Characterizing Ion Transport in Non-Aqueous Electrolyte Solutions for Li-Ion and Li- Metal Batteries

摘要

A majority of ionic conductivity in current state-of-the-art liquid electrolytes results from the movement of the anion rather than the electrochemically active Li~+ ion. Passing current through such an electrolyte can cause severe ionic concentration gradients to extend into porous electrodes, which at high currents can reduce active material utilization and result in high overpotentials that cause deleterious side reactions to occur (e.g., Li plating on graphite electrodes). The severity of these concentration gradients is directly influenced by the transference number (t_+), which describes the ratio of current carried by the electrochemically active Li~+ ion to the total current passed. Nonaqueous polyelectrolyte solutions (PESs) are a promising, but underexplored, route to high transference number electrolytes that demonstrate potential for both high ionic conductivity and t_+. This combination is achieved by anchoring the anion to a polymer backbone - allowing for high t+ by slowing down the motion of the electrochemically inactive anion - while maintaining high ion conductivity through improved ion dissociation and solvent-mediated Li~+ transport. New measurement techniques are necessary to rigorously understand ion-transport and structure-property relationships in this new class of electrolytes.