Delithiation of layered oxide electrodes triggers irreversible oxygen loss, one of the primary degradation modes in lithium-ion batteries. However, the delithiation-dependent mechanisms of oxygen loss remain poorly understood. Here we investigate the oxygen non-stoichiometry in Li_1.18–xNi_0.21Mn_0.53Co_0.08O_2–δ electrodes as a function of Li content by using cycling protocols with long open-circuit voltage steps at varying states of charge. Surprisingly, we observe substantial oxygen loss even at moderate delithiation, corresponding to 2.5, 4.0 and 7.6 ml O₂ per gram of Li_1.18–xNi_0.21Mn_0.53Co_0.08O_2–δ after resting at upper capacity cut-offs of 135, 200 and 265 mAh g⁻¹ for 100 h. Our observations suggest an intrinsic oxygen instability consistent with predictions of high oxygen activity at intermediate potentials versus Li/Li⁺. In addition, we observe a large chemical expansion coefficient with respect to oxygen non-stoichiometry, which is about three times greater than those of classical oxygen-deficient materials such as fluorite and perovskite oxides. Our work challenges the conventional wisdom that deep delithiation is a necessary condition for oxygen loss in layered oxide electrodes and highlights the importance of calendar ageing for investigating oxygen stability.

层状氧化物电极的去污会触发不可逆的氧损失，这是锂离子电池中的主要降解模式之一。然而，脱锂依赖性的氧损失机制仍然知之甚少。在这里，我们研究了 Li_1.18-x Ni_0.21Mn_0.53Co_0.08O _2-δ 电极中的氧非化学计量与 Li 含量的关系，方法是使用在不同充电状态下具有长开路电压步长的循环方案。令人惊讶的是，即使在中度脱锂作用下，我们也观察到大量的氧损失，相当于每克 Li_1.18-x Ni_0.21Mn_0.53Co_0.08O _2-δ 在 135、200 和 265 mAh ^g-1 的上限容量截止下静置 100 小时后，氧气损失为 2.5、4.0 和 7.6 ml O₂-。我们的观察结果表明，固有氧不稳定性与中间电位相对于 Li/Li⁺ 的高氧活性预测一致。此外，我们观察到相对于氧非化学计量学的化学膨胀系数很大，大约是萤石和钙钛矿氧化物等经典缺氧材料的三倍。我们的工作挑战了传统观点，即深度脱锂是层状氧化物电极中氧损失的必要条件，并强调了日历老化对于研究氧稳定性的重要性。