An ionic liquid gel polymer electrolyte suitable for large-scale positive electrode in-situ coating and its preparation method and application

Abstract

The present invention discloses an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes, as well as its preparation method and application. The raw materials of the polymer electrolyte, measured in parts by weight, include: 30-50 parts of a polymer monomer prepolymer slurry; 5-20 parts of an ionic liquid; 10-40 parts of a lithium salt; 5-10 parts of an inorganic filler; 5-10 parts of a cross-linking agent; and 0.05-2 parts of a photoinitiator. The polymer monomer prepolymer slurry is a mixture of a copolymer and a monomer comprising polyethylene glycol methyl ether acrylate and a functional acrylate monomer having a monofunctional group. The ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes provided by the present invention can achieve a tight positive electrode-electrolyte interface between the positive electrode and the solid electrolyte, reduce interfacial impedance, and improve the cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical lithium metal batteries, and particularly relates to an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes, and a preparation method and application thereof. Background Art

[0002] With the rapid development of electronic devices, current lithium-ion batteries face the problem of compatibility between high specific energy and high safety. Recently, lithium metal batteries have been widely used due to their highest specific capacity (3860mAh g -1 ) and the lowest electrochemical potential (-3.04V compared to the standard hydrogen electrode) have attracted much attention. However, lithium metal batteries can experience lithium dendrite growth during charge and discharge. These dendrites can pierce the separator, leading to a short circuit. This short circuit can cause thermal runaway, decomposing the electrolyte within the battery, and potentially leading to fire and explosion.

[0003] Solid electrolytes have excellent rigidity and can effectively inhibit the growth of dendrites. Currently, solid electrolytes are divided into inorganic solid electrolytes, organic solid electrolytes and organic-inorganic hybrid composite solid electrolytes. Among them, composite solid electrolytes have both good rigidity and flexibility, and can effectively inhibit the piercing of dendrites. Ionic liquids are low-temperature or room-temperature molten salts composed of anions and cations. They have high boiling points and are not easy to burn. In polymer electrolytes, they can achieve fast ion conduction, wet the interface, and improve ion conductivity. They are the key to effectively reducing the impedance of the interface and achieving stable circulation of solid electrolytes. The in-situ polymerization method can make the connection between the electrode and the electrolyte tight, reduce the interface impedance, and improve the battery cycle stability.

[0004] Currently, the methods for preparing polymer electrolytes are divided into electrospinning, solvent coating, hot pressing, thermal polymerization, and photopolymerization. Both electrospinning and hot pressing require expensive equipment and are inefficient. Solvent coating uses toxic solvents such as anhydrous acetonitrile, dimethylformamide, and N-methylpyrrolidone. Furthermore, these methods result in lengthy processes for preparing polymer electrolyte membranes. Thermal polymerization, on the other hand, requires significant energy and has low reaction efficiency, making it difficult to achieve continuous, large-scale production of uniform composite solid electrolytes in actual industrial production.

[0005] Acrylate is a polymer monomer material that is relatively easy to photopolymerize. It can realize monomer free radical polymerization under the action of photoinitiator and ultraviolet light, and the preparation method is simple and efficient. The photopolymerization curing method currently used to prepare solid electrolytes has the problem of being unable to be applied on a large scale. Most photopolymerizable acrylate monomers do not have the thixotropy of non-Newtonian fluids, that is, they do not have good controllability of coating thickness, resulting in the use of in-situ polymerization in the battery or auxiliary film-forming templates for photocuring the electrolyte membrane during the preparation process. These methods will bring challenges to the large-scale production of battery assembly. CN111509186B discloses a lithium-ion solid-state battery positive electrode and its preparation process and lithium-ion solid-state battery, specifically, a solid electrolyte coating slurry is coated on the positive electrode. This method adds N-methylpyrrolidone (NMP) to the slurry. The addition of solvent requires subsequent long-term solvent volatilization to be removed, resulting in defects caused by solvent volatilization on the surface of the electrolyte. Too long a solvent volatilization time will directly affect the efficiency of the overall preparation process. CN114142098A discloses a method for preparing a 3D-printed solid-state battery and its application. Specifically, a large amount of electrolyte (50-80%) is added to the 3D printing ink. Excessive electrolyte components will affect the battery's cycle performance. In addition, due to the low ratio of polymerized monomers to inorganic fillers, the mechanical properties of the resulting electrolyte layer will also be affected. This patent uses 3D printing ink to prepare the electrode in situ electrolyte layer through a two-step process, which is relatively cumbersome. The 3D printing ink does not have large-scale applicability in the first step and is limited to the preparation of single-chip electrodes. CN111430791B discloses an in-situ polymerized polycaprolactone-based all-solid-state electrolyte and its preparation method and application. The coated electrode mentioned in the patent is prepared by coating a polycaprolactone-based acrylate on the surface of a stainless steel electrode. Although the electrolyte can have good interfacial contact on the stainless steel, this preparation process still increases the assembly process of the battery in actual production and is not fully suitable for large-scale preparation.

