In general, vehicles commonly use, as their fuel, petroleum (e.g. gasoline, light oil) and gases (e.g. LPG, LNG), the deposits of which are limited, the prices of which are on the rise, and which cause environmental contamination. Therefore, there has been an increasing demand for alternative fuels.
Electric batteries have recently been commercialized to a considerable extent as alternative vehicle fuels, but they need to be charged for a long period of time, which degrades efficiency and makes their widespread use difficult.
USPTO Backgrounds
USPTO Backgrounds