Download Alkaline Zinc Manganese Dioxide Battery

Experiment 4: Alkaline Battery
Practicum Electrochemistry / Energy Systems
Experiment 4
Alkaline Zn-MnO4 battery
1. Motivation
Alkaline batteries account for 80 % of manufactured batteries in the USA and over 10 billion
individual units produced worldwide. In Japan, alkaline batteries account for 46 % of all primary
battery sales. In Switzerland, alkaline batteries account for 68 %, in the UK 60 % and in the EU 47 % of
all battery sales including secondary types.[1] In 2004, 1.2 billion alkaline battieres were placed on the
market in Germany.[2]
Alkaline batteries are used in many household items such as mp3 players, CD players, digital
cameras, pagers, toys, lights, and radios, to name a few.[1]
2. What students will learn?
Students will construct their own alkaline primary battery and perform discharge test. They will
understand the simplicity of design and affordable materials with low toxicity that make overall lowprice power system. They have to remember electrochemistry, they will gain useful hands-on
experiment and some technical skills.
3. Theoretical background
The alkaline battery is an advanced form of zincmanganese dioxide batteries and thus of the
Leclanché element. It shows a better
performance due to three times higher capacity
compared to conventional batteries.[4,5] The
active material of the negative electrode is zinc
in powder form to reach a high specific surface.
The powder is hold by a synthetic gel. The
positive electrode consists of manganese dioxide
as active material and graphite as conducting
additive, both also in powder form.[6] A solution
of potassium hydroxide with a mass fraction of
30 % to 45 %[3,5] is used as electrolyte and thus
not consumed during the reaction. The positive
and the negative electrodes are separated by a
material, which has to be permeable for
hydroxide ions, since equal amounts of them are
consumed and produced in both halfcells. The
half-reactions are:[4–6]
Figure 1:
Construction of an alkaline manganese primary cell[3]
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Experiment 4: Alkaline Battery
−
Zn(s) + 2OH(aq)
MnO2(s) + H2 O(l) + e
−
Practicum Electrochemistry / Energy Systems
 ZnO(s) + H2 O(l) + 2e−
�E0 = −1.33 V�
(1)
�E = +0.12 V�
(2)
 ZnO(s) + MnO(OH)(s)
�E0 = +1.45 V�
(3)
 MnO(OH)(s) +
−
OH(aq)
The overall reaction is as follows:
Zn(s) + 2MnO2(s) + H2 O(l)
0
After the complete reduction of Mn4+ to Mn3+ a second step leading to Mn2+ takes place:
MnO(OH)(s) + H2 O(l) + e−
−
 Mn(OH)2(s) + OH(aq)
(4)
This reaction is irreversible. By taking certain measures like reduction of the amount of zinc and thus
limiting the capacity of the negative electrode, preventing the battery from falling under a cut-off
voltage of 0.9 V, the alkaline battery can be made rechargeable.[3,6]
4. Materials and apparatus
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•
•
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manganese dioxide powder
zinc powder
6M potassium hydroxide
sodium carboxymethyl cellulose powder
graphite powder
graphite rod
stainless steel battery can with cap
cellulose separator
plastic spacer
commercial battery holder
mortar, watch glass, pipette, glass vial,
spatula
• balance
• potentiostat-galvanostat
Figure 2: Battery components
5. Experimental
a) Battery construction
First, anode paste and cathode paste have to be prepared. The total mass of the battery material
shall be 9 g in a molar ratio of the active components according to equation 3. For the cathode, use
manganese dioxide, graphite and potassium hydroxide solution in a weight ratio of 70:10:20. For the
anode, mix zinc, sodium carboxymethylcellulose and potassium hydroxide in a weight ratio of
60:10:30. Calculate the necessary masses at home!
1. Prepare the cathode paste after grinding the graphite in the mortar.
2. Fill the cathode paste into the steel can. Try to spread it over as much steel surface as possible.
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Experiment 4: Alkaline Battery
Practicum Electrochemistry / Energy Systems
3. Press the separator into the cathode material and soak it with 1.5 g potassium hydroxide
solution.
4. Prepare the anode material on the watch glass and fill it into the steel can.
5. Stick the graphite rod into the anode paste.
6. Put the plastic spacer onto the anode material.
7. Close the can with the cap.
Safety precaution: concentrated KOH in use!
b) Battery testing
1. Insert the battery into the battery holder.
2. Connect positive and negative pins to current supply. Connect the cathode of the battery as
working electrode and the anode as counter electrode.
3. Record the open circuit voltage of the cell (OCV).
4. Discharge battery at constant current of 0.001 A until it reaches the cut-off voltage mentioned
above.
6. Analysis of results and discussion
1. Plot the OCV curve and the discharge curve of the battery.
2. Compare practical cell voltage 𝐸pr of your battery to the theoretical voltage 𝐸th .
3. Compare theoretical capacity and actual capacity of the cathode of your battery in Ah g–1.
The theoretical capacity 𝑞th is calculated from equation 5, where 𝑧 is the number of
transferred electrons, 𝐹 is the Faraday constant, and 𝑀 is the molar mass of the active cathode
material.
𝑞th =
𝑧𝐹
𝑀
(5)
The practical capacity 𝑞pr is calculated from equation 6, where 𝐼 is the applied current, 𝑡cutoff is
the time until the cut-off voltage is reached, and 𝑚 is the mass of the active cathode material.
𝑞pr =
𝐼 𝑡cutoff
𝑚
(6)
4. Calculate theoretical specific energy and average specific power of your battery.
The theoretical specific energy 𝑒th is calculated from equation 7, the average specific power
𝑝av is calculated from equation 8, where 𝐼 is the applied current, 𝑡cutoff is the time until the cutoff voltage is reached, 𝐸(𝑡) is the voltage as function of the time, and 𝑚 is the mass of the
battery. Compare theoretical capacity and actual capacity of the cathode of your battery in
Ah g–1.
𝑒th =
𝑝av =
𝑡
𝐼 ∫0 cutoff 𝐸(𝑡)𝑑𝑑
𝑡
𝑚
𝐼 ∫0 cutoff 𝐸(𝑡)𝑑𝑑
𝑡
𝑚 ∫0 cutoff 𝑑𝑑
3
(7)
(8)
Experiment 4: Alkaline Battery
Practicum Electrochemistry / Energy Systems
Compare the calculated values with at least two other Zn-MnO2 systems from scientific and
commercial resources.
5. Discuss the performance of your battery. Compare the parameters of the alkaline battery to
another primary battery, e.g. the Leclanché element, and discuss the benefits over other
primary batteries. How can the performance be improved?
Always specify used literature!
7. References
[1]
[2]
[3]
[4]
en.wikipedia.org/wiki/Alkaline_battery, 27.07.2015.
de.wikipedia.org/wiki/Alkali-Mangan-Zelle, 27.07.2015.
R. M. Dell, Solid State Ionics 2000, 134, 139–158.
R. M. Dell, D. A. J. Rand, Understanding Batteries, chapter 5.2: Alkaline-manganese Cells, pp.
59–64, The Royal Society of Chemistry, 2001.
[5] J. O. Besenhard, Handbook of Battery Materials, chapter 2.1: Alkaline-Manganese Batteries,
pp. 19–21, John Wiley & Sons, 2008.
[6] M. Winter, R. J. Brodd, Chem. Rev. 2004, 104, 4245–4270.
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