Attainable Gravimetric and Volumetric Energy Density of Li–S and Li Ion Battery Cells with Solid Separator-Protected Li Metal Anodes

As a result of sulfur’s high electrochemical capacity (1675 mA h/gs), lithium–sulfur batteries have received significant attention as a potential high-specific-energy alternative to current state-of-the-art rechargeable Li ion batteries. For Li–S batteries to compete with commercially available Li ion batteries, high-capacity anodes, such as those that use Li metal, will need to be enabled to fully exploit sulfur’s high capacity. The development of Li metal anodes has focused on eliminating Coulombically inefficient and dendritic Li cycling, and to this end, an interesting direction of research is to protect Li metal by employing mechanically stiff solid-state Li+ conductors, such as garnet phase Li7La3Zr2O12 (LLZO), NASICON-type Li1+x Al x Ti2–x (PO4)3 (LATP), and Li2S–P2S5 glasses (LPS), as electrode separators. Basic calculations are used to quantify useful targets for solid Li metal protective separator thickness and cost to enable Li metal batteries in general and Li–S batteries specifically. Furthermore, maximum electrolyte-to-sulfur ratios that allow Li–S batteries to compete with Li ion batteries are calculated. The results presented here suggest that controlling the complex polysulfide speciation chemistry in Li–S cells with realistic, minimal electrolyte loading presents a meaningful opportunity to develop Li–S batteries that are competitive on a specific energy basis with current state-of-the-art Li ion batteries.