Diffusion is one of the three mechanisms by which ions are transported and describes particle transport by concentration compensation. Particles migrate uninfluenced from regions of higher concentration to regions of lower concentration.

At the cathode/electrolyte phase boundary, the depletion of metal ions in the cathode film leads to the formation of the Nernst´sche diffusion layer. In this area, mass transport is only possible by diffusion. The diffusion velocity can be accelerated by increasing the ion mobility (e.g. by increasing the temperature).