A sodium battery developed by researchers at The University of Texas at Austin significantly reduces fire risks from the technology, while also relying on inexpensive, abundant materials to serve as its building blocks.

Though battery fires are rare, increased battery usage means these incidents are on the rise.

Elon Musk has said a suspected arson attack which has halted production at Tesla's Berlin car factory was "dumb".

A far-left activist group says it targeted the site because of the amount of resources and labour it uses.

The company says car-making is unlikely to resume before next week, with the outage likely to cost it "in the high nine-digit euro range."

Tesla wants to double the size of its German factory - a plan which is opposed by some environmentalists.