Probing Electrode Electro-Chemo-Mechanical Coupling Behaviors through Mechanical Cyclic Voltammetry (mCV)

Abstract

Electrode deformations during charging and discharge process are directly related to the power performance and cyclability of the energy storage devices. Understanding the electrode deformation and changes in mechanical responses during electrochemical events and their impact on devices’ performance is crucial for achieving high power and high energy storage devices. In-situ atomic force microscopy (AFM) is well suited to tackle this task as it allows tracking local sub-nanometer volume changes and other mechanical responses. With a spatial resolution of tens of nanometer, this approach is capable of mapping the electro-chemo-mechanical behavior under the conditions close to the device operation and access information about local redox mechanisms.In this work, the electro-chemo-mechanical coupling behaviors of different pseudocapacitive materials was studied via in-situ AFM. The concept of mechanical cyclic voltammetry (mCV) curves was developed, and the relationship between electrochemical current and strain were investigated with simplified models. The results revealed that multiple ion-intercalation processes with different mechanical responses are involved during electrode cycling. The mechanical CV mapping highlighted the local heterogeneity and showed that the charging mechanisms varied across the electrode. These local variations could be further corelated to local morphology, crystal orientations or chemical compositions. Besides providing information of redox heterogeneity, the mechanical CV methodology allows us to circumvent the common issues that are often encountered in the global electrochemical characterizations, for example cell resistance and unwanted parasitic reaction.The work was supported by the Fluid Interface Reactions, Structures and Transport (FIRST), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Measurements were performed at the Center for Nanophase Materials Sciences (CNMS), which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences.