Lithium ion conductive dense film and preparation method and application thereof

Abstract

The invention relates to a lithium ion conductive dense membrane and a preparation method and application thereof. The lithium ion conductive dense membrane comprises a polymer base membrane, ion conductive inorganic particles and a polymer solid electrolyte, the polymer base membrane is of a net structure; the Gurley value of the lithium ion conductive dense film is larger than or equal to 1000, and the porosity is smaller than or equal to 5%. The lithium ion conductive dense membrane provided by the invention has the advantages of high lithium ion conductivity, high transport efficiency and high lithium ion selectivity, and can be applied to electrodialysis lithium extraction. And under the action of external voltage, lithium ions are directionally migrated to the air negative electrode subjected to oxygen reduction reaction through the lithium ion conductive dense membrane to form a lithium hydroxide solution, and other metal hetero-ions are isolated on the positive electrode side by the lithium ion conductive dense membrane, so that lithium enrichment is realized. And meanwhile, transportation of the membrane to lithium ions does not depend on pores in the conductive membrane, so that the service life can be prolonged while the lithium ion separability and the transportation efficiency of the salt lake lithium extraction method are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction from brine, and in particular to a lithium ion conductive dense membrane, a preparation method thereof and uses thereof. Background Art

[0003] Current methods for lithium extraction from brine mainly include chemical precipitation method, calcination impregnation method, extraction method, adsorption method, membrane separation method, etc., but most of these methods have defects.

[0004] The precipitation method needs to use a large amount of chemical raw materials to generate lithium salt precipitation, producing a large amount of side reaction pollutants and having a low lithium salt production rate. The calcination impregnation method is to first calcine the mixed salt obtained from concentrated brine at high temperature, remove impurities after water leaching, and finally concentrate the leaching solution and introduce Na 2 CO 3 to obtain lithium salt precipitation. This method involves multiple concentration processes, with high energy requirements and complex processes. The extraction method uses extractants to extract and separate lithium resources from salt lake brine. Most extractant systems are limited to the laboratory level. In addition, there is also the problem that the extraction solvent volatilizes and pollutes the environment. The adsorption method anchors lithium in the brine through physical and chemical reactions between the brine and the adsorbent, and then uses the desorbing solution to enrich lithium in the lithium extraction solution, thereby achieving the effect of lithium extraction. This method has poor versatility and there is also the problem of adsorbent fragmentation and dissolution during the application process.

[0005] The membrane separation method generally uses the differences in the sizes and hydration energies of different metal ions to selectively retain metal ions, and has the advantages of simple process, low cost and high yield. However, due to the similarities in ionic radius and other aspects between lithium ions and metal ions such as sodium ions and magnesium ions, the metal ion selectivity of the membrane separation method still needs to be further improved, and the complex structure of the membrane often results in poor long-term production capacity of the membrane.

[0006] CN106629786A discloses an electrodialysis lithium extraction method, which is based on the principle transport and retention of metal cations by an ion conductive membrane. However, in the lithium extraction system of this patent, a commercial selective monovalent ion exchange membrane is used. The selectivity of such membranes is often based on the differences in ion size and hydration energy, and the selectivity for lithium ions is poor, and precise single-ion selective transport cannot be achieved. In addition, the transport of lithium ions in such membranes often depends on the voids and pores in the membrane, and impurity ions often accumulate on the membrane surface or in the pores, polluting the membrane.

[0007] The lithium extraction methods in the prior art all require the use of a large amount of chemical raw materials, often involving multiple processes, and have a series of defects such as complex processes, high costs, and environmental pollution. The adsorption method has the problem of poor versatility, and the breakage of the adsorbent will also cause the production capacity to gradually decline over time. The membrane separation method mostly selectively intercepts metal ions by utilizing the differences in the sizes and hydration energies of different metal ions. When the relevant properties of impurity ions such as magnesium ions and sodium ions are similar to those of lithium ions, it is difficult to achieve the complete and separate separation of lithium ions. Moreover, the impurity ions often accumulate on the surface or in the pores of the filter membrane, causing pollution to the filter membrane and reducing the long-term production capacity of the filter membrane.

[0008] Therefore, how to develop a conductive membrane with a simple process, not prone to blockage of the surface pores of the filter membrane, and capable of efficiently separating lithium ions has become an urgent problem to be solved at present. Summary of the Invention

[0009] To solve the above technical problems, the purpose of the present invention is to provide a lithium-ion conductive dense membrane, its preparation method and uses. The lithium-ion conductive dense membrane provided by the present invention has strong transport selectivity for Li + It can improve the selectivity of ion transport under an applied current, realize the enrichment of LiOH at the cathode, and thus complete the process of extracting lithium from brine. In the lithium-ion dense membrane provided by the present invention, ions are transported through a solid-state ion conductor, having a single transport selectivity, good lithium-ion separation effect, wide application range, and since the ion transport in the present invention does not depend on pores, the long-term production capacity is strong.

[0010] To achieve this purpose, the present invention adopts the following technical solutions:

[0011] In the first aspect, the present invention provides a lithium-ion conductive dense membrane, which comprises a polymer-based membrane, ion-conductive inorganic particles, and a polymer solid electrolyte; the polymer-based membrane is a network structure.

[0012] The ion-conductive inorganic particles and the polymer solid electrolyte are respectively and uniformly filled in the pores of the polymer-based membrane, and at the same time, the polymer solid electrolyte wraps the fiber filaments in the polymer-based membrane.

