A High-rate and Long-life Intermediate-temperature Na-NiCl2 Battery with Dual-functional Ni-carbon Composite Nanofibers Network.

: Improved power and cycle performances have been eagerly required in intermediate-temperature sodium-metal halide (Na-MH) batteries. The existence of the low conductivity NiCl2 layer and the growth of the Ni and the NaCl particles limit the broader application of Na-NiCl2 battery. Herein, nickel-carbon nanofiber composite networks (NCCNs) are synthesized by a multisolution electrospinning method to construct a novel three-dimensional cathode for Na-NiCl2 battery. The battery with the NCCNs-based cathode shows significant improvement on rate and cycle performance at 190 oC. A capacity twice than that of a conventional electrode after 100 cycles and 80% of the initial capacity after 400 cycles are observed at a current of 57 mA g-1. The NCCNs-based cathode even normally works more than 350 cycles without obvious degradation at a high current of 338 mA g-1, that is, a rate of 2C. Furthermore, in-situ electrochemical impedance spectroscopy reveals faster electron and ion transport process precisely on the charging and discharging processes of the NCCNs-based cathode. It is found that the NCCNs can not only play the role of a continuous conductivity network, but also limit the growth of grains. With the blocking effect of the carbon fibers, the volume expansions of Ni and NaCl grains are well restricted and their sizes were smaller than 500nm and 7μm after 50 cycles, respectively.