TOKYO Demand for miniaturized components among portable-phone makers has moved the front lines of competition in the rechargeable battery market to cells under 4 mm thick. To get there, vendors are marshaling novel lithium-ion structures, most based on a polymer gel electrolyte.
The latest vendors to join the charge to the small Li-ion batteries are Sanyo Electric and Toshiba the latter via a nonpolymer technology and a joint venture with Asahi Glass Corp. Sony and Matsushita spearheaded the drive in January with separate introductions that tapped polymer electrolyte technology.
Sanyo Electric Co. Ltd.'s entry, set to debut next month, is a 3.8-mm-thick card-shaped product that takes the polymer route. Toshiba Battery Co. Ltd., meanwhile, has tweaked conventional Li-ion technology to yield a battery measuring 3.6 mm thick, previously the exclusive domain of polymer electrolyte-based offerings. Joint venture A&T Battery intends to ramp production of the cells to 1 million per month early next year.
Battery capacity typically decreases proportionally with thickness, whereas phone manufacturers are calling for continual increases in capacity. Sanyo claims to have cleared the technical hurdle by devising a gel material that dissolves the electrolyte uniformly, thus reducing the required volume of polymer and maximizing performance.
Sanyo's battery uses the same electrode combination lithium oxide cobalt and carbon as conventional lithium-ion batteries. Full capacity is 570 mA-hr at 20C; about 50 percent of full capacity is retained at --20C, marking an improvement in polymer batteries' traditionally marginal low-temperature performance, according to Satoru Fukunaga, Sanyo Energy's battery division manager.
The battery measures 3.6 x 35 x 62 mm. The discharge voltage is 3.7 V, volumetric energy density is 270 Wh/liter and gravimetric energy density is 156 Wh/kg.
The Toshiba approach sticks with a liquid electrolyte but, like the polymer approaches, employs a laminate film in place of the metal exterior packages used for conventional lithium-ion batteries. The cell's electrodes are lithium oxide cobalt and carbon. A spokesman said Toshiba managed to get the battery thickness under 4 mm, and to ensure high reliability and safety, by optimizing the electrode materials and improving the electrolyte liquid. He said the battery's low-temperature performance 40 percent of full capacity at --20C exceeds that of conventional lithium-ion batteries, which he said can drop to 24 percent of full capacity at --20C.
The battery measures 3.6 x 35 x 62 mm and weighs in at 13 grams. Capacity is rated at 540 mA-hr with a discharge voltage of 3.8 V. Volumetric energy density is 290 Wh/liter; gravimetric energy density is 160 Wh/kg.
The card-size batteries introduced by Matsushita and Sony in January respectively measure 3.6 and 3.8 mm thick. The other dimensions are the standard card-sized 35 x 62 mm. Matsushita expects to achieve monthly production of 1 million units this fall and Sony next spring.