阅读说明：本技术 一种有机-无机复合固态电解质薄膜及其制备方法、固态锂金属电池 (Organic-inorganic composite solid electrolyte film, preparation method thereof and solid lithium metal battery ) 是由 林秀婧 李壮 张婷婷 储成成 刘瑞卿 马延文 于 2020-06-05 设计创作，主要内容包括：本发明公开了一种有机-无机复合固态电解质薄膜及其制备方法,以及基于该固态电解质薄膜的固态锂金属电池,该电解质薄膜是以聚合物作为基体骨架,基体骨架中填充有离子液体和无机离子导体,所述离子液体含有锂盐。本发明采用溶液浇铸法得到固态电解质薄膜,制备方法简单、具有较高的离子电导率(>10<Sup>-4</Sup>S cm<Sup>-1</Sup>)。在室温条件下,控制其电流密度为0.1mA cm<Sup>-2</Sup>,所组装的对称金属锂电池可稳定循环1350圈,运行时间高达2700h；组装的Li∣LiFePO<Sub>4</Sub>电池具有良好的循环性能,在1C下可稳定循环100圈,比容量保持在110mAh g<Sup>-1</Sup>以上。(The invention discloses an organic-inorganic composite solid electrolyte film, a preparation method thereof and a solid lithium metal battery based on the solid electrolyte film. The invention adopts the solution casting method to obtain the solid electrolyte film, has simple preparation method and higher ionic conductivity>10 ‑4 S cm ‑1 ). Controlling the current density to be 0.1mA cm at room temperature ‑2 The assembled symmetrical lithium metal battery can stably circulate 1350 circles, and the running time is as high as 2700 hours; assembled Li-LiFePO 4 The battery has good cycle performance, can stably circulate for 100 circles under 1C, and the specific capacity is kept at 110mAh g ‑1 The above.)

1. An organic-inorganic composite solid electrolyte film characterized in that: the electrolyte film takes a polymer as a matrix framework, and the matrix framework is filled with ionic liquid, wherein the ionic liquid contains lithium salt.

2. The organic-inorganic composite solid electrolyte thin film according to claim 1, characterized in that: and the matrix skeleton is also filled with an inorganic ion conductor.

3. The organic-inorganic composite solid electrolyte thin film according to claim 1, characterized in that: the polymer is polyvinylidene fluoride.

4. The organic-inorganic composite solid electrolyte thin film according to claim 1, characterized in that: the ionic liquid is one of N-methyl-N-methoxyethyl pyrrolidine bistrifluoromethylsulfonyl imide salt, N-methyl-N-butyl pyrrolidine bistrifluoromethylsulfonyl imide and 1-ethyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt.

5. The organic-inorganic composite solid electrolyte thin film according to claim 1, characterized in that: the inorganic ion conductor is LAGP.

6. The organic-inorganic composite solid electrolyte thin film according to claim 1, characterized in that: the lithium salt is bis (trifluoromethyl) sulfonyl imide lithium, and the concentration of the lithium salt in the ionic liquid is 1mmol g^-1。

7. A method for producing an organic-inorganic composite solid electrolyte thin film according to any one of claims 1 to 6, characterized in that: the method comprises the following steps:

(1) filling an ionic liquid containing lithium salt or the ionic liquid containing lithium salt and an inorganic ionic conductor into a polymer by adopting a solution stirring method to obtain a mixed solution;

(2) and (2) forming a film from the mixed solution obtained in the step (1) by a solution casting method.

8. The method for producing an organic-inorganic composite solid electrolyte thin film according to claim 7, characterized in that: the step (1) comprises the following steps: dissolving 0.08-1.2 parts by weight of polymer powder in 0.5-1.0 part by weight of solvent, after uniform dissolution, adding 0.1-0.15 part by weight of ionic liquid containing lithium salt, adding inorganic ion conductor powder, and stirring for 12-18h at the rotation speed of 600-800 r/min; wherein, the solvent adopted by the solution stirring method is N-methyl pyrrolidone, and the inorganic ion conductor powder accounts for 0-40% of the total mass of the raw materials.

9. The method for producing an organic-inorganic composite solid electrolyte thin film according to claim 7, characterized in that: the step (2) comprises the following steps: pouring the mixed solution on a glass plate, scraping the film by using an applicator, drying the glass plate in vacuum at the temperature of 60-80 ℃ for 8-12h, and stripping after drying.

