A Highly Hierarchical Hollow Sodium Sulfide Nanospheres Embedded in Spongy Carbon Composite As Cathode for High-Rate Performance Sodium-Sulfur Batteries

Abstract

Sodium-sulfur (Na-S) batteries have shown great promise as the next-generation energy storage systems owing to its high specific energy, low cost and high earth abundance of both Na and S. However, the low electronic conductivity and ionic conductivity of the active materials cause slow kinetics of Na-S chemistry and make high-rate performance impossible. Herein, a facile and scalable approach has been employed 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 Na-S batteries. The shortened Na-ion diffusion pathway benefited from the hollow structures together with the fast electron transfer from the carbon matrix contributes to high electrochemical reactivity, leading to high capacity and superior cycling performance at various current rates. At current densities of 1.4 and 2.1 A/g, high initial discharge capacities of 980 and 790 mAh/g (based on sulfur) can be achieved, respectively, with reversible capacities stabilized at 600 and 400 mAh/g (based on sulfur) after 100 cycles. As a proof of concept, we demonstrate Na-metal free Na-S batteries paired with Sn embedded in carbon as anode, which shows an exciting cycling performance of an initial capacity of 550 mAh/g (based on sulfur) with a capacity retention over 80% for over 50 cycles. Our work could provide guidance on rational materials design towards the success of room-temperature high-rate Na-S batteries.[1] Reference: [1] C. Wang, H. Wang, X. Hu, E. Matios, J. Luo, Y. Zhang, X. Lu, W. Li, Adv. Energy Mater, 2018, 1803251. Figure 1