Electrochromic Effect of Indium Tin Oxide in Lithium Iron Phosphate Battery Cathodes for State-of-Charge Determination

Abstract

In this article, we discuss the origin of an optical effect in lithium iron phosphate (LFP) battery cathodes, which depends on the electrical charge transferred into the battery. Utilizing indium tin oxide (ITO) as an electrode additive, we were able to observe a change in reflectivity of the cathode during charging and discharging with lithiation and delithiation being clearly visible in the form of lithiation fronts. Further investigations using in situ video microscopy and in situ Raman spectroscopy on test cells with an optical window indicate that ITO additionally acts as an electrochromic marker within the LFP cathode. This enhances the optical effect due to local potentials around the lithiation fronts, which enables the voltage-dependent reflectivity of the ITO to be visible in the LFP cathode. Structural analysis with scanning electron microscopy and X-ray crystallography is presented as well. The observed effect allows for novel battery research methods and for a possible commercial application as a sensor for state-of-charge estimation.

Investigation of charge carrier dynamics in positive lithium-ion battery electrodes via optical in situ observation

“…We further report primarily on antimony tin oxide (ATO) nanopowder as an electrode additive to enhance the optical observability of the LFP cathode due to the replacement of the usual carbon (C) nanopowder as conductive agent. Overall, ATO behaves similar to indium tin oxide (ITO), which we used previously [28][29][30], but offers some advantages as discussed later on. For this reason, the estimation of the apparent diffusion coefficient is discussed in details only for the LFP/ATO cathode in the present manuscript.…”

Experimental and computational characterization of carbon fibre based structural battery electrode laminae

“…The longitudinal electrode expansion measurements are performed utilizing an optical in situ observation method described in detail in previous works [49,50]. This method uses Digital Image Correlation (DIC) to track the deformation of the specimen from video recorded microscopical observations during electrochemical cycling.…”

“…The electrode thickness and applied current are altered to study how the electrochemical performance of the cell is affected by these parameters. Further, Li-insertion induced longitudinal expansion of carbon fibre electrodes is measured in situ during charge/discharge processes using a Digital Image Correlation (DIC) technique, which is based on previous video microscopical electrode observations [49,50]. Expansion data for carbon fibres in liquid electrolyte (i.e.…”

Fibre Optic Sensor for Characterisation of Lithium‐Ion Batteries

“…Roscher et al studied the positive electrode material lithium iron phosphate (LFP) using indium tin oxide (ITO) additives as electrochromic markers in a window cell with in situ video microscopy. [15] They reported a voltagedependent reflectivity of the ITO, which correlated with charging and discharging of the LFP/ITO electrode. Other optical methods that have been employed in battery research include Fibre Bragg Grating (FBG) sensors, [9] to directly measure strain or temperature or to indirectly study intercalation steps or ion diffusion in graphite electrodes through temperature and strain values.…”

“…Roscher et al. studied the positive electrode material lithium iron phosphate (LFP) using indium tin oxide (ITO) additives as electrochromic markers in a window cell with in situ video microscopy [15] . They reported a voltage‐dependent reflectivity of the ITO, which correlated with charging and discharging of the LFP/ITO electrode.…”