Composite polymer solid electrolyte, preparation method thereof and secondary battery

Abstract

The invention provides a composite polymer solid electrolyte and a preparation method thereof and a secondary battery, the composite polymer solid electrolyte comprises a diaphragm and an MOFs material growing on at least one side surface of the diaphragm in situ, and a solvent type electrolyte is packaged in a pore channel of the MOFs material. Polymers containing lithium salt are coated among MOFs material particles and on the surfaces of the MOFs material particles. The solvent type electrolyte is a nonionic liquid-based electrolyte and comprises a solvent, a diluent with flame retardant property and a first lithium salt, and the concentration of the first lithium salt is greater than or equal to 2mol / L. The MOFs material can increase the mechanical strength of the polymer electrolyte, and the polymer can improve the flexibility of the MOFs material; the MOFs adsorbs a solvent, regulates lithium salt anions through coordination, combines a porous structure channel of the MOFs, interface interaction with a polymer and packaged local high-concentration lithium salt, increases ion migration modes, and improves ion conductivity. And meanwhile, the flame-retardant diluent can improve the safety performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of solid-state electrolytes, and relates to a composite polymer solid-state electrolyte, a preparation method thereof and a secondary battery. BACKGROUND

[0002] With the continuous upgrading of the demand for battery safety and energy density in the new energy field, the limitations of traditional liquid electrolyte batteries gradually become apparent. Liquid electrolyte is prone to leakage and flammability, and can easily cause thermal runaway under high voltage or high temperature conditions. In addition, a high impedance layer is easily formed between the liquid system and the electrode interface, which restricts the cycle life and power performance of the battery. To break through these bottlenecks, solid-state batteries have become the research and development direction of the next generation of high-safety power batteries and energy storage batteries due to their core advantages of no free liquid electrolyte, high voltage resistance and inhibition of lithium dendrite growth.

[0003] The performance of a solid-state battery depends on the selection of a solid-state electrolyte. Currently, the main solid-state electrolytes are mainly divided into three categories: inorganic solid-state electrolytes, polymer solid-state electrolytes and composite solid-state electrolytes. Among them, polymer electrolytes have become a hot spot for the development of solid-state batteries due to their good mechanical ductility and excellent interface contact. Composite polymer electrolytes formed by adding inorganic oxides and other schemes have improved the problems of low ionic conductivity (particularly significant at room temperature), high interface impedance, low mechanical strength and poor electrochemical stability at high voltage to some extent. Metal-organic frameworks (MOFs) have ordered pore structures and high specific surface areas, and can be used as additives or fillers to optimize polymer electrolytes, thereby constructing ion-ordered transport channels, improving ion dissociation capacity and enhancing mechanical properties.

[0004] Existing composite polymer electrolytes modified by MOFs improve the ionic conductivity of the composite polymer electrolytes modified by MOFs and further improve the electrical performance of the assembled batteries by grafting organic lithium salt anions to the organic matter in the MOFs, grafting polymerizable functional groups to the polymer monomers to form polymers, synthesizing anion skeletons, filling ionic liquids in the pores, or selecting metal ions on the skeleton of the MOFs to further form complex structures with lithium salts or polymers. However, the above methods have the problems of difficult synthesis of organic matter, and the ionic conductivity of the composite electrolyte is usually still less than 10 -4 S / cm order of magnitude, which still needs to be greatly improved compared with liquid lithium ion batteries.

[0005] Therefore, how to develop a composite polymer electrolyte with high ionic conductivity and a simple synthesis method is of great significance for promoting the development of solid-state batteries or semi-solid-state batteries. SUMMARY

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite polymer solid electrolyte, its preparation method, and a secondary battery. The composite polymer solid electrolyte provided by this invention utilizes metal-organic frameworks (MOFs) as fillers to increase the mechanical strength of the polymer electrolyte, while the polymer enhances the flexibility of the MOFs. A locally concentrated lithium salt electrolyte containing a flame-retardant diluent is encapsulated within the MOFs. Through the adsorption and regulation of solvent molecules, the coordination and regulation of lithium salt anions, the inherent channels provided by the MOFs' porous structure, and the interfacial interactions with the polymer, the MOFs increase the channels and pathways for lithium ion migration, thereby increasing the lithium ion transference number and improving ionic conductivity, which is beneficial for improving battery performance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a composite polymer solid electrolyte, the composite polymer solid electrolyte comprising a membrane and MOFs material in situ grown on at least one side of the membrane, wherein a solvent-based electrolyte is encapsulated in the pores of the MOFs material, and the MOFs material particles and surfaces are coated with a polymer containing lithium salt; the solvent-based electrolyte is a nonionic liquid-based electrolyte, comprising a solvent, a diluent with flame-retardant properties and a first lithium salt, wherein the concentration of the first lithium salt is ≥2 mol / L.

