‘Cry(o)ing’ Out for Safer Batteries—The Application of Cryo-Microscopy to Study Early-Stage Dendritic Growth in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the leading battery technology today, boasting high power and energy densities (250 – 350 Wh kg-1 and 100 – 265 Wh L-1, respectively) and a growing range of applications, including grid-level energy storage systems. Despite this, LIBs are prone to dendrite formation when conditions are unfavourable, which hinders their performance, reduces their Coulombic efficiency and can lead to internal short circuits (ISCs) and thermal runaway (TR). Dendrites therefore pose a critical safety issue in LIBs. To date, however, the mechanism of the nucleation and early-stage growth of these structures is still not well understood, mainly due to limitations in current characterisation techniques. These limitations include inadequate resolving capabilities, such that studying nanoscale degradation processes is not possible, as well as challenges in imaging and quantifying light elements that are air- and/or beam-sensitive (Li, H, O, S and C). Improving our understanding of this relationship, particularly during early-stage growth, is necessary to develop more effective mitigating strategies against this particular degradation.<br/>In this work, an in situ electrochemical cell is used to visualise dendrite formation in a full cell-equivalent configuration. We are able to directly vary electrochemical conditions (namely the state of charge (SoC) and C-rate) and correlate real-time electrochemistry measurements with the onset of dendritic growth. Once this growth is probed, the cell is disassembled and immediately plunge frozen using liquid nitrogen to ‘fix’ the system in place, which is necessary to study the interfacial properties and lithium distribution. The plating is characterised using atom probe tomography (APT) to provide three-dimensional compositional information with sub-nanometre resolution.<br/>This work is the first of its kind to characterise graphite electrodes using a complete cryogenic workflow, providing crucial insights for researchers globally to tackle other challenging carbonaceous systems, particularly in the study of battery materials. This research will provide an improved understanding of the growth mechanism and possible mitigation measures for dendrites in LIBs, aiding the accelerated development of vehicle electrification and large-scale grid energy storage.