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