Electrolyte-membrane composite material, and preparation method and application thereof

Abstract

The application discloses an electrolyte-diaphragm composite material and a preparation method and application thereof. The composition of the electrolyte-diaphragm composite material comprises a carrier fluorine-containing polyimide porous membrane and loaded ionic liquid, the fluorine-containing polyimide porous membrane is composed of fluorine-containing polyimide fibers, and the composition of the ionic liquid comprises fluorine-containing lithium salt and organic compounds capable of complexing with lithium ions. The preparation method of the electrolyte-diaphragm composite material is very simple, the fluorine-containing polyimide porous membrane and the ionic liquid are prepared respectively, and then the two are combined. The electrolyte-diaphragm composite material has excellent thermal stability, a wide electrochemical window, a high lithium ion transference number, stable interface performance and excellent lithium dendrite inhibition capacity. When the electrolyte-diaphragm composite material is combined with a lithium metal negative electrode and a ternary positive electrode, a high-voltage and high-energy-density lithium metal battery can be prepared, which is helpful to promoting the development of high-specific-energy and high-power energy storage equipment, and has a very wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to an electrolyte-separator composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of 5G communication technology and new energy vehicles, the demand for electrochemical energy storage devices is growing rapidly. However, current lithium-ion rechargeable batteries have essentially reached their energy limits due to the limitations of graphite anodes. Furthermore, commercially available electrolytes are prone to safety issues such as leakage, fire, and explosion, making it difficult to meet the application requirements of high-power and large-scale energy-consuming devices. Therefore, the research and development of battery systems with high energy density, long lifespan, and high safety is urgently needed.

[0003] Lithium metal anodes, with their extremely high energy density and lowest reduction potential, have become important anode materials, while ternary cathodes (especially LiNi)... 0.8 Co 0.1 Mn 0.1 O2 (NCM811) possesses high specific capacity and high charge / discharge potential, and its raw materials are widely available and have low production costs, making it the mainstream system for high-voltage electrodes. Combining lithium metal anodes with ternary cathodes holds promise for the development of high-energy-density storage batteries. However, the application of commercial electrolytes to lithium metal anodes can cause lithium dendrite growth and the formation of "dead lithium." Lithium dendrites piercing the separator can lead to short circuits and safety accidents, while "dead lithium" causes rapid capacity decay.

[0004] Therefore, in order to realize the development and application of lithium metal anodes and ternary cathodes, it is necessary to prepare a new electrolyte system with high safety, high lithium conductivity and effective suppression of lithium dendrite growth. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte-diaphragm composite material, its preparation method, and its application.

[0006] The technical solution adopted in this invention is:

[0007] An electrolyte-membrane composite material comprises a fluorinated polyimide porous membrane as a carrier and an ionic liquid supported thereon; the fluorinated polyimide porous membrane is composed of fluorinated polyimide fibers; the ionic liquid comprises a fluorinated lithium salt and an organic compound capable of complexing with lithium ions.

[0008] Preferably, the thickness of the fluorinated polyimide porous membrane is 10 μm to 40 μm.

[0009] Preferably, the diameter of the fluorinated polyimide fiber is 80 nm to 900 nm.

[0010] Preferably, the fluorinated polyimide in the fluorinated polyimide fiber is made by reacting a fluorinated diamine monomer with a non-fluorinated dianhydride monomer, or by reacting a non-fluorinated diamine monomer with a fluorinated dianhydride monomer, or by reacting a fluorinated diamine monomer with a fluorinated dianhydride monomer.

[0011] Preferably, the fluorinated diamine monomer is a diamine containing at least one of -F, -CF3, -CH2-CF3, and -OCF2CF3.

[0012] More preferably, the fluorinated diamine monomer is 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene.

[0013] Preferably, the fluorine-free diamine monomer is at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, and benzidine.

[0014] Preferably, the fluorinated dianhydride monomer is a dianhydride containing at least one of -F, -CF3, -CH2-CF3, and -OCF2CF3.

[0015] More preferably, the fluorinated dianhydride monomer is 4,4′-(hexafluoroisopropene) phthalic anhydride.

