Exploration of vanadium benzenedicarboxylate as a cathode for rechargeable lithium batteries

The electrochemical reaction with lithium of a vanadium-based metal-organic framework V^IV(O)(bdc) [MIL-47], which is isostructural to the iron compound MIL-53(Fe), was investigated. The large open channels which can accommodate small guest species, such as Li⁺ ions, together with the redox properties of the tetravalent vanadium ions make this material of potential interest as a rechargeable intercalation electrode for lithium batteries. The electrochemical properties were investigated in Li|1 M LiPF₆ in ethylene carbonate (EC) and dimethyl carbonate (DMC)|V(O)(bdc) cells between 4.0 and 1.5 V vs. Li/Li⁺. V(O)(bdc) cathodes can be reversibly cycled in Li cells with good rate capability and specific capacity. At a current density of C/12, Li/V(O)(bdc) cells can be cycled between 0 < x > 0.7 in Li_xV(O)(bdc) with ∼100% coulombic efficiency corresponding to 82 mAh g^-1 which is a higher capacity than that found for MIL-53(Fe). The cell performance and electrochemical profiles at various current conditions are discussed. Structural evolution taking place during lithium intercalation was monitored by powder X-ray diffraction on phases of Li_xV(O)(bdc) (0 < x < 2) chemically prepared by using n-BuLi. Previous studies of the reaction of lithium with metal-organic frameworks are briefly reviewed for comparison with the data presented for Li_xV(O)(bdc).