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

Abstract

design, characterization, equipment, modelling, artificial intelligence, engineering, etc. [3] The main challenges are quite frequently addressed in the literature, including i) the development of a new electroactive material with higher operating voltage/specific capacity, which would increase the overall energy density of the battery; ii) the safety issues concerning the Li metal counter electrode and its uncontrollable interface, called dendrites; iii) the power density of the system, which merits proper electrode architecture and material design; and iv) the replacement of organic liquid electrolytes that are responsible for certain safety issues such as flammability and decomposition caused by electrochemical stability windows smaller than 4 V. [4] Understanding the underlying reaction mechanisms governing the electrochemical processes is an engaging yet challenging task. This is because of the complexity of battery technology: multiple interactions exist that can concern several length scales, from the mm to the nm scale, including the bulk, the surface, the interphase, and their own interactions between each other. [5,6] Another way to actively ensure the development of better/ safer battery systems is a thorough investigation using several advanced characterization techniques (ideally operando, that is, during battery operation) that can probe multiscale lengths. [7,8] Bulk reactions are typically well-understood and monitored because these processes generally occur on a microscopic scale. Furthermore, several characterization techniques were initially developed to monitor bulk reactions, providing substantial knowledge at the macroscopic scale, such as structural evolution. [9] Surface/interphase/interface investigation is more complex primarily because of the size of the "surface" layer (only a few nanometres) and the "fragility" (mechanical and transient nature) of this layer due to its chemical composition. [10,11] Indeed, the surface layer is mainly composed of organic/polymeric species that can easily "burn" during the investigation. A persistent issue that has not yet been properly addressed in the literature is beam damage, which is one of the most common threats to proper interface/interphase investigation. [8,12] This is because the chemical composition of the layer changes rapidly during beam damage. Moreover, interphase/interface/surface chemistries evolve faster than the time-scale resolution of various applied characterization techniques and are primarily 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 dim...

Probing the Mechanically Stable Solid Electrolyte Interphase and the Implications in Design Strategies

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