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Chemistry of batteries NiCd, NiMH and Lithium

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Chemistry of batteries

NiCd, NiMH and

Lithium

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How does a NiCd battery work?

Firstly, how does an electrochemical cell work? A cell is a single electrochemical device with a single

anode and a single cathode. A battery is a collection of cells, usually connected in series to obtain a

higher terminal voltage.

The battery in your phone is made up of a number of cells, in the case of the Nokia Orange the battery is

nominally 6VDC and hence made up of 5 cells each of 1.2V. A picture of the battery insides can be

seen here.

A cell has a voltage which is fixed by its chemical composition. Batteries, whether they are primary

(use once) or secondary (rechargeable) are devices which convert chemical energy into electrical

energy. In the case of the latter, they can take electrical energy and store it as chemical energy for later

use. The key to electrochemistry are the processes of oxidation and reduction. Remember the phrase"

"LEO (the lion) goes GER (grr??)"—L ose Electrons Oxidation—Gain Electrons Reduction.

When one oxidizes a material, it gives up electrons it becomes more positively charged, or enters a

higher oxidation state. Likewise, when one reduces a material, one is adding electrons to it and either

making it negatively charged or reducing its oxidation state.

Now, one can make a cell using two materials, say A and B and immersing them in a solution which can

conduct electricity, called an electrolyte. Now, let us say that material A is easily oxidized — it likes to

lose electrons, while B is a material that likes to be reduced. When these two materials are immersed in

an electrolyte, and a circuit is completed from A to B, A is oxidized and electrons are released to flow to

the circuit. After performing electrical work, the electrons flow into B, where B is reduced. The circuit

from B to A is completed by the flow of ions in the electrolyte. (An ion is a charged atom or radical of

a molecule capable of transferring electrical charge).

A secondary cell can be reversed by forcing electrons into A, and reducing the oxidized A to regain

unoxidised A for use again. This, of course, is an oversimplified view, as only certain combinations of

materials and electrolytes provides useful and practical batteries.

Oh, one more bit of nomenclature: The cathode is where reduction takes place, and the anode is where

oxidation takes place. So, in a battery which is producing current, the positive terminal is the cathode,

and the negative terminal is the anode. Yes, this is counterintuitive from our understanding of diodes,

where the cathode is negative with respect to the anode.

The NiCd system

When the cell is fully charged the cathode is composed of Nickelic Hydroxide. Nickel is one of those

elements that has multiple oxidation states— it can lose a different number of electrons per atom,

depending on how hard it is coerced. Nickel is usually found with oxidation states of 0 (free metal), +2,

+3 and +4. The +2 state is referred with a -ous suffix, while the +3 and +4 states are referred with a -ic

suffix. So, nickelic hydroxide is really NiOOH (the nickel has a charge of +3) or Ni(OH) (the nickel has

a charge of +4)

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Chemistry of batteries NiCd, NiMH and Lithium How does a NiCd battery work? Firstly, how does an electrochemical cell work? A cell is a single electrochemical device with a single anode and a single cathode. A battery is a collection of cells, usually connected in series to obtain a higher terminal voltage. The battery in your phone is made up of a number of cells, in the case of the Nokia Orange the battery is nominally 6VDC and hence made up of 5 cells each of 1.2V. A picture of the battery insides can be seen here. A cell has a voltage which is fixed by its chemical composition. Batteries, whether they are primary (use once) or secondary (rechargeable) are devices which convert chemical energy into electrical energy. In the case of the latter, they can take electrical energy and store it as chemical energy for later use. The key to electrochemistry are the processes of oxidation and reduction. Remember the phrase" "LEO (the lion) goes GER (grr??)"—L ose Electrons Oxidation—Gain Electrons Reduction. When one oxidizes a material, it gives up electrons it becomes more positively charged, or enters a higher oxidation state. Likewise, when one reduces a material, one is adding electrons to it and either making it negatively charged or reducing its oxidation state. Now, one can make a cell using two materials, say A and B and immersing them in a solution which can conduct electricity, called an electrolyte. Now, let us say that material A is easi ...
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