Battery Agenda
Presented by NBEAA and Friends 1/12/2010
Updated 1/13/2010 1 PM
Goals of this Session
What is a Battery?
Battery History
Parts of a Battery
Standard Electrode Potential
Electrolytes
Make a Battery
Measuring Battery Power
Chemical Reactions
Make a Better Battery
Experimental Results
Goals of this Session
Prepare students to be viable contenders at the upcoming 4th through
6th grade Science Olympiad.
Build on classroom textbook, lecture and lab experiences to provide a
deeper understanding of batteries, with an emphasis on the chemistry
of the electrical power they provide. Energy storage capacity and
rechargability, two other key aspects of batteries, are not covered in
depth during this session.
Provide an opportunity to learn scientific observation and note taking
skills.
Motivate students to like science through fun, hands-on laboratory
experiments.
NOTE: ELECTROCHEMISTRY CAN BE VERY DANGEROUS. DO
NOT ATTEMPT ANY OF THE FOLLOWING OR OTHER
CHEMISTRY EXPERIMENTS WITHOUT ADULT SUPERVISION OF
SOMEONE WHO UNDERSTANDS CHEMISTRY. BURNS,
BLINDNESS, EXPLOSIONS AND EVEN DEATH MAY OCCUR!
What is a Battery?
A battery is an electrical energy storage device that comes in
many different forms. Attributes include:
- chemistry
- power
- capacity
- size
- weight
- shape
- voltage
- rechargability
- toxicity
- portable or stationary
- open, vented, sealed or solid
- series and parallel cell configuration
This is actually a cell,
but is commonly called a
battery. Batteries are a
group of cells.
Brainstorm different types of batteries you are aware of, what
they are used for, and describe the attributes that you are
aware of.
Battery History
Rechargeable batteries in bold.
First battery, “Voltaic Pile”, Zn-Cu with NaCl electrolyte, nonrechargeable, but short shelf life
1800
Italy
Alessandro Volta
First battery with long shelf life, “Daniel Cell”, Zn-Cu with
H2SO4 and CuSO4 electrolytes, non-rechargeable
1836
England
John Fedine
First electric carriage, 4 MPH with non-rechargeable
batteries
1839
Scotland
Robert Anderson
First rechargeable battery, “lead acid”, Pb-PbO2 with
H2SO4 electrolyte
1859
France
Gaston Plante
First mass produced non-spillable battery, “dry cell”, ZnCMn02 with ammonium disulphate electrolyte, nonrechargeable
1896
Germany
Carl Gassner
Ni-Cd battery with potassium hydroxide electrolyte
invented
1910
Sweden
Walmer Junger
First mass produced electric vehicle, with “Edison
nickel iron” NiOOH-Fe rechargeable battery with
potassium hydroxide electrolyte
1914
US
Thomas Edison and
Henry Ford
Modern low cost “Eveready (now Energizer) Alkaline” nonrechargeable battery invented, Zn-MnO2 with alkaline
electrolyte
1955
US
Lewis Curry
NiH2 long life rechargeable batteries put in satellites
1970s
US
NiMH batteries invented
1989
US
Li Ion batteries sold
1991
US
LiFePO4 invented
1997
US
Parts of a Battery
“anode”
negative electrode
negative terminal
“cathode”
electrolyte
case
positive electrode
positive terminal
Standard Electrode Potential
Standard Electrode Potential is the tendency of the chemical to acquire electrons.
Also called Electro-Motive Force or EMF. Measured in Volts.
Electrode materials used in this session include:
Electrode Type
Material
Abbreviation
Standard Potential
Cathode
Copper
Cu
+0.34 V
Anode
Iron
Fe
-0.44 V
Zinc
Zn
-0.76 V
Aluminum
Al
-1.66 V
The open circuit voltage of a battery is determined by the difference
between the cathode and the anode. For example, a pure Cu-Zn cell is
0.34 - (- 0.76) = 0.34 + 0.76 = 1.10 Volts. We measure up to 1.00 Volts.
The highest known voltage metal battery would be Ag-Li (silver-lithium) at
1.98 + 3.04 = 5.02 Volts, but silver is rare and quite expensive.
Electrolytes
Electrolytes are usually liquids that contain electrically charged ions which are used
to conduct electricity between the electrodes of a battery.
Electrolytes used in this session:
Electrolyte Type
Solution
Comment
Acids
Vegetable oil
Weak acid
Coffee
6 pH
Milk
6 pH
Apple juice
3 pH
Balsamic vinegar
3 pH
lemon juice
2 pH
Salt water
Can have high ion concentration
Salts
The more small free ions in the solution that can move quickly, the more
power a battery can deliver. Lower pH and heavy salts tend to have
more ions and increase power.
