New salts for next-gen lithium-ion batteries

Lithium-ion batteries are set to take a dominant role in electric vehicles and other applications in the near future — but the battery materials currently in use fall short in terms of safety and performance. Monash University scientists, working with Australian battery producer Calix, have now come up with new chemistry as a way of addressing this challenge.

“The lithium salt currently being used in lithium-ion batteries is lithium hexafluorophosphate, which poses a fire and safety hazard as well as toxicity,” said Professor Doug MacFarlane, co-leader of the Monash team.

“In smaller, portable devices, this risk can be partially mitigated. However, in a large battery pack, such as electric vehicle and outdoor grid-scale energy storage systems, the potential hazard is much intensified. Higher voltage and power batteries are also on the drawing board but cannot use the hexafluorophosphate salt.”

The chemists have now described a novel lithium salt which might overcome the challenges of electrolyte design and replace the hexafluorophosphate salt, published in the journal Advanced Energy Materials.

“Our aim has been to develop safe fluoroborate salts, which are not affected even if we expose them to air,” said lead study author Dr Binayak Roy.

“The main challenge with the new fluoroborate salt was to synthesise it with battery-grade purity, which we have been able to do by a recrystallisation process.

“When put in a lithium battery with lithium manganese oxide cathodes, the cell cycled for more than 1000 cycles, even after atmospheric exposure — an unimaginable feat compared to the hypersensitive hexafluorophosphate salt.”

According to Dr Roy, when combined with a novel cathode material in a high-voltage lithium battery, this electrolyte far outperformed the conventional salt. Moreover, the salt was found to be very stable on aluminium current collectors at higher voltages, as required for next-generation batteries.

The research is a result of a collaborative effort within the Australian Research Council (ARC) Training Centre for Future Energy Storage Technologies (StorEnergy) and conducted in collaboration with Calix, a company that is producing high-quality manganese-based battery materials. The research will assist Calix to achieve its goal of large-scale fabrication of Australian-based lithium-ion batteries, aiming for grid-scale energy storage systems for rollout in Australia.

“Calix is developing a platform technology to produce high-performance, cost-competitive battery materials in Australia,” said Dr Matt Boot-Handford, General Manager for R&D at Calix. “We are working closely with our research partners at Monash and Deakin through StorEnergy to support the development of electrolyte systems that are compatible with Calix’s electrode materials.

“The superior electrochemical performance and stability demonstrated by the Monash team’s new electrolyte system, paired with Calix’s lithium manganese oxide electrode material, is an exciting and important milestone that brings us one step closer to making batteries featuring Calix next-generation electrode materials a commercial reality.”

“In the near future we hope to turn these new anions into thermally stable, non-flammable liquid salts, making them beneficial for batteries operating at high temperatures,” Dr Kar concluded.

Image credit: ©stock.adobe.com/au/danielskyphoto

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