High Power Sodium-Ion Batteries and Hybrid Electochemical Capacitors Using Mo or Nb-Doped Nano-Titania Anodes

Abstract:

Nano-sized anatase (TiO₂) and doped anatase (Mo_0.1Ti_0.9O₂ and Nb_0.25Ti_0.75O₂) materials (ca. 5 nm) were synthesized using continuous hydrothermal flow synthesis and evaluated as negative electrodes in Na-ion batteries and hybrid capacitors. Na-ion half-cells (vs. Na metal counter electrodes) for the Mo-doped titania (Mo_0.1Ti_0.9O₂) and Nb-doped titania (Nb_0.25Ti_0.75O₂) electrodes both showed significantly higher specific discharge capacities than undoped anatase (ca. 75 mAh g⁻¹ compared to only 30 mAh g⁻¹ for undoped TiO₂ at 1 A g⁻¹). This improved performance was attributed to higher pseudocapacitive contributions to charge storage, as well as improved sodium ion diffusion and lower charge transfer resistance. Na-ion hybrid electrochemical capacitors (Na-HECs) were made from the electrodes with activated carbon positive electrodes. As expected, Na-HECs using doped titania showed superior performance to the undoped anatase, with power densities up to 10.5 kW kg⁻¹ or energy densities of over 60 Wh kg⁻¹ (based on the weight of active material in both anode and cathode). The Mo_0.1Ti_0.9O₂/AC Na-ion hybrid capacitor also showed excellent specific capacitance retention of ca. 75% over 3000 cycles at 5 mA cm⁻² (1 A g⁻¹).

Authors:

Dustin Bauer, Alexander J. Roberts, Sai Gourang Patnaik, Dan J. L. Brett, Paul R. Shearing, Emma Kendrick, Noriyoshi Matsumi, Jawwad A. Darr

Organisation / Departament Address:

Department of Chemistry, University College London, London WC1H 0AJ, United Kingdom