The Zn–MnO
2
Battery: The Influence of Aqueous LiOH
and KOH Electrolytes on the Intercalation Mechanism
Manickam Minakshi,
a,z
Pritam Singh,
b
Melody Carter,
c
and Kathryn Prince
c,z
a
Department of Extractive Metallurgy and
b
Department of Chemistry, Murdoch University, Murdoch, WA
6150, Australia
c
Australian Nuclear Science and Technology Organization, Menai, NSW 2234, Australia
Intercalation chemistry of the zinc–manganese dioxide Zn–MnO
2
electrochemical cell aiming at the development of aqueous
rechargeable batteries is presented. This study includes electrochemical characterization of MnO
2
in saturated aqueous lithium
hydroxide LiOH and potassium hydroxide KOH electrolytes. The lithium insertion into MnO
2
results in the formation of
Li
x
MnO
2
. The reversible deintercalation process prevails in the presence of LiOH electrolyte. Rather than the usual protonation
H
+
which is apparent in the literature while using KOH electrolyte, in this work, K
+
ion insertion into MnO
2
is observed.
However, the K
+
ion insertion is found to be irreversible. The intercalation mechanism is confirmed using various techniques to
characterize the discharged MnO
2
cathode in LiOH and KOH electrolytes. The influence of small amounts of Bi
2
O
3
bismuth
oxide additive on the discharge behavior of MnO
2
is also discussed.
© 2008 The Electrochemical Society. DOI: 10.1149/1.2932056 All rights reserved.
Manuscript submitted April 9, 2008; revised manuscript received April 28, 2008. Available electronically June 2, 2008.
Alkaline zinc–manganese dioxide Zn–MnO
2
batteries are in
demand because they are mercury-free and have a high-rate capa-
bility. Since its introduction in the early 1960s, the Zn–MnO
2
alka-
line battery has become the dominant battery system in the portable
battery market. Zinc has a wide variety of applications as a negative
electrode material in Zn–Mn, Zn–Ag, Zn–Ni, and Zn–Air batteries.
Manganese dioxide MnO
2
is one of the most common cathodic
battery materials. MnO
2
is inexpensive, nontoxic, and readily avail-
able. Today, MnO
2
has become an attractive material for recharge-
able cells due to economic and ecological reasons. The literature on
MnO
2
as a cathode material in aqueous KOH electrolyte is exten-
sive. The discharge mechanism proposed by Kozawa and
co-workers
1
is now widely adopted by other workers. This mecha-
nism is based on intercalation of protons protonation; H
+
into the
lattice of the MnO
2
, and the irreversibility is explained due to the
destruction of the crystal lattice during deep discharge and volume
changes, leading to loss of contact between the active MnO
2
.
2-4
The
cited authors also emphasized the protonation mechanism and the
necessity to eliminate possible loss of contact between the active
MnO
2
particles. In the mid-1980s work focused on MnO
2
cathodes
in KOH electrolytes was somewhat redirected toward the investiga-
tion of additives, i.e., Bi
3+
, Pb
2+
into MnO
2
cathodes to make the
batteries rechargeable. This led to an important breakthrough made
by Wroblowa et al.
5-7
They demonstrated that MnO
2
doped with a
suitable additive enabled the battery to be cycled many times. This
was explained on the basis of reversible intercalation of protons into
the MnO
2
.
To the best of our knowledge, all the MnO
2
studies in aqueous
solutions were based on a protonation mechanism and limited to
KOH electrolyte.
8-12
There are no systematic characterization stud-
ies on the products formed on discharge of the cells using, for ex-
ample, techniques like X-ray diffraction XRD, Fourier transform
infrared FTIR spectroscopy, electron energy loss spectroscopy
EELS, and secondary ion mass spectrometry SIMS. In one of our
recent studies
13
we have reported the use of aqueous LiOH as an
electrolyte resulting in the incorporation of lithium ions into the host
MnO
2
structure during the discharge process.
Our present contribution is an extension of the work which was
reported earlier.
13
The main objectives of this paper are to report on
i understanding the difference in the electrochemical behavior be-
tween LiOH and KOH electrolyte, ii identifying the products
which are formed when MnO
2
is discharged in batteries containing
LiOH or KOH electrolyte and studying the intercalation chemistry,
and iii characterizing the cathode material using various physical
techniques. The products formed after discharge were characterized
by XRD, EELS, FTIR and SIMS depth profile analysis.
Experimental
The cell design, experimental details, and the method of sample
preparation for the various physical characterization methods have
been described elsewhere.
13,15
A list of chemicals used in this study
is given in Table I. For the two electrode battery tests, a pellet
30 mg of cathode mixture was prepared for each by mixing, in a
mortar and pestle, 75 wt % of MnO
2
, 20 wt % of acetylene black
to aid conductivity, and 5 wt % of poly vinylidene difluoride
PVDFused as a binder. In the sample containing 3 wt % of
Bi
2
O
3
, 72 wt % MnO
2
was used instead of 75 wt %. A Swagelok-
type electrochemical cell
15
was constructed with the disklike pellet
as the cathode, Zn metal as anode, and filter paper Whatman filters
no. 12 as the separator between the anode and cathode. The elec-
trolyte was either a saturated solution of lithium hydroxide LiOH
containing 1 mol L-1 zinc sulfate ZnSO
4
or 7 M concentration of
potassium hydroxide KOH. Chemicals were dissolved in deion-
ized water to prepare solutions of required concentrations.
The experimental procedures for the cyclic voltammetry and gal-
vanostatic studies and the standard cell configuration were similar to
those reported earlier.
15,16
A saturated calomel electrode SCE
served as the reference electrode. Reported potentials are relative to
SCE. An EG&G PAR Potentiostat/Galvanostat model 273 A, oper-
ated by model 270 software EG&G, was used to scan at 25 Vs
-1
in all experiments. For X-ray analysis a Siemens D500 diffracto-
meter using Co K radiation was used. The FTIR spectra were re-
z
E-mail: minakshi@murdoch.edu.au; lithiumbattery@hotmail.com
Table I. List of chemicals.
Chemical Supplier
Grade
%
MnO
2
battery quality Sigma–Aldrich 90+
Bi
2
O
3
Sigma–Aldrich 99
Zn foil Zn BDH Chemicals 99.9
Lithium hydroxide
monohydrate
LiOH·H
2
O
Sigma Chemicals 99.9
Zinc sulfate
hepathydrate
ZnSO
4
·7H
2
O
Ajax Chemicals 99
Potassium hydroxide
KOH
Fine Chemicals Analytical
Zinc sulfate
heptahydrate
Ajax Chemicals 99.9
Electrochemical and Solid-State Letters, 11 8 A145-A149 2008
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