Alkaline Battery

An electric battery is essentially a source of DC electrical energy. It converts stored chemical energy into electrical energy through an electrochemical process. This then provides a source of electromotive force to enable currents to flow in electric and electronic circuits. A typical battery consists of one or more voltaic cells. 

The fundamental principle in an electrochemical cell is spontaneous redox reactions in two electrodes separated by an electrolyte, which is a substance that is ionic conductive and electrically insulated.

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. Batteries are designed so that the energetically favorable redox reaction can occur only when electrons move through the external part of the circuit.

The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction. Because most of the resulting voltages are around 2V, cells are connected in series to obtain more practical electrical potentials (i.e. six 2V lead acid cells are connected in series to obtain a typical 12V battery).

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.

Composition of Alkaline Battery

As shown in the figure, the porous anode and cathode make up the largest parts of the battery. Both electrodes are made of particles, with electrolyte filling the void areas of the electrode. The electric power of the Zn-MnO₂ battery comes from the electrochemical reactions of the cathode and anode active materials. A porous separator keeps the cathode and anode from touching each other. The function of the two current collectors is to build a connection between the battery and the outer electrical circuit.

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⁻ [E_oxidation° = +1.28 V]

2MnO_2(s) + H₂O_(l) + 2e⁻ → Mn₂O_3(s) + 2OH⁻_(aq) [E_reduction° = +0.15 V]

Overall reaction:

Zn_(s) + 2MnO_2(s) ⇌ ZnO_(s) + Mn₂O_3(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.

Advantages and Disadvantages of Alkaline Batteries

Characteristics of Alkaline Batteries

To compare and understand the capability of each battery, some important parameters are characteristic of each battery, also within a type of battery. These parameters are a reference when a battery is needed, and specific qualities are required since batteries are used in all types of devices and for infinite purposes.

Frequently Asked Questions

How to store alkaline batteries?

One of the main advantages of alkaline batteries is that they are easy to store. They are chemically stable, and they have a very low self-discharge rate. Alkaline batteries typically lose 2 to 3 percent of their original charge per year when stored at room temperature (20–30 °C).

Manufacturers recommend storage of zinc–carbon batteries at room temperature. Storage at higher temperatures reduces the expected service life. At lower temperatures, the self-discharge rate is even lower and manufacturers do not recommend that. If so, they need to be returned to normal room temperature before use, and that condensation on the battery jacket must be avoided.

Why do batteries leak?

Alkaline batteries are prone to leaking potassium hydroxide (KOH), a caustic agent that can cause respiratory, eye and skin irritation. The reason for leaks is that as batteries discharge — either through usage or gradual self-discharge — the chemistry of the cells changes and some hydrogen gas is generated. The outer casing of the battery prevents the hydrogen gas from leaking. However, if a battery is left unused in a device for an extended period, the resulting gas buildup can rupture the casing and cause leakage. 

What leaks out of batteries?

It is the electrolyte that can start to leak and form white crystals on the outside of the battery. Potassium hydroxide is the most common chemical to leak out of batteries. Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc. It’s a highly corrosive base that can cause skin irritation and respiratory issues if inhaled.

Is a leaking battery harmful?

A leaking battery is a serious problem that can make your phone or other electronic devices unusable. In addition, since the chemical that leaks out of a battery is typically an acid, it can harm the environment and human eyes and skin. If you touch a leaking battery, it can cause skin burns. Rinse immediately with running water. 

How can you prevent batteries from leaking?

The risk of leaks out of batteries can be reduced by the following precautions:

• Do not attempt to recharge disposable alkaline cells
• Do not mix different battery types in the same device
• Try to replace all of the batteries in the device at the same time
• Storing batteries in a dry place and at room temperature
• Remove batteries for storage of devices

Rechargeable Alkaline Battery

A rechargeable alkaline battery, also known as alkaline rechargeable or rechargeable alkaline manganese (RAM), is a type of alkaline battery that is capable of recharging for repeated use. Their capacity is about 2/3 that of primary cells. They are of dry-cell construction, completely sealed, and not requiring maintenance. Cells have a limited cycle life, which is affected by deep discharge; the first cycle gives the greatest capacity, and if deeply discharged a cell may provide only 20 cycles. The available energy on each cycle decreases. Like primary alkaline cells, they have a relatively high internal resistance, making them unsuitable for high discharge current (for example, discharging their full capacity in one hour).

Why are alkaline batteries (AAA or AA) made to be 1.5V while rechargeables are 1.2V?

In general, batteries convert stored chemical energy into electrical energy through an electrochemical process. This then provides a source of electromotive force to enable currents to flow in electric and electronic circuits.

• Primary (single-use or alkaline) batteries use cells that have 1.5V open circuit voltage when fresh. 
• Secondary (rechargeable) batteries use cells from NiMh or NiCd, which have 1.2V open circuit voltage.

In practice, alkaline batteries and rechargeable batteries can be used interchangeably in sets. They have only different voltage characteristics. It is given by their different chemistry. Primary cells gradually drop in voltage from use. They start at 1.5 volts, drop to 1.2 and continue to 1.0 where the appliance stops working. Secondary cells operate more uniformly, even with only 1.2 volts. They have flat discharge where they pretty much stay at 1.2 volts until depleted and then drop off very quickly to below 1.0 volts.

Since electronic devices are usually made to run from cell voltages of 1.0 to 1.5 volts, alkaline batteries and rechargeable batteries perform similarly. In fact, it’s generally considered that secondary 1.2 V cells work better than alkalines having lower output impedance and more consistent voltage from start to finish of a charge.

Other Types of Batteries

The following list summarizes notable electric battery types composed of one or more electrochemical cells. Four lists are provided in the table. The first list is a battery classification by size and format. Then, the primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry. The third list is a list of battery applications. The final list is a list of different battery voltages.