Unlocking the Ligand‐Dominated Redox Activity in π–d Conjugated Coordination Polymers for High‐Capacity and Stable Potassium Storage

Abstract

AbstractPotassium‐ion batteries (KIBs) offer a cost‐effective, resource‐abundant alternative to lithium‐ion systems, yet the development of high‐performance anodes with adequate capacity, stability, and rate capability remains a major challenge. Here, an electronic structure engineering strategy is introduced via d‐orbital configuration optimization in a novel class of π–d conjugated coordination polymers (TM‐BTA, TM = Ni, Co, Mn). Orbital‐level and charge density analyses reveal that the metal center's electronic configuration governs metal–ligand interaction strength, thereby modulating charge delocalization and ligand redox behavior. Among the series, Ni2⁺ exhibits the strongest π–d conjugation with nitrogen donor atoms, stabilizing C═N bonds and enabling highly reversible C═N/C─N transformations as the dominant redox process. This optimized coordination lowers the K⁺ adsorption energy barrier by 44% compared to Co2⁺ and Mn2⁺, markedly improving kinetics. As a result, Ni‐BTA delivers a high reversible capacity of 452 mAh g−1 with 99.2% retention over 500 cycles at 100 mA g−1, and maintains 292 mAh g−1 after 4,000 cycles at 1,000 mA g−1. In situ spectroscopy and DFT calculations reveal a ligand‐centered three‐electron redox mechanism, where nitrogen heterocycles dominate K⁺ storage and electrochemically inert Ni centers maintain structural integrity. This work establishes a general design principle for KIB anodes via d‐orbital engineering in coordination polymers.