Nickel Cobalt Oxide Decorated Cerium Oxide Nanorods for Polysulfide Trapping and Catalytic Conversion in Advanced Lithium Sulfur Batteries

Abstract

Lithium sulfur batteries (LSBs) are promising candidates for next-generation rechargeable batteries due to the active material sulfur being earth abundant, low cost and environmentally friendly element. But the most important feature of LSBs is that the theoretical capacity of sulfur is ~1645 mAh g-1 which is ~5 times higher than the conventional lithium-ion batteries. However, even with these valuable assets, LSB has not yet been commercialized due to the inherent problems of fast capacity loss resulting in low cycle lifetime. This capacity loss originates from the migration of dissolved sulfur discharge products in the electrolyte known as the notorious polysulfide shuttling effect.To deal with this issue, several research efforts have been made to trap the high order lithium polysulfides by a) physically encapsulation using high surface area carbonaceous materials and b) chemically binding the lithium polysulfides in its cathode host. Several materials are very popular to efficiently bind the lithium polysulfides such as transition metal oxides, nitrides, sulfides and have helped making significant advances to long cycle life lithium sulfur batteries. However, to make the transition to design next generation LSBs, there is a need for materials that can facilitate fast polysulfide conversion by catalytic reaction that will reduce the diffusion and agglomeration of polysulfides in the liquid organic electrolyte, resulting in high capacity and long cycle lifetime.With this strategy in mind, we have designed NiCoOx decorated on CeO2 nanorods support as cathode host material for LSBs to provide dual adsorption-catalysis synergy. The CeO2 nanorods with enriched surface defects can effectively bind the lithium polysulfides whereas the NiCoOx nanoclusters can provide highly efficient electrocatalytic sites to improve the conversion kinetics of elemental sulfur to high order lithium polysulfides to finally the lower order polysulfides. As a result, the derived LSBs exhibited excellent electrochemical performance with high capacity of 1236 mAh g-1 at 0.2C with a sulfur loading of 1.33 mg cm-2. Even with high sulfur loading 2.66 mg cm-2 the LSBs exhibits 755 mAh g-1 at 0.2C with a capacity decay of only 0.08% per cycle after 170 cycles. The battery also operates at the sulfur loading of 4 mg cm-2 and 5.33 mg cm-2 for more than 100 which is convincing considering commercialization of LSB. Key words: lithium sulfur batteries, lithium polysulfides, shuttle effect, cerium oxide, catalysis.