Enabling rapid charging lithium metal-based rechargeable batteries through suppression of dendrite growth and ion depletion in the electrolyte via surface acoustic wave-driven mixing

Abstract

Lithium metal is an attractive material for use as anodes in batteries due to its high energy density. However, it is unstable during recharging, with non-uniform Li deposition that leads to porosity, dendrites, rechargeable lithium metal batteries (LMB) have been unrealistic for fifty years with serious safety problems. Over this time, research on chemistry modifications have produced modest improvements, but none that have justified considering LMB over lithium-ion batteries in rechargeable applications. Nonuniform Li deposition during charging occurs due to a Li ion depletion layer adjacent to the anode, especially at high charge rates. By including a small surface acoustic wave device (SAW) into the LMB that produces intense acoustic waves in the electrolyte, rapid submicron boundary layer mixing flow may be generated during charging. This flow largely eliminates the Li ion depletion layer, and because the SAW device is small, solid state, and requires only 10 mW h/cm2 during battery charging, there is a realistic possibility of incorporating this technology into current batteries under consideration for an electric vehicle, consumer device, and medical applications. The elimination of the ion depletion layer furthermore allows high-rate charging, as we will demonstrate in our electrochemistry and morphological results. The underlying physics will be explained using a closed-form model formed from intermediate asymptotics, and will show the crucial impact of the Peclet number in avoiding the ion depletion layer.