[0016] Preferably, the fluorine-free dianhydride monomer is at least one of 4,4′-biphenyl ether dianhydride, pyromellitic dianhydride, biphenyl dianhydride, and 4,4′-terephthalodioxydiphthalic anhydride.

[0017] Preferably, the fluorinated lithium salt is at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate.

[0018] Preferably, the organic compound that can complex with lithium ions is at least one of ether compounds, sulfone compounds, carbonate compounds, succinic acid, γ-butyrolactone, and acetic anhydride.

[0019] Preferably, the ether compound is at least one selected from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0020] Preferably, the sulfone compound is at least one selected from sulfolane, dimethyl sulfoxide, and dimethyl sulfone.

[0021] Preferably, the carbonate compound is at least one of ethylene carbonate, propylene carbonate, and dimethyl carbonate.

[0022] Preferably, the molar ratio of the lithium salt to the organic compound that can complex with lithium ions is 1:0.6 to 6.

[0023] A method for preparing an electrolyte-membrane composite material as described above includes the following steps:

[0024] 1) A fluorinated polyimide is prepared by mixing diamine monomer and dianhydride monomer and carrying out a polycondensation reaction. At least one of the diamine monomer and dianhydride monomer contains a fluorinated group. Then, electrospinning is performed to obtain a porous membrane of fluorinated polyimide.

[0025] 2) Fluorine-containing lithium salts and organic compounds that can complex with lithium ions are mixed to obtain ionic liquids;

[0026] 3) The fluorinated polyimide porous membrane from step 1) is impregnated with the ionic liquid from step 2) to obtain the electrolyte-membrane composite material.

[0027] Preferably, the molar ratio of the diamine monomer and the dianhydride monomer in step 1) is 1:0.8 to 1.2.

[0028] Preferably, the polycondensation reaction in step 1) is carried out at 5°C to 250°C for 6 to 30 hours.

[0029] Preferably, the mixing in step 2) is carried out at 10℃ to 50℃ for 10h to 36h.

[0030] A lithium metal battery comprising the above-mentioned electrolyte-separator composite material.

[0031] Preferably, the positive electrode of the lithium metal battery is a ternary positive electrode.

[0032] Preferably, the negative electrode of the lithium metal battery is a lithium metal electrode.

[0033] The beneficial effects of this invention are: the electrolyte-membrane composite material of this invention has excellent thermal stability, wide electrochemical window (>4.3V), high lithium-ion transference number, stable interface properties and excellent ability to suppress lithium dendrites. When combined with lithium metal anode and ternary cathode, it can be used to prepare high-voltage, high-energy-density lithium metal batteries, which helps to promote the development of high-specific-energy, high-power energy storage devices and has a very broad application prospect.

[0034] Specifically:

[0035] 1) The electrolyte-membrane composite material of the present invention comprises a fluorinated polyimide porous membrane as a carrier and a loaded ionic liquid. The ionic liquid has a single cation complex structure and a fluorinated anion structure, which can endow the electrolyte-membrane composite material with good thermal stability, a wide electrochemical stability window and high ionic conductivity. Moreover, there is a certain interaction between the fluorinated groups in the fluorinated polyimide porous membrane and the fluorinated anions in the ionic liquid, which can increase the lithium ion transference number and endow the system with efficient lithium ion conduction ability (ion transference number as high as 0.82).

[0036] 2) The electrolyte-membrane composite material of the present invention has better electrochemical stability and mechanical properties. When it comes into contact with lithium metal, it can form a stable solid-state electrode interface (SEI), which can promote the uniform and stable deposition of lithium ions at the interface, thereby effectively inhibiting the formation and growth of lithium dendrites, which is beneficial to preparing a metal lithium battery with high stability and high safety.

[0037] 3) Compared with commercial electrolyte systems, the electrolyte-membrane composite material of the present invention does not contain volatile solvent molecules, has high safety, and can form a stable contact interface with both high-voltage positive electrode material and lithium metal negative electrode. The assembled high-voltage battery has good cycle performance and rate performance at room temperature.

[0038] 4) The preparation process of the electrolyte-diaphragm composite material of the present invention is relatively simple, does not require special equipment, is worthy of in-depth research, and meets the conditions for industrial production. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure and composition of the electrolyte-diaphragm composite material in Example 1.

