Built-in Electric Field Within CoSe-FeSe Heterostructure for Enhanced Sulfur Reduction Reaction in Li-S Batteries.

The conversion of LiS to LiS is the most important and slowest rate-limiting step in the complex sulfur reduction reaction (SRR) for Li-S batteries, the adjustment of which can effectively inhibit the notorious "shuttle effect". Herein, a CoSe-FeSe heterostructure embedded in 3D N-doped nanocage as a modified layer on commercial separator is designed (CoSe-FeSe@NC//PP). The CoSe-FeSe heterostructure forms a built-in electric field at the two-phase interface, which leads to the optimized adsorption force on polysulfides and the accelerated reaction kinetics for LiS-LiS evolution. Density functional theory (DFT) calculations and experimental results combine to show that the liquid-solid reaction (LiS-LiS/LiS) is significantly enhanced in terms of thermodynamics and electrodynamics. Consequently, the batteries assembled with CoSe-FeSe@NC//PP delivered an excellent rate capability (606 mAh g under 8.0 C) and a long cycling lifespan (only 0.056% at 1.0 C after 1000 cycles). In addition, the cells can provide high initial capacity of 887 mAh g at sulfur loading of 5.8 mg cm and 0.1 C. This work would provide valuable insights into binary metal selenide heterostructures for liquid-solid conversion in Li-S batteries.