Functionalized lithium supplementing diaphragm and preparation method thereof

Abstract

The invention provides a functionalized lithium supplementing diaphragm and a preparation method, the functionalized lithium supplementing diaphragm is composed of a lithium supplementing layer and abase film layer, and the lithium supplementing layer comprises a lithium-containing compound, a polymer substrate and a flexibilizer; the base film layer comprises a polymer base material; and the lithium supplementing layer and the base film layer are prepared through melting double-layer co-extrusion. The functionalized lithium supplementing diaphragm replaces a traditional lithium ion battery diaphragm, lithium ions can be supplemented for the first circle after the battery is assembled, the performance of the battery is improved, and the performance of the battery cannot be damaged after the charging of the first circle. The inventor unexpectedly finds that the lithium supplementing agent and the polymer base material are matched according to a proper ratio, and a proper thickness is extruded in a double-layer co-extrusion manner, so that the formed three-dimensional porous composite structure can realize good lithium supplementing, and can prevent the lithium supplementing agent from falling into an electrolyte to cause reduction of the lithium supplementing efficiency.

Description

technical field [0001] The invention relates to the technical field of lithium-ion batteries, in particular to a functionalized lithium-replenishing diaphragm and a preparation method. Background technique [0002] Lithium-ion batteries have become ideal power sources for portable electronic devices such as mobile phones and notebook computers due to their outstanding advantages such as high working voltage, high specific energy, large capacity, long service life, light weight, and small size. The research on electric vehicles and hybrid electric vehicles as power sources has become one of the hotspots in the research and development of developed countries. At present, the most used lithium battery is a negative electrode lithium ion battery based on carbon materials. Although it has the above-mentioned many advantages, there are nearly 5-20% of lithium ions deintercalated from the positive electrode (if it is a new type of negative electrode such as silicon carbon, This ra...

AI Technical Summary

Problems solved by technology

Lithium supplementation of negative electrode mainly uses lithium foil or lithium powder to directly lithiate graphite negative electrode, but lithium foil, especially lithium powder, has serious safety hazards because of its smaller particle size and higher activity. There are many improvements to this method of lithium supplementation Technical reports, such as patent CN105702943A discloses a lithium ion battery negative electrode material lithium replenishment method, through the external lithium sheet, the battery test system is used to form the lithium replenishment device to achieve negative electrode lithium replenishment; patent CN104577086A discloses a pre-lithiation method, Dissolve metallic lithium in a non-aqueous solvent, prepare a graphene-coated mesoporous SiO negative electrode in this dispersion, and sinter to obtain a lithium-replenishing negative electrode; although it is safer than directly using lithium foil or lithium powder to replenish lithium However, on the whole, the improved lithium supplementation technology has high requirements on the operating environment, and the battery is assembled after lithiation of the negative electrode, which is more cumbersome.

Positive electrode lithium supplementation is mainly to directly add a lithium supplementary sacrificial agent to the positive electrode material, and irreversibly remove lithium ions during the first cycle of charging, thereby providing lithium ions consumed by the first cycle of negative electrodes. The method of replenishing lithium on the positive electrode sheet is to spray or drop an organic lithium solution on the surface of the positive electrode sheet in an inert atmosphere, so that the lithium ions in the organic lithium solution are reduced to metallic lithium and embedded in the positive electrode sheet to realize lithium replenishment. High requirements and toxic organic reagents have potential safety risks for operators and are not convenient for large-scale industrial production; patent CN110120493A provides a method of slurrying and smearing lithium-supplementing materials together with positive electrode materials, conductive agents, and binders Positive electrode lithium replenishment method, although this method avoids the safety problem of dry lithium replenishment, but the lithium replenishment sacrificial agent will have a certain impact on the mass transfer inside the entire electrode after the decomposition of the positive electrode side; patent CN109755448A will include Li 5 FeO 4 Lithium-supplementing coatings such as lithium-containing compounds, nano-inert inorganic fillers, and binders are coated on the separator substrate to prepare a lithium battery separator with lithium-supplementing coatings, which can reduce the thermal shrinkage of the diaphragm while supplementing lithium, but This technology is processed on a commercial diaphragm substrate. The entire diaphragm preparation process is cumbersome, and the reagents used are more, the cost is high, and there are many defects that are not conducive to commercialization and industrial production: 1. The thickness of the commercial diaphragm itself It is to match the battery, which is generally about 20 μm. If the coating is coated with a lithium-supplementing agent, to achieve effective lithium supplementation, the thickness of the coating should be more than 10 μm, and the overall thickness of the lithium-supplementing separator will be higher than 30 μm, which will make it difficult to assemble. Battery; Second, since the lithium-containing coating is coated on the separator substrate through a lithium-containing slurry and dried at 40-75°C, the separator will be blocked after drying, resulting in a decrease in lithium ion mobility, resulting in electrochemical performance Three, the obtained lithium battery diaphragm, because the lithium replenishing agent is coated on the substrate, the adhesion is insufficient, causing the diaphragm to fall off during the folding and curling process when the battery is assembled, and the efficiency of lithium replenishment is reduced; four, In this method, the lithium-containing slurry must contain binders, conductive agents, etc., which is equivalent to introducing impurities, which will reduce the energy density of the battery and also adversely affect the electrochemical performance.

Images