10. A solid state lithium metal battery comprising a positive electrode, a negative electrode, and an electrolyte disposed between the positive and negative electrodes, characterized in that: the electrolyte is the organic-inorganic composite solid electrolyte film of claim 1, and the material of the positive electrode is lithium iron phosphate.

Technical Field

The invention belongs to the technical field of lithium metal batteries, and particularly relates to an organic-inorganic solid electrolyte film, a preparation method thereof and a solid lithium metal battery assembled by applying the electrolyte film.

Background

In recent years, the increasing demand for electronic devices, electric vehicles, and large capacity energy storage systems has prompted the search for lithium batteries with high power/energy density and good safety. Among the currently available battery technologies, lithium-based batteries (e.g., lithium ion batteries) are considered the most promising batteries due to their relatively high energy density. Conventional lithium batteries generally employ an organic liquid electrolyte having a relatively low ionic resistance, and have the disadvantages of safety, insufficient life, high cost, low power density, and the like, despite the advantages of high conductivity, excellent wettability of the electrode surface, and the like. All-solid-state batteries are safer, have longer cycle life, higher energy density, and have lower requirements for packaging and state-of-charge monitoring circuitry than liquid electrolyte lithium batteries, and thus, have gained increasing attention from researchers. Typical lithium batteries are composed of a positive active material, a diaphragm, an electrolyte and metallic lithium, and a solid electrolyte adopted in an all-solid battery can replace the diaphragm and the electrolyte, so that the battery structure is simpler.

The solid electrolyte material applied to the all-solid-state battery needs to have the characteristics of high ionic conductivity of ①, good chemical stability of ②, good electrochemical stability of ③ to lithium, common solid electrolytes comprise inorganic solid electrolytes and polymer electrolytes, and the inorganic solid electrolytes widely researched at present mainly comprise NASICON (LAGP/LATP and the like, M.Weiss, D.A.er, A.Senyshyn, J.Janek, W.G.Zeier, ACS applied.Mater. interfaces.2018,10, 10935-10944)],[J.Y.Liang,X.X.Zeng,C.D.Zhang,P.F.Wang,J.Y.Ma,Y.X.Yin,X.W.Wu,Y.G.Guo,L.J.Wan,J.Am.Chem.Soc.2018,140, 6767-6770](Li), LISICON type (Li)₁₀GeP₂S₁₂)[N.Kamaya,K.Homma,Y.Yamakawa,M. Hirayama,R.Kanno,M.Yonemura,T.Kamiyama,Y.Kato,S.Hama,K.Kawamoto,A. Mitsui,Nat.Mater.2011,10,682.]Perovskite type (Li)_0.34La_0.56TiO₃)[S.Stramare,V.Thangadurai, W.Weppner,Chem.Mater.2003,15,3974.]Garnet type (Li)₇La₃Zr₂O₁₂) LIPON, sulfide systems, etc., which have the advantages of excellent thermal stability and capability of ensuring that the battery works at higher temperature; furthermore, a wider electrochemical working window can be suitable for high voltage electrode materials. Although the inorganic solid electrolytes are of various types, they have advantages and disadvantages, and cannot combine all advantages. For example, the room temperature ion conductivity of NASICON type solid electrolytes and perovskite type solid electrolytes can reach 10^-3S cm^-1But Ti in the system⁴⁺Is easily reduced into Ti during the contact with metallic lithium³⁺Destabilizing the electrolyte material; LISICON type solid electrolyte and lithium metal and CO in air₂The reaction is easy to occur, and the relatively low ionic conductivity is reduced along with the increase of time; the room temperature ionic conductivity of LIPON solid electrolyte is only 10^-6S cm^-1And is difficult to form a composite electrode with an electrode material, and can only be used for a thin film battery at present; the sulfide glass solid electrolyte has better thermal stability and very high ionic conductivity (10 to 10)^-2S cm^-1) However, sulfide readily absorbs water to release H₂And (4) S gas. In addition, the rigid interface between the electrode and the solid electrolyte makes the interfacial resistance large, resulting in low cycle performance which is one of the main difficulties that needs to be overcome for successful commercialization of all-solid batteries [ c.w.wang, y.h.gong, b.y.liu, k.fu, y.g.yao, e.hitz, y.j.li, j.q.dai, s.m.xu, w.luo, e.d.wachsman, l.b.hu, Nano lett.2017,17, 565-571; T.Liu, Y.B.Zhang, X.Zhang, L.Wang, S.X.ZHao, Y.H.Lin, Y.Shen, J.Luo, L.L.Li, C.W.nan, Journal of Materials Chemistry A,2018,6(11), 4649-]。

