A U.S.-based company says it has developed a new lithium-ion battery with an energy density of 400 watt-hours per kilogram — roughly twice the density of existing rechargeable batteries — an innovation the company claims could significantly increase the range of electric cars and ultimately cut the price of battery packs by 50 percent. Using a $4 million federal grant from the Advanced Research Projects Agency — Energy, scientists at Envia Systems were able to increase the battery’s energy density by including manganese in the materials of its cathode, the positive electrode to which the lithium ions are transferred. By blending carbon with silicon in the anode (the electrode from which the ions flow to create an electric current), they were able to bypass the tendency of silicon anodes to fail after a few cycles. While the denser, more-compact batteries developed at an Envia center in China could eventually cut the cost of electric vehicles, the company will first have to subject the technology to testing by automakers and independent analysts.

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