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

加拿大每年都要花费数十亿美元来应对气候变化的负面影响。因此，必须减少温室气体排放，特别是在运输和发电方面，以缓解问题。长寿命锂离子电池在电动汽车（EV）的广泛采用和间歇性可再生能源产生的大规模电力方面发挥着至关重要的作用。使用高镍层状氧化物阴极，如比容量高于200 mAh/g的LiNi0.8Mn0.1Co0.1O2阴极（NMC 811），是降低电池成本和提高可持续性的最有前途的工业现实选择。不幸的是，NMC 811在高电压工作条件下性能迅速下降。寄生阴极表面反应，再加上过渡金属（TM）和晶格氧上的局部结构演变，被认为是NMC 811降解的可能根本原因。然而，衍射和形态学研究推测在二次和/或一次颗粒中形成的裂纹是根本原因。关于降解机制的分歧源于以下事实：（1）事后分析，其中由于电池样品的环境敏感性，可靠性较低;（2）即使在仅循环NMC 811颗粒的情况下，通过原位研究也无法完全解决复合电池电极降解中的固有异质性。为了解决这些挑战，我建议开发一个operando高分辨率的化学成像平台，并将该平台应用于图像结构和运输异质性复合电池电极（放电）充电过程中。长期目标将通过三个短期目标来实现：1）通过将重叠关联扫描透射X射线显微镜（STXM）与原位STXM细胞相结合来开发新型成像平台; 2）开发用于制备将由平台成像的复合电极的方案;以及3）系统研究各种NMC 811复合电极的纳米级降解机制。这将首次将结构演变与充放电动力学行为联系起来，两者都是在实际的NMC 811复合电极中的纳米尺度上。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，电解质添加剂以及非活性电极组分如粘合剂和导电添加剂的分布。因此，考虑这些参数的长寿命NMC 811电池的合理设计将是可能的。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，以开发下一代电池来应对全球气候变化。

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.