Method for removing Li2CO3 on surface of LLZO type electrolyte and preparing composite electrolyte membrane

Abstract

The invention discloses a method for removing Li2CO3 on the surface of an LLZO type electrolyte and a preparation method of a composite electrolyte membrane. The method comprises the following steps: S1, preparing a trifluoromethanesulfonate solution; s2, dispersing LLZO powder of which the surface is coated with Li2CO3 into the prepared trifluoromethanesulfonate solution, and carrying out normal-temperature ultrasonic treatment; s3, adding a lithium salt with a corresponding proportion into the solution, and standing at room temperature for 24 hours to form a precursor solution A; and S4, taking a certain amount of the precursor solution A, dropwise adding the precursor solution A to two sides of the diaphragm, and continuously standing at room temperature for 24 hours until the precursor solution A is completely polymerized to form the organic-inorganic composite solid electrolyte membrane. The used trifluoromethanesulfonate can improve the lithium ion conduction performance of the composite electrolyte membrane while performing affinity treatment on Li2CO3 on the surface of LLZO, optimizes lithium deposition, and reduces the growth of lithium dendrites; meanwhile, trifluoromethanesulfonate is used as an initiator for ring-opening polymerization of a precursor solution, and the composite electrolyte is subjected to in-situ polymerization in the battery, so that the interface impedance of the battery is reduced, and the operation stability of the LLZO-based organic-inorganic composite solid electrolyte is ensured.

Description

Technical Field

[0001] The present invention relates to the fields of solid-state batteries and new energy, and particularly to a method for removing Li2CO3 on the surface of an LLZO-type electrolyte and preparing a composite electrolyte membrane. Background Art

[0002] Solid-state batteries are considered to have excellent development prospects. Lithium lanthanum zirconium oxide Li7La3Zr2O 12 (LLZO)-type inorganic solid electrolytes have excellent ionic conductivity and mechanical properties, and are generally used for blending with polymer electrolytes to obtain a composite solid electrolyte separator with both flexibility and high ionic conductivity.

[0003] However, it has been found through research that LLZO-type solid electrolytes in air are unstable and easily react to form lithium carbonate Li2CO3 on the surface in the presence of water and carbon dioxide in the air. Li2CO3 has the characteristics of lithium aversion and ionic insulation. When the surface of the LLZO-type solid electrolyte is coated with Li2CO3, its ionic conductivity is severely reduced, affecting the performance of various prepared electrolyte separators, and also affecting the stability of the battery. At the same time, due to the rigidity of the ceramic particles themselves in the traditionally prepared pure LLZO solid electrolyte, the contact with the positive and negative electrode interfaces is often not tight enough during battery assembly, resulting in too high interfacial impedance and the battery cannot operate stably for a long time.

[0004] Currently, for the removal of Li2CO3 on the surface of LLZO, and for the removal of surface impurities of LLZO, researchers choose methods such as acid treatment, high-temperature treatment, and mechanical polishing. The above methods have all effectively removed Li2CO3. However, when the acid treatment content is too high, hydrogen ions will react excessively with LLZO particles, causing damage to their structure and affecting performance; the environmental temperature required for high-temperature treatment is too high and is not suitable for general use; and the mechanical polishing method can only treat the surface of sheet-like LLZO, and at the same time, problems such as incomplete internal treatment and fragmentation due to uneven stress during treatment need to be considered. And through simple surface coating technology, when the coating material is not selected reasonably, there may be a problem of coating residue on the surface of LLZO, which in turn affects the ionic conductivity of LLZO. And for the composite solid electrolyte prepared by simply blending polymer inorganic particles, although the flexibility and toughness of the separator are improved, due to the addition of polymers with low ionic conductivity, the overall ionic conductivity performance of the composite solid electrolyte decreases.

