3D-Printed Ultrahigh-Conductivity Polymer Gel Electrodes with High Mass Loading for Thickness-Independent Zinc-Ion Hybrid Micro-Supercapacitors

Simultaneously achieving high mass loading and uncompromised capacitance performance represents a critical challenge for advancing zinc-ion hybrid micro-supercapacitors (ZHMSCs) toward practical applications. This study addresses this fundamental limitation by developing direct ink writing (DIW) 3D-printed Zn2+-poly(3,4-ethylenedioxythiophene):polystyrene sulfonate/MXene (Zn-PM) gel electrodes for high mass loading ZHMSCs. Synergistic PEDOT:PSS/MXene interactions enable formulation of high-concentration viscoelastic printable gel inks, yielding thick gel electrodes with ultrahigh mass loading (32.2 mg cm-2) and high shape fidelity via precise 3D printing. Rationally engineered Zn-PM gel electrodes undergo phase separation, complete PSS removal, and PEDOT electronic structure transition through MXene doping, Zn2+ coordination, and freeze-thawing processing, thereby constructing 3D continuous conducting networks with ultrahigh conductivity (2326 S cm-1) and hierarchical porous architectures with accelerated rapid ion transport kinetics. The fabricated quasi-solid-state ZHMSCs, integrating 3D-printed Zn-PM gel cathodes and electrodeposited Zn nanosheet anodes, exhibit a groundbreaking areal capacitance of 2179 mF cm-2 and energy density of 333.6 mu Wh cm-2 with thickness-independent energy storage characteristics, outperforming current state-of-the-art zinc-ion hybrid capacitors. This work provides a new paradigm for engineering ultrahigh mass-loading micro-energy storage devices via synergistic integration of rational electrode architecture engineering and advanced 3D printing fabrication strategies.