[0013] The Gurley value of the lithium-ion conductive dense membrane is ≥1000, for example, it can be 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0014] The porosity of the lithium-ion conductive dense film is ≤5%, for example, it can be 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5% or 1%, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] The lithium-ion conductive dense film provided by the present invention uses a polymer solid electrolyte and ion-conductive inorganic particles to fill a polymer-based film, and has the advantages of strong lithium-ion conduction ability, high transport efficiency, and strong selectivity for lithium ions. The lithium-ion conductive dense film is composed of a polymer-based film with an internally interconnected "loofah sponge"-like network structure, ion-conductive inorganic particles, and a continuous polymer solid electrolyte. The network-structured substrate film can effectively carry the polymer solid electrolyte and ion-conductive inorganic particles, thereby forming a large number of transport channels for the directional movement of lithium ions; the Gurley value of the lithium-ion conductive dense film is ≥1000. The low porosity of the lithium-ion conductive dense film can increase the effective contact area between lithium ions and the lithium-ion conductive dense film, while reducing the pores inside the lithium-ion conductive dense film through which impurity ions can pass, improving selectivity and separation efficiency.

[0016] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0017] Preferably, based on the total mass of the lithium-ion conductive dense film being 100 wt%, the mass fraction of the ion-conductive inorganic particles is 5 wt% - 50 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable, and preferably 10 wt% - 20 wt%.

[0018] In the present invention, by further controlling the mass fraction of the ion-conductive inorganic particles to be 5 wt% - 50 wt%, the ionic conductivity and mechanical strength of the lithium-ion conductive dense film can be improved, and the porosity of the lithium-ion conductive dense film can be reduced. If the mass fraction of the ion-conductive inorganic particles is too low, the ionic conductivity and separation efficiency of the lithium-ion conductive dense film will decrease; if the mass fraction of the ion-conductive inorganic particles is too high, the porosity of the lithium-ion conductive dense film will increase due to poor interfacial contact between the inorganic particles, thereby reducing the selectivity of the lithium-ion conductive dense film.

[0019] Preferably, the mass fraction of the polymer solid electrolyte is 5 wt% - 50 wt%, and the mass fraction of the ion-conductive inorganic particles is 5 wt% - 50 wt%. For example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 10 wt% - 20 wt%. The balance is the polymer-based membrane.

[0020] Preferably, the polymer-based membrane is a high-porosity base membrane.

[0021] The present invention further adopts a high-porosity base membrane. Using a high-porosity base membrane is beneficial to the construction of an internal lithium-ion selective transport pathway and can more effectively achieve the selective separation of Li + . At the same time, the high-porosity base membrane provides sufficient space for the filling of ion-conductive inorganic particles and polymer electrolytes, and can further improve the ionic conductivity and separation coefficient of the lithium-ion conductive dense membrane.

[0022] Preferably, the polymer-based membrane includes any one or a combination of at least two of a cellulose-based membrane, a PET-based membrane or a glass fiber-based membrane.

[0023] Preferably, the ion-conductive inorganic particles include an oxide solid electrolyte material and / or a lithium salt material having ion-electron conductivity.

[0024] Preferably, the thickness of the lithium-ion conductive dense membrane is 5 μm - 100 μm. For example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 7 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0025] Preferably, the ion-conductive inorganic particles include large particles with an average particle size of 200 nm - 5 μm and small particles with an average particle size of 20 nm - 100 nm. For example, the average particle size of the large particles can be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable. The average particle size of the small particles can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0026] In the present invention, the ion-conductive inorganic particles are filled in the pores by blending large particles and small particles, which can effectively fill the pores of the polymer-based membrane. If ion-conductive inorganic particles with a smaller average particle size are further used, the interfacial contact between the inorganic particles and between the inorganic particles and other components in the ion-conductive dense membrane can be improved, further reducing the porosity of the ion-conductive membrane, reducing the transport path of impurity ions in the ion-conductive membrane, and further improving the selectivity of the ion-conductive membrane for Li + .

[0027] Preferably, based on the total mass of the ion-conductive inorganic particles being 100 wt%, the large particles with an average particle size of 200 nm - 5 μm in the ion-conductive inorganic particles account for 0 wt% - 60 wt%, including 0 wt%, and the small particles with an average particle size of 20 nm - 100 nm account for 40 wt% - 100 wt%, including 100 wt%. For example, the large particles with an average particle size of 200 nm - 5 μm can account for 0 wt%, 5 wt%, 10 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 33 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt%, or 60 wt%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the oxide solid electrolyte material includes any one or a combination of at least two of lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium oxide (LLZO), tantalum-doped lithium lanthanum zirconium oxide (LLZTO), or lithium aluminum titanium phosphate (LATP). Typical but non-limiting combinations include the combination of lithium lanthanum titanium oxide and lithium lanthanum zirconium oxide, the combination of lithium lanthanum zirconium oxide and tantalum-doped lithium lanthanum zirconium oxide, the combination of lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate, the combination of lithium lanthanum zirconium oxide, tantalum-doped lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate, the combination of lithium lanthanum titanium oxide, tantalum-doped lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate, the combination of lithium lanthanum titanium oxide and lithium aluminum titanium phosphate, the combination of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, tantalum-doped lithium lanthanum zirconium oxide and lithium aluminum titanium phosphate.

[0029] Preferably, the lithium salt material having ion-electronic conductivity includes any one or a combination of at least two of lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), or lithium manganese iron phosphate (LMFP). Typical but non-limiting combinations include the combination of lithium cobalt oxide (LCO) and lithium iron phosphate (LFP), the combination of lithium manganese oxide (LMO) and lithium nickel cobalt manganese oxide (NCM), the combination of lithium nickel cobalt aluminum oxide (NCA) and lithium manganese iron phosphate (LMFP), the combination of lithium cobalt oxide (LCO), lithium iron phosphate (LFP) and lithium manganese oxide (LMO), the combination of lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), the combination of lithium cobalt oxide (LCO), lithium iron phosphate (LFP), lithium manganese oxide (LMO) and lithium manganese iron phosphate (LMFP).

