Introduction of Alkaline batteries
Alkaline batteries are the type of primary batteries
consists of dry cells and an alkaline electrolyte that reduces corrosion of dry
cells and a collection of dry cells in a specific cover or body are called the
alkaline batteries. Alkaline batteries depend upon the reaction between zinc
and manganese dioxide with dry cells. The duration of alkaline batteries has 5
to 7 years (approximately) and the voltages across each cell are 1.5volt.
The name alkaline batteries are because of the alkaline
electrolyte present in them. Other batteries also use alkaline electrolyte but
the active materials are different in them. The alkaline electrolyte of
alkaline batteries consists of potassium hydroxide and zinc chloride
Alkaline batteries are also a type of secondary batteries
which are rechargeable secondary batteries. These batteries are easily used
many times to recharge them.These batteries consists of very high energy
density and long life as compared to the primary alkaline batteries.
Chemical reaction
Alkaline batteries are also a type of galvanic cell. It
includes an oxidation reduction reaction between zinc and manganese oxide.
These chemicals are surrounded by an alkaline solution of potassium hydroxide.
When an oxidation reduction reaction occurs?
Oxidation reduction reaction occurs when electrons are
transferred between species. For example if we took a piece of zinc and placed
it in a liquid mixture of manganese oxide and potassium hydroxide, it would
react according to the following balanced chemical equation and produce a lot
of heat.
Zn + 2MnO2↔ZnO +Mn2O3 E°=1.43V
Suppose that a piece of zinc is placed in a solution of KOH
in one jar and some MnO2 mixed with KOH in another jar. The reactants are all
present but nothing would happen and there is no way for electrons to move from
the zinc to the MnO2 because both jars have no anyway of interaction between
them.
Now we attach a piece of wire to first jar with the second jar.
Now electrons start moving from one jar to the other and we can see a quick
pulse of electrons flowing through the wire with the help of voltmeter. The
pulse ends almost immediately, because the movement of the electrons between
zinc and MnO2 creates charge separation. The former becomes positively charged
and the later will be negatively charged. To fix this problem we need some sort
of salt bridge. A salt bridge allows positive and negative ions to move between
the jars.to remove the separation of jars; a piece of paper is soaked in KOH
solution. Now when we connect the wire, electrons flow from the zinc to the MnO2,
negatively charged OH− ions move through the salt bridge toward the
zinc, and positively charged K+ions move through the salt bridge toward
the MnO2. The charge stays balanced in both jars, so there is no
electrostatic force which prevents electrons from moving, and they flow freely
through the wire. The battery half reaction is as follows:
Zn + 2OH− ⟶ZnO
+ H2O + 2e− E°=1.28V
and
2MnO2 + H2O + 2e− ⟶Mn2O3 + 2OH− E°=0.15V
2MnO2 + H2O + 2e− ⟶Mn2O3 + 2OH− E°=0.15V
Overall Reaction
Zn + 2MnO2↔ZnO +Mn2O3 E°=1.43V
Construction of alkaline batteries
Alkaline batteries are produced in cylindrical form similar
to zinc carbon batteries and are made in the form of buttons. These batteries
are made by including several cells connected with each other. A cylinder is a
stainless steel and is named cathode. A compressed paste of manganese dioxide
with carbon powder is added into it to increase the conductivity of the battery.
The center of the cathode is separated with a separator. The separator is made
up of synthetic polymer the negative electrode is connected to the second half
of the cylinder which is filled with a gel containing zinc powder and potassium
hydroxide electrolyte. The zinc powder provides more surface area for chemical
reaction to take place. More manganese dioxide is added at the end of the
cylinder to prevent from gassing and for longer life.
Rechargeable alkaline batteries
Some alkaline batteries are designed to be recharged. These
rechargeable alkaline batteries are not sufficient to fulfill their needs.
These batteries are made in very small amount as compared to non-rechargeable
alkaline batteries. To recharge these batteries may cause leakage of liquids or
may be damaged or may cause explosion. These types of batteries have a limit to
recharge usually maximum 10 times of recharge. This limit is not for all
batteries.it depends upon the quality of material used in the battery.
Uses
Alkaline batteries are used in household items such as
breadboard circuits, toys, flashlights, portable
electronic circuits, digital cameras etc.
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