Kenichi Takeuchi

Solid polymer electrolytes for lithium cells

Abstract This paper reports on ionic conductivity, mechanical characteristics, thermal stability, and electrochemical stability of solid polymer electrolytes (SPEs) that use a cross-linked poly(ethylene oxide) and a cross-linked ethylene oxide copolymer both containing a plasticizer. We obtained the SPEs that have a high ionic conductivity of 2.4 × 10 −3 S cm −1 at 20 °C, a mechanical strength that creates no problems in practical use, and higher thermal stability than liquid electrolytes. Batteries using these SPEs were manufactured and submitted to various tests. The results showed that the low-temperature and rate characteristics of these batteries were comparable with those of liquid electrolyte batteries. The results of loading, bending and twisting tests indicated that no internal shorting of the batteries occurred. These batteries did not swell at high temperatures at which liquid electrolyte batteries usually do.

The 200 V 2 kWh energy storage multicell system with 25 Wh Li/LiV3O8 single cells

Abstract A 200 V 2 kWh Li/LiV 3 O 8 multicell system was constructed by seventy-seven 25 Wh single component cells in series connection and was operated under connection with a commercial power line. The discharge power of 1.94 kWh and the energy efficiency of over 93% were demonstrated almost as designed. The rate capability of this multicell system was poor compared with that of a single cell. The internal resistance of the system resulted in the iR loss, and the safely set operating voltage limits for the system reduced the output energy of individual cells. The non-uniformity of the operating voltage and of the state-of-charge for all component cells were also analyzed in addition to the local temperature rise in the stack.

Application of solid-polymer electrolyte in lithium batteries: ultra-thin film battery

Abstract 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 σ = 2 × 10 −3 S cm −1 at 25 °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 MnO 2 , 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.