French and Swiss team find that adding quartz to sulphur electrolyte can stabilise capacity loss
Researchers have developed a novel method that could aid development of a commercial lithium-sulphur (Li-S) battery.
While Li-S chemistry is a promising replacement for li-ion – it is has a greater energy density and could be made at a lower cost – in general, cells built so far tend to function only for a few charging cycles before losing capacity. But a team of materials scientists from the Paul Scherrer Institute (PSI) in Switzerland and the Université Grenoble Alpes in France have studied why this loss occurs, and have found that the addition of quartz powder to the liquid electrolyte goes some way towards mitigating this loss.
The researchers reported their results in the latest edition of the scientific journal Nature Energy.
PSI used X-rays to track the chemical reactions that take place within the battery enabling them to study changes in lithium-sulphur compounds and how this affects capacity loss.
They also recorded how quartz powder – the principal constituent of sand and the main ingredient of glass –increases the available energy and curbs the capacity loss that sets in over time. They quantified those improvements, recording that Li-S battery performance is improved by 25-30%.
This occurs because of the interaction between quartz and lithium polysulphides inside the electrolyte. These soluble Li-S molecules form during the operation of the battery and travel back and forth between the two electrodes with every charging and discharging cycle. Some react with the lithium anode of the battery and accumulate on the surface, reducing the amount of available sulphur and diminishing the battery’s capacity. Over several cycles this will severely reduce performance.
Quartz powder binds these polysulphides and helps to preserve available battery capacity, and increases the efficiency of the discharging process (Coulombic efficiency) from around 80% to 90% – although still a far cry from the 99.9% efficiency of li-ion.
While there are other methods of polysulphide control, they can be complex and expensive. By contrast, quartz is readily available, very cheap, and does not require a complicated process to be mixed into the electrolyte.
Li-S is still some way from large-scale commercialisation, and perhaps even further from widespread use in EVs. However, small breakthroughs such as these could help the technology gain ground as chemists and materials researchers look beyond the horizons of Li-ion.