Honda has independently developed a high-performance ultra-capacitor (electrical two-layered condenser) to serve as a supplementary power source to the FCX's main power source - the fuel cell stack - for more powerful performance under various driving conditions. The ultra-capacitor combines the electrical storage capacity needed for high output and high responsiveness with solid reliability. It stores energy produced during deceleration and braking and provides powerful drive assist during startup, acceleration and at other times when an extra boost is required. The ultra-capacitor's internal resistance is lower than that of a battery, and moreover, because it stores and discharges electricity in response to fluctuations in the fuel cell stack, it doesn't require a converter for voltage regulation as in a battery system, so it delivers higher output. The result is improved drive-power performance and higher system efficiency.
The ultra-capacitor retains the same high-performance activated-carbon electrode that was used previously, while the configuration of the electrode wrapped-element construction has been reexamined to increase the number of wraps per electrode without increasing size. This increase in electrode charge density delivers a significantly higher energy storage capacity, resulting in a 10% improvement in energy storage and output compared to the previous ultra-capacitor. Its charging and discharge functionality is among the best in the world.
(Based on Honda in-house testing)