WEB Interfacial studies of solid-state lithium ion battery materials by 4D-STEM, X-ray microscopy, and EELSWednesday (01.01.2020) 00:45 - 01:00 Part of:
Li-ion battery systems are used in consumer electronics. However, usage of these systems in large scale energy applications, like solar generated power storage, is limited due to constraints in capacity. The capacity of these batteries is affected by Li-ion transport, which is assumed to be hindered by interfacial resistance. Determining the structure-chemistry relationship at the solid electrolyte-electrode interface or the interface that forms due to phase separation is crucial for identifying various mechanisms that alter Li-ion transport within battery systems.
This work evaluates the phase separation interface of LiFePO¬4 particles at varying stages of chemical delithiation and the solid electrolyte-electrode interface of pristine and charged LIPON-LiCoO2 batteries. LiFePO4 is a model cathode material for investigating interfacial phase separation as it separates into Li-rich and Li-poor regions during cycling. LIPON-LiCoO2 is a model battery stack for investigating the solid electrolyte-electrode interface as it has an inherent, secondary LiCoO2 interfacial layer, which undergoes significant changes in chemistry after charging.
Four dimensional scanning transmission electron microscopy (4D-STEM) was performed to determine changes in strain and crystallinity as a function of chemical cycling for the LiFePO4 particles and as a function of ex-situ¬ biasing for the LIPON-LiCoO2 battery stack. X-ray microscopy was used to determine the chemistry of the LiFePO4 platelets, while electron energy loss spectroscopy (EELS) was used to determine the electronic bonding configuration of the LIPON-LiCoO¬2 interface. For LiFePO4 platelets, pixel-by-pixel correlated 4D-STEM and X-ray maps indicates linear evolution of lithiation and lattice parameter for the mean 50% chemically delithiated platelets, but for local regions within these platelets, a non-linear evolution of structure and composition occurs. For the biased LIPON-LiCoO2 battery stack, a phase transformation from spinel to rocksalt CoO is observed at the interface.
Evolution of structure and chemistry as a function of cycling across the LiFePO4 phase separation interface as well as the LIPON-LiCoO2 interface can be correlated via 4D-STEM, X-ray microscopy, and EELS. From this correlation, local variations in structure and chemistry at these interfaces as they affect Li-ion transports mechanisms will then be discussed.