Why pair a battery with a supercapacitor: the mechanism in three notes
I have published three linked notes on the mechanism behind hybrid energy storage. Between them they answer one question — why pair a battery with a supercapacitor at all — without asking anyone to take a claim on trust. Each is on the hub in full; this is the short version of all three, with links. One: a battery and a supercapacitor are not two grades of the same thing A battery stores energy chemically. Charge is held by redox reactions in the bulk of the electrode: ions move into and out of the lattice and the material itself changes state. The whole volume participates, so the energy per kilogram is large — and because the process involves mass transport and a chemical change, it takes time and it wears the electrode out. A supercapacitor stores energy electrostatically. Ions gather against the electrode surface and disperse again. Nothing reacts, nothing changes phase. Only the surface participates, so the energy per kilogram is small — and because nothing is being worn out, i...