An in-situ alloyed Ni-Fe Co-reaction electrode for high-stability and high-rate Na-metal halide batteries

Na-metal halide batteries are regarded as one of the most promising candidates for large-scale energy storage systems owing to their high energy density and high safety. However, the problems of low kinetics and poor stability caused by the low-conductive chlorides have restricted the development of Na-metal halide batteries. Here, we design a facile approach that combines electrospinning and electrodeposition to prepare electrodes with a nanostructured composite containing carbon nanofibers and Ni-Fe alloy (CNF@Ni-Fe alloy). It is confirmed that the Ni-Fe alloy can stably be oxidized and reformed when discharges from 2.36 V to 2.32 V. Benefiting from the unique nanoscale arrangement of Ni-Fe, the heterogeneous distribution of FeCl 2 and NiCl 2 effectively overcomes the block of low-conductive chlorides. Furthermore, the coreaction of Ni 2+ and Fe 2+ directly decreases the polarization potential, resulting in the improvement of reaction kinetics. Notably, batteries with the CNF@Ni-Fe alloy display a high specific capacity of 199.7 mAh g −1 and a capacity retention rate of 99% after 50 cycles at 0.6 C. The CNF@Ni-Fe alloy cathodes also deliver long-term stability with 104.5 mAh g −1 capacity retention after 600 cycles at 2 C and a good rate capability of 5 C.