Supercapacitors store instantly a large volume of electric energy and supplies instantly or continuously higher current, by the mechanism of absorbing and de-absorbing electric charge.
More precisely, supercapacitors make use of an electrolyte, a substance made of positively and negatively charged particles. When the electrodes are charged, the electrolyte polarizes according to the charge of the electrodes. This separation of charge creates two oppositely charged layers that act like new charged plates.
Put simply, it polarizes an electrolytic solution to store energy electrostatically.
The energy storage mechanism of a supercapacitor is highly reversible, which allows for the supercapacitor to be charged and discharged up to a million times.