(Invited) Electrocatalysis and Surface Chemistry in Lithium Sulfur Batteries

This talk will focus on the application of electrocatalysis and surface/interface chemistry to solve the cycling stability problem of lithium sulfur batteries, which are a type of future high energy rechargeable battery that can deliver a few times more energy than the prevalent lithium ion batteries of the same mass. One critical problem is the adsorption of lithium polysulfides, the key reaction intermediates that control the electrochemical performance of the sulfur cathode. We find that 3d transition metal oxides effectively bind polysulfides via oxygen-lithium or metal-sulfur bonding, whereas metal phosphides and chalcogenides only do so with their oxidized surfaces. When the electrolyte/sulfur ratio is lowered for even higher energy density (lean electrolyte condition), we discover that catalysis is needed to overcome the potential limiting reaction barrier associated with the conversion of reaction intermediates. With this understanding, we have developed high capacity sulfur cathode materials achieving hundreds of stable charging-discharging cycles. This surface/interface chemistry approach also enables us to analyze the cycling behavior of the lithium/sodium metal anode and to develop electrode/electrolyte interphases for improving the charging-discharging efficiency and cycling stability, including lithium metal electrodes working with solid-state electrolyte.