What is a Battery?

A battery is a device made up of one or more electrochemical cells that converts chemical energy into electrical energy. Electrochemical cell is also termed as Voltaic cell or Galvanic cell named after the scientists Alessandro Volta and Luigi Galvani respectively. Electrochemical cell has a long history of use dated around 2000 years back when 1 to 2 volt was generated using clay cased battery. Batteries when arranged in series and parallel combination for required current and voltage are termed as Module, while group of modules when connected together, is termed as Battery Pack. 

Note: A battery actually is made up of one or more electrochemical cells, so they are most often used interchangebly.

Battery Components

Primarily, there are six battery components, 1. Cathode: It is the positive electrode of the cell. 2. Anode: It is the negative electrode of the cell. 3. Electrolyte: It is a media to provide ion transfer within the cell. 4. Terminal/Tab: It provide the connection between the battery electrodes and external circuit. 5. Casing: It is the structural element which houses the components of a battery. 6Separator: It is a thin membrane to separate electrodes to prevent short circuit while permits the flow of ions through it.

Battery Types

Batteries can broadly be classified on the basis of (a) Usage (b) Electrolytes (c) Electrodes. On the basis of usage, there are Primary cell (single use/ non-rechargeable) and Secondary cell (reusable/ rechargeable). On the basis of electrolytes, primarily there are Dry cell (uses paste electrolyte which eliminates the possibility of spillage), Alkaline cell (uses alkaline electrolytes of potassium hydroxide) and Flow batteries (electrolytes contained in a separate tank is made to flow through a electrochemical cell). 

1. Primary cell: The electrochemical cells which undergo irreversible chemical reaction and convert chemical energy to electrical energy only, ie. they are for single use and once discharged they are discarded. These discarded cells contribute to huge amount of waste generation which is a threat to environment. Daniel cells and Leclanche cell are two types of primary cell. Daniel cell (Cathode-Copper, Anode- Zinc, Electrolyte-Copper sulphate solution) consist of copper container having copper sulphate solution and a zinc rod immersed in dilute sulphuric acid held in a porous vessel to allow ion movement across it. The zinc as anode oxidize produces zinc ion, while copper cathode recieve copper ion resulting into its reduction to copper metal which deposits at the cathode which creates a flow of current from copper to zinc electrodes as current flows in direction opposite to flow of electrons, which flows from zinc to copper electrode (from external circuit when load is connected). Leclanche Cell (Cathode-Carbon, Anode- Zinc, Electrolyte-Ammonium chloride solution) consist of a glass vessel having ammonium chloride solution, which has zinc rod dipped into it as an electrode, and a porous pot filled with a mixture of manganese dioxide and charcoal powder. There is a carbon rod in the porous pot as another electrode, thus the current flows from carbon electrode to zinc electrode as electrons from zinc to carbon electrode flows due to the oxidation of zinc. The electromotive force (EMF) of the Leclanche cell is approximately 1.5 volts, which is greater than the EMF of the Daniel cell i.e. 1.1 volt approximately.

2. Secondary cell: The electrochemical cells which undergo reversible chemical reaction and convert chemical energy to electrical energy and vice versa when connected to electrical sources are called secondary cell. These cell are discharged during used and are again recharged when connected to electricity. The recharging and charging can be done as per the cycle life of it. The higher is the cycle life the greater number of times the cells can be used repeatedly. Secondary cells are one of the promising solution to sustainable solution to efficient utilization of energy resources.

However, based on the geometry/shape, batteries are also classified into four types:

1. Cylindrical: It is one of the most common type of battery widely used as primary or secondary battery. In these batteries, the anode, cathode, separator and current collectors are rolled up on a cylidrical rod then put inside a rigid cylindrical casing of a suitable metal. The mechanical strength of such batteries are more and the stress due to internal pressure development is uniformly distributed. Due to cylindrical shape,  the packing efficiency is low while making a battery module but the cooling efficiency is improved due to the presence of voids between the batteries allowing fluid flow for cooling.

2. Prismatic: These batteries are formed by putting the layers of anode, cathode, separator and current collectors over one another and rolling it just to put it inside a rigid box like casing. Since the prismatic batteries are box shaped, there are no voids between various batteries while arranging it for module development. Consequently, the packing efficiency is more but the cooling efficiency is less. 

3. Pouch: These batteries are actually prepared with a flexible casing with stacked instead of wound layers of anode, cathode, separator and current collectors over one another. Due to flexible casing, the battery becomes flexible and can be fitted in devices with minimal available space. Pouch shaped batteries must be provided some allowance to accommodate bulging which may occur after several cycle of charging and discharging. Since, the layers of anode, cathode, separator are stacked, hence pouch batteries may generally have several electrochemical cells.

4. Button: They are flat and round in shape which resembles coins hence commonly called as coin cell/battery. The casing of such batteries are rigid. They are specifically designed for its use in small electronic devices such as wrist watch, digital thermometers etc., which require very less power. Portable devices consumes less power, button cell/battery are used as primary batteries and last for long. 

Note: Cylindrical LIB cells are used in Tesla, prismatic cells are used in BMW, and Nissan uses pouch cells.

References:

1. Shashi Kala, A. Mishra, Vishesh Shukla (2020). Battery Technologies and its future prospects. Journal of Indian Chemical Society.

2. Schmuch, R.; Wagner, R.; Hörpel, G.; Placke, T.; Winter, M. Performance and cost of materials for lithium-based rechargeable automotive batteries. Nat. Energy 2018, 3, 267–278.

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