Effects of Microencapsulation of Hydrogen Storage Alloy on the Performances of Sealed Nickel/Metal Hydride Batteries

Abstract

Particles of hydrogen storage alloy was microencapsulated with porous thin film (about one micron thickness) of copper. The microencapsulated alloy powder was used as an anode material in a sealed nickel/metal hydride battery. The battery characteristics were compared with those of a battery with a bare (noncoated) alloy anode. The battery using the copper coated alloy had about a four times longer cycle life than the one using the bare alloy due to the role of copper as an oxygen barrier for protecting the alloy surface from oxidation. In addition, charge‐discharge characteristics were improved greatly by the copper coating, especially at high rates and at low temperatures due to the role of copper as a microcurrent collector for facilitating charge transfer reaction on the alloy surface. Thus, the microencapsulation of the alloy powder improves the performances of the alloy electrode. The 0.2C discharge voltage was 1.26V at 20°C. The coulombic efficiencies were; 94% at 0.2C rate and at 20°C, 90% at 0.5C rate and at 0°C. The discharge capacity decreased at the temperatures above 40°C at which the equilibrium pressure of hydrogen absorption exceeded an internal pressure of the battery. The charge retention was 65% after a storage for 30 days at 20°C.