Electrochemical Property of Cobalt Vanadium Oxide CoV3O8 for ...

Electrochemical Property
of Cobalt Vanadium Oxide CoV 3 O 8
for Lithium Ion Battery
Graduate School of Energy Science,
Kyoto University, Japan
Shin-nosuke Ichikawa,
Mitsuhiro Hibino, Takeshi Yao

Introduction
Transition metal oxides have been extensively studied in terms of electrode
materials for lithium ion batteries.
Vanadium oxides are one of the most promising materials due to
availability, low toxicity, and low cost.
Vanadium oxides are liable to collapse structurally by repetitions of
discharge and charge, leading to capacity fade.
With a view to improve such poor cycle ability, variety of vanadium
oxides have been prepared, for example, amorphous vanadium pentoxide
V 2 O 5 , and vanadium based complex oxides, LiV 3 O 8 , NiO-V 2 O 5 , TiO-V 2 O 5
etc.
In this study,
we investigate one of vanadium oxides CoV 3 O 8
toward development of novel electrode materials for lithium ion batteries.

Previous knowledge of CoV 3 O 8
CoV 3 O 8 has been synthesized by hydrothermal method for the first time,
and its single crystal structure has been analyzed by Oka and Yao[1].
CoV 3 O 8 has tunnel space along the c axis in the crystal structure and is
expected to have good electrochemical performance.
VO 4 Tetrahedron
VO 5 Bipyramid
MO 6 (M=Co,V) Octahedron
b
a
Fig. Polyhedral representation of the crystal
structure of CoV 3 O 8 projected onto ab plane.
[1] Y. Oka, T. Yao, N. Yamamoto and Y. Ueda,
J. Solid State Chem., 141, 133-139(1998).

Aim of this study
Aim of this study is to develop cobalt vanadium oxide CoV 3 O 8 into an
electrode material for lithium ion battery.
In order to investigate the electrochemical property of CoV 3 O 8 , we need
enough amount of this sample.
But, if CoV 3 O 8 is synthesized by hydrothermal method, we can obtain only
a small amount of the product.
In this study
CoV 3 O 8 is synthesized by solid-state reaction in order to prepare enough
amount, and examined as an electrode material for lithium ion battery.

Method : Preparation and structural analysis
Preparation and structural analysis of CoV 3 O 8
CoO V 2 O 4
V 2 O 5
• mixed in the molar ratio of Co:V:O = 1:3:8
• pressed cold-isostatically into a pellet
• sealed in a silica tube
• heat-treated at 600 o C for three days
CoV 3 O 8
• Powder X-ray diffraction pattern was taken.
• The crystal structure was analyzed
by the Rietveld method.

Method : Electrochemical measurement
Electrochemical measurement of CoV 3 O 8
Three electrode cell
Working electrode : active material, acetylene black, poly(tetrafluoroethylene)
in the weight ratio 80:15:5
Counter electrode : lithium metal
Reference electrode : lithium metal
Electrolyte : 1 mol dm -3 LiClO 4 in Ethylene carbonate and
1,2-Dimethoxyethane (1:1 v/v%)
Cyclic voltammetry
Potential : between 1.5 and 4.0V
vs. Li + /Li
Scan rate : 0.1mV s -1
Discharge-charge cycle test
Potential : between 1.5 and 4.0V
vs. Li + /Li
Current density : 80mA g -1

Method : Structural analysis
Investigation of structural change of CoV 3 O 8
induced by repetitions of discharge and charge
The electrode material after 21st discharge
• detached from the electrochemical cell
• placed on a zero background plate of quartz
• set in a sealed holder in a argon gas system
Powder X-ray diffraction pattern was taken.

