Rational design of high nitrogen-doped and core-shell/mesoporous carbon nanospheres with high rate capability and cycling longevity for pseudocapacitive sodium storage

Carbonaceous materials are extensively used as sodium-ion battery (SIB) anodes for their cost-effectiveness, high conductivity and reasonably high capacity. Unfortunately, these anodes suffer from poor rate performances and unsatisfactory lifespan. Herein, the design and construction of high nitrogen-doped, core-shell and intra-core mesoporous structured carbon nanospheres (designated as HN-CSMCNs) for high-rate and stable SIBs is reported. HN-CSMCNs are facilely synthesized by the self-assembly of block copolymer polystyrene-b-poly(acrylic acid), cetyltrimethylammonium bromide and dopamine hydrochloride, and subsequent pyrolysis under an NH₃atmosphere. As an anode for SIBs, HN-CSMCNs exhibit outstanding specific capacity (ca.251 mA h g^-1at 0.1 A g^-1), rate capability (ca.104 mA h g^-1at 15 A g^-1), and more importantly, especially stable cycling properties with a capacity ofca.153 mA h g^-1being retained after 20?000 cycles at 10 A g^-1. Electrochemical analysis demonstrates that the core-shell and intra-core mesoporous structures, expanded inter-planar distance and high pyrrolic/pyridinic-N doping of HN-CSMCNs together contribute to the superior sodium storage capabilityviaa pseudocapacitive-dominated electrochemical kinetics, thus leading to superior electrochemical performances for SIBs.