Herein, we demonstrate a new non-aqueous potassium-ion hybrid capacitor (KIC) using novel P3-K0.45Mn0.5Co0.5O2 and commercial activated carbon (CAC) as the cathode and anode, respectively. A simple sol-gel method is used to synthesize the P3-K0.45Mn0.5Co0.5O2 cathode nanoplatelets. The structural and morphological studies are performed using various characterization techniques, and their electrochemical performances are studied in half-cell configurations against metallic K. The P3-K0.45Mn0.5Co0.5O2 nanoplatelets can reversibly host K+ ions delivering a high capacity of 140 mAh g(-1) in the wide voltage window of 1.2-3.9 V. Exhibiting smooth voltage profiles, it offers reasonable rate capability and cyclability, retaining over 80% capacity after 50 cycles. Involving a two-phase (P3-O3) redox mechanism, P3-K0.45Mn0.5Co0.5O2 forms robust cathode material for potassium-ion batteries. With Activated Carbon, the capacitor could provide very high energy and power densities of 43 Wh kg(-1) and 30 kW kg(-1), respectively, in the voltage range of 0-3.0 V. Even at a 3-s charge-discharge rate (10 A g(-1)), an energy density of 14.5 Wh kg(-1) could be retained (corresponding to a power of 15 kW kg(-1)). Also it could retain 88% of its energy density with a substantially high stability up to 30,000 cycles at 10 A g(-1).