A high-voltage-resistant polymer-based electrolyte membrane, a preparation method and applications thereof

Abstract

The application belongs to the technical field of battery materials, and particularly relates to a high-voltage-resistant polymer-based electrolyte film and a preparation method and application thereof. The preparation method of the high-voltage-resistant polymer-based electrolyte film provided by the application comprises the following specific steps: step S1, dissolving a polymer and a lithium salt in an organic solvent to prepare a uniform solution; step S2, adding a high-voltage-resistant additive lithium difluorophosphate into the solution obtained in step S1 and stirring uniformly; and step S3, adding a plasticizer additive into the solution obtained in step S2 and stirring uniformly, and then pouring the solution into a film or coating the solution on a diaphragm, and then drying to obtain the high-voltage-resistant polymer-based electrolyte film. The high-voltage-resistant polymer-based electrolyte film prepared by adding the high-voltage-resistant additive and the plasticizer has a high oxidation electrochemical window, can match a high-voltage nickel-cobalt-manganese ternary positive electrode material to improve the energy density of a solid-state battery, and the obtained solid-state battery has good long cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a high-voltage-resistant polymer-based electrolyte film and a preparation method and application thereof. BACKGROUND

[0002] Liquid lithium batteries have been widely used in 3C, power batteries, energy storage and other fields. Solid-state batteries use non-flammable and non-volatile solid-state electrolytes to replace flammable organic liquid ester electrolytes, which can improve the safety of the battery system, better adapt to high-energy positive and negative electrodes, and reduce the weight of the system, thereby achieving the improvement of energy density. Increasing the working voltage range of lithium batteries is one of the important ways to increase the energy density of the batteries. For solid-state batteries, the solid-state electrolyte needs to have good compatibility with lithium metal and be matched with high-voltage positive materials, and has high-voltage resistance.

[0003] At present, solid-state electrolytes mainly include two types: inorganic solid-state electrolytes and polymer solid-state electrolytes. The inorganic solid-state electrolyte mainly includes oxide and sulfide, wherein the oxide material has relatively low ion conductivity and large interface impedance between the positive and negative electrodes; the preparation conditions of the sulfide material are relatively harsh, and the industrialization is more difficult. The polymer solid-state electrolyte has the advantages of good thermal stability, high stability to lithium, good cycle performance, and can be prepared into a flexible thin film battery, and is the most easily industrialized direction at present. However, the polymer solid-state electrolyte currently studied still generally has the problem of not being resistant to high voltage, thereby the cycle stability of matching the ternary positive material is poor, and it is difficult to effectively improve the energy density of the battery. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a high-voltage-resistant polymer-based electrolyte film and a preparation method and application thereof. The prepared high-voltage-resistant polymer-based electrolyte film has a high oxidation electrochemical window, can improve the energy density of the solid-state battery by matching the high-voltage nickel-cobalt-manganese ternary positive material, and the obtained solid-state battery has good long cycle stability.

[0005] In order to achieve the above purpose, the technical scheme adopted by the application is as follows:

[0006] A preparation method of a high-voltage-resistant polymer-based electrolyte film, comprising the following steps:

[0007] Step S1, dissolving the polymer and the lithium salt in the organic solvent to prepare a uniform solution;

[0008] Step S2, adding the high-voltage additive lithium difluorophosphate into the solution obtained in step S1 and stirring uniformly;

[0009] Step S3, the plasticizer additive is added into the solution obtained in step S2, stirred uniformly, then the solution is cast into a film or coated on a separator, dried to obtain a high-voltage resistant polymer-based electrolyte film.

[0010] Further, in step S1, the polymer is selected from one or more of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, polycaprolactone.

[0011] Further, in step S1, the lithium salt is selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium bisfluorosulfonylimide.

[0012] Further, in step S1, the organic solvent is selected from one or more of acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, acetone, tetrahydrofuran, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate.

[0013] Further, in step S2, the mass of the high-voltage additive accounts for 1% to 8% of the mass of the polymer.

[0014] Further, in step S3, the plasticizer is selected from one or more of ethylene carbonate, trimethyl phosphite, butanedinitrile, octanedinitrile, polycarbonate.

[0015] The application also provides a high-voltage resistant polymer-based electrolyte film prepared by the above method.

[0016] The application also provides a use of the high-voltage resistant polymer-based electrolyte film in a solid-state battery, and a solid-state battery prepared by matching the high-voltage resistant polymer-based electrolyte film with a high-voltage positive active material and a negative material.

[0017] Further, the high-voltage positive active material is ternary nickel-cobalt-manganese.

[0018] Further, the negative material is a lithium sheet.

