Anisotropic Lithiation Onset in Silicon Nanoparticle Anode Revealed by in Situ Graphene Liquid Cell Electron Microscopy

Abstract

Recent real-time analyses have provided invaluable information on the volume expansion of silicon (Si) nanomaterials during their electrochemical reactions with lithium ions and have thus served as useful bases for robust design of high capacity Si anodes in lithium ion batteries (LIBs). In an effort to deepen the understanding on the critical first lithiation of Si, especially in realistic liquid environments, herein, we have engaged in situ graphene liquid cell transmission electron microscopy (GLC-TEM). In this technique, chemical lithiation is stimulated by electron-beam irradiation, while the lithiation process is being monitored by TEM in real time. The real-time analyses informing of the changes in the dimensions and diffraction intensity indicate that the very first lithiation of Si nanoparticle shows anisotropic volume expansion favoring the ⟨110⟩ directions due to the smaller Li diffusion energy barrier at the Si-electrolyte interface along such directions. Once passing this initial volume expansion stage, however, Li diffusion rate becomes isotropic in the inner region of the Si nanoparticle. The current study suggests that the in situ GLC-TEM technique can be a useful tool in understanding battery reactions of various active materials, particularly those whose initial lithiation plays a pivotal role in overall electrochemical performance and structural stability of the active materials.

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…199,200 Note that electron microscopy using electron beams caused a localized electrochemical reaction, resulting in Li salts (LiPF 6 ) to decompose into LiF, PF 5 , and Li more quickly, and finally accelerating lithiation processes. 124,200,201 Cheong, et al, proved that, when using GLC, the volume expansion of SnO 2 during cycling was inhibited at a low magnification ( Figure 5B), which is attributed to the fact that GLC leads to less lithiation. 124,202 Under higher resolution, agglomeration of decomposed electrolytes and diffusion of Li into SnO 2 are seen ( Figure 5C).…”

“…126,127 Moreover, when using GLC, the liquid containing reactants can be effortlessly maintained between the two graphene sheets during real-time observation in TEMs. 124,125 This kind of in situ GLC-TEM technique offers a new insight to elucidate the detailed reaction steps at the electrode/electrolyte interface, and can also be employed to view different interfacial phenomena in different active materials that are designated for electrochemical storage devices.…”

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

“…[1][2][3][4][5] However, safety concerns still limit the full practical utilization of these batteries. 6 Especially gas evolution is a formidable technological and fundamental challenge 7 since gas generated in hermetically sealed batteries can lead to detrimental effects: on the one hand, gas generation during storage results in a diminished shelf life and eventually a markedly reduced cycle lifetime.…”

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

“…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.…”