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 1.5 volts.
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.
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
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.