[0030] Preferably, the polymer solid electrolyte includes a polymer material and / or a crosslinking agent.

[0031] Preferably, the polymer material includes any one or a combination of at least two of polytetrafluoroethylene, polyethylene oxide, polyvinyl alcohol, or cationic polyionic liquid, preferably cationic polyionic liquid. Typical but non-limiting combinations include the combination of polytetrafluoroethylene and polyethylene oxide, the combination of polyvinyl alcohol and cationic polyionic liquid, the combination of polyethylene oxide and polyvinyl alcohol, the combination of polytetrafluoroethylene, polyethylene oxide and cationic polyionic liquid, the combination of polytetrafluoroethylene, polyethylene oxide, polyvinyl alcohol and cationic polyionic liquid.

[0032] Preferably, the general formula of the cationic polyionic liquid monomer is A + [B] - , where the anion [B] - includes TFSI (bis(trifluoromethanesulfonyl)imide anion), FSI- (bis(fluorosulfonyl)imide anion), PF 6 - or BF 4 -Any one or a combination of at least two of them, cation A + The structure includes any one or a combination of at least two of the following structures of formula (1) - formula (10), and contains at least one unsaturated group.

[0033]

[0034] The present invention further selects cationic polymerized ionic liquid monomers. Compared with other polymers, since ionic liquids have the effect of promoting the dissociation of lithium salts, after filling the pores with such cationic polymerized ionic liquid monomers, the ion transport performance of the ion-conductive dense membrane for lithium ions is enhanced.

[0035] Preferably, the cross-linking agent includes any one or a combination of at least two of polyethylene glycol diacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, or ethylene glycol dimethacrylate. Typical but non-limiting combinations include the combination of polyethylene glycol diacrylate and trimethylolpropane trimethacrylate, the combination of 1,4-butanediol diacrylate and ethylene glycol dimethacrylate, the combination of trimethylolpropane trimethacrylate and trimethylolpropane trimethacrylate, the combination of trimethylolpropane trimethacrylate and ethylene glycol dimethacrylate, and the combination of polyethylene glycol diacrylate, 1,4-butanediol diacrylate, and ethylene glycol dimethacrylate.

[0036] In a second aspect, the present invention provides a method for preparing a lithium-ion conductive dense membrane as described in the first aspect. The preparation method includes the following steps:

[0037] (1) Mixing ion-conductive inorganic particles, polymer solid electrolyte monomers, initiators, and solvents to obtain a pore-filling slurry;

[0038] (2) Introducing the pore-filling slurry into a polymer-based membrane, and after drying, polymerization reaction, and rolling, a lithium-ion conductive dense membrane is obtained.

[0039] The preparation method of the present invention is simple. By filling the pores after mixing the raw materials, in-situ polymerization of the polymer solid electrolyte monomers can be achieved, which can effectively fill the polymer-based membrane with the polymer solid electrolyte and ion-conductive inorganic particles. While fully constructing the lithium-ion transport path inside the lithium-ion conductive dense membrane, the porosity is reduced, and the transport efficiency and selectivity of the lithium-ion conductive dense membrane are further enhanced. The ion-conductive dense membrane prepared by the method of in-situ polymerization has excellent selective transport performance for lithium ions and can well achieve the separation of Li from brine + purpose.

[0040] Preferably, the polymerization reaction in step (2) is a photopolymerization reaction and / or a thermal polymerization reaction.

[0041] The present invention introduces a polymer solid electrolyte material into a lithium-ion conductive dense film by an in-situ polymerization method. The photo / thermal polymerization method is simple and efficient, can effectively control the reaction process, and the prepared lithium-ion conductive dense film has a high degree of polymerization, good wettability, and controllable mechanical strength.

[0042] Preferably, the method of the photo-polymerization reaction is as follows: The polymer-based film injected with the hole-filling slurry is placed on a transparent glass plate and irradiated with an ultraviolet lamp. The irradiation time on both sides is 0 min - 10 min, excluding 0 min. For example, it can be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min or 10 min, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. Preferably, it is 2 min - 5 min.

[0043] Preferably, the method of the thermal polymerization reaction is as follows: The polymer-based film injected with the hole-filling slurry after drying is heated under vacuum conditions. The heating temperature is 40°C - 100°C. For example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. Preferably, it is 60°C - 80°C.

[0044] Preferably, the heating time in the thermal polymerization reaction is 2 h - 24 h. For example, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but not limited to the listed values. Other unlisted values within the numerical range are equally applicable. Preferably, it is 6 h - 12 h.

[0045] Preferably, the initiator includes any one or a combination of at least two of azobisisobutyronitrile (AIBN), potassium persulfate, sodium persulfate, benzoyl peroxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (photoinitiator 819), or 2-hydroxy-2-methyl-1-phenylpropan-1-one (photoinitiator 1173). Typical but non-limiting combinations include the combination of azobisisobutyronitrile (AIBN) and potassium persulfate, the combination of potassium persulfate and sodium persulfate, the combination of sodium persulfate and benzoyl peroxide, the combination of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (photoinitiator 819), and the combination of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (photoinitiator 819) and 2-hydroxy-2-methyl-1-phenylpropan-1-one (photoinitiator 1173).

[0046] Preferably, the solvent includes any one or a combination of at least two of N-methylpyrrolidone, acetonitrile, 1,3-dioxolane, N,N-dimethylformamide (DMF), N,N-dimethylacetamide, dimethyl ether, ethyl acetate, chloroform, or n-hexane. Typical but non-limiting combinations include the combination of N-methylpyrrolidone and acetonitrile, the combination of acetonitrile and 1,3-dioxolane, the combination of N,N-dimethylacetamide and dimethyl ether, the combination of ethyl acetate, chloroform, and n-hexane, and the combination of N-methylpyrrolidone, acetonitrile, and n-hexane.

