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

We report for the first time a Na-ion battery anode material composed of P-doped CoSe 2 nanoparticles (P-CoSe 2 ) 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-CoSe 2 nanoparticles. In particular, heteroatom P-doping within CoSe 2 introduces stronger P-Co bonds and additional P-Se bonds that significantly improve the structure stability of P-CoSe 2 for highly stable sodiation/desodiation over long-term cycling. P-doping also improves the electrical conductivity of the CoSe 2 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-CoSe 2 (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.