Charge and discharge mechanism

During charging, an external source drives electrons through collectors toward the anode while sodium ions migrate through electrolyte and separator to maintain charge balance; discharge reverses the directions and supplies the load. Confusing ion and electron paths leads to incorrect views of shorts and resistance.

Layered oxides, polyanionics, and Prussian blue analogues have different sodium sites and structural responses, while hard carbon and other anodes have their own storage processes. Explain charge and discharge with the electrode pair rather than assigning one mechanism to every sodium-ion cell.

At higher rates, lower temperatures, or after aging, voltage profiles and usable capacity can change. Causes may include transport limits, interfaces, or material structure; diagnosis needs current, temperature, rest time, and test protocol together.