[0047] Preferably, the ion-conductive inorganic particles account for 5wt% - 50wt% of the hole-filling paste. For example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, or 50wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably 10wt% - 20wt%.

[0048] Preferably, the polymer solid electrolyte monomer accounts for 5wt% - 50wt% of the hole-filling paste. For example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, or 50wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably 10wt% - 20wt%.

[0049] Preferably, the initiator accounts for 0.01 wt% - 5 wt% of the total mass of the polymer solid electrolyte monomer and the initiator. For example, it can be 0.01 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 0.1 wt% - 2 wt%.

[0050] Preferably, the solvent accounts for 40 wt% - 95 wt% of the hole-filling slurry. For example, it can be 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt% or 95 wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 50 wt% - 90 wt%.

[0051] Preferably, the drying is carried out under normal pressure or in a vacuum state.

[0052] Preferably, the drying temperature is 30°C - 100°C. For example, it can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 40°C - 80°C.

[0053] Preferably, the drying time is 1 h - 24 h. For example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 2 h - 12 h.

[0054] Preferably, the roll-pressed thickness is set to 50% - 100% of the thickness of the ion-conductive membrane before roll-pressing, excluding 100%. For example, it can be 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt% or 100 wt%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable, and preferably it is 75% - 95%.

[0055] The present invention further reduces the porosity of the existing ion-conducting membrane by introducing a rolling process, enhancing the selectivity of the membrane during ion transport.

[0056] Preferably, before and / or after rolling, and before obtaining the lithium-ion conducting dense membrane, the step (2) is repeated 1 to 6 times for the lithium-ion conducting dense membrane.

[0057] As a preferred technical solution of the preparation method of the present invention, the preparation method includes the following steps:

[0058] (1) Mix ion-conducting inorganic particles, polymer solid electrolyte monomers, initiators, and solvents according to a mass ratio to obtain a pore-filling slurry.

[0059] (2) Immerse the polymer-based membrane in the pore-filling slurry for 5 to 10 hours. After completion, scrape off the remaining pore-filling slurry on the surface of the polymer-based membrane, and vacuum dry for 2 to 12 hours at 40°C to 80°C to remove the solvent. Perform photopolymerization or thermal polymerization reactions, and repeat the above immersion-drying-polymerization reaction process 1 to 6 times. After rolling, a lithium-ion conducting dense membrane is obtained.

[0060] The conditions for the photopolymerization reaction are: Place the polymer-based membrane containing the pore-filling slurry on a transparent glass plate and irradiate it with an ultraviolet lamp, irradiating both sides for 2 to 5 minutes respectively.

[0061] The conditions for the thermal polymerization reaction are: Heat the dried polymer-based membrane containing the pore-filling slurry under vacuum conditions, and heat at 60°C to 80°C for 6 to 12 hours.

[0062] In a third aspect, the present invention provides a use of the lithium-ion conducting dense membrane as described in the first aspect, and the lithium-ion conducting dense membrane is used for extracting lithium from brine by electrodialysis.

[0063] Under the action of an external electric field for the lithium-ion conducting dense membrane provided by the present invention, the ions in the brine migrate directionally, and the cations migrate to the cathode. Among them, Li + can be transported to the cathode through the solid lithium-ion conductor in the dense membrane, while other impurity metal cations cannot complete the migration through the dense membrane. Finally, Li + is enriched at the cathode. At the same time, the selective transport of lithium ions by the lithium-ion conducting dense membrane provided by the present invention does not depend on the pores in the conductive membrane, and the damage to the long-term production capacity of the conductive membrane caused by membrane blockage can be inhibited, effectively improving the service life of the lithium-ion conducting dense membrane. At the same time, the voltage applied to the device can be reduced, the cost is lower, the structure is safe and stable, and the application range is wider.

[0064] The numerical ranges described in the present invention include not only the above-listed point values, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the described ranges.

[0065] Compared with the prior art, the present invention has at least the following beneficial effects:

[0066] (1) The lithium-ion conductive dense film provided by the present invention uses a polymer solid electrolyte and ion-conductive inorganic particles to fill a polymer-based film, having the advantages of strong lithium-ion conduction ability, high transport efficiency, strong selectivity for lithium ions, and at the same time can reduce the voltage applied to the device, lower cost, safe and stable structure, and wider application range.

[0067] (2) The preparation method of the present invention is simple. By mixing raw materials, in-situ polymerization of polymer solid electrolyte monomers is carried out to effectively fill the polymer-based film with the polymer solid electrolyte and ion-conductive inorganic particles. While fully constructing the internal lithium-ion transport path of the lithium-ion conductive dense film, the porosity is reduced, further enhancing the transport efficiency and selectivity of the lithium-ion conductive dense film. The ion-conductive film prepared by the in-situ polymerization method has excellent selective transport performance for lithium ions and can well achieve the separation of Li from brine. + purpose.

