Sion Power has developed a lithium sulfur battery with and energy density of 350Wh/kg, and they claim that a density of 600Wh/hg will be achievable relatively soon. They do not specifically cite a cycle life for this battery but if I attempt to interpret the cycle life information given in this presentation I conclude that Sion Power’s Current lithium sulfur battery has a cycle life at full depth of discharge considerably less than 1000 cycles. Cycle life is currently the Achilles heel of lithium sulfur batteries. Unwanted side reaction of the lithium sulfide formed in the sulfur cathode as well as mechanical damage due the the growing and shrinking of the sulfur cathode conspire to limit the cycle life of this battery technology. Like Oxis Energy Sion Power’s applications page does not mention the obvious market of consumer electronics, making be suspect that the cost of the batteries is fairly high compare to lithium ion batteries. The high theoretical energy density of lithium sulfur batteries makes them an attractive alternative to lithium ion batteries, but I do not think that this technology is ready for prime time.
Lithium sulfur batteries have a much higher theoretical maximum energy density than lithium ion batteries (3 to 5 time according to this article). To date, however, practical implementation of this battery chemistry have have achieve only a fraction of the theoretical maximum energy density and have relatively short cycle life because of undesirable side reaction of the lithium sulfide formed in the sulfur cathode and because of physical degradation of the cathode due to swelling and shrinking during the charge/discharge cycle. Lots of fundamental research is being done trying to overcome both of these problems, but commercialization still seems to be in the indefinite future.
It is not clear whether Oxis’ technology represent to leading edge of commercialization for this technology or not. Cost is a key in addition to performance. On their applications web page Oxis mentions electric vehicles, grid energy storage for renewable, and mobile power for military applications. The fact that they do not mention consumer electronics makes me suspect that their technology is probably expensive. Why would they neglect this large existing, performance hungry market if they had costs competitive with lithium ion batteries? I think that I will not hold my breath waiting for Oxis’ batteries to revolutionize energy storage markets.