A team of researchers led by a group from the University of Maryland has developed a halogen conversion–intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 mAh g-1 (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li+. Combining this cathode with a passivated graphite anode, the team created a 4V-class aqueous Li-ion full cell with an energy density of 460 Wh kg-1 of total composite electrode and about 100% Coulombic efficiency.
The cell is based on an anion conversion–intercalation mechanism that combines the high energy densities of conversion reactions, the excellent reversibility of intercalation and the improved safety of aqueous batteries. A paper on their work appears in the journal Nature.
Proposed conversion–intercalation chemistry. Schematic of the conversion–intercalation mechanism occurring in the LBC-G composite during its oxidation in WiBS aqueous-gel electrolyte. The two-stage reactions involve the oxidation of Br− (about 4.0 V) and Cl− (about 4.2 V) and their subsequent intercalation into the graphitic structure. The discharge is a complete reversal of the charge process.