LITHIUM-SULFUR BATTERY TECHNOLOGY READIED FOR MARINE MARKET

OXIS Energy will provide the cells and Williams Advanced Engineering will integrate the 400kWh system into a boat designed by Singapore-based Yachts de Luxe. The 40-foot electric vessel will be the first luxury boat in the world to be powered by lithium-sulfur cells and associated custom management systems.

The aim is to achieve a range between 70 and 100 nautical miles at cruising speed – setting new standards for range in electric boats.

“Lithium-sulfur is approximately half the weight of lithium-ion technology, and this translates directly to the battery weight,” says Dr Mark Crittenden, Head of Battery Development and Integration at OXIS Energy, so the vessel’s improved range will be achieved as a larger capacity battery can be built for a given weight.

A gravimetric density of 500Wh/kg has been achieved, and with a theoretical limit of 2,700Wh/kg, it is an on-going area of research for OXIS Energy. The chemistry of the cells also differs from lithium-ion technology, as it allows full discharge to 1.9V per cell.

Crittenden says: “Safety comes in two main areas. The first is through the choice of lithium-sulfur which has strong and proven safety characteristics. The second is through the design of the battery, including choice of a high-quality battery management system to control and monitor the cells and through an appropriate redundant architecture, whereby if part of the battery fails, the remaining part of the battery will continue to operate.”

Unlike many other developers, OXIS has developed all three cell components, the cathode, anode and the electrolyte. The cells have successfully passed a series of tests including short circuit, over-charging and nail and bullet penetration.

The cells contain no toxic or rare earth materials, and at the end of life, the materials used can be disposed of without damaging the environment.

The performance of the battery system will be maximised via algorithms within the management system including a state-of-charge algorithm which estimates the remaining energy in the battery, providing the user with accurate information.

Crittenden notes there are two advantages that boost the cost-effectiveness of the technology. “The first is that one of the key components, sulfur, is amongst the most abundant elements on Earth, so it is inexpensive at less than $20 per tonne. This compares to cobalt prices at around $40,000 per tonne.

“The second is that lithium-sulfur cells have a very high gravimetric energy density, and with more energy stored per kilogram of material, costs per energy stored reduces. Thus, at a similar production scale, lithium-sulfur is a cost-effective solution.”

The two companies have a history of collaboration including the UK-funded Lithium Sulfur Future Automotive Battery (LiS:FAB) project and the ALISE program, a European collaboration focused on the development and commercial scale-up of the new materials and electrochemical processes used in lithium sulfur technology.

OXIS has developed an ultra-low-temperature battery which can operate at -60oC. This was made possible by the development of a low temperature electrolyte system. The company has also developed a pressure-tolerant battery pack which can operate at depths of 6,600 meters at 4oC.

Crittenden says lithium-sulphur technology should be considered for all applications where having a lighter battery is an advantage.