A bi-functional catalyst strategy to selectively regulate sulfur redox kinetics in lithium–sulfur batteries

Abstract

Designing electrochemical catalysts has become a research hotspot due to their accelerating the polysulfide conversion of the sulfur cathode to inhibit the “shuttle effect” in lithium–sulfur batteries. However, it is still a great challenge to design the heterogeneous selective electrochemical catalyst for inhibiting the “shuttle effect”. Herein, nickel cobalt phosphide and cobalt phosphide as the heterogeneous catalyst active sites embedded in the nitrogen-doped hollow carbon nanocages (NiCoP@CoP/NC) are reported, used for multi-step and multi-phase sulfur electrode reaction, and it is found that metal-sulfur d-p hybridization can effectively indicate the intrinsic catalytic activity of metal site. Division of labor and cooperation of the bi-active NiCoP@CoP as heterogeneous catalysts propel the stepwise polysulfide conversion. NiCoP and CoP sites preferentially accelerate the long-chain polysulfide conversion reaction (S8⇌LiPSs) and the short-chain polysulfide conversion reactions (LiPSs⇌Li2S), respectively. Moreover, the hollow and porous N-doped carbon structure can successfully suppress the volume effect and improve the conductivity of the sulfur cathode. The unique design can obtain an effective inhibition of the shuttle effect and rapid electrode reaction. As a result, LiS batteries demonstrate a high initial capacity of 1063 mAh g−1 and a low-capacity decay of 0.04% per cycle within 1000 cycles. Our work provides a feasible idea for the design of host materials in Li–S batteries.