low temperature lithium battery
© Xinhua
Chinese researchers say they have made a breakthrough in the development of small lithium batteries that can withstand low temperatures.
Chinese researchers say they have found a way to produce a tiny, lightweight lithium battery for use in mobile phones and electric cars that can hold up to 80 per cent of its charge in temperatures as low as minus 40 degrees Celsius.

The breakthrough came by using a combination of a new material called hard carbon along with lithium vanadium phosphate, the team from the Dalian Institute of Chemical Physics said in a paper published in this month's edition of the scientific journal Nano Energy.

"Our goal is to develop an all-season battery that is low-cost but high-safety for consumer products," said Song Zihan, its lead author.

It was an unprecedented approach, but "we proved it works", he said.

The idea of a battery that can withstand extreme cold is not new, and they are already in use in space and in the Arctic and Antarctic.

But they tend to be very bulky because of the heating system and large amount of insulation they need to function properly at sub-zero temperatures.

Such measures are neither physically nor economically viable for applications like smartphones, cameras, laptops or electric cars. The trick, Song said, was replacing the soft graphite in normal lithium batteries with hard carbon.

Graphite is a good conductor and often used for the anode at the bottom of a battery, where electrons are generated. But the performance of graphite drops as the mercury slides.

Song said that hard carbon was a new material that had attracted a lot of research interest in recent years, and compared with graphite, it had a much higher tolerance for the cold.

That was because of its highly irregular and "almost messy" structure, comprising layers of carbon atoms that are interconnected with each other, he said.

However, hard carbon also caused a rapid depletion of the lithium ions that served as an agent carrying the electric flow in battery, he said.

In the past, researchers have tried adding lithium powders or flakes to improve battery life, but the approach has proven costly and dangerous, mostly because pure lithium is highly reactive.

So Song and his colleagues used a composite material called lithium vanadium phosphate as the positive cathode on top of the battery.

The composite was capable of providing enough extra lithium ions for the hard carbon's need without increasing the risk of fire or explosion, and it was cheap, he said.

"The pairing of hard carbon and lithium vanadium phosphate worked a charm," Song said.

But the technology is still a long way from being commercially viable.

The battery Song's team made is far too small for any real-life applications, and enlarging it would require some "innovative engineering solutions", he said.

Another scientist involved in the project said the team was working with battery manufacturers to see if the technology could be commercialised.