A battery is an energy storage device that stores chemical energy for later release as electrical energy as electricity. A battery can be defined as an electrochemical cell with one or more series of reactions(the combination of several electrochemical cells) that can be used as a direct source of electric current at a constant voltage. Moreover, the battery can be used as the source for direct electricity. It is useful notes for a school science project.
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Types of Batteries:
- Primary Battery or Primary Electrochemical Cell: In these types of batteries the electrochemical cell reaction is not reversible, all the electrochemical reactants are converted to oxidative or reductive products. It can’t produce electricity on no more reactant species.
- Secondary Battery or Secondary Electrochemical Cell: In these types of secondary batteries the electrochemical cell reaction is reversible, which can be done by passing direct electric current in the opposite or reverse direction. It may be used through a large number of electrochemical cycles of charging and discharging.
Characteristics of Battery:
(i) The voltage of Electrochemical cell: Voltage of the battery depends on the electromotive force (emf) of the electrochemical cells which can be obtained by famous Nernst’s equation.
E0 cell = ( E0 cathode – E0 anode ) – (2.303 RT/ n F ) log Q
= E0 cell – (0.0592 V/n) log [conc. of Products/conc. of Reactants]
(ii) Standard Electrode potential of cell (E0 cell): If Ecell is more of positive value, the Ecell becomes higher and vice versa.
(iii) The temperature of electrochemical cell: An increase in temperature of the electrochemical cell decreases the value of E cell and vice versa.
(iv) The current is the rate at which the battery discharging. If the battery with the capacity to produce more current, then the battery discharge very faster. A battery can deliver high current only if the transfer of the electron is fast in the electrochemical cell reaction.
(v) The capacity of the electrochemical nature of the battery depends on the mass of the active material in the battery which is given by Faraday’s
C capacity = w nF/M
where, w= mass of the active electrochemical material, M= molar mass of active electrochemical material.
Alkaline Batteries (Primary Battery):
In alkaline batteries (primary battery) is called the non-reversible or non-rechargeable battery. Alkaline such as KOH is used as the electrolyte for conduction of ions and Zn in powdered form is mixed with KOH to get a gel. In transition metal zinc (Zn) easily undergoes oxidation or corrosion. In alkaline conditions, Zn won’t undergo corrosion reactions. This gel paste is active electrochemical material of the battery. Graphite rod in the center of the battery is surrounded by a gel paste containing MnO₂ and the outside body is made up of Zn metal foil.
Electrochemical Reaction at Cathode:
2 MnO₂ (s) + H₂O (l) + 2 e- ⟶ Mn₂O₃ (s) + 2 OH- (aq)
Electrochemical Reaction at Anode:
Zn (s) + 2 OH – (aq) ⟶ Zn(OH)₂(s) + 2 e-
Net Electrochemical Cell Reaction:
Zn (s) + 2 MnO₂ (s) + H₂O (l) ⟶ Zn(OH)₂ (s) + Mn₂O₃ (s)
Advantages of Alkaline Battery:
(i) Zn does not dissolve in basic medium. Zn undergoes corrosion reaction in an acid medium
(ii) It maintains better voltage as the current drawn from its electrochemical reaction.
(iii) The life of the alkaline battery is longer than the dry cell since there is no corrosion of Zn. But it purely depends on the usage of battery.
Alkaline batteries are used in camera exposure controls, calculators, torch light, watches, etc.
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Lead acid battery (Lead acid accumulator) or Acid storage cell or Car battery:
These batteries were developed sometimes back and are now used very widely. The design does not change drastically. Modification and improved versions have flooded the market. Once it was thought that these batteries using an electrolyte solution cannot be sealed airtight. But recently sealed
lead acid batteries have been developed.
Construction of lead or car battery:
Lead grids are coated with a paste consisting of lead monoxide (PbO) and dilute sulphuric acid (22%). One set of grids is connected together to a common terminal; similarly another set is connected to another terminal. The two set are arranged such that plates of one set are adjacent to the plates of the other set. Porous PVC diaphragm sheets are placed intermittently, separating one plate from the other eclectically.
The assembly is housed in an ebonite or PVC container. The container is then filled with dilute sulphuric acid. The container is closed by a lid which is provided with holes for filling up of acid.
First Charging of lead battery or car battery:
The terminal of one set of plates is connected to the positive and other set to the negative terminals of a DC rectifier. A suitable current under a suitable voltage is passed for the required time. During this charge , lead monoxide coating on the set of plates connected to the terminal of the rectifier is oxidized to porous, spongy, and electro active lead dioxide. The lead dioxide coating present on the other set of plates connected to the negative terminal is reduced to porous, spongy, and electroactive lead. Now the battery is ready for use that is discharged.
PbO ⟶ PbO₂ (+) Oxidation
PbO ⟶ Pb (-) Reduction
Reactions during discharging of lead or car battery:
At anode of car battery (oxidation of Pb)
Lead is oxidized to Pb2+ ions, which further combines with SO42- forms insoluble PbSO₄
Pb ⟶ Pb²⁺ + 2e⁻
Pb²⁺ + SO₄²⁻ ⟶ PbSO₄
Pb + SO₄²⁻ ⟶ PbSO₄+ 2e⁻
At the cathode of the car battery (reduction of PbO₂)
PbO₂ is reduced to Pb²⁺ ions, which further combines with SO₄²⁻ forms insoluble PbSO₄
PbO₂ + 4H⁺ + 2e⁻ ⟶ Pb²⁺ + 2H₂O
Pb²⁺ + SO₄²⁻ ⟶ PbSO₄
PbO₂ + 4H⁺ + SO₄²⁻ +2e⁻ ⟶ PbSO₄ +2H₂O
The overall reaction during charging of lead or car battery is,
Pb + PbO₂ + 2H2SO4 ⟶ 2PbSO₄+ 2H₂O + Energy (exothermic)
Lead sulfate is precipitated at both electrodes. When 21.4% H2SO4 is used as an electrolyte at 25⁰C, the voltage is about 2.0 V. Lead cell is commonly used in automobiles (combination six cells in series to form a battery with an emf of 12 V.
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Reactions during Charging of car battery:
When an external emf greater than 2 V from the generator is passed to the battery,(the positive pole of the generator is attached to the positive pole of the battery) the cell reaction gets reversed.
The reaction at the Cathode: (charging car battery)
PbSO₄ + 2 e- ⟶ Pb + SO42-
Reaction at the anode:
PbSO₄ + 2H₂O + 2e- ⟶ PbO₂ + 4H⁺ +SO₄²⁻
Net chemical reaction:
2PbSO₄ + 2 H₂O + Energy ⟶ Pb + PbO₂+ 4H⁺ +SO₄²⁻
During the charging process the concentration of the sulphuric acid increase, while during the discharging process, the concentration of sulphuric acid decreases.
Lead acid storage or car battery used in gas engine ignition, mines, laboratories, hospitals, broadcasting stations, automobiles as a car battery, power stations, etc.
Nickel –Cadmium (nicad) Batteries:
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