Bridging the Energy‐Filtering Gap in Filtering Lithium‐Ion Capacitors with Covalent Organic Framework Nanofilms

ABSTRACT Filtering lithium‐ion capacitors (FLICs) are promising next‐generation miniaturized components that integrate high‐density energy storage with alternating current (AC) line filtering for advanced compact electronic systems. However, a fundamental trade‐off between charge‐storage capacity and ion/electron transport kinetics, constrained by sluggish anode kinetics in LICs remains a key bottleneck for simultaneously achieving both functions. Herein, a novel LIC that integrates high energy storage and AC line filtering by employing flexible ionic covalent organic framework (iCOF) nanofilms to overcome the transport bottleneck. Strong acid catalyzed highly‐crystalline TpPa‐SO 3 H anode nanofilms facilitate rapid Li + relay transmission, while thickness‐dependent DHPATG cathode nanofilms offer abundant active sites for high‐capacity storage. This complementary pairing ensures well‐matched electrode kinetics and capacity, thereby bridging the long‐standing performance gap in LICs. This DHPATG//TpPa‐SO 3 H LIC device exhibits a remarkable energy density of 363.2 mWh cm −3 at 6 W cm −3 , along with a high volume capacitance of 1.31 F cm −3 under AC conditions and a phase angle of −71° at 120 Hz. Moreover, the device also effectively converts diverse AC input signals into direct current (DC) outputs, comparable to commercial AEC. This work exploits new iCOF‐enabled energy storage and AC filtering devices, offering a viable alternative for miniaturized electronics and energy harvesting systems.