Effect of Rare-Earth Elements on the Temperature Performances of Power Nickel-Metal Hydride Batteries for Electric Tools

Combined with the preparation of sub-C size power nickel metal-hydride (Ni-MH) batteries for electric tools, the influence of rare-earth elements on the charge-discharge performances of Ni-MH batteries at the high-rate and temperature extremes (65 and ) was especially investigated. With a mixture of 3% additives adding to the active slurry of positive electrode, a increase of oxygen-generated overvoltage was formed at the end of the charging process and the charge efficiency of batteries was improved from 34 to 69% at . In addition, it was shown that the particle size, composition, and microstructure of hydrogen storage alloy powders in the negative electrode are closely related with the discharge performances of battery at high rate and low temperature. A mixture of three -type hydrogen-storage alloy powders with different particle size and composition of La, Ce, and Co was used as the active materials in the negative electrodes. The discharge capacity and voltage of prototype sub-C Ni-MH batteries thus prepared approached and at and , and their cycle lifetimes at the alternative discharging mode and were over 280 and , respectively. Sub-C Ni-MH batteries prepared in the state-of-the-art meet the requirements of electric tools.