Low temperature performance of sodium–nickel chloride batteries with NaSICON solid electrolyte

• The phase transition of NaSICON was convinced by high temperature XRD and electrochemical study.
• NaSICON was used as a new type solid electrolyte for sodium–nickel chloride batteries successfully operable at 195 °C.
• Significant enhanced rate performance was obtained for NaSICON battery cells compared with β″-Alumina cells.

A new type of sodium–nickel chloride batteries using NaSICON solid electrolytes (Na1 + xZr2SixP3 − xO12) was successfully investigated at much lower operation temperature of 195 °C compared with that of conventional Zebra batteries adapting same electrochemistry. The gradual phase transition in NaSICON from monoclinic to rhombohedral was perceived at 100–180 °C by high temperature XRD investigation. From symmetrical Na/NaSICON/Na cell test, the abrupt increase of cell resistance was observed at 177–180 °C, which reveals the change of ionic conduction mechanism in NaSICON solid electrolytes due to phase transformation. The sintered NaSICON solid electrolytes exhibit full densified morphology but somewhat lower average flexural strength of ~ 98 MPa compared with that reported for the β″-Alumina solid electrolytes commercially available. The low temperature electrochemical performances of sodium–nickel chloride batteries were compared by using NaSICON and β″-Alumina solid electrolytes at 195 °C. The lower internal resistances of the cell using NaSICON were confirmed by impedance spectroscopy and cyclic voltammetry tests. Also proto-type cell tests revealed the clear advantages of NaSICON cell (N-Cell) over β″-Alumina cell (β-Cell) at low temperature performances below 200 °C due to high Na+ ionic conductivity.