With the recent rapid progress in the electronics industry, the trend towards making electronic equipment more compact and lightweight has been accelerating. In addition to the need for batteries for use in such electronic equipment to be more lightweight and more compact, emphasises the need for a battery to be able to meet any shape requirement. We developed a solid-polymer electrolyte that has a high ionic conductivity of sigma=2x10(-3) S cm-1 at 25-degrees-C, and using this electrolyte, we then developed an ultra-thin film primary battery of the size of a credit card and with a thickness of 0.1 mm. This battery is composed of MnO2, a solid-polymer electrolyte and lithium, and has a volumetric energy density of 400 W h/l. In addition to this primary battery, we are currently developing an ultra-thin film secondary battery. An ultra-thin film battery, which employs our solid-polymer electrolyte, is advantageous in reducing risks such as the high reactivity of metallic lithium, heat accumulation inside the battery and internal shorting due to growth of deposited lithium.
