Side‐View Operando Optical Microscopy Analysis of a Graphite Anode to Study Its Kinetic Hysteresis

Abstract

Operando analyses have provided several breakthroughs in the construction of high‐performance materials and devices, including energy storage systems. However, despite the advances in electrode engineering, the formidable issues of lithium intercalation and deintercalation kinetics cannot be investigated by using planar observations. This study concerns side‐view operando observation by optical microscopy of a graphite anode based on its color changes during electrochemical lithiation. Since the graphite color varies according to the optical energy gap during lithiation and delithiation, this technique can be used to study the corresponding charge–discharge kinetics. In addition, the cell configuration uses liquid electrolytes similar to commercial cells, allowing practical application. Furthermore, this side‐view observation has shown that microscale spatial variations in rate and composition control the insertion and deinsertion, revealing the kinetics throughout the whole electrode. The results of this study could enhance the fundamental understanding of the kinetics of battery materials.

Characterization and Quantification of Depletion and Accumulation Layers in Solid‐State Li+‐Conducting Electrolytes Using In Situ Spectroscopic Ellipsometry

“…[ 15 ] Furthermore, the exact concentration changes in and the thickness of these layers are determined with fits using an effective medium approximation (EMA). Similar to the eye visible, optical changes of Li‐intercalation into a graphite anode, [ 21 ] we assumed that the presence and absence of Lithium do change the optical properties in a way detectable by the ellipsometer. Significant changes of the refractive index and extinction coefficient in the visible range upon Li + de‐/intercalation were quantified for lithium manganese oxide.…”

Enhancing cycle life and usable energy density of fast charging LiFePO4-graphite cell by regulating electrodes’ lithium level

“…The golden color was observed at the electrode edges for the T 80-80 electrode. The different colors on the graphite electrodes indicate different levels of lithiation ( Kang et al., 2020 ; Finegan et al., 2020 ; Guo et al., 2016 ; Shellikeri et al., 2017 ) induced by non-uniform charge distribution experienced by the electrode during long cycles. The graphite electrode of the T 80-100 and T 100-80 cells did not reveal any color contrast, and they visually looked similar to the BOL electrode ( Figure S5 ).…”

Nonlinear Electrochemical Analysis: Worth the Effort to Reveal New Insights into Energy Materials

“…An important advantage of Raman microscopy is that all modern equipment integrates a digital camera providing an optical picture of the area where the Raman spectra are taken from, thus, the Raman maps can be directly correlated with the corresponding color and morphology of the electrode surface. [ 28 ] The techniques to analyze the optical pictures were significantly refined during the last two decades and nowadays sophisticated conclusions can be drawn for both, negative [ 29 ] and positive [ 30 ] electrodes investigated under operando conditions. These results are then helpful in the detailed interpretation of the Raman maps from a particular area of the electrode.…”