Recently, the research team at the University of Science and Technology of China (USTC), headed by Professor Peng Tan from the Department of Thermal Science and Energy Engineering within the School of Engineering Science, has achieved a notable breakthrough in delineating the reaction kinetics of lithium-ion battery electrodes. Leveraging in-situ stress analysis technology (ISLE), the team meticulously monitored the normal stress variations in lithium iron phosphate (LFP) electrodes during both the charging and discharging cycles. This enabled them to accurately reconstruct the spatiotemporal progression of reaction sites throughout the electrode's thickness.

This study shed light on the stress signals that arise from lattice volume fluctuations in LFP electrodes during the processes of lithium insertion and extraction. Through an inverse analysis of these non-uniform stress signals, the team was able to deduce the spatiotemporal distribution of active reaction sites. Their experiments uncovered that the strain transfer efficiency in the electrode's central region was merely 61.2% (for thin electrodes) and 55.6% (for thick electrodes) of that observed at the edges. Moreover, they observed that during charging, the reaction front moved from the electrode surface towards the current collector. In the case of thick electrodes, the reaction front even demonstrated two instances of reverse migration.

These insights offer a fresh mechanical perspective for comprehending the heterogeneous behavior of phase-separating electrodes and furnish empirical evidence to guide the structural design of thick electrodes. The pertinent findings were featured as a cover story in the esteemed international journal ACS Energy Letters.