High-Rate and Long-Life Intermediate-Temperature Na-NiCl2 Battery with Dual-Functional Ni-Carbon Composite Nanofiber Network.

Improved power and cycle performances are 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 composite nanofiber (NCCN) networks are synthesized by a multisolution electrospinning method to construct a novel three-dimensional cathode for Na-NiCl2 battery. The battery with the NCCN-based cathode shows significant improvement in rate and cycle performance at 190 °C. A capacity twice 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 NCCN-based cathode 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 processes precisely on the charging and discharging processes of the NCCN-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 500 nm and 7 μm after 50 cycles, respectively.