[0009] It is understandable that the above-mentioned "the pores of MOFs materials are encapsulated with solvent-based electrolytes" refers to the electrolytes being physically adsorbed or chemically bonded to the pores of MOFs.

[0010] In this invention, MOFs materials are grown in situ on the separator. Compared with simply coating MOFs materials on the separator, this enhances the adhesion between the MOFs materials and the separator. The support of the separator is conducive to the distribution of MOFs particles in the polymer and avoids the sedimentation and agglomeration of MOFs particles in the slurry. During in-situ growth, the interaction between MOFs crystals reduces the interfacial impedance between particles, which is more conducive to the construction of MOFs-based lithium-ion transport channels.

[0011] Compared to encapsulated ionic liquid-based electrolytes, the encapsulation of solvent-based electrolytes within the pores of MOFs allows solvent molecules to form bonds with the MOF framework, dispersing the electron cloud distribution of solvent molecules and weakening their effect on lithium ions. This makes it easier for lithium salts to dissociate into free lithium ions, resulting in less resistance and faster migration rates within the regular pores of the MOFs. The increased concentration of free lithium ions and accelerated migration work together to significantly improve the ionic conductivity of the system. Furthermore, solvent-based electrolytes encapsulating locally high concentrations of lithium salts can improve the interfacial compatibility between the composite polymer solid electrolyte and the electrodes, playing a positive role in suppressing lithium dendrite formation and improving battery performance. Simultaneously, the flame-retardant diluent can be released from the MOF framework during thermal runaway, thereby improving the battery's flame retardancy and safety. Furthermore, by coating the particles and surfaces of MOFs with lithium-containing polymers obtained through in-situ polymerization, the flexibility of MOFs materials can be improved, the ionic conductivity of the composite polymer solid electrolyte can be further increased, and the formation of a good interface between the electrolyte and the electrode substrate can be facilitated.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, the diaphragm comprises a fibrous diaphragm.

[0014] Preferably, the diaphragm is made of any one of polyester, polyimide, polytetrafluoroethylene, or aramid.

[0015] Preferably, the thickness of the diaphragm is 5μm to 60μm, such as 5μm, 10μm, 20μm, 30μm, 40μm, 50μm or 60μm.

[0016] Preferably, the MOF material includes HKUST-1 or MOF-5.

[0017] Preferably, the MOFs material accounts for 1% to 85% of the mass of the composite polymer solid electrolyte, such as 1%, 10%, 20%, 30%, 50%, 70%, 80%, or 85%.

[0018] Preferably, the solvent includes an organic solvent.

[0019] Preferably, the diluent comprises any one or a combination of at least two of the following: tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trifluoroethyl) phosphate derivatives, bis(2,2,2-trifluoroethyl) methyl phosphate, or bis(2,2,2-trifluoroethyl) methyl phosphate derivatives.

[0020] Preferably, the mass ratio of the solvent to the diluent is 1:(1~4), for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4, etc.

[0021] Preferably, in the solvent-based electrolyte, the concentration of the first lithium salt is 2 mol / L to 6.5 mol / L, such as 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, or 6.5 mol / L.

[0022] In this invention, the ordered channels of MOFs material can guide the directional migration of solvated ions in the electrolyte, thereby alleviating the hindrance to ion conduction caused by the increased viscosity of high-concentration lithium salt and improving ion conductivity; the added diluent also alleviates the increase in viscosity to a certain extent.

[0023] Preferably, the lithium salt in the lithium-containing polymer includes a second lithium salt, and the polymer in the lithium-containing polymer includes any one or a combination of at least two of polymethyl methacrylate (PMMA), polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polyacrylonitrile, or polyacrylamide.

[0024] It should be noted that the present invention does not limit the types of the first and second lithium salts, and commonly used lithium salt types in the art are applicable to the present invention. Exemplarily, the first and second lithium salts each independently include any one or a combination of at least two of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0025] Preferably, the lithium salt-containing polymer accounts for 1% to 15% of the mass of the composite polymer solid electrolyte, such as 1%, 3%, 5%, 7%, 10%, 12%, or 15%.

[0026] In a second aspect, the present invention provides a method for preparing a composite polymer solid electrolyte as described in the first aspect, the method comprising:

[0027] (1) MOFs material is grown in situ on at least one side surface of the diaphragm to obtain a composite diaphragm;

[0028] (2) Immerse the composite membrane described in step (1) in a solvent-based electrolyte. After the immersion is completed, remove the excess liquid from the surface of the composite membrane to obtain a composite membrane encapsulated with a solvent-based electrolyte.

