Environmentally friendly, inexpensive iron-titanium tunneled oxide anodes for Na-ion batteries

Within this paper, we investigate the electrochemical performance of NaFeTiO4, Na0.9Fe0.9Ti1.1O4, Na0.8Fe0.8Ti1.2O4 tunneled structured anodes for Na-ion batteries. Sol-gel synthesis enables to obtain anode materials characterized by improved morphology leading to enhanced electrochemical behavior in Na-ion batteries. Impedance spectroscopy and UV-VIS measurements reveal that electronic component dominates in total electrical conductivity, which is one order of magnitude higher for Na0.9Fe0.9Ti1.1O4, Na0.8Fe0.8Ti1.2O4 in comparison to NaFeTiO4. Among the studied materials, Na0.8Fe0.8Ti1.2O4 possesses the highest charge capacity of 180 mAh g−1 during the first cycle at C/20 and can retain 80% of the initial capacity after 30 cycles with an average charging voltage of 1.3 V vs. Na+/Na. Experiments in temperatures from −20 °C to +60 °C reveal that Na0.8Fe0.8Ti1.2O4 preserve a significant fraction of its capacity: 70 mAh g−1 at −20 °C and 177 mAh g−1 at 60 °C. Application of ether-based diglyme solvents instead of ester-based results in reduced irreversible reactions during the initial discharge-charge cycle, better performance under higher loads, and lower charge transfer and SEI resistance. The results prove that Na0.8Fe0.8Ti1.2O4 is an auspicious material for future low-cost Na-ion batteries with stable performance in a wide temperature range.