'Bullet proof vest' boost for solid state lithium metal batteries

April 23, 2019 //By Nick Flaherty
'Bullet proof vest' boost for solid state lithium metal batteries
Researchers at Columbia University in New York have developed a way of safely boosting the lifetime of solid state lithium metal batteries with a nano-coating of boron nitride (BN).

Conventional lithium ion cells struggle with low energy density, resulting in shorter battery life, and, because of the highly flammable liquid electrolyte inside them, they can short out and even catch fire. Energy density could be improved by using lithium metal to replace the graphite anode used in Li-ion batteries, as lithium's theoretical capacity for the amount of charge it can deliver is almost 10 times higher than that of graphite. But during lithium plating, dendrites often form and if they penetrate the membrane separator in the middle of the battery, they can create short-circuits, raising concerns about battery safety. The new technique forms what researchers call a 'bullet proof vest' around the solid state lithium metal.

"We decided to focus on solid, ceramic electrolytes. They show great promise in improving both safety and energy density, as compared with conventional, flammable electrolytes in Li-ion batteries," said Yuan Yang, assistant professor of materials science and engineering at Columbia. "We are particularly interested in rechargeable solid-state lithium batteries because they are promising candidates for next-generation energy storage."

Most solid electrolytes are ceramic, and therefore non-flammable, eliminating safety concerns. In addition, solid ceramic electrolytes have a high mechanical strength that can actually suppress lithium dendrite growth, making lithium metal a coating option for battery anodes. However, most solid electrolytes are unstable against Li as they can be easily corroded by lithium metal and cannot be used in batteries.

"Lithium metal is indispensable for enhancing energy density and so it's critical that we be able to use it as the anode for solid electrolytes," said Qian Cheng, postdoctoral research scientist in the department of applied physics and applied mathematics who works in Yang's group and lead author of the paper  in Joule. "To adapt these unstable solid electrolytes for real-life applications, we needed to develop a chemically and mechanically stable interface to protect these solid electrolytes against the lithium anode. It is essential that the interface

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