Abstract
AbstractAlthough lithium, and other alkali ion, batteries are widely utilized and studied, many of the chemical and mechanical processes that underpin the materials within, and drive their degradation/failure, are not fully understood. Hence, to enhance the understanding of these processes various ex situ, in situ and operando characterization methods are being explored. Recently, electrochemical atomic force microscopy (EC‐AFM), and related techniques, have emerged as crucial platforms for the versatile characterization of battery material surfaces. They have revealed insights into the morphological, mechanical, chemical, and physical properties of battery materials when they evolve under electrochemical control. This critical review will appraise the progress made in the understanding batteries using EC‐AFM, covering both traditional and new electrode–electrolyte material junctions. This progress will be juxtaposed against the ability, or inability, of the system adopted to embody a truly representative battery environment. By contrasting key EC‐AFM literature with conclusions drawn from alternative characterization tools, the unique power of EC‐AFM to elucidate processes at battery interfaces is highlighted. Simultaneously opportunities for complementing EC‐AFM data with a range of spectroscopic, microscopic, and diffraction techniques to overcome its limitations are described, thus facilitating improved battery performance.
Highlights
Numerous important processes occur at/through the solid/liquid interface studied, many of the chemical and mechanical processes that underpin the of battery electrodes and undermaterials within, and drive their degradation/failure, are not fully understood
This is common in the study of battery materials as atomic force microscopy (AFM) imaging is often slow, meaning imaging is undertaken while potential control is ‘paused’ to avoid missing fast-changing reactions
Quantitative indentation tests of the SEI by AFM confirmed it comprised of an inner inorganic layer and a soft outer organic layer, consistent with that found at carbon anodes.[93]
Summary
In contrast to microscopies that produce images by the interaction of light or electron beams with a sample, SPM techniques harness local physical and electromagnetic interactions taking place between a probe with a sharp tip and the surface of a specimen, providing nanoscale, or below, resolution imaging.[27,28]. In situ EC-AFM entails the imaging of the sample within the electrochemical cell (i.e., within the ‘battery’), but it does not explicitly need to be under electrochemical control, for example, imaging an electrode in liquid electrolyte, but only before and after charge/discharge This is common in the study of battery materials as AFM imaging is often slow, meaning imaging is undertaken while potential control is ‘paused’ to avoid missing fast-changing reactions. C-AFM can be applied to perform advanced in situ measurements, for instance, localized AFM-based impedance spectroscopy under controlled environments.[39] Closely related techniques have utilized various input/detection arrangements to provide high-resolution contrast in the electronic properties (resistivity mapping) of electrode components which, for example, can enable different materials to be distinguished.[40]. This capability is important for battery electrodes as it can provide extensive interfacial understanding, allowing examination of important process such as the evolution of the SEI, an area where there is still significant debate within the battery research community.[44]
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