Advanced lithium battery chemistries beyond lithium-ion have demonstrated high energy density (>300 Wh/kg) but need further work to improve and demonstrate cycle life, shelf life, rate capability, and safety matching or exceeding that of lithium-ion batteries. A lithium sulfur battery can theoretically reach energy densities of 2600 Wh/kg and has high potential to meet energy density needs for portable power including electric vehicles. Nevertheless, the Li-S system has not yet been implemented because of multiple obstacles: poor electrical conductivity of elemental sulfur, lack of a system that reduces the capacity robbing polysulfide shuttle (PS) effect, a suitable electrolyte that can suppress dendrite formation, and thicker cathode layers necessary to realize the energy density of a lithium sulfur couple.

Past research to improve sulfur cathode conductivity and eliminate the PS effect has included infusing sulfur within electrically conductive carbon micro- and nano-scale particles. This approach addresses both the PS shuttle and sulfur’s poor electrical conductivity; however it presents a barrier for lithium ions, which slows reaction, reduces power, and limits cathode thickness¹. Effective sulfur encapsulation require both electronic and ionic conduction to build thicker cathode structures that retain battery power, capacity, and cycle life.

Typically liquid electrolytes facilitate high sulfur loadings and cathode capacity in a lithium sulfur battery however they also encourage the polysulfide shuttle through the porous polymer separator and don’t prevent dendrites. Excessive amounts of liquid electrolyte also reduces the practical energy density of a lithium sulfur cell. Solid-state electrolytes have the potential to play at least three significant roles in a lithium sulfur battery: (1) provide a barrier to stop PS shuttle effect, (2) prevent lithium dendrite formation, and (3) reduction of liquid electrolyte.

This presentation will discuss the development of a lithium sulfur battery based on combining a solid state electrolyte, entrapped sulfur cathode, and a lithium metal anode necessary to meet needs for high energy density, rechargeable energy storage. New processing methods that improve performance of sulfur carbon composites for cathodes will be discussed. The feasibility of low cost practical carbon materials for sulfur carbon composite cathodes will also be discussed in relation to the new processing methods. Methods and results of using solid state electrolytes in lithium sulfur cell design will also be discussed related to their impact on liquid electrolyte reduction and cathode capacity improvement. Finally optimization targets for a metallic lithium anode, solid electrolyte, and sulfur cathode materials will be discussed in relation to goals for cell specific energy.

1) Manthiram, Arumugam, et al. "Rechargeable lithium-sulfur batteries." Chem. Rev 114.23 (2014): 11751-11787.