Batteries

Physics

Power Cell

Device for storing chemical energy and then releasing it in the form of electricity when current is needed

Battery

More than

one power

cell working

together

9 V battery

Inside a 9 V are 6-1.5 V power cells connected in a row.

Parts of a Power Cell

1. Anode –Metal–High affinity for oxygen–Draw oxygen from cathode to become oxidized

Parts of a Cell

2. Cathode–Metallic oxide–Lower affinity for oxygen–Becomes reduced when oxygen is taken

Parts of a Cell

3.Separator–Insulator–Keeps cathode separated from anode to control reaction

Parts of a Cell

4.Current Collector – Connected to anode and cathode– Good conductor

5.Electrolyte– Usually liquid (ionized water, acid/base)– “Domino Effect” of oxygen from cathode to

anode

Operation of Power Cell

As anode becomes oxidized, an electron must be given up

Electron flows through anode’s current collector through circuit (outside of battery) as electrical current back to cathode’s current collector

Carbon-Zinc (C-Zn)

1.5 voltsWorks well if using 100 mA or lessLow capacity3 year shelf life

anode and anode collector

Cathode collector

MnO2

NH4Cl ZnCl2

Alkaline

1.5 V: lose voltage graduallyHigh Capacity (electrical energy)

– Last longer5 year shelf-lifeBetter in high drain devices than C-Zn

MnO2, graphite

Zn powder

steel

Metal nail

Electrolyte KOH

Lithium

Started off as button cellAnode: lithiumCathode: magnesium dioxide3 V: Takes up less space with

more voltage

Lithium

High CapacityLow Drain RateToxic: Special disposalLight Weight

Button Cell

Anode: Zinc or LithiumCathode: Silver or Mercury

OxideCompactLarge Life

Recharging Batteries

A current from an outside source is pushed through the cell in the opposite direction from the original current

Oxygen goes from anode to cathode

Nickel-Cadmium (Ni-Cd)

1.2 VoltsLow capacityMemory effect (Rechargeable)

– If you re-charge the battery too soon, you lower its capacity

Nickel-Metal Hydride (NiMH)

1.2 VBest rechargeable batteryHigh CapacityGood for high drainage

devices

Lithium-Ion

3.6 VSlow-loss of charge (5% per month)Best energy to weight ratioNo memory effectPopular for portable electronics (cell

phones, IPod)

Ideal Power Cell

Unlimited shelf lifeMaximum energy for minimum

spaceLight weightRechargeable (fast and

complete)

Ideal Power Cell (cont.)

Consumer proof/SafeResistant to environmental

extremesCostPerform in a variety of different

applications

Diode

Made of semi-conducting materialOnly permits current to pass in one

directionL.E.D.: light emitting diode

– Longer leg must be connected to positive side of circuit (cathode)