Host–Guest Interactions of Metal–Organic Framework Enable Highly Conductive Quasi-Solid-State Electrolytes for Li–CO₂ Batteries

High-energy lithium (Li)-based batteries, especially rechargeable Li-CO₂ batteries with CO₂ fixation capability and high energy density, are desirable for electrified transportation and other applications. However, the challenges of poor stability, low energy efficiency, and leakage of liquid electrolytes hinder the development of Li-CO₂ batteries. Herein, a highly conductive and stable metal<b>-</b>organic framework-encapsulated ionic liquid (IL@MOF) electrolyte system is developed for quasi-solid-state Li-CO₂ batteries. Benefiting from the host-guest interaction of MOFs with open micromesopores and internal IL, the optimized IL@MOF electrolytes exhibit a high ionic conductivity of 1.03 mS cm^-1 and a high transference number of 0.80 at room temperature. The IL@MOF electrolytes also feature a wide electrochemical stability window (4.71 V versus Li⁺/Li) and a wide working temperature (-60 °C ∼ 150 °C). The IL@MOF electrolytes also enable Li⁺ and electrons transport in the carbon nanotubes-IL@MOF (CNT-IL@MOF) solid cathodes in quasi-solid-state Li-CO₂ batteries, delivering a high specific capacity of 13,978 mAh g^-1 (50 mA g^-1), a long cycle life of 441 cycles (500 mA g^-1 and 1000 mAh g^-1), and a wide operation temperature of -60 to 150 °C. The proposed MOF-encapsulated IL electrolyte system presents a powerful strategy for developing high-energy and highly safe quasi-solid-state batteries.