In-situ Raman investigation and application of MXene-stabilized polypyrrole composite for flexible aqueous batteries

Although polypyrrole (PPy) has been recognized as a promising organic electrode for rechargeable aqueous batteries (RABs), the practical application is still restricted by its rapid capacity fading after repeated cycles. Herein, a multilayer structural MXene-stabilized PPy (MXene@PPy) composite has been purposefully designed via a facile dip-coating approach, wherein the MXene coating effectively inhibits the structural degradation and irreversible redox reaction of PPy during the electrochemical process, demonstrated by electrochemical measurements combined with in-situ Raman investigation. Density functional theory (DFT) calculation further confirms the obvious electron transfer from MXene to PPy, leading to the formation of electron-rich region on PPy and hole-rich region on MXene, thereby promoting the redox reaction of PPy in the MXene@PPy composite with increased density of states (DOS). As an electrode, the MXene@PPy composite exhibits a large specific capacity of 124.9 mAh g−1 at 1.0 mA cm−2, high coulombic efficiency of ∼100%, superior charge-transfer capability, excellent rate performance and long-term cycling stability with high capacity retention of ∼80.3% over 2500 cycles in acidic aqueous electrolyte. For real application, a high-performance flexible RAB device constructed with such MXene@PPy composite electrode has been substantiated as the efficient power source, revealing its potential applications in high-safety portable/wearable electronics.