[0029] (3) A mixed solution containing polymer monomers, a second lithium salt, an initiator and a solvent is coated onto one side of the composite membrane in which the solvent-based electrolyte is encapsulated in step (2) and grown in situ. The composite polymer solid electrolyte is obtained after in situ polymerization.

[0030] In this invention, although both steps (2) and (3) contain lithium salt and solvent, they have different functions. Step (2) impregnates the solvent-based electrolyte to achieve its encapsulation in the pores of MOFs material. Step (3) polymerizes the mixed solution containing polymer monomer, second lithium salt, initiator and solvent in situ to form a lithium salt-containing polymer coating on the surface of MOFs material.

[0031] Preferably, the in-situ growth method in step (1) includes: immersing the membrane in a mixed solution containing metal salt, ligand and solvent for reaction, and then heat-treating the reacted membrane to obtain the composite membrane.

[0032] It should be noted that, since different MOFs materials are synthesized in different ways, this invention does not limit the specific method of heat treatment; it is sufficient to perform the heat treatment according to the synthesis conditions of the selected MOFs material.

[0033] Preferably, the impregnation in step (2) is carried out under conditions of ultrasound and stirring.

[0034] Preferably, the soaking time in step (2) is 6h to 24h, such as 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h or 24h.

[0035] Preferably, the immersion temperature in step (2) is 2℃~50℃, such as 2℃, 3℃, 4℃, 5℃, 40℃, 42℃, 45℃, 48℃ or 50℃.

[0036] Preferably, the method for removing excess liquid from the surface of the composite membrane in step (2) includes vacuum filtration.

[0037] Preferably, the polymer monomer in step (3) includes any one or a combination of at least two of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, acrylonitrile, or acrylamide.

[0038] In this invention, the corresponding polymers can be prepared by in-situ polymerization using the above-mentioned polymer monomers.

[0039] Preferably, the initiator in step (3) includes azobisisobutyronitrile (AIBN).

[0040] It should be noted that this invention does not limit the type of solvent in the solvent-based electrolyte described in step (2) or the type of solvent in the mixed solution described in step (3). Solvents commonly used in secondary battery electrolytes in this art are applicable to this invention. For example, any one or a combination of at least two of ethylene glycol dimethyl ether (DME), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC), or methyl ethyl carbonate (EMC). Furthermore, functional additives commonly used in electrolytes in this art, such as vinylene carbonate (VC) and / or ethylene sulfate (DTD), can be added to the mixed solution described in step (3) to further improve the performance of the composite polymer solid electrolyte.

[0041] Preferably, the mixed solution in step (3) further includes a crosslinking agent, which includes ethylene glycol diacrylate.

[0042] Preferably, in step (3), the concentration of the second lithium salt in the mixed solution is 0.6 mol / L to 6.5 mol / L, for example, 0.6 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L or 6.5 mol / L.

[0043] In this invention, by adding a high concentration of lithium salt during the polymer preparation stage, the ionic conductivity of the composite polymer solid electrolyte is improved, and it is also beneficial to the formation of a good interface between the electrolyte and the electrode material.

[0044] Preferably, the coating method in step (3) includes spraying.

[0045] Preferably, the in-situ polymerization temperature in step (3) is 55℃~70℃, for example, 55℃, 60℃, 65℃ or 70℃.

[0046] Preferably, the in-situ polymerization time in step (3) is 6h to 24h, such as 6h, 7h, 8h, 9h, 10h, 11h, 12h, or 24h.

[0047] Thirdly, the present invention also provides a secondary battery, the secondary battery comprising a composite polymer solid electrolyte as described in the first aspect, the secondary battery comprising a semi-solid battery.

[0048] It should be noted that the semi-solid battery can be assembled in the following order: negative electrode shell, spring sheet, gasket, lithium sheet, composite polymer solid electrolyte described in the first aspect, positive electrode sheet, positive electrode shell; or in the following order: negative electrode shell, spring sheet, gasket, lithium sheet, conventional electrolyte solution, composite polymer solid electrolyte described in the first aspect, (conventional electrolyte solution), positive electrode sheet, positive electrode shell; or in the following order: negative electrode shell, spring sheet, gasket, lithium sheet, mixed solution described in step (3) of the second aspect, composite separator encapsulated with solvent-based electrolyte described in step (2) of the second aspect, (mixed solution described in step (3) of the second aspect), positive electrode sheet, positive electrode shell. Then, the assembled battery is left to stand at 55℃~70℃ for 6h~24h to allow the polymer to solidify in situ, thus obtaining a semi-solid battery. The standing temperature is such as 55℃, 60℃, 65℃ or 70℃, and the standing time is such as 7h, 8h or 9h. It is understandable that the above "(conventional electrolyte solution)" means that it can be added or not; "(mixed solution described in step (3) of the second aspect)" means optional: that is, if both sides of the membrane contain lithium salts, this step is required; if only one side of the membrane contains lithium salts, this step is not required.