[0068] (3) Under the action of an external electric field in the lithium-ion conductive dense film provided by the present invention, the ions in the brine migrate directionally, and the cations migrate to the cathode. Among them, Li + can be transported to the cathode through the solid lithium-ion conductor in the dense film, while other impurity metal cations cannot complete the migration through the dense film. Finally, the enrichment of Li at the cathode is realized. At the same time, the transport of lithium ions by the lithium-ion conductive dense film provided by the present invention does not depend on the pores in the conductive film, and the damage of film blockage to the long-term production capacity of the conductive film can be inhibited, effectively improving the service life of the lithium-ion conductive dense film. + In the cathode enrichment. At the same time, the lithium-ion conductive dense film provided by the present invention does not rely on the pores in the conductive film for the transport of lithium ions, and the damage of film blockage to the long-term production capacity of the conductive film can be inhibited, effectively improving the service life of the lithium-ion conductive dense film. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a schematic structural diagram of the lithium-ion conductive dense film prepared in Example 1 of the present invention. Among them, 1 - ion-conductive inorganic particles, 2 - polymer-based film, 3 - polymer solid electrolyte;

[0070] Figure 2 is a schematic structural diagram of the lithium extraction device of the present invention. Among them, 4 - graphite electrode, 5 - brine pool, 6 - lithium-ion conductive dense film, 7 - fresh water pool, 8 - platinum wire electrode;

[0071] Figure 3 is the Li near the cathode during the lithium extraction process in Example 1 of the present invention. + / Mg 2+ and the separation coefficient (the ratio of Li near the cathode and the anode) + / Mg 2+ versus time. Specific Embodiments

[0072] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and through specific embodiments. However, the following examples are merely simple examples of the present invention and do not represent or limit the scope of the claimed protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0073] In the following examples and comparative examples, unless otherwise specified, all reagents and consumables are purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and technical means used are conventional methods and means in the art.

[0074] Example 1

[0075] This example provides a lithium-ion conductive dense film, which includes a polymer-based film, ion-conductive inorganic particles, and a polymer solid electrolyte; the polymer-based film has a network structure; the Gurley value of the lithium-ion conductive dense film is 2855, and the porosity is 2.5%;

[0076] Based on the total mass of the lithium-ion conductive dense film being 100 wt%, the mass fraction of the ion-conductive inorganic particles is 9.75 wt%; the mass fraction of the polymer solid electrolyte is 9.25 wt%; the thickness of the lithium-ion conductive dense film is 75 μm.

[0077] The preparation method of the lithium-ion conductive dense film provided in this example includes the following steps:

[0078] (1) Mix lithium iron phosphate powder as ion-conductive inorganic particles (the mass ratio of large particles with an average particle size of 3 μm and small particles with an average particle size of 50 nm is 1:1), a polymer solid electrolyte monomer (methyl methacrylate), a photoinitiator (819), and a DMF solvent in a mass ratio, and stir at room temperature for 12 h to obtain a hole-filling slurry;

[0079] Based on the total mass of the hole-filling slurry being 100 wt%, among them, the mass fraction of the ion-conductive inorganic particles is 10 wt%, the mass fraction of the polymer solid electrolyte monomer (methyl methacrylate) and the photoinitiator is 10 wt%, and among them, the photoinitiator accounts for 1 wt% of the total mass of the polymer solid electrolyte monomer (methyl methacrylate) and the photoinitiator.

[0080] (2) Immerse the cellulose-based membrane in the hole-filling slurry for 6 h. After completion, scrape off the remaining hole-filling slurry on the surface of the polymer-based membrane and vacuum dry it at 55 °C for 12 h to remove the solvent. After drying, place the membrane on a transparent glass plate and irradiate it with an ultraviolet lamp for 3 min on each side. Carry out the photopolymerization reaction, and repeat the above immersion-drying-polymerization reaction process 2 times to obtain a lithium-ion conductive dense membrane.

[0081] The structural schematic diagram of the prepared lithium-ion conductive dense membrane is as Figure 1 shown. It can be seen from Figure 1 that the network-shaped cellulose-based membrane serves as a carrier to support the polymer solid electrolyte, and inorganic conductive particles are uniformly distributed inside the solid electrolyte.

[0082] Example 2

[0083] This example provides a lithium-ion conductive dense membrane, which is only different from Example 1 in that in step (2), the cellulose-based membrane is replaced with a high-porosity glass fiber-based membrane.

[0084] Example 3

[0085] This example provides a lithium-ion conductive dense membrane, which is only different from Example 2 in that methyl methacrylate is replaced with allyltrimethylammonium bis(trifluoromethanesulfonyl)imide salt with the same mass fraction.

[0086] Example 4

[0087] This example provides a lithium-ion conductive dense membrane, which is only different from Example 3 in that 10% allyltrimethylammonium bis(trifluoromethanesulfonyl)imide salt in the hole-filling slurry is replaced with 9% allyltrimethylammonium bis(trifluoromethanesulfonyl)imide salt + 1% polyethylene glycol diacrylate (PEGDA).

[0088] Example 5

[0089] This example provides a lithium-ion conductive dense membrane, which is only different from Example 4 in that the lithium iron phosphate powder with large particles having an average particle size of 3 μm and small particles having an average particle size of 50 nm mixed in a mass ratio of 1:1 in the hole-filling slurry is replaced with lithium iron phosphate powder having an average particle size of 50 nm with the same mass.

[0090] Example 6

[0091] This example provides a lithium-ion conductive dense membrane, which is only different from Example 5 in that the lithium iron phosphate powder with an average particle size of 50 nm in the hole-filling slurry is replaced with lithium lanthanum zirconium oxide (LLZO) powder having an average particle size of 50 nm with the same mass.

[0092] Example 7

[0093] This embodiment provides a lithium-ion conductive dense film, which is only different from Embodiment 6 in that a rolling process is introduced after each drying, and after rolling, the ion conductive film is placed on a transparent glass plate and irradiated with an ultraviolet lamp for 3 minutes on each side.

[0094] Embodiment 8

[0095] This embodiment provides a lithium-ion conductive dense film, which is only different from Embodiment 1 in that the mass fraction of the ion conductive inorganic particles is 4 wt%.

[0096] Embodiment 9

[0097] This embodiment provides a lithium-ion conductive dense film, which is only different from Embodiment 1 in that the mass fraction of the ion conductive inorganic particles is 55 wt%.

[0098] Embodiment 10

[0099] This embodiment provides a lithium-ion conductive dense film, which is only different from Embodiment 1 in that when preparing the lithium-ion conductive dense film, the cellulose-based film is replaced with a nylon mesh cloth (pore size of 150 μm and thickness of 98 μm).

