Design of efficient, reliable, and wide-band filter electrochemical capacitors via matching positive with negative electrodes

A transition to green energy demands ultrafast-charging devices such as millisecond-charging filter capacitors. Filter capacitors convert alternating current into direct current for grid-level energy storage and digital communications. This study explores replacing electrolytic capacitors with electrochemical capacitors (ECs) to provide compact filtering solutions. ECs' 1,000-fold higher capacitance allows tiny filter devices to meet the pressing needs of upscaling green power grids and shrinking electronic components. We have identified the coupling effects between positive and negative electrodes and correlated EC reversibility to the electrochemical stabilities and charge-exchange kinetics of individual electrodes. Properly matching positive with negative electrodes creates 1.8 V filter electrochemical capacitors (FEC), which retain 91.4% (821.7 μF cm−2) of capacitance and 96.0% phase angle after 1.2 M cycles due to their synchronized ultrafast charge/discharge. The superior capacitance performance improves filtering efficiency and reliability in wide frequency bands. These findings open avenues to designing ECs for alternating current line filtering.