Li-ion Cathodes
Our research on Li-ion cathodes explores how redox chemistry and structural evolution influence energy density and voltage stability, particularly in Li-rich materials.
First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk
Li-rich cathode materials are promising for next-generation Li-ion batteries but exhibit large first-cycle voltage hysteresis. Using Li1.2Ni0.13Co0.13Mn0.54O2, we show by resonant inelastic X-ray scattering and ¹⁷O NMR that oxygen redox proceeds via formation of molecular O2 trapped in the bulk rather than peroxo-like species. This O2 is reduced back to O²⁻ on discharge at lower voltage, explaining the voltage hysteresis in Li-rich cathodes.
Trapped O2 and the origin of voltage fade in layered Li-rich cathodes
In layered Li-rich cathodes such as O3-type Li1.2Ni0.13Co0.13Mn0.54O2, oxygen redox proceeds via the formation of molecular O2 trapped in nano-sized voids within the bulk, which is initially largely reducible back to O²⁻ on discharge. With extended cycling, growth of these voids renders an increasing fraction of the trapped O2 electrochemically inactive and promotes O2 loss from open voids, leading to a progressive loss of O-redox capacity and voltage fade.
Factors affecting capacity and voltage fading in disordered rocksalt cathodes for lithium-ion batteries
Li-rich disordered rocksalts could realise Li-ion batteries with very high energy densities, but they suffer from capacity and voltage fade, which is often attributed to oxygen redox. By comparing two similar examples with and without oxygen redox, we disentangle the origins of this performance loss. This new understanding allows us to demonstrate how to suppress capacity and voltage fade in disordered rocksalts by improving electronic contact between particles and reducing oxygen redox.