Quantitative 4D-STEM imaging of light elements in Li-ion battery materials

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The aim of the project is to develop and apply low-dose imaging methods based on 4D-STEM for imaging light elements alongside heavier ones to enable understanding of performance and degradation of high-capacity Li-ion batteries. Recent developments in camera technology has allowed the collection of the full detector plane intensity in the scanning transmission electron microscope (STEM) as a function of illuminating probe position. The availability of this rich data-set enables low-dose imaging of materials containing elements with a wide range of atomic numbers. Such a capability has great potential in the study of Li-ion battery cathode materials where the interaction between Li, O and transition metals is controls hysteresis, voltage fade and degradation mechanisms.The overall objectives of the project are:i. The development experimental and data processing approaches to low-dose imaging with 4D-STEM including ptychography. This work will involve optimising the microscope control for data acquisition and the development of appropriate data processing algorithms. In particular, ptychography offers the potential to detect light elements with minimal electron dose and to correct for any residual optical misalignments in post-processing. The latter capability is important for radiation-sensitive materials such as Li-ion battery materials because it is not necessary to use dose to perform the fine tuning of the optical alignment.ii. To explore the origins of performance degradation in high-capacity cathode materials. Lithium-rich cathode materials show higher energy storage capacities which is explained by the O species being involved in the redox in addition to the transition metals. Such materials show large charge-discharge hysteresis effects and voltage fade, explained through O loss. The imaging capabilities developed will be used to examine cathode materials at various stages of charge-discharge cycles to understand how the O-loss process occurs.iii. Image bonding effects in Li ion batteries such as Li-metal and high-capacity cathodes. Recent work has shown that ptychographic reconstructions from 4D-STEM data set are sensitive to electron redistribution due to bonding. Such information is invaluable for a range of Li ion battery materials, and the aim here will be to explain the mechanical anisotropy of Li metal by examining whether the directionality of its bonding can be measured.This project falls within the EPSRC research areas of Energy (electron chemical energy storage), Physical Sciences (electron optics and imaging methods) and Research Infrastructure (building new capabilities). The project is in collaboration with the company PNDetector in Munich, Germany (pndetector.com).Student is case conversion with company PN Detectors GmbH