[0006] It can be seen that the existing technology for the preparation of in-situ self-supporting polymer electrolytes for positive electrodes is still imperfect and has certain defects. Therefore, there is an urgent need to improve the preparation method and electrolyte formulation. The present invention proposes a type of ionic liquid gel polymer electrolyte. By regulating the viscosity of the polymer prepolymer slurry, in-situ coating on the positive electrode surface is achieved, and the positive electrode self-supporting polymer electrolyte can be prepared on a large scale, thereby simplifying the preparation process of solid-state lithium batteries, reducing the internal resistance of the battery, and improving the battery performance. This method has broad application prospects and is applicable to the application of a variety of organic-inorganic hybrid composite solid electrolytes. Summary of the Invention

[0007] The purpose of the present invention is to solve the deficiencies of the prior art and to provide an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes, as well as a preparation method and application thereof.

[0008] The present invention addresses the issues of capacity decay in the application of solid-state electrolytes for lithium batteries due to excessive interfacial impedance, the use of toxic solvents during preparation, and the lengthy and difficult large-scale preparation process. The invention invents an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes and its preparation method, achieving a green, solvent-free, and scalable coating process. The method is applicable to a variety of organic-inorganic hybrid solid electrolyte systems. The self-supporting in-situ coating-type positive electrode gel polymer electrolyte prepared by the present invention has good cycle performance and mechanical properties, and a good positive electrode-electrolyte contact interface. This simple and rapid preparation method significantly eliminates the dependence on solvents and the use of electrolyte and positive electrode composite equipment, which helps simplify the battery assembly process and solves the impedance problem of the positive electrode-electrolyte interface contact.

[0009] The ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes provided by the present invention can achieve a tight positive electrode-electrolyte interface between the positive electrode and the solid electrolyte, reduce the interface impedance, and improve the cycle stability of the battery.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] An ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes, wherein the raw materials of the polymer electrolyte, measured in parts by weight, include:

[0012]

[0013] The polymer monomer prepolymer slurry is a mixture of a copolymer and a monomer including polyethylene glycol methyl ether acrylate and a functional acrylate monomer having a monofunctional group, wherein the functional acrylate monomer having a monofunctional group is one or more of tetrahydrofurfuryl (meth)acrylate, ethoxylated tetrahydrofuran acrylate, glycidyl methacrylate, and 4-acryloylmorpholine.

[0014] Preferably, the ionic liquid comprises one or two of N-methyl-N-butylpyrrole bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide;

[0015] Preferably, the polyethylene glycol methyl ether acrylate includes a molecular structure of H2C=CHCO2(CH2CH2O) nOne or more CH3 acrylic ester monomers, wherein n represents the number of repetitions of the side chain ethylene glycol group (CH2CH2O) of the acrylic ester monomer, and the value of n ranges from 2 to 20.

[0016] Preferably, the cross-linking agent includes one or more of polyethylene glycol diacrylate, pentaerythritol triacrylate, propylene glycol di(meth)acrylate, and trimethylolpropane triacrylate.

[0017] Preferably, the inorganic filler includes one or more of lithium lanthanum zirconium oxide LLZO, lithium lanthanum zirconium aluminum oxide LLZAO, and lithium lanthanum zirconium tantalum oxide LLZTO; the inorganic filler is spherical particles; and the particle size of the inorganic filler is within 500 nm.

[0018] Preferably, the lithium salt includes one or two of lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(oxalatoborate) LiBOB, lithium difluorooxalatoborate LiDFOB, lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, and lithium nitrate LiNO3;

[0019] Preferably, the photoinitiator includes one or more of 651 benzil dimethyl ether, TPO (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide, benzophenone, 2,4-diethylthioxanthone, and 2-hydroxy-2-methylphenylpropane-1-one.

[0020] The above-mentioned method for preparing an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of a positive electrode comprises the following steps:

[0021] (1) Preparation of polymer monomer prepolymer slurry: Polyethylene glycol methyl ether acrylate, a functional acrylate monomer having a monofunctional group, and a photoinitiator are blended, and ultraviolet light-initiated polymerization is carried out under inert gas to obtain a polymer monomer prepolymer slurry having a viscosity of 300-10000 cP, and then the polymerization reaction is stopped; the polymer monomer prepolymer slurry has good thixotropy;

[0022] (2) Mixing raw materials: stirring and mixing the crosslinking agent, polymer monomer prepolymer slurry, ionic liquid, lithium salt, photoinitiator and inorganic filler;

[0023] (3) Coating: The mixed slurry obtained in step (2) is evenly coated on the surface of the positive electrode material, and the coating thickness of the solid electrolyte slurry is 20 μm-300 μm;

[0024] (4) UV curing: The coated slurry is UV cured to obtain an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes.

