Hollow slightly oxidized CoP confined into flyover-type carbon skeleton with multiple channels as an effective adsorption-catalysis matrix for robost Li-S batteries

Abstract

Outstanding sulfur electrochemistry in lithium-sulfur (Li-S) batteries relies heavily on the high conductivity of electrodes and the interaction of sulfur species and their reservoir matrix, which requires a reasonable design of the microstructure of each component. Herein, hollow slightly oxidized cobalt phosphides (h-O-CoP) nanoparticles are in-situ implanted into the flyover-type carbon framework composed of the N-doped C polyhedrons threaded with 1D carbon nanotubes (CNTs) on 2D graphene sheets (h-O-CoP-NCG). During the synthesis process, a facile “go-between” strategy and post-heat treatment phosphating technique of the corresponding precursors is implemented to generate abundant electrocatalytic-adsorption sites and provide better electron/ion transportation for durable Li-S batteries. Combining the merits of h-O-CoP active sites and conductive NCG channels, the h-O-CoP-NCG enables stable and efficient sulfur electrochemistry including superior rate capability of ∼857 mAh g−1 at 4 C and robust cyclability over 500 cycles at 2 C with an average decay rate of 0.033% per cycle. Even under high sulfur loading (4.2 mg cm−2), the capacity retention remains 91.6% after 300 cycles at 0.5 C. DFT calculations confirm the metallic characteristics of O-CoP (011)-Li2S via the orbital hybridization of the Co 3d-S 2p and the strong adsorption of O-CoP (011) and Li2S6, thereby enhancing the performances of the sulfur cathode.