Anode-Cathode

When a battery is discharging the electrons, e , move from the – to + terminal and while it is charging the electrons travel from the + to the – terminal. Both, during the discharge and recharge electrons move from the Anode to the Cathode. {Anode and Cathode swap places}.

These electrons are generated by the reduction and oxidation reactions (redox) inside the cell. Oxidation is loss (OIL) of electrons and Reduction is gain (RIG) of electrons. During discharge, oxidation occurs at the – electrode. These generated, or lost electrons move to the load and received at the + terminal where reduction occurs. The reverse occurs during recharge process.

In chemistry, we define Cathode as the electrode where reduction takes place and Anode the electrode where oxidation occurs. Both, during the discharge and recharge electrons move from the Anode to the Cathode. {Anode and Cathode swap places}.

The direction of electric current, I is opposite to the direction of electron flow. So when the battery is discharging the current travels from the + to the – terminal and while recharging the opposite occurs. Electrical Engineers define Cathode as the electrode from which the conventional current leaves and the Anode as the electrode through which the current enters into the device. Hence during discharge of the battery the + terminal is the Cathode and when the battery is recharging the – terminal becomes the Cathode. Thus, The chemistry and electrical engineering definition of Cathode and Anode are aligned.

In conclusion, the 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.

Reference

  1. Frith, J.T., Lacey, M.J. & Ulissi, U. A non-academic perspective on the future of lithium-based batteries. Nat Commun 14, 420 (2023)

Lithium ion cell

Lithium Ion Cell

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.

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