P-074

Aigerim Omirkhan

ao915@ic.ac.uk

James O. Douglas, Neil Mulcahy, Lukas Worch, Ramin Jannat, Ifan E. L. Stephens, Mary P. Ryan

Imperial College London, United Kingdom

Nanoscale analysis of delithiated NMC811 cathode materials: understanding battery degradation using cryogenic workflow for Atom Probe Tomography

Advancing energy materials is critical to addressing the growing demand for efficient and sustainable energy storage systems. Among these, polycrystalline layered LiNi0.8Mn0.1Co0.1O2 (PC NMC811) cathode materials are widely used in state-of-the-art electric vehicles due to their high storage capacity. However, capacity degradation, partly triggered by cathode cracking remains a significant bottleneck. Our previous research have shown that mechanical strength of PC NMC811 reduces during the delithiation, underscoring the need to investigate its chemical composition in this state. Conventional materials characterisation techniques face limitations, such as air exposure, beam damage, and difficulties in detecting light elements such as Li.

To address these challenges, we employ a fully cryogenic materials characterisation workflow, where the material is frozen in liquid nitrogen in a partially delithiated state and transported between the microscopes using vacuum transfer suitcase. Using plasma Focused Ion Beam (pFIB) microscope, we lift out a sample containing the PC NMC811 and electrolyte interface and subsequently fabricate a thin needle for Atom Probe Tomography. This setup is unique in the world and experiments involving delithiated NMC811 are extremely challenging owing to mechanical instability of the material. Obtaining this data represents a significant achievement, highlighting the importance and complexity of the experimental methods employed. 

Here, we report nanoscale chemical composition variations in delithiated PC NMC811 using Atom Probe Tomography. By comparing these results to lithiated NMC811 nanoscale composition, we can make predictions on local chemistry evolution as a function of state of charge. Freezing the electrochemical state of the battery combined with the low atomic number element imaging at nanoscale interface enables us to characterise the interface between the PC NMC811 and electrolyte in its native state allowing us unprecedented insight into relationship between structure, interface stability and reactivity. This insight can then be used to understand battery material degradation including poorly understood transition metal dissolution and be ultimately applied to design better energy materials.