[0025] Preferably, in step (1), the ratio of the polyethylene glycol methyl ether acrylate, the functional acrylate monomer having a monofunctional group, and the photoinitiator is 80:20:0.5-90:10:0.5;

[0026] Preferably, the inert gas in step (1) is nitrogen;

[0027] Preferably, the curing energy of the UV curing in step (4) is 500-5000 mJ.

[0028] Preferably, the coating method in step (3) includes any one of blade coating, wire rod coating, slit coating and transfer roller coating.

[0029] Preferably, the positive electrode material in step (3) includes any one of NCM ternary material, NCA ternary material, lithium iron phosphate, and lithium cobalt oxide.

[0030] The application of the above-mentioned ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes in the preparation of lithium metal solid-state batteries.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The present invention uniformly disperses commercial inorganic additive particles, ionic liquid, crosslinking agent, and photoinitiator in a pre-polymerized slurry, and uses ultraviolet light to initiate polymerization to prepare an ionic liquid gel composite polymer electrolyte for in-situ printing of the positive electrode. The prepared electrolyte has good interface contact with the positive electrode, can effectively reduce the internal resistance of the battery, and simplify the process of solid-state lithium battery assembly.

[0033] (2) The addition of trace amounts of ionic liquids can effectively improve the thermal stability of the electrolyte, effectively improve the cycle performance of the entire battery, and inhibit the growth of lithium dendrites.

[0034] (3) After the mixture is polymerized, a comb-like cross-linked network polymer is formed. The side chains of the comb-like polymer are polyethylene glycol methyl ether and functional monomer functional groups. The comb-like structure is beneficial to reducing the crystallinity of the polymer and increasing the amorphous state, while the cross-linked network structure formed by PEGDA at both ends is beneficial to improving the flexibility and mechanical strength of the electrolyte.

[0035] (4) This method is suitable for large-scale in-situ printing of ionic liquid gel polymer electrolytes for positive electrodes. No solvent is required during the polymerization process, which can avoid the tedious process of solvent evaporation. This method can not only achieve controllable electrolyte coating size, but also be compatible with a variety of organic-inorganic composite electrolyte systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1This is a scanning electron microscope cross-sectional morphology of the positive electrode self-supporting gel polymer electrolyte prepared in Example 2;

[0037] Figure 2 Flowchart of the preparation method of the composite polymer electrolyte with in-situ coating of the positive electrode involved in Examples 1-7 of the present invention and the comparative examples;

[0038] Figure 3 This is a constant current charge and discharge curve diagram of a lithium-on-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 1;

[0039] Figure 4 This is a constant current charge and discharge curve diagram of a lithium-on-lithium symmetrical battery assembled with a solid-state lithium battery polymer electrolyte obtained in Example 2;

[0040] Figure 5 The constant current charge-discharge curve of a lithium-on-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 3;

[0041] Figure 6 The constant current charge-discharge curve of a lithium-on-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 4;

[0042] Figure 7 The constant current charge-discharge curve of a lithium-on-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 5;

[0043] Figure 8 This is a full battery cycle performance diagram of the polymer electrolyte in-situ coated lithium iron phosphate positive electrode obtained in Example 1;

[0044] Figure 9 This is a full battery cycle performance diagram of the lithium iron phosphate positive electrode in situ coated with a polymer electrolyte obtained in Example 2;

[0045] Figure 10 This is a full battery cycle performance diagram of lithium iron phosphate assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 1.

[0046] Figure 11 The constant current charge and discharge curve of the lithium-on-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 2;

[0047] Figure 12 This is the constant current charge-discharge curve of a lithium-on-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 3;

[0048] Figure 13 This is the constant current charge and discharge curve of a lithium-on-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 4;

[0049] Figure 14This is the constant current charge and discharge curve of a lithium-on-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 5. Specific implementation methods

[0050] The specific implementation of the present invention is further described below in conjunction with specific embodiments, but the implementation of the present invention is not limited thereto.

[0051] Example 1

[0052] Preparation of positive electrode sheet: 70% lithium iron phosphate, 10% PVDF, 10% PEO, 10% Super P and NMP were mixed and stirred evenly to obtain positive electrode slurry, and then the slurry was evenly coated on the surface of the positive electrode collector of carbon-coated aluminum foil, and dried at 60°C for 24h to obtain the positive electrode sheet.

