Designing Lithium-Sulfur Batteries with High-Loading Cathodes at a Lean Electrolyte Condition.

Abstract

Developing lithium-sulfur cells with a high-loading cathode at a lean-electrolyte condition is the key to bringing the lithium-sulfur technology into the energy-storage market. However, it has proven to be extremely challenging to develop a cell that simultaneously satisfies the abovementioned metrics while also displaying high electrochemical efficiency and stability. Here, we present a concept of constructing a conductive cathode substrate with a low surface area and optimized nanoporosity (i.e., limited micropores in the porous matrix) that enables achieving a high sulfur loading of 13 mg cm-2 and a high sulfur content of 75 wt % with an extremely low electrolyte/sulfur ratio of just 4.0 μL mg-1. The high-loading nanocomposite cathodes demonstrate high-areal capacities of 9.3 mA h cm-2, high energy densities of 18.6 mW h cm-2, and superior cyclability with excellent capacity retention of 85% after 200 cycles. These values are higher than the benchmarks set up for developing future commercial lithium-sulfur cells (i.e., areal capacity of >2-4 mA h cm-2, energy density of >8-13 mW h cm-2, and a long cycle life of 200 cycles with a capacity retention of 80%). The cathode design further exhibits high-rate capability from C/20 to 1 C rates and great potential to attain ultrahigh sulfur loading and a content of 17 mg cm-2 and 80 wt %. The key nanostructural feature that enables realizing fast-charge transport is the low surface area and limited microporosity that avoid the fast consumption of the electrolyte during cell cycling.