High Voltage Electrodes for Li-Ion Batteries and Efficient Water Electrolysis: An Oxymoron?

We demonstrate that key parameters for efficient electrocatalytic oxidation of water are the energetics of the redox complexes associated with their ionization and electrochemical potentials coupled to the change of metal-oxygen band hybridization. We investigate the catalytic activity of the LiCoPO₄-LiCo₂P₃O₁₀ tailored compound, which is a 5 V cathode material for Li-ion batteries. The reason for the weak catalytic activity of the lithiated compound toward the oxygen evolution reaction is a large energy difference between the electronic states involved in the electrochemical reaction. A highly active catalyst is obtained by tuning the relative energetic position of the electronic levels involved in the charge transfer reaction, which in turn are governed by the lithium content. A significant lowering of the overpotential from >550 mV to ∼370 mV at 10 mA cm^-2 is achieved via a decrease of the ionization potential and shifting the electrochemical potential near the electronic states of the molecule, thereby facilitating water oxidation.