Copper-zinc cells, rechargeable

Primary cells are non rechargeable cells, in which the electrochemical reaction is irreversible. They contain only a fixed amount of the reacting compounds and are discharged only once. If the educts are consumed by discharging, the cell cannot, or should not, be used again. A well-known example of a primary cell is the Daniell element, consisting of zinc and copper. 

The Daniell cell cannot be recharged in this manner. If we try it, copperfll) ions will migrate to the zinc electrode solution, where they will react directly with the zinc and prodnce a copper-plated electrode. Then, the cell will not function. 

We can now see why batteries have limited lifetimes. As the redox reaction proceeds in the cell just described, the reactants deplete the zinc atoms oxidize and the copper ions reduce. Over time, the zinc electrode dissolves away, and the Cu2+ solution is depleted the battery no longer produces electric current and must be discarded. In a rechargeable batteiy, the recharge cycle uses an external source to force electrons to travel in the opposite direction. The reaction goes in reverse and regenerates the reactants. 

A simple example of a primary (non-rechargeable) reversible cell is the Daniell cell, consisting of a zinc electrode immersed in an aqueous solution of zinc sulphate, and a copper electrode in copper sulphate solution ... 

---