Cathode, Anode and Electrolyte

Cathode, Anode and Electrolyte are the basic building blocks of Cells and Batteries.

Lithium ion cell

Lithium Ion Cells

When discharge begins the lithiated carbon releases a Li+ ion and a free electron. Electrolyte, that can readily transports ions, contains a lithium salt that is dissolved in an organic solvent. The Li+ ion, which moves towards the electrolyte, replaces another Li + ion from the electrolyte, which moves towards the cathode. At the cathode/electrolyte interface, Li+ ions then become intercalated into the cathode and the associated electron is used by the external device.

Ande and cathode deifinition in chemistry

Anode-Cathode

Anode and Cathode are not fixed and change positions depending on whether the cell is being charged or discharged. It is therefore incorrect to state that the electrons move from Cathode to Anode during the recharging process. The – and + electrodes (terminals) however stay put. For example, in a typical Lithium ion cobalt oxide battery, graphite is the – electrode and LCO is the + electrode at all times.

Cathode

When discharging a battery, the cathode is the positive electrode, at which electrochemical reduction takes place. As current flows, electrons from the circuit and cations from the electrolytic solution in the device move towards the cathode. Although these processes are reversed during cell charge in secondary batteries, the positive electrode in these systems is still commonly, if somewhat inaccurately, referred to as the cathode, and the negative as the anode.

Cathode active material in Lithium Ion battery are most likely metal oxides. Some of the common CAM are given below

  • Lithium Iron Phosphate – LFP or LiFePO4
  • Lithium Nickel Manganese Cobalt oxide – LiNiMnCoO2 or NMC
  • Lithium Manganese Oxide – LiMnO2
  • Lithium Cobalt Oxide – LiCoO2

Many materials in cathode especially Lithium, Cobalt are rare and expensive. One of the ways to improve Lifecycle sustainability of Li Ion Batteries is to recycle the batteries especially to recover the cathode materials.

Cathode materials market was estimated $30Billion in 2023 and expected to grow to $70Billion by 2030. Cathode material today represents 30% approx of EV Battery cost.

Anode

The Anode is the negative or reducing electrode that releases electrons to the external circuit and oxidizes during and electrochemical reaction. In a lithium ion cell the anode is commonly graphite or graphite and silicon.

Anode Components

The anode is not just graphite or graphite and silicon. It needs additives to increase the conductivity and a binder to hold it all together.

  1. Active material
    • graphite
      • natural
      • synthetic
    • graphite and silicon
    • silicon
  2. Conductive additive
    • Carbon Black
  3. Binder
    • Carboxymethyl Cellulose (CMC)
    • Styrene Butadiene Rubber (SBR)

Electrolyte

Electrolyte is an ionic transport medium. It can be liquid or solid. Liquid electrolytes transport ions between the electrodes and thus facilitate flow of electrical current in the cell or batteries.

Charging and Discharging cycle

To understand better cathode, anode and electrolyte lets see what role they play in functioning of a cell or battery.

Discharging cycle

Charging cycle

References

  1. Dr. Carl Reynolds, Dr. Mona Faraji Niri, Dr. Marc Francis Hidalgo, Dr. Robert Heymer, Dr. Luis Román, Giar Alsofi, Halima Khanom, Ben Pye, James Marco, Prof. Emma Kendrick, Impact of Formulation and Slurry Properties on Lithium-ion Electrode Manufacturing, Chemistry Europe, December 2023