Spray-drying synthesis of Na2Ti3O7 and electrochemical characterization using different electrolytes

Na2Ti3O7 is considered as a promising intercalation anode material for sodium ion batteries thanks to its low insertion potential (0.3V vs Na0/Na+) and relatively good theoretical capacity (178 mAh/g) [1,2,3]. Nevertheless, it has a poor long term cycling stability that still needs to be solved. Besides, the importance of the choice of the electrolyte for Na-ion batteries was recently reviewed [4]. We report here a new spray-drying synthesis of Na2Ti3O7. By contrast to the solid-state synthesis, the advantages of the spray-drying method are a high homogeneity of the precursors and good control of the particle size and morphology (typically spherical particles of 3-30 µm, depending on the injection mode, concentration, pressure, temperature, etc.). Therefore, the heat treatment time is decreased. In this work, we studied the formation mechanism of Na2Ti3O7. We identified sequences of intermediate phases, starting from spray-dried TiO2 and NaOH or Na2CO3 precursors. In order to improve the performances of our material, we also tested the influence of the electrolyte on the electrochemical performances in half cell. The effect of the solvent (PC, EC, DMC and Diglyme) but also of the salt (NaClO4, NaPF6, NaTFSI, NaFSI and NaOTf) was examined and significant differences were observed.

[1] Zukalová et al., Journal of Solid State Electrochemistry, 2018, 22, 2545–2552
[2] J. Nava-Avendaño et al., Journal of Material Chemistry A, 2015, 3, 22280-22286
[3] M. Zarrabeitia et al., Acta Materialia, 2016, 104, 125-130
[4] A. Ponrouch et al., Journal of Material Chemistry A, 2015, 3, 22-42