Result : X-ray diffraction and the Rietveld method
CoV 3 O 8 obtained by solid-state reaction
CoV 3 O 8 obtained by hydrothermal method
Same crystal structure
Intensity / count
15000
10000
5000
R wp = 0.091
R B = 0.049
R F = 0.028
GOF = 2.77
Δ
0
2500
0
-2500
10 20 30 40 50 60
2θ -MoKα / o
Fig. Rietveld result for CoV 3 O 8 .
935 reflections
The calculated XRD pattern
agreed with
the observed XRD pattern

Result : Cyclic voltammetry
Current density / mA g -1
80
40
0
-40
-80
-120
-160
1.95V
2.1V
around 2.7V
2.4V
0.1mV / s
1st cycle
2nd cycle
1.6 2.0 2.4 2.8 3.2 3.6 4.0
Potential vs. Li + /Li / V
Fig. Cyclic voltammogram of CoV 3 O 8 .
0.72
0.36
0.00
-0.36
-0.72
-1.08
-1.43
Current / mA

Result : Discharge-charge cycle test
Potential vs. Li + /Li / V
4.0
3.6
3.2
2.8
2.4
2.0
1.6
20
1 2
2.4V
2.1V
1.95V
Around 2.7V
0 20 40 60 80 100 120
Specific capacity/mAh g -1
Fig. Discharge-charge curves of CoV 3 O 8 .

Result : Discharge-charge cycle test
Potential vs. Li + /Li / V
4.0
3.6
3.2
2.8
2.4
1
2
20
Specific capacity / mAh g -1
0 50
2.0
20 Good cycle performance
1.6
0 20 40 60 80 100 120
0
10 20 30 40
Specific capacity/mAh g -1 Cycle
Fig. Discharge-charge curves of CoV 3
O 8
. Fig. Discharge and charge capacities of CoV 3
O 8
.
120
100
80
60
40
discharge
charge
Lithium reacted electrochemically
with CoV 3 O 8 reversibly.
After the 2nd cycle, coulomb
efficiency was almost unity.

Result : XRD pattern
• No peak angles of CoV 3 O 8
changed.
• The intensity of the peaks
of CoV 3 O 8 declined.
• Unidentified peaks appeared.
Fig. XRD profiles of the electrode material after 21st discharge
and the initial CoV 3 O 8 as a reference.
Lithium
inserted

Interpretation
Potential vs. Li + /Li / V
4.0
3.6
3.2
2.8
2.4
2.0
1
2
20
Large slope
1.6
0 20 40 60 80 100 120
Specific capacity/mAh g -1
This behavior implies
• Amorphous phase is generated during the first discharge process.
• Lithium is inserted into and extracted from the newly generated
amorphous phase after the second cycle.

Interpretation
Intensity (a.u.)
Fig. XRD profiles of the electrode material after
21st discharge and the initial CoV 3 O 8 as a reference.
The intensity of the peaks decreased.
Fig. XRD profile of the electrode
material after 21st discharge.
The halo appeared around 30 o
The generation of amorphous phase
Good reversibility

Summary
CoV 3
O 8
, which has tunnel space along the c axis in the crystal structure,
was synthesized by solid-state reaction.
Both electrochemical measurements and XRD indicated the following.
For the first lithium insertion into CoV 3
O 8
, the crystal phase of CoV 3
O 8
was changed into amorphous phase.
The amorphous phase is allowed to discharge and charge reversibly
after the second cycle.
The good cycle performance of CoV 3
O 8
may be caused by lithium
insertion into and extraction from the generated amorphous phase.
We concluded that
CoV 3
O 8
is promising for an electrode material of lithium ion battery.

XRD profile of zero background plate of quartz
500
Intensity / count
400
300
200
Zero background plate of quartz
100
0
10 20 30 40 50 60 70 80 90
2θ-CuKα / o
Fig. XRD profile of zero background plate of quartz

XRD profiles : Amorphous phase
Initial CoV 3 O 8
Electrode material after 21st discharge
Intensity (a.u.)
10 20 30 40 50 60 70 80 90
2θ-CuKα / o

XRD profiles : Intensity of the peaks of CoV 3 O 8
Initial CoV 3
O 8
Electrode material after 21st discharge
Intensity (a.u.)
10 20 30 40 50 60 70
2θ-CuKα