[0005] Therefore, the prior art still needs to be improved to meet the removal of Li2CO3 on the surface of LLZO, and at the same time prepare an organic-inorganic composite electrolyte separator that can solve the interface contact problem and has excellent ionic conductivity. Summary of the Invention

[0006] In view of the problems of the above technology, the purpose of the present invention is to provide a method for removing Li2CO3 on the surface of LLZO-type electrolyte and preparing a composite electrolyte membrane, aiming to simply and efficiently remove Li2CO3 on the surface of LLZO only through a displacement reaction process, so as to achieve the affinity removal of surface impurities to protect the internal structure, and at the same time design an organic-inorganic composite solid electrolyte membrane to improve the problem of poor interface contact with the positive and negative electrodes.

[0007] The technical solution of the present invention is as follows:

[0008] A method for removing Li2CO3 on the surface of LLZO-type electrolyte and preparing a composite electrolyte membrane, comprising the steps:

[0009] Step 1: Prepare a trifluoromethanesulfonate solution;

[0010] Step 2: Take LLZO powder with Li2CO3 coated on the surface and disperse it in the prepared trifluoromethanesulfonate solution, and perform ultrasonic treatment at room temperature;

[0011] Step 3: Add a corresponding proportion of lithium salt to the solution prepared in Step 2 above, and let it stand at room temperature for 24 h to form a precursor solution;

[0012] Step 4: Pipette a certain amount of the precursor solution and drop it on the separator, and continue to let it stand at room temperature for 24 h until the precursor solution is completely polymerized to form an organic-inorganic composite solid electrolyte membrane.

[0013] Preferably, the solvent for dissolving trifluoromethanesulfonate in Step 1 is 1,3-dioxolane (DOL) and fluoroethylene carbonate (FEC), and the organic solvent DOL is soaked with lithium chips before use to remove trace water in the solvent.

[0014] Preferably, the volume ratio of the organic solvents 1,3-dioxolane and fluoroethylene carbonate in Step 1 is 10:(1-10);

[0015] Preferably, the ultrasonic treatment time in Step 2 is 30-40 min.

[0016] If only LLZO powder with a treated surface is to be obtained, the organic solvent can be replaced with one of anhydrous acetonitrile, N,N-dimethylformamide, acetone, etc. After adding trifluoromethanesulfonate and LLZO and performing ultrasonic treatment therein, it is continuously washed and centrifuged several times with anhydrous ethanol or acetonitrile, and the solid is dried in a vacuum oven, and the drying conditions are at 60-80 °C, the oven pressure is 10-30 Pa, and the drying time is 10-24 h.

[0017] Preferably, the mass ratio of LLZO powder to trifluoromethanesulfonate in Step 2 is 10:(1-7).

[0018] Preferably, the content of the inorganic substance (i.e., LLZO powder) in the organic-inorganic composite electrolyte precursor solution prepared in Step 3 is 30-40%.

[0019] The precursor solution is a homogeneous slurry composed of a lithium salt, 1,3-dioxolane, fluoroethylene carbonate, LLZO, and trifluoromethanesulfonate. The lithium salt is selected from one of LiClO4, LiTFSI, and LiFSI.

[0020] Preferably, in Step 3, the precursor solution is stirred evenly at room temperature at a rotation speed of 200-400 r / min for 1-2 h.

[0021] Preferably, the separator used in Step 4 is one of various porous separators such as PP membrane, PI membrane, cellulose membrane, electrospun membrane, or 3D printed membrane.

[0022] Preferably, the amount of the precursor solution dropped on the separator in Step 4 is 40-60 μL to form an organic-inorganic composite solid electrolyte.

[0023] Preferably, the operation process of Step 4 is that during the process of assembling the battery, when the precursor solution still has a flowing state, it is injected into the separator. After the battery assembly is completed, the assembled battery is left standing at room temperature to enable the precursor solution to fully polymerize in-situ.

