Nitrogen-doped carbon decorated with metal carbide and metal in Li-S chemistry up to 3500 cycles

Abstract

In pursuit of the new generation commercial batteries, lithium-sulfur batteries (LSBs) put up great feasibility. However, as a consequence of slow redox kinetics for lithium polysulfides (LiPSs) and presence of lithium dendrites, the commercialization processes have been seriously hindered. These bottleneck problems can be solved by modifying the polypropylene (PP) separator. The present study focuses on a design of Co/Mo₂C/nitrogen-doped carbon (Co/Mo₂C/NC) composite with a hollow hexahedron heterostructure, which serves as an anchor agent for immobilizing LiPSs and accelerating the redox reactions. Co reinforcing the absorbency to LiPSs is revealed by density functional theory (DFT) calculations. Mo₂C enhances the absorbency to LiPSs and picks up speed of transport for lithium-ion. Additionally, NC exhibits the remarkable catalytic performance for LiPSs. Through the synergic action of Co, Mo₂C, and NC, the catalytical efficiency is significantly improved for conversion of LiPSs. Therefore, an enhanced PP separator (named as Co/Mo₂C/NC-PP) is prepared to hold back the shuttle of LiPSs. On the side, the experiment certifies that the Co/Mo₂C/NC-PP separator assembled lithium-sulfur battery (LSB) shows a favorable electrochemical performance. At 0.5C, the LSB brings out 1268 mAh/g for the first discharge capacity and capacity retention rate is up to 79 % after 100 cycles. In the meantime, the original discharge capacity has 992 mAh/g at 1C, each cycle only experiences a minor attenuation of 0.013 % during 3500 cycles as well. Even if the areal sulfur loading is 6.0mg cm⁻² and 2.5μL mg⁻¹ for lean electrolyte/sulfur (E/S) ratio, a good capacity retention is still kept at 0.2C. This strategy opens up a fresh way for efficient design of separator modification material for high-performance LSBs.