Regulating Dynamic Electrochemical Interface of LiNi0.5Mn1.5O4 Spinel Cathode for Realizing Simultaneous Mn and Ni Redox in Rechargeable Lithium Batteries

• Published in: Advanced energy materials Vol. 12; no. 46
• Main Authors: Lim, Gukhyun, Shin, Dongki, Chae, Keun Hwa, Cho, Min Kyung, Kim, Chan, Sohn, Seok Su, Lee, Minah, Hong, Jihyun
• Format: Journal Article
• Language: English
• Published: 08.12.2022
• Subjects: cathode‐electrolyte interfaces; EC‐free electrolytes; Mn‐rich cathodes; multi‐cation redox; rechargeable Li batteries; spinel oxides; surface reconstruction
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202202049

The exploding electric‐vehicle market requires cost‐effective high‐energy materials for rechargeable lithium batteries. The manganese‐rich spinel oxide LiNi0.5Mn1.5O4 (LNMO) can store a capacity greater than 200 mAh g−1 based on the multi‐cation (Ni2+/Ni4+ and Mn3+/Mn4+) redox centers. However, its practical capacity is limited to Ni2+/Ni4+ redox (135 mAh g−1) due to the poor reversibility of Mn3+/Mn4+ redox. This instability is generally attributed to the Jahn–Teller distortion of Mn3+ and its disproportionation, which leads to severe Mn dissolution. Herein, for the first time, the excellent reversibility of Mn3+/Mn4+ redox within 2.3–4.3 V is demonstrated, requiring revisiting the previous theory. LNMO loses capacity only within a wide voltage range of 2.3–4.9 V. It is revealed that a dynamic evolution of the electrochemical interface, for example, potential‐driven rocksalt phase formation and decomposition, repeatedly occurs during cycling. The interfacial evolution induces electrolyte degradation and surface passivation, impeding the charge‐transfer reactions. It is further demonstrated that stabilizing the interface by electrolyte modification extends the cycle life of LNMO while using the multi‐cation redox, enabling 71.5% capacity retention of LNMO after 500 cycles. The unveiled dynamic oxide interface will propose a new guideline for developing Mn‐rich cathodes by realizing the reversible Mn redox. Dynamically evolving electrochemical interface causes the capacity fading of LiNi0.5Mn1.5O4 spinel cathodes cycled in a wide voltage range utilizing both Mn and Ni redox reactions, revisiting the long‐lasting failure mechanism based on the Jahn–Teller distortion. Simple electrolyte modification is demonstrated as an effective strategy to improve the cycle life of the cathode by tuning the interfacial stability.