Lithium-sulfur battery developer Oxis said in October that it had successfully tested its development cell technology to 400Wh/kg of energy density. The UK firm said it had been reached after increasing gravimetric energy density by creating new Li-S formulations including battery materials such as conductive carbon materials, polymer binders and electrolyte additives.

David Ainsworth, chief technical officer at Oxis, told Battery & Energy Storage Bulletin, “400Wh/kg is significant — the best lithium batteries around at the moment are around 250Wh per kilo. This is a milestone that we have reached in the past couple of months.

“The next stage is trying to scale up that technology so we can produce tens of hundreds of cell units and work on other aspects, such as cycle life.”

Although Oxis’ batteries don’t have a cycle life suitable for the heavier durations required of electric vehicles — though cells are being deployed for testing in vehicle demonstrations — Ainsworth said that by comparison, a Nissan Leaf battery would contain around 140 Wh/kg and a Tesla around the 200 mark. In theory a Li-S battery could potentially offer two to three times the driving range.

Oxis says it is targeting high-technology areas such as aerospace applications and satellites, which have a strong requirement for high energy density and do not need a large number of cycles.

“There’s bags of potential for this technology and although it might be a few years before it’s in the mainstream, before it’s in an electric vehicle like the Leaf, it will certainly grow in high technology, the unmanned aerial vehicles, the very high-value applications,” said Ainsworth.

The firm says that cost comparisons can only give a picture of what may eventually be the pricing, given that the firm is a start-up. “That said, if we were to make 10 million cell units, which is a typical lithium-ion production run, Li-S would be incredibly cheap. The cost of sulfur, for instance, is negligible — a few dollars per kilo — unlike the NMC cathodes and so on that are being used in lithium-ion.”

Lithium sulfur technology had been around since the late 1960s, but there had been “a lot of technological challenges in trying to get the technology to market”, including improving cycle life and increasing the capacity in the cathodes, two areas Oxis scientists are focusing on.