Ni-less cathode with 3D free-standing conductive network for planar Na-NiCl2 batteries

Abstract

The sodium-nickel chloride (Na-NiCl2) batteries technology has been considered as one of the most promising candidates for large-scale electrical energy storage application owing to its abundant electrode material resource, high energy density and safety. However, ultra-excessive Ni in the cathode leads to high material cost and the growth of cathode particles during cycles makes degradation of batteries performances, which hinder the further application of Na-NiCl2 batteries. To address these challenges, we designed a free-standing Ni-less cathode with Ni/NaCl particles uniformly distributed in the three-dimensional (3D) conductive matrix constructed by carbonfiber (CF) and multiwalled carbon nanotubes (MWCNTs). The 3D hierarchical structure synthesized by low-cost vacuum filtration method can offer sufficient void space to accommodate the growth of NaCl particles and effectively enhance the electronic conductivity of the cathode. When the molar ratio of Ni/NaCl in the cathode is reduced to 1.0, a specific capacity of 90 mAh g−1 for planar Na-NiCl2 batteries can be achieved after 170 cycles at 190 °C with a capacity retention of 67%, which is higher than that of traditional tubular Na-NiCl2 batteries.