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Mahesh

15/11/23 09:00 AM IST

Types and Working of Elcetric battery

In News
  • The electric battery has increased the penetration of motorisation and wirelessness in our lives. Electric batteries hold and release electrical energy that they have acquired by converting other forms of energy.
History of electrical batteries
  • All chemical reactions are fundamentally about how the electrons in the bonds between atoms are rearranged.
  • The bridge between this fact and the electrochemical cells that were the precursors of modern batteries is most apparent in an experiment that Luigi Galvani conducted in 1780.
  • Galvani touched together two plates of different metals and then touched both at the same time to a frog’s leg. He found that the leg contracted but couldn’t say why.
  • The next major pre-industrial innovation on this front was the voltaic pile built by Alessandro Volta in 1800.
  • This cell consisted of copper and zinc plates arranged in alternating fashion, separated by sheets of paper soaked in salty water. Volta found that this set-up could produce a steady current for some time but, like Galvani, couldn’t explain why.
  • The British chemist John Daniel improved on Volta’s design: he filled a copper pot with copper sulphate, and inside that placed an earthen pot containing a zinc electrode sitting inside sulphuric acid.
  • This more sophisticated set-up could produce an electric current for an even longer duration.
Electric Battery
  • A voltaic, or galvanic, cell uses redox reactions to produce an electric current.
  • The cell consists of two half-cells.
  • Each half-cell is made of a metal electrode immersed in an electrolyte of that metal – say, a zinc electrode in zinc sulphate and a copper electrode in copper sulphate.
  • The two metal electrodes are connected by a wire.
  • The two tubs of electrolyte are connected by a salt bridge (a material that conducts ions while remaining electrically neutral).
  • In the zinc half-cell, zinc ions (Zn2+) from the electrode dissolve in the zinc sulphate, releasing two electrons into the electrode.
  • In the copper half-cell, the reverse happens: copper ions (Cu2+) from the copper sulphate deposit onto the electrode, which now requires two electrons.
  • So the wire connecting the electrodes transports two electrons from the zinc to the copper electrode.
  • Similarly, the salt bridge connecting the two electrolytes allows the Zn2+ and the sulphate (SO42-) ions to meet and exchange electrons.
  • Since the wire connecting the zinc to the copper electrodes carries electrons, an external circuit connected to it can draw the electron flow for various applications.
  • A battery is a collection of cells.
Concept of a battery
  • The cathode is the positively charged electrode, the one to which electrons arrive.
  • The anode is the negatively charged electrode, which ‘supplies’ electrons.
  • In an oxidation reaction, electrons are released, and in a reduction reaction they are consumed.
  • So zinc oxidises at the anode and copper reduces at the cathode. This is the redox reaction at the heart of every electrochemical cell.
  • The energy imparted to the electrons by the half-cells is called the source voltage (previously called the electromotive force). The terminal voltage is like a driving force that pushes the electrons from the anode to the cathode.
  • The higher the source voltage, the greater the cell’s electrochemical potential. For example, nickel-cadmium batteries and zinc-copper cells have voltages of 1.2 V and 1.5 V respectively, whereas lithium-ion cells have more than 3 V.
  • A well-known problem that degrades the performance of electrochemical cells is corrosion.
  • Another source is galvanic corrosion, whereby one of the electrodes in a cell dissolves faster into the electrolyte over time because it is more reactive, before the less reactive electrode starts to erode.
Types of Batteries
  • The Li-ion battery won the developers of its foundational principles the Nobel Prize for chemistry in 2019.
  • This battery is a voltaic as well as an electrolytic cell. A voltaic cell converts chemical energy to electrical energy.
  • An electrolytic cell converts electrical energy to chemical energy. A battery that can do both is thus rechargeable.
  • In a Li-ion polymer cell used in smartphones, a lithium metal oxide is the cathode and graphite is the anode. The electrolyte is a semisolid polymer gel. Microporous polyethylene is used to separate the two half-cells.
  • The basics are as follows: In the voltaic phase, lithium oxidises to Li+ in the anode and releases an electron.
  • The electron moves via the external circuit to the cathode whereas the Li+ moves via the electrolyte to the cathode.
  • There, the ion slips between the layers of carbon sheets that graphite is made of, in a process called intercalation.
  • In the electrolytic phase, an over-voltage is applied to the cell so that it charges: the Li+ moves from the graphite to intercalate in the metal oxide, getting ready for the next discharge.
Hydrogen fuel cell
  • Hydrogen fuel cells are of great interest today.
  • At the anode, a catalyst separates hydrogen into protons and electrons.
  • The electrons flow through an external circuit and the protons through the electrolyte – both to the cathode. At the cathode, the particles react with oxygen from the air to create heat and water.
  • A cell like this will work as long as hydrogen is supplied, and is expected to be a key component of the hydrogen economy.
  • In January 2023, the Indian government approved the Rs-19,744-crore National Green Hydrogen Mission to make India a “global hub” to utilise and export green hydrogen.
Source- The Hindu

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