[0040] Figure 2 This is a SEM image of the electrolyte-diaphragm composite material from Example 1.

[0041] Figure 3 The TGA curve is for the electrolyte-diaphragm composite material of Example 1.

[0042] Figure 4 The images show the Raman spectra of the electrolyte-diaphragm composite materials of Example 1 and Comparative Example 1.

[0043] Figure 5 The LSV curve is shown for the 2025 coin cell assembled from the electrolyte-separator composite material of Example 1.

[0044] Figure 6 The figures show the ionic conductivity-temperature relationship curves of the electrolyte-diaphragm composite materials of Examples 1, 2, Comparative Examples 1 and 2.

[0045] Figure 7 Voltage-time curves during constant current cycling tests of lithium-lithium symmetric batteries assembled with electrolyte-membrane composite materials for Example 1 and Comparative Example 1.

[0046] Figure 8 The graph shows the test results of the discharge capacity and coulombic efficiency of the high-voltage lithium metal battery Li / NCM811 assembled from the electrolyte-membrane composite material in Example 1 at different rates. Detailed Implementation

[0047] The present invention will be further explained and described below with reference to specific embodiments.

[0048] Example 1:

[0049] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0050] 1) Mix 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride at a molar ratio of 1:1, react at 30°C for 5 h, and then heat to 185°C for 18 h to obtain fluorinated polyimide, which is then electrospun to obtain a fluorinated polyimide porous membrane.

[0051] 2) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and triethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at room temperature for 36 hours at a speed of 250 r / min to obtain an ionic liquid.

[0052] 3) Thoroughly wet the fluorinated polyimide porous membrane (circular, 1.2 cm in diameter, and 25 μm thick) obtained in step 1) with 40 μL of the ionic liquid obtained in step 2) (the fluorinated polyimide porous membrane has a liquid absorption rate as high as 855%, which can significantly improve the ionic conductivity of the electrolyte-membrane composite material), thus obtaining the electrolyte-membrane composite material (structure and composition schematic diagram shown in Figure 1). Figure 1 (As shown).

[0053] Example 2:

[0054] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0055] 1) Mix 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride at a molar ratio of 1:1, react at 30°C for 5 h, and then heat to 185°C for 18 h to obtain fluorinated polyimide, which is then electrospun to obtain a fluorinated polyimide porous membrane.

[0056] 2) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at 40°C for 24 hours with the stirrer speed at 200 r / min to obtain an ionic liquid.

[0057] 3) The fluorinated polyimide porous membrane (circular, 1.2 cm in diameter and 25 μm thick) from step 1) is fully impregnated with 40 μL of the ionic liquid from step 2) (the liquid absorption rate of the fluorinated polyimide porous membrane is as high as 820%, which can significantly improve the ionic conductivity of the electrolyte-membrane composite material), thus obtaining the electrolyte-membrane composite material.

[0058] Example 3:

[0059] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0060] 1) Mix 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride at a molar ratio of 1:1, react at 30°C for 5 h, and then heat to 185°C for 18 h to obtain fluorinated polyimide, which is then electrospun to obtain a fluorinated polyimide porous membrane.

[0061] 2) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and triethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at 50°C for 26 hours with the stirrer speed at 200 r / min to obtain an ionic liquid.

[0062] 3) The fluorinated polyimide porous membrane (circular, 1.2 cm in diameter and 25 μm thick) from step 1) is fully impregnated with 40 μL of the ionic liquid from step 2) (the liquid absorption rate of the fluorinated polyimide porous membrane is as high as 840%, which can significantly improve the ionic conductivity of the electrolyte-membrane composite material), thus obtaining the electrolyte-membrane composite material.

[0063] Example 4:

[0064] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0065] 1) Mix 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride at a molar ratio of 1:1, react at 30°C for 5 h, and then heat to 185°C for 18 h to obtain fluorinated polyimide, which is then electrospun to obtain a fluorinated polyimide porous membrane.

[0066] 2) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at 50°C for 20 h with the stirrer speed at 180 r / min to obtain an ionic liquid.