[0100] Embodiment 11

[0101] This embodiment provides a lithium-ion conductive dense film, which is only different from Embodiment 1 in that when preparing the lithium-ion conductive dense film, all the lithium iron phosphate powders are large particles with an average particle size of 3 μm.

[0102] Comparative Example 1

[0103] This comparative example provides a lithium-ion conductive film, which is only different from Embodiment 1 in that when preparing the lithium-ion conductive dense film, 10% of the methyl methacrylate pre-dissolved with photoinitiator 819 in the hole-filling slurry is replaced with the ion conductive inorganic particle lithium iron phosphate powder (the mass ratio of large particles with an average particle size of 3 μm to small particles with an average particle size of 50 nm is 1:1), that is, the hole-filling slurry does not contain a polymer solid electrolyte.

[0104] Comparative Example 2

[0105] This comparative example provides a lithium-ion conductive film, which is only different from Embodiment 1 in that when preparing the lithium-ion conductive dense film, lithium iron phosphate is replaced with sodium vanadate phosphate.

[0106] Comparative Example 3

[0107] This comparative example provides a lithium-ion conductive film, which is only different from Embodiment 1 in that when preparing the lithium-ion conductive dense film, no polymerization reaction is carried out.

[0108] Comparative Example 4

[0109] This comparative example provides a lithium-ion conductive membrane, which is only different from that in Example 1 in that methyl methacrylate and the initiator in step (1) are replaced by polymethyl methacrylate, and the polymerization reaction in step (2) is not carried out.

[0110] Test method: The prepared lithium-ion conductive dense membranes in the examples and comparative examples were tested. The structural schematic diagram of the lithium extraction device of the present invention is referred to Figure 2 (4 - graphite electrode, 5 - brine pool, 6 - lithium-ion conductive dense membrane, 7 - fresh water pool, 8 - platinum wire electrode). The above-mentioned dense ion conductive membrane was used to separate the anode brine (Mg 2+ concentration is 10 g / L, Li + concentration is 0.1 g / L) and the cathode fresh water. An external voltage of 1.0 V was applied for 0.5 h, and the cathode solution was taken to detect Mg 2+ and Li + concentrations 15 min after power-on and after the power-on was completed. The test results are shown in Table 1 below.

[0111] Figure 3 is the change of Li + / Mg 2+ and the separation coefficient (the ratio of Li + / Mg 2+ near the cathode to that near the anode) with time during the lithium extraction process in Example 1 of the present invention. It can be seen from the figure that after 15 min of power-on, effective enrichment of lithium ions was achieved near the cathode, and the lithium / magnesium ratio near the cathode did not increase significantly after continuing to power on for 15 min, which confirmed that the lithium-ion conductive dense membrane prepared in Example 1 has excellent separation efficiency and can complete the enrichment process of lithium ions in a short time.

[0112] Test standard: Please refer to Figure 2 , using the lithium-ion conductive dense membrane prepared in the example to separate the anode brine (Mg 2+ concentration is 10 g / L, Li + concentration is 0.1 g / L) and the cathode fresh water. An external voltage of 1.0 V was applied for 0.5 h, and the cathode solution was taken to detect Mg 2+ and Li + concentrations 15 min after power-on and after the power-on was completed. The results are shown in Table 1.

[0113] Table 1

[0114] Gurley value 15-minute separation coefficient Example 1 2855 16.73 Example 2 2780 18.61 Example 3 2824 19.47 Example 4 2916 19.92 Example 5 3678 20.66 Example 6 3606 24.14 Example 7 4114 24.69 Example 8 4142 12.54 Example 9 2236 10.59 Example 10 839 8.74 Example 11 2551 13.86 Comparative Example 1 428 1.35 Comparative Example 2 2683 1.18 Comparative Example 3 397 0.69 Comparative Example 4 3239 0.35

[0115] It can be seen from the test results that:

[0116] (1) As can be seen from Example 1, the lithium-ion conductive dense film provided by the present invention uses a polymer solid electrolyte and ion-conductive inorganic particles to fill a polymer-based film, and has the advantages of strong lithium-ion conduction ability, high transport efficiency, and strong selectivity for lithium ions. The ion-conductive film prepared by in-situ polymerization has excellent selective transport performance for lithium ions, and can well achieve the separation of Li from brine. + Purpose.

[0117] (2) By comparing Example 1 and Example 2, it can be found that: by further preferably using a high-porosity base film as the polymer-based film in the present invention, it is more conducive to the construction of a lithium-ion selective transport path, and can more effectively achieve the selective separation of Li. + Selective separation.

[0118] (3) By comparing Example 2 and Example 3, it can be found that: after the present invention further preferably uses a polymerizable ionic liquid monomer-based ion conductor to replace the original polymer filling holes, due to the dissociation effect of the ionic liquid on the lithium salt, the transport performance of the ion-conductive film for lithium ions is enhanced.

[0119] (4) By comparing Example 3 and Example 4, it can be found that: by further introducing PEGDA (polyethylene glycol diacrylate) as a cross-linking agent in the present invention, the polymer structure changes into a three-dimensional network type, the mechanical properties of the ion-conductive film are enhanced, and the ether oxygen bond in PEGDA is beneficial to enhancing the transport performance of the ion-conductive film for lithium ions.

[0120] (5) By comparing Example 4 and Example 5, it can be found that: by further reducing the particle size of the ion-conductive inorganic particles in the present invention, the porosity of the ion-conductive film is further reduced, the transport path of impurity ions in the ion-conductive film is reduced, and the selectivity of the ion-conductive film for Li is further improved. + Selectivity.

