Metal-Organic Frameworks for Nanoconfinement of Chlorine in Rechargeable Lithium-Chlorine Batteries

Making primary lithium-thionyl chloride (Li-SOCl2) battery rechargeable in the lithium-chlorine (Li-Cl2) chemistry is an important milestone towards the development of high energy battery technology. Although porous carbons were used in the Li-Cl2 battery, they lack strong interaction with Cl2, which limit their electrochemical performance. Herein, we propose and design metal-organic frameworks (MOFs) with functional groups for nanoconfinement of chlorine by chemisorption in the Li-Cl2 battery. Predicted by theoretical calculations, highly porous MOF functionalized with -NH2 groups, namely UiO-66-NH2, is screened out as a model to apply in the Li-Cl2 battery. The Li-Cl2 battery using NH2-functionalized MOF (Li-Cl2@MOF) demonstrates high specific capacities up to 2000 mAh/g with excellent rate capability, and highly stable 500 cycles under a specific capacity of 1000 mAh/g at room temperature. It also exhibits superior low temperature performance, displaying a high voltage of 3.5 V and CE of 99.7% with stable 300 cycles under a capacity of 1000 mAh/g at -25 °C. Further, the Li-Cl2@MOF cell exhibits a high areal capacity of 4.4 mAh/cm2 in coin cells and a CE of 99% for over 120 cycles in large-scale pouch cells. Low-dose high-resolution transmission electron microscopy, cryogenic transmission electron microscopy, and X-ray photoelectron spectroscopy are utilized to reveal the storage mechanism on nanoconfinement of Cl2 and LiCl by UiO-66-NH2 in the Li-Cl2@MOF battery. This work provides opportunities for the promising application of functionalized MOFs as cathodes in rechargeable Li-Cl2 batteries.