[0067] 3) The fluorinated polyimide porous membrane (circular, 1.2 cm in diameter and 25 μm thick) from step 1) is fully impregnated with 30 μL of the ionic liquid from step 2) (the liquid absorption rate of the fluorinated polyimide porous membrane is as high as 818%, which can significantly improve the ionic conductivity of the electrolyte-membrane composite material), thus obtaining the electrolyte-membrane composite material.

[0068] Comparative Example 1:

[0069] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0070] 1) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at room temperature for 36 hours at a speed of 250 r / min to obtain an ionic liquid.

[0071] 2) The commercial polyolefin separator Celgard2500 (circular, 1.2 cm in diameter and 25 μm thick) was fully impregnated with 20 μL of the ionic liquid from step 1) to obtain the electrolyte-separator composite material.

[0072] Comparative Example 2:

[0073] An electrolyte-diaphragm composite material, the preparation method of which includes the following steps:

[0074] 1) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether were mixed at a molar ratio of 1:1 and stirred at 40°C for 24 hours with a stirrer speed of 200 r / min to obtain an ionic liquid.

[0075] 2) The commercial polyolefin separator Celgard2500 (circular, 1.2 cm in diameter and 25 μm thick) was fully impregnated with 20 μL of the ionic liquid from step 1) to obtain the electrolyte-separator composite material.

[0076] Performance testing:

[0077] 1) Scanning electron microscope (SEM) image of the electrolyte-diaphragm composite material of Example 1 is shown below. Figure 2 (In the figure, a and b represent different magnifications) as shown.

[0078] Depend on Figure 2 It can be seen that the carrier fluorinated polyimide porous membrane in the electrolyte-diaphragm composite material of Example 1 is composed of interpenetrating nanofibers with a diameter of 200nm to 900nm. This structure helps to improve the affinity for ionic liquids and also helps to suppress the growth of lithium dendrites.

[0079] Furthermore, the same tests revealed that the microstructure of the electrolyte-diaphragm composite materials in Examples 2-4 was highly similar to that of the electrolyte-diaphragm composite material in Example 1. The carrier fluorinated polyimide porous membrane in the electrolyte-diaphragm composite material was composed of interpenetrating nanofibers with a diameter of 80 nm to 900 nm.

[0080] 2) Thermogravimetric analysis (TGA) curves of the electrolyte-diaphragm composite material in Example 1 are as follows: Figure 3 As shown (Test conditions: nitrogen atmosphere, test temperature range: room temperature to 600℃, heating rate: 10℃ / min).

[0081] Depend on Figure 3It can be seen that the 5wt% thermal weight loss temperature of the electrolyte-diaphragm composite material in Example 1 reaches 194℃, which is higher than the decomposition temperature of commercial electrolytes (170℃~185℃). Furthermore, the glass transition temperature of the electrolyte-diaphragm composite material in Example 1 is above 240℃, while commercial polyolefin diaphragms soften, shrink, and fail at 120℃. Therefore, the electrolyte-diaphragm system in Example 1 exhibits excellent thermal stability and safety.

[0082] Furthermore, the same tests revealed that the thermal stability of the electrolyte-diaphragm composite materials in Examples 2-4 was very close to that of the electrolyte-diaphragm composite material in Example 1.

[0083] 3) Raman spectra of the electrolyte-diaphragm composite materials of Example 1 and Comparative Example 1 are as follows: Figure 4 As shown (Test conditions: laser emitter wavelength 785nm, scanning range 100cm) -1 ~1300cm -1 ).

[0084] Depend on Figure 4 It can be known that:

[0085] a) Regarding the electrolyte-diaphragm composite material of Example 1, at 742.8 cm⁻¹ -1 and 870cm -1 The structures at these locations correspond to the free anion TFSI- and the cation complex [Li(G3)], respectively. + The peak indicates, on the one hand, the successful preparation of the ionic liquid and its structural stability in fluorinated polyimide nanofiber membranes; on the other hand, TFSI - The absorption peak shifts to a lower wavenumber, indicating that there is a certain interaction between the fluorinated polyimide and the anion, demonstrating the feasibility of the overall design approach.

