rpm for 12 h to obtain an ionic liquid solution; the monomer solution and the ionic liquid solution were mixed with 5 mg of 2-hydroxy-2-methyl-1-phenyl-1-propanone and ultrasonically dispersed at 25 °C for 30 min at 50 W to obtain a precursor solution; the precursor solution was dropwise added to a glass substrate (with three 40 μm thick spacers sandwiched between two 10 × 10 cm substrates). 2 A crosslinking polymerization reaction was carried out on the glass substrates between them under ultraviolet light irradiation. The wavelength of the ultraviolet light was 365 nm, the irradiation time was 20 min, and the light intensity was 50 mW / cm². 2 The glass plate was removed to obtain a fluorinated phase-separated polymer ion gel electrolyte with a thickness of 100 μm (108 μm).

[0069] Example 2

[0070] The difference from Example 1 is that the ionic liquid is replaced with 1-methyl-1-propylpyrrolidine onium bis(fluorosulfonyl)imide, and the rest is the same as in Example 1.

[0071] Example 3

[0072] The difference from Example 1 is that the fluorinated monomer is replaced with trifluoroethyl acrylate, and the rest is the same as in Example 1.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that the ionic liquid is removed; otherwise, the contents are the same as in Example 1.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that the fluorinated monomer and crosslinking agent are removed, while the rest is the same as in Example 1.

[0077] Application Example 1

[0078] A viscous slurry was formed by adding 80% by mass of lithium iron phosphate material (NCM811 material), 10% carbon black, and 10% polyvinylidene fluoride (PVDF, as a binder) to N-methylpyrrolidone (5g by mass). The slurry was magnetically stirred at 200 rpm for 24 hours at 25°C to form a viscous slurry. The slurry was coated onto an aluminum foil with a thickness of 23 μm and placed in a vacuum drying oven. It was vacuum dried at 0.016 MPa and 120°C for 24 hours to form a positive electrode coating with a thickness of 50 μm. After drying, the material was cooled to room temperature and cut into circular electrode sheets with a diameter of 13 mm to obtain the positive electrode sheet.

[0079] The fluorinated phase-separated polymer ion gel electrolyte and positive electrode prepared in Example 1 were assembled with the negative electrode (lithium sheet, 600 μm thick) into a 2025 type button battery (NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery, abbreviated as NCM811 / / Li battery).

[0080] Performance testing

[0081] (1) Figure 1 This is a SEM image of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1. From... Figure 1 It can be seen that the fluorinated phase-separated polymer ion gel electrolyte prepared by the present invention has no obvious large-sized pores, the material surface is relatively regular, and the molecular cross-linking is relatively uniform, which is conducive to the transport of lithium ions. The fine texture on the surface is the aggregated structure of polymer molecular chains and the dispersed phase of additives.

[0082] (2) The conductivity of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1 was tested under different temperature conditions (30–80 °C). The trend of conductivity change with temperature is shown in the figure below. Figure 2 As shown. From Figure 2 It can be seen that the fluorinated phase-separated polymer ion gel electrolyte exhibits good ionic conductivity at different temperatures, reaching 5.29 × 10⁻⁶ at 30℃. -4 S·cm -1 .

[0083] (3) Figure 3 The linear sweep voltammetry curve is shown for the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1. Figure 3 It can be seen that the antioxidant potential of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1 is 5.3V, which is above 5V. This is because the introduced fluorinated monomer and ionic liquid are both high voltage resistant, which can improve the chemical stability of the fluorinated phase-separated polymer ion gel electrolyte to lithium metal and reduce its decomposition during charging and discharging.

[0084] (4) Figure 4 The image shows the It curves and impedance spectra before and after polarization of a Li / / Li symmetric battery prepared using the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1. The inset shows the impedance spectra before and after polarization. Figure 4 It can be seen that the lithium-ion transference number of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1 is 0.82 at room temperature. This is because the introduced ionic liquid can promote the dissociation of lithium salt, reduce the interaction between lithium ions and other ions, and make lithium ions more mobile in the lithium-ion system. The ionic liquid has high ionic conductivity and low viscosity, which can provide a relatively unobstructed transport channel for lithium ions, which is conducive to the migration of lithium ions. Moreover, the high t Li+ It can effectively alleviate concentration polarization and improve the rate capacity of the battery.

