Batteries and supercapacitors are two complementary electrochemical energy-storage technologies. They typically contain positive and negative electrodes with the active electrode materials coated on a metal current collector (normally copper or aluminium foil), a separator between the two electrodes, and an electrolyte that facilitates ion transport. The electrode materials actively participate in charge (energy) storage, whereas the other components are passive but nevertheless compulsory for making the device work.
Batteries offer high energy density but low power density while supercapacitors provide high power density with low energy density. Although lithium-ion batteries are the most widely employed batteries today for powering consumer electronics, there is a growing demand for more rapid energy storage (high power) and higher energy density. Researchers are thus looking to create materials that combine the high-energy density of battery materials with the short charging times and long cycle life of supercapacitors. Such materials need to store a large number of charges (such as Li ions) and have an electrode architecture that can quickly deliver charges (electrons and ions) during a given charge/discharge cycle.