Synergistically constructed lamination-like network of redox-active polyimide and MXene via π-π interactions for aqueous [formula omitted] storage

Abstract

As a nonmetallic charge carrier, ammonium ion (NH4+) has garnered significant attention in the construction of aqueous batteries due to its advantages of low molar mass, small hydration size and rapid diffusion in aqueous solutions. Polymers are a kind of potential electro-active materials for aqueous NH4+ storage. However, traditional polymer electrodes are typically created by covering the bulky collectors with excessive additives, which could lead to low volume capacity and unsatisfactory stability. Herein, a nanoparticle-like polyimide (PI) was synthesized and then combined with MXene nanosheets to synergistically construct an additive-free and self-standing PI@MXene composite electrode. Significantly, the redox-active PI nanoparticles are enclosed between conductive MXene flakes to create a 3D lamination-like network that promotes electron transmission, while the π-π interactions existing between PI and MXene contribute to the enhanced structural integrity and stability within the composite electrode. As such, it delivers superior aqueous NH4+ storage behaviors in terms of a notable specific capacity of 110.7 mA·h·cm–3 and a long lifespan with only 0.0064% drop each cycle. Furthermore, in-situ Raman and UV–Vis examinations provide evidence of reversible and stable redox mechanism of the PI@MXene composite electrode during NH4+ uptake/removal, highlighting its significance in the area of electrochemical energy storage.