Enhancing cathodic redox of metal-organic frameworks through biomimetic O2 adsorption

Abstract

The energy density of conventional Li-ion/ Li-metal batteries is being approached their limitation due to the reliance on transition metal cationic redox. Although the anionic redox reactions of organic ligands in metal-organic cathode materials offer high specific capacity, they encounter substantial hurdles such as low redox potential and limited cyclability. To address this fundamental dilemma, we developed a biomimetic approach by designing metal-organic Fe2(dobdc) (Fe-MOF-74) with a channel framework structure that mimics the strong adsorption of methemoglobin for peroxide/superoxide species. When FeII2(dobdc) adsorbs O2 in unsaturated coordination, FeIII2(O2)2(dobdc) containing dispersed superoxide is formed and demonstrate a high specific capacity of 250.2 mAh g−1 in the voltage range of 2.0–4.5 V, making it a promising candidate for using as the high-energy-density cathode in Li-metal battery. Both experimental and computational evidence confirms that confined structure and biomimetic design enable FeIII2(O2)2(dobdc) cathode materials to realize synergistic electrochemical reactions of metal cations (Fe3++ e−↔ Fe2+) and oxygen anions (O2−+ e−↔ O22−) with high discharge voltages and high reversibility. This biomimetic design, along with confined structure strategies, opens a new pathway for discovering effective electrode materials with diverse Li-ion storage models.