Advances in Ma terials Physics and Che mist ry, 2012, 2, 185-188
doi:10.4236/ampc.2012.24B048 Published Online December 2012 (http ://
Copyright © 2012 SciRes. AMPC
Synthesis and Electrochemical Characterization of Li2MnSiO4
with Different Crystal Structure as Cathode Material in
Lithium Rechargeable Batteries
Joongpyo Shim1, Sora Won1, Gyungse Park3, Ho-Jung Sun2
1Department of Nano & Chemical Engineering, Kunsan National University, Gunsan, Jeonbuk, Korea
2Department of M ater ial S cien ce & Engineer in g , Kuns an National University, Guns an, Jeonb uk, Korea
3Department of Chemistry, Kunsan National University, Gunsan, Jeonbuk, Korea
Email:, r , p arkg@kun
Received 2012
Li2MnSiO4 with d ifferent crystal stru cture was synthesi zed by solid state reaction method . Their cryst al structure an d electrochemical
propert ies have been characterize d by X-ray dif fraction and charge-discharge tes t. The materi al prepared at 900oC in N2 atmosphere
had γ-phase and its crystal structure changed to β-phase by post-heating at 400oC in air after 900oC sintering. In electrochemical
measure ment, t wo materials (γ- and β-phase) showed ~3 and ~45mAh/g, resp ectively. The differen t capacit ies of these two material s
might b e due to the change of cryst al structure.
Keywords: Li2MnSiO4; Crystal Structure; Cathode; Lithium Rechar geable Battery
1. Introduction
Recently, the lithium extraction/insertion in polyanion frame
works, for example, (XO4)n- (X = P, S and Si) materials, has
been shown by many researchers [1-3]. In particular, LiFePO4
has been intensively studied as possible substitution for
commercially available LiCoO2. But, its redox voltage and
theoretical capacity have been limited to ~3.5V and 170mAh/g,
respectively [4]. One of them, Li2MnSiO4, as cathode material
in lithium rechargeable batteries provides very promising
candidates to explore in place of LiCoO2 because its high
theoretical capacity of 333mAh/g. The Mn redox couple
(Mn2+/Mn4+) is of particular interest due to a high potential (vs.
Li/Li+), plentiful resource and environmentally friendly
material. Dominko at al. firstly found that only 0.6 Li+ ions
could be extracted at the first cycle, and 0.3 Li+ could be
reversibly extracted and inserted at 5th cycle at C/30 r ate [5].
Politaev et al. reported the monoclinic Li2MnSiO4 was
synthesized by high temperature sintering instead of orthorhombic
structure by low temperature synthesis [6]. As explained by
them and others [7], monoclinic Li2MnSiO4 is a superlattice of
the high temperature orthorhombic Li2(4b)Li(2a)PO4, where Mn 2+
ions are located in the 2a tetrahedral sites within the [SiO4]4-
anionic silicate framework that replaces the [PO4]3- anionic
phosphate framework. Many studies showed that it was
difficult to form pure orthorhombic Li2MnSiO4 from low
temperature synthesis below 800oC [8,9].
There are few studies on two forms of Li2MnSiO4 on elec-
trochemical chara cteristi cs. The aim of this work is to report the
crystal structure change and the electrochemical properties of
Li2MnSiO4 powders synthesized by different processes.
2. Experimental
Li2MnSiO4 was prepared using solid state reaction as following
process. Starting materials were lithium hydroxide (LiOH,
Aldrich), manganese carbonate (MnCO3, Aldrich) and fumed
silica (SiO2, Aldrich). Stoichiometric amounts of all precursors
were weighed, grinded and mixed in mortar homogeneously.
Thereafter, the product was dried at 100oC and then slowly
heated to 900oC for 12h under nitrogen atmosphere to avoid the
oxidation of Mn ion from Mn2+ to Mn3+ or Mn4+ b y the reacti on
with oxygen [5]. Additional process, post heating at 400oC for
5h in air, was conducted to change crystal structure of
Li2MnSiO4. Weight loss during heat-treatment was determined
by ther mal gravimetric analysi s ( TGA, TA Instrument).
