Battery AgendaPresented 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

Brainstorm different types of batteries you are aware of, what they are used for, and describe the attributes that you are aware of.

This is actually a cell, but is commonly called a battery. Batteries are a

group of cells.

Battery HistoryRechargeable batteries in bold.

First battery, “Voltaic Pile”, Zn-Cu with NaCl electrolyte, non-rechargeable, 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”, ZnC-Mn02 with ammonium disulphate electrolyte, non-rechargeable

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” non-rechargeable 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

negative terminal positive terminal

electrolyte

case

“anode”

negative electrode

“cathode”

positive electrode

Standard Electrode Potential

Electrode Type Material Abbreviation Standard PotentialCathode Copper Cu +0.34 VAnode Iron Fe -0.44 V

Zinc Zn -0.76 VAluminum Al -1.66 V

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:

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

2 pHlemon juice

Electrolyte Type Solution CommentAcids Vegetable oil Weak acid

Coffee 6 pHMilk 6 pHApple juice 3 pHBalsamic vinegar 3 pH

Salts Salt water Can have high ion concentration

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:

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

negative terminal positive terminal

salt water electrolyte

open jar case

galvanized nail anode copper wire cathode

Make a Battery

negative terminal positive terminal

orange juice and pulp electrolyte (acetic acid)

orange skin case

galvanized nail anode copper wire cathode

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

Voc

Rint

Rload

VloadOhm’s Law: V = I x R

Vload = Voc when Rload is very large

Vload = ½ Voc at maximum power

Power = V x I

Maximum power = Voc ^ 24 * Rint

Adjust Rload until Vload = ½ x Voc, then measure Rload in Ohms, using

a multimeter

Lower internal resistance and higher Voc increase power

Battery

Chemical Reactions

Chemical ReactionsSome of the elements used today:

anodescathode electrolyte jar

Chemical ReactionsCu-Zn-NaCl/H2O Cell During Discharge

anode cathodeload

Cu(s)Zn(s)

Cu2+Zn2+

2e-

Na+Cl-

H2(g)++++++++++

- -- -- -- -- -

electrolyte

Zn(s) > Zn2+ + 2e-primary

Anode reactions

Zn2+ + 2e- > Zn(s)

secondary

Cu2+ + 2e > Cu(s)2H+ + 2e- > H2 (g)reduction

Cu(s) > Cu2+ + 2e-oxidation

secondaryprimary

Cathode reactions

OH-

H2O

H+

Up to 1.1V EMF

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

Stainless steel spoke, aluminum sheet, de-galvanized nail, coated screw, galvanized sheet, galvanized nail

Single nail, multiple nails

Anode

Item Variations to try today

Cathode Copper wire, copper tubing

Straight wire, coiled wire

Electrolyte Vegetable oil, coffee, milk, apple juice, balsamic vinegar, lemon juice, salt water

1” deep, 2” deep

Experimental Results: ElectrodesPrint and fill in this table for 1” lemon juice electrolyte contact depth with electrodes.

Describe why you got these results.

Electrolyte Cathode Anode Voc Rint Pmax = Voc^2/(4*Rint)

Lemon juice Cu wire Zn nail

Cu tube Stainless Fe spoke

Al sheet

De-Zn Fe nail

Coated Fe screw

Zn sheet

Zn nail

Experimental Results: ElectrolytePrint and fill in this table for 1” electrolyte contact depth with electrodes.

Cathode Anode Electrolyte Voc Rint Pmax = Voc^2/(4*Rint)

Cu tube Zn nail Vegetable oil

Lemon

Tap water

Salt water

Coffee

Milk

Apple juice

Balsamic vinegar

Lemon juice

Describe why you got these results.

Appendix

Experimental Results: Electrodes~1” lemon juice electrolyte contact depth with electrodes. Collected 1/12/10.

0.831156.72De-Zn Fe nail4

0.470198.61Al sheet3

0.0013,020-.10Stainless Fe spokeCu tube2

7

6

5

1

Electrolyte Cathode Anode Voc, Volts Rint, Ohms Pmax, milliWatts=Voc^2/(4*Rint)

Lemon juice Cu wire Zn nail .84 7,160 0.025

Coated Fe screw .92 131 1.615

Zn sheet 1.00 135 1.852

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.

0.000n/a.00Vegetable oilZn nailCu tube1

9

8

7

6

5

4

3

2

Cathode Anode Electrolyte Voc, Volts Rint, Ohms Pmax, milliWatts=Voc^2/(4*Rint)

Lemon .85 1,672 0.108

Tap water .92 1,029 0.206

Coffee .85 729 0.248

Milk .90 567 0.357

Apple juice .90 369 0.549

Balsamic vinegar .85 193 0.936

Lemon juice .90 88 2.301

Salt water .82 40 4.203

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 mushingup 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 disassociatingCu electrode put in to electrolyte and dissolving slowlyZn electrode put in electrolyte dissolving fasterthe load attached and the Zn dissolving even fasterthe electrons moving through the load, note doing work, emitting light and generating heatthe Na+ and Cl- moving towards their respective electrodes to balance chargethe water being disassociated by the EMFthe hydrogen gas formingthe hydrogen gas risingthe 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