Grafted polypropylene diaphragm and manufacturing method

Abstract

The diaphragm is non-woven fabric of polypropylene backing material with hydrophilic group. Raw fibers are hot melted composite fiber with dual constituents in low melting point and superfine ultra short vinylon fiber; or the said composite fiber, superfine ultra short vinylon fiber, and superfine glass microfiber. Being in 60-90% in raw fibers, the said composite fiber includes inner core of polypropylene, and cortical layer of polyethylene. Through graft polymerization, the said hydrophilic group combines to non-woven fabric of polypropylene backing material. The fabricating method includes steps: hydrophilic preprocessing for raw fibers; making mesh; heat forming; hot rolling; grafting modification. Features are: simple method, permanent hydrophilic capability for keeping moisture, antioxidation, alkali proof, high tensile strength, and small discharge rate. The disclosed diaphragm is adaptive to technical requirement of diaphragm in nickel hydrogen battery.

Description

technical field [0001] The invention relates to a grafted polypropylene diaphragm and a manufacturing method thereof, belonging to the technical field of battery diaphragms. Background technique [0002] Nickel-metal hydride (MH / Ni) battery is a new type of rechargeable battery developed in recent years. It has high specific energy and a capacity of 1.5 to 2 times that of nickel-cadmium batteries of the same volume. There is no pollution hazard to the environment and human body caused by heavy metals such as cadmium and mercury. It is called green power supply. At the end of the last century, the Ministry of Science and Technology promoted the industrialization of MH / Ni batteries and the localization of MH / Ni battery materials. So far, MH / Ni battery technology, production, and market have made great progress, and China has become the world's largest battery producer and exporter. The localization of MH / Ni battery materials has been implemented, but 95% of the battery separ...

AI Technical Summary

Problems solved by technology

However, there are still three disadvantages as follows: one, the basic material of separator paper still contains binder, and other common battery separator adhesive molding techniques are still used.

Since most of the binders are water-soluble, the existence of binders makes the battery separator have a high loss rate of alkali resistance, poor oxidation resistance, and poor air permeability. After the battery is made of this separator, the charge-discharge cycle life is short, High charge and discharge resistance

In addition, after the separator absorbs the strong alkaline electrolyte, when the rechargeable battery is repeatedly charged and discharged, the temperature inside the battery is repeatedly raised and lowered, and the temperature and oxidation resistance of the binder in the separator decreases, resulting in a decrease in the ability of the separator to absorb and maintain the electrolyte. The result is that other materials in the battery can continue to be used, but the diaphragm terminates its service life ahead of time, which shortens the charge-discharge cycle life of the MH / Ni battery; Layer or three layers of hot-melt composite, poor uniformity of the diaphragm, poor oxidation resistance, therefore, can not reach the level of similar foreign products; second, in the method of manufacturing diaphragm paper, the polyolefin fiber is first grafted and modified, and then wet-laid

Although it can be wet-laid, it cannot be hot-melt bonded

Because after grafting modification, the surface of the fiber has been grafted with hydrophilic groups, and the molecular structure of the surface layer has changed. After encountering high temperature, the surface layer polyethylene cannot form a vitrified semi-fluid state, so it is impossible to produce adhesion with other fibers. node, it is impossible to realize two-layer or three-layer hot-melt compounding of non-woven substrates, so the obtained separator paper cannot reach the thickness, strength, air permeability, liquid absorption rate, and microporosity required by the battery separator; third, use γ Rays or ultraviolet rays, electron beams, so that hydrophilic monomers can be grafted and copolymerized on polyolefin fibers

The equipment used in this method has high investment and complex technical conditions, and it will also affect the environment and personnel safety.

Images