Make a Battery
galvanized nail anode
salt water electrolyte
negative terminal
open jar case
copper wire
cathode
positive terminal
Make a Battery
galvanized nail anode
negative terminal
orange juice and pulp electrolyte
(acetic acid)
orange skin case
copper wire
cathode
positive terminal
Other wet acidic fruits and vegetables can be used.
Measuring Battery Power
2 Cu-Zn- lemon juice cells powering an LED; 1.6 Volts, 0.6 milliAmps, 1 milliWatt
Measuring Battery Power
48 LiFePO4 cells powering a car: 140 Volts, 325 Amps, 45 kiloWatts
Draws 45 MILLION times more power than one LED!
Measuring Battery Power
1 Cu-Zn-salt water cell loaded with variable resistor
Measuring Battery Power
Battery
Ohm’s Law: V = I x R
Rint
Vload
Vload = Voc when Rload is very
large
Vload = ½ Voc at maximum power
Voc
Power = V x I
Rload
Maximum power = Voc ^ 2
4 * Rint
Adjust Rload until Vload = ½ x Voc,
then measure Rload in Ohms, using
a multimeter
Lower internal resistance and higher
Voc increase power
Chemical Reactions
cathode
anodes
Chemical Reactions
Some of the elements used today:
electrolyte
jar
Chemical Reactions
Cu-Zn-NaCl/H2O Cell During Discharge
2e-
cathode
anode
load
Up to 1.1V EMF
Zn(s)
++
++
++
++
++
Zn2+
electrolyte
Cl-
Na+
OH-
H+
oxidation
reduction
H2(g)
Cu(s)
Cu2+
H2O
Anode reactions
primary
------
Cathode reactions
secondary
primary
Zn(s) > Zn2+ + 2e-
secondary
Cu(s) > Cu2+ + 2e-
Zn2+ + 2e- > Zn(s)
2H+ + 2e- > H2 (g)
Cu2+ + 2e > Cu(s)
Zn and Cu both dissolve in electrolyte without load attached, Zn faster than Cu; much faster when load
attached. Electrons travel from the anode through the load to the cathode, causing a charge imbalance.
NaCl spontaneously disassociates in to ions when put in water. It balances the charge by moving next to
the oppositely charged electrode without chemically reacting and forming a bond.
H2O is disassociated in to OH- and H+ in the presence of the EMF. OH- balances charge like Cl- does; H+
combines with 2e- to form hydrogen gas. NOTE: a larger cell could be explosive!
Chemical Reactions
These electrodes were left in
balsamic vinegar overnight
All Zn removed from Fe
Some Cu removed
Make a Better Battery
Improvements:
More power
More ions in electrolyte
More electrode surface area
Higher electrode potential difference
More portable
Add vented lid
Add rigid terminals
Brainstorm how an even better battery
can be made.
Describe how commercial batteries are
made.
Make a Better Battery
Item
Variations to try today
Cathode
Copper wire, copper tubing
Straight wire, coiled wire
Anode
Stainless steel spoke, aluminum sheet, de-galvanized
nail, coated screw, galvanized sheet, galvanized nail
Single nail, multiple nails
Electrolyte
Vegetable oil, coffee, milk, apple juice, balsamic
vinegar, lemon juice, salt water
1” deep, 2” deep
Experimental Results: Electrodes
Print and fill in this table for 1” lemon juice electrolyte contact depth with electrodes.
Electrolyte
Cathode
Anode
Lemon juice
Cu wire
Zn nail
Cu tube
Stainless Fe spoke
Voc
Rint
Al sheet
De-Zn Fe nail
Coated Fe screw
Zn sheet
Zn nail
Describe why you got these results.
Pmax =
Voc^2/(4*Rint)
Experimental Results: Electrolyte
Print and fill in this table for 1” electrolyte contact depth with electrodes.
Cathode
Anode
Electrolyte
Cu tube
Zn nail
Vegetable oil
Voc
Rint
Lemon
Tap water
Salt water
Coffee
Milk
Apple juice
Balsamic vinegar
Lemon juice
Describe why you got these results.
Pmax =
Voc^2/(4*Rint)
Appendix
Experimental Results: Electrodes
~1” lemon juice electrolyte contact depth with electrodes. Collected 1/12/10.
1
2
Electrolyte
Cathode
Anode
Lemon juice
Cu wire
Zn nail
Cu tube
Stainless Fe spoke
Voc, Volts
Rint, Ohms
Pmax, milliWatts
=Voc^2/(4*Rint)
.84
7,160
0.025
-.10
3,020
0.001
3
Al sheet
.61
198
0.470
4
De-Zn Fe nail
.72
156
0.831
5
Coated Fe screw
.92
131
1.615
6
Zn sheet
1.00
135
1.852
7
Zn nail
.90
88
2.301
Why?
