Caging NaV(PO)F Microcubes in Cross-Linked Graphene Enabling Ultrafast Sodium Storage and Long-Term Cycling.

Sodium-ion batteries are widely regarded as a promising supplement for lithium-ion battery technology. However, it still suffers from some challenges, including low energy/power density and unsatisfactory cycling stability. Here, a cross-linked graphene-caged NaV(PO)F microcubes (NVPF@rGO) composite via a one-pot hydrothermal strategy followed by freeze drying and heat treatment is reported. As a cathode for a sodium-ion half-cell, the NVPF@rGO delivers excellent cycling stability and rate capability, as well as good low temperature adaptability. The structural evolution during the repeated Na extraction/insertion and Na ions diffusion kinetics in the NVPF@rGO electrode are investigated. Importantly, a practicable sodium-ion full-cell is constructed using a NVPF@rGO cathode and a N-doped carbon anode, which delivers outstanding cycling stability (95.1% capacity retention over 400 cycles at 10 C), as well as an exceptionally high energy density (291 Wh kg at power density of 192 W kg). Such micro-/nanoscale design and engineering strategies, as well as deeper understanding of the ion diffusion kinetics, may also be used to explore other micro-/nanostructure materials to boost the performance of energy storage devices.