Carbonized metal-organic framework cathodes for secondary lithium-bromine batteries

Secondary lithium-bromine (Li–Br2) batteries offer cell potentials near 4 V and storage capacities over 1200 Whkg−1-LiBr. Here, we demonstrate Li–Br2 cells with two types of carbonized metal-organic frameworks (MOFs). Carbonized MIL-53(Al) electrodes show capacities of 224 mAhg−1 LiBr (at 3.4 V) and 72% capacity retention after 100 cycles, while carbonized ZIF-8 electrodes show specific capacities of 273 mAhg−1 LiBr and 88% capacity retention over 100 cycles at 1C (at 3.4 V). Surface characterization (XPS, EDS) and porosimetry indicate that the ZIF-8 derived MOF electrodes are heavily microporous with heteroatom (C–N) doping. The increased capacity and reversibility of ZIF-8 derived carbon during cyclic voltammetry and cycling measurements is ascribed to higher LiBr loadings, enhanced bromine trapping and adsorption due to the electrode microporosity and heteroatom bonding.