[0049] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The composite polymer solid electrolyte provided by this invention utilizes MOFs (Metal-Oxide-Fractions) as fillers to increase the mechanical strength of the polymer electrolyte, while the polymer enhances the flexibility of the MOFs. Through the adsorption and regulation of solvent molecules, the coordination and regulation of lithium salt anions, the inherent channels provided by the MOFs' porous structure, the interfacial interactions with the polymer, and the locally encapsulated high concentration of lithium salt within the MOFs, the channels and pathways for lithium ion migration are increased, leading to a higher lithium ion transference number, improved solvation structure, and promoted lithium ion dissociation, thus enhancing ionic conductivity and improving battery performance. Simultaneously, the flame-retardant diluent also improves battery safety. Attached Figure Description

[0052] Figure 1 This is a schematic diagram illustrating the principle of the composite polymer solid electrolyte preparation method provided by the present invention.

[0053] 1-MOFs material grown in situ on the membrane; 2-solvent-based electrolyte; 3-polymer containing lithium salt. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0056] Example 1

[0057] This embodiment provides a composite polymer solid electrolyte, comprising a membrane and MOFs materials in situ grown on both sides of the membrane. A solvent-based electrolyte is encapsulated within the pores of the MOFs material. The MOFs material particles and their surfaces are coated with a lithium-containing polymer. The MOFs material is HKUST-1. The solvent-based electrolyte contains tris(2,2,2-trifluoroethyl) phosphate, a flame-retardant diluent, and the lithium salt concentration in the solvent-based electrolyte is 2 mol / L. A schematic diagram of the preparation method is shown below. Figure 1 As shown, MOFs material 1, which is first grown in situ on a membrane, is first prepared. Then, a solvent-based electrolyte 2 is encapsulated in the pores of the MOFs. Finally, a lithium salt-containing polymer 3 is coated on the surface of the MOFs and in the interparticle spaces, as detailed below:

[0058] (1) In-situ growth of MOFs on the diaphragm: Copper nitrate trihydrate (Cu(NO3)2·3H2O) and 1,3,5-benzenetricarboxylic acid were dissolved in N,N-dimethylformamide (DMF). After stirring at a constant temperature for 20 min, the solution was transferred to a polytetrafluoroethylene reactor, a polyimide membrane was placed in it, and it was placed in a 75℃ oven for 24 h. After the reaction was completed and cooled to room temperature, the polyimide membrane was removed, washed with deionized water, and then washed three times with ethanol. The washed product was placed in a vacuum oven and heated from room temperature to 100℃ at a rate of 3℃ / min and held at that temperature for 6 h. Then it was heated to 180℃ at a rate of 5℃ / min and held at that temperature for 6 h to obtain an in-situ grown polyimide membrane of HKUST-1.

[0059] (2) Encapsulating solvent-based electrolyte in MOF channels: LiTFSI was dissolved in solvent DME, stirred and mixed evenly, and then tris(2,2,2-trifluoroethyl) phosphate, a diluent with flame-retardant properties, was added and stirred evenly to obtain a locally high-concentration electrolyte. The mass ratio of DME to tris(2,2,2-trifluoroethyl) phosphate was 1:2, and the concentration of LiTFSI was 2 mol / L. The polyimide membrane of HKUST-1 grown in situ in (1) was immersed in the locally high-concentration electrolyte and slowly ultrasonically stirred at 45°C for 8 h to allow the locally high-concentration electrolyte to fully enter the channels of HKUST-1. The membrane was removed and vacuum filtered to remove excess liquid from the surface to obtain a composite membrane encapsulated with solvent-based electrolyte.

[0060] (3) Conventional electrolyte solution: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 3:3:4. 0.6 mol / L lithium hexafluorophosphate (LiPF6) is added, along with 3.3% vinylene carbonate (VC) and 0.75% ethylene sulfate (DTD) of the total mass of (EC+EMC+DMC). The mixture is then thoroughly mixed to obtain the conventional electrolyte solution.

[0061] The surface of MOFs is coated with a lithium salt-containing polymer: a mixed solution containing polymer monomer MMA, lithium salt LiTFSI, ethylene glycol diacrylate (EGDA), initiator AIBN and the above conventional electrolyte solution in a mass ratio of 6:5.5:1:0.15:88 is sprayed onto the composite membrane containing the solvent-based electrolyte in (2). The electrode is kept in a 60°C oven for 8 hours to allow the polymer to solidify in situ, thus obtaining the composite polymer solid electrolyte.

