Nanostructured anatase TiO2 anodes combined with ionic-liquid based-electrolytes for safe Na-ion batteries

Abstract

Na-ion batteries (NIBs) are promising candidates to be used in sustainable energy storage systems (ESS) because sodium reserves are abundant and ubiquitous around the world. As emerging technology, searching of new active electrode materials are one of the most active research lines in NIBs. Among the negative electrode (anode) materials, anataseTiO2-based anodes with low working voltage, low cost and environmental friendliness are attracting much attention (1). To improve the electrochemical performances of this kind of anodic materials, especially at elevated currents, to dispose of nanostructured TiO2-based anodes is a valuable way. Following an original synthesis procedure that combines thermally-driven self-assembly of nanomicelles with seeding-assisted chemistry, preparation of mesoporous anatase TiO2 nanostructures (NSTiO2) with uniform colloidal size and good textural properties were performed (2). Managing the synthesis conditions, we have prepared spherical nanostructures with tailoring primary and secondary particle sizes. FE-SEM studies showed that anatase nanocrystals are assembled into spherical nanostructures with monodispersed colloidal size (Fig. 1a). Ionic liquids based-electrolytes, with low volatility and non-flammability, allow improving the safety of rechargeable batteries (3). Thus, the electrochemical properties of the NS-TiO2 samples were evaluated in Na-half cells using the Pyr14TFSI ¿NaTFSI as ionic-liquid based electrolyte, at several temperatures.As an example, rate capability performances are compared in Fig. 1b. The observed differences will be explained considering the sophisticated morphological features of the synthesized NSTiO2. The A11-50 sample, with primary particles of 11nm assembled in nanostructured spheres of 50 nm, exhibits the high reversible capacity of ¿230 mAhg-1 at 0.2C, and it is able to retain 82% of this capacity at 1C (336 mAg-1). Cells assembled with the A11-50 sample as anodic material combined with ionic liquid based-electrolytes have high potentially to be used in large-size Na-ion batteries where high safety is mandatory.