Organic cathode materials for rechargeable magnesium-ion batteries: Fundamentals, recent advances, and approaches to optimization

Rechargeable magnesium-ion batteries (MIBs) are favorable substitutes for conventional lithium-ion batteries (LIBs) because of abundant magnesium reserves, a high theoretical energy density, and great inherent safety. Organic electrode materials with excellent structural tunability, unique coordination reaction mechanisms, and environmental friendliness offer great potential to promote the electrochemical performance of MIBs. However, research on organic magnesium battery cathode materials is still preliminary with many significant challenges to be resolved including low electrical conductivity and unwanted but severe dissolution in useful electrolytes. Herein, we provide a detailed overview of reported organic cathode materials for MIBs. We begin with basic properties such as charge storage mechanisms (e.g., n-, p-, and bipolar-type), moving to recent advances in various types of organic cathodes including carbonyl-, nitrogen-, and sulfur-based materials. To shed light on the diverse strategies targeting high-performance Mg-organic batteries, elaborate summaries of various approaches are presented. Generally, these strategies include molecular design, polymerization, mixing with carbon, nanosizing and electrolyte/separator optimization. This review provides insights on exploring high-performance organic cathodes in rechargeable MIBs.