Mesoporous N-doped carbon-coated CoSe nanocrystals encapsulated in S-doped carbon nanosheets as advanced anode with ultrathin solid electrolyte interphase for high-performance sodium-ion half/full batteries

Sodium-ion batteries (SIBs) are receiving increased attention due to their cost-effective and similar energy-storage mechanism to lithium-ion batteries. Metal selenides have been widely studied owing to their relatively high theoretical capacity. However, requirements for high capacity and excellent rate capability have been still an urgent challenge for energy storage systems. To address such issues, we report mesoporous N-doped carbon-coated CoSe nanocrystals encapsulated in S-doped carbon nanosheets (CoSe-SC@NC) as advanced anode for SIBs. In such a design, CoSe nanoparticles are evenly distributed among the carbon nanosheets, alleviating the volume expansion and maintaining the structural integrity. S/N-doping and mesoporous carbon coating improve electronic conductivity and accelerate ion transfer. Therefore, CoSe-SC@NC exhibits an ultrahigh initial coulombic efficiency (92.4%), high sodium storage capacity (505.4 mA h g(-1) at 0.2 A g(-1) after 100 cycles), and superior long cycling stability at 1 A g(-1) (capacity retention of 412.2 mA h g(-1) after 1336 cycles), as well as ultrathin and robust solid electrolyte interphase. Ultimately, the full cell is assembled and delivered a remarkable capacity of 98.7 mA h g(-1) at 2C rate. Moreover, the improved sodium storage mechanism is further analyzed by in situ X-ray diffraction and ex situ transmission electron microscopy.