This means a sodium-ion battery carries less energy than a lithium-ion battery of the same size—a problem for cars, since that means shorter range. Currently, the energy density of its cube-shaped battery is 165 watt-hours per kilogram—around 80% of that of a lithium iron phosphate battery, the mainstream lithium battery in China. Chen is dubbed “the father of Chinese lithium batteries” for leading a team that developed the country’s first such cell three decades ago. CATL, the world’s largest battery maker, has said it will mass-produce sodium-ion batteries for electric cars by the end of this year. The company aims to launch a fast-charging sodium-ion battery that powers heavy trucks this month.