NaSICON: A promising solid electrolyte for solid-state sodium batteries

A surge of interest has been brought to all-solid-state batteries (ASSBs) as they show great prospects for enabling higher energy density and improved safety compared to conventional liquid batteries. Na Super Ionic CONductors (NaSICONs) proposed by Goodenough and Hong in 1976 are the most promising materials class for Na-based ASSBs owing to their excellent ion conductivity (>1mScm(-1)), high thermal and chemical/electrochemical stability, as well as good chemical/electrochemical compatibility with electrode materials. The major challenge facing NaSICON-type electrolytes is the generally high interfacial resistance and thus sluggish charge transfer kinetics across the NaSICON/cathode interface. Great endeavors in the past few years have led to progress in the improvement of the ion-conducting property, and a dramatic decrease in the NaSICON/electrode interface resistance. Excellent cycling performance and rate capability have been achieved through interface engineering. In this review article, we summarize the state-of-the-art findings for various derivatives of NaSICON structured solid electrolytes, with the aim of providing a deeper understanding of the underlying mechanism for the improvement of ion conductivity, and the intrinsic reasons for the enhanced interface charge transfer kinetics. These strategies can be readily extended to other solid electrolytes. We hope this review will inspire more work on NaSICON-type solid electrolytes and solid-state batteries.