Core-Shell Cathode Design with Molybdenum Trioxide as the Electrocatalytic Trapping Layer for High-Energy Density Room-Temperature Sodium Sulfur Batteries

Room-temperature sodium sulfur batteries are receiving immense attention because of their low cost and higher energy density compared to lithium ion batteries. The key challenges of room-temperature sodium sulfur batteries are the polysulfide shuttling and sluggish reaction kinetics of polysulfide conversion. To mitigate these two issues, molybdenum trioxide is chosen to catalytically covert the sodium polysulfide as well as chemically anchor the polysulfide toward the cathode. This proof of concept is implemented and realized through the change in the design of the cathode wherein the sulfur is used as the core layer and MoO3 is used as the catalytic shell layer for shielding the polysulfide migration. The core-shell design of the cathode delivers a specific capacity of 1198 mA h g-1 at a current density of 50 mA g-1, which is about 4.2 times enhancement in specific capacity when compared to the single-layered cathode with a cycling stability of 1000 cycles. The core-shell cathode design offers a more stable open circuit potential for over 20 days and low charge transfer resistance. The enhancement in specific capacity is attributed to the formation of polythionate complexes through the reaction of MoO3 with the polysulfides which helps in strong binding of soluble species as evident from the spectroscopy studies. This is the first attempt of utilizing catalytic MoO3 for binding sodium polysulfide in room-temperature sodium sulfur batteries and will provide a new practical approach for the development.