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Toray’s new ion-conductive polymer membrane for EV batteries increases ion conductivity by 10x

March 18, 2024

Toray Industries, Inc. has developed an ion-conductive polymer membrane that offers a tenfold increase in ion conductivity compared to previous versions. This advancement could potentially expedite the implementation of solid-state batteries, air batteries, and other lithium metal batteries, thereby extending the range of electric vehicles, industrial drones, urban air mobility systems, and other modes of transportation.

The shift towards electric mobility has led to a surge in demand for lithium-ion batteries with higher energy densities. Consequently, there is a push to develop lithium metal batteries, which have anodes that provide the highest theoretical energy capacity. However, the high surface reactivity of lithium metal and the stability issues related to its dissolution and precipitation morphology during charging and discharging cycles present significant challenges. One notable issue is the growth of lithium dendrites, which can cause short circuits. Metallic lithium anodes in batteries using solid electrolytes face similar problems and have not yet seen practical applications.

Toray has addressed these issues by developing polymer membranes that offer ion conductivity through hopping conduction. This mechanism allows lithium ions to move between interacting sites within the polymer membranes, effectively jumping across sites, while the membranes remain non-porous. This innovation was made possible by Toray’s expertise in molecular design technology, particularly with aramid polymers, which the company has honed over many years.

Toray’s research indicates that by enhancing the hopping site structure and designing a new polymer with more hopping sites, they have achieved the highest ionic conductivity in the 10-4 S/cm range for a hopping-conductive polymer film. The company has confirmed that the polymer film functions effectively as a protective film on lithium metal surfaces, mitigating the aforementioned issues and potentially extending the service lives of batteries using lithium metal anodes.

In collaboration with Professor Nobuyuki Imanishi of the Graduate School of Engineering at Mie University, Toray has verified the achievement of 100 charge-discharge cycles for the first time in a dual-component lithium-air battery using this polymer membrane as a separator. The company plans to accelerate research to swiftly establish technology for deployment on solid-state, air, and other advanced batteries.

Some of the development work for the new membrane was funded by the New Energy and Industrial Technology Development Organization (NEDO). Toray intends to present its technology at the 91st Annual Meeting of the Electrochemical Society of Japan, scheduled for March 14 through 16 this year.