Ultra-efficient graphene battery has energy density of oil

Cambridge researchers have demonstrated a prototype device that is over 90 per cent efficient and could have significant implications for electric vehicles, renewable energy and consumer technology.

The theoretical energy density of lithium-oxygen batteries is up to 10 times greater than that found in current lithium-ion cells. This is equivalent to gasoline and would enable an electric car with a battery one-fifth the cost and one-fifth the weight of those currently on the market to travel the 650 kilometres between London and Edinburgh on a single charge.

Although the technology is still a long way off commercial viability, the researchers showed a lithium-oxygen demonstrator cell with a higher energy capacity, increased efficiency and improved material stability over previous attempts.

It contained a ‘fluffy’ electrode made from a highly porous form of graphene that boosted the energy efficiency significantly above previous attempts to be comparable with lithium-ion technology.

The study was led by Cambridge University chemist Clare Grey, who heads the energy activities in the Graphene Flagship, a pan-European consortium of academic and industrial partners looking to commercialise graphene.

“What we’ve achieved is a significant advance for this technology and suggests whole new areas for research – we haven’t solved all the problems inherent to this chemistry, but our results do show routes forward towards a practical device,” she said.

The demonstration device showed fewer of the chemical reactions that degrade battery cells than previous examples at lithium-oxygen batteries, making it far more stable following multiple charge-discharge cycles.

However, the researchers admit that other issues still need to be addressed and that commercial applications of the technology are over a decade away.

For this to occur, scientists need to solve how to protect the metal electrode to prevent the growth of spindly lithium metal fibres known as dendrites, which can cause batteries to explode if they short-circuit the cell.

Additionally, as with previous attempts at lithium-oxygen cells, the demonstrator cell can only be cycled in a pure oxygen environment. Atmospheric carbon dioxide, nitrogen and moisture are all damaging to the metal electrode.

Tao Liu, first author of a paper on the research, said: “There’s still a lot of work to do, but what we’ve seen here suggests that there are ways to solve these problems – maybe we’ve just got to look at things a little differently.”