This Monday, California-based Envia Systems made an announcement that could mean big things for the mainstream acceptance of electric vehicles. The company claims to have broken the world record for energy density in a rechargeable lithium-ion cell, with an automotive-grade battery that reportedly has a density of 400 watt-hours/kilogram (Wh/kg). Not only is that figure two to three times higher than what is currently possible with commercially-available cells, but Envia also claims that its battery should cost less than half the price of existing li-ion batteries.

Testing of the battery was performed by the Electrical Power Systems Department at the Naval Surface Warfare Center in Crane, Indiana. The tests were sponsored by ARPA-E (Advanced Research Projects Agency - ENERGY), a division of the U.S. Department of Energy.

According to Envia, the battery "demonstrated energy density between 378-418 Wh/kg for rates between C/3 to C/10 for a 45 Amp-hour (C/3) cell." Similar cells, which the company has had cycling in its lab for over 300 cycles, are also slated for further testing.

The secret to the battery's high energy density is said to lie in the company's proprietary cathode, anode, and electrolyte materials.

Close-up images of Envia's HCMR cathode (left) and its silicon-carbon nanocomposite anode

The chemistry of the High Capacity Manganese Rich (HCMR) cathode is a fine-tuned version of that of the "layered-layered" cathode, created at Argonne National Laboratory. It consists of nickel, cobalt, manganese and Li2MnO3 (lithium-manganese-oxide). Envia has introduced a patented nanocoating process to that mix, to enhance cycle life and safety. The HCMR is said to have twice the capacity of regular cathodes, and should be available for use in pilot vehicle projects later this year.

A low-cost silicon-carbon nanocomposite acts as the anode. The composition of the Envia-developed electrolyte isn't being revealed, although it is reportedly able to remain stable at higher voltages than currently-used materials.

General Motors, which recently invested US$7 million in Envia, will be performing further tests on the battery. It has also secured the rights to use the HCMR cathode in its electric vehicles.

Source: Envia Systems via IEEE Spectrum