Lithium-sulfur batteries

Hayley Everett

How can lithium-sulfur batteries open up new performance gains for the electric vehicles of the future?

The surge towards electrification of transport means there is an increasing need for a range of battery technologies and options for development. While still playing an important role, lithium-ion batteries have begun to reach their limit in terms of performance improvements. Lithium-sulfur, meanwhile, is one of the alternatives with the greatest potential benefits that is also close to being commercially available.

Dr Jennifer Hack and Dr James Robinson of University College London’s (UCL) Electrochemical Innovation Lab are the lead researchers on the LiSTAR research project, which aims to develop new battery cell concepts and technologies. Alongside Daniel Auger, Reader in Electrification, Automation and Control at Cranfield University’s Advanced Vehicle Engineering Centre, the researchers explain the objectives of the project and its progress to date…

The potential of lithium-sulphur

Research into lithium-sulfur batteries is part of a major £29 million UK research programme into energy storage funded by the Faraday Institution. The LiSTAR research project, the Lithium-Sulfur Technology Accelerator — led by UCL (and a team headed by the UK’s battery technology visionary Professor Paul Shearing) and also involving the universities of Birmingham, Cambridge, Coventry, Cranfield, Imperial College London, Nottingham, Oxford, Southampton, and Surrey — aims to maximise the commercial potential of the lithium-sulfur technology, bridging the gap between research and industry — and putting the UK at the forefront of new battery technologies

Lithium-sulfur batteries have a number of potential advantages over existing lithium-ion battery technology. The availability of lithium-sulfur batteries will mean a lighter option for vehicles: important for electrification of short-haul aircraft (where fuel load is everything) and light goods vehicles (allowing them to have more capacity and not tip over into the 7.5 tonne category).

Today’s typical lithium-ion batteries produce around 250 watt hours per kg of mass, compared with what is expected to be 400-600 watt hours per kilogram from lithium-sulfur. At this stage, researchers believe lithium-sulfur may also become a cheaper technology for industry and consumers.

UCL’s work is partly focused on developing new battery cell concepts: a ‘quasi solid state’ cell focusing on employing a different operating mechanism for the chemistry using electrolytes with low sulfur solubility, extending the operating life of the battery. Other development areas across the consortium include developing non-flammable electrolytes to improve safety, the removal of lithium nitrate to expand the operating temperature window, and ways of improving power and energy densities by developing new electrodes and employing advanced diagnostic tools for cells.

The Cranfield team is developing a sophisticated battery management system: providing accurate information on charge levels, and insights into how operation of the vehicle impacts on battery life. The work will also involve running simulations to model the behaviour of the battery in particular vehicle types.

Battery management matters because understanding what is happening inside a lithium-sulfur battery is harder than with lithium-ion. There is just the one stage of electrochemical processes in lithium-ion, but four in lithium-sulfur. The charge is also very ‘flat’, meaning there are regions of the battery where it is very difficult to ‘see’ the charge.

The LiSTAR project expects to deliver workable lithium-sulfur batteries for niche industry use within two years, creating an initial platform for widespread take-up across transport manufacturers.

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