Anti-oxidized electrostatic self-assembly of 3D high-density Polyimide@MXene composite for superior aqueous Mg2+ storage

Abstract As a conjugated carbonyl polymer, polyimide (PI) with redox-active sites has attracted increasing research attention owing to its efficient multivalent-ion storage behaviors in low-cost and risk-free neutral aqueous electrolytes. However, the practical applications of PI remain restricted because of its low tapped density, sluggish electron transfer and structural instability. Herein, we developed a novel three-dimensional (3D) high-density PI@MXene composite through efficient electrostatic self-assembly, wherein MXene oxidation could be prevented during composite preparation. Synergistically coupling the conductive layered MXene with electro-active PI provides a 3D architecture with high tapped density (~1.12 g cm−3), enhanced electrochemical kinetics and rapid redox reaction in MgCl2 neutral aqueous electrolytes. These features can be further confirmed via Fourier transform infrared spectroscopy upon charging/discharging and density functional theory (DFT) calculations along with the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap. As an electrode, the 3D high-density PI@MXene composite exhibits remarkable aqueous Mg2+ storage (~502.2 F g−1) and superior rate and cycling performances than those of most reported polymer-based electrodes in aqueous electrolytes. As proof of concept, we fabricated a flexible Mg-ion storage device with reliable electrochemical performance and ultra-long cycling life over 20 000 cycles, stimulating its application in high-safety portable/wearable electronics.