EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The replacement of the presently used liquid electrolytes by a non-flammable solid electrolyte is an important avenue to create safer batteries. The Natrium Superionic CONductor (NaSiCON) Na1+xZr2SixP3-xO12 (0 < x < 3) that displays high bulk ionic conductivity and good stability towards other NaSiCON-based electrodes is a good solid electrolyte in NaSiCON-based batteries. Here, we analyze the thermodynamic properties of the NaSiCON electrolyte by constructing the Na1+xZr2SixP3-xO12 phase diagram, based on density functional theory calculations, a cluster expansion framework, and Monte Carlo simulations. Through the phase diagram, we identify the concentration domains providing the highest Na+-ion conductivity and previously unreported phase-separation behaviour across three different single-phase regions. Our work is an important addition in understanding the thermodynamics of NaSiCON-based materials and in the development of inexpensive Na-ion batteries. From our results we propose that the addition of SiO44- moieties to single-transition metal NaSiCON-phosphate-based electrodes will slow significantly the kinetics toward phase separation. Based on the phase diagram, we further analyse the effect of the local environments on the ion mobilities based on Nudged Elastic Band simulations. These clarify the intricate mechanisms of ion transport of NaSiCON materials and their optimization.

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