Understanding Diffusion and Electrochemical Reduction of Li⁺ Ions in Liquid Lithium Metal Batteries

Lithium metal has drawn significant interest as an anode material for next generation lithium (Li) batteries. However, due to its propensity to form dendrites in commonly used electrolytes during repeated cycling, it has not yet been commercialized in secondary batteries. The formation of a Li protrusion is determined by the relative speed of Li⁺ ions being reduced and how fast they can be replenished in the vincinity of electrode. However, it is very difficult to quantify such kinetic parameters of Li⁺ ion in different electrolytes, not mentioning the identification of the desired electrolyte recipe to mitigate Li dendrite formation. Herein, we use microelectrodes to study the growth mechanism of electroplated Li by measuring the Li⁺ diffusion coefficient (D_Li) and exchange current density (i_o) in different electrolytes. The different Li morphologies formed on microelectrodes are well correlated to their diffusion rate and electrochemical reduction speed on the electrode, providing a fast electrochemical tool to screen compatible electrolytes for Li metal batteries.