Alkaline Battery
An alkaline battery (IEC code: L) is a type of primary battery that provides direct electric current from the electrochemical reaction between zinc and manganese dioxide (MnO2) in the presence of an alkaline electrolyte.
The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide (KOH) instead of the acidic ammonium chloride (NH4Cl) or zinc chloride (ZnCl2) electrolyte of the zinc–carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.
The primary alkaline battery is a widely used product, which is essential for powering many portable devices, such as power tools, radios, toys, and remote controls. The most common size of alkaline battery is the well-known AA battery. Alkaline batteries are most commonly used in portable devices that have low current drains, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available.
Chemistry of Alkaline Batteries
In simple terms, each battery is designed to keep the cathode and anode separated to prevent a reaction. The stored electrons will only flow when the circuit is closed. This happens when the battery is placed in a device, and the device is turned on.
When the circuit is closed, the stronger attraction for the electrons by the cathode (e.g. manganese dioxide in alkaline batteries) will pull the electrons from the anode (e.g. zinc) through the wire in the circuit to the cathode electrode. This battery chemical reaction, this flow of electrons through the wire, is electricity.
If we go into detail, batteries convert chemical energy directly to electrical energy. Chemical energy can be stored, for example, in Zn or Li, which are high-energy metals because they are not stabilized by d-electron bonding, unlike transition metals.
Even though a wide range of types of batteries exists with different combinations of materials, all of them use the same principle of the oxidation-reduction reaction. In an electrochemical cell, spontaneous redox reactions take place in two electrodes separated by an electrolyte, which is an ionic conductive and electrically insulated substance. The redox reaction is a chemical reaction that produces a change in the oxidation states of the atoms involved. Electrons are transferred from one element to another. As a result, the donor element, which is the anode, is oxidized (loses electrons), and the receiver element, the cathode, is reduced (gains electrons).
In an alkaline battery, the negative electrode is zinc, and the positive electrode is high-density manganese dioxide (MnO2). The alkaline electrolyte of potassium hydroxide, KOH, is not consumed during the reaction. Only the zinc and MnO2 are consumed during discharge. The alkaline electrolyte of potassium hydroxide remains, as there are equal amounts of OH− consumed and produced.
The half-reactions are:
Zn(s) + 2OH−(aq) → ZnO(s) + H2O(l) + 2e− [Eoxidation° = +1.28 V]
2MnO2(s) + H2O(l) + 2e− → Mn2O3(s) + 2OH−(aq) [Ereduction° = +0.15 V]
Overall reaction:
Zn(s) + 2MnO2(s) ⇌ ZnO(s) + Mn2O3(s) [e° = +1.43 V]
Applying this battery chemistry to the real world, the electrons generated during the reaction are used to power devices when the circuit is closed.
