A key challenge in high energy density Li-ion battery (LiB) cathodes is the lattice oxygen loss and corresponding surface reconstruction that significantly limits the available capacity. Therefore, elucidating these phenomena remains an ongoing pursuit with practical implications. The transient nature of oxygen evolution from LiB cathodes makes their experimental investigation a challenge. Researchers have used X-ray based techniques to study oxygen loss but most of these measurements are limited by their ex-situ nature. On the other hand, measurements of gas evolution using in-situ mass spectrometry allow detection of the evolved gases, but the measurements present significant signal-to-noise challenges for quantitative work. Herein, using Scanning Electrochemical Microscopy (SECM), we report an in-situ, real-time oxygen detection strategy. In our SECM measurements, we positioned an ultramicroelectrode (UME) close to the operating cathode surface to detect evolving oxygen via the one-electron oxygen reduction reaction (ORR), as shown in Figure 1. SECM revealed a unique two-stage oxygen evolution behavior from commercial LiB cathodes. Beyond the expected oxygen loss above 3.6 V (vs Li/Li+), the SECM captured an incipient oxygen release at ~3.1 V during the first charge cycle of LiCoO2 and LiNi0.33Mn0.33Co0.33O2. SECM imaging highlighted spatial heterogeneity of oxygen evolution, while finite element simulation quantifies oxygen release at 4.7×10-8 moles/cm2 for the transient evolution and flux of 2.8×10-11 moles/cm2.s for the continuous evolution. The developed strategy sets SECM as a benchmark for studying highly sensitive transient surface processes and provides an unprecedented insight into the surface degradation of cathode materials.

In-situ, real-time detection and quantification of oxygen evolution from Li-ion battery cathodes via scanning electrochemical microscopy

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.