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Exploring the Influence of V2O5 Content on the Mechanism of Electrical Transport in the Na2O-V2O5-Nb2O5-P2O5 Glass System: A Perspective through Model-Free Scaling Procedures
1 , 1 , 2 , 2 , 3 , 4 , * 1
1  Division of Materials Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, Zagreb, Croatia
2  Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic
3  Department of Physics, Faculty of science, Bijenička cesta 32, 10000 Zagreb, Croatia
4  Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, Zagreb, Croatia
Academic Editor: Cosimo Trono

Published: 31 October 2023 by MDPI in 4th International Electronic Conference on Applied Sciences session Poster Session

Sodium-vanadium-phosphate-based materials have garnered significant interest as cathodes for high-rate sodium-ion batteries, owing to their stable framework, minimal volume change, thermodynamic stability, and excellent sodium storage capacity with fast ion transport kinetics1. Furthermore, as these materials consist of both alkali and transition metal (TM) ions, which can exist in various oxidation states (V4+, V5+), these systems can exhibit the mixed ionic-polaronic conduction mechanism. Such feature has proven to be highly effective in facilitating the intercalation and deintercalation of alkali ions2. Another crucial property of cathode materials is thermal stability which can be significantly enhanced by incorporating metal oxides such as Nb2O53. Based on this premise, the current study focuses on investigating the electrical properties of glasses within the Na2O-V2O5-Nb2O5-P2O5 system. The P2O5 component is gradually replaced by Nb2O5 while maintaining constant Na2O and V2O5 content. By varying the concentration of V2O5 (10 and 25 mol%), the influence of its content on the electrical transport mechanism is examined, enabling the evaluation of its possible polaronic contribution. Solid-state impedance spectroscopy (SS-IS) is employed to examine electrical transport across a wide frequency (0.01 Hz to 1 MHz) and temperature (–90 °C to 240 °C) range and the conductivity spectra are studied in detail using two model-free scaling procedures, namely Summerfield and Sidebottom scaling. The successful construction of conductivity master curves for all glasses with lower V2O5 content (10 mol%) validates the time-temperature superposition (TTS) and confirms a purely ionic conduction mechanism, indicating that V2O5 does not contribute to electrical conductivity via a polaronic mechanism. However, master curves cannot be obtained for glasses with higher V2O5 (25 mol%) and low Nb2O5 content (0 and 5 mol%), suggesting the presence of mixed ionic-polaronic conductivity with a dominant polaronic contribution. Furthermore, with the addition of Nb2O5 above 10 mol%, the ionic conductivity mechanism prevails. The findings of this study provide valuable insights into the mixed-conductive glass system and role of V2O5 and/or Nb2O5, and demonstrate the ability to tune the mechanism of electrical conductivity by adjusting the content of oxide glass and its ratio.

This work is supported by the CSF under the projects IP-2018-01-5425 and DOK-2021-02-9665.

1. Wang, C. et al. A multiphase sodium vanadium phosphate cathode material for high-rate sodium-ion batteries. J. Mater. Sci. Technol. 66, 121–127 (2021).
2. Wang, C. & Hong, J. Ionic/electronic conducting characteristics of LiFePO4 cathode materials. Electrochem. Solid-State Lett. 10, A65 (2007).
3. Getachew, B., Ramesh, K. P. & Honnavar, G. V. Nickel ferrite doped lithium substituted zinc and niobo vanadate glasses: thermal, physical, and electrical characterization. Mater. Res. Express 7, 095202 (2020).

    Keywords: phosphate glasses; electrical properties; ionic conductivity; polaronic conductivity; impedance spectroscopy; conductivity spectra; scaling procedures; model-free