[0086] b) Regarding the electrolyte-diaphragm composite material of Comparative Example 1, at 743.3 cm... -1 and 870cm -1 The respective locations exhibit the corresponding free anion TFSI - Cation complex structure [Li(G3)] + The signal indicates that the solvated ionic liquid still maintains a stable complexed cation structure in the Celgard 2500 membrane, while the anion TFSI - The absorption peak wavenumber is higher than that of the anion TFSI in Example 1. - The characteristic absorption peaks indicate that there is an interaction between fluorinated polyimide and anions, which increases the distance between anions and complexed cations and increases the number of free anions.

[0087] 4) The electrolyte-membrane composite material from Example 1 was assembled into a 2025 coin cell by placing it between a stainless steel sheet (working electrode) and a lithium metal sheet (reference electrode). The electrochemical stability of the electrolyte-membrane composite material was then tested using linear voltammetry (LSV). The potential scan range was 2V to 6V, and the scan rate was 1mV / s. The obtained LSV curve is shown below. Figure 5 As shown.

[0088] Depend on Figure 5 It can be seen that the electrolyte-membrane composite material of Example 1 has high electrochemical stability, and its oxidation decomposition potential can reach 4.5V, which can meet the practical application of high-voltage batteries.

[0089] Furthermore, the same tests revealed that the oxidative decomposition potential of the electrolyte-membrane composite materials in Examples 2-4 was close to that of the electrolyte-membrane composite material in Example 1, indicating that they could also meet the practical application requirements of high-voltage batteries.

[0090] 5) The electrolyte-separator composite materials of Examples 1, 2, Comparative Example 1, and 2 were placed between two lithium metal sheets and then packaged in a 2032 button cell to form a lithium-lithium symmetric battery. The ionic conductivity as a function of temperature was then tested using a Chenhua electrochemical workstation. The obtained ionic conductivity-temperature relationship curves are shown below. Figure 6 As shown.

[0091] Depend on Figure 6 It can be seen that the ionic conductivity increases with increasing temperature. At 30℃, the ionic conductivity of the electrolyte-diaphragm composite materials of Examples 1, 2, Comparative Examples 1 and 2 are 0.39 mS / cm, 0.62 mS / cm, 0.24 mS / cm and 0.38 mS / cm, respectively; at 100℃, they are 1.80 mS / cm, 2.33 mS / cm, 1.17 mS / cm and 1.91 mS / cm, respectively. This indicates that the electrolyte-diaphragm composite materials of Examples 1 and 2 have good thermal stability and high ionic conductivity (reaching 10 mS / cm) over a wide temperature range. -4 S / cm~10 -3 The electrolyte-membrane composite material of Comparative Example 1 showed lower ionic conductivity at both 30°C and 100°C than that of Example 1. The electrolyte-membrane composite material of Comparative Example 2 also showed lower ionic conductivity at both 30°C and 100°C than that of Example 2. This is because the commercially available diaphragm Celgard 2500 has a lower liquid absorption rate, which also indicates that the fluorinated polyimide porous membrane has better hydrophilicity and higher ionic conductivity.

[0092] Furthermore, the same test revealed that the electrolyte-diaphragm composite material of Example 3 had an ionic conductivity of 0.31 mS / cm at 30°C, exceeding 10. -4 The conductivity is on the order of S / cm, which also meets the application requirements of lithium batteries at room temperature. The electrolyte-separator composite material of Example 4 has an ionic conductivity of 0.52 mS / cm at 30°C, which is slightly lower than that of the electrolyte-separator composite material of Example 2, but still meets the application requirements of lithium batteries at room temperature.

[0093] 6) The electrolyte-separator composite material of Example 1 and Comparative Example 1 was placed between two lithium metal sheets and then packaged in a 2032 type button cell to form a lithium-lithium symmetric battery. The battery was then tested using a Blue Battery testing system at 30°C and 0.5 mA / cm². 2 A constant current cycle test was performed on the lithium-lithium symmetric battery at a current density, with each cycle consisting of 1 hour of charge-discharge. The voltage-time relationship curves obtained are shown below. Figure 7 As shown.

