Journal of Power Sources 172 (2007) 410–415
Short communication
Synthesis of spinel LiMn
2
O
4
nanoparticles through
one-step hydrothermal reaction
C.H. Jiang
a,b,∗
, S.X. Dou
b
, H.K. Liu
b
, M. Ichihara
c
, H.S. Zhou
a,∗∗
a
Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology,
Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan
b
Institute for Superconducting and Electronic Materials,
University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia
c
Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
Received 6 June 2007; received in revised form 18 July 2007; accepted 23 July 2007
Available online 27 July 2007
Abstract
Phase pure spinel LiMn
2
O
4
nanoparticles can be directly synthesized by one-step hydrothermal reaction of -MnO
2
with LiOH in an initial
Li/Mn ratio of 1 at 200
◦
C. The reaction might involve a redox reaction between Mn
4+
and OH
-
, and the formation of LiMn
2
O
4
at the same time
under the proposed hydrothermal conditions. This hydrothermal process is simple since only -MnO
2
powders are used as the Mn source, whereas
without use of any oxidants, reductants, or low valence Mn source. The electrochemical performance of the as-synthesized LiMn
2
O
4
nanoparticles
towards Li
+
insertion/extraction was examined. Rather good capacity and cycle performance, and an especially excellent high rate capability, were
observed for the sample that was hydrothermally reacted for 3 days.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Spinel LiMn
2
O
4
; Hydrothermal synthesis; Li-ion batteries; Rate capability
1. Introduction
Li-ion batteries are the major power sources of today’s
portable electronic devices and also possibly for future elec-
tric vehicles, provided that the power and energy densities
could be further improved. The positive electrode material of
commercialized Li-ion batteries is LiCoO
2
, which has many
disadvantages, such as toxicity, cause of exposure, scare raw
materials, and high price. Alternative positive electrode materi-
als, such as Li(Ni,Mn,Co)O
2
, LiMn
2
O
4
, LiFePO
4
, Li
2
FeSiO
4
,
and so on, have been proposed as replacements. Among these
materials, spinel LiMn
2
O
4
has attracted special interest because
of its significant advantages over LiCoO
2
in terms of its non-
toxicity, safety, and abundant raw materials [1,2]. Regarding
this material, a large amount of work involving the synthe-
∗
Corresponding author at: Energy Technology Research Institute, National
Institute of Advanced Industrial Science and Technology, Umezono 1-1-1,
Tsukuba, Ibaraki 305-8568, Japan.
∗∗
Corresponding author.
E-mail addresses: chunhai jiang@yahoo.com (C.H. Jiang),
hs.zhou@aist.go.jp (H.S. Zhou).
sis, Li insertion/extraction mechanism, element substitution,
and electrochemistry have been done in order to facilitate its
practical applications [3–7]. In general, the electrochemical per-
formance of LiMn
2
O
4
is intimately related to its phase purity,
crystallinity, particle size, and morphology [8]. All of these
aspects can be correlated to the materials synthesis. Conven-
tionally, spinel LiMn
2
O
4
was prepared by solid-state reaction
of manganese oxides, nitrate or carbonate with lithium hydrox-
ide, nitrate or carbonate at temperatures as high as 700–900
◦
C
[1–8]. The final products usually contain large irregular particles
with a broad size distribution, as well as impurity phases. Also,
it is difficult to control the crystalline growth, compositional
homogeneity, morphology, and microstructure. Some soft chem-
istry routes, such as sol–gel [9,10], Pechini [11], emulsion [12],
melt-impregnation [13], spray-drying [14], etc., have also been
proposed. These methods lead to homogeneous spinel materials
with smaller particle size. However, these methods also suffered
from high temperature heat treatment, use of expensive reagents,
and process complexity.
In recent years, the hydrothermal method has been demon-
strated as an attractive low temperature route to prepare
crystalline spinel LiMn
2
O
4
[15–19]. However, the proposed
0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2007.07.039