Spontaneous Built‐In Electric Field in C3N4‐CoSe2 Modified Multifunctional Separator with Accelerating Sulfur Evolution Kinetics and Li Deposition for Lithium‐Sulfur Batteries

Abstract 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.