Multi- Scale Quantitative Imaging of Dynamic Processes in Beyond-Li-ion Nanobatteries

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Scanning transmission electron microscopy (STEM) currently provides unique atomic scale information about the structural changes occurring in battery materials after cycling has taken place. However, as this information is obtained post-mortem, usually either from solid-state electrode/electrolyte systems or from solid-liquid electrode/electrolyte interfaces observed under cryogenic conditions, the full potential of Operando STEM methods to identify the chemical species evolving during dynamic battery processes in both current state-of-the-art liquid electrolytes and in potential future solid-state electrolytes, has yet to be realised. The current limitations in Operando STEM for liquids are caused by the electrochemical chip design, whereby the liquid electrolyte needs to be unrealistically thin to ensure that there is sufficient image/analytical quality/sensitivity - the experimental set-up does not reproduce the complexities of a real battery and hence the observations are difficult to correlate with processes in technologically relevant batteries. Here, I propose to develop a first "real" nanobattery Operando cell for rapid and accurate testing of primarily beyond Li-ion chemistries, such as aqueous and/or non-aqueous Li and/or Ca batteries. This comparison of water-based and organic-based electrolytes, coupled with either 1+ or 2+ ions, provides a range of potential interactions that can be examined to understand the fundamental processes occurring at electrode/electrolyte interfaces and how they control the overall properties and lifetime of the battery system. In particular, the new experimental design proposed here will allow beam induced radiolytic species at nanomolar concentrations to be identified directly, filling a key knowledge gap in current experimentation where it is impossible to isolate the chemical changes caused by the electron beam during the operando experiment from the complex reactions initiated electrochemically. To facilitate this identification even further, this project will also focus on the use of compressive sensing STEM methodologies to optimise the sampling strategies and reduce the overall beam damage in the system, while increasing the temporal resolution of the observations. Furthermore, cross-contamination and cross-over of the electroactive chemical species will be minimized by the combination of these experimental strategies, permitting the implementation and testing of novel electrode/electrolyte combinations with a wide range of performance enhancing additives. A key novel component here is the coupling of a mass spectrometer with the nanobattery operando STEM cell for quantification of all chemical species generated during cycling. This means aqueous/non-aqueous Ca/Li batteries can be uniquely benchmarked and their potential for future applications be defined. A final part of this work is to use ptychography/holography to map local field changes across electrode/electrolyte interfaces. This work will focus primarily on solid-state systems initially using an open cell design for the operando testing and then be extended to the Ca/Li electrolytes in the liquid cell (a more challenging experiment given the stability and signal/noise issues), permitting a direct connection between the existing designs for liquid cells and the future incorporation of safer, solid state systems. The overall goal of this proposal is to create a multi-modal Operando (S)TEM platform that can be used to link nanoscale structure/composition and field changes with ion diffusion, thereby providing the core properties that can then accelerate the implementation of new battery chemistries.