In September, U.K.-based polymer lithium-sulfur battery developer OXIS Energy closed a $24 million funding round from South African investor Sasol New Energy, followed in November by a contract from the British Ministry of Defence. The developments at OXIS highlight a year of encouraging activity for lithium-sulfur battery (LSB) technology.
OXIS Energy was founded in 2004 in Oxford, U.K. The company states it has been granted 27 patents, with 32 additional pending. The CEO is Huw W. Hampson-Jones. There are significant Russian technical roots via CTO Vladimir Kolosnitsyn.
The lithium-sulfur battery theoretically has up to five times the storage density of lithium-ion (in practice maybe triple), along with good safety and deep-discharge behavior. However, persistent problems, especially with cycle life, have been a challenge to commercialization. Critical reactants are permanently lost due to solubility reactions, when they pass through a polysulfide stage during cycling. Early cells had a cycle life in the single digits, although recent versions have done much better (vehicle applications require several thousand cycles).
A year of lithium-sulfur activity
• In October 2011, the U.S. Department of Energy awarded $5 million to a consortium headed by Penn State and Johnson Controls, for LSB research.
• In January 2012, long-term (17-year) lithium-sulfur stalwart Sion Power announced a $50 million equity investment from BASF.
• In March 2012, Stanford Linear Accelerator Center (SLAC) researcher Dr. Johanna Nelson published a breakthrough study on polysulfide loss. A powerful x-ray system was able to image the battery during cycling, radically modifying previous hypotheses. (For a readable account, see here.) The study bears, among other names, that of Dr. Yi Cui, a respected battery theorist.
• Also in March 2012, a LMU Munich/University of Waterloo team published results of an LSB study using a mesoporous carbon cathode. Performance was dramatically enhanced on several parameters, leading to a nominal 1200 watt-hours per kilogram, as well as further improvement in problem areas.
• In September 2012 at the Cascadia Beyond Oil conference in Seattle, recently retired General Motors Vice Chairman Bob Lutz predicted that electric vehicles will be switching to lithium-sulfur batteries within five years. He has been stating for some time that lithium-sulfur or possibly metal-air chemistry is what will bring electric vehicles to the mainstream.
• In November 2012, the second largest of 66 grants (and the largest in energy storage) awarded in the Advanced Research Projects Agency-Energy (Arpa-E) “Open 2012” grant round was $4.5 million for a water-based LSB. The grant was awarded to PolyPlus in partnership with Johnson Controls. PolyPlus had until recently been receiving more attention for its lithium-air work than for its lithium-sulfur research.
Caution is warranted in assessing new battery developments -- the devil is in the details. For example, the LSB does not yet approach as high-rate a discharge as has been achieved with lithium-ion and nickel-metal hydride, so vehicles may need a supplementary surge buffer, perhaps an ultracapacitor. Furthermore, in recent years, old-line battery manufacturers such as Johnson Controls have tended to fare better than startups (witness the recent bankruptcies of Ener1 and A123 Systems).
However, the prize here is serious. Imagine a Chevy Volt with a 150-pound battery pack (instead of almost 400 pounds), or a Nissan Leaf with a 200-mile electric range (instead of about 75). With apologies to Envia and others, there is unlikely to be nearly as much headroom for improvement in the lithium-ion battery at this point.