[0085] (5) Under conditions of 25℃, the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled according to Case 1 of the Xinwei Battery Cycling System was subjected to charge-discharge cycle tests at different rates. The results are as follows: Figure 5 , Figure 6 As shown. Among them, Figure 5 Rate cycling diagram of the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled in Application Example 1; Figure 6 Cycling plot of the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled in Application Example 1 at room temperature and 0.5C current density.

[0086] from Figure 5It can be seen that the 0.1C discharge specific capacity of the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled using Example 1 is 196.16 mAh·g. -1 The 0.2C discharge specific capacity is 189.65 mAh·g. -1 The 0.5C discharge specific capacity is 176.17 mAh·g. -1 The 1C discharge specific capacity is 158.34 mAh·g. -1 The 2C discharge specific capacity is 122.19 mAh·g. -1 When the current density returns to 1C and 0.5C respectively, the discharge specific capacity is comparable to the initial discharge specific capacity.

[0087] from Figure 6 It can be seen that the NCM811 / fluorinated phase-separated polymer ion gel electrolyte / Li battery assembled in Example 1 retains 98.55% of its capacity after 152 cycles.

[0088] The above indicates that the fluorocarbon and ionic liquid-driven polymer electrolyte prepared by this invention can provide the necessary Li + The transport channel suppresses side reactions on the Li metal surface and promotes uniform Li deposition, thereby achieving sufficient electrochemical durability to meet the practical requirements of solid-state lithium metal batteries.

[0089] (6) Figure 7 This is a folded diagram of the fluorinated phase-separated polymer ion gel electrolyte prepared in Example 1. From... Figure 7 As can be seen from the above, the fluorinated phase-separated polymer ion gel electrolyte prepared by the present invention can return to its original shape after being folded two and three times, indicating that it has flexibility.

[0090] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A fluorinated phase-separated polymer ion gel electrolyte, characterized in that, It includes a solid phase and a liquid phase; the solid phase is a copolymer of a fluorinated acrylate monomer and a crosslinking agent containing carbon-carbon double bonds; The fluorinated acrylate monomer is hexafluorobutyl acrylate or trifluoroethyl acrylate; The carbon-carbon double bond crosslinking agent is polyethylene glycol diacrylate; the mass ratio of the fluorinated acrylate monomer to the carbon-carbon double bond crosslinking agent is (5~50):(0.1~10); The liquid phase comprises an ionic liquid and a lithium salt dissolved in the ionic liquid; The organic cations in the ionic liquid include one or more of 1-vinyl-3-methylimidazolium, 1-methyl-1-allylpyrrolidine, 1-methyl-1-propylpyrrolidineonium, 1-ethyl-3-methylimidazolium, and 1-n-butyl-1-methylpyrrolidine, and the anions include one or more of bis(trifluoromethanesulfonyl)imide ion, bis(trifluoromethanesulfonamide) ion, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, and dinitrileamine ion; The mass ratio of the fluorinated acrylate monomer to the ionic liquid is (5~50):(20~70).

2. The fluorinated phase-separated polymer ion gel electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

3. The fluorinated phase-separated polymer ion gel electrolyte according to claim 1, characterized in that, The preparation method of the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds includes the following steps: mixing the fluorinated acrylate monomer, the crosslinking agent containing carbon-carbon double bonds and the photoinitiator, and carrying out a crosslinking polymerization reaction under light irradiation to obtain the copolymer of the fluorinated acrylate monomer and the crosslinking agent containing carbon-carbon double bonds.

4. The fluorinated phase-separated polymer ion gel electrolyte according to claim 3, characterized in that, The photoinitiator includes at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

5. The method for preparing the fluorinated phase-separated polymer ion gel electrolyte according to any one of claims 1 to 4, characterized in that, Includes the following steps: Fluorinated acrylate monomers, carbon-carbon double bond crosslinking agents, ionic liquids, lithium salts, and photoinitiators are mixed, and the resulting precursor solution is coated onto a substrate. After crosslinking polymerization under light irradiation, the substrate is removed to obtain a fluorinated phase-separated polymer ion gel electrolyte.

6. The application of the fluorinated phase-separated polymer ion gel electrolyte according to any one of claims 1 to 4 or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method according to claim 5 in lithium metal batteries.

7. A lithium metal battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the fluorinated phase-separated polymer ion gel electrolyte according to any one of claims 1 to 4 or the fluorinated phase-separated polymer ion gel electrolyte prepared by the preparation method according to claim 5.

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