[0019] Advantages

[0020] The existing polymer-based electrolyte has a narrow electrochemical window, which makes it difficult to match a high-voltage positive electrode. The high-voltage resistant polymer-based electrolyte film prepared by the application has a higher electrochemical window, can match a high-voltage positive electrode, effectively improves the energy density of the solid-state battery, and at the same time, the solid-state battery assembled by matching the high-voltage resistant polymer-based electrolyte film with the high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111) has a voltage platform basically stable after 100 cycles of charging and discharging curves, showing good long cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 LSV test curve of the polymer-based electrolyte film prepared for the example and the comparative example;

[0022] Figure 2 Long cycle performance test graph of the solid-state battery assembled by matching the polymer-based electrolyte film prepared for example 1 and example 2 with a high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111);

[0023] Figure 3 Long cycle performance test graph of the solid-state battery assembled by matching the polymer-based electrolyte film prepared for example 3 and comparative example 1 with a high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111);

[0024] Figure 4 Charge-discharge curve graph of the solid-state battery assembled by matching the polymer-based electrolyte film prepared for example 3 with a high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111);

[0025] Figure 5 Charge-discharge curve graph of the solid-state battery assembled by matching the polymer-based electrolyte film prepared for comparative example 1 with a high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111). DETAILED DESCRIPTION

[0026] The present application will be further illustrated by specific examples, which are exemplary, intended to illustrate the problem and explain the present application, and are not a limitation.

[0027] Example 1

[0028] A preparation method of a high-voltage-resistant polymer-based electrolyte, comprising the following steps:

[0029] Step S1, 1g of polyethylene oxide (PEO) and 0.362g of lithium bis(trifluoromethyl sulfonyl) imide (LiTFSI) are dissolved in acetonitrile, and heated to dissolve at 60°C;

[0030] Step S2, 0.01g of lithium difluorophosphate (LiOP2F2) is added to the solution obtained in step S1, and stirred for 1h;

[0031] Step S3, 0.1g of ethylene carbonate (EC) is added to the solution obtained in step S2, and stirred for 12h, the mixed solution is cast on a polytetrafluoroethylene plate to form a film, and blow-dried to obtain a high-voltage-resistant polymer-based electrolyte film.

[0032] Example 2

[0033] A preparation method of a high-voltage-resistant polymer-based electrolyte, comprising the following steps:

[0034] Step S1, 1 g of polyethylene oxide (PEO) and 0.362 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in acetonitrile, and heated to dissolve at 60°C;

[0035] Step S2, 0.04 g of lithium difluorophosphate (LiOP2F2) was added to the solution obtained in step S1, and stirred for 1 h;

[0036] Step S3, 0.1 g of ethylene carbonate (EC) was added to the solution obtained in step S2, and stirred for 12 h. The mixed solution was cast on a polytetrafluoroethylene plate to form a film, and blow-dried to obtain a high-voltage-resistant polymer-based electrolyte film.

[0037] Example 3

[0038] A method for preparing a high-voltage-resistant polymer-based electrolyte, comprising the following steps:

[0039] Step S1, 1 g of polyethylene oxide (PEO) and 0.362 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in acetonitrile, and heated to dissolve at 60°C;

[0040] Step S2, 0.08 g of lithium difluorophosphate (LiOP2F2) was added to the solution obtained in step S1, and stirred for 1 h;

[0041] Step S3, 0.1 g of ethylene carbonate (EC) was added to the solution obtained in step S2, and stirred for 12 h. The mixed solution was cast on a polytetrafluoroethylene plate to form a film, and blow-dried to obtain a high-voltage-resistant polymer-based electrolyte film.

[0042] Comparative Example 1

[0043] A method for preparing a non-high-voltage-resistant polymer-based electrolyte, comprising the following steps:

[0044] 1 g of polyethylene oxide (PEO) and 0.362 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) were dissolved in acetonitrile, and heated to dissolve at 60°C, and stirred for 12 h. The mixed solution was cast on a polytetrafluoroethylene plate to form a film, and blow-dried to obtain a non-high-voltage-resistant polymer-based electrolyte film.

[0045] Linear sweep voltammetry (LSV) test experiment

[0046] Figure 1Results of linear sweep voltammetry (LSV) test experiments for the polymer-based electrolyte films prepared in the above examples and comparative examples. The polymer-based electrolyte film prepared in Comparative Example 1 was not added with high-voltage resistant additive lithium difluorophosphate (LiOP2F2), and the polymer-based electrolyte films prepared in Example 1, Example 2 and Example 3 were added with different proportions of high-voltage resistant additive lithium difluorophosphate (LiOP2F2). The oxidation electrochemical window of the polymer-based electrolyte film prepared in Comparative Example 1 was 3.6 V, and the oxidation electrochemical windows of the polymer-based electrolyte films prepared in Example 1, Example 2 and Example 3 were all higher than 4 V, in which the oxidation electrochemical window of the polymer-based electrolyte film prepared in Example 3 was 4.8 V, indicating that the high-voltage resistant performance of the polymer-based electrolyte film was greatly improved after the addition of lithium difluorophosphate (LiOP2F2). With the increase of the dose of high-voltage resistant additive lithium difluorophosphate (LiOP2F2), the oxidation electrochemical window of the polymer-based electrolyte film was also steadily improved, further indicating that lithium difluorophosphate (LiOP2F2) played a key role in improving the high-voltage resistant performance of the polymer-based electrolyte film.

