The highest theoretical energy density for a battery with lithium-ion chemistry is 406 W-hr/kgm. So it was a big deal when Envia Systems in Newark, Calif. devised a li-ion cell that hit 400 W-hr/kgm, a new record.
But don't get too excited yet. The record holder is a pouch cell that still needs to be commercialized. When it is ready for prime time, Envia expects the battery to slash the price of a 300-‐mile-range electric vehicle by more than halving the cost of the battery pack.
The cell's dimensions are approximately 97 mm wide, 190 mm long and 10 mm thick. The cell weighs about 365 grams. Battery tests took place at the Electrochemical Power Systems Dept. at the Naval Surface Warfare Center (NSWC) in Crane, Ind., and were sponsored by ARPA-‐E, the DoE's equivalent of Darpa. Tests at various cycling rates at NSWC showed an energy density between 378-‐418 W-hr/kgm for rates between C/3 (the rate of discharge that would leave the battery empty in three hours) to C/10 for a 45 A-hr (C/3) cell. Similar cells have been cycling in Envia’s test labs for over 300 cycles.
Cycling data is important because high-energy batteries tend to be hard on their anodes and cathodes. Eventually, anodes and cathodes get coated with oxides that reduce battery capacity, or they grow spikes that foul the the battery and diminish its life. These effects build up with each charge/discharge cycle. Thus anode and cathode design is an important part of ensuring a reasonable battery life. Envia's anode cathode structures are proprietary and the company is releasing few details about them.
NSWC Crane will also test these cells to validate cycling performance.
More info: http://enviasystems.com/announcement/