A Kinetic Indicator of Ultrafast Nickel-Rich Layered Oxide Cathodes

Elucidating high-rate cycling-induced nonequilibrium electrode reactions is crucial for developing extreme fast charging (XFC) batteries. Herein, we unveiled the distinct rate capabilities of a series of Ni-rich layered oxide (NRLO) cathodes by quantitatively establishing their dynamic structure-kinetics relationships. Contrary to conventional views, we discovered electrode kinetic properties obtained ex-situ near equilibrium states failed to assess the effective rate capability of NRLOs at ultrafast C rates. Further, the kinetic phase heterogeneity, characterized by the dynamic separations in in-situ X-ray diffraction patterns and deviations in NRLO c-axis lattice parameters, exclusively correlated with the capacity reduction under XFC and became an effective indicator of the NRLO rate capability. Enhancing the cycling temperature boosted the rate capability of studied NRLOs by ∼10%, which was further verified to mitigate the kinetic phase heterogeneity during XFC. Overall, this study lays the groundwork for tuning the kinetic phase heterogeneity of electrodes to develop ultrafast batteries.