Journal of Power Sources 172 (2007) 908–912
Short communication
Electrochemical properties of tin phosphates
with various mesopore ratios
Joon-Gon Lee, Dongyeon Son, Chunjoong Kim, Byungwoo Park
∗
Department of Materials Science and Engineering, and Research Center for Energy Conversion and Storage,
Seoul National University, Seoul 151-744, Republic of Korea
Received 12 April 2007; received in revised form 12 June 2007; accepted 12 July 2007
Available online 2 August 2007
Abstract
Tin phosphates with various mesopore ratios are synthesized with surfactants as templates. The mesopore ratios of the tin phosphates are
controlled by adjusting the surfactant: inorganic precursor ratios. As an anode material for Li-ion batteries, the mesoporous and non-mesoporous
mixture with a high mesopore ratio exhibits enhanced cycling stability. Compared with the ∼34% (∼135 mAh g
−1
) capacity retention after 50
cycles of the non-mesoporous tin phosphate (between 2.5 and 0.001 V), the tin-phosphate anodes with mesopore ratios of 42, 82 and 100% show
capacity retentions that are enhanced by more than 50%, showing charge capacities of ∼260, ∼290, and ∼325 mAh g
−1
, respectively (after 50
cycles). The mesoporous structures may alleviate the large volume change of the Sn nanoparticles embedded in the lithium-phosphate matrix
during charge–discharge. Cycling tests of the 100% mesoporous tin phosphate between 0.8 and 0.001 V exhibit no capacity decay: ∼325 mAh g
−1
remains after 50 cycles. This is probably because re-oxidation of metallic tin with lithium-phosphate matrix does not occur.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Energy storage; Electrochemical properties; Mesopore; Lithium-ion battery; Tin phosphate; Capacity retention
1. Introduction
The development of portable electronics and hybrid elec-
tric vehicles (HEVs) requires Li-ion batteries with high specific
energy. Although commercially used graphite anodes have good
electrochemical properties, their capacity (372 mAh g
−1
for
LiC
6
) is insufficient to satisfy the market requirements. Thus,
tin-based anode materials such as metallic tin [1,2], tin oxides
[3–5], and tin phosphates [6,7] have attracted much atten-
tion. Their theoretical capacities are two- or three-times larger
(metallic tin: 959 mAh g
−1
, SnO
2
: 781 mAh g
−1
and Sn
2
P
2
O
7
:
572 mAh g
−1
, all for Li
4.4
Sn) than that of graphite anodes. They
have poor capacity retention however, due to their large volume
change of over 300% during lithiation/delithiation. To enhance
their capacity retention, mesoporous structures [8,9], which are
generally synthesized using surfactants as templates and have
pore sizes between 2 and 50 nm, have been applied to these
tin-based materials [10–14].
∗
Corresponding author. Tel.: +82 2 880 8319; fax: +82 2 885 9671.
E-mail address: byungwoo@snu.ac.kr (B. Park).
The mesoporous structures of tin-based materials may act as
buffer structures to alleviate the large volume change. Though
tin-phosphate materials that consist of mesoporous and non-
mesoporous composites have previously been studied [12–14],
the effects of the mesopore ratio on their electrochemical prop-
erties remain unclear. In this study, tin phosphates with various
mesopore ratios are synthesized, and their electrochemical prop-
erties examined.
2. Experimental
Tin phosphates with various mesopore ratios were pre-
pared by mixing various amounts of SnF
2
and H
3
PO
4
,
and dissolving them in 40 ml of distilled–deionized
water. Then, 5.5 g of cetyl-trimethyl-ammonium bromide
(CTAB: CH
3
(CH
2
)
15
N(CH
3
)
3
Br) was dissolved in 20 ml of
distilled–deionized water, and this solution was added to the
SnF
2
/H
3
PO
4
solution. The molar ratio of SnF
2
/H
3
PO
4
was
fixed at 1.35, while CTAB/H
3
PO
4
molar ratios of 0.11, 0.22,
0.54 and 1.10 were prepared. The mixture was stirred at
40
◦
C for 1 h, loaded in an autoclave, and then kept at 90
◦
C
for 24 h. After cooling to room temperature, the precipitates
0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2007.07.051