Lithium metal battery boost from non-porous separator

Lithium metal battery boost from non-porous separator

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By Nick Flaherty

Toray Industries in Japan has developed a non-porous separator for lithium metal battery cells that could dramatically increase the safety and aloow them to be used 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. However lithium metal anodes have not seen practical use, however, as lithium dendrites form on the metal surfaces during charging, penetrating separators and causing short circuits that can causde overheating and even fires.

The lithium dendrites form along the pores of the microporous film used in the cell construction. Eliminating separator pores can stop such growth, but this greatly reduces the permeability of the lithium-ions and so limits the charging and discharging rates. The design of the separator has to suppress dendrites while maintaining ion conductivity along with higher heat resistance and thermal stability for lithium metal cells with higher energy density.

Toray used a high heat resistance aramid polymer to control the gaps between molecular chains and the affinity to lithium ions. It had already developed a mass-produced, rigid para-aramid film under the mictron brand that is widely used in data storage tapes. It ranks just behind polyimide in terms of heat resistance and so it is also used in thin-film circuit materials.

Using this para-aramid material for a battery cell separator created a highly ion-conductive polymer with high heat resistance as a non-porous separator on a microporous separator. The company was able to show suppression dendrite formation in lithium metal anode batteries while keeping ion conductivity. 

Toray showes that a battery with such a separator suppressed short circuits attributable to dendrites and maintained more than 80 percent of its capacity after 100 charge/discharge cycles. This will accelerate research and development to swiftly establish technologies with lithium metal anodes batteries.

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