[0062] Example 2

[0063] The difference between this embodiment and Embodiment 1 is that the polyimide diaphragm membrane is replaced with an aramid membrane;

[0064] The remaining preparation methods and parameters are consistent with those in Example 1.

[0065] Example 3

[0066] The difference between this embodiment and Embodiment 1 is that the diluent tris(2,2,2-trifluoroethyl) phosphate in the solvent-based electrolyte is replaced with bis(2,2,2-trifluoroethyl) methyl phosphate.

[0067] The remaining preparation methods and parameters are consistent with those in Example 1.

[0068] Example 4

[0069] The difference between this embodiment and Example 1 is that the LiTFSI concentration in step (2) is 3 mol / L;

[0070] The remaining preparation methods and parameters are consistent with those in Example 1.

[0071] Example 5

[0072] The difference between this embodiment and embodiment 1 is that the mass ratio of DME to tri(2,2,2-trifluoroethyl) phosphate in step (2) is 1:1;

[0073] The remaining preparation methods and parameters are consistent with those in Example 1.

[0074] Example 6

[0075] The difference between this embodiment and Embodiment 1 is that the LiTFSI concentration in step (3) is 2 mol / L;

[0076] The remaining preparation methods and parameters are consistent with those in Example 1.

[0077] Example 7

[0078] The difference between this embodiment and Embodiment 1 is that the polymer monomer in step (3) is acrylonitrile;

[0079] The remaining preparation methods and parameters are consistent with those in Example 1.

[0080] Example 8

[0081] The difference between this embodiment and Embodiment 1 is that the lithium salt in step (2) is LiFSI;

[0082] The remaining preparation methods and parameters are consistent with those in Example 1.

[0083] Example 9

[0084] The difference between this embodiment and Embodiment 1 is that the MOF material is MOF-5;

[0085] Step (1) is as follows: Dissolve dihydrate and zinc acetate (Zn(CH3COO)2), terephthalic acid and triethylamine in DMF solvent, place the polyimide membrane in the solution, and stir the solution for 3 hours. After the reaction is completed, take out the polyimide membrane, wash it with deionized water, and then wash it three times with ethanol. Place the washed product in a vacuum oven, raise the temperature from room temperature to 100℃ at a rate of 3℃ / min, hold the temperature for 6 hours, and then raise the temperature to 180℃ at a rate of 5℃ / min, hold the temperature for 6 hours to obtain the in-situ grown MOF-5 polyimide membrane.

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Example 10

[0088] The difference between this embodiment and Embodiment 1 is that the MOF material is ZIF-67;

[0089] Step (1) is as follows: Cobalt nitrate hexahydrate is dissolved in methanol to obtain solution A; 2-methylimidazole is dissolved in methanol to obtain solution B; a polyimide membrane is added to solution A; solution B is slowly added to solution A; the mixed solution is stirred at room temperature for 0.5 h, then allowed to stand for 12 h, the polyimide membrane is taken out and washed 3 times with methanol; the washed product is placed in a vacuum oven and heated from room temperature to 60 °C at a rate of 3 °C / min, and kept at the temperature for 8 h to obtain a polyimide membrane of ZIF-67 grown in situ;

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that the MOFs material does not encapsulate the solvent-based electrolyte in the pores and does not perform step (2).

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that the channels of the MOFs material are encapsulated with an ionic liquid-based electrolyte; in step (2), LiTFSI is dissolved in [EMIM][TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) ionic liquid;

[0096] The remaining preparation methods and parameters are consistent with those in Example 1.

[0097] Comparative Example 3

[0098] The difference between this embodiment and Example 1 is that the LiTFSI concentration in step (2) is 0.2 mol / L;

[0099] The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that the MOFs material is composited with the membrane by an adhesive, and no polyimide membrane is added in step (1). After the reaction is completed, HKUST-1 powder is obtained. Then, HKUST-1 powder, adhesive PVDF and NMP are mixed to obtain a slurry. The slurry is coated on the membrane and dried to obtain a polyimide membrane coated with HKUST-1.

[0102] The remaining preparation methods and parameters are consistent with those in Example 1.

[0103] Application Example 1.1

[0104] This application example provides a semi-solid battery, which is assembled in the following order: negative electrode shell, spring sheet, pad, lithium sheet, conventional electrolyte solution described in step (3) of Example 1, composite polymer solid electrolyte provided in Example 1, positive electrode sheet, and positive electrode shell.