[0053] Preparation of polymer electrolyte slurry:

[0054] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =500), 20g of glycidyl methacrylate and 0.5g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25°C. The mixture was polymerized under ultraviolet light in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 3000 cP, after which the reaction was stopped;

[0055] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, lithium salt LiTFSI, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler LLZTO in amounts of 12 g, 2 g, 5 g, 0.15 g and 2 g to a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0056] Preparation of in-situ coated polymer electrolyte for positive electrode:

[0057] The prepared slurry was poured onto the positive electrode sheet, covered with a PET release film, and a 75 μm polymer electrolyte coating was applied using a scraper. The film was then irradiated under a UV lamp for 10 minutes with a curing energy of 2000 mJ to obtain a positive electrode-supported polymer electrolyte membrane.

[0058] The prepared positive electrode in situ printed polymer electrolyte was assembled with lithium sheets into a button-type full battery in an argon glove box.

[0059] Preparation of polymer electrolyte:

[0060] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0061] Example 2

[0062] Preparation of positive electrode sheet: 70% lithium iron phosphate, 10% PVDF, 10% PEO, 10% Super P and NMP were mixed and stirred evenly to obtain positive electrode slurry, and then the slurry was evenly coated on the surface of the positive electrode collector of carbon-coated aluminum foil, and dried at 60°C for 24h to obtain the positive electrode sheet.

[0063] Preparation of polymer electrolyte slurry:

[0064] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =1000), 20 g of 4-acryloylmorpholine ACMO and 0.5 g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25° C., and then polymerized under ultraviolet light with a curing energy of 1000 mJ in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 1000 cP, after which the reaction was stopped;

[0065] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, N-methyl-N-butylpyrrole di(trifluoromethylsulfonyl)imide salt, lithium salt LiPF6, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler LLZAO in amounts of 12 g, 2.5 g, 2.5 g, 5 g, 0.2 g and 3 g to a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0066] Preparation of in-situ coated polymer electrolyte for positive electrode:

[0067] The prepared slurry was poured onto the positive electrode sheet, covered with a PET release film, and a 75 μm polymer electrolyte coating was applied using a scraper. The film was then irradiated under a UV lamp for 10 minutes with a curing energy of 3000 mJ to obtain a positive electrode-supported polymer electrolyte membrane.

[0068] The prepared positive electrode in situ coated polymer electrolyte was assembled with lithium sheets into a button-type full cell in an argon glove box.

[0069] Preparation of polymer electrolyte:

[0070] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 3000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0071] Example 3

[0072] Preparation of polymer electrolyte slurry:

[0073] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =1000), 20g of tetrahydrofurfuryl (meth)acrylate and 0.5g of photoinitiator benzophenone were added to a four-necked flask and stirred at a constant temperature of 25°C. The mixture was polymerized by ultraviolet irradiation in a nitrogen atmosphere with a curing energy of 2000mJ to obtain a prepolymer slurry with a viscosity of about 3000cP;

[0074] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, lithium salt LiTFSI bis(trifluoromethylsulfonyl)imide lithium, photoinitiator benzophenone and inorganic filler LLZTO in amounts of 12 g, 2.5 g, 2.5 g, 5 g, 0.3 g and 3 g to a glass bottle and stir at 40 ° C for 2 h until uniformly mixed.

[0075] Preparation of polymer electrolyte:

[0076] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0077] Example 4

[0078] Preparation of polymer electrolyte slurry:

[0079] Step (1): 90g polyethylene glycol methyl ether acrylate (M w =1000), 10 g of tetrahydrofurfuryl (meth)acrylate and 0.5 g of photoinitiator TPO2,4,6-trimethylbenzoyl)diphenylphosphine oxide were added to a four-necked flask and stirred uniformly at a constant temperature of 25°C. The mixture was polymerized by ultraviolet irradiation in a nitrogen atmosphere with a curing energy of 2000 mJ to obtain a prepolymer slurry with a viscosity of about 3000 cP;

[0080] Step (2): The prepolymer slurry, crosslinker polypropylene glycol diacrylate, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, lithium salt LiClO4 lithium perchlorate, photoinitiator TPO2,4,6-trimethylbenzoyl)diphenylphosphine oxide and inorganic filler LLZTO were added into a glass bottle in amounts of 12 g, 3 g, 2.5 g, 12 g, 0.3 g and 3 g, and stirred at 40 ° C for 2 h until uniformly mixed.

[0081] Preparation of polymer electrolyte:

[0082] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0083] Example 5

[0084] Preparation of polymer electrolyte slurry:

[0085] Step (1): 90g polyethylene glycol methyl ether acrylate (M w =1000), 10 g of tetrahydrofurfuryl (meth)acrylate and 0.5 g of photoinitiator 651 benzil dimethyl ether were added to a four-necked flask and stirred at a constant temperature of 25° C., and polymerized under ultraviolet light in a nitrogen atmosphere with a curing energy of 2000 mJ to obtain a prepolymer slurry with a viscosity of about 3000 cP;

[0086] Step (2): Add the polymer monomer prepolymer slurry, crosslinker butanediol di(methyl)acrylate, lithium salt LiTFSI bis(trifluoromethylsulfonyl)imide lithium, photoinitiator 651 benzil dimethyl ether and inorganic filler LLZTO into a glass bottle in amounts of 12 g, 2.5 g, 8 g, 0.3 g and 3 g, and stir at 40 ° C for 2 h until mixed evenly.

