Lithium-rich layered oxide cathodes have an advantage of high energy density. However, continuous capacity fading and voltage hysteresis have largely restricted their practical application. In this work, we investigated in depth the voltage-fading mechanism of Li-rich materials by in situ Raman spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, and high-resolution transmission electron microscopy (HRTEM). It has been found that the chemical and structural evolution of a Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ cathode is quasi-reversible in a whole charge–discharge cycle. The structural evolution is evidently irreversible upon long-term cycling, resulting in the dissolution of cations from the lattices and structural collapse, which in turn leads to undesirable voltage fading. This finding is important for a better understanding of the redox reaction mechanisms of high-capacity Li-rich cathodes.

中文翻译：

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深入了解富锂层状氧化物阴极材料的化学和结构演变

富锂的分层氧化物阴极具有高能量密度的优点。但是，连续的容量衰减和电压滞后大大限制了它们的实际应用。在这项工作中，我们通过原位拉曼光谱，X射线吸收近边缘结构（XANES）光谱和高分辨率透射电子显微镜（HRTEM）深入研究了富锂材料的电压衰减机理。已经发现Li _1.2 Ni _0.15 Co _0.1 Mn _0.55 O ₂的化学和结构演变在整个充放电循环中，阴极都是可逆的。长期循环后，结构演变显然是不可逆的，导致阳离子从晶格中溶出并发生结构塌陷，进而导致不良的电压衰减。这一发现对于更好地理解高容量富锂阴极的氧化还原反应机理很重要。