The crystal structures of samples were identified by X-ray
diffraction (XRD, PANalytical, EMPYREAN) in Cu Kα
radiation. The sample morphology and the chemical composition
were analyzed by using a field emission scanning electron
microscope (FE-SEM, FESEM, Hitachi, S-4800) with energy
disp ersive X-ray spect r oscope (EDS, Horiba, EX-250).
The electrode for electrochemical testing was prepared from
70 wt% Li2MnSiO4, 20 wt% carbon (Super-P) as conductive
agent, and 10 wt% PVdF as binder. Firstly, all materials were
mixed in NMP (1-met h yl -2-pyrrolidone, Aldrich) for m).
The10h by ball-mill and then cast on an Al foil current col-
lector (20 electrodes were dried at 120oC under vacuum to re-
move solvent and stored in an Ar-filled glovebox. Electro-
chemical measurements were carried out on CR 2032 coin cell
(Hoshen) which was assembled in glovebox. The electrolyte
was 1. 0M LiPF6 in a mixture (1:1:1) of ethylene carbonate ( EC),
ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC)
(Technosemichem). The coin cells were assembled with lithium
foil (Aldr ich) as negati ve electrode an d polyprolylene sep arator
(Celgard) . The charge & discharge tests wer e performed u s ing a
battery c ycler (WBCS 3000, WonAte ch) in th e voltage range o f
Copyright © 2012 SciRes. A MPC
2.0 4.7V (vs. Li/Li+) at room temperature.
3. Results and Discussion
TGA was carried out to observe the weight loss of precursors
and the starting synthesis temperature, as shown in Figure 1.
The mixture of precursors lost about 20% weight around 300oC,
which was assigned to the evaporation of CO2 and H2O. And
then, the weight of precursor decreased slowly until 700oC.
Therefore, it assumes that the formation of Li2MnSiO4 starts
above 700oC.
Figure 2 shows XRD patterns of Li2MnSiO4 sintered at 900oC
in N2 for 12h, and post-heated at 400oC in air for 5h after sin-
tering. The XRD pattern of Li2MnSiO4 obtained after 900oC
sintering indicates the formation of monoclinic (space group
P21/n) structure (γ-phase). To get pure orthorhombic Li2MnSiO4
from monoclinic phase, post-heating process was conducted at
400oC in air for 5h. As shown in Figure 1(b), disappearing the
diffraction peaks for (110) and (101) after post-heating in air,
orthorhombic Li2MnSiO4 (β-phase, space group Pmn21) was
clearl y formed.
The lattice parameter [a = 6.3113Å, b = 5.3805Å, and c =
4.9924Å] of β-Li2MnSiO4 material was calculated by Rietveld
refinement analysis and are consistent with values published by
others [1 0, 11].
Figure 1. Thermogravimetric analysis of the mixture of precursors
under N2 atmosphere.
Figure 2. XRD patterns of Li2MnSiO4 sintered (a) at 900oC in N2
for 12h and post-heated (b) at 400oC in air for 5h after sintering.
The change of morphology for the Li2MnSiO4 befor e and af-
ter post-heating was examined by FE-SEM and shown in Fig-
ure 3. Li2MnSiO4 does not have uniform size distribution with
a particl e diameter o f app roximatel y ~1µm containing nanosized
particles (~100nm). A dramatic change of morphology after
post-heating was not observed in Figure 3(b). Bigger size par-
ticles (>1 µm) are insufficiently conductive to allow for lithium
ion diffusion and electric connection because very low conduc-
tivity of Li2MnSiO4. Therefore, carbon coating or incorporation
should be considered the increase the electric conductivity and
ion diffusivity [12]. EDS analysis was used to investigate a
qualitative atomic composition and the results are shown in
Figure 4. The content of Mn and Si is almost same and is not
changed after post-heat ing.
Figure 5 shows the charge-discharge behaviors of synthe-
sized two Li2MnSiO4 materials at room temperature.
γ-Li2MnSiO4 had ~3mAh/g of discharge capacity, even though
its theoretical capacity is 333mAh/g as 2 moles of Li+ are ex-
tracted from formula unit. The discharge capacity was in-
creased dramaticall y changin g crystal structu re from γ-ph ase to
β-phase. β- Li2MnSiO4 shows ~45mAh/g of discharge capacity
Figure 3. SEM images of Li2MnSiO4 (a) before and (b) after
post-heat in g at 400oC.
