Rational design and synthesis of advanced Na3·32Fe2·34(P2O7)2 cathode with multiple-dimensional N-doped carbon matrix
The application of Na3·32Fe2·34(P2O7)2 sodium cathodes with abundant resources and robust structure is severely hindered by the poor electronic conductivity. A multiple-dimensional carbon matrix could provide a satisfactory electronic conductivity as well as facilitate structural stability via wrapping and bridging of the active material. With an analysis of the raw materials and their respective reactions, Na3·32Fe2·34(P2O7)2@C (NFP-Cs) composites with a hybrid carbon matrix have been synthesized. The reactions in the system result in versatile N-doped carbon structures, including thin carbon layers, carbon rods, carbon nanosheets and carbon scaffolds. This integrated carbon architecture wraps and bridges the Na3·32Fe2·34(P2O7)2 particles, not only promoting electronic conductivity, but also serving as a buffer to minimize volume changes and stabilize the structural integrity of the composite. Furthermore, the nitrogen doping could generate more defects and active sites, which provide improved conductivity and better redox activity. Finally, the synthesized composite material has demonstrated impressive rate capabilities (100 mAh g−1 at 0.1 C and 66 mAh g−1 at 20 C), and outstanding cycling stability (90.5% at 1 C after 1000 cycles, 89.9% at 5 C after 2000 cycles). This study takes the utmost advantage of the synthesis, which is also easily scaled-up for mass production.