Atomic-Scale Observation of Lithiation Reaction Front in Single SnO2 Nanowire

Abstract

Development of new high-performance electrode materials for in lithium ion batteries (LIBs), especially the anode materials, has been under intense research during the past decade. The design of new electrode materials to a great extent depends on how the lithiation front propagates into the anode material. Therefore, revealing the atomic scale lithiation mechanism is central to unfolding the performance of electrode materials during the operation of LIBs. Although recent studies of in situ TEM LIBs [1][2] have revealed morphology evolution, structure and chemical changing in the anode materials during the electrochemical reaction, there is currently lack of critical knowledge about the atomistic mechanisms of dynamical lithiation.In the present work, taking advantage of an aberration-corrected scanning transmission electron microscopy (STEM), we show that the dynamic lithiation process of anode materials with atomic resolution can be revealed. Atomically resolved imaging of the lithiation process in SnO 2 nanowires illustrated that at the very initial stage of lithiation, lithium ions preferred to diffuse along [001] direction in the {200} planes, which introduced the lattice expansion and dislocations. The movement, reaction and generation of ] 1 1 1 [ b mixed dislocations effectively facilitated lithium ion insertion into the crystalline interior. At the later stages of lithiation, the Li-induced amorphization of rutile SnO 2 and the formation of crystalline Sn particles in an amorphous matrix were observed. In situ high resolution TEM imaging revealed that the morphological evolution and mobility of the interface between the crystalline Sn and amorphous Li x Sn were orientation-dependent during lithiation.

Phase Evolution of Tin Nanocrystals in Lithium Ion Batteries

“…The delithiation converted the Li–Sn alloy nanoparticles back to β-Sn, with a much smaller volume change than that occurring during lithiation. In situ TEM images of lithiated SnO 2 nanowires consistently show that the initial Li insertion produces spherical Li x Sn nanoparticles embedded in the amorphous lithium oxide matrix, while the wire shape remains despite the large high distortion. , The present result showing that the β-Sn phase is produced upon the lithiation of SnO 2 (and SnS) and that the crystalline form is maintained during the charge/discharge cycles is consistent with these previous works. The XRD peaks of Li–Sn alloys were not detected under our experimental conditions.…”

Tetragonal Phase Germanium Nanocrystals in Lithium Ion Batteries

“…In situ TEMs have consistently shown significant swelling along the ⟨110⟩ direction but negligible swelling along the ⟨111⟩ direction if both faces are exposed . Various reasons, based on thermodynamic, kinetic, and mechanical models, have been offered as possible explanations for this anisotropic effect. − Yassar and co-workers reported in situ TEM images of lithiated SnO 2 nanowires, indicating that the lithium ions’ initial preference to diffuse along the [001] direction in the {200} planes of rutile (tetragonal) phase SnO 2 introduced the lattice expansion . Here, the lattice expansion of the ST12 phase Ge NCs would be due to Li insertion in the Ge lattices.…”

Lithiation of Tin Oxide: A Computational Study

“…Another peculiarity of Sn-based systems was later reported by Zhong et al and further investigated by Nie et al In their experiments they saw that the transformation into lithia occurs along stripes when a nanowire of SnO 2 gets floated with lithium. Such a nucleation is very different from the usually assumed core–shell mechanism and remains to be understood.…”