Tracking lithium transport and electrochemical reactions in nanoparticles

Expectations for the next generation of lithium batteries include greater energy and power densities along with a substantial increase in both calendar and cycle life. Developing new materials to meet these goals requires a better understanding of how electrodes function by tracking physical and chemical changes of active components in a working electrode. Here we develop a new, simple in-situ electrochemical cell for the transmission electron microscope and use it to track lithium transport and conversion in FeF 2 nanoparticles by nanoscale imaging, diffraction and spectroscopy. In this system, lithium conversion is initiated at the surface, sweeping rapidly across the FeF 2 particles, followed by a gradual phase transformation in the bulk, resulting in 1–3 nm iron crystallites mixed with amorphous LiF. The real-time imaging reveals a surprisingly fast conversion process in individual particles (complete in a few minutes), with a morphological evolution resembling spinodal decomposition. This work provides new insights into the inter- and intra-particle lithium transport and kinetics of lithium conversion reactions, and may help to pave the way to develop high-energy conversion electrodes for lithium-ion batteries. Developing next generation batteries requires better understanding of the dynamics of electrochemical reactions in working electrodes. Using a transmission electron microscope, Wang et al . develop a means to track the real time flow of lithium atoms in electrodes during the discharge of a functioning electrochemical cell.