The term "active material" refers to the substances in batteries and capacitors that participate in the electrochemical reactions responsible for energy storage and release. In batteries, the active materials are typically found in the electrodes, where they undergo oxidation and reduction during charging and discharging. The choice of active material significantly impacts the battery's capacity, voltage, and overall performance. For example, lithium cobalt oxide is a common active material in lithium-ion batteries. In capacitors, the active material is usually part of the electrode, contributing to the device's capacitance. Developing new active materials is a key area of research in advancing energy storage technologies.