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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

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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

  • 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 History

Rechargeable batteries in bold.


Parts of a Battery

“anode”

negative electrode

“cathode”

positive electrode

electrolyte

negative terminal

positive terminal

case


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:

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:

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

copper wire cathode

salt water electrolyte

negative terminal

open jar case

positive terminal


Make a Battery

galvanized nail anode

orange juice and pulp electrolyte (acetic acid)

copper wire cathode

negative terminal

orange skin case

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

Vload = Voc when Rload is very large

Vload = ½ Voc at maximum power

Power = V x I

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

Rint

Vload

Voc

Rload



Chemical Reactions

Some of the elements used today:

cathode

anodes

electrolyte

jar


Chemical Reactions

Cu-Zn-NaCl/H2O Cell During Discharge

2e-

cathode

anode

load

Up to 1.1V EMF

++++++++++

H2(g)

- - - - - - - - - -

Na+

Cl-

Zn(s)

Cu(s)

OH-

H+

Cu2+

Zn2+

electrolyte

H2O

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.



Experimental Results: Electrodes

Print and fill in this table for 1” lemon juice electrolyte contact depth with electrodes.

Describe why you got these results.


Experimental Results: Electrolyte

Print and fill in this table for 1” electrolyte contact depth with electrodes.

Describe why you got these results.



Experimental Results: Electrodes

~1” lemon juice electrolyte contact depth with electrodes. Collected 1/12/10.

  • Why?

  • Thin Cu wire has small surface area.

  • Stainless Fe spoke must have a thick surface layer impeding the reaction.

  • Expected higher voltage in Al; must have a surface layer.

  • Fe has 0.32V lower EMF and reactivity than Zn, similar to 0.28V measured to Zn sheet.

  • Fe screw probably zinc plated, but must also have a surface layer.

  • Purer Zn in sheet form raises voltage, but must also have a surface layer.

  • Copper tube has larger surface area.


Experimental Results: Electrolyte

~1” electrolyte contact depth with electrodes. Collected 1/12/10.

  • Why?

  • No water to provide the H+ for cathode reduction.

  • Membranes inside lemon must impede ion flow in ~2 pH acetic acid electrolyte. Crushing lemon may improve power.

  • Not enough ions to balance the charge in the electrolyte.

  • Weak acid, pH probably >6, some more ions than tap water.

  • Stronger acid; pH probably <6, phosphoric acid in milk must have lower pH.

  • Even stronger acid, pH probably >3.

  • Yet even stronger acid, pH probably <3.

  • Yet again even stronger acid, pH ~2.

  • 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:

  • Better time management – did not get to measuring resistances at the end. Either break in to multiple 1-hour sessions or remove/streamline material

  • 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

  • Figure out what the surface layers are on the dog electrodes; file them off and see if they improve

  • Mount LEDs and variable resistor on wood with nail terminals to speed up data collection process without making the experiment too polished and kitted

  • Add deeper electrolyte to data collection matrix to show surface area; add measurements of electrode surface areas and do correlation

  • 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

  • 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

  • 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

  • Add pictures of historical batteries – Voltaic Pile, Daniel Cell, other cell cross sections

  • 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

  • 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

  • Do capacity testing vs. discharge rate and different quantities of Zn; compare Daniel cell to single jar version

  • Make a Voltaic pile out of pennies, aluminum foil, and wet and salty cloth

  • 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


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