Unveiling the Unique Redox Chemistry in a Strongly Correlated Cu-Benzenehexathiol Coordination Polymer

Two-dimensional (2D) π–d conjugated coordination polymers (CPs) are emerging as attractive electrode materials for rechargeable batteries. However, the origin of their high charge storage capacity remains evasive due to the impact of extrinsic defects and the parasitic chemistry of the conducting additives. Here, directly utilizing metallic Cu-BHT (BHT = benzenehexathiol) thin film as a cathode in a Li-organic battery provided a unique platform to clarify its charge storage mechanism. Remarkably, to properly understand the redox chemistry of Cu-BHT, we first unveiled the detrimental impact of defect spins on its intrinsic magnetic properties. Through monitoring the evolution of spin states during the electrochemical process, we demonstrated that the delocalized π-electron band was responsible for the large storage capacity of the Cu-BHT system, contrary to prevailing theories in traditional CPs. This mechanism was validated by a series of comprehensive spectroscopy and electrochemical measurements, further supported by the significantly enhanced temperature-independent paramagnetic term and band structure calculations. Our work provides key insights for the electrochemical storage mechanism of conjugated CPs and will serve as an important motivation to explore new metallic CP-based electrode materials.