Multi-variable Bayesian optimization for a new composition with high Na+ conductivity in the Na3PS4 family†
Abstract
Na3PS4 is an archetypal room-temperature (RT), Na+-conducting, solid-state electrolyte. Various compositional modifications of this compound via iso/aliovalent substitution are known to provide a high ionic conductivity (σion) that is comparable to that of liquid electrolytes. In this work, we implemented a Bayesian optimization (BO) algorithm to discover new compositions with a high σion in a multi-dimensional search space. BO has attracted a great deal of attention in materials research since it is successfully used as a closed-loop optimization strategy for materials discovery. The systematically designed search space used for our BO implementation consisted of compositional variables (A = Ca2+, Y3+, La3+; M1 = P5+, Sb5+; M2 = Si4+, Ge4+, Sn4+; Q = S2−, Se2−, Te2−; X = Cl−, Br−, I− in (Na, A)3δ(M1, M2, W)(Q, X)4) and processing variables (synthetic temperature and time). Na2.81(W0.22Si0.10Sb0.68)S3.93Br0.07 selected through BO was further refined via logical reasoning. Subsequently, Br-free Na2.88(W0.22Si0.10Sb0.68)S4 was discovered. Heavily co-doped Na3SbS4 by Si4+ and W6+ show high σion (20.2 and 7.4 mS cm−1) at RT and −20 °C, respectively, which can be ascribed to the notably low activation barrier (0.14 eV) in the Na3PS4 family. Herein, a low electronic conductivity (2 × 10−7 S cm−1) and stable Na plating/stripping is also discussed. These types of behavior suggest that Na2.88(W0.22Si0.10Sb0.68)S4 could be a promising solid-state electrolyte (SSE) of the Na3PS4 family.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers