Correlated migration invokes higher Na+‐ion conductivity in NaSICON‐type solid electrolytes

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Na super ion conductor (NaSICON), Na1+nZr2SinP3–nO12 is considered one of the most promising solid electrolytes; however, the underlying mechanism governing ion transport is still not fully understood. Here, the existence of a previously unreported Na5 site in monoclinic Na3Zr2Si2PO12 is unveiled. It is revealed that Na+‐ions tend to migrate in a correlated mechanism, as suggested by a much lower energy barrier compared to the single‐ion migration barrier. Furthermore, computational work uncovers the origin of the improved conductivity in the NaSICON structure, that is, the enhanced correlated migration induced by increasing the Na+‐ion concentration. Systematic impedance studies on doped NaSICON materials bolster this finding. Significant improvements in both the bulk and total ion conductivity (e.g., σbulk = 4.0 mS cm−1, σtotal = 2.4 mS cm−1 at 25 °C) are achieved by increasing the Na content from 3.0 to 3.30–3.55 mol formula unit−1. These improvements stem from the enhanced correlated migration invoked by the increased Coulombic repulsions when more Na+‐ions populate the structure rather than solely from the increased mobile ion carrier concentration. The studies also verify a strategy to enhance ion conductivity, namely, pushing the cations into high energy sites to therefore lower the energy barrier for cation migration. © 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
Correlated-particle models, Charged particles, Solid electrolytes, Monoclinic lattices, Cations, Doped materials
Zhang, Z., Zou, Z., Kaup, K., Xiao, R., Shi, S., Avdeev, M., Hu, Y. S., Wang, D., He, B., Li, H., Huang, X., Nazar, L. F., & Chen, L. (2019) Correlated migration invokes higher Na+‐ion conductivity in NaSICON‐type solid electrolytes. Advanced Energy Materials, 9(42), 1902373. doi:10.1002/aenm.201902373