Insight into the Atomic Structure of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material in the First Cycle

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• 作者：Mingxiang Lin ; Liubin Ben ; Yang Sun ; Hao Wang ; Zhenzhong Yang ; Lin Gu ; Xiqian Yu ; Xiao-Qing Yang ; Haofei Zhao ; Richeng Yu ; Michel Armand ; Xuejie Huang
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：January 13, 2015
• 年：2015
• 卷：27
• 期：1
• 页码：292-303
• 全文大小：882K
• ISSN：1520-5002

文摘

Application of high-voltage spinel LiNi_0.5Mn_1.5O₄ cathode material is the closest and the most realistic approach to meeting the midterm goal of lithium-ion batteries for electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs). However, this application has been hampered by long-standing issues, such as capacity degradation and poor first-cycle Coulombic efficiency of LiNi_0.5Mn_1.5O₄ cathode material. Although it is well-known that the structure of LiNi_0.5Mn_1.5O₄ into which Li ions are reversibly intercalated plays a critical role in the above issues, performance degradation related to structural changes, particularly in the first cycle, are not fully understood. Here, we report detailed investigations of local atomic-level and average structure of LiNi_0.5Mn_1.5O₄ during first cycle (3.5鈥?.9 V) at room temperature. We observed two types of local atomic-level migration of transition metals (TM) ions in the cathode of a well-prepared LiNi_0.5Mn_1.5O₄//Li half-cell during first charge via an aberration-corrected scanning transmission electron microscopy (STEM). Surface regions (鈭? nm) of the cycled LiNi_0.5Mn_1.5O₄ particles show migration of TM ions into tetrahedral Li sites to form a Mn₃O₄-like structure. However, subsurface regions of the cycled particles exhibit migration of TM ions into empty octahedral sites to form a rocksalt-like structure. The migration of these TM ions are closely related to dissolution of Ni/Mn ions and building-up of charge transfer impedance, which contribute significantly to the capacity degradation and the poor first-cycle Coulombic efficiency of spinel LiNi_0.5Mn_1.5O₄ cathode material. Accordingly, we provide suggestions of effective stabilization of LiNi_0.5Mn_1.5O₄ structure to obtain better electrochemical performance.