[0024] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0025] (1) In the method for removing surface impurities Li2CO3 of the LLZO-based solid electrolyte and preparing the composite solid electrolyte membrane of the present invention, by adding trifluoromethanesulfonate (X(OTf), where X represents various metal elements), a displacement reaction occurs with Li2CO3 to convert Li2CO3 on the surface of LLZO into XCO3, which is easier to precipitate and falls off from the surface of LLZO. Through the displacement reaction, the Li2CO3 impurities on the surface of LLZO can be effectively treated without damaging the structure of LLZO itself.

[0026] (2) By adding trifluoromethanesulfonate, one of the products of the displacement reaction, lithium trifluoromethanesulfonate, is uniformly dispersed in the composite electrolyte membrane as a lithium salt, which can improve the ionic conductivity of the composite electrolyte membrane; the other product XCO3 of the displacement reaction is detached from the surface of LLZO through the ultrasonic process and is dispersed in the polymer electrolyte slurry in the form of an inorganic filler, reducing the crystallinity of the polymer electrolyte and improving the electrochemical performance of the composite electrolyte membrane.

[0027] (3) Magnesium trifluoromethanesulfonate used in the present invention can also be used as an initiator for the ring-opening polymerization of the organic solvent 1,3-dioxolane, reducing the internal resistance of the battery through in-situ polymerization in the battery.

[0028] (4) The trifluoromethanesulfonate used in the present invention is magnesium trifluoromethanesulfonate. Besides effectively removing the surface impurities of LLZO, the addition of magnesium element can form a lithium-magnesium alloy on the lithium metal negative electrode side, optimize lithium deposition, and optimize the growth of lithium dendrites.

[0029] (5) During the process of removing impurities from the surface of LLZO in the present invention, the required environment does not have overly high requirements. It only needs to carry out a displacement reaction between the trifluoromethanesulfonate and Li2CO3 on the surface of LLZO in an argon environment to complete the removal of surface impurities, and the experimental operation is simple and controllable. Description of the Drawings

[0030] Figure 1 It is a process flow chart for the removal of surface impurities Li2CO3 of LLZO-type solid electrolyte and the preparation method of composite solid electrolyte membrane.

[0031] Figure 2 It is an impedance curve diagram (constant temperature test at 60°C) of the film formed by compounding LLZO solid powder with PEO before and after being treated with Mg(OTF)2.

[0032] Figure 3 It is a TEM comparison diagram of LLZO solid powder before and after being treated with Mg(OTF)2.

[0033] Figure 4 It is a comparison diagram of infrared spectra of the surface Li2CO3 content of LLZO solid powder before and after treatment.

[0034] Figure 5 It is an XRD comparison diagram of the surface Li2CO3 content of LLZO solid powder before and after treatment.

[0035] Figure 6 It is a Li-Li symmetric battery formed by compounding LLZO solid powder with PEO before and after being treated with Mg(OTF)2, 0.1mA / cm 2 , 0.1mAh / cm 2 (constant temperature test at 60°C).

[0036] Figure 7 It is a picture of the composite electrolyte after the ring-opening in-situ polymerization of LLZO-DOL by the initiator.

[0037] Figure 8 It is a numerical graph of lithium ion migration after the in-situ polymerization of LLZO-DOL composite electrolyte.

[0038] Figure 9 It is a cycle life curve of the LFP / DOL-LLZO / Li solid-state battery at a rate of 1C (room temperature test).

[0039] In the figure, LLZO@air represents the LLZO-PEO composite electrolyte with a Li2CO3 coating on the surface, and LLZO@Mg represents the modified LLZO-PEO composite electrolyte after treating the surface Li2CO3 with Mg(OTF)2. Detailed implementation manners

[0040] Refer to Figure 1 , the present invention aims to provide a method for removing Li2CO3 from the surface of LLZO-based electrolytes and preparing composite electrolyte membranes. To make the purpose, technical solutions and functions of the present invention more clearly and accurately expressed, the following specific examples are further described in detail by combination.

[0041] In the following Example 1 category, the optimal ratio of Mg(OTF)2 used to remove Li2CO3 from the surface of LLZO is first explored by blending traditional polymers with LLZO to form a film. Then, on the basis of this ratio, the Example 2 category explores the ratio used to initiate the ring-opening in-situ polymerization of DOL.

