Controllable Carbon Shell Encapsulation via Rapid Joule Heating Calcination for High-Performance Asymmetric...

Asymmetric supercapacitors (ASCs) comprising two different pseudocapacitive electrodes offer a promising route toward higher energy density, yet the serious self-discharge behavior and poor cycle life hinder their wider applications. This work proposes a controllable carbon shell encapsulation strategy based on rapid Joule heating calcination to construct high-performance ASC with suppressed self-discharge and robust cycling stability. As a result, the as-assembled ASC (H-Fe₃O₄@C-15//H-NiCo₂S₄@C-40) exhibits a maximum energy density of 105.6 W h kg^-1 at a power density of 749 W kg^-1, and long cycling lifespan with 93.7% capacitance retention after 25 000 cycles. Furthermore, current ASC also demonstrates moderated self-discharge, with its open-circuit voltage decaying from 1.48 to 0.75 V over 31102 s. Theoretically, the density functional theory (DFT) results adequately uncover that the significantly improved self-discharge performance should originate from the increased adsorption energy between the electrode and the electrolyte ions. Meaningfully, this controllable carbon shell encapsulation strategy represents a universal and feasible approach to effectively suppress self-discharge and extend the cycle life of ASC.