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Sonochemically synthesized vanadyl phosphate dihydrate cathodes
Sonochemically Synthesized Vanadyl Phosphate
change in capacity under high discharge rate of 0.3
C is observed. Sonochemically prepared sample
exhibits also good reversibility for the
Telecommunication Basic Research Lab.,
electrochemical lithium insertion/extraction.
Electronics and Telecommunications Research
Preliminary results on the electrochemical
performance indicate that sonochemically
synthesized VOPO 4 2H2O can be a promising
cathode material for rechargeable lithium battery.
Recently, chemical bonding nature-potential level
correlation has been investigated for Nasicon-type
electrode materials Lix
M2(XO4)3 (M = transition
metal; X = S, P, As) [1,2], where the higher ionicity of the M-O bond was found to give rise to the higher
potential of the Mn+/M(n+1)+ redox couple. Electrochemical lithium insertion in the
rhombohedral Li3V2(PO4)3  and the β-form of
VOPO4  was investigated. The potentials in
batteries based on these materials showed 3.77 and
3.98 V vs. Li+/Li, respectively. However, less
attention has been paid to vanadyl phosphate
dihydrate VOPO 4 2H2O because of being more interested in its catalytic property. VOPO 4 2H2O has been usually prepared by long-term boiling of a V
suspension in aqueous phosphoric acid according to
Ladwig’s method . We have developed a method for rapid synthesis of VOPO 4 2H2O.
In this paper, we report on sonochemical
. First discharge curve for the
follows. The aqueous phosphoric solution contained
Goodenough, S. Okada, H. Ohtsuka, H. Arai, and
J. Yamaki, Solid State Ionics
, 92, 1 (1996)
2O5 powder was exposed to high-intensity
ultrasound radiation for 15 min by employing a direct
2. C. Masquelier, A.K. Padhi, K.S. Nanjundaswamy,
immersion titanium alloy horn operating at 20 kHz,
and J.B. Goodenough, J. Solid State Chem.
with intensity of ~ 70 W/cm2. The temperature of the
reaction solution rose to 70 oC during sonication. The
resulting yellow solid was filtered, washed several
Masquelier, and L. Nazar, Chem. Mater.
, 12, 3240
times with acetone and dried at ambient atmosphere.
The synthesized material was characterized
4. J. Gaubicher, T. Le Mercier, Y. Chabre, J.
using X-ray diffraction (XRD), Fourier transformed
Angenault, and M. Quarton, J. Electrochem. Soc.
infrared (FTIR), transmission electron microscopy
(TEM) and thermogravimetric analysis (TGA).
5. G. Ladwig, Anorg. Allg. Chem.
, 338, 266 (1965)
Electrochemical studies were carried out using a
Macfile-II galvanostat system. A Swagelok-type cell
consisted of the mixture of the synthesized
VOPO 4 2H2O, the Super P black (MMM Carbon Co.)
and the polytetrafluoroethylene (70:20:10 wt%) as a
cathode, Li foil as an anode and 0.95 M solution of
LiPF6 in ethylene carbonate/ dimethyl carbonate
(50:50 vol%) as an electrolyte, which was
discharged and charged under the constant current
ranging from 4.16 to 39.4 mA/g. Results and Discussion
XRD confirms the phase purity of tetragonal
VOPO 4 2H2O with a = 6.2 Å and c = 7.4 Å. The particle size of the sonochemically synthesized material is determined to be 1 – 3 µm by TEM, which is smaller than the size (about 10 µm) of the sample prepared by the long-term refluxing method.
Electrochemical reduction of VOPO 4 2H2O under
a constant current of 4.16 mA/g (corresponding to 0.03 C) shows that almost 1 Li can be inserted, which results in the capacity of 135 mAh/g (Fig. 1). The cell potential shows a plateau at 3.6 V. Little
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