OSAKA, Japan — The first lithium polymer batteries — lithium-ion variants that could enable a generation of slimmer cellular phones — went into production this week at Matsushita, and at least three other Japanese companies say they expect to have similar products out this year.

The new battery type, which uses the same anode and cathode materials as lithium ion but employs a gel electrolyte rather than a liquid, promise batteries that are not only thinner but also easier to manufacture. But lithium polymer offers no power enhancements over lithium ion, and at least one company is asking whether the new chemistry will offer a sufficient advancement in battery profile to justify the cost of development.

Matsushita Battery Industrial Co. Ltd., a subsidiary of Matsushita Electric Industrial Co. Ltd., started volume production of thin lithium polymer batteries on Jan. 20, according to a spokesman for the manufacturer. "Several companies in Japan and overseas are watching for the timing of commercialization," the spokesman said. "We expect that the market will grow to 15 million units this year, of which we want to claim about a 50 percent stake."

The company has put the batteries on a bullish curve. Initial production of 300,000 cells per month is expected to ramp to 600,000 units/month in the summer and to 1 million units/month in the fall.

Hitachi Maxell, meanwhile, says it will begin supplying a polymer battery to a PDA vendor in the spring. Sony Corp., a leading lithium-ion battery supplier, also plans to begin production this year. And second-tier supplier Yuasa Corp. (Osaka) says it has prepared a pilot line for lithium polymer and is negotiating with customers.

But Sanyo Electric, another force in lithium-ion technology, has adopted a wait-and-see attitude. The company already offers 5-mm-thick lithium ion batteries and has said that a distinct differentiation between the current and emerging chemistries is essential if polymer batteries are to find a market.

Masashi Kubota, senior analyst of consumer electronics at ING Baring Securities (Japan) Ltd., foresees strong demand for polymer batteries in cell-phone applications because the new technology will allow further size reductions.

Sony and Sanyo, Kubota added, have claimed market leadership in lithium ion, "so Matsushita is trying to roll back with the polymer battery — the so-called next-generation battery."

Arranged as a stack, the Matsushita lithium polymer battery incorporates a cobalt oxide lithium film cathode, a carbon film anode and a polymer between the electrodes. The polymer functions as an electrolytic solution and a separator. The gel electrolyte enables the use of a soft outer case.

Stacks can vary in thickness from 0.5 mm to 0.7 mm and can be layered to achieve varying overall thickness and capacity. Large sheets will be possible in the future, the Matsushita spokesman said.

The company's first product has five stacks, for a total stack thickness of 3.6 mm and a capacity of 500 mAh (charged at 4.2 V). The capacity is smaller than the 600 mAh typical of cellular-phone batteries, but "cellular phones are designed to be lower in power consumption, and we expect that the 500 mAh will provide almost the same [number of] operation hours," the spokesman said.

The complete box-shaped battery is 35 x 62 mm and weighs about 15 grams. It will be supplied to an undisclosed cellular-phone vendor starting next month.

The Matsushita battery's major specifications are identical to those of lithium-ion batteries. Volumetric energy density is 250 Wh/l, gravimetric energy density is 120 Wh/kg, and voltage is 3.7 V. The battery is good for about 500 charge and discharge cycles, according to the company.

Matsushita Battery has already provided samples to more than 10 customers. Broad sampling is slated for April.