In the early 1830s, Michael Faraday laid the foundations of electrochemistry and solid-state ionics by discovering the motion of ions in liquid and solid electrolytes. Earlier, around 1800, Alessandro Volta used a liquid electrolyte in his voltaic pile, the first electrochemical battery, but failed to realize that ions are involved in the process. Meanwhile, in his work on decomposition of solutions by electric current, Faraday used not only the ideas of ion, cation, anion, electrode, anode, cathode, electrolyte and electrolysis, but even the present-day terms for them. Faraday associated electric current in an electrolyte with the motion of ions, and discovered that ions can exchange their charges with an electrode while they were transformed into elements by electrolysis. He quantified those processes by two laws of electrolysis. The first law (1832) stated that the mass of a product at the electrode, Δm, increases linearly with the amount of charge passed through the electrolyte, Δq. The second law (1833) established the proportionality between Δm and the “electrochemical equivalent” and defined the Faraday constant F as F  = (Δq/Δm)(M/z), where M is the molar mass and z is the charge of the ion.
In 1834, Faraday discovered ionic conductivity in heated solid electrolytes AgS and PbF. In PbF, the conductivity increase upon heating was not sudden, but spread over a hundred degrees Celsius. Such behavior, called Faraday transition, is observed in the cation conductors NaS and LiSiO and anion conductors PbF, CaF, SrF, SrCl and LaF.
Later in 1891, Johann Wilhelm Hittorf reported on the ion transport numbers in electrochemical cells, and in the early 20th century those numbers were determined for solid electrolytes.