Electrolyte oxidation pathways in lithium-ion batteries,Journal of the American Chemical Society

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Electrolyte oxidation pathways in lithium-ion batteries
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-07-22 , DOI: 10.1021/jacs.0c06363
Bernardine L D Rinkel ₁ , David S Hall _{1,

2} , Israel Temprano ₁ , Clare P Grey _{1,

2}

Affiliation

The mitigation of decomposition reactions of lithium-ion battery electrolyte solutions is of critical importance in controlling device lifetime and performance. However, due to the complexity of the system, exacerbated by the diverse set of electrolyte compositions, electrode materials, and operating parameters, a clear understanding of the key chemical mechanisms remains elusive. In this work, operando pressure measurements, solution NMR, and electrochemical methods were combined to study electrolyte oxidation and reduction at multiple cell voltages. Two-compartment LiCoO2/Li cells were cycled with a lithium-ion conducting glass-ceramic separator so that the species formed at each electrode could be identified separately and further reactions of these species at the opposite electrode prevented. One principal finding is that chemical oxidation (with an onset voltage of ~4.7 V vs Li/Li+ for LiCoO2), rather than electrochemical reaction, is the dominant decomposition process at the positive electrode surface in this system. This is ascribed to the well-known release of reactive oxygen at higher states-of-charge, indicating that reactions of the electrolyte at the positive electrode are intrinsically linked to surface reactivity of the active material. Soluble electrolyte decomposition products formed at both electrodes are characterised, and a detailed reaction scheme is constructed to rationalise the formation of the observed species. The insights on electrolyte decomposition through reactions with reactive oxygen species identified through this work have direct impact on understanding and mitigating degradation in high voltage/higher energy density LiCoO2-based cells, and more generally for cells containing nickel-containing cathode materials (e.g. LiNixMnyCozO2; NMCs), as they lose oxygen at lower operating voltages.

中文翻译：

锂离子电池中电解质氧化途径

减轻锂离子电池电解质溶液的分解反应对于控制设备寿命和性能至关重要。然而，由于系统的复杂性，再加上不同的电解质成分、电极材料和操作参数，对关键化学机制的清晰理解仍然难以捉摸。在这项工作中，操作压力测量、溶液核磁共振和电化学方法相结合，研究了多种电池电压下的电解质氧化和还原。两室 LiCoO2/Li 电池使用锂离子导电玻璃陶瓷隔板进行循环，以便可以分别识别在每个电极上形成的物质，并防止这些物质在相对电极上的进一步反应。一个主要发现是化学氧化（起始电压为~4.7 V vs LiCoO2 的 Li/Li+），而不是电化学反应，是该系统正极表面的主要分解过程。这归因于众所周知的活性氧在较高荷电状态下的释放，表明正极处电解质的反应与活性材料的表面反应性有内在联系。表征在两个电极上形成的可溶性电解质分解产物，并构建详细的反应方案以使观察到的物种的形成合理化。

更新日期：2020-07-22

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