1. Working principle of batteries

The working principle of secondary batteries is based on a controlled and reversible reaction occurring between two electrode materials that are separated by an electrolyte. This reaction is an oxidation-reduction reaction, in which the two electrodes exchange charges: negatively-charged electrons flow through an external electrical circuit from one electrode to the other, while positively-charged ions move through the electrolyte inside the battery cell. The direction of charge flow is from the negative electrode to the positive electrode on discharge, and vice versa on recharge.