[0042] Obviously, the following examples are only used for specific explanations of the present invention. Magnesium trifluoromethanesulfonate / aluminum is selected as a specific example to treat the trifluoromethanesulfonate of LLZO, but the present invention is not limited thereto.

[0043] A method for removing Li2CO3 from the surface of LLZO-based electrolytes and preparing composite electrolyte membranes. When exploring the optimal ratio of Mg(OTF)2 for removing Li2CO3 from the surface of LLZO, it includes the following steps:

[0044] Step 1: Prepare a trifluoromethanesulfonate solution;

[0045] Step 2: Take the LLZO powder with a Li2CO3 coating on the surface and disperse it in the prepared trifluoromethanesulfonate solution, and perform ultrasonic treatment at room temperature;

[0046] Step 3: Add the corresponding proportion of lithium salt to the solution prepared in Step 2 above, and let it stand at room temperature for 24 h to form a precursor solution;

[0047] Step 4: Pipette a certain amount of the precursor solution and drop it on the separator, and continue to let it stand at room temperature for 24 h until the precursor solution is completely polymerized to form an organic-inorganic composite solid electrolyte membrane.

[0048] In the embodiment of the optimal ratio of Mg(OTF)₂ for removing Li₂CO₃ from the surface of LLZO: magnesium triflate (Mg(OTf)₂) is a polar magnesium salt, which is dissolved using a polar organic solvent selected from one of anhydrous acetonitrile, N,N-dimethylformamide (DMF), and acetone; the above polar organic solvents can also be used to dissolve the polymer electrolyte, and the polymer electrolyte is selected from one of polyethylene oxide (PEO), polyvinylidene difluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polypropylene carbonate (PPC), etc.; the lithium salt added to the slurry is selected from one of lithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0049] Example 1-1

[0050] (1) Weigh the drugs according to the mass ratio of LLZO powder to magnesium triflate of 10:1, weigh 0.009 g of magnesium triflate, and dissolve it evenly with 2 ml of anhydrous acetonitrile solvent to obtain solution A;

[0051] (2) Weigh 0.09 g of LLZO solid powder with Li₂CO₃ coated on the surface, add it to solution A, and disperse it evenly by ultrasonic treatment for 40 min to further obtain mixed solution B;

[0052] In this process, through the displacement reaction between magnesium triflate and Li₂CO₃, and in the violent reaction environment of ultrasonic treatment, Li₂CO₃ on the surface of LLZO is effectively removed.

[0053] (3) Weigh 0.3 g of PEO and 0.1086 g of LiTFSI, and dissolve and disperse them evenly with 8 ml of anhydrous acetonitrile solvent to obtain solution C;

[0054] The prepared mixture was stirred and dissolved evenly on a heating table. The temperature of the heating table was set at 70 °C, the stirring speed was 750 r / min, and the stirring time was 12 h;

[0055] (4) After solution C was evenly dispersed, solution A was transferred into solution C, and stirred at 40 °C at 400 r / min for 1 h to obtain a uniformly mixed organic-inorganic composite electrolyte precursor slurry;

[0056] (5) The organic-inorganic composite electrolyte precursor slurry was poured into a mold, dried in a vacuum oven at a pressure of 10 Pa and 60 °C for 24 h, and then taken out and quickly transferred into a glove box and cut into a composite separator with a diameter of 19 mm for standby. The glove box environment was oxygen ≤ 0.01 ppm and water ≤ 0.01 ppm.

[0057] Example 1-2

[0058] The difference from Example 1-1 was that the drugs were weighed according to the mass ratio of LLZO powder to magnesium trifluoromethanesulfonate salt of 10:2. 0.018 g of magnesium trifluoromethanesulfonate salt was weighed for solution preparation, and then blended with the polymer PEO and cast into a film. After that, it was cut into a diameter of 19 mm in a glove box for standby.

