Progress on the Attenuation Mechanism and Modification of the Cobalt-Free Spinel LiNi_0.5Mn_1.5O₄

Cobalt-free LiNi_0.5Mn_1.5O₄ (LNMO) has recently emerged as a highly promising cathode material owing to its benefits of a high operating voltage platform (≈4.7 V vs Li), high theoretical energy density (≈650 Wh kg^-1), eco-friendliness, and resource abundance. However, it has also demonstrated low cycle and poor rate performances. Researchers have hitherto identified multiple LNMO failure and degradation mechanisms, including the Jahn-Teller effect, Transition Metal (TM) dissolution, electrolyte decomposition, and Oxygen Vacancies (OVs). The Jahn-Teller effect causes structural material degradation, while TM dissolution could lead to the loss of reactive species and interfacial side reactions. On the other hand, OVs and electrolyte decomposition accelerate capacity decay. Notably, deeply understanding LNMO structural failure mechanisms and the targeting of corresponding modifications presents a vital avenue for modulating its surface-interface structure and improving its electrochemical performance. Although researchers have extensively investigated the failure mechanisms of LNMO to elucidate its modification strategies, a comprehensive and detailed summary of the latest research advancements has yet to be provided. In this work, the research background, encompassing the advantages and disadvantages of LNMO cathode materials, is first introduced. The crystal structure and discharge mechanisms, among other fundamental principles of LNMO, are subsequently analyzed. Finally, recent research findings on the aforementioned failure mechanisms in high-voltage spinel LNMO are synthesized. Subsequently, a critical assessment of recent advancements in modification strategies targeting the failure mechanisms of LNMO is performed, encompassing the tools employed (e.g., doping modification, surface coating, morphology and size management, and surface orientation management) as well as their synergistic effects. Finally, potential future research directions to guide the rational design of high-performance LNMO, particularly manganese-based spinel cathode material, are proposed.