In Situ TEM Study on Conversion-Type Electrodes for Rechargeable Ion Batteries

Conversion-type materials have been considered as potentially high-energy-density alternatives to commercially dominant intercalation-based electrodes for rechargeable ion batteries and have attracted tremendous research effort to meet the performance for viable energy-storage technologies. In situ transmission electron microscopy (TEM) has been extensively employed to provide mechanistic insights into understanding the behavior of battery materials. Noticeably, a great portion of previous in situ TEM studies has been focused on conversion-type materials, but a dedicated review for this group of materials is missing in the literature. Herein, recent developments of in situ TEM techniques for investigation of dynamic phase transformation and associated structural, morphological, and chemical evolutions during conversion reactions with alkali ions in secondary batteries are comprehensively summarized. The materials of interest broadly cover metal oxides, chalcogenides, fluorides, phosphides, nitrides, and silicates with specific emphasis on spinel metal oxides and recently emerged 2D metal chalcogenides. Special focus is placed on the scientific findings that are uniquely obtained by in situ TEM to address fundamental questions and practical issues regarding phase transformation, structural evolution, electrochemical redox, reaction mechanism, kinetics, and degradation. Critical challenges and perspectives are discussed for advancing new knowledge that can bridge the gap between prototype materials and real-world applications.

Automated summary

Conversion-type materials are being explored as potential high-energy-density alternatives for rechargeable ion batteries, with in situ TEM being extensively employed to provide mechanistic insights into the behavior of battery materials. This review comprehensively summarizes recent developments in in situ TEM techniques for investigating dynamic phase transformation and associated structural, morphological, and chemical evolutions during conversion reactions with alkali ions in secondary batteries, with a special emphasis on spinel metal oxides and 2D metal chalcogenides. Unique scientific findings obtained through in situ TEM are highlighted, addressing fundamental questions and practical issues related to phase transformation, structural evolution, electrochemical redox, reaction mechanism, kinetics, and degradation.