Frogspawn-Coral-Like Hollow Sodium Sulfide Nanostructured Cathode for High-Rate Performance Sodium-Sulfur Batteries

Room-temperature (RT) sodium-sulfur (Na-S) batteries are attractive cost-effective platforms as the next-generation energy storage systems by using all earth-abundant resources as electrode materials. However, the slow kinetics of Na-S chemistry makes it hard to achieve high-rate performance. Herein, a facile and scalable approach has been developed to synthesize hollow sodium sulfide (Na2S) nanospheres embedded in a highly hierarchical and spongy conductive carbon matrix, forming an intriguing architecture similar to the morphology of frogspawn coral, which has shown great potential as a cathode for high-rate performance RT Na-S batteries. The shortened Na-ion diffusion pathway benefits from the hollow structures together with the fast electron transfer from the carbon matrix contributes to high electrochemical reactivity, leading to superior electrochemical performance at various current rates. At high current densities of 1.4 and 2.1 A g(-1), high initial discharge capacities of 980 and 790 mAh g(sulfur)(-1) can be achieved, respectively, with reversible capacities stabilized at 600 and 400 mAh g(sulfur)(-1) after 100 cycles. As a proof of concept, a Na-metal-free Na-S battery is demonstrated by pairing the hollow Na2S cathode with tin-based anode. This work provides guidance on rational materials design towards the success of RT high-rate Na-S batteries.