[0087] Preparation of polymer electrolyte:

[0088] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 3000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0089] Example 6

[0090] Preparation of polymer electrolyte slurry:

[0091] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =1000), 20 g of glycidyl methacrylate and 0.5 g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25° C., and then polymerized under ultraviolet light in a nitrogen atmosphere with a curing energy of 2000 mJ to obtain a prepolymer slurry with a viscosity of about 3000 cP;

[0092] Step (2): Add the polymer monomer prepolymer slurry, crosslinker butanediol di(methyl)acrylate, lithium salt LiFSI bis(trifluoromethylsulfonyl)imide lithium, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler LLZTO into a glass bottle in amounts of 12 g, 3 g, 12 g, 0.4 g and 5 g, and stir at 40 ° C for 2 h until uniformly mixed.

[0093] The prepared polymer electrolyte slurry was poured onto the release film and coated by a doctor blade and then UV-cured for 10 min to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane with a curing energy of 2000 mJ. The obtained polymer electrolyte membrane was assembled into a lithium-to-lithium symmetrical battery. -2 At this current density, the polarization overpotential of the battery is above 600mV.

[0094] Example 7

[0095] Preparation of polymer electrolyte slurry:

[0096] Step (1): 90g polyethylene glycol methyl ether acrylate (M w =500), 10 g of 4-acryloylmorpholine ACMO and 0.5 g of photoinitiator 651 benzil bismethyl ether were added to a four-necked flask and stirred at a constant temperature of 25° C., and polymerized under ultraviolet light in a nitrogen atmosphere with a curing energy of 2000 mJ to obtain a prepolymer slurry with a viscosity of about 3000 cP;

[0097] Step (2): Add the polymer monomer prepolymer slurry, crosslinker pentaerythritol triacrylate, lithium salt LiTFSI bis(trifluoromethylsulfonyl)imide lithium, photoinitiator 651 benzil dimethyl ether and inorganic filler LLZTO into a glass bottle according to the mass of 12g, 4g, 12g, 0.5g and 7g, and stir at 40°C for 2h until mixed evenly.

[0098] Preparation of polymer electrolyte:

[0099] The prepared polymer electrolyte slurry was poured onto the positive electrode and then coated with a doctor blade and then UV-cured for 10 min with a curing energy of 3000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-to-lithium symmetrical battery and heated at 60 °C and 0.1 mA cm -2 At this current density, the polarization overpotential of the battery is above 800mV.

[0100] Comparative Example 1

[0101] Preparation of positive electrode sheet: 70% lithium iron phosphate, 10% PVDF, 10% PEO, 10% Super P and NMP were mixed and stirred evenly to obtain positive electrode slurry, and then the slurry was evenly coated on the surface of the positive electrode collector of carbon-coated aluminum foil, and dried at 60°C for 24h to obtain the positive electrode sheet.

[0102] Preparation of polymer electrolyte slurry:

[0103] Step (1): 80 g of polyethylene glycol methyl ether acrylate, 20 g of 4-acryloylmorpholine and 0.5 g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25° C., and then polymerized by ultraviolet light in a nitrogen atmosphere with a curing energy of 2000 mJ to obtain a prepolymer slurry with a viscosity of about 3000 cP;

[0104] Step (2): Add the polymer monomer prepolymer slurry, crosslinking agent pentaerythritol triacrylate, N-methyl-N-butylpyrrole di(trifluoromethylsulfonyl)imide salt, lithium salt LiPF6 lithium hexafluorophosphate, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler LLZAO in amounts of 12 g, 2.5 g, 2.5 g, 5 g, 0.15 g and 3 g to a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0105] Preparation of polymer electrolyte:

[0106] The prepared polymer electrolyte slurry was poured onto a release film, and a self-supporting 150 μm polymer electrolyte membrane was prepared by UV curing (since the self-supporting membrane had poor mechanical properties at 75 μm and could not be prepared, a 150 μm self-supporting membrane was prepared for comparison), and the obtained polymer electrolyte membrane was assembled into a button-type full battery.

