Improvement in Power Density of Rechargeable Air Battery using Hydrogen Storage Alloy
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1216-W08-42
Improvement in Power Density of Rechargeable Air Battery using Hydrogen Storage Alloy Masatsugu Morimitsu1, Takahito Kondo2, Naoki Osada2, Koji Takano3 1
Department of Environmental Systems Science, Doshisha University,
2
Department of Science of Mathematical Modeling and Environment, Doshisha University,
1-3 Tatara-miyakodani, Kyo-tanabe, Kyoto 610-0394, Japan 3
Research Laboratory, Kyushu Electric Power, Co., Inc., 2-1-47 Shiobaru, Minami-ku, Fukuoka
815-8520, Japan
ABSTRACT A novel class of secondary battery comprising MH and air electrodes was developed for potential uses in high power density and high energy density applications such as electric or hybrid vehicles and power storage units supporting fuel cell and solar power systems. The air electrode consisted of nickel-based gas diffusion electrode using Ir2Bi2O7-z as oxygen evolution and reduction catalyst. Coin-type of cells using alkaline solutions as electrolyte were designed and fabricated, and the charge-discharge behaviors were evaluated with constant current operation. The discharge voltage and power density were improved by using a thin film membrane, in which the electrolyte was impregnated, between the air and MH electrodes, and the maximum power density was comparable to that of commercially available Ni-MH secondary battery. The MH utilization and the current efficiency of a charge-discharge cycle were found to be more than 90%. INTRODUCTION A zinc-air battery is well known as a commercially available metal-air battery, which is used for a power supply of hearing aid and has some attractive properties such as no limitation on capacity of the positive electrode and a high theoretical energy density, since the active mass of the positive electrode is oxygen in air. However, commercially available metal-air batteries are limited to be a primary zinc-air battery, and no rechargeable metal-air battery has been developed, except mechanically rechargeable zinc-air batteries, although many efforts have been done to realize a secondary metal-air battery [1-9]. One of the reasons is a difficulty to develop a bi-functional air electrode enabling oxygen reduction and evolution reversibly. For example, the air electrode of a zinc-air primary battery consists of catalyst/carbon mixed material, and carbon is consumed when the battery is recharged due to generation of carbon dioxide. On the other hand, we have developed a new bi-functional air electrode consisting of nickel, PTFE, and pyrochlore-type oxide, Bi2Ir2O7-Z, and have demonstrated that the air electrode has a good reversibility for oxygen reactions and a high durability for charge-discharge cycles up to 2000 cycles [10]. We have been also trying to develop a new class of secondary air battery with the bifunctional air electrode and focusing on hydrogen storage alloys as the negative material in combination with an alkaline electrolyte [11-12]. This secondary air battery is expressed as an
MH-air battery, which has a cell configuration analogue to Ni-MH battery where the nickel oxid
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