Storage of nickel-rich LiNi_1-x-yMn_xCo_yO₂ positive active materials under improper environmental conditions brings about undesirable surface reactions causing poor Li-ion cell electrochemical performances and gas generation. In this paper, a detailed stepwise investigation of the increasing reactivity of 532, 622, 811 and 901 NMC materials towards a specific H₂O/CO₂ atmosphere is reported. Water-soluble salts as lithium carbonate, hydroxide and sulfates are accurately quantified thanks to acid-base titration and inductively coupled plasma atomic emission spectroscopy techniques. On the other hand, the presence of insoluble species as transition metal oxyhydroxides and oxides is unveiled through a thermal decomposition study using thermogravimetric mass spectrometer coupling technique. Their formation and thermal decomposition mechanisms are proposed after careful analysis of the characteristic mass loss and O₂, CO₂ and H₂O evolution profile in the 50–500 °C region. Interestingly, the results also highlight an in situ lithiated layered oxide material reformation reaction. To assess their chemical reactivity towards LiPF₆-based electrolyte, the latter was analyzed through ¹⁹F nuclear magnetic resonance after storage with various reference salts and 811 NMC. LiPO₂F₂ is detected from storage tests with Li₂CO₃, Li₂O and Li₂SO₄, and fluorophosphate-type molecules are detected from LiOH; this experiment can help discriminate between LiOH and Li₂O as NMC surface species.

富镍的LiNi _1-xy Mn _x Co _y O ₂正极活性材料在不当的环境条件下的储存会引起不良的表面反应，从而导致锂离子电池的电化学性能下降和产生气体。本文详细逐步研究了532、622、811和901 NMC材料对特定H ₂ O / CO ₂的增加的反应性据报道气氛。借助于酸碱滴定和电感耦合等离子体原子发射光谱技术，可以准确定量碳酸锂，氢氧化物和硫酸盐等水溶性盐。另一方面，通过使用热重质谱耦合技术的热分解研究揭示了不溶性物质作为过渡金属羟基氧化物和氧化物的存在。在仔细分析了50–500°C区域的特征质量损失以及O ₂，CO ₂和H ₂ O的演化曲线后，提出了它们的形成和热分解机理。有趣的是，结果还突出显示了原位锂化层状氧化物材料的重整反应。为了评估其对基于LiPF ₆的电解质的化学反应性，在使用各种参考盐和811 NMC储存后，通过¹⁹ F核磁共振分析了后者。从Li ₂ CO ₃，Li ₂ O和Li ₂ SO _4的储藏测试中检测到LiPO ₂ F ₂，从LiOH中检测到氟磷酸盐类分子。这个实验可以帮助LiOH和Li区分₂ O为NMC表面物质。