[0059] Example 1-3

[0060] The difference from Example 1-1 was that the drugs were weighed according to the mass ratio of LLZO powder to magnesium trifluoromethanesulfonate salt of 10:3. 0.027 g of magnesium trifluoromethanesulfonate salt was weighed for solution preparation, and then blended with the polymer PEO and cast into a film. After that, it was cut into a diameter of 19 mm in a glove box for standby.

[0061] Example 1-4

[0062] The difference from Example 1-`1 was that the drugs were weighed according to the mass ratio of LLZO powder to magnesium trifluoromethanesulfonate salt of 10:5. 0.045 g of magnesium trifluoromethanesulfonate salt was weighed for solution preparation, and then blended with the polymer PEO and cast into a film. After that, it was cut into a diameter of 19 mm in a glove box for standby.

[0063] Example 1-5

[0064] The difference from Example 1-1 was that the drugs were weighed according to the mass ratio of LLZO powder to magnesium trifluoromethanesulfonate salt of 10:7. 0.063 g of magnesium trifluoromethanesulfonate salt was weighed for solution preparation, and then blended with the polymer PEO and cast into a film. After that, it was cut into a diameter of 19 mm in a glove box for standby.

[0065] Comparative Example 1-1

[0066] The difference from Example 1-1 is that in the comparative example, no treatment was added, and the solution was directly prepared. After that, it was blended with the polymer PEO and cast into a film, and then cut into a diameter of 19 mm in a glove box for standby.

[0067] Comparative Example 1-2

[0068] The difference from Example 1-1 is that 0.027 g of hydrochloric acid was weighed for solution preparation. After that, it was blended with the polymer PEO and cast into a film, and then cut into a diameter of 19 mm in a glove box for standby.

[0069] Comparative Example 1-3

[0070] The difference from Example 1-1 is that 0.027 g of trifluoromethanesulfonic acid was weighed for solution preparation. After that, it was blended with the polymer PEO and cast into a film, and then cut into a diameter of 19 mm in a glove box for standby.

[0071] Eight groups of composite electrolyte membranes of the above examples and comparative examples were assembled into button cells with a 2032-type 304 stainless steel battery case in a glove box in the form of steel sheet / composite electrolyte membrane / steel sheet, and the ionic conductivity performance of the composite separator was tested at 60 °C (as shown in Table 1).

[0072] Table 1 Conductivity of organic-inorganic composite electrolyte membranes treated with different proportions of additives

[0073]

[0074] Note: In the removal effect column in the table: × means not completely removed, √ means completely removed, and - means not removed.

[0075] The above test results show that: in Example 1-3, the effect of Li2CO3 impurities on the surface of LLZO reached the best. The ionic conductivity of the modified composite separator increased from 1.358×10 -4 S / cm to 3.481×10 -4 S / cm, and its impedance curve is as Figure 2 shown.

[0076] LLZO treated with anhydrous ethanol or anhydrous acetonitrile solvent according to the mass ratio of Example 1-3 was washed vigorously, and the supernatant was removed by centrifugation. After repeating the above operations several times, the centrifuged precipitate was dried in a vacuum oven. The surface conditions of LLZO before and after treatment were photographed using a transmission electron microscope. It can be observed that under the treatment of Mg(OTF)2 with a ratio of 10:3, the Li2CO3 impurities on the surface of LLZO were basically removed (as Figure 3 shown).

[0077] At the same time, infrared spectroscopy and X-ray diffraction analysis were carried out on LLZO before and after treatment. It can be found from the infrared comparison spectra that the carbonate group is at 1438 cm-1 and the characteristic peaks at 863 cm -1 no longer appeared after being treated with Mg(OTF)2 at a ratio of 10:3, and the Li2CO3 on the surface of LLZO was treated (as Figure 4 shown); meanwhile, in the XRD comparison Figure 5 The disappearance of the characteristic peak of Li2CO3 near 22° also indicates that the removal of impurities on the surface of LLZO has been achieved.

