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Nov. 19, 2020
Toray Industries, Inc.
Toray Creates Non-Porous Separator for Lithium-Ion Batteries, that Could Dramatically Increase Capacity by Enhancing Safety of Lithium Metal Anode Batteries
Tokyo, Japan, November 19, 2020 – Toray Industries, Inc., announced today that it has created a non-porous separator for lithium-ion batteries, that could dramatically increase capacity by enhancing safety of lithium metal anode batteries, notably in wearable electronic devices, drones, and electric vehicles.

Lithium-ion battery market continues to expand, underscoring the need to lift the capacity and energy density of lithium-ion batteries. This situation has focused attention on lithium metal anode because of their high theoretical capacity and low redox potential (see glossary note 1). This anode has not seen practical use, however, as lithium dendrites form on lithium metal surfaces during charging, penetrating separators and causing short circuits that deteriorate safety.

Lithium dendrites (see glossary note 2) form along the pores of microporous film. Eliminating separator pores can stop such growth, but the downside is greatly reduced lithium-ion permeability. It is essential to suppress dendrites while maintaining ion conductivity. Batteries with lithium metal anode have greater capacity, therefore safety requirements become more serious than conventional ones, necessitating higher heat resistance and thermal stability of separators.

Toray tackled this challenge by utilizing the high heat resistance aramid polymer (see glossary note 3) molecular design technology that it amassed over the years to control the gaps between molecular chains and the affinity to lithium ions. It thereby created a highly ion-conductive polymer with outstanding heat resistance. The company was able to suppress dendrite formation in lithium metal anode batteries while keeping ion conductivity by employing this polymer as a non-porous separator comprising a pore-free layer onto a microporous separator.

Toray showes that a battery with such a separator suppressed short circuits attributable to dendrites and maintained more than 80% of its capacity after 100 charge/discharge cycles. It will accelerate research and development to swiftly establish technologies with lithium metal anodes batteries so it can drive ultra-high capacity and safety for tomorrow’s lithium-ion batteries.

Toray will detail its new technology at the 61st Battery Symposium in Japan on Friday, November 20.

Toray will continue leveraging its core technologies of synthetic organic and polymer chemistry, biotechnology, and nanotechnology to research and develop advanced materials that transform societies in keeping with its commitment to innovating ideas, technologies, and products that deliver new value.
Glossary
1) Redox potential
This is a measure of the oxidization or reduction of electrons in substances. In a battery, a low reduction potential of the anode and a high oxidation potential of the cathode makes it possible to increase voltage and attain a high capacity.
2)Lithium dendrites
These spiky structures form as batteries charge, detracting from performance and leading to short circuits.
3)Aramid
Aramid represents aromatic polyamide, one of the super engineering plastics. The polymer exhibits outstanding heat resistance and highest rigidity. Toray is unique in offering a mass-produced para-aramid film, under the mictron™ brand. Owing to its high rigidity, it is used widely in data storage tapes. It ranks just behind polyimide in terms of heat resistance, so it is also employed in thin-film circuit materials.

Non-perforated lithium-ion separators