Electrochemical Environments for Operando Three-Dimensional Studies of Rechargeable Batteries

Abstract

In the quest for sustainable alternatives to fossil fuel consumption and accompanying greenhouse gas emissions, rechargeable batteries have an integral role to play within the renewable energy ecosystem. Due to their high energy density and extensive commercial availability, Li-ion batteries have recently been favored in the electrification of transportation amongst other applications. Whilst great strides have been made in improving the safety and performance of Li-ion batteries since their commercialization in the 1980’s, scarcity and geopolitical risk surround metals that are critical to Li-ion positive electrodes, such as cobalt, copper, and nickel. More nascent in the developmental pipeline are Li-S and Li-air technology and chemistries with Na, Mg, Zn, etc. as the working ion, promising capacity gains of an order of magnitude, lower cost or improved safety. Regardless of the working ion, most rechargeable batteries are bound by one common feature – the electrochemical reactions within each cell typically occur on heterogenous porous electrodes. Microstructure variations and broader interactions with other cell components lead to a confluence of factors, emerging across several time- and length-scales, that affect the rate of degradation within batteries, the complexities of which have yet to be fully understood. With the advent of electron, X-ray and neutron scattering techniques, great progress has been made in capturing the physicochemical states within batteries. Through X-ray based techniques alone, detailed information can be obtained about the electronic states (X-ray absorption spectroscopy), crystalline states (X-ray diffraction) and mass densities (transmission X-ray microscopy) of materials (1), revealing the influence of intricate electrode microstructures on performance bottlenecks and degradation pathways. The insights offered by these techniques are vastly expanded by the development of suitable in-situ and operando electrochemical cells, which enable the same spatial volume to be tracked within controlled electrochemical environments (2), although many studies in the literature often cite poorer electrochemical performance compared to other large format cell geometries. This talk will focus on recent developments in in-situ and operando electrochemical cells, highlight examples of in-situ studies performed on lithium-based batteries, and discuss some of the challenges faced in constructing appropriate cell designs. In combination with lab-based instrumentation, longitudinal studies of battery degradation can be conducted at various length-scales, whilst the high temporal resolution achievable at synchrotron facilities enable highly dynamic processes to be captured. The overarching goals of these investigations range from accelerating the development of next generation battery chemistries by elucidating complex reaction mechanisms, to informing better design and engineering that will improve the safety and longevity of Li-ion batteries.