[0094] Depend on Figure 7 It can be known that:

[0095] a) The lithium-lithium symmetric battery assembled with the electrolyte-separator composite material in Example 1 exhibited a stable potential curve and low overpotential in each constant current cycle. This indicates that the concentration polarization phenomenon in the system is low at this current density, allowing lithium ions to be deposited more uniformly on the surface of the lithium metal electrode. It also indicates that the system forms a stable SEI interface with the lithium metal, and its bulk and interfacial resistance remain essentially unchanged during lithium ion deposition. Furthermore, the lithium-lithium symmetric battery assembled with the electrolyte-separator composite material in Example 1 did not experience a sudden voltage drop to approximately 0V (short circuit) during more than 1500 hours of constant current cycling, demonstrating that the electrolyte-separator composite material in Example 1 has excellent ability to suppress lithium dendrite growth and can meet the application requirements of long-term cycling of lithium metal batteries.

[0096] b) The lithium-lithium symmetric battery assembled with the electrolyte-membrane composite material of Comparative Example 1 showed significant fluctuations after constant current cycling for more than 400 hours. After constant current cycling for more than 480 hours, the potential suddenly decreased, indicating that lithium dendrites had grown rapidly to penetrate the membrane, thus causing a short circuit in the battery. It can be seen that the electrolyte-membrane composite material of Comparative Example 1 is inferior to the electrolyte-membrane composite material of Example 1 in terms of interface stability of lithium metal and lithium dendrite suppression ability. This further highlights the performance advantages of the ionic liquid-fluorinated polyimide porous membrane system.

[0097] 7) NCM811 was used as the positive electrode of the battery (active material loading of approximately 1 mg / cm³). 2The positive electrode has a mass ratio of NCM811:binder:conductive carbon black = 8:1:1. Lithium metal is used as the negative electrode, and the electrolyte-separator composite material from Example 1 is used as both the separator and electrolyte. A high-voltage lithium metal battery, Li / NCM811, is assembled. Charge-discharge cycle tests are then conducted at 30°C and within a voltage range of 3.0V to 4.3V. The discharge capacity and coulombic efficiency at different rates are shown below. Figure 8 As shown.

[0098] Depend on Figure 8 It can be seen that the high-voltage lithium metal battery assembled with electrolyte-separator composite material in Example 1 has high cycle capacity and retention rate at different rates, exhibiting excellent rate stability, with an average coulombic efficiency higher than 99.0%. Its average capacity and average coulombic efficiency at 1C high rate are 150.2 mAh / g and 99.7%, respectively.

[0099] Furthermore, the same tests revealed that the high-voltage lithium metal batteries assembled from the electrolyte-separator composite materials in Examples 2-4 also exhibited high capacity and excellent rate stability.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An electrolyte-diaphragm composite material, characterized in that, The composition includes a fluorinated polyimide porous membrane and a supported ionic liquid; the fluorinated polyimide porous membrane is composed of fluorinated polyimide fibers; the diameter of the fluorinated polyimide fibers is 80 nm to 900 nm; the fluorinated polyimide is prepared by polycondensation reaction of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride; the ionic liquid is composed of a fluorinated lithium salt and an organic compound capable of complexing with lithium ions; the fluorinated lithium salt is lithium bis(trifluoromethanesulfonyl)imide; the organic compound capable of complexing with lithium ions is at least one of triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; the molar ratio of the fluorinated lithium salt and the organic compound capable of complexing with lithium ions is 1:

1.

2. The electrolyte-diaphragm composite material according to claim 1, characterized in that: The thickness of the fluorinated polyimide porous membrane is 10 μm to 40 μm.

3. A method for preparing the electrolyte-diaphragm composite material as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Fluorinated polyimide is prepared by polycondensation of 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene and 4,4′-biphenyl ether dianhydride, and then electrospinned to obtain a porous membrane containing fluorinated polyimide. 2) Fluorine-containing lithium salts and organic compounds that can complex with lithium ions are mixed to obtain ionic liquids; 3) The fluorinated polyimide porous membrane from step 1) is impregnated with the ionic liquid from step 2) to obtain the electrolyte-membrane composite material.

4. The preparation method according to claim 3, characterized in that: The polycondensation reaction in step 1) is carried out at 5℃ to 250℃ for 6h to 30h; the mixing in step 2) is carried out at 10℃ to 50℃ for 10h to 36h.

5. A lithium metal battery, characterized in that, The composition includes the electrolyte-diaphragm composite material as described in claim 1 or 2.

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