Copyright © 2012 SciRes. A MPC
Figure 4. EDS analysis of Li2MnSiO4 (a) before and (b) after
post-heat in g at 400oC.
Figure 5. Charge-discharge curves of γ-Li2MnSiO4 synthesized at
900oC, and β-Li2MnSiO4 post-heated at 400oC after 900oC sinter-
which is 15 times higher than γ-Li2MnSiO4. Very low capaci-
ties of two materials are attributed to extremely low electric
conductivity of Li2MnSiO4 (3 x 10-14 Scm-1) [13]. To increase
the electric conductivity of active material, carbon was coated
on the surface conventionally. However, several studies re-
ported that uncoated Li2MnSiO4 usually had very low capacit y
In the charge-discharge profiles of two materials, β-Li2
MnSiO4 has two plateaus during cycling, but γ-Li2MnSiO4 does
not. dQ/dV plots of β-Li2MnSiO4 was shown in Figure 6 to
identify the potentials of plateaus. The peaks may correspond to
the vol tages plateaus of th e Mn2+/3+ and Mn3+/4+ redox co uples.
β-Li2MnSiO4 shows one sharp cathodic peak at ~2.9V, and two
small peaks at ~4.0 and ~4.1V during first charge. In contrast,
γ-Li2MnSiO4 does not show any peak during both charging and
discharging (not shown). At second cycle, the cathodic sharp
peak moved from ~2.9V to 3.0V, but the anodic peak did not.
Arroyo-de Dompablo et al. calculated average lithium extrac-
tion voltage from Li2MSiO4 (M = Mn, Fe, Co and Ni) [16].
They obser ved that in all cases extraction of the second lithium
ion may occur at very high voltage (>4.5V) except for
Li2MnSiO4, existing the possibility of the decomposition of
LiPF 6 based electrolyte. But, by their calculation, the first and
second lithium ion extraction from Li2MnSiO4 occurred at 4.1
and 4.5V, respectively. Muraliganth et al. reported Li2MnSiO4
showed a si ngle cath odic peak at ~ 4V and bro ad anodic peak at
~3V at first cycle [17]. However, it did not exhibit a sharp peak
at secon d cycle, as suming struct ural rear rangemen t and conver-
sion of the crystal structure into an amorphous phase during the
first charge. Similar behavior was observed in the results of
Yang’s group [11]. They reported that no strong peaks from
XRD results could be observed when the electrodes were dis-
charged below 3.2V. Unlike their results, our β-Li2MnSiO4 had
clearly sharp peaks at second cycle because its structure still
had crystallinity. However, we did not find any evidence or
explanation for first peaks around 2.8~3.0V in our β-Li2
MnSiO4, which was reported in many literatures. We are still
trying to define for that. Conclusively, the lithium extraction
from β-Li2MnSiO4 is more effective than that from γ-Li2
MnSiO4. Politaev et al. reported that the two structure types
differed in their mode of connecting tetrahedral and in connec-
tivity of their rigid part, (MnSiO4)2- [6]. The β-Li2MnSiO4
structure is layered (2D) whereas γ-Li2MnSiO4 structure is a
framework (3D). They also described that the former had more
freedom for Li+ ion motion and, possibly, for Mn displacement
into octahedral voids. In our work, the difference between two
structures on electrochemical property may be attributed to
same reason why they suggested.
Figure 6. dQ/dV plots for charge-dischar g e cu rv es o f β- Li2MnSiO4.
Copyright © 2012 SciRes. A MPC
4. Conclusions
A solid state reaction method has been used to synthesize
Li2MnSiO4 with different crystal structure and with a minimal
level of impurities. γ-Li2MnSiO4 has been produced by high
temperature sintering at 900oC and then post-heating at 400oC
changed its crystal structure from γ-phase to β-phase. In elec-
trochemical measurement, two materials (γ- and β-phase)
showed ~3 and ~45mAh/g, respectively. In the
charge-discharge profiles of two materials, β-Li2MnSiO4 had
two plateaus during cycling, but γ-Li2MnSiO4 did not. The
difference between two materials on electrochemical property
may be attributed to the crystal structure because β-phase had
more freedo m for Li+ ion m oti o n than γ-phase.
5. Acknowledgements
This work was supported by R&D Program through the Na-
tional Fusion Research Institute of Korea (NFRI) funded by the
government funds.
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