Unlocking 5 V-Class Lithium-Ion Batteries: Challenges and Perspectives on High-Voltage LNMO Cathodes

High-voltage spinel-type lithium nickel manganese oxide (LiNi_0.5Mn_1.5O₄, LNMO) is considered a promising cathode material for lithium-ion batteries due to its high operating voltage (∼4.7 V vs Li/Li⁺) and cobalt-free composition, which enables it to deliver approximately 1.5 times higher energy-to-cost efficiency compared to lithium nickel cobalt manganese oxides (NCM). Although LNMO was among the earliest high-voltage cathode materials studied, it has attracted less commercial attention than layered materials such as NCM and lithium nickel aluminum oxides (NCA). This is primarily attributed to persistent challenges during operation, notably rapid capacity fading induced by structural degradation in both the bulk and interfacial regions under high-voltage and high-temperature conditions. Consequently, a comprehensive understanding of LNMO degradation mechanisms, coupled with the development of targeted design strategies, is essential to overcome these limitations. This review emphasizes the structural characteristics of LNMO, both in the bulk and at the interface, that influence its electrochemical performance. Particular focus is placed on recent advancements in strategies such as doping, coating, and morphology control, which have demonstrated effectiveness in mitigating critical issues, including volume changes, oxygen release, transition metal dissolution, and cation migration. Based on findings from various experimental studies and computational modeling, this review aims to elucidate the origins of performance degradation in LNMO and to propose rational design strategies to improve its cycle life and safety. Overall, this work provides a comprehensive roadmap for advancing LNMO, a historically underutilized spinel cathode with significant potential for next-generation high-voltage Li-ion batteries.