The synthesis and characterization of a Na₃V₂(PO₄)₃ cathode material for room-temperature sodium-ion battery is reported. The NVP material was prepared by a two-step process via sol-gel nitrate combustion method for precursor preparation and subsequent pyrolysis under Argon. Sodium-ion batteries have emerged as a promising candidate for large-scale energy storage due to sodium’s abundance and low cost of raw materials. However, in order to justify lower energy densities compared to Li-ion systems, Co-containing cathodes have to be avoided.[1,2]

The materials have been investigated using SEM, EDX, XRD and TOF-SIMS methods. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD).

The electrode slurry was prepared by mixing the active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto aluminium foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. The half-cells (EL-Cell GmbH) were assembled and electrolyte mixtures prepared in an Argon-filled glovebox (O₂ < 0.1 ppm, H₂O < 0.1 ppm). Sodium metal was used as counter and reference electrode and 1M NaClO₄ in propylene carbonate (PC) as the electrolyte in half-cell measurements.

SEM image of the NVP cathode surface in Fig. 1a shows homogeneous distribution of NVP particles and Super P carbon. The NVP particles are of 300 – 500 nm in diameter. The rate-performance of the NVP electrode (Fig. 1b) can be improved by creating a carbon shell around the particles.

The results of single cell measurements for optimized NVP cathode and Glucose-derived Hard Carbon [3–5] anode will be discussed.

Acknowledgements

The present study was supported by European Regional Development Fund (Centres of Excellence TK141 (2014-2020.4.01.15-0011) and TK117 (3.2.0101–0030), TeRa project SLOKT12026T, Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026), “Institutional development programme for research and development and higher education institutions” (ASTRA) (Graduate School of Functional Materials and Technologies, Materials Technology Projects SLOKT12180T and SLOKT12181T, Energy Technology Project SLOKT10209T), Estonian Research Council (Institutional Research Grant IUT20–13, Personal Research Grant PUT1033 and by NAMUR project 3.2.0304.12-0397. Mr. Väli thanks Estonian Students Fund in USA for financial support.

References

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