STUDY OF EARLY CYCLING DETERIORATION OF A NI MH BATTERY BY ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY/

a.c. impedance measurements are made on spiral-wound, size 4/5A, Ni/MH batteries, which are prepared by using direct-seal technology. Both t he positive and the negative electrodes are fabricated by filling in a porous nickel substrate with the active materials. The main purpose o f the investigation is to determine the cause(s) of the early cycling deterioration of this foam-type battery. The results demonstrate that the cycle-life curve can be divided into three parts. After little cha nge in capacity and voltage, deterioration of the Ni/MH battery occurs as the voltage performance decreases. This is followed by a sharp dec rease in both the discharge capacity and the voltage performance. The decrease in voltage performance is due to drying of the separator, whi ch increases the total ohmic resistance of the battery, while the decr ease of discharge capacity is due to an inactive surface that increase s the charge-transfer resistance of the battery. (C) 1998 Elsevier Sci ence S.A. All rights reserved.