Development and Evaluation of an Asymmetric Capacitor with a Nickel/Carbon Foam Positive Electrode

Abstract

A lightweight, nickel hydroxide/carbon foam positive electrode has been demonstrated; its maximum cycle life is being optimized. A carbon negative was chosen, giving an asymmetric capacitor cell configuration. The binder content was varied (3, 5 and 10%/wt. PTFE) in the negative electrode (Ketjenblack). BET surface area and the effective resistance of the carbon electrodes have been measured to evaluate the affect of binder on the electrochemical properties. Electrochemical properties improved at 3%/wt PTFE; otherwise, the negative electrode has not been optimized for capacitance in this study. For asymmetric cells with 5%/wt PTFE, the optimum mass ratio (negative/positive) is 3.7. A life of 125,000 cycles with > 98 % coulombic efficiency and > 80 % capacity retention has been demonstrated at a 17 C rate (with a Swagelok type cell). Based on these encouraging results, it is believed that hermetically sealed cells will allow commercially competitive cell lives of 300,000 cycles, or more.