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

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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.