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.