[0047] Long cycle performance test experiments of the solid-state batteries assembled from the polymer-based electrolyte films

[0048] The polymer-based electrolyte films prepared in Example 1, Example 2, Example 3 and Comparative Example 1 were assembled into CR2023 type button cells to test the electrochemical performance, the positive active material was ternary nickel-cobalt-manganese (NCM111), the positive active material loading was about 2.0 mg / cm 2 , the negative electrode was lithium sheet, and the battery was tested after being placed in an oven at 60°C for 8 hours. The test voltage range was 2.7-4.2 V, and the test rate was 0.2C (1C = 160 mA / g).

[0049] Figure 2 Long cycle performance test results of the solid-state batteries assembled from the polymer-based electrolyte films prepared in Example 1 and Example 2 and matched with high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111), Figure 3 Long cycle performance test results of the solid-state batteries assembled from the polymer-based electrolyte films prepared in Example 3 and Comparative Example 1 and matched with high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111). Compared with the long cycle stability of the CR2023 type button cell assembled from the polymer-based electrolyte film prepared in Comparative Example 1, the CR2023 type button cells assembled from the polymer-based electrolyte films prepared in Example 1, Example 2 and Example 3 showed better long cycle stability.

[0050] Table 1 is the capacity retention results of the polymer-based electrolyte films prepared in Example 1, Example 2, Example 3 and Comparative Example 1 after 100 cycles of the CR2023 type button cell assembled. The discharge specific capacity of the CR2023 type button cell assembled with the polymer-based electrolyte film prepared in Comparative Example 1 decreased significantly after 100 cycles, and the capacity retention rate was 4.8%. The discharge specific capacity of the CR2023 type button cell assembled with the polymer-based electrolyte film prepared by adding different proportions of high-voltage resistant additive lithium difluorophosphate (LiOP2F2) did not show significant changes compared to the first cycle discharge specific capacity, and the capacity retention rate was higher than 75%, showing good long cycle stability. Among them, the capacity retention rate of the CR2023 type button cell assembled with the polymer-based electrolyte film prepared by adding the highest dose of high-voltage resistant additive lithium difluorophosphate (LiOP2F2) was 91.7%, showing the best long cycle stability. Therefore, lithium difluorophosphate (LiOP2F2) plays a key role in improving the long cycle stability of the solid-state battery assembled with the polymer-based electrolyte film.

[0051] Table 1 first cycle and 100 cycle discharge specific capacity data

[0052]

[0053]

[0054] Charge-discharge curve test experiment of assembled solid-state battery

[0055] Figure 4 The charge-discharge curve of the solid-state battery assembled with the polymer-based electrolyte film prepared in Example 3 and the high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111), Figure 5 The charge-discharge curve of the solid-state battery assembled with the polymer-based electrolyte film prepared in Comparative Example 1 and the high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111). The charge-discharge curve of the solid-state battery assembled with the polymer-based electrolyte film prepared in Example 3 and the high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111) remained basically stable after 100 cycles, and the curve shape did not change significantly, which was consistent with the good long cycle performance of the battery. The charge-discharge curve of the solid-state battery assembled with the polymer-based electrolyte film prepared in Comparative Example 1 and the high-voltage positive electrode ternary nickel-cobalt-manganese (NCM111) changed significantly after 50 cycles, showing a significantly increased polarization potential and a sharply reduced reversible specific capacity. Therefore, lithium difluorophosphate (LiOP2F2) plays a key role in maintaining the steady state of the charge-discharge curve of the solid-state battery assembled with the polymer-based electrolyte film.

Claims

1. A method for preparing a high-voltage resistant polymer-based electrolyte membrane, characterized in that: Includes the following steps: Step S1: Dissolve the polymer and lithium salt in an organic solvent to form a homogeneous solution; Step S2: Add the high-voltage additive lithium difluorophosphate to the solution obtained in step S1 and stir until homogeneous. Step S3: Add the plasticizer additive to the solution obtained in step S2, stir evenly, then cast the solution into a film or coat it onto the diaphragm, and dry it to obtain a high-voltage resistant polymer-based electrolyte membrane. In step S1, the polymer is selected from one or more of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, and polycaprolactone. In step S1, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium bis(fluorosulfonyl)imide; In step S1, the organic solvent is selected from one or more of acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, acetone, tetrahydrofuran, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. In step S2, the high-voltage additive accounts for 1% to 8% of the polymer mass; In step S3, the plasticizer is selected from one or more of ethylene carbonate, trimethyl phosphite, succinic acid, octanoic acid, and polycarbonate.

2. A high-voltage resistant polymer-based electrolyte membrane, characterized in that: It was prepared using the method for preparing high-voltage resistant polymer-based electrolyte membrane according to claim 1.

3. The application of a high-voltage resistant polymer-based electrolyte membrane in solid-state batteries, characterized in that: The solid-state battery is prepared by matching the high-voltage resistant polymer-based electrolyte membrane of claim 2 with a high-voltage positive electrode active material and a negative electrode material.

4. The application of the high-voltage resistant polymer-based electrolyte membrane according to claim 3 in solid-state batteries, characterized in that: The high-voltage positive electrode active material is a ternary nickel-cobalt-manganese alloy.

5. The application of the high-voltage resistant polymer-based electrolyte membrane according to claim 3 in solid-state batteries, characterized in that: The negative electrode material is lithium foil.

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