Batteries are all over the place — in our cars, our PCs, laptops, portable MP3 players and cell
phones. A battery is essentially a can full of chemicals that produce electrons. Chemical
reactions that produce electrons are called electrochemical reactions.
A lithium-ion battery is made of one or more power-generating compartments called cells. Each cell has
essentially three components: a positive electrode (connected to the battery's positive or + terminal),
a negative electrode (connected to the negative or − terminal), and a chemical called an electrolyte in
between them. The positive electrode is typically made from a chemical compound called lithium-cobalt
oxide (LiCoO2) or, in newer batteries, from lithium iron phosphate (LiFePO4). The negative electrode is
generally made from carbon (graphite) and the electrolyte varies from one type of battery to another—but
isn't too important in understanding the basic idea of how the battery works.
All lithium-ion batteries work in broadly the same way. When the battery is charging up, the lithium-based
positive electrode gives up some of its lithium ions, which move through the electrolyte to the negative
electrode and remain there. The battery takes in and stores energy during this process. When the battery
is discharging, the lithium ions move back across the electrolyte to the positive electrode, producing the
energy that powers the battery. In both cases, electrons flow in the opposite direction to the ions around
the outer circuit (DIAGRAM A). Electrons do not flow through the electrolyte: it's effectively an insulating
barrier, so far as electrons are concerned.
The movement of ions (through the electrolyte) and electrons (around the external circuit, in the opposite
direction) are interconnected processes, and if either stops so does the other. If ions stop moving through
the electrolyte because the battery completely discharges, electrons can't move through the outer circuit
either—so you lose your power. Similarly, if you switch off whatever the battery is powering, the flow of
electrons stops and so does the flow of ions. The battery essentially stops discharging at a high rate (but
it does keep on discharging, at a very slow rate, even with the appliance disconnected).
Unlike simpler batteries, lithium-ion ones have built in electronic controllers that regulate how they charge
and discharge. They prevent the overcharging and overheating that can cause lithium-ion batteries to
explode in some circumstances.
The trouble with ordinary batteries
You know a battery is essentially a chemical experiment happening in a small metal canister. Connect the
two ends of a battery to something like a flashlight and chemical reactions begin: chemicals inside the
battery slowly but systematically break apart and join themselves together to make other chemicals,
producing a stream of positively charged particles called ions and negatively charged electrons. The
ions move through the battery; the electrons go through the circuit to which the battery is connected,
providing electrical energy that drives the flashlight. The only trouble is this chemical reaction can happen
only once and in only one direction: that's why ordinary batteries usually can't be recharged.
Rechargeable batteries = reversible reactions
Different chemicals are used in rechargeable batteries and they split apart through entirely different
reactions. The big difference is that the chemical reactions in a rechargeable battery are reversible:
when the battery is discharging the reactions go one way and the battery gives out power; when the
battery is charging, the reactions go in the opposite direction and the battery absorbs power. These
chemical reactions can happen hundreds of times in both directions, so a rechargeable battery will
typically give you anything from two or three to as much as 10 years of useful life (depending on how
often you use it and how well you look after it).
Voltaic Pile (Diagram B)
The voltaic pile was the first electrical battery that could continuously provide an electrical current to a
circuit. It was invented by Alessandro Volta, who published his experiments in 1800. The voltaic pile then
enabled a rapid series of discoveries including the electrical decomposition (electrolysis) of water into
oxygen and hydrogen by Nicholson and Carlisle (1800) and the discovery or isolation of many chemical
elements. The entire 19th century electrical industry was powered by batteries related to Volta's until the
advent of the dynamo (the electrical generator) in the 1870s.
Volta's invention built on Luigi Galvani's 1780s discovery of how a circuit of two metals and a frog's leg
can cause the frog's leg to respond, Volta demonstrated in 1794 that when two metals and brine-soaked
cloth or cardboard are arranged in a circuit they produce an electric current. In 1800, Volta stacked
several pairs of alternating copper(or silver) and zinc discs (electrodes) separated by cloth or cardboard
soaked in brine(electrolyte) to increase the electrolyte conductivity. When the top and bottom contacts
were connected by a wire, an electric current flowed through the voltaic pile and the connecting wire.
Diagram A
Diagram B
Diagram C
Name:______________________
Pre-Lab Reading
Key terms:
Electrolyte- liquid containing ions (charged particles)
Electrode- a conductor, in this case, and end of the battery, so (+) end and (-) end
1) What are the power generating compartments called? ______________
2) What are the three basic parts of a battery?
a)
b)
c)
3) When a battery is charging up describe what is going on: draw a diagram below the has the
electrodes in place already, add in Lithium ions and electrolyte
Positive electrode
Negative electrode
4) When a battery is discharging describe what is going on: draw a diagram below the has the
electrodes in place already, add in Lithium ions and electrolyte
Positive electrode
Negative electrode
LOOK AT DIAGRAM A ON PAGE TWO OF THE READING TO HELP UNDERSTAND
5) The electrolyte acts as a ________ barrier.
6) What happens if ions stop moving through the electrolyte?
7) What happens to your power as a result of this?
8) What happens when you power down the device the battery is in?
9) If you leave batteries in a device that is turned off do they still drain? Explain:
THE TROUBLE WITH ORDINARY BATTERIES
10) How can you start the chemical reaction in a battery?
11) The _______ move through the battery; the ___________ go through the circuit to which the
battery is connected, providing electrical energy that drives the flashlight.
12) In a regular battery the chemical reaction can only do what?
RECHARGEABLE BATTERIES
13) The chemical reactions in a rechargeable battery are what?
14) How long can rechargeable batteries work? Depending on what?
VOLTAIC PILE
15) It was the first battery to do what?
16) About when was it invented?
17) What do you simply need to get a frog’s leg to move?
18) Draw your own diagram of a Voltaic pile below using pennies, nickels, and brine (vinegar)
soaked paper towels.
19) Draw a diagram of a battery using a potato, nail, and penny below