Electrochemically Controlled Solid Electrolyte Interphase Layers Enable Superior Li-S Batteries

Lithium-sulfur (Li-S) batteries suffer from shuttle reactions during electrochemical cycling, which cause the loss of active material sulfur from sulfur-carbon cathodes, and simultaneously incur the corrosion and degradation of the lithium metal anode by forming passivation layers on its surface. These unwanted reactions therefore lead to the fast failure of batteries. The preservation of the highly reactive lithium metal anode in sulfur-containing electrolytes has been one of the main challenges for Li-S batteries. In this study, we systematically controlled and optimized the formation of a smooth and uniform solid electrolyte interphase (SEI) layer through electrochemical pretreatment of the Li metal anode under controlled current densities. A distinct improvement of battery performance in terms of specific capacity and power capability was achieved in charge-discharge cycling for Li-S cells with pretreated Li anodes compared to pristine untreated ones. Importantly, at a higher power density (1 C rate, 3 mA cm^-2), the Li-S cells with pretreated Li anodes protected by a controlled elastomer (Li-Protected-by-Elastomer, LPE)) show the suppression of the Li dendrite growth and exhibit 3-4 times higher specific capacity than the untreated ones after 100 electrochemical cycles. The formation of such a controlled uniform SEI was confirmed, and its surface chemistry, morphology, and electrochemical properties were characterized by X-ray photoelectron spectroscopy, focused-ion beam cross sectioning, and scanning electron microscopy. Adequate pretreatment current density and time are critical in order to form a continuous and uniform SEI, along with good Li-ion transport property.