[0107] Comparative Example 2

[0108] Preparation of polymer electrolyte slurry:

[0109] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =500), 20g of glycidyl methacrylate and 0.5g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25°C. The mixture was polymerized under ultraviolet light in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 3000 cP, after which the reaction was stopped;

[0110] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, lithium salt LiTFSI, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler TiO2 in amounts of 12 g, 2 g, 5 g, 0.15 g and 1 g into a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0111] Preparation of polymer electrolyte:

[0112] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0113] Comparative Example 3

[0114] Preparation of polymer electrolyte slurry:

[0115] Step (1): 80g polyethylene glycol methyl ether acrylate (M w =500), 20g of glycidyl methacrylate and 0.5g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25°C. The mixture was polymerized under ultraviolet light in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 3000 cP, after which the reaction was stopped;

[0116] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, lithium salt LiTFSI, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler TiO2 in amounts of 12 g, 2 g, 5 g, 0.15 g and 2 g to a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0117] Preparation of polymer electrolyte:

[0118] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0119] Comparative Example 4

[0120] Preparation of polymer electrolyte slurry:

[0121] Step (1): 80g polyethylene glycol methyl ether acrylate (M w=500), 20g of glycidyl methacrylate and 0.5g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25°C. The mixture was polymerized under ultraviolet light in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 3000 cP, after which the reaction was stopped;

[0122] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, lithium salt LiTFSI, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler montmorillonite MMT in amounts of 12 g, 2 g, 5 g, 0.15 g and 2 g to a glass bottle and stir at 40 ° C for 2 h until mixed evenly.

[0123] Preparation of polymer electrolyte:

[0124] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0125] Comparative Example 5

[0126] Preparation of polymer electrolyte slurry:

[0127] Step (1): 100g polyethylene glycol methyl ether acrylate (M w =500) and 0.5g of photoinitiator 2-hydroxy-2-methylphenylpropane-1-one were added to a four-necked flask and stirred at a constant temperature of 25°C. The polymerization was carried out under ultraviolet light in a nitrogen atmosphere to obtain a prepolymer slurry with a viscosity of about 3000 cP, and then the reaction was stopped;

[0128] Step (2): Add the polymer monomer prepolymer slurry, crosslinker polypropylene glycol diacrylate, lithium salt LiTFSI, photoinitiator 2-hydroxy-2-methylphenylpropane-1-one and inorganic filler LLZTO in amounts of 12 g, 2 g, 5 g, 0.15 g and 2 g to a glass bottle, and stir at 40 ° C for 2 h until mixed evenly.

[0129] Preparation of polymer electrolyte:

[0130] The prepared polymer electrolyte slurry was poured onto a release film, coated with a doctor blade, and then UV-cured for 10 minutes with a curing energy of 2000 mJ to prepare a 250 μm-300 μm self-supporting polymer electrolyte membrane. The obtained polymer electrolyte membrane was assembled into a lithium-on-lithium symmetrical battery.

[0131] Performance comparison and effect evaluation:

[0132] Figure 1This is a scanning electron microscope cross-sectional morphology of the positive electrode self-supporting gel polymer electrolyte. It can be seen that there is good interface contact between the electrolyte and the positive electrode, which is beneficial to reducing the interface impedance between the positive electrode and the electrolyte.

[0133] Figure 2 This is a flow chart of the preparation method of the composite polymer electrolyte for in-situ coating of the positive electrode. The slurry is coated on the prepared positive electrode surface, and the preparation of the positive electrode self-supporting polymer electrolyte is achieved by ultraviolet light curing. This process is green, solvent-free and scalable.

[0134] Battery charge and discharge testing: Using a CT2001A BlueDian battery test system, the assembled batteries were placed in a 60°C constant temperature chamber and tested using a BlueDian battery charge and discharge tester. For full LFP cells, the charge and discharge voltage range was 2.8-3.8V. The test results and analysis are as follows:

[0135] Figure 3 The constant current charge and discharge curve of the lithium-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 1 is shown in FIG. -2 The polarization overpotential of the battery under current density is above 120mV, and it can be stably cycled for up to 1100h.

[0136] Figure 4 The constant current charge and discharge curve of the lithium-to-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 2 is shown in Figure 2. -2 It can cycle stably for more than 2000 hours at the current density, and the polarization overpotential of the battery is above 60mV.

[0137] Figure 5 The constant current charge-discharge curve of the lithium-to-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 3 is shown in Figure 2 at 0.1 mA cm -2 It can cycle stably for more than 2000 hours at the current density, and the polarization overpotential of the battery is above 70mV.

[0138] Figure 6 The constant current charge-discharge curve of the lithium-to-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 4 is as follows: the polarization overpotential of the battery is above 500mV, and the charge-discharge rate is 0.1mA cm -2 The long cycle time can reach 1000h under the current density.

[0139] Figure 7 The constant current charge-discharge curve of the lithium-to-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Example 5 is shown in Figure 2 at 0.1 mA cm -2 The polarization overpotential of the battery is above 200mV at the current density.

