Battery separators are used to maintain the electrolytic solution by being inserted between positive electrode and negative electrodes, in order to prevent the polar regions from making contact. Thin microporous bodies, such as nonwovens, papers or microporous films are used for the separator. These separators are used property by certain types of batteries, mainly nickel metal hydride batteries, nickel-cadmium batteries and lithium primary cells. Among these batteries, the one with the greatest demand for separators is nickel-metal hydrogen batteries.

Although nickel metal hydride batteries have been widely used as a power source for the portable device, it has been replaced by high performance lithium batteries and the amount of production of small, Ni-MH for the portable device has sharply decreased.

While demand for large Ni-MH has been expanded because it was adopted by the power source of hybrid cars, they are mainly used in all types of automobiles now. The output of the Ni-MH in Japan—in terms of the number of cells—has been decreasing with 1.026 million pieces at the peak in 2000. It has been changing in the 300 billion level after 2003 although it increased to 420 million pieces in 2016.

Demand Prospects
Nonwovens used in Ni-MH separators are made using the techniques for water jets and thermal bonded nonwovens after the web is made using a paper making method. The technical materials include a polyolefin like polyethylene or polypropylene. Although the nonwovens manufacturers that make these products are Japan Vilene, Daiwabo Polytec, Nippon Kodosh and Mitsubishi Paper Mills, Japan Vilene dominates the market currently.

Although the quanity demand of separator material in Japan is estimated at 16 million square meters, future demand is not expected to grow significantly. Auto manufacturers are changing the power source of the hybrid auto from Ni-MH to LiB. Main hybrid cars that currently use Ni-MH batteries are Toyota Aqua and Prius. However, in the past year, some of these vehicles are now using LiB and this percentage is increasing with every model upgrade. This will lessen demand for Ni-MH batteries.

Under these circumstances, the nonwovens separator could not expect to grow with Ni-MH, so, the use of LiB batteries is increasing. However, these battery types use microporous films, mainly. This, of course, may change and already some LiB batteries are using nonwoven separators. If this conversion continues, the growth of nonwovens will also occur.

By Kin Ohmura