Tailoring Carbon Cathode Microstructure for Synergistic Integration of Hybrid Ion Capacitor and Dual‐Ion Battery

Hybrid potassium‐ion capacitors (PICs) and potassium dual‐ion batteries (PDIBs) represent two types of potassium‐based electrochemical energy storage devices. Their differences in the microstructure of carbon cathodes enable PICs and PDIBs to possess high power and energy density, respectively. Herein, a hybrid device integrating PIC and PDIB, called as dual‐ion capacitor‐battery hybrid device (DICB), is designed by modifying the microstructure of carbon cathode, to simultaneously acquire high power and energy density. By utilizing the carbon cathode combining highly‐disordered and pseudo‐graphitic microstructures, the resultant DICB demonstrates excellent energy density (320.4 Wh kg−1) and power density (15.9 kW kg−1) with 1.5‐4.5 V. By utilizing the carbon cathode having both pseudo‐graphitic and highly‐graphitic microstructures, the corresponding DICB can achieve an elevated energy density (351.7 Wh kg−1) within a wider voltage range 1.5‐5.0 V. Experiments reveal that in the mixed microstructures of carbon cathodes, highly‐disordered part mainly exhibits capacitive contribution, the pseudo‐graphitic part provides both capacitor‐ and battery‐type energy storage behaviors, and the highly‐graphitic part offers additional capacity through ion insertion/extraction in the higher voltage region. Consequently, the carbon cathode with mixed microstructure can introduce both capacitor‐ and battery‐type energy storage behaviors in a device, thereby regulating the energy and power output characteristics of the DICB. Pseudo‐graphitic carbon combined with highly‐disordered or highly‐graphitic carbon can introduce capacitor‐ and battery‐type energy storage mechanisms in positive electrodes within two different voltage ranges, thereby enabling the successful construction of dual‐ion capacitor‐battery hybrid device.