Solid-Solution Lithium Intercalation and Magnetic Insights in Core–Shell LiNi x Mn2-xO4 Cathodes

Abstract To achieve high-energy-density lithium-ion batteries, the development of high-voltage cathode materials remains a critical challenge. Although LiNixMn2-xO4 (LNMO) exhibits an intrinsically high operating voltage, its practical application is hindered by structural instability and interfacial degradation. In this study, core–shell LNMO cathodes with tunable Ni/Mn distributions were designed to regulate structural and electronic properties and enhance electrochemical performance. Three configurations (AC, AB, and BA) were synthesized and systematically investigated. Among them, the LNMO-AC sample exhibits a highly disordered spinel structure with a uniform nanoscale shell and reduced particle aggregation. X-ray absorption near-edge structure (XANES) analysis reveals composition-dependent variations in Mn valence states, while electron magnetic resonance (EMR) and superconducting quantum interference device (SQUID) measurements suggest distinct magnetic responses associated with local structural heterogeneity and defect-induced interactions. Operando X-ray diffraction (XRD) and electrochemical measurements indicate that lithium intercalation in LNMO-AC tends to follow a more continuous, solid-solution-like reaction behavior compared to the pristine sample, which contributes to improved structural stability during cycling. The enhanced electrochemical performance is attributed to the synergistic effect of a disordered core facilitating lithium transport and a structurally stable shell suppressing interfacial degradation. These findings highlight the interplay between cation disorder, magnetic behavior, and electrochemical functionality, providing insights into the rational design of high-voltage LNMO cathodes for advanced lithium-ion batteries.