[0121] (6) By comparing Example 5 and Example 6, it can be found that: by further preferably using the fast lithium-ion conductor lithium lanthanum zirconium oxide (LLZO) to replace lithium iron phosphate in the present invention, the lithium-ion transport path in the base film is improved, and the transport performance of the ion-conductive film for lithium ions is enhanced.

[0122] (7) By comparing Example 6 and Example 7, it can be found that: by further introducing a rolling process in the present invention, the porosity of the existing ion-conductive film is further reduced, and the selectivity of the film during ion transport is enhanced.

[0123] (8) It can be seen from the comparison between Example 1 and Examples 8 - 9 that by further controlling the mass fraction of the ion-conductive inorganic particles to be 5wt% - 50wt%, the present invention can improve the ionic conductivity and mechanical strength of the lithium-ion conductive dense film, and reduce the porosity of the lithium-ion conductive dense film. If the mass fraction of the ion-conductive inorganic particles is too low, the ionic conductivity of the lithium-ion conductive dense film decreases, and the transport efficiency of the ionic conductive film for lithium ions decreases; if the mass fraction of the ion-conductive inorganic particles is too high, due to the poor interfacial contact between the inorganic conductive particles and the lack of support of the polymer solid electrolyte for the inorganic conductive particles, the porosity of the lithium-ion conductive dense film increases, and the selectivity of the ionic conductive film for lithium ions decreases.

[0124] (9) It can be seen from the comparison between Example 1 and Example 10 that by further adopting a high-porosity base film, using a high-porosity base film is beneficial to the construction of a selective transmission path for lithium ions, and can more effectively achieve the selective separation of Li + . At the same time, the high-porosity base film provides sufficient space for the filling of ion-conductive inorganic particles and polymer electrolytes, and can further improve the ionic conductivity and separation coefficient of the lithium-ion conductive dense film.

[0125] (10) It can be seen from the comparison between Example 1 and Example 11 that the method of introducing small particle ion-conductive inorganic particles into the blend adopted by the present invention can effectively fill the pores of the polymer base film. Reducing the particle size of the ion-conductive inorganic particles can improve the interfacial contact between the ion-conductive inorganic particles and between the ion-conductive inorganic particles and other components in the ion-conductive film, further reducing the porosity of the ion-conductive film, reducing the transport path of impurity ions in the ion-conductive film, and further improving the selectivity of the ion-conductive film for Li + .

[0126] (11) It can be seen from the comparison between Example 1 and Comparative Example 1 that due to the interfacial contact problem between the ion-conductive inorganic particles, if the polymer solid electrolyte is not added, there will inevitably be a large number of pores in the ion-conductive film, and the porosity of the ion-conductive film further increases, resulting in a decrease in the selectivity of the ion-conductive film for Li + , which is not conducive to the selective permeation of lithium ions through the ion-conductive film.

[0127] (12) It can be seen from the comparison between Example 1 and Comparative Example 2 that when the ion-conductive inorganic particles are replaced with other substances, the ion-conductive film cannot effectively selectively transport lithium ions and cannot achieve the selective separation of lithium ions in the brine. The ion-conductive inorganic particles selected by the present invention are more conducive to enhancing the selectivity and efficient transport of the lithium-ion conductive dense film for lithium ions.

[0128] (13) It can be seen from Example 1 and Comparative Example 3 that the ion conductive membrane prepared by the in-situ polymerization method of the present invention has excellent selective transport performance for lithium ions, and can well achieve the separation of Li from brine. + The purpose is that the photo / thermal polymerization method is simple and efficient, can effectively control the reaction process, the prepared lithium ion conductive dense membrane has good wettability, and the mechanical strength is more controllable. If the photo / thermal polymerization reaction is not carried out, the polymer solid electrolyte cannot be formed, and the internal passage of the base membrane is only filled with ion conductive inorganic particles. Due to the poor interfacial contact between the ion conductive inorganic particles, the porosity of the lithium ion conductive membrane increases and the internal lithium ion transport passage decreases. The ion conductive membrane has a reduced selectivity and transport efficiency for Li. +

[0129] (14) It can be seen from Example 1 and Comparative Example 4 that the ion conductive membrane prepared by the in-situ polymerization method has excellent selective transport performance for lithium ions, and can well achieve the separation of Li from brine. + The purpose is that if in-situ polymerization is not carried out but the polymer electrolyte is directly added, due to the large volume of the polymer electrolyte, effective infiltration and filling of the polymer base membrane cannot be achieved. At the same time, the polymer remaining on the surface of the ion conductive membrane dissolves and breaks during application, ultimately resulting in a large number of pores remaining inside the ion conductive membrane and a reduced selectivity for lithium ions.

[0130] In summary, the lithium ion conductive dense membrane provided by the present invention uses a polymer solid electrolyte and ion conductive inorganic particles to fill the polymer base membrane, and has the advantages of strong lithium ion conduction ability, high transport efficiency, and strong selectivity for lithium ions. The transport of lithium ions by the lithium ion conductive dense membrane provided by the present invention does not depend on the pores in the conductive membrane, and the damage of membrane blockage to the long-term production capacity of the conductive membrane can be inhibited, effectively improving the service life of the lithium ion conductive dense membrane. Under the action of an external electric field, the ions in the brine migrate directionally, and the cations migrate to the cathode. Among them, Li + can be transported to the cathode through the solid lithium ion conductor in the dense membrane, while other impurity metal cations cannot complete the migration through the dense membrane. Finally, the enrichment of Li + at the cathode is achieved. When the lithium ion conductive dense membrane of the present invention is used for electro-dialysis separation of lithium ions from brine, the voltage applied by the device is lower, the cost is lower, the structure is safe and stable, and the application range is wider.

