Abstract For achieving higher energy density lithium-ion batteries, the improvement of cathode active materials is crucial. The most promising cathode materials are nickel-rich layered oxides LiNixCoyMnzO2 (NCM) and over lithiated NCM (often called HE-NCM). Unfortunately, the full capacity of NCM cannot be utilized due to its limited cycle-life at high state-of-charge (SOC), while HE-NCM requires high voltages. By operando emission spectroscopy, we show for the first time that highly reactive singlet oxygen is released when charging NCM and HE-NCM to an SOC beyond ≈80%. In addition, on-line mass-spectrometry reveals the evolution of CO and CO2 once singlet oxygen is detected, providing significant evidence for the reaction between singlet oxygen and electrolyte to be a chemical reaction. It is controlled by the SOC rather than by potential, as would be the case for a purely electrochemical electrolyte oxidation. Singlet oxygen formation therefore imposes a severe challenge to the development of high-energy batteries based on layered oxide cathodes, shifting the focus of research from electrochemically stable 5 V-electrolytes to chemical stability toward singlet oxygen.

中文翻译：

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层状过渡金属氧化物正极材料的单线态氧析出及其对锂离子电池的影响

摘要 为了实现更高能量密度的锂离子电池，正极活性材料的改进至关重要。最有前途的正极材料是富镍层状氧化物 LiNixCoyMnzO2 (NCM) 和锂化 NCM（通常称为 HE-NCM）。不幸的是，由于 NCM 在高荷电状态 (SOC) 下的循环寿命有限，因此无法充分利用 NCM 的全部容量，而 HE-NCM 需要高电压。通过操作发射光谱，我们首次证明当 NCM 和 HE-NCM 充电至 SOC 超过 ≈80% 时会释放高活性单线态氧。此外，一旦检测到单线态氧，在线质谱揭示了 CO 和 CO2 的演化，为单线态氧与电解质之间的反应是化学反应提供了重要证据。它由 SOC 控制，而不是由电位控制，就像纯电化学电解液氧化的情况一样。因此，单线态氧的形成对基于层状氧化物阴极的高能电池的开发提出了严峻的挑战，将研究重点从电化学稳定的 5 V 电解质转移到化学稳定性转向单线态氧。