Rocksalt electrode can lead to safer, fast-charging Li-ion batteries

Rocksalt, similar to ordinary kitchen table salt, may help solve a major lithium-ion (Li-ion) battery puzzle that left many battery technologists splitting their hair.

Though Li-ion batteries are used for a variety of commercial applications, including mobile phones, laptop computers electric cars, recharging them fast in a safe manner has been a challenge.

Now, a team of researchers at the University of California San Diego (UCSD) may have found a way to recharge Li-ion batteries within minutes for thousands of cycles safely.

In a paper published in the journal Nature on Wednesday, the researchers led by nanoengineering professors Ping Liu and Shyue Ping Ong at UCSD reported a discovery of a new anode material from disordered rocksalt – in which atoms of lithium, vanadium and oxygen arranged similarly as common table salt but in a random fashion.

Currently, two materials are used as anodes in most commercially available Li-ion batteries. The most common, a graphite anode, is extremely energy-dense — a lithium-ion battery with a graphite anode can power a car for hundreds of kilometres without needing to be recharged. However, recharging a graphite anode too quickly can result in fire and explosions due to a process called lithium metal plating. A safer alternative, the lithium titanate anode, can be recharged rapidly but results in a significant decrease in energy density, which means the battery needs to be recharged more frequently.

The new disordered rocksalt anode – which goes by the chemical formula Li3V2O5 — helps achieve a crucial middle ground: it is safer to use than graphite, yet offers a battery with at least 71 per cent more energy than lithium titanate.

“The capacity and energy will be a little bit lower than graphite, but it’s faster, safer and has a longer life. It has a much lower voltage and therefore much-improved energy density over current commercialized fast-charging lithium-titanate anodes,” said Haodong Liu, a postdoctoral scholar in Liu’s lab and first author of the paper. “So with this material we can make fast-charging, safe batteries with long life, without sacrificing too much energy density,” he said in a statement.

The researchers formed a company called Tyfast to commercialise this discovery. The startup’s first markets will be electric buses and power tools since the characteristics of the Li3V2O5 disordered rocksalt make it ideal for use in devices where recharging can be easily scheduled.

Researchers in Professor Liu’s lab plan to continue developing this lithium-vanadium oxide anode material, while also optimising other battery components to develop a commercially viable full cell.

“For a long time, the battery community has been looking for an anode material operating at a potential just above graphite to enable safe, fast-charging lithium-ion batteries. This material fills an important knowledge and application gap,” said Ping Liu. “We are excited for its commercial potential since the material can be a drop-in solution for today’s lithium-ion battery manufacturing process.”

The researchers showed that the Li3V2O5 anode can be cycled for over 6,000 cycles with negligible capacity decay, and can charge and discharge energy rapidly, delivering over 40 per cent of its capacity in 20 seconds. The low voltage and high rate of energy transfer are due to a unique redistributive lithium intercalation mechanism with low energy barriers.

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