High-Energy-Density, Long-Life Lithium-Sulfur Batteries

Abstract

The current lithium-ion technology is based on insertion-compound cathodes and anodes, which limit the charge-storage capacity and energy density. Also, transition-metal ions with multi-electron redox reactions generally encounter a large step in the voltage profile on going from one redox couple to the other. To increase the energy density, much attention is being paid in recent years towards conversion-reaction electrodes, such as sulfur and oxygen as they offer two-electron transfer per sulfur or oxygen atom. However, the Li-S cells suffer from low electrochemical utilization and poor static (high self-discharge) and dynamic (short cycle life) stabilities, arising from the low electronic conductivity of both the end members S8 and Li2S, migration of dissolved polysulfide intermediates from the cathode to the anode, large volume changes during charge/discharge, and poor cycle life and dendrite formation with the lithium-metal anode. To overcome the above difficulties, this presentation will focus on both novel electrode architectures as well as innovative cell designs. Specifically, the presentation will focus on approaches to enhance the electrochemical utilization of sulfur, suppress the migration of dissolved polysulfides to the anode, stabilize the lithium-metal anode surface, and utilize Li2S as a cathode. For example, novel cell configurations with a microporous carbon paper interlayer between the cathode and the separator, as well as polymeric separators coated with unique carbon architectures to trap and reutilize the migrating ploysulfides and enhance the electrochemical utilization, will be presented. Particularly, attention will be paid to the increase in the sulfur content (wt. %) and sulfur loading (mg/cm2) and the challenges associated with it to make the energy density of lithium-sulfur cells well above that of the currently available lithium-ion cells. In addition, additives to form a stable solid-electrolyte (SEI) layer in situ on a lithium-metal anode will be presented. Also, additives to lower the activation barrier during the first charge of Li2S cathode will be discussed.