Safety diaphragm for lithium ion battery and preparation method for safety diaphragm

Abstract

The invention discloses a safety diaphragm for a lithium ion battery and a preparation method for the safety diaphragm. The safety diaphragm is prepared from raw materials of inorganic fibers, cotton fibers, polyvinylidene fluoride, sodium carboxymethylcellulose, absolute ethyl alcohol, polyethylene microspheres, triethoxyvinyl silane, polyacrylamide and the like, wherein the inorganic fibers are fibers with positive temperature coefficient characteristics; and the safety diaphragm is prepared by the steps of preparation of a polyethylene microsphere intermediate layer, preparation of a reinforced coating layer, coating of the reinforced coating layer, high-temperature curing of the diaphragm, and the like. According to the safety diaphragm and the preparation method therefor, the fibers in the battery diaphragm are used as a reinforced body, so that the diaphragm is not sharply shrunk easily after the diaphragm suffers from high temperature; multiple kinds of materials with positive temperature coefficient characteristics are added, so that ionic migration in an electrolyte of the lithium ion battery can be blocked in a high-temperature condition; the preparation method for the lithium ion battery diaphragm is simple and reasonable in method; the prepared diaphragm adopts a layered structure; a polyethylene thin film layer prepared from the polyethylene microspheres has a supporting effect; and a fiber layer on the outer side has a reinforcing effect.

Description

technical field [0001] The invention relates to the technical field of manufacturing lithium ion batteries, in particular to a safety diaphragm for lithium ion batteries and a preparation method thereof. Background technique [0002] Compared with other types of batteries such as lead-acid and nickel-cadmium, lithium-ion batteries have the advantages of large specific capacity, high working voltage, fast charging speed, wide working temperature range, long cycle life, small size, light weight, green and pollution-free, etc. At present, it has been widely used in mobile phones, notebook computers, electric tools and other fields, and its application scope is becoming more and more extensive. The rapid development of new digital electronic products has put forward more and more demands on the energy density and high reliability of lithium-ion batteries. high demands. [0003] The diaphragm of a lithium-ion battery is an important component of a lithium-ion battery. The diaphr...

AI Technical Summary

Problems solved by technology

At present, commercialized lithium-ion battery separators are mostly porous polymer membranes made of polypropylene and polyethylene. Polymer materials have excellent porosity, and their tensile properties and strength are suitable for existing product processes. However, they are not enough The most important thing is that polymer materials will shrink to varying degrees at high temperatures. Taking traditional polypropylene and polyethylene materials as examples, when the temperature exceeds 100 degrees Celsius, obvious thermal shrinkage will occur, and the inside of the battery will It causes direct contact between positive and negative active materials, causing safety problems. At the same time, the polymer microporous membrane has poor liquid absorption performance and cannot maintain a sufficient amount of electrolyte during the entire life of the battery, resulting in poor battery cycle performance. In this case, High-temperature resistant membranes made of fibrous non-woven fabrics and other materials have also appeared. However, this type of separator has uneven pore formation, high battery self-discharge rate, poor puncture strength, low tensile strength, and pore deformation is easy to occur under high tension. , Poor processing performance also brings potential safety hazards. At the same time, because this type of separator still allows ions in the electrolyte to pass through when the lithium battery is overheated, and due to the increase in temperature, the ion migration rate continues to accelerate, resulting in the internal temperature of the lithium-ion battery. Continue to rise, causing a vicious circle inside the lithium-ion battery, and eventually even serious safety accidents such as explosions, endangering the personal safety of users or causing property damage