[0078] Subsequently, the PEO-LLZO composite solid electrolyte treated with a mass ratio of 10:3 was used to assemble a button cell in a glove box using a 2032-type 304 stainless steel battery case with lithium foil / composite electrolyte membrane / lithium foil. The charge-discharge cycle was carried out at 60 °C, and the charge-discharge current was 0.1 mA / cm 2 , and the charge-discharge time was 1 h for both. The charge-discharge comparison curves of the lithium symmetric battery are as Figure 6 shown. It can be seen that the PEO-LLZO composite electrolyte membrane treated with Mg(OTF)2 has a lower overpotential. At the same time, after more than 2500 hours of charge-discharge cycling, the overpotential of the symmetric battery did not increase significantly, which fully proves that Mg(OTF)2 not only treats the surface of LLZO but also exhibits excellent ability to optimize lithium deposition and improve cycle stability.

[0079] The mass ratio of Mg(OTF)2-treated LLZO obtained through the above examples was used to prepare a new composite solid electrolyte membrane.

[0080] Example 2-1

[0081] A pipette was used to transfer 1,3-dioxolane and fluorinated ethylene carbonate solvents in a ratio of 10:2 and mixed evenly. The solvent was added to 30 wt% LLZO and mixed evenly; then Mg(OTF)2 was added in the ratio of Example 1-3 and dissolved thoroughly; and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added at 1 mol / L. After being dissolved thoroughly at room temperature, the remaining solvent was added and stirring was continued to obtain a precursor solution. Figure 7 is an optical picture of the precursor solution after standing at room temperature for 48 h. It can be seen that the ring-opening polymerization reaction was completed after 48 h.

[0082] Application Example 1

[0083] (1) Prepare a trifluoromethanesulfonate solution according to the ratio obtained in Example 2-1;

[0084] (2) Add 30 wt% LLZO to the solution, mix evenly, and perform ultrasonic treatment;

[0085] (3) Add LiTFSI in the corresponding proportion to the above solution, stir evenly and then let it stand for 24 h to form a precursor solution;

[0086] (4) Draw 60 μl of the precursor solution prepared in step (3) in the form of injection and add it to the electrospun separator made of PAN. Assemble a 2032-type button battery in the order of steel sheet-separator-steel sheet-spring sheet, and continue to let the battery stand at room temperature for 24 h. After the ring-opening polymerization reaction is complete, perform performance tests.

[0087] The lithium ion transference number of the composite solid electrolyte separator prepared in Application Example 1 is as Figure 8 shown. After 48 h, the electrolyte exhibits an excellent lithium ion transference number of 0.81.

[0088] Application Example 2

[0089] Draw 60 μl of the precursor solution prepared in Example 2-1 in the form of injection and add it to the electrospun separator made of PAN. Assemble a 2032-type button battery in the order of lithium sheet-separator-lithium iron phosphate positive electrode sheet-gasket-spring sheet, and continue to let the battery stand at room temperature for 24 h. After the ring-opening polymerization reaction is complete, perform performance tests.

[0090] The charge and discharge cycle performance of the lithium metal battery prepared in Application Example 2 is as Figure 9 shown. It can be seen that after cycling 200 times at a 1C rate, the battery still has a discharge specific capacity of 141.02 mAh / g, and the charge and discharge efficiency is 99.96%.

[0091] Example 2-2

[0092] Compared with Example 2-1, the difference is that 10 wt% of LLZO powder is added to the solvent, and then it is left standing at room temperature for 48 h to wait for the ring-opening polymerization reaction to be complete.

[0093] Experimental results show that when the solid content is low, the remaining content of magnesium trifluoromethanesulfonate that can be used for the ring-opening of DOL is too low, the degree of ring-opening of the precursor solution is too low, and it still has fluidity and cannot form a film.

[0094] Example 2-3

[0095] Compared with Example 2-1, the difference is that 60 wt% of LLZO powder is added to the solvent, and then it is left standing at room temperature for 48 h to wait for the ring-opening polymerization reaction to be complete.

