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 2ecathode
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 3. 7. Yet even stronger acid, pH probably