title: Nano-sized Mo- and Nb-doped TiO2as anode materials for high energy and high power hybrid Li-ion capacitors.
abstract: Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5-3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg-1at a power of 180 W kg-1with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg-1at 180 W kg-1better, showing 36 Wh g-1at 3200 W kg-1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0-3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg-1and 2.5 Wh kg-1at power densities of 6700 W kg-1and 14 000 W kg-1, respectively.
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom. School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, 923-1211 Nomi, Ishikawa, Japan.
authors.forename: Dustin
authors.initials: D
authors.lastname: Bauer
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Roberts
authors.forename: Noriyoshi
authors.initials: N
authors.lastname: Matsumi
authors.forename: Jawwad A
authors.initials: JA
authors.lastname: Darr