Fiber-Type Ni(OH) 2 Electrode for Nickel-Metal Hydride Battery: Super High-Rate Charge/Discharge and Long Cycle-Life Performances

Abstract

Fiber-type nickel-hydroxide electrodes were prepared by the electrodeposition of pure Ni(OH)2 on nickel-plated carbon fibers. Nickel-metal hydride (Ni-MH) test cells containing the fiber-type Ni(OH)2 electrodes exhibited good electrode performances, such as a 300 mAh/g large discharge capacity, 2000 long cycle-life and high-rate charge/discharge even at the 100 ∼ 500C rates. The high-rate discharge capability is suppressed by the CoOOH coating of the fiber-type electrode. Synchrotron XRD patterns showed that a large amount of the γ-NiOOH phase, which causes capacity decay of the conventional electrode, is formed during the charging process. The expansion ratio of the average cell volumes between the charged and discharged states was estimated to be approximately 8%. This low value would permit a good capacity retention for the fiber-type electrode.