Stereochemical origin of potential hysteresis in lithium metal batteries with lithium-rich cation-disordered rocksalt positive electrodes.

Li-rich cation-disordered rocksalts (DRXs) are promising active materials for designing high-capacity positive electrodes for non-aqueous lithium-based batteries. However, the use of DRX-based positive electrodes results in pronounced cell potential hysteresis and low energy efficiency. The reasons for these detrimental behaviours remain unclear owing to the complex structural evolution of DRXs during battery operation. Here, via extensive physicochemical and electrochemical characterizations, we show that multiscale stereochemistry, particularly structure distortion at the atomic scale and short-range ordering in nanoscale domains, can thermodynamically and kinetically affect the potential hysteresis of Li||DRX cells. By using DRX models, we show that redox-inactive d0 transition metals (d0 TMs) influence the regulation of localized nanostructures. In particular, the out-of-centre distortion of d0 TMO6 octahedra, driven by the pseudo Jahn-Teller effect, decreases cation short-range order, thereby facilitating a high-rate Li+ percolation pathway. Moreover, the pseudo Jahn-Teller effect of d0 TMs is found to weaken the ligand-to-metal charge transfer process of Ni-O and thermodynamically enhance the reversibility of the lattice oxygen redox. As a result, the kinetic and thermodynamic factors contributing to the potential hysteresis of Li metal cells with Nb-containing DRX at the positive electrode are effectively mitigated.