Unraveling Dual-Redox Mechanisms in Ni-Based Conjugated Coordination Polymers for High-Performance Rechargeable Magnesium Batteries.

Rechargeable magnesium metal batteries (RMBs) have recently attracted increasing attention due to their high theoretical volumetric capacity and inherent safety. However, the development of suitable cathode materials remains a major challenge. Conjugated coordination polymers (CCPs) are attractive cathode materials for energy storage due to their stable redox-active frameworks and intrinsic electronic conductivity. However, the Mg2+ storage mechanisms of CCPs remain poorly understood, and the application of CCPs as cathodes for RMBs has been seldom reported. Herein, a series of 1D CCPs based on 2,5-dihydroxy-1,4-benzoquinone (DHBQ) coordinated with Ni2+, Mn2+, and Cu2+ (denoted as NiDHBQ, MnDHBQ, and CuDHBQ) is designed. Among them, NiDHBQ delivers the highest reversible capacity of 228.2 mAh g-1 at 100 mA g-1 and superior cycling stability, enabled by dual redox activity from both the Ni2+ centers and C═O groups. Comprehensive spectroscopic analysis (XPS, FTIR, XANES/EXAFS) and DFT calculations reveal that the extended d-π conjugation and low Mg2+ migration barrier facilitate rapid charge transport and structural robustness. In contrast, CuDHBQ suffers from irreversible Cu2+ reduction, and MnDHBQ remains electrochemically inactive in Mn2+. This work will enlighten further in-depth investigations for the molecular designs of advanced CCPs-based cathode materials.