Lu Li1 Swastik Basu1 Yiping Wang1 Long Chen2 Sankha Mukherjee3 Chandra Singh3 Wencai Ren2 Hui-ming Cheng2 Jian Shi2 Yunfeng Shi1 Shankar Narayanan1 Nikhil Koratkar1

1, Rensselaer Polytechnic Institute, Troy, New York, United States
2, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, , China
3, University of Toronto, Toronto, Ontario, Canada

Lithium sulfur (Li-S) battery, with specific capacity several times that of state of the art lithium ion battery, has become one of the hottest topics of next generation energy storage systems. However, due to the harsh environment inside the Li-S battery and the multi-steps reaction mechanism, the degradation of battery components are more serious than lithium ion batteries. For the sulfur cathode part, the insulating nature of charge/discharge products (sulfur/lithium sulfide) and the dissolution of intermediate reaction products (lithium polysulfides (LiPSs)) in electrolyte with subsequent parasitic reactions lead to low sulfur utilization and poor cycle life. As for the lithium anode side, the uncontrollable lithium dendrite growth is easy to penetrate the separator and cause internal short circuits triggering security issues of the batteries.
In this presentation, to solve the problems of LiPSs dissolution and low cathode conductivity, we rationally design a sulfur cathode structure by depositing few-layer phosphorene nanosheets on a conductive carbon scaffold as LiPSs immobilizer and catalyst to effectively trap LiPSs, improve the cycle life, lower the polarization, and accelerate the redox reaction of Li-S battery. Further, based on the electrochemical tests and first-principles density functional theory, an outlook will be given on how to choose LiPSs' immobilizers in the Li-S battery with consideration on the balance of battery performance and the loading fraction of the immobilizers. [1]
To solve the lithium dendrite issues in the Li-S battery, we start with the Li/Li symmetric cells to study the nucleation and growth of Li dendrites related to the current densities. Unlike the general opinion that the dendrite problem is exacerbated at high current densities, what we find is when the current density is high enough passing through the Li electrode, there is a significant self-heating phenomenon for the dendrites. The local heating caused by current gives flux and flow to Li, triggering extensive surface diffusion, which smoothens the dendrites and enables the equilibrium flat configuration to be established quicker. And this repeated doses of high current density healing treatment enables the safe cycling of Li-S battery with high Coulombic efficiency.[2]

[1] Li, L.; Chen, L.; Mukherjee, S.; Gao, J.; Sun, H.; Liu, Z.; Ma, X.; Gupta, T.; Singh, C. V.; Ren, W., et al., Phosphorene as a Polysulfide Immobilizer and Catalyst in High-Performance Lithium–Sulfur Batteries. Adv. Mater. 2017, 29, 1602734
[2] Li, L.; Basu, S.; Wang, Y.; Chen, Z.; Hundekar, P.; Wang, B.; Shi, J.; Shi, Y.; Narayanan, S.; Koratkar, N., Self-Heating–Induced Healing of Lithium Dendrites. Science 2018, 359, 1513-1516.