P-doped CoSe2 nanoparticles embedded in 3D honeycomb-like carbon network for long cycle-life Na-ion batteries

Abstract We report for the first time a Na-ion battery anode material composed of P-doped CoSe2 nanoparticles (P-CoSe2) with the size of 5–20 nm that are uniformly embed in a 3D porous honeycomb-like carbon network. High rate capability and cycling stability are achieved simultaneously. The honeycomb-like carbon network is rationally designed to support high electrical conductivity, rapid Na-ion diffusion as well as the accommodation of the volume expansion from the active P-CoSe2 nanoparticles. In particular, heteroatom P-doping within CoSe2 introduces stronger P-Co bonds and additional P-Se bonds that significantly improve the structure stability of P-CoSe2 for highly stable sodiation/desodiation over long-term cycling. P-doping also improves the electrical conductivity of the CoSe2 nanoparticles, leading to highly elevated electrochemical kinetics to deliver high specific capacities at high current densities. Benefiting from the unique nanostructure and atomic-level P-doping, the P-CoSe2(2:1)/C anode delivers an excellent cycle stability with a specific capacity of 206.9 mA h g−1 achieved at 2000 mA g−1 after 1000 cycles. In addition, this material can be synthesized using a facile pyrolysis and selenization/phosphorization approach. This study provides new opportunities of heteroatom doping as an effective method to improve the cycling stability of Na-ion anode materials.