Multifunctional TiO2@C/MnO2 Core@Double-shell Nanowire Arrays as High
Performance 3D Electrode for Rechargable Li-ion batteries
Jin-Yun Liao,a Drew Higgins,a Gregory Lui,a Victor Chabot,a Xingcheng Xiao,*,b and Zhongwei
Chen*,a
a
Department of Chemical Engineering, Waterloo Institute for Nanotechnology, University of
Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1
b
General Motors Global Research & Development Center, 30500 Mound Road, Warren,
Michigan 48090, United States
Experimental Methods
Preparation of TiO2@C/MnO2 core@double-shell nanowire arrays: First a piece of titanium
foil was ultrasonically cleaned in water, acetone and ethanol for 15 min each, before placing it
against the wall of a 40 ml Teflon-lined stainless steel autoclave filled with 30 mL of 1 M NaOH
in aqueous solution. Then, the sealed autoclave was put in an electric oven at 220 °C for 18 h.1,2
After completion of the hydrothermal reaction, the titanium foil covered with Na2Ti2O5·H2O
nanowires was immersed in 0.5 M HCl solution for 3 h to replace Na+ with H+, rendering
H2Ti2O5·H2O nanowire arrays on Ti foil. Then, the Ti foil was removed from HCl solution and
rinsed with water and ethanol, then dried at 60 °C. The TiO2 nanowire arrays were obtained after
heat treatment of the H2Ti2O5·H2O nanowire arrays in a tube furnace at 550 °C for 3 h in air with
a ramping rate of 2 ºC/min. Second, the as-prepared TiO2 nanowire arrays underwent another
hydrothermal process with a 0.03 M glucose solution at 180 °C for 18h, followed by heat
treatment at 500 °C for 3 h in Ar to obtain the carbon coated TiO2 nanowire arrays (TiO2@C).
Finally, the electro-active MnO2 nanoparticle coatings were decorated onto these TiO2@C
nanowire arrays by immersing them into 0.03 M KMnO4 aqueous solution for 18 h at room
temperature. A thin layer of MnO2 nanoparticles was obtained on the TiO2@C nanowires.
Subsequently, the MnO2 nanoparticles coated TiO2@C nanowire arrays (TiO2@C/MnO2) were
rinsed with deionized water and dried at 100 °C overnight in a vacuum oven.
Materials Characterization: The phase purity and crystal structure of the obtained materials
were studied using an X-ray diffraction (XRD, Bruker AXS D8 Advance) system with Cu Kα
radiation from 5-70º. Field emission scanning electron microscopy (FE-SEM, LEO FESEM
1530), transmission electron microscopy (TEM, JEOL 2010F, equipped with energy dispersive
X-ray spectroscopy (EDS)) and high-resolution transmission electron microscopy (HRTEM)
were used to examine the morphologies, crystalline structures, and element distributions of the
samples. The Raman spectra were collected on a Bruker Senterra spectrometer equipped with a
20mW diode laser, using an excitation wavelength of 532 nm and the spectrum range was from
45 cm-1 to 4000 cm-1. X-ray photoelectron spectroscopy (XPS, Thermal Scientific K-Alpha XPS
spectrometer) was used to investigate the Mn, C, and other element valences in TiO2@C and
TiO2@C/MnO2 nanowires.
Evaluation of Electrochemical Behavior: The electrochemical characterization was performed
using 2032-type coin cells with two-electrodes, assembled in an Ar-filled dry glove box using
TiO2-based nanowire arrays (TiO2, TiO2@C and TiO2@C/MnO2)/Ti-foil and Li metal as the
working electrode and counter electrode, respectively. 1M LiPF6 in ethyl carbonate
(EC)/dimethyl carbonate (DMC) (3/7 by volume) was used as an electrolyte and two pieces of
porous 25 µm thick polypropylene were used as separators. The discharge-charge cycling was
performed between 0.01-3 V (vs. Li/Li+) at room temperature, using different C-rates from 0.1C
to 30 C on a battery tester (Neware) (1 C=335 mA/g). Electrochemical impedance spectroscopy
(EIS) was carried out in the frequency range from 100 KHz to 100 mHz on an electrochemical
workstation (Versa STAT MC, Princeton Applied Research), and the amplitude of the alternating
voltage was 10 mV. The impedance parameters were determined by fitting of the impedance
spectra using Z-view software. Cyclic voltammetry (CV) testing was performed between 0.01
and 3 V (vs Li/Li+) with a scan rate of 0.1 mV s-1. To determine the active electrode mass and
prepare half-cells for testing we removed one side of the nanowires, the change was calculated as
the active mass. The diameter of the electrodes is 1 cm, and the average mass loading of the
nanowire arrays within the coin cells are around 0.8 mg for TiO2, 1.0 mg for TiO2@C and 1.2 mg
for TiO2@C/MnO2 nanowire arrays.
Figure S1. XRD patterns of the nanowire arrays supported on Ti foil substrates.
Figure S2. Full range of the XPS spectrum for TiO2@C/MnO2 nanowires (a), and the high
resolution K2p XPS spectra of both TiO2@C and TiO2@C/MnO2 nanowires (b).
Figure S3. TEM images and SAED patterns of TiO2 nanowire (a), and TiO2@C core@shell
nanowire (b).
Figure S4. TEM image and EDS line scan spectrum of Ti, O, Mn and C for TiO2@C/MnO2
core@double-shell nanowire.
1
Liu, B.; Boercker, J. E.; Aydil, E. S. Nanotechnology 2008, 19, 505604.
2
Liao, J. Y.; Lei, B. X.; Chen, H. Y.; Kuang, D. B.; Su, C. Y. Energy Environ. Sci. 2012,
5, 5750.