Polymer Electrolyte (SPE) refers to the incorporation of a lithium salt (e.g., LiClO)₄、LiAsF₆、 LiPF₆、LiBF₄LiTFSI, etc.) into a polymer matrix (e.g., polyethers, polyesters, polyamines, etc.). Common polymer matrices are polyethylene oxide (PEO), polymethyl methacrylate (PMMA), Polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polypropylene carbonate (PPC), and the like. Even though electrolytes of varying degrees of polymerization have been extensively studied, they suffer from considerable drawbacks, for example, at T_gWhen the degree of crystallization of PEO is increased, Li⁺The movement in the crystallization zone is limited and the migration is difficult, so that the single PEO-based polymer electrolyte has low conductivity of only 10 at room temperature^-7～10^-6S cm^-1[M.Clericuzio,W.O.Parker Jr,M.Soprani,M.Andrei,Solid State Ionics.,1995,82(3-4),179-192.]Meanwhile, the transference number of lithium ions is low, only 0.2-0.3, and the lithium ion battery is difficult to apply to practical batteries.

The combination of organic and inorganic solid electrolytes into a composite solid electrolyte can integrate the advantages of the two electrolytes and avoid the disadvantages of the two electrolytes, and is considered to be a promising strategy. Most commonly, inorganic solid electrolytes are dispersed as fillers in the polymer backbone in a mechanically mixed manner. Chinese patent publication No. CN 108091928A discloses a scheme of compounding organic polymer and inorganic oxide solid electrolyte powder to prepare a flexible organic/inorganic composite electrolyte, which effectively inhibits lithium dendrite in the use process of a battery; chinese patent publication No. 107403954a discloses a preparation scheme of filling a lithium inorganic solid electrolyte in a polymer having a continuous three-dimensional sponge network structure, developing a solid electrolyte membrane having good processability, mechanical properties, corrosion resistance and oxidation resistance; chinese patent publication No. CN105098234A discloses a solid electrolyte layer containing a polymer and an inorganic filler, which can improve the cycle performance and safety performance of a lithium ion battery at high temperature. However, the disclosed prior art still fails to solve the problem of low conductivity of the solid electrolyte membrane at room temperature, and electrochemical tests for cell performance need to be performed at higher temperatures.

Disclosure of Invention

An object of the present invention is to provide an organic-inorganic composite solid electrolyte thin film and a method for preparing the same, so as to obtain an electrolyte thin film having a high room temperature ionic conductivity.

In order to achieve the purpose, the invention adopts the technical scheme that:

an organic-inorganic composite solid electrolyte film is characterized in that a polymer is used as a matrix framework, and ionic liquid is filled in the matrix framework and contains lithium salt.

Preferably, the matrix skeleton is also filled with an inorganic ion conductor.

Preferably, the polymer is polyvinylidene fluoride (PVDF).

Preferably, the Ionic Liquid (IL) is one of N-methyl-N-methoxyethyl pyrrolidine bistrifluoromethylsulfonyl imide salt (Pyr1(201) TFSI), N-methyl-N-butyl pyrrolidine bistrifluoromethylsulfonyl imide (Pyr14TFSI), 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt (EMITFSI).

Preferably, the inorganic ion conductor is LAGP (Li)_1.5Al_0.5Ge_1.5(PO₄)₃)。

Preferably, the lithium salt is lithium bistrifluoromethylsulfonyl imide (LiTFSI).

Preferably, the concentration of the lithium salt in the ionic liquid is 1mmol g^-1。

A preparation method of an organic-inorganic composite solid electrolyte film comprises the following steps:

(1) filling an ionic liquid containing lithium salt or the ionic liquid containing lithium salt and an inorganic ionic conductor into a polymer by adopting a solution stirring method to obtain a mixed solution;

(2) and (2) forming a film from the mixed solution obtained in the step (1) by a solution casting method.