1. Thin Cu wire has small surface area.
2. Stainless Fe spoke must have a thick surface layer impeding the reaction.
3. Expected higher voltage in Al; must have a surface layer.
4. Fe has 0.32V lower EMF and reactivity than Zn, similar to 0.28V measured to Zn sheet.
5. Fe screw probably zinc plated, but must also have a surface layer.
6. Purer Zn in sheet form raises voltage, but must also have a surface layer.
7. Copper tube has larger surface area.
Experimental Results: Electrolyte
~1” electrolyte contact depth with electrodes. Collected 1/12/10.
Cathode
Anode
Electrolyte
Cu tube
Zn nail
Vegetable oil
.00
n/a
0.000
2
Lemon
.85
1,672
0.108
3
Tap water
.92
1,029
0.206
4
Coffee
.85
729
0.248
5
Milk
.90
567
0.357
6
Apple juice
.90
369
0.549
7
Balsamic vinegar
.85
193
0.936
8
Lemon juice
.90
88
2.301
9
Salt water
.82
40
4.203
1
Voc, Volts
Rint, Ohms
Pmax, milliWatts
=Voc^2/(4*Rint)
Why?
1. No water to provide the H+ for cathode reduction.
2. Membranes inside lemon must impede ion flow in ~2 pH acetic acid electrolyte. Crushing lemon may
improve power.
3. Not enough ions to balance the charge in the electrolyte.
4. Weak acid, pH probably >6, some more ions than tap water.
5. Stronger acid; pH probably <6, phosphoric acid in milk must have lower pH.
6. Even stronger acid, pH probably >3.
7. Yet even stronger acid, pH probably <3.
8. Yet again even stronger acid, pH ~2.
9. Na+ and Cl- ion saturation concentration must be more than the weaker acids tested. HCl may be better
but can burn skin vs. salt which does not hurt.
Ideas for next time:
1.
Better time management – did not get to measuring resistances at the end. Either break in to multiple 1-hour sessions or
remove/streamline material
2.
Verify H20 goes to OH- and H+ and not 2H+ and O2-; if so, then why does electrolysis generate H2 and O2, shouldn’t this battery EMF do
the same? Try to capture the gasses safely? Easier to do with caps on each half of a Daniel cell
3.
Figure out what the surface layers are on the dog electrodes; file them off and see if they improve
4.
Mount LEDs and variable resistor on wood with nail terminals to speed up data collection process without making the experiment too
polished and kitted
5.
Add deeper electrolyte to data collection matrix to show surface area; add measurements of electrode surface areas and do correlation
6.
Measure more fruits and vegetables, clean electrodes and then cut out areas touched by electrodes so the rest can be eaten; try mushing
up the lemon to see if it works better with the membranes split
7.
Get pH testers – litmus paper, electronic probe, perhaps borrow one, or take data and present it; determine ionic concentration vs. pH and
difference in reactivity between types of electrolyte acids and salts
8.
Improve, simplify and speed up presentation of chemical reactions slide #16 by drawing bubbly shaped molecules, then doing a succession
of a few slides that can be played as a movie that shows:
all molecules in their separate states
the salt put in water and disassociating
Cu electrode put in to electrolyte and dissolving slowly
Zn electrode put in electrolyte dissolving faster
the load attached and the Zn dissolving even faster
the electrons moving through the load, note doing work, emitting light and generating heat
the Na+ and Cl- moving towards their respective electrodes to balance charge
the water being disassociated by the EMF
the hydrogen gas forming
the hydrogen gas rising
the end state when the Zn(s) runs out
The state of each item when removed from the assembly
9.
Add pictures of historical batteries – Voltaic Pile, Daniel Cell, other cell cross sections
10.
Do a Daniel cell with two jars and a salt bridge, compare power data, and explain how it works and why it is better, similar to above
11.
Make a far more powerful safe non-toxic battery – salt water battery with larger and easily replaceable zinc plates and large copper plate,
portable, with cap on one terminal and vent, that can run the home made DC motor presented earlier, add homemade capacitor between
battery and motor to use lower power battery for higher power bursts needed, eventually in EV component assembly display for car shows;
may need to be a Daniel cell; eventually make simplified motor controller, charger, DCDC converter, BMS and VMU displays that attach
12.
Do capacity testing vs. discharge rate and different quantities of Zn; compare Daniel cell to single jar version
13.
Make a Voltaic pile out of pennies, aluminum foil, and wet and salty cloth
14.
Make a safe non-toxic rechargable battery. Don’t know how to do it; study NiMH, other toxic/dangerous batteries, research what schools
and battery companies have done for educational purposes, consult with chemists from these institutions