Correlated Migration Invokes Higher Na+‐Ion Conductivity in NaSICON‐Type Solid Electrolytes. Issue 42 (1st October 2019)

• Record Type: Journal Article
• Authors: Zhang, Zhizhen; Zou, Zheyi; Kaup, Kavish; Xiao, Ruijuan; Shi, Siqi; Avdeev, Maxim; Hu, Yong‐Sheng; Wang, Da; He, Bing; Li, Hong; Huang, Xuejie; Nazar, Linda F.; Chen, Liquan
• Is Part Of: Advanced energy materials. Volume 9:Issue 42(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-10-01
• Subjects: correlated migration -- high energy site -- ion conduction mechanism -- NaSICON -- solid electrolytes; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201902373
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: Na super ion conductor (NaSICON), Na1+ n Zr2 Sin P3– n O12 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 Na3 Zr2 Si2 PO12 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. Abstract : A new high‐energy Na site is found in the Na super ion conductor (NaSICON) structure. Theoretical studies reveal that correlated migration is the dominant conduction mechanism and can be invoked by increasing Na + ‐ion concentration. More importantly, a strategy is experimentally validated that enhances ion conductivity, namely, by forcing cations into high‐energy sites via repulsive forces, as a result the energy barrier for cation migration can be lowered.