Primary and Secondary Batteries

Electrochemistry

E. Valenzuela

What is a battery?

• An electrochemical device which transforms the energy liberated in a chemical reaction directly into electricity.

How do we use batteries?

• Portable sources of electric power.

• Storage energy.i. Electric vehicles.ii. Emergency.iii. In conjunction with renewable power sources.

Generation-Consumption Curve

How did start?

Classification

• Primary Cells. a. Designed to be used once and discarded

• Secondary Cells. a. A rechargeable electric cell that converts chemical

energy into electrical energy by a reversible chemical reaction. Also called storage cell.

b. can be recharged and can therefore be used to store electrical energy in the form of chemical energy

Advances in performance.

Good business !

$50 000 million US

Leclanché cell

1.5 Volts

Common, low-cost primary battery; available in a variety of sizes.

Low consumption devices.Flashlight, portable radios, toys.

Leclanché cell

Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) → ZnCl2 + Mn2O3(s) + 2 NH3(aq) + H2O

The Leclanche or zinc-carbon dry cell battery has existed for over 100 years and had been the most widely used of all the dry cell batteries because of its low cost, relatively good performance, and ready availability.

Alkaline cell

1.5 Volts

• High current applications.• Four times the capacity of a

equivalent size rechargeable Nickel Cadmium or Nickel Metal Hydride cells.

• Four to nine times longer lifespan than the equivalent Leclanché cell.

Early 1960’s - Ten Batteries, two transistors!

Pacemakers

14

Modern Pacemaker – one battery, thousands of “transistors”

The Lithium/Iodine battery

• One could argue that, based on standard battery performance criteria, it’s not a very good battery!• It can’t start a car, run a cell phone, or even power a flashlight.• It has very high internal resistance• It doesn’t work well when it’s cold.• It doesn’t work well when it’s too hot (above 55⁰C).• Temperatures above 60⁰C will permanently damage the cell. It

explodes like a bomb at 180.5ºC (the melting point of lithium).• It’s not inexpensive to manufacture.

• BUT – Put it at 37⁰C and ask it to provide 10 – 50 microamperes of current, and it will do it reliably for many years.

PacemakersLithium / iodine batteries.

3.1 V

Li + 1⁄2I2 → LiI

Last 15 years.Low current.

Other primary cells.• Button cells.

Mercury 1.4 VZn + HgO → ZnO + Hg

Zinc / Air 1.65 VZn + 1⁄2O → ZnO

Silver Oxide 1.55VZn + Ag2O → ZnO + 2Ag

Mark #7 torpedoes. Alfa class submarines.

Hints for the exam

• Definitions such as:• Energy density.• Power density.• Self discharge.• Battery internal resistance.• Maximum power transfer theorem.