DAMAGE IN COMPOSITE NIMH POSITIVE ELECTRODES

Mechanical degradation in fibrous composite electrodes in use in NiMH (nickel metal hydride) batteries is being studied. NiMH cells exhibit failure in the positive plate due to swelling induced during the elect rochemical reaction, which leads to gradual breakdown of the connectiv ity of the substrate microstructure. Particularly, loss of electrical conductivity as related to losses in mechanical properties upon cell c ycling (constant current cycles with substantial overcharge) are being investigated experimentally. These properties are measured for the dr y substrate material before and after battery cycling, and the losses observed suggest key failure mechanisms including mechanical damage. R esults suggest tradeoffs between use of higher density nickel substrat es and improved energy densities using mechanical and resistivity proo f tests.