Lithium-Ion Cell (Li-ion battery)

• It is a rechargeable batter in which Li-ion moves between anode and cathode during charging and discharging
• More popular than other batteries due to higher negative value of reduction potential and lower atomic mass of Li. Only 6.94g of Li is required to produce 1 mole of electrons
• Positive electrode is made of crystalline mixed oxide LiCoO2.

  Crystal contains Li+ and Co3+ ion occupying voids of oxide array.

  They are synthesized by hydrolysis of respective metal salts under hydrothermal conditions.
• Negative electrode is made of graphite
• Electrolyte is a solution of Li salt like LiPF6, LiBF4, LiClO4 in an organic solvent like ether or a solid phase polymer electrolyte which can transport Li+ ion
• A Solid Electrolyte Interface/Separator (SEI) separate the anode and cathode compartments
• During charging

  • the cell acts as an electrolytic cell
  • anode is LiCoO2
  • cathode is graphite
• During charging at anode, Li+ ions gets removed from the crystal lattice and in the respective lattice sites Co3+ oxidizes to Co4+ to maintain electrical neutrality in the lattice
• During charging at cathode, Li+ ion produced at anode migrates through the electrolyte and gets reduced to Li atom at graphite electrode. Li atoms are inserted between the layers of carbon atoms. This is called Lithiated Graphite (LixCg) containing no Li metal as such.

  This is why it is called Li-ion battery and not Li battery
• When Lithium ion cells are managed to charge completely, anodic material becomes CoO2 which is an explosive material due to liberation of O2 gas on decomposition.

  Hence, there are automatic built-in circuit breakers that allow charging only up to 90%
• During discharging

  • cell acts as electrochemical cell
  • anode is graphite
  • cathode is LiCoO2
• The most popular cathode material is graphite because every 6 Carbon atoms can accommodate a Li atom
• Li-ion cell based on LiCoO2 has emf = 3.7 V

  Used in cell phones, laptops, digital cameras, etc.
• Li-ion cell based on LiFePO4 has emf = 3.3 V

  Suitable for making large size battery for automobile applications