Batteries are galvanic cells, or a series of cells, that produce an electric current. When cells are combined into batteries, the potential of the battery is an integer multiple of the potential of a single cell. There are two basic types of batteries: primary and secondary. Primary batteries are “single use” and cannot be recharged. Dry cells and (most) alkaline batteries are examples of primary batteries. The second type is rechargeable and is called a secondary battery. Examples of secondary batteries include nickel-cadmium (NiCd), lead acid, and lithium ion batteries.
Fuel cells are similar to batteries in that they generate an electrical current, but require continuous addition of fuel and oxidizer. The hydrogen fuel cell uses hydrogen and oxygen from the air to produce water, and is generally more efficient than internal combustion engines.
The lead – acid battery is made up of a series of cells. One cell consists of a lead peroxide positive plate and a lead negative plate both immersed in a dilute sulphuric acid solution. The sulphuric acid is known as the ‘electrolyte’. In other words, lead acid batteries often use sulphuric acid as the major component of the electrolyte.
A battery electrolyte is an acid or a base that dissociates into positive and negative charged ions that react with the anode and cathode as a battery undergoes an oxidation-reduction reaction.
Actual construction uses interleaved plates in the cell in order to produce a compact arrangement with a greater capacity. The complete battery is usually surrounded by a heavy-duty plastic, hard rubber or bitumen case.
In the charged condition the battery contains lead, lead peroxide and sulphuric acid. During discharge, i.e. the providing of electrical power, some of the lead peroxide and the lead will change to lead sulphate and water. The sulphuric acid is weakened by this reaction and its specific gravity falls.
When the battery is charged, i.e. electrical power is put into it, the reactions reverse to return the plates to their former material and the water produced breaks down into hydrogen gas which bubbles out.
Lead-acid batteries can be classified as secondary batteries. The chemical reactions that occur in secondary cells are reversible. The reactants that generate an electric current in these batteries (via chemical reactions) can be regenerated by passing current through the battery (recharging).
The chemical process of extracting current from a secondary battery (forward reaction) is called discharging. The method of regenerating active material is called charging.
The basic cell of the alkaline battery consists of a nickel hydroxide positive plate and a cadmium and iron negative plate immersed in a solution of potassium hydroxide.
In other words, Alkaline batteries typically use sodium hydroxide or potassium hydroxide as the main component of the electrolyte. Alkaline batteries are often used in applications where long-lasting, high-energy output is needed, such as cellular phones, portable CD players and radios, pagers, and flash cameras.
An interleaved construction is again used and each cell is within a steel casing. This casing is electrically ‘live’ being in contact with the electrolyte and possibly one set of plates. A battery consists of a group of cells mounted in hardwood crates with space between each. The cells are connected in series to give the battery voltage.
In the charged condition the positive plate is nickel hydroxide and the negative plate cadmium. During discharge oxygen is transferred from one plate to the other without affecting the specific gravity of the potassium hydroxide solution. The negative plate becomes cadmium oxide and the positive plate is less oxidized nickel hydroxide. Charging the battery returns the oxygen to the positive plate.
Types of Alkaline Batteries
1. There are four types of batteries based on the composition of the active materials in the plates. These are their names:
- Nickel iron (or Edison).
- Nickel- cadmium (or Nife).
- Silver zinc.
- Alkum battery.
2. These batteries can also be classified as sealed or non-sealed depending on how they are assembled.
3. The alkaline battery is also classified as an enclosed pocket or open pocket battery based on the design of the plates.
Alkaline Dry Cell Structure
Chemically, an alkaline dry cell battery has a zinc anode and a manganese dioxide cathode. The electrolyte is a non-acidic basic paste. An electrolyte used in alkaline batteries is potassium hydroxide. Physically, an alkaline battery consists of a steel can be packed with manganese dioxide in its outermost internal cathode region and is filled with zinc and the electrolyte within the center-most internal anode region. The electrolyte surrounding the anode mediates the chemical reaction between the anode and the cathode.
Lead Acid Dry Cell Structure
Chemically, a lead-acid dry cell battery has a zinc anode and a carbon rod/manganese dioxide cathode. The electrolyte is generally an acidic paste. An electrolyte consists of a mixture of ammonium chloride and zinc chloride. Physically, a lead acid battery is constructed the reverse of an alkaline battery. The zinc container serves as an outer anode whereas the carbon rod/manganese dioxide occupies the inner region as the cathode. The electrolyte is mixed with the cathode and mediates the chemical reaction between the cathode and the anode.
Advantages of Lead Acid Battery
- It is available in all shapes and sizes.
- It does not require any maintenance.
- It is best in terms of reliability and working capabilities.
- It withstands slow, fast and overcharging.
- It is capable to withstand long term inactivity with or without solvent.
- Large current capability.
- It offers best value for power and energy per KWH.
- It offers longest life cycle.
- Can be made for a variety of applications
- About 97% of lead can be recycled and reused in new batteries.
- Relatively cheap to manufacture and buy (they provide the lowest cost per unit capacity for rechargeable cells).
- It offers low self discharge, which is lowest among rechargeable batteries.
- It offers good performance at low and high temperature.
Advantages of Alkaline Battery Over Lead-acid Battery
- A large amount of power can be drawn from them, when compared to lead-acid.
- Alkaline battery is equally effective in continuous and intermittent applications.
- Take a longer time to discharge.
- They are light, thus can be moved to and fro easily.
- Have a high resistance to temperature. They are not vulnerable to damage caused by a high amount of heat. They performs equally well at room temperature and at low temperatures.
- Require little care to maintain – the level of the electrolyte does not need to be corrected.
- They last for a longer time.
- Offers high safety. Chemicals present in an alkaline battery are not harmful, they only cause mild effects like irritation. This is opposite to a lead-acid battery which has very poisonous lead metal and a corrosive acid. This means if an alkaline battery explodes it will cause minimal damage, while a lead acid will cause massive damage.
- The internal resistance of an alkaline battery is also low.
- It has a sufficiently long shelf-life.
- This battery has a low leakage rate.
- It is more dimensionally stable.
Disadvantages of Lead Acid Battery
- Fails after a few years of use. Its lifespan is typically 300 – 500 cycles.
- Cannot always be used in a variety of orientations
- Corrosive electrolyte (can cause burns to people and corrosion on metalwork)
- Lead is not environmentally friendly
- Acid needs disposing of with care
- Not suitable for fast charging
- Must be stored in charged state once electrolyte introduced
- Typical charging efficiency only around 70%
Disadvantages of Alkaline Battery
- Alkaline batteries are bulkier than other lithium batteries which give much higher energy.
- Alkaline batteries have a high internal resistance. This reduces the output.
- A defective battery charger can cause the alkaline batteries to explode.
- Alkaline batteries kept in devices that are not used for a long time, can leak and thus completely ruin the device itself because of the corrosive nature of the leaked material.