[0131] The applicant declares that the above is only the specific implementation manner 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 thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.​

Claims

1. A lithium ion conductive dense film, characterized in that: The lithium ion conductive dense film comprises a polymer base film, ion conductive inorganic particles and a polymer solid electrolyte; the polymer base film is a mesh structure; The ion-conductive inorganic particles and the polymer solid electrolyte are respectively and evenly filled in the pores of the polymer-based membrane, and the polymer solid electrolyte wraps the fiber filaments in the polymer-based membrane; The lithium ion conductive dense film has a Gurley value of ≥1000 and a porosity of ≤5%.

2. The lithium ion conductive dense film according to claim 1, characterized in that: Based on the total mass of the lithium ion conductive dense film being 100wt%, the mass fraction of the ion conductive inorganic particles is 5wt%-50wt%, preferably 10wt%-20wt%; Preferably, the mass fraction of the polymer solid electrolyte is 5wt%-50wt%, preferably 10wt%-20wt%; the remainder is the polymer base film.

3. The lithium ion conductive dense film according to claim 1 or 2, characterized in that: The polymer base film is a high-porosity base film; Preferably, the polymer-based film includes any one of a cellulose-based film, a PET-based film or a glass fiber-based film, or a combination of at least two thereof.

4. The lithium ion conductive dense film according to any one of claims 1 to 3, characterized in that: The thickness of the lithium ion conductive dense film is 5 μm-100 μm.

5. The lithium ion conductive dense film according to any one of claims 1 to 4, characterized in that: The ion-conductive inorganic particles include oxide solid electrolyte materials and / or lithium salt materials having ionic and electronic conductivity; Preferably, the ion-conductive inorganic particles include large particles with an average particle size of 200 nm to 5 μm and small particles with an average particle size of 20 nm to 100 nm; Preferably, based on the total mass of the ion conductive inorganic particles being 100wt%, the large particles having an average particle size of 200nm-5μm in the ion conductive inorganic particles account for 0wt%-60wt%, including 0%, and the small particles having an average particle size of 20nm-100nm account for 40wt%-100wt%, including 100wt%; Preferably, the oxide solid electrolyte material includes any one or a combination of at least two of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, tantalum-doped lithium lanthanum zirconium oxide or lithium aluminum titanium phosphate; Preferably, the lithium salt material with ionic and electronic conductivity includes any one of lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide or lithium manganese iron phosphate, or a combination of at least two thereof.

6. The lithium ion conductive dense film according to any one of claims 1 to 5, characterized in that: The polymer solid electrolyte includes a polymer material and / or a cross-linking agent; Preferably, the polymer material comprises any one of polytetrafluoroethylene, polyethylene oxide, polyvinyl alcohol or a cationic polyionic liquid or a combination of at least two thereof, preferably a cationic polyionic liquid; Preferably, the cross-linking agent includes any one of polyethylene glycol diacrylate, trimethylolpropane trimethacrylate, 1,4-butylene glycol diacrylate or ethylene glycol dimethacrylate, or a combination of at least two thereof.

7. A method for preparing a lithium ion conductive dense film according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: (1) mixing ion conductive inorganic particles, polymer solid electrolyte monomers, an initiator and a solvent to obtain a pore filling slurry; (2) The pore-filling slurry is introduced into the polymer-based film, and after drying, polymerization reaction, and rolling, a lithium ion conductive dense film is obtained.

8. The preparation method according to claim 7, characterized in that: The polymerization reaction in step (2) is a photopolymerization reaction and / or a thermal polymerization reaction; Preferably, the photopolymerization reaction method is: placing the polymer base film injected with the hole filling slurry on a transparent glass plate and irradiating it with an ultraviolet lamp, and the irradiation time of both sides is 0min-10min, excluding 0min, and preferably 2min-5min; Preferably, the method of the thermal polymerization reaction is: heating the dried polymer base film injected with the pore-filling slurry under vacuum conditions, the heating temperature being 40° C.-100° C., preferably 60° C.-80° C.; Preferably, the heating time in the thermal polymerization reaction is 2h-24h, preferably 6h-12h.

9. The preparation method according to claim 7 or 8, characterized in that: The initiator includes any one of azobisisobutyronitrile, potassium persulfate, sodium persulfate, dibenzoyl peroxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide or 2-hydroxy-2-methyl-1-phenyl-1-propanone or a combination of at least two thereof; Preferably, the solvent comprises any one or a combination of at least two of N-methylpyrrolidone, acetonitrile, 1,3-dioxolane, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl ether, ethyl acetate, chloroform or n-hexane; Preferably, the ion conductive inorganic particles account for 5wt%-50wt% of the pore filling slurry, preferably 10wt%-20wt%; Preferably, the total mass of the polymer solid electrolyte monomer and the initiator accounts for 5wt%-50wt% of the pore filling slurry, preferably 10wt%-20wt%; Preferably, the initiator accounts for 0.01wt%-5wt% of the total mass of the polymer solid electrolyte monomer and the initiator, preferably 0.1wt%-2wt%; Preferably, the solvent accounts for 40wt%-95wt% of the pore-filling slurry, preferably 50wt%-90wt%; Preferably, the drying is carried out under normal pressure or vacuum; Preferably, the drying temperature is 30°C-100°C, preferably 40°C-80°C; Preferably, the drying time is 1h-24h, preferably 2h-12h; Preferably, the rolling thickness is set to 50%-100% of the thickness of the ion conductive membrane before rolling, excluding 100%, preferably 75%-95%; Preferably, before and / or after rolling, and before obtaining the lithium ion conductive dense film, the process further comprises repeating step (2) 1 to 6 times on the lithium ion conductive dense film.

10. Use of the lithium ion conductive dense film according to any one of claims 1 to 6, characterized in that: The lithium ion conductive dense membrane is used for extracting lithium from electrodialysis brine.

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