New electrolyte gel for safer batteries

A recent fire on a Boeing 787 on the ground in Boston, US, was caused by a battery failure, which resulted in the release of flammable electrolytes, heat damage and smoke. If they had used a safer electrolyte, the risk would have been reduced.

Electrolytes are essential components of supercapacitors, batteries and fuel cells. The most widely used electrolyte is a liquid type, since its overall ionic conductivity and value of transference numbers are better than solid-type electrolytes. However, safety concerns caused by its leakage and explosive nature caused an extensive call for the research on the development of solid-type electrolytes.

The most important parameter of electrolytes used in electrochemical cells is ionic conductivity. The use of solid-state electrolytes has been limited due to low ionic conductivity caused by their immobile matrix regardless of their own merits such as no leak, non-volatility, mechanical strength and processing flexibility. Another parameter to be considered is transference of the number of ions. High values of the cationic transference number achieved by solid or gel electrolytes have resulted in low ionic conductivity leading to inferior cell performances.

The research team at Ulsan National Institute of Science and Technology (UNIST), South Korea, has found a new physical organogel electrolyte with two unique characteristics: an irreversible thermal gelation and a high value of the lithium-ion transference number.

The research team acquired the two required properties simultaneously in polymer gel electrolytes: a liquid-electrolyte-level conductivity with a high transference number. Cyanoethly polyvinyl alchohol (PVA-CN) played a key role in the highly conductive gel electrolyte while another cyano resin, cyanoethlyle pullulan (Pullulan-CN), was used as a control representing a liquid electrolyte containing cyano chains. The PVA-CN-containing liquid electrolyte was thermally gelated even without any chemical crosslinkers or polymerisation initiators.

“We believe that this new type of electrolyte gel provides us with design flexibility in devices as well as enhanced safety and stability to electrochemical devices,” said Prof Song.