Journal of Power Sources 185 (2008) 1386–1391
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Journal of Power Sources
journal homepage: www.elsevier.com/locate/jpowsour
Electrochemical behaviour of tin borophosphate negative
electrodes for energy storage systems
Atef Y. Shenouda
a,∗
, Hua Kun Liu
b
a
Central Metallurgical Research and Development Institute (CMRDI), Tebbin, Helwan, Helwan, Egypt
b
Institute for Superconducting and Electronic Materials, ARC Centre of Excellence for Electromaterials Science, University of Wollongong, NSW 2522, Australia
article info
Article history:
Received 3 July 2008
Received in revised form 12 August 2008
Accepted 16 August 2008
Available online 27 August 2008
Keywords:
Lithium battery negative electrode
Tin borophosphate electrode
Antimony doping
abstract
Tin borophosphate compounds doped with antimony, Sn
2
BP
1-x
Sb
x
O
6
(x = 0–0.3), have been prepared and
studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transmission infrared
spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) and
galvanostatic measurements. XRD patterns of all the samples were indexed to the tetragonal system. The
EIS showed that the conductivities are enhanced by antimony doping. It was observed that the Warburg
impedance coefficient (
w
) was 1163.265 cm
2
s
-0.5
for the Sn
2
BP
0.9
Sb
0.1
O
6
(x = 0.1) sample, and this
was the lowest value compared to those of the other samples. Sn
2
BP
0.9
Sb
0.1
O
6
(x = 0.1) showed the highest
specific discharge capacity of 1050 mAh g
-1
among all the samples and a reversible capacity of 540 mAh g
-1
at the 150th cycle.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Tin oxide compounds (TOC) have been suggested as high
capacity anode materials for lithium-ion batteries [1,2]. Their
rechargeability is based on the reversibility in the electrochemi-
cal reactions involving structurally related phases of Li–Sn alloys
[3]. The alloy phase is believed to be dispersed in an oxide matrix
consisting primarily of the decomposition products formed dur-
ing the first Li intercalation reaction. The most notable deficiencies
of tin oxide compounds are their irreversible capacity loss in the
first charge cycle and their poor cyclability relative to carbon-based
anodes. The TOC that delivers the best electrochemical perfor-
mance is reported with SnB
0.56
P
0.40
Al
0.42
O
0.36
composition [4]. The
synthesis of this compound is difficult because of the high melting
point of the Al
2
O
3
raw material, necessitating processing tempera-
tures as high as 1100
◦
C. Special equipment and care are also needed
to reduce the evaporative loss of volatile components such as B
2
O
3
and P
2
O
5
. In this investigation, BPO
4
was used instead to reduce the
volatility problem of B
2
O
3
and P
2
O
5
. BPO
4
reacts with SnO at ele-
vated temperatures to form Sn
2
BPO
6
, which was used as a model
TOC anode in rechargeable lithium test cells. Its electrochemical
performance is comparable with those of Sn
2
B
2
O
5
and Sn
2
P
2
O
7
,
which are TOCs with only one glass formation promoter (B or P).
There has been a resurgence of interest in the use of lithium-alloy
∗
Corresponding author. Tel.: +20 25010642; fax: +20 25010639.
E-mail address: ayshenouda@yahoo.com (A.Y. Shenouda).
anodes because of their low first cycle capacity losses [5]. Most
recent implementations have addressed the major deficiency of
bulk alloys (material fragmentation consequent upon the large vol-
ume changes in intercalation and de-intercalation) by dispersing
the active material as ultra-fine particles in a suitable matrix [6–8].
The matrix is often an inactive phase, but an active host material
may also be used [9]. The effectiveness of this approach is deter-
mined by the ability of the matrix to restrain the particle growth of
the active phase. It is in this latter category that TOCs may still hold
an edge over the multiphase alloy systems.
Three tin compounds, namely Sn
2
P
2
O
7
, Sn
2
B
2
O
5
, and Sn
2
BPO
6
,
have been prepared by melt-quenching the appropriate reaction
mixtures [10]. The borate glass was the easiest to form, but it was
visually the least homogeneous and delivered the poorest electro-
chemical performance. Hence, the amount of B in any glassy TOC
should be carefully controlled to reach a balance between the ease
of synthesis and electrochemical performance.
Although similar alloying and de-alloying mechanisms were
involved in charge and discharge reactions, Sn
2
P
2
O
7
and Sn
2
BPO
6
cycled much better than Sn
2
B
2
O
5
at the current density of
20 mA g
-1
. When the cells were cycled at higher current and a
higher discharge potential limit (150 mA g
-1
and 1.4 V, respec-
tively), Sn
2
BPO
6
displayed the best capacity retention relative to
Sn
2
P
2
O
7
and Sn
2
B
2
O
5
. This is perhaps due to the robustness of the
BPO
6
4-
structure in charge and discharge reactions.
The major advantage of TOC over carbonaceous anodes is their
large specific capacities on either the gravimetric or volumet-
ric basis. They are, however, hampered by the large irreversible
0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2008.08.042