π-Conjugated Polyimide-Based Organic Cathodes with Extremely-Long Cycling Life for Rechargeable Magnesium Batteries

Abstract Rechargeable magnesium (Mg) batteries hold great promise for large-scale energy storage applications. However, the high polarity of divalent Mg2+ ions may induce sluggish Mg2+ diffusion kinetics in cathode materials, leading to inferior reversible capacity and rate performance. Herein, we report that aromatic dianhydride-derived polyimides (PIs) with reversible multi-electron redox properties can serve as advanced organic cathode materials for rechargeable Mg batteries. The π-conjugated molecular units of PIs provide abundant redox-active sites for the storage of Mg2+ ions, leading to large open-circuit voltage and high specific capacity. Experimental results and density functional theory (DFT) calculations of two different PI molecules indicate that the relatively narrow HOMO-LUMO energy gap and compact π-π stacking structure can help improve the Mg2+ storage performances. After blended with carbon nanotubes (CNTs) by in-situ polymerization and coupled with ionic liquid-modified non-nucleophilic organic electrolyte, the cathodes based on PI/CNTs composites display high rate performance, as well as impressive long-term cyclability at large current rate of 20 C for over 8000 cycles. We expect this work may call forth more efforts to develop advanced organic electrode materials for rechargeable batteries based on multi-electron reactions.