Revisiting Rechargeable Lithium Metal Batteries: a Surprising Route to Safe Operation
Professor, Medically Advanced Devices Lab
Center for Medical Devices and Instrumentation
Department of Mechanical and Aerospace Engineering
University of California, San Diego
Lithium (Li) has long been known to be the best anode material for rechargeable batteries, however, lithium metal batteries (LMB) have never been successfully used in rechargeable applications due to dendrite formation, resulting in thermal runaway and fire or explosion. During charging, Li ions nonuniformly deposit onto the Li anode from the cathode via the electrolyte. This occurs due to the inhomogeneous ion distribution in the electrolyte from a thick Li ion depletion layer, typically >400 µm. Our objective is to reduce the diffusion layer from 400 µm to 1 µm by using surface acoustic wave-driven mixing flow of the electrolyte. In suppressing dendrite growth, we preserve the charge capacity of the battery. A small 100 MHz SAW device used to recirculate the electrolyte is compatible with lithium electrochemistry, as it is made in our lab of single-crystal lithium niobate. It is a solid-state resonator that can be scaled from as little as 250 µm^3 in volume to ~5 x 5 x 0.05 cm, depending on the application. By externally inducing the flow along the anode, we avoid interfering with the anode’s solid electrolyte interphase (SEI) layer that forms during use. Outside this 1 µm viscous boundary layer, the Li ion concentration is homogeneous: dendrites are precluded. We will show evidence of ~99% Coulumbic efficiency over 150 cycles with a discharge capacity ~85% of theoretical capacity or greater. We discuss details of the SAW-driven acoustic streaming and some issues with charging rates and our solutions that promise to offer charging rates beyond 6C.