Three-dimensional operando optical imaging of single particle and electrolyte heterogeneities inside Li-ion batteries

Abstract

Understanding (de)lithiation heterogeneities in battery materials is key to ensuring optimal electrochemical performance and developing better energy storage devices. However, this remains challenging due to the complex three dimensional morphology of microscopic electrode particles, the involvement of both solid and liquid phase reactants, and range of relevant timescales (seconds to hours). Here, we overcome this problem and demonstrate the use of bench-top laser scanning confocal microscopy for simultaneous three-dimensional operando measurement of lithium ion dynamics in single particles, and the electrolyte, in batteries. We examine two technologically important cathode materials that are known to suffer from intercalation heterogeneities: LixCoO2 and LixNi0.8Mn0.1Co0.1O2. The single-particle surface-to-core transport velocity of Li-phase fronts, and volume changes – as well as their inter-particle heterogeneity – are captured as a function of C-rate, and benchmarked to previous ensemble measurements. Additionally, we visualise heterogeneities in the bulk and at the surface of particles during cycling, and image the formation of spatially non-uniform concentration gradients within the liquid electrolyte. Importantly, the conditions under which optical imaging can be performed inside absorbing and multiply scattering materials such as battery intercalation compounds are outlined.

Electrochromic Corundum-like Compound Based on the Reversible (De)insertion of Lithium: Li2Ni2W2O9

“…A self-standing electrode (LNWO: 94.8 wt %/Carbon black Super P: 5 wt %/PTFE: 0.2 wt %) was cycled against lithium metal in a cell designed for this type of experiment (see Figure S2). , The full setup for the experiment is shown in Figure a.…”

“…It displays reversible electrochemical activity associated with the Ni 3+ /Ni 2+ redox couple when cycled against lithium metal at high potentials. Moreover, anodic electrochromism is clearly established, thanks to operando optical microscopy operated at the single-particle level. − …”

Interrogating the Light-Induced Charging Mechanism in Li-Ion Batteries Using Operando Optical Microscopy

“…The particle edges in the differential image are slightly negative likely to refractive index mismatches between the particle and matrix. 39 When the battery is exposed to the green LED light, however (photocharging condition), a significant decrease in the differential contrast (darkening) is observed at the edges of the particles that is concurrent with an increase in contrast (brightening) at the center, as shown in Figure 4b. Under these conditions, there is an ∼18% increase in the normalized (with respect to image at 2.2 V) intensity of the particle center (averaging pixels in a 1 μm diameter circle at the particle center of mass (see Supplementary note 4)) throughout the photocharge.…”

“…No changes to the cell reflection intensity are observed in this instance, as expected, because no change in the lithiated state may reasonably be induced beyond 4.0 V. The results are 5d. The data contained in the histograms do not compare the absolute changes in reflectivity between particles, as these may be also influenced by external factors such as the required imaging plane and exact particle size and/or orientation 39 (see Supplementary note 4 for further discussion). In summary, we use optical microscopy techniques to investigate the (de)lithiation processes in Li x V 2 O 5 particles under a variety of electrochemical, photocharging, and thermal conditions.…”

Operando Label-Free Optical Imaging of Solution-Phase Ion Transport and Electrochemistry

“…4 It could also be readily combined with established strategies to optically detect oxygen and hydrogen evolution, 39 especially since the sensitivity required to see gaseous products is orders of magnitude lesser than what we have demonstrated for solution-phase species, and to potentially probe three-dimensional ion transport in such contexts. 49,56 Second, the MSE analysis used here could serve as a general approach to reveal nondiffusive behavior or spatially dependent transport parameters. Specifically, similar to the case for carrier transport probed by spatiotemporal methods, 51,52 deviations from diffusive transport manifest as nonlinear MSE curves that would be readily discerned.…”