Nano-scale kinetic degradation mechanism of high-voltage LiNi0.8Mn0.1Co0.1O2 cathodes in Li-ion batteries

每年，加拿大都要花费数十亿美元来应对气候变化的负面影响。因此，减少温室气体排放，特别是减少交通和发电方面的温室气体排放，以缓解这些问题势在必行。长寿命锂离子电池在电动汽车(EVS)的广泛采用和可再生能源的大规模发电方面发挥着至关重要的作用。采用LiNi0.8Mn0.1Co0.1O2等高镍层状氧化物正极(NMC811)，比容量大于200mAhg，是降低电池成本、提高可持续性的最有前景的工业现实选择。不幸的是，NMC811在高电压操作下性能迅速下降。寄生阴极表面反应与过渡金属(TM)和晶格氧的局域结构演化相结合，被认为是NMC811退化的根本原因。然而，衍射和形貌研究推测，二次和/或一次粒子中裂纹的形成是根本原因。关于退化机制的分歧源于以下事实：(1)由于电池样品的环境敏感性而导致可靠性较低的验后分析，以及(2)即使在仅循环NMC811颗粒的情况下，即使通过现场研究也不能完全解决复合电池电极退化的内在异质性。为了应对这些挑战，我提议开发一个OPANDO高分辨率化学成像平台，并应用该平台来成像(DIS)充电过程中复合电池电极内的结构和传输异质性。这一长期目标将通过三个短期目标来实现：1)将扫描X射线扫描显微镜(STXM)与原位STXM单元相结合，开发新型成像平台；2)开发用于平台成像的复合电极的制备方案；3)系统研究各种NMC811复合电极的纳米级降解机理。这将首次在实用的NMC811复合电极中将结构演变与充放电动力学行为联系起来，两者都是在纳米尺度上的。因此，我们可以更好地了解各种电极参数在复合电极降解中的作用，包括NMC 811表面涂层、电解液添加剂以及非活性电极组分的分布，如粘结剂和导电剂。此后，考虑这些参数的长寿命NMC811电池的合理设计将成为可能。加拿大光源是加拿大唯一的国家同步加速器设施，该新型化学成像平台的开发将有利于其他国家和国际电池研究，以开发下一代电池，以应对全球气候变化。

Every year, Canada has to spend billions of dollars to deal with the negative impact of climate change. Therefore, it is imperative to reduce greenhouse emissions especially in transportation and power generation to alleviate the problems. Long life lithium-ion battery plays a crucial role in enabling the widespread adoption of electric vehicles (EVs) and large-scale electricity generated from intermitting renewable sources. Using high-Ni layered oxide cathodes such as LiNi0.8Mn0.1Co0.1O2 cathode (NMC811) with a specific capacity of higher than 200mAh/g is the most promising industrial reality choice in reducing battery cost and improving sustainability. Unfortunately, NMC811 suffers from quick performance degradation under high-voltage operation. Parasitic cathode surface reaction, being coupled with localized structural evolution on transition-metals (TM) and lattice oxygen, is believed to be the possible root cause of NMC811 degradation. However, diffraction and morphology study speculate the cracking formation in the secondary and/or primary particle is the root cause. The disagreement on the degradation mechanism originates from the facts that (1) post-mortem analysis, where reliability is low due to the environmental sensitive of the battery samples and (2) intrinsic heterogeneity in the degradation of composite battery electrodes cannot be fully addressed even by in-situ studies when just NMC811 particles were cycled. To address these challenges, I propose to develop an operando high-resolution chemical imaging platform and apply this platform to image structure and transport heterogeneity within composite battery electrodes during (dis)charging. The long-term goal will be achieved through three short-term objectives: 1) development of the novel imaging platform by the combination of ptychography scanning transmission X-ray microscopy (STXM) with an in-situ STXM cell; 2) development of a protocol for preparing a composite electrode to be imaged by the platform; and 3) systematic studies of nano-scale degradation mechanism of various NMC811 composite electrodes. This will link structure evolution with charge-discharge kinetic behaviour, both at the nano-scale in a practical NMC811 composite electrode, for the first time. Hence, we can gain a better idea of the roles of varieties of electrode parameters in composite electrodes degradation, including NMC 811 surface coating, electrolyte additives, and distribution of non-active electrode components such as the binder and conductive additives. Thereafter, a rational design of a long-life NMC811 battery with considerations of these parameters will be possible. The development of this novel chemical imaging platform at Canadian Light Source, the only national synchrotron facility in Canada, will benefit other national and international battery studies for the developments of next-generation batteries to deal with global climate change.