Spontaneous Built-In Electric Field in C 3 N 4 -CoSe 2 Modified Multifunctional Separator with Accelerating Sulfur Evolution Kinetics and Li Deposition for Lithium-Sulfur Batteries.

The discovery of the heterostructures that is combining two materials with different properties has brought new opportunities for the development of lithium sulfur batteries (LSBs). Here, C 3 N 4 -CoSe 2 composite is elaborately designed and used as a functional coating on the LSBs separator. The abundant chemisorption sites of C 3 N 4 -CoSe 2 form chemical bonding with polysulfides, provides suitable adsorption energy for lithium polysulfides (LiPSs). More importantly, the spontaneously formed internal electric field accelerates the charge flow in the C 3 N 4 -CoSe 2 interface, thus facilitating the transport of LiPSs and electrons and promoting the bidirectional conversion of sulfur. Meanwhile, the lithiophilic C 3 N 4 -CoSe 2 sample with catalytic activity can effectively regulate the uniform distribution of lithium when Li + penetrates the separator, avoiding the formation of lithium dendrites in the lithium (Li) metal anode. Therefore, LSBs based on C 3 N 4 -CoSe 2 functionalized membranes exhibit a stable long cycle life at 1C (with capacity decay of 0.0819% per cycle) and a large areal capacity of 10.30 mAh cm -2 at 0.1C (sulfur load: 8.26 mg cm -2 , lean electrolyte 5.4 µL mg s -1 ). Even under high-temperature conditions of 60 °C, a capacity retention rate of 81.8% after 100 cycles at 1 C current density is maintained.