Composite electrolyte membrane based on functional polymer and preparation method thereof, and lithium-sulfur secondary cell

[0047] Examples:

[0048] A lithium-sulfur secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and an organic electrolyte.

[0049] The electrolyte in this embodiment uses a composite electrolyte membrane specially made by the present invention.

[0050] The positive pole piece of the positive electrode in this embodiment is generally composed of a current-conducting current collector and a positive electrode active material, conductive material, adhesive, and other additives coated on the current collector; the positive electrode active material in this embodiment is selected as a simple substance Sulfur; the conductive material is a carbon-based conductive agent, such as conductive carbon black, acetylene black or graphite powder; the binder is polyvinylidene fluoride; wherein the mass percentages of the positive electrode active material, the conductive material and the binder are respectively 70%, 19%, and 11%; the current collector can be aluminum foil or aluminum mesh; during preparation, the positive electrode active material, conductive material, adhesive, etc. are weighed in the aforementioned proportions, ball milled and mixed for 3h to 4h, and then a scraper is used Prepare the positive pole piece so that the positive electrode active material load is 6mg/cm 2 , Cut into 10cm long, 5cm wide positive pole piece, and vacuum dry at 60℃ for 12h.

[0051] The negative electrode in this embodiment includes a negative electrode active material, and the negative electrode active material is a lithium foil;

[0052] The organic electrolyte in this embodiment is mainly composed of a non-aqueous solvent and a lithium salt; the non-aqueous solvent includes ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL); the lithium salt is lithium hexafluorophosphate; The organic electrolyte is a 1M lithium hexafluorophosphorus-DME-DOL mixed solution.

[0053] When preparing the lithium-sulfur secondary battery of this embodiment, the prepared positive pole piece, the composite electrolyte membrane and the lithium foil prepared above are wound in a glove box to prepare a battery cell. The thickness of the lithium foil used is 100μm, and then added The organic electrolyte is placed for 24 hours after packaging to test the electrical properties. Perform charge and discharge performance test, the voltage is limited to 2.5V~1.5V at room temperature, and the current is 0.75mA/cm 3; The prepared lithium-sulfur secondary battery C/10 charge and discharge, charge and discharge cycle 100 times, the capacity retention rate is 81.7%, the battery cycle performance curve is as follows Figure 4 Shown.

[0054] The composite electrolyte membrane used in the foregoing embodiment is mainly composed of a polymer porous membrane and a functional electrolyte coating located on both sides of the composite electrolyte membrane. The functional electrolyte coating includes a perfluorinated membrane coated on one side of the polymer porous membrane. Lithium sulfonamide type single lithium ion type polymer electrolyte coating and a gel polymer coating which is coated on the other side of the polymer porous diaphragm and has stability to lithium negative electrode and has a free radical trapping function. The perfluorosulfonamide lithium monolithium ion polymer in the perfluorosulfonamide lithium monolithium ion polymer electrolyte coating is prepared by using perfluorosulfonyl fluoride resin as a raw material and adopting a polymer similar conversion method. The gel polymer coating is mainly composed of polymers, solvents, free radical annihilation effect additives and nano-SiO 2 It is prepared by mixing, coating, and drying according to the proportion; the polymer used in this example is polymethyl methacrylate (PMMA); the radical annihilation effect additive is tri-tert-butyl phenol, and the addition amount is polymerization 2% of the substance mass; the solvent is tetrahydrofuran, and the addition amount of the solvent is 5 times the mass of the polymer. The polymer porous membrane in this embodiment is a polytetrafluoroethylene porous membrane among olefin porous membranes. The electron microscope picture of the composite electrolyte membrane coated with a gel polymer coating and a perfluorosulfonamide lithium monolithium ion polymer coating in this embodiment is as follows figure 2 with image 3 Shown (see before coating figure 1 ).

[0055] The method for preparing the functional polymer-based composite electrolyte membrane in this embodiment specifically includes the following steps:

[0056] (1) Prepare PTFE porous membrane and perfluorosulfonyl fluoride resin;

[0057] (2) Preparation of methyl lithium containing double electron withdrawing groups; the methyl lithium containing double electron withdrawing groups used in this example is lithium malononitrile, which is mainly prepared by the following steps: 1.69 g of propylene Dinitrile was dissolved in a mixed solvent of 10g anisole, 10g toluene, 10g N-methylpyrrolidone, and then the mixed raw materials were dropped into a 250ml single-neck flask containing 0.71g lithium hydride, and the reaction was refluxed and stirred at 30°C under a nitrogen atmosphere. 6 After the reaction is complete, filter to remove unreacted raw material lithium hydride and precipitation by-products to obtain an intermediate product containing lithium malononitrile mixed solution (light red, clear and transparent solution); according to the requirements of stoichiometric ratio, lithium hydride and malonate Nitriles should be reacted in a 2:1 equivalent, but because lithium hydride is a relatively active reactant, side reactions are prone to occur. Therefore, in addition to purifying the reaction system, the reaction system should also be controlled in excess with an excess ratio of 50%. In order to facilitate the complete substitution of malononitrile, and the subsequent reaction to obtain a higher polymer yield;

[0058] (3) Add 25g of the prepared perfluorosulfonyl fluoride resin to the mixed solution containing lithium malononitrile prepared in step (2), stir and reflux for 15 hours at 70°C under a nitrogen atmosphere, and obtain the side Perfluorosulfonamide lithium polymer containing lithium dicyandiamide groups;

[0059] (4) The perfluorosulfonamide lithium polymer containing lithium dicyandiamide group in the side chain prepared above was washed with a mixed solvent of ethanol and water, and then dried to obtain 24 g of solid product; then added to 480 g In dimethyl sulfoxide, the amount added is controlled so that the solid content reaches 5%, stir to dissolve at 70°C, filter out a small amount of insoluble matter with a 60-mesh screen to obtain a clear and transparent solution—perfluorosulfonamide lithium polymer electrolyte solution; The perfluorosulfonamide lithium polymer electrolyte solution is distilled and concentrated to a concentration of 10%, and it is scraped on the PTFE porous membrane with a doctor coater. The film thickness is 5μm. After initial drying, add a non-solvent (ethanol/water 1/2 mixed Solution) soak, replace dimethyl sulfoxide to form a second film, vacuum dry at 120°C for 0.5h, and cool down to obtain a composite film coated with a functional electrolyte coating on the positive electrode side;

[0060] (5) Mix 10g of polymer polymethyl methacrylate with good stability to lithium negative electrode, 50g of solvent tetrahydrofuran and 0.2g of radical annihilation effect additive tri-tert-butylphenol, and add nano SiO 2 1g. Then, the mixed solution was coated on the other side of the composite film prepared above with a knife coater. After the solvent evaporates, the composite film with double-sided coating was placed in a vacuum oven at 80°C for 24 hours to prepare a The functional polymer composite electrolyte membrane is moved into a glove box filled with dry argon for use.

[0061] In the above preparation method of the present invention, preferably, in the step (3), the addition of a non-solvent facilitates the complete removal of the electrolyte membrane volatiles; the drying heat treatment refers to vacuum drying at a temperature of 90°C to 200°C Heat treatment for 0.5h to 4h.