Operando Optical Analysis of LiFePO₄ Composite Electrodes

Abstract

Elucidating reaction inhomogeneity of composite electrodes is key to improve the performances of batteries such as rate capability and durability. Because the reaction inhomogeneity often disappears after a certain relaxation period, operando analytical techniques are indispensable. We hereby propose that operando optical analysis as a common lab method can be applied to visualize the reaction inhomogeneity of LiFePO 4 composite electrodes for lithium-ion batteries with sufficient space and time resolutions. The results indicate that the brightness of the charged phase was higher than that of the discharged phases, which can be used to separate the phases and thus to elucidate the reaction inhomogeneity in the cross section of the composite electrode. A metastable phase Li 3/4 FePO 4 was also captured at a low temperature with the optical analysis.

Fiber Optic Monitoring of Composite Lithium Iron Phosphate Cathodes in Pouch Cell Batteries

“…Some light may also escape through refraction or scattering events at the interface between the fiber core and the surrounding medium due to surface defects and irregularities of the optical fibers if conditions of TIR are not fully met . A trend of slightly higher optical response from LiFePO 4 composite electrodes toward shorter wavelengths during charge and discharge was also observed by Arai et al who showed that the charged phase, FePO 4 , shows higher brightness compared to the lithiated LiFePO 4 using an electrochemical window cell and a confocal optical system . The measured reflectivity of LFP during charge and discharge was converted to intensities of red, green and blue color where blue light with representative wavelengths of 470 ± 30 nm showed a higher output signal.…”

“…26 A trend of slightly higher optical response from LiFePO 4 composite electrodes toward shorter wavelengths during charge and discharge was also observed by Arai et al who showed that the charged phase, FePO 4 , shows higher brightness compared to the lithiated LiFePO 4 using an electrochemical window cell and a confocal optical system. 27 The measured reflectivity of LFP during charge and discharge was converted to intensities of red, green and blue color where blue light with representative wavelengths of 470 ± 30 nm showed a higher output signal. The authors also presented, based on theoretically obtained refractive index and extinction coefficient of LiFePO 4 and FePO 4 , that the calculated reflectivity was higher for the delithiated phase compared to LiFePO 4 , especially at lower wavelengths in the range of 400−500 nm, which is in line with our observations.…”

Phase Transition Kinetics of LiFePO₄ Biphasic Systems in Aqueous and Non-aqueous Electrolytes

“…17 This behavior has been supported also by the optical measurements. 18 Phase transitions are reported to be the ratedetermining factor in some other biphasic systems. 19 One of the common methods to evaluate the phase transition kinetics is chronoamperometry by the potential step measurement where the current response, associated with the fraction of the phase transition product, is measured as a function of time.…”

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

“…A key difference between WF and LSCRM is that in the latter, specified depths of a material can be individually probed (sectioning). Over the last decade optical reflection microscopies, predominantly with WF or single plane illumination, have emerged as in-expensive tool for also tracking battery electrode dynamics [15][16][17][18][19][20][21] . This is because the reflectivity of many micron sized features on the electrode surface can dramatically increase, decrease or spectrally shift on (de)lithiation 22,23 .…”