In situ graphene liquid cell electron microscopy of lithiation behaviors in high density lithium storage materials

Abstract

To develop next-generation high-capacity lithium ion batteries, it is necessary to overcome the limited capacity of conventional materials and to develop new high-capacity lithium storage materials. As alternatives, alloy-type anode materials such as silicon (Si) and tin (Sn) and sulfur (S)-based cathode materials have received a great number of interests in academic researches and industrial applications. When these are implemented, several times higher theoretical capacity can be expected than that obtained through combination of existing graphite-based anodes and lithium metal oxide cathodes. In spite of the high lithium storage capacity, however, continuous active mass loss occurs due to drastic volume and phase changes during cycling, which leads to severe capacity fading and poor cycle life. In order to overcome this, it is necessary to understand the deterioration mechanisms of the materials through real-time transmission electron microscopy, and to suggest a reasonable design strategy. In this thesis, the lithiation behaviors of Si, Sn and S nanoparticles were revealed by first introducing in situ graphene liquid cell electron microscopy into the research field of lithium ion battery materials. And based on insights obtained from these studies, new material design strategies were also proposed. By further improving, this new in situ technique is expected to contribute to unveiling the lithiation behavior of various energy storage materials which have been veiled so far.