High ionic conducting NaSICON enabled by mechanical activation enhanced reaction

NaSICON-type materials have been investigated since 70s and become an attractive candidate for energy storage and many other emerging applications owing to their good ionic conductivity. However, further enhancement in ionic conductivity at room temperature (RT) and facile processing methods to synthesize NaSICON in an energy efficient and low cost manner are required to enable various emerging applications. This study reports a new processing method, termed as mechanical-activation-enhanced reactions, to address these challenges simulta-neously. It is shown that Na3Zr2Si2PO12 membranes with little or no impurity, relative densities-95 %, and total ionic conductivity of 1.53 x 10-3 S/cm at RT can be synthesized through one high-energy ball milling process followed by one step of high-temperature reaction(s) and sintering at the same time, greatly simplifying the procedure for synthesizing NaSICON membranes while achieving the outstanding ionic conductivity reported in the literature. It is found that mechanical activation at RT has significantly increased the reactivity of the re-actants, accelerated the reaction kinetics in forming NaSICON, and increased the bottleneck size of the NaSICON crystal for Na ion transport. This study has provided a new direction to synthesize high performance, low cost NaSICON membranes and offered guidelines for achieving NaSICON membranes with superior ionic conductivity in the future.