Conversion of polysulfides on core–shell CoP@C nanostructures for lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) have received considerable attention due to their high theoretical energy density, low cost, and abundant sulfur resources. However, the shuttle effect and slow redox kinetics seriously hinder the development of LSBs. To resolve these issues, one-dimensional (1D) porous carbon-encapsulated CoP (CoP@C) nanotube-like nanostructures were rationally designed and successfully prepared through a simple two-step hydrothermal reaction. The CoP quantum dots in this structure can not only capture polysulfides, but also electrocatalyze the conversion of polysulfides. The electrocatalytic effect of CoP was systematically investigated by electrochemical tests. The experimental results and DFT calculations consistently revealed the fundamental mechanism of chemically anchoring lithium polysulfides (LiPSs) by CoP, the polysulfide conversion pathway, and the precipitation behavior of Li2S. Meanwhile, the as-prepared CoP@C/MWCNT/S electrode achieved a high initial discharge capacity of 1237.6 mAh/g at 0.5C, retained 92.3 % of the capacity and a high Coulombic efficiency (nearly 100 %) after 100 cycles, and exhibited an outstanding rate capability at as high as 5C. This work reveals the application potential of cobalt phosphide materials in the development of advanced LSBs.