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

Abstract The exploding electric‐vehicle market requires cost‐effective high‐energy materials for rechargeable lithium batteries. The manganese‐rich spinel oxide LiNi 0.5 Mn 1.5 O 4 (LNMO) can store a capacity greater than 200 mAh g −1 based on the multi‐cation (Ni 2+ /Ni 4+ and Mn 3+ /Mn 4+ ) redox centers. However, its practical capacity is limited to Ni 2+ /Ni 4+ redox (135 mAh g −1 ) due to the poor reversibility of Mn 3+ /Mn 4+ redox. This instability is generally attributed to the Jahn–Teller distortion of Mn 3+ and its disproportionation, which leads to severe Mn dissolution. Herein, for the first time, the excellent reversibility of Mn 3+ /Mn 4+ 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.