Development of a High Energy Density, Long Cycle Life and Safety Enhanced Li-S Battery

Abstract

Rechargeable lithium-sulfur (Li-S) batteries are widely considered the most promising “Beyond Li-ion” candidates, notably for their high theoretical energy density. The low and moderate atomic weight of Li and S, respectively, translates to a battery chemistry pairing that is lightweight. Since each S atom can ultimately host two lithium ions (Li+), compared with 0.5–0.7 Li+ per host atom in Li-ion batteries [1], the Li-S battery chemistry offers a much higher Li storage capacity potential. Assuming a complete redox couple reaction, S8 + 16Li+ + 16e- ↔ 8Li2S, the S cathode can have a high theoretical specific capacity of 1672 mAh/g with an average discharge voltage of ~2.1V (vs. Li/Li+), which leads to a theoretical specific energy of ~2500 Wh/kg based on the active material weight of a Li-S cell [2]. Other compelling attributes of Li-S batteries include high S natural abundance, low cost of S materials and safety characteristics owing to an intrinsic tolerance to overcharge [3]. In addition, the primary constituents of Li-S batteries are non-toxic and environmentally friendly [4].However, currently no commercial Li-S battery exists due to some significant technical challenges that have thus far prevented the realization of the tremendous energy density and performance potentials of Li-S batteries. These technical challenges include: low practical specific energy or energy density yield, significant capacity loss with cycling, high self-discharge rates, low Coulombic efficiency and safety concerns due to the use of Li metal anode [5].We will present our efforts in the development of a high energy density, long cycle life, safe and economically scalable Li-S battery technology via a holistic approach to nanoengineer/functionalize cell components including active components (i.e., S cathode, Li metal anode) and inactive components (e.g., separator, electrolyte), to address the Li-S battery cycle life degradation challenges and safety concerns. We will show that our comprehensive approaches afforded high discharge specific capacity, Coulombic efficiency (CE) and stable cycle life of the resultant Li-S cells (Figure 1).Our study demonstrates that the holistic approach of nanoengineering/functionalizing the active and inactive cell components represent a very promising strategy to develop a high energy density, long cycle life and safety enhanced Li-S battery technology.