Operando Photonic Band Gap Probe of Battery Electrode Materials

TL;DR

This paper introduces an operando spectroscopic method using photonic crystal-structured electrodes to monitor real-time changes in electrode structure and charge state during battery operation, aiding in understanding and optimizing electrode materials.

Contribution

The study demonstrates a novel in-situ optical technique leveraging photonic crystals to track structural and phase changes in battery electrodes during operation.

Findings

Photonic stopband shifts correlate with lithiation levels.

Operando optical spectra reveal electrode structural evolution.

Method applicable to various photonic crystal-structured electrodes.

Abstract

Innovative new materials are consistently emerging as electrode candidates from lithium-ion battery research, promising high energy densities and high-rate capabilities. Understanding potential structural changes, morphology evolution, degradation mechanisms and side reactions during lithiation is important for designing, optimising and assessing aspiring electrode materials. In-situ and operando analysis techniques provide a means to investigate these material properties under realistic operating conditions. Here, we demonstrate an operando spectroscopic method using photonic crystal-structured electrodes that uses the optical transmission spectrum to monitor changes to the state of charge or discharge during lithiation and the change to electrode structure, in real-time. Photonic crystals possess a signature optical response, with a photonic bandgap (or stopband) presenting as a structural colour reflection from the material. We leverage the presence of this photonic stopband, alongside its intricate relationship to the electrode structure and material phase, to correlate electrode lithiation with changes to the optical spectrum during operation. In this work, we explore the optical and electrochemical behaviour of a TiO2 anode in a lithium-ion battery, structured as an inverse opal photonic crystal. In principle, the operando technique demonstrated here is versatile and applicable to a wide range of electrochemical electrode material candidates when structured with ordered porosity akin to a photonic crystal structure.