In Situ TEM Study on the Growth Process of Amorphous Layer on SnO 2 Nanoparticle During Sodiation on Real Time Scale

Abstract

KoreaAs the secondary rechargeable batteries, lithium-ion batteries (LIBs) have been commercialized, to some extent, in different applications, such as electric vehicle (EV), cell phones, cameras, and other small-scale electronic devices [1,2]. Nevertheless, relatively scarce amount of lithium (Li) present in the world can significantly downplay its commercialization in the far future, because there is increasing demand for large-scale electric grid or energy storage system that can be devised in a costeffective way. In order to overcome the limited Li resources, different alternative batteries have been suggested.[2] Among them, sodium-ion battery (SIB) has become one of main feasible and practical candidates mainly due to the abundance and cheap cost that sodium (Na) can offer, compared with Li.Since the initial discovery of SIBs, many different materials have been researched for their potential applications as electrodes for SIBs [3]. Among them, Sn-based materials (Sn, SnO 2 , and others) have attracted much attention due to their high theoretical capacity, abundance, and suitable electrochemical reactions with Na [4,5]. However, although significant studies on utilizing different nanostructures for Sn-based materials have taken place, little is still known about the sodiation behaviour of Sn-based materials. Especially, understanding on how their interfacial properties change in the process of sodiation is significantly limited, though it is an important part to investigate. Therefore, here we have investigated how the interface of SnO 2 nanoparticles actually changes in the process of sodiation in real time scale though transmission electron microscopy (TEM) using graphene liquid cell (GLC). Monolayer graphene was fabricated by chemical vapor deposition (CVD) process. Subsequently, SnO 2 -containing electrolytes are encapsulated between the two graphene sheets, which were loaded on TEM grid. Upon e-beam irradiation, the electrolytes in GLC are decomposed and move towards the active material [6], which allow us to observe the sodiation process in real time. SnO 2 nanoparticle was immersed in the propylene carbonate (PC)-based electrolytes, where sodiation process takes place in all directions of the nanoparticle.High resolution transmission electron microscopy (HRTEM) image of SnO 2 nanoparticle is shown in Figure 1. It clearly shows that the crystal structure of SnO 2 nanoparticle is cassiterite structure. Figure 2 shows the morphological evolution of the interface of SnO 2 nanoparticles, from 0 s to 412 s. In the initial state (0 s), SnO 2 nanoparticles are surrounded by the electrolyte, where it does not have any interfacial films. In the process of sodiation, large decomposed electrolytes start depositing on the nanoparticle (190 s) and subsequently forms outer interfacial layers on some parts of the nanoparticle (340 s). Finally, at 412 s, it is clearly shown that the amorphous layer is formed on the outer surface of SnO 2 nanoparticle, where it has relatively uniform thickness. In addition, at 412 s, ...

Graphene Liquid Cell Electron Microscopy: Progress, Applications, and Perspectives

“…As the reaction proceeds, stabilization of the nonuniform SEI layer takes place, which is more thermodynamically favorable to minimize the surface energy. Finally, a more uniform SEI layer forms, which is consistent with the SEI layers observed in various electrode materials used for LIBs. − The real-time observation of interfacial phenomena using GLC-TEM can be applied to a broad range of materials, such as SnO 2 /Fe 2 O 3 /rGO, a TiO 2 layer on SnO 2 , and SnO 2 nanotubes, and chemical reactions, such as lithiation, sodiation, and magnesiation …”

“…Finally, a more uniform SEI layer forms, which is consistent with the SEI layers observed in various electrode materials used for LIBs. 139−141 The real-time observation of interfacial phenomena using GLC- TEM can be applied to a broad range of materials, such as SnO 2 / Fe 2 O 3 /rGO, 142 a TiO 2 layer on SnO 2 , 143 and SnO 2 nanotubes, 144 and chemical reactions, 145 such as lithiation, sodiation, 146 and magnesiation. 147 Furthermore, GLC-TEM is also applied to reveal the lithiation mechanism of Li−S batteries.…”