Japanese Nonwoven Battery Applications.

Electric automobiles are a growing area for nonwovens.

Within the variety of uses for nonwovens, battery electrode separators represent a leading value-added application. Typical examples of batteries with nonwoven electrode separators are nickel-cadmium batteries and nickel-hydrogen batteries. These batteries are used in notebook personal computers and cell phones. However, it is in the field of car power batteries for use in electric automobiles where there is expected to be increasing demand for nonwoven electrode separators.

Electric automobiles are classified in two ways--as a pure electric vehicle (PEV) driven only with an electric motor and as a hybrid electric vehicle (HEV) driven with an electric motor and an engine. Both types feature a motor driven by electric power battery or batteries. Currently PEV-type cars are inferior in travel performance and are not suitable as typical passenger cars. In addition, electric automobiles have not been made price competitive with conventional cars, although they release only a small quantity of gas exhaust. Because of these restrictions, electric automobiles were not mass produced as passenger cars until 1997, when Toyota Motor, Tokyo, Japan, commercialized the first HEV-type passenger car with a price equivalent to conventional cars with gasoline engines. Two years later in 1999, Honda Motor, Tokyo, Japan, placed its own HEV-type passenger cars on the market. Both Toyota and Honda use a nickel-hydrogen battery made by Panasonic EV Energy to power their HEV cars. In Toyota's HEV-type cars, six nickel-hydrogen electric cells are connected in a series to form a battery module; each of its cars feature 40 modules, or 240 cells. In comparison, Honda's cars each carry 120 cells.

Each of the individual electric cells that form a nickel-hydrogen battery consist of a positive nickel electrode, a negative electrode made of a hydrogen-adsorbed metallic alloy and an alkaline electrolytic aqueous solution. In addition, an electrode separator (or separators) is inserted between the positive and negative electrodes. The electrode separators, which are made of polyolefin nonwovens, are soaked in the alkaline electrolytic solution and offer alkali- and oxidation-resisting properties. However, polyolefin nonwovens--which are not excellent in aqueous permeability--do not keep the electrolytic solution well. To overcome this problem, the polyolefin nonwoven electrode separators are subjected to an aqueous affinity improving treatment.

The nonwovens used in the electrode separators of both Toyota and Honda nickel-hydrogen batteries are produced by Japan Vilene, Tokyo, Japan. The electrode separator market is an advantageous field for Japan Vilene because although other nonwoven manufacturers aim toward this market, it is difficult to enter it at present. It is not easy to develop nonwovens suitable for electrode separators; the product requires various specific properties and certain knowledge is needed to produce them.

Car power batteries are much larger than those used in personal computers and cell phones, requiring larger nonwoven separators to be used per battery. At the same time, the batteries loaded in one electric car contain more than 100 units of electric cells. With the increasing production of electric automobiles, the consumption of electrode separators will increase accordingly.

Kin Ohmura is the president of the Osaka Chemical Marketing Center, which specializes in nonwovens, synthetic fibers and industrial textiles. His Far East Report appears every other month in NONWOVENS INDUSTRY.