Abstract
Rechargeable lithium-based batteries are one of the key enabling technologies driving the shift to renewable energy, and research into novel technologies has intensified to meet growing demands in applications requiring higher energy and power density. The mechanisms behind battery degradation can be investigated across multiple length-scales with X-ray imaging methods; at the nano-scale severe constraints are imposed on sample size in order to obtain adequate signal to noise. Here, we present a novel laser-milling technique to prepare geometrically optimal samples for X-ray nano-tomography. Advantages of this technique include significantly reduced sample preparation time, and a suitable geometry for mosaic acquisition, enabling a larger field of view to be captured at high spatial resolution, thus improving statistics. The geometry of the resulting electrode remains highly suitable for nano-tomography, and yet permits in situ and operando experiments to be carried out on standard electrode coatings, providing new insights into transient phenomena whilst closely mimicking standard electrochemical cells.
Highlights
IntroductionThe rising demand for portable power sources with high energy densities has generated unprecedented levels of interest in Li-ion and post-Li-ion rechargeable battery technologies, which include lithium-sulfur (Li-S) and lithium-air (Li-air) batteries
Sample preparation for nano-computed tomography (CT) can be challenging for both low-Z and high-Z materials because the transmission required for a high contrast-to-noise ratio (CNR) falls within a relatively narrow band[13] and is further constrained by the fixed energy of lab-based X-ray sources
For an ideal charge-coupled device (CCD) detector, where photon noise is directly proportional to the square root of intensity incident on the detector, Reiter et al calculated the CNR to be at its theoretical maximum at about 14% transmission
Summary
The rising demand for portable power sources with high energy densities has generated unprecedented levels of interest in Li-ion and post-Li-ion rechargeable battery technologies, which include lithium-sulfur (Li-S) and lithium-air (Li-air) batteries These cell chemistries exist in various stages of commercialisation: whilst Li-ion batteries are the state-of-the-art technology within the commercial domain, Li-S and Li-air batteries have the potential to surpass their energy density by an order of magnitude; they suffer from increased rates of degradation that have far impeded successful commercialization. All batteries inevitably degrade during their storage and operation, resulting in reduced electrical and Coulombic efficiencies and a finite cycle life These degradation processes arise from numerous factors that may be induced or exacerbated by heterogeneities within the cell. Area detectors employed for imaging are typically a few thousand pixels across
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