Interfaces and Interphases in Batteries: How to Identify and Monitor Them Properly Using Surface Sensitive Characterization Techniques

Abstract Interfaces, interphases, surfaces, and bulk are the main elements in a battery that require to be monitored and understood to control battery life during cycling and electrochemical ageing. To date, bulk‐related processes are generally easier to address in terms of characterization techniques because in‐depth investigations of most of these processes can be performed in operando mode (that is, during battery cycling). However, investigations of surfaces, interfaces, and interphases possess some challenges due to the involved nanosize dimensions, which render it difficult to select adequate techniques and interpret data appropriately. In addition, the evolving chemistry can suffer beam damage during investigation, and the use of postmortem/ex situ samples are not fully reliable. Moreover, the definitions of the terms “interface,” “interphase,” “interfacial,” and “interfacial region” are not clearly consistent, the details of which will be discussed in this study. Finally, techniques that can address interfacial processes in batteries are reviewed by highlighting their primary advantages and disadvantages.