[0105] Preparation of positive or negative electrode sheets: (1) Positive electrode sheet: Lithium iron phosphate, conductive carbon black Super-P and binder vinylidene fluoride (PVDF) are mixed uniformly at a mass ratio of 95:3:2, and then N-methyl-2-pyrrolidone (NMP) is added to obtain a positive electrode slurry. The positive electrode slurry is coated onto both sides of an aluminum foil in sequence, and after drying and rolling, a positive electrode sheet is obtained; (2) Negative electrode substrate: Graphite, conductive carbon black Super-P, thickener carboxymethyl cellulose (CMC), binder styrene-butadiene rubber (SBR) and polyacrylic acid (PAA) are mixed uniformly at a mass ratio of 96:1:1.2:1.8, and then dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated onto both sides of a copper foil in sequence, and after drying and rolling, a negative electrode sheet is obtained.

[0106] Application Example 1.2

[0107] This application example provides a semi-solid battery. The semi-solid battery is assembled in the following order: negative electrode shell, spring sheet, gasket, lithium sheet, mixed solution described in step (3) of Example 1, composite separator encapsulated with solvent-based electrolyte described in step (2) of Example 1, mixed solution described in step (3) of Example 1, positive electrode sheet, and positive electrode shell. The assembled battery is then left to stand at 60°C for 8 hours to allow the polymer to solidify in situ, thus obtaining a semi-solid battery.

[0108] Application Example 2-10

[0109] The difference between Application Example 2-10 and Application Example 1.1 is that Application Example 2-10 uses the composite polymer solid electrolyte provided in Example 2-10.

[0110] The remaining preparation methods and parameters are consistent with those in Application Example 1.1.

[0111] Compare and contrast examples 1-4

[0112] The difference between Comparative Application Examples 1-4 and Application Example 1.1 is that Comparative Application Examples 1-4 use the composite polymer solid electrolyte provided in Comparative Examples 1-4.

[0113] The remaining preparation methods and parameters are consistent with those in Application Example 1.1.

[0114] Performance testing

[0115] Phase analysis, ionic conductivity, and flammability tests were performed on the composite polymer electrolytes in Examples 1-10 and Comparative Examples 1-4. The test methods and conditions are as follows:

[0116] Phase analysis: X-ray diffraction was performed using a Bruker D8 diffractometer (Germany). The light source was copper Kα rays (wavelength 0.1541 nm), the operating voltage was 40 kV, the operating current was 40 mA, the scanning rate was 8° / min, and the scanning range was 5–50 degrees (2 theta).

[0117] Ionic conductivity testing: Electrochemical impedance spectroscopy (EIS) was used to measure the ionic conductivity of stainless steel (SS) / electrolyte / stainless steel (SS) batteries within the frequency range of 0.1 to 100 Hz. The battery diameter was 16 mm. The ionic conductivity of the samples was measured at 25 °C. The ionic conductivity was calculated as follows: σ = L / (R × S), where σ, L, R, and S represent the ionic conductivity, sample thickness, impedance value, and cross-sectional area of ​​the sample, respectively. The test parameters are shown in Table 1.

[0118] The electrochemical performance of the semi-solid-state batteries prepared for use cases 1-10 and comparative application cases 1-4 was tested for cycle performance. The test conditions were as follows: Cyclic performance testing was performed on the cells of each application case and the comparative application case at 25℃ according to the following procedure: 5 min rest; 0.5C constant current charging to 3.8V, constant voltage charging to 0.05C; 5 min rest; 0.5C constant current discharging to 3.0V; 5 min rest; then proceed to the next cycle. The initial discharge capacity D1 and the discharge capacity D100 in the 80th cycle were recorded; the cycle capacity retention rate of the battery was calculated using D80 / D1. The test results are shown in Table 1.

[0119] Table 1

[0120]

[0121] The phase composition of the products obtained in steps (1), (2), and (3) of the preparation process of the composite polymer solid electrolyte was analyzed, and the results are as follows:

[0122] Since the MOFs materials, membrane types, polymer types and preparation methods used in Examples 1, 3-6, 8 and Comparative Examples 1-3 are the same, their test results are also the same. The characteristic peaks of the product obtained in step (1) are similar to the standard spectrum of HKUST-1, as well as the amorphous peaks and a few peaks from the polyimide membrane; the characteristic peaks of the product obtained in step (2) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks changes, indicating that there is material filling in the pores, with amorphous peaks and a few peaks from the polyimide membrane; the characteristic peaks of the product obtained in step (3) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks changes, indicating that there is material filling in the pores, with amorphous peaks and a few peaks from the polyimide membrane and the polymer PMMA, but no obvious PMMA crystallization peaks are observed.