[0140] Figure 8 This is the full battery cycle performance diagram of the polymer electrolyte in-situ coated lithium iron phosphate positive electrode obtained in Example 1. The discharge capacity of the full battery can reach 130 mAh g at 0.5C. -1 , after 100 cycles, the capacity retention rate is 66%.

[0141] Figure 9 This is the full battery cycle performance diagram of the polymer electrolyte in-situ coated lithium iron phosphate positive electrode obtained in Example 2. The discharge capacity of the full battery at 0.5C conditions can reach 158mAh g -1 As shown above, the capacity retention rate after 100 cycles is 90%, and the capacity retention rate after 200 cycles is 80%.

[0142] Figure 10 This is a cycle performance diagram of a full-cell lithium iron phosphate assembled with a solid-state lithium battery polymer electrolyte obtained in Comparative Example 1. The performance of the full-cell is measured at 0.5C, and its capacity retention rate after 50 cycles is 20%.

[0143] Figure 11 The constant current charge-discharge curve of the lithium-to-lithium symmetrical battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 2 is shown in Figure 2 at 0.1 mA cm -2 Under the current density, the polarization overpotential of the battery is above 180mV, and the stable long cycle time is less than 500h.

[0144] Figure 12 The constant current charge-discharge curve of the lithium-to-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 3 is shown in Figure 2. -2 Under the current density, the polarization overpotential of the battery is above 100mV, and the stable long cycle time is less than 15h.

[0145] Figure 13 The constant current charge-discharge curve of the lithium-to-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 4 is shown in Figure 2 at 0.1 mA cm -2 The polarization overpotential of the battery under current density is 120-250mV, and the polarization overpotential increases significantly with the extension of charge and discharge time.

[0146] Figure 14 The constant current charge-discharge curve of the lithium-to-lithium symmetric battery assembled with the solid-state lithium battery polymer electrolyte obtained in Comparative Example 5 is shown in Figure 2. -2 The polarization overpotential of the battery under current density is 50-250mV, and the polarization overpotential increases significantly with the extension of charge and discharge time.

[0147] From the above analysis, it can be seen that when Example 1 is compared with Comparative Examples 2, 3, and 4, the cycle stability of the battery is significantly better, the overpotential of the symmetrical battery is smaller, and the stable cycle time is longer, indicating that as an inorganic filler, LLZTO is better than TiO2 and montmorillonite MMT. When Example 1 is compared with Comparative Example 5, the cycle stability of the battery is significantly better, indicating that the two-component polymer monomer prepolymer slurry is better than the single-component polyethylene glycol methyl ether acrylate monomer prepolymer slurry. Compared with Example 1, the cycle stability of the battery of Examples 2 and 3 is significantly better, and the overpotential of the lithium-lithium symmetrical battery assembled with the materials obtained in Examples 2 and 3 is smaller, indicating that the impedance of the prepared gel polymer electrolyte during charge and discharge is smaller, and the lithium-lithium symmetrical battery is 0.1 mA cm -2 The gel electrolyte can be stably cycled for more than 2000h at a current density of 1.5C, indicating that the gel electrolyte has strong stability to lithium and can inhibit the growth of lithium dendrites. The above experimental comparison illustrates the advantages of the components. Comparing Examples 1 and 2 with Comparative Example 1, we can see that in-situ coating of the gel polymer electrolyte on the positive electrode can effectively improve the discharge capacity and battery cycle life of the lithium iron phosphate full battery. The discharge capacity at 0.5C reaches 158mAh g -1 It is shown that the ionic liquid gel polymer in situ coated on the positive electrode of the present invention and the preparation method thereof can effectively reduce the interfacial contact between the positive electrode and the electrolyte, and can effectively improve the electrochemical stability of the battery. At the same time, the method for preparing the electrolyte of the present invention adopts a green, solvent-free and scalable coating process, which is applicable to a variety of organic-inorganic composite systems and has good industrial application prospects and environmental benefits.

[0148] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any equivalent changes, modifications, or variations made by those skilled in the art using the technical solution of the present invention to the above embodiment shall still fall within the scope of the technical solution of the present invention.

