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Deep-dive endurance boost A pressure-tolerant lithium-sulphur (Li-S) battery pack has been developed that can improve the endurance and speed of ‘deep dive’ autonomous underwater vehicles (writes Nick Flaherty). The MAS (Marine Autonomous Systems) Consortium has demonstrated that Li-S cells can operate at depths of up to 6000 m, and is now building a battery pack for a deep-dive submarine to be tested in mid-2017. The battery uses a pressure-tolerant multi-chemistry battery management system (BMS) designed by Steatite Batteries. Li-S cells were tested at pressures and temperatures equivalent to undersea depths of 6000 m at the National Oceanography Centre in Southampton, UK, showing that the effective energy capacity, called the neutral buoyancy energy density, is nearly twice that of lithium-ion reference cells. Several cells have been used to carry out life tests, and have now reached more than 60 cycles for slow discharges and 80 cycles for faster discharges. “The project is progressing well, and successful completion of the cell development phase represents a major milestone,” said Paul Edwards, divisional director at Steatite Batteries. “We are now entering the battery development phase involving continued development of the BMS.” AUV power Lithium-sulphur batteries can provide twice the energy density of lithium-ion technology for AUVs at depths of up to 6000 m