[0123] The MOFs materials, polymer types, and preparation methods used in Example 2 are the same as those in Example 1, but the membrane is an aramid membrane. Therefore, the characteristic peaks of the product obtained in step (1) of Example 2 are still similar to the standard spectrum of HKUST-1, as well as the amorphous peaks and a few peaks from the aramid membrane; the characteristic peaks of the product obtained in step (2) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks has changed, indicating that there is material filling in the pores, and the amorphous peaks and a few peaks are from the aramid membrane; the characteristic peaks of the product obtained in step (3) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks has changed, indicating that there is material filling in the pores, and the amorphous peaks and a few peaks are from the aramid membrane and the polymer PMMA, but no obvious PMMA crystallization peaks are observed.

[0124] The MOFs material, membrane type and preparation method used in Example 7 are the same as those in Example 1, only the polymer type is different from that in Example 1. Therefore, the test results of the products prepared in steps (1) and (2) are the same as those in Example 1. However, the results of the product obtained in step (3) are as follows: the characteristic peaks of the product are similar to the standard spectrum of HKUST-1, but the relative height of the peaks has changed, indicating that there is material filling in the pores. There are amorphous peaks and a few peaks from the polyimide membrane and the polymer polyacrylonitrile, but no obvious polyacrylonitrile crystal peaks are seen.

[0125] The types of membranes, polymers, and preparation methods used in Examples 9 and 10 were the same as in Example 1, except that the types of MOFs materials differed from those in Example 1. Therefore, the test results of Examples 9 and 10 were as follows: The characteristic peaks of the product obtained in step (1) were similar to the standard spectra of MOF-5 and ZIF-67, respectively, with amorphous peaks and a few peaks originating from the polyimide membrane; The characteristic peaks of the product obtained in step (2) were similar to the standard spectra of MOF-5 and ZIF-67, respectively, but the relative heights of the peaks changed, indicating that the pores were filled with material, with amorphous peaks and a few peaks originating from the polyimide membrane; The characteristic peaks of the product obtained in step (3) were similar to the standard spectra of MOF-5 and ZIF-67, respectively, but the relative heights of the peaks changed, indicating that the pores were filled with material, with amorphous peaks and a few peaks originating from the polyimide membrane and the polymer PMMA, but no obvious PMMA crystallization peaks were observed.

[0126] The characteristic peaks of the product obtained in step (1) of Comparative Example 4 are similar to the standard spectrum of HKUST-1. After the powder is coated onto the diaphragm, it contains peaks of HKUST-1, PVDF, and polyimide. The characteristic peaks of the product obtained in step (2) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks changes, indicating that there is material filling in the pores, including peaks from PVDF and polyimide membranes. The characteristic peaks of the product obtained in step (3) are similar to the standard spectrum of HKUST-1, but the relative height of the peaks changes, indicating that there is material filling in the pores. There are amorphous peaks and a few peaks from PVDF, polyimide membranes, and polymer PMMA, but no obvious PMMA crystallization peaks are observed.

[0127] The results of the phase tests above show that the preparation method provided by the present invention successfully prepared the corresponding composite polymer solid electrolyte, and the method has good repeatability, which can ensure the uniformity of the product.

[0128] As shown in Table 1, the composite polymer solid electrolytes prepared by the present invention are all non-flammable in the fire test, indicating that they have excellent heat resistance. However, Comparative Example 1 is ignitable in the fire test because it does not contain solvent-based electrolyte and lacks a diluent with flame-retardant properties, resulting in decreased heat resistance. Secondly, the composite polymer electrolyte obtained by this invention has high ionic conductivity. After being assembled into a battery, the initial specific capacity and cycle capacity retention of the battery are both high. In contrast, in Comparative Example 2, since the ionic liquid-based electrolyte is encapsulated in the MOF material, its ionic conductivity drops to less than 40% of that in Example 1. In Comparative Example 3, the low concentration of lithium salt also causes a decrease in ionic conductivity. In Comparative Example 4, since the MOF material is simply coated onto the separator, it is easy for it to agglomerate on the separator, resulting in a significant decrease in both ionic conductivity and capacity retention. In addition, a comparison of the data from Examples 1, 9, and 10 also shows that the type of MOF material also affects the performance of the composite polymer solid electrolyte. When the type is HKUST-1 or MOF-5, it is more conducive to improving battery performance.

[0129] In summary, the composite solid electrolyte provided by this invention can achieve the following effects:

[0130] (1) The electrolyte of locally high-concentration lithium salt can enter the channels of metal-organic framework (MOFs) for encapsulation. Solvent molecules form bonds with the MOFs framework, which disperses the electron cloud distribution of solvent molecules and weakens their effect on lithium ions, making it easier for lithium salt to dissociate into free lithium ions. When migrating in the regular channels of MOFs, the resistance is smaller and the rate is faster. The increase in free lithium ion concentration and the acceleration of migration work together to significantly improve the ionic conductivity of the system.

