Ultralong Cycle Stability and High Rate Performance of Aqueous Ammonium-Ion Hybrid Supercapacitors Enabled by In Situ Polymerization of PANI on Ti₃C₂T_x MXene

Aqueous ammonium ion (NH4+) hybrid supercapacitors (A-HSCs) have attracted considerable attention because of their safety, accessibility, and eco-friendliness. However, the development of suitable electrode materials, particularly for anodes, remains challenging. Although Ti3C2Tx MXene exhibits considerable potential as an electrode material, its restacking tendency limits ion transport and electrochemical performance. In addition, previous studies mainly focused on acidic electrolytes, which can lead to poor stability and corrosion issues, highlighting the need to explore Ti3C2Tx application in neutral NH4+-based electrolytes. In this study, we present a high-performance anode for A-HSCs constructed from Ti3C2Tx/polyaniline composite materials. Compared with the original Ti3C2Tx MXene, the enhanced interlayer spacing, improved conductivity, and enhanced stability of the composite resulted in a remarkable specific capacitance of 217 F g–1 at 1 A g–1 with 97% capacitance retention over 100,000 cycles at 20 A g–1 in a three-electrode system. Ex-situ XRD and XPS analyses confirmed the favorable and reversible NH4+ storage behavior of the Ti3C2Tx/PANI composite. The assembled A-HSCs demonstrated exceptional energy densities, exceeding 69.84 Wh kg–1 at a power density of 899.9 W kg–1. Ti3C2Tx/PANI-based microdevices fabricated using laser engraving technology retained 91.9% of the original capacitance at 10 A g–1 after 4000 cycles and maintained excellent performance under 180° bending. The findings of this study demonstrate Ti3C2Tx/PANI’s potential for NH4+ storage materials and offer insights into (NH4)2SO4 gel electrolytes for flexible A-HSCs.