The step (1) comprises the following steps: dissolving 0.08-1.2 weight parts of polymer powder in 0.5-1.0 weight parts of solvent, adding 0.1-0.15 weight parts of ionic liquid containing lithium salt after uniform dissolution, adding inorganic ion conductor powder, and stirring at 600-800r min^-1Stirring for 12-18 h; wherein, the solvent adopted by the solution stirring method is N-methyl pyrrolidone (NMP), and the inorganic ion conductor powder accounts for 0-40% of the total mass of the raw materials.

The step (2) comprises the following steps: pouring the mixed solution on a glass plate, scraping the film by using an applicator, drying the glass plate in vacuum at the temperature of 60-80 ℃ for 8-12h, and stripping after drying.

Still another object of the present invention is to provide a solid-state lithium metal battery assembled based on the above organic-inorganic composite solid electrolyte thin film, the technical solution is as follows:

a solid-state lithium metal battery comprises a positive electrode, a negative electrode and an electrolyte arranged between the positive electrode and the negative electrode, wherein the electrolyte is the organic-inorganic composite solid-state electrolyte, and the positive electrode is made of lithium iron phosphate.

Has the advantages that: the invention adopts the solution casting method to obtain the solid electrolyte film, has simple preparation method and higher ionic conductivity>10^-4S cm^-1). Controlling the current density to be 0.1mA cm at room temperature^-2The assembled symmetrical lithium metal battery can stably circulate 1350 circles, and the running time is as high as 2700 hours; assembled Li-LiFePO₄The battery has good cycle performance, can stably circulate for 100 circles under 1C, and the specific capacity is kept at 110mAh g^-1The above.

Compared with the prior art, the method has the advantages that:

(1) the preparation method of the organic-inorganic composite solid electrolyte film provided by the invention blends PVDF, IL and LAGP, takes NMP as a solvent, coats and dries the solution into the film by blade coating, has simple preparation method, does not need chemical methods such as hydrothermal method or CVD (chemical vapor deposition), has low requirement on equipment and can be produced in large batch.

(2) Compared with organic electrolyte, the lithium ion battery has the advantages that under the same current density, the cycle life is longer, the voltage lag is more stable, and the lithium ion battery shows excellent stability to lithium;

(3) the lithium metal battery prepared from the organic-inorganic composite solid electrolyte film has excellent performance; under the multiplying power of 1C, the circulation is stable, the coulombic efficiency is kept to be more than 99%, a uniform SEI film is obtained, and lithium dendrites are effectively inhibited.

Drawings

FIG. 1 is a photograph and a scanning electron microscope photograph of an organic-inorganic composite solid electrolyte thin film in an example; in fig. 1, (a) is a photograph of an organic-inorganic composite solid electrolyte thin film in a bent state, (b) is a photograph of an organic-inorganic composite solid electrolyte thin film in a flat state, and (c) is a scanning electron microscope low-magnification image of the organic-inorganic composite solid electrolyte thin film; (d) is a high-power picture of a scanning electron microscope of an organic-inorganic composite solid electrolyte film;

FIG. 2 is a graph showing electrochemical properties of an organic-inorganic composite solid electrolyte thin film in the example; wherein (a) and (b) are intrinsic impedance diagrams and ion conductivity bar charts of the organic-inorganic composite solid electrolyte film at different temperatures, and (c) and (d) are lithium ion transference number curve diagrams and bar charts of the organic-inorganic composite solid electrolyte film at room temperature;

FIG. 3 is a graph showing electrochemical properties of a solid-state lithium metal symmetrical battery fabricated from an organic-inorganic composite solid electrolyte thin film prepared in examples; wherein (a) is 0.1mA cm^-2A cyclic performance plot at current of; (b) is 0.5mA cm^-2A cyclic performance plot at current of;

fig. 4 is a graph of electrochemical performance of a solid lithium metal half cell fabricated from the organic-inorganic composite solid electrolyte thin film prepared in the example; wherein, (a) is a first circle charge-discharge curve under the multiplying power of 0.2C, 0.5C and 1C; (b) a cycle efficiency chart under 1C multiplying power;

fig. 5 shows the ionic conductivity of the comparative example at room temperature.

Detailed Description

The present invention is further described with reference to the following examples, which should not be construed as limiting the scope of the invention.