Claims

1. An ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes, characterized in that: The raw materials of the polymer electrolyte include, in parts by weight: 30-50 parts of a polymer monomer prepolymer slurry, wherein the polymer monomer prepolymer slurry is a mixture of a copolymer and a monomer including polyethylene glycol methyl ether acrylate and a functional acrylate monomer having a monofunctional group, wherein the functional acrylate monomer having a monofunctional group is selected from one or more of tetrahydrofurfuryl (meth)acrylate, ethoxylated tetrahydrofuran acrylate, glycidyl methacrylate, and 4-acryloylmorpholine, and the polymer monomer prepolymer slurry has a viscosity of 300-10000 cP and is thixotropic; 5-20 parts of ionic liquid; 10-40 parts of lithium salt; 5-10 parts of an inorganic filler, wherein the inorganic filler is a spherical particle with a particle size of ≤500 nm; 5-10 parts of cross-linking agent; Photoinitiator 0.05-2 parts; The preparation of the ionic liquid gel polymer electrolyte comprises the following steps: (1) Preparation of polymer monomer prepolymer slurry: Polyethylene glycol methyl ether acrylate, a functional acrylate monomer having a monofunctional group, and a photoinitiator are blended, and ultraviolet light-initiated polymerization is carried out under inert gas to obtain a polymer monomer prepolymer slurry having a viscosity of 300-10000 cP, and then the polymerization reaction is stopped; the amount ratio of the polyethylene glycol methyl ether acrylate, the functional acrylate monomer having a monofunctional group, and the photoinitiator is 80:20:0.5-90:10:0.5; (2) Mixing raw materials: stirring and mixing the crosslinking agent, polymer monomer prepolymer slurry, ionic liquid, lithium salt, photoinitiator and inorganic filler; (3) Coating: The mixed slurry obtained in step (2) is evenly coated on the surface of the positive electrode material, and the coating thickness of the solid electrolyte slurry is 20 μm-300 μm; (4) UV curing: The coated slurry is UV cured to obtain an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes.

2. The ionic liquid gel polymer electrolyte suitable for large-scale positive electrode in-situ coating according to claim 1, characterized in that: The ionic liquid includes one or two of N-methyl-N-butylpyrrole bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide; The polyethylene glycol methyl ether acrylate includes a molecular structure of H2C=CHCO2(CH2CH2O) n One or more CH3 acrylic ester monomers, wherein n represents the number of repetitions of the side chain ethylene glycol group (CH2CH2O) of the acrylic ester monomer, and the value of n ranges from 2 to 20.

3. The ionic liquid gel polymer electrolyte suitable for large-scale positive electrode in-situ coating according to claim 1, characterized in that: The cross-linking agent includes one or more of polyethylene glycol diacrylate, pentaerythritol triacrylate, propylene glycol di(meth)acrylate, and trimethylolpropane triacrylate.

4. The ionic liquid gel polymer electrolyte suitable for large-scale positive electrode in-situ coating according to claim 1, characterized in that: The inorganic filler includes one or more of lithium lanthanum zirconium oxide LLZO, lithium lanthanum zirconium aluminum oxide LLZAO, and lithium lanthanum zirconium tantalum oxide LLZTO; the inorganic filler is spherical particles; and the particle size range of the inorganic filler is within 500 nm.

5. The ionic liquid gel polymer electrolyte suitable for large-scale positive electrode in-situ coating according to claim 1, characterized in that: The lithium salt includes one or two of lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(oxalatoborate) LiBOB, lithium difluorooxalatoborate LiDFOB, lithium perchlorate LiClO4, lithium tetrafluoroborate LiBF4, and lithium nitrate LiNO3; The photoinitiator includes one or more of benzil dimethyl ether, (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide, benzophenone, 2,4-diethylthioxanthone, and 2-hydroxy-2-methylphenylpropane-1-one.

6. The method for preparing an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of a positive electrode according to any one of claims 1 to 5, characterized in that: The steps include: (1) Preparation of polymer monomer prepolymer slurry: Polyethylene glycol methyl ether acrylate, a functional acrylate monomer having a monofunctional group, and a photoinitiator are blended, and ultraviolet light-initiated polymerization is carried out under inert gas to obtain a polymer monomer prepolymer slurry having a viscosity of 300-10000 cP, and then the polymerization reaction is stopped; the amount ratio of the polyethylene glycol methyl ether acrylate, the functional acrylate monomer having a monofunctional group, and the photoinitiator is 80:20:0.5-90:10:0.5; (2) Mixing raw materials: stirring and mixing the crosslinking agent, polymer monomer prepolymer slurry, ionic liquid, lithium salt, photoinitiator and inorganic filler; (3) Coating: The mixed slurry obtained in step (2) is evenly coated on the surface of the positive electrode material, and the coating thickness of the solid electrolyte slurry is 20 μm-300 μm; (4) UV curing: The coated slurry is UV cured to obtain an ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes.

7. The preparation method according to claim 6, characterized in that The inert gas in step (1) is nitrogen; the curing energy of the ultraviolet curing in step (4) is 500-5000mJ.

8. The preparation method according to claim 6, characterized in that The coating method in step (3) includes any one of blade coating, wire rod coating, slit coating and transfer roller coating.

9. The preparation method according to claim 6, characterized in that The positive electrode material in step (3) includes any one of NCM ternary material, NCA ternary material, lithium iron phosphate, and lithium cobalt oxide.

10. Use of the ionic liquid gel polymer electrolyte suitable for large-scale in-situ coating of positive electrodes according to any one of claims 1 to 5 in the preparation of lithium metal solid-state batteries.

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