engleski

The role of structural changes in sodium ion transport mechanism in phosphate glasses

The constant rise of special requirements for energy storage systems has resulted in a rapid increase in the research of materials suitable for solid electrolytes and electrodes in all- solid-state ion batteries. In demand for safer, more efficient and less costly solutions, the question arises whether more naturally abundant sodium can replace lithium in ion batteries [1, 2]. In this study, two sodium ion conducting glass series are investigated: 40Na2O–(60-x)P2O5– xGeO2 and 40Na2O–10B2O3–(50-x)P2O5–xGeO2, x=0– 30 mol% in order to verify the mixed glass former effect (MGFE). Glass former exchange resulted in the significant electrical conductivity enhancement for both systems. Such behaviour is related to the increased mobility of Na+ ions, due to the depolymerization of the (boro)phosphate network and the emergence of easily conductive pathways after germanate incorporation and formation of different mixed Ge/B/P structural units. With the help of 1D/2D MAS NMR techniques, we are able to determine and quantify structural units formed in the network and gain insight into local environment and links between these units, which is crucial for determining the sodium ion transport mechanism. For better understanding of ionic transport in phosphate glasses, these results are compared to the study of 40Na2O–(60-x)P2O5–xMoO3/WO3, x=0–50 mol% glasses. In these systems, the ionic conductivity also increases significantly, as P2O5 is replaced by MoO3/WO3 (conditional network formers) implying that the mixture of phosphate and molybdate/tungstate units in glass network strongly facilitates transport of Na+ ions similarly as in classical MGFE. The ability to adjust the electrical properties of these MGFE systems by simple compositional changes and structure tuning is a very useful feature for their specific use.

Phosphate glasses ; Mixed glass former effect ; Ion transport

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