[0096] Experimental results show that when the solid content is too high, the remaining content of magnesium trifluoromethanesulfonate used for the ring-opening of DOL is too high, the DOL in the precursor solution is over-ring-opened, the overall prepared separator is too hard, and the ionic conductivity drops significantly, and it is no longer suitable as a solid electrolyte membrane.

[0097] Obviously, the above examples of the present invention are only illustrative for explaining the present invention and not a limitation on the invention. Any obvious extensions or changes made on the basis of the present invention are within the scope of protection of the present invention.

Claims

1. A method for removing Li2CO3 on the surface of LLZO-based electrolyte and preparing a composite electrolyte membrane, characterized in that, It includes the following steps: Step 1: Prepare a trifluoromethanesulfonate solution; Step 2: Take LLZO powder coated with Li2CO3 and disperse it in the prepared trifluoromethanesulfonate solution, and perform ultrasonic treatment at room temperature; Step 3: Add the corresponding proportion of lithium salt to the solution prepared in Step 2 above, and let it stand at room temperature for 24 h to form a precursor solution; Step 4: Pipette a certain amount of the precursor solution and drop it on the separator, and continue to let it stand at room temperature for 24 h until the precursor solution is completely polymerized to form an organic-inorganic composite solid electrolyte membrane.

2. The method for removing Li2CO3 on the surface of the LLZO-based electrolyte and preparing the composite electrolyte membrane according to claim 1, wherein, The organic solvent for dissolving trifluoromethanesulfonate in Step 1 includes 1,3-dioxolane (DOL) and fluoroethylene carbonate (FEC), and the volume ratio of the organic solvents 1,3-dioxolane and fluoroethylene carbonate is 10:(1-10).

3. The method for removing Li2CO3 on the surface of the LLZO-based electrolyte and preparing the composite electrolyte membrane according to claim 1 or 2, characterized in that, The trifluoromethanesulfonate in Step 1 is magnesium trifluoromethanesulfonate, aluminum trifluoromethanesulfonate-based salt.

4. The method for removing Li2CO3 on the surface of the LLZO-based electrolyte and preparing the composite electrolyte membrane according to claim 1 or 2, characterized in that, The mass ratio of LLZO powder to trifluoromethanesulfonate in Step 2 is 10:(1-7).

5. The method for removing Li2CO3 on the surface of the LLZO-based electrolyte and preparing the composite electrolyte membrane according to claim 4, characterized in that, The content of inorganic matter (i.e., LLZO powder) in the precursor solution of the organic-inorganic composite electrolyte prepared in Step 3 is 30-40%.

6. The method for removing Li2CO3 from the surface of the LLZO-type electrolyte and preparing the composite electrolyte membrane according to claim 5, wherein The precursor solution of the organic-inorganic composite electrolyte prepared in Step 3 is subjected to solution blending at room temperature.

7. The method for removing Li2CO3 from the surface of the LLZO-type electrolyte and preparing the composite electrolyte membrane according to claim 1, wherein, The separator loaded with the precursor solution is one of various porous separators such as PP membrane, PI membrane, cellulose membrane, electrospun membrane or 3D printed membrane.

8. The method for removing Li2CO3 on the surface of the LLZO-based electrolyte and preparing the composite electrolyte membrane according to claim 1, wherein, The dosage of the precursor solution dropped on the separator is 40-60 μL.

9. The method for removing Li2CO3 on the surface of the LLZO-type electrolyte and preparing the composite electrolyte membrane according to claim 1, wherein, The process of continuing to stand for 24 h in Step 4 is: during the battery assembly process, the precursor solution is dropped on the separator, and the assembled battery is left to stand at room temperature so that the precursor solution can be fully polymerized.

10. The method for removing Li2CO3 from the surface of the LLZO-type electrolyte and preparing the composite electrolyte membrane according to claim 1, wherein, The lithium salt described in Step 3 is selected from one of LiClO4, LiPF6, LiFSI, LiTFSI.

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