[0131] (2) The in-situ growth of metal-organic frameworks on the membrane also significantly enhances the interaction between the composite polymer solid electrolyte and the membrane, and increases the adhesion between the metal-organic framework and the membrane; the support of the membrane fiber is conducive to the distribution of MOF particles in the polymer, and eliminates the sedimentation and agglomeration of MOF particles in the slurry; the in-situ growth of MOF crystals and the interaction between the crystals reduce the interfacial impedance between particles and enhance the construction of lithium-ion transport channels based on MOFs.

[0132] (3) The encapsulation of local high-concentration electrolyte containing flame-retardant diluent in the MOF channels also improves the safety performance of composite polymer electrolyte.

[0133] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite polymer solid-state electrolyte, characterized by, The composite polymer solid-state electrolyte comprises a separator and a MOFs material grown in situ on at least one side surface of the separator, the MOFs material encapsulating a solvent-based electrolyte in its pores, and the MOFs material being coated with a lithium-containing salt-containing polymer between particles and on a surface thereof; The solvent-based electrolyte is a non-ionic liquid-based electrolyte, comprising a solvent, a diluent with flame-retardant properties, and a first lithium salt, the concentration of the first lithium salt being greater than or equal to 2 mol / L.

2. The composite polymer solid-state electrolyte of claim 1, wherein, The separator comprises a fiber-based separator. Preferably, the material of the separator comprises any one of polyester, polyimide, polytetrafluoroethylene, or aramid fiber. Preferably, the thickness of the separator is 5 μm to 60 μm.

3. The composite polymer solid-state electrolyte according to claim 1 or 2, characterized in that, The MOFs material comprises HKUST-1 or MOF-5. Preferably, the mass fraction of the MOFs material in the composite polymer solid-state electrolyte is 1% to 85%.

4. The composite polymer solid-state electrolyte according to any one of claims 1 to 3, wherein The diluent comprises any one of tris(2,2,2-trifluoroethyl) phosphate, a tris(2,2,2-trifluoroethyl) phosphate derivative, bis(2,2,2-trifluoroethyl) methyl phosphate, or a bis(2,2,2-trifluoroethyl) methyl phosphate derivative, or a combination of at least two thereof. Preferably, the mass ratio of the solvent to the diluent is 1:(1 to 4). Preferably, in the solvent-based electrolyte, the concentration of the first lithium salt is 2 mol / L to 6.5 mol / L.

5. The composite polymer solid-state electrolyte according to any one of claims 1 to 4, wherein The lithium salt in the lithium-containing salt-containing polymer comprises a second lithium salt, and the polymer in the lithium-containing salt-containing polymer comprises any one of polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polyacrylonitrile, or polyacrylamide, or a combination of at least two thereof. Preferably, the mass fraction of the lithium-containing salt-containing polymer in the composite polymer solid-state electrolyte is 1% to 15%.

6. A method of producing the composite polymer solid-state electrolyte according to any one of claims 1 to 5, characterized by, The preparation method comprises: (1) growing a MOFs material in situ on at least one side surface of a separator to obtain a composite separator; (2) immersing the composite separator obtained in step (1) in a solvent-based electrolyte, and removing excess liquid on the surface of the composite separator after the immersion is completed to obtain a composite separator encapsulating a solvent-based electrolyte; (3) coating a mixed solution containing a polymer monomer, a second lithium salt, an initiator, and a solvent to one side surface of the composite separator encapsulating a solvent-based electrolyte obtained in step (2) on which the MOFs material is grown in situ, and obtaining the composite polymer solid-state electrolyte after in-situ polymerization.

7. The preparation method according to claim 6, characterized in that, The method for growing in situ in step (1) comprises immersing a separator in a mixed solution containing a metal salt, a ligand, and a solvent to react, and then performing heat treatment on the separator after the reaction to obtain the composite separator.

8. The production method according to claim 6 or 7, characterized by, The immersion in step (2) is performed under ultrasonic and stirring conditions. Preferably, the immersion time in step (2) is 6 h to 24 h. Preferably, the immersion temperature in step (2) is 2°C to 50°C. Preferably, the way of removing the excess liquid on the surface of the composite separator in step (2) comprises vacuum suction filtration.

9. The method of any one of claims 6-8, wherein, The concentration of the second lithium salt in the mixed solution in step (3) is 0.6 mol / L to 6.5 mol / L. Preferably, the coating method of step (3) comprises spraying. Preferably, the temperature of the in-situ polymerization of step (3) is 55-70℃. Preferably, the time of the in-situ polymerization of step (3) is 6-24h.

10. A secondary battery characterized by comprising: The secondary battery comprises the composite polymer solid-state electrolyte according to any one of claims 1-5, and the secondary battery comprises a semi-solid battery.

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