Hierarchical microstructure constructed with graphitic carbon-coated Ni ₃ S ₂ nanoparticles anchored on N-doped mesoporous carbon nanoflakes for optimized sodium storage

A hierarchical microstructure constructed with graphitic-carbon-coated Ni₃S₂ nanoparticles anchored on N-doped mesoporous carbon nanoflakes was fabricated using a nickel-based micro-nano structure as a precursor and polydopamine as a carbon source. By optimizing the microstructure, the obtained Ni₃S₂/carbon composite compounded with the thickest carbon nanoflakes delivers ultrafast and stable Na-ion storage performance, and can maintain a reversible charge capacity of 372 mA h g^-1 at a current density of 5 A g^-1 over 250 cycles, and 316 mA h g^-1 even at a current density of 20 A g^-1 for 2000 cycles. These remarkable electrochemical properties can be attributed to its hierarchical microstructure of graphitic-carbon-coated Ni₃S₂ particles and N-doped mesoporous carbon nanoflakes, which provide easy accessibility to the electrolyte, fast electron transport and Na⁺ diffusion, and even relieve the strain caused by the volume expansion upon cycling.