Correlating Charge Heterogeneity and First-Cycle Irreversible Capacity Loss in Lithium-Ion Batteries

Abstract

Establishing a direct correlation between nickel charge heterogeneity and first-cycle irreversible capacity (IRC) loss is essential for optimizing high-energy lithium-ion battery (LIB) cathodes. However, the interplay between charge distribution and IRC loss remains poorly understood. In this study, we reveal that spatial variations in nickel oxidation states are a key contributor of IRC loss by systematically investigating their evolution in NCM 333 and NCM 811 cathodes using diffraction, spectroscopy, and nanoscale microscopy techniques. Using LiNiO2 (Ni3+) as a reference, first-derivative XANES analysis determined the pristine-state Ni oxidation states of NCM 333 and NCM 811 to be approximately +2.2 and +2.6, respectively. Nanoscale transmission X-ray microscopy (TXM-XANES) enabled direct quantitative visualization of Ni chemistry and charge distribution, revealing pronounced spatial Ni charge heterogeneity at different cycling states. Single-pixel XANES analysis further uncovered localized Ni chemistry variations, highlighting distinct redox behaviors between core and near-surface regions that strongly correlate with IRC loss. Notably, in low-Ni-content NCM 333, the Ni valence state remains uniformly distributed across all states of charge during cycling. In contrast, high-Ni-content NCM 811 exhibits significant Ni valence state non-uniformity, disrupting charge balance and hindering complete capacity utilization, ultimately leading to IRC loss. By quantitatively linking Ni charge heterogeneity to irreversible lithium loss, this study provides a mechanistic foundation for mitigating IRC loss and optimizing Ni-rich cathode performance. These insights pave the way for designing next-generation cathodes with suppressed IRC loss, prolonged cycle life, and enhanced electrochemical stability, addressing critical challenges in high-performance LIB development.