Nickel Cadmium Battery Electrochemistry Explained.

 A battery is a collection of one or more electrochemical cells that converts chemical energy contained within its active materials directly into electric energy. Many types of batteries are commonly used in modern day applications, and they are named by the elements that make up the electrochemical cell of the battery they include 


1) Nickel Cadmium (Ni-Cd)

2) Lithium Ion (Li-Ion)

3) Nickel-Metal Hydride (NiMH)

4) Lead Acid

The nickel-cadmium (NiCd) battery was invented by Swedish scientist Waldemar Jungner in 1899. Nickel oxyhydroxide (NiOOH) and Cadmium (CD) is submerged inside Potassium hydroxide (KOH).

Components of an Electrochemical cell

Anode: Oxidation occurs at the anode

Cathode: Reduction occurs at the cathode.

Electrodes: In order to hook up an external circuit you need have something to physically connect the wire to. There are two types of electrodes, active and inert. An Inert electrode is made of a substance that does not undergo oxidation or reduction.

Electrolyte: An electrolyte is an aqueous solution of ionic compounds that functions as a conducting medium for ions to move between the cathode to the anode.

How a Nickel Cadmium Electrochemical Cell works.

A Nickel Cadmium electrochemical cell uses 

Nickel oxyhydroxide (NiO(OH)) as the cathode or positive electrode (+) 

Metallic Cadmium (Cd)as the anode or negative electrode (-)

Potassium Hydroxide (KOH) and H2O as the electrolyte where 25%-30% of the total volume is Potassium Hydroxide acid and 70% is Demin water.

Discharging the Cell

When a load is connected across from negative to positive, the positive electrode (Nickel oxyhydroxide) is reduced or gains electrons from the oxidation or loss of reactions happening at the negative electrode. 

How it happens
The Potassium Hydroxide (KOH) is dissociated into Potassium(K+) and Hydroxyl (OH-) ions. The Hydroxyl ions go near the negative electrode and reacts with Cadmium to form Cadmium Hydroxide (Cd(OH)₂), thereby releasing electrons into the circuit.

Anode Reaction = Cd+2OH−→Cd(OH)2​+2e−

The electrons flow through the wires to the load and returns at the positive electrode. At the positive electrode Nickel oxyhydroxide (NiO(OH)) combines with water (H2O) and accepts electrons (2e-) to produce Nickel Hydroxide (Ni(OH)2) and Hydroxide Ions (OH-)

Cathode Reaction = 2NiO(OH)+2H2​O+2e−→2Ni(OH)2​+2OH−

As the battery is operated, the reactants in the cathode and anode are completely reacted and transformed into Cd(OH)₂ and Ni(OH)₂.  At this point, there is no more active material in the electrochemical cell to react, and no more electrons flow.

The battery is now low and requires charging.

Recharging the Cell.
When charging a NiCd battery, electricity from a charger forces the electrons to flow in reverse, converting Cadmium Hydroxide back into Cadmium metal and Nickel Hydroxide back into Nickel Oxyhydroxide.

Over Charging Electrons from the applied external current primarily drives the restoration of the active materials in the cell. Once the anode and cathode have been fully restored, further application of electrical energy has nowhere to go. At this point voltage applied starts to drive electrolysis of water. This results in the breakdown of H₂O into hydrogen (H₂) and oxygen (O₂) gases.

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