Flowing and Freezing—Correlative Operando Liquid and Cryogenic Microscopy of Nanoscale Liquid-Solid Interfaces

Liquid-solid interfaces are essential components of a range of different biological, chemical, and physical systems and processes and play an essential role in the field of electrochemistry. These types of electrochemical interfaces are often highly complex, multifarious and involve low atomic weight and mobile elements such as hydrogen, lithium, and carbon. The dynamic and beam-sensitive nature of these interfaces makes them extremely difficult to quantitatively characterise in their state of interest using standardised techniques. The performance of many of these electrochemical systems is currently limited due to a lack of high-resolution characterisation techniques which are capable of providing nanoscale understandings of complex interactions that occur between light mobile electrolyte species and various electrode materials, where information pertaining to the morphology, chemistry, and phase of these interfaces at the nanoscale is lacking. This is particularly evident with respect to nanoscale processes occurring in various battery systems, such as dendrite growth and solid-electrolyte interface (SEI) formation and growth, where high-resolution compositional and functional understandings of these phenomena have remained ambiguous after decades worth of research.<br/>Operando liquid-based microscopy techniques such as Liquid Cell Transmission Electron Microscopy (LCTEM) provide the biggest opportunity to directly observe dynamic electrochemical processes at high resolutions in real-time. LCTEM is capable of observing changes in structure, morphology, phase, and elemental distributions in liquid-based systems at the nanoscale, and this has been used to probe various electrochemical processes using specialised MEMs based chip designs that allow for in operando electrical biasing. While this setup does give unique nanoscale insights into these processes, key problems with respect to spatial resolution and beam-induced effects hinder the necessary sub-nanometre spatial resolution needed to resolve complex dynamic liquid-based electrochemical phenomena such as SEI growth and formation, particularly phenomena involving light elements. While various strategies have been employed to overcome these problems through state-of-the-art dose limitation techniques and alternative liquid cell setups involving 2D materials, the necessary resolutions have not been achieved under in operando conditions.<br/>The work presented here seeks to provide an alternative approach where operando liquid microscopy is combined with high-resolution cryogenic microscopy in order to provide both dynamic and atomic scale understandings of nanoscale electrochemical phenomena. The emerging field of cryogenic microscopy for material science has been proven capable of capturing a solid-liquid interface in its state of interest through techniques such as cryogenic STEM and cryogenic atom probe tomography (APT). Cryo APT is capable of providing 3D compositional analysis of frozen nanoscale volumes with ppm chemical sensitivity. Cryo APT is inherently a static microscopy technique, only capable of providing a snapshot of a particular system when in actuality these nanoscale processes are completely dynamic. This makes dynamic liquid microscopy techniques and high-resolution cryogenic microscopy techniques extremely complimentary.<br/>This work has successfully combined operando LCTEM with cryogenic APT through the use of a cryogenic FIB/SEM, vacuum cryo transfer module technology (VCTM), and an inert glovebox. The combination of these distinct microscopy techniques has allowed for dynamic sub-nanometre understandings of various phenomena within nanoscale electrochemical systems such as dendrite growth as well as SEI growth and formation. This presentation will discuss the workflow needed to realise this combination and the results produced thus far.