Lithium sulphur battery designs offer a theoretical energy density roughly five times that of lithium ion batteries, and the researchers used a porous, sponge-like aerogel of reduced graphene oxide as a free-standing electrode in the battery cell to get higher utilisation of the sulphur.
The best lithium ion batteries currently on the market operate at about 300 watt-hours per kg, with a theoretical maximum of around 350. Lithium sulphur batteries meanwhile, have a theoretical energy density of around 1000 to 1500 watt-hours per kg. “Sulphur is cheap, highly abundant, and much more environmentally friendly. Lithium sulphur batteries also have the advantage of not needing to contain any environmentally harmful fluorine, as is commonly found in lithium ion batteries,” said Aleksandar Matic, Professor at Chalmers Department of Physics, who leads the research group.
However, so far lithium sulphur battery designs have been unstable with a low lifetime. Current versions degenerate fast and have a limited life span with an impractically low number of cycles, so many research groups have been looking at the technology (as shown in the stories below). In testing of their new prototype, the Chalmers researchers demonstrated an 85% capacity retention after 350 cycles.
There are four parts to a traditional battery. First, there are two supporting electrodes coated with an active substance, which are known as an anode and a cathode. In between them is an electrolyte, generally a liquid, allowing ions to be transferred back and forth. The fourth component is a separator, which acts as a physical barrier, preventing contact between the two electrodes whilst still allowing the transfer of ions.
The researchers had previously combined the cathode and electrolyte into one liquid, a ‘catholyte’. This saves weight in the lithium sulfur battery, as well as offer faster charging and better power capabilities. Now, with the development of the graphene aerogel, the concept has proved viable, offering some very promising results.