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 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 volts Works well if using 100 mA or less Low capacity 3 year shelf life

anode and anode collector Cathode collector MnO 2 NH 4 Cl ZnCl 2

Alkaline 1.5 V: lose voltage gradually High Capacity (electrical energy) – Last longer 5 year shelf-life Better in high drain devices than C-Zn

MnO 2, graphite Zn powder steel Metal nail Electrolyte KOH

Lithium Started off as button cell Anode: lithium Cathode: magnesium dioxide 3 V: Takes up less space with more voltage

Lithium High Capacity Low Drain Rate Toxic: Special disposal Light Weight

Button Cell Anode: Zinc or Lithium Cathode: Silver or Mercury Oxide Compact Large 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 Volts Low capacity Memory effect (Rechargeable) – If you re-charge the battery too soon, you lower its capacity

Nickel-Metal Hydride (NiMH) 1.2 V Best rechargeable battery High Capacity Good for high drainage devices

Lithium-Ion 3.6 V Slow-loss of charge (5% per month) Best energy to weight ratio No memory effect Popular for portable electronics (cell phones, IPod)

Ideal Power Cell Unlimited shelf life Maximum energy for minimum space Light weight Rechargeable (fast and complete)

Ideal Power Cell (cont.) Consumer proof/Safe Resistant to environmental extremes Cost Perform in a variety of different applications

Diode Made of semi-conducting material Only permits current to pass in one direction L.E.D.: light emitting diode – Longer leg must be connected to positive side of circuit (cathode)