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

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.