Revealing the Phase-Transition Dynamics and Mechanism in a Spinel Li₄Ti₅O₁₂ Anode Material through in Situ Electron Microscopy

Abstract

Spinel Li4Ti5O12 is considered as a promising anode material for long-life lithium-ion batteries because of the negligible volumetric variation during the insertion and extraction of Li ions. Phase transition is an inevitable process during the migration of Li ions, and the transition process and mechanism need detailed investigation down to the atomic scale. In this study, we investigated the behavior and mechanism on the phase transition of Li4Ti5O12 through in situ transmission electron microscopy (TEM). It has been found that the spinel-structured Li4Ti5O12 was gradually transformed to a rock salt structure under electron beam irradiation. A sharp interface with an epitaxial relationship was observed between the transformed rock salt phase and the parent spinel phase. Furthermore, the heterostructure with different crystal structures of Li4Ti5O12 has been precisely tailored with electron beam irradiation. Our detailed in situ TEM results and theoretical calculations led to unprecedented level on the understanding of phase-transition mechanism in Li4Ti5O12. This study demonstrates a possible approach to precisely engineer the crystal structure of materials and to realize a well-designed heterostructure in electrode materials.

Different Oxygen Desorption Durabilities of Lithium Titanium Oxides as Confirmed by Transmission Electron Energy-Loss Spectroscopy Analysis of Li4Ti5O12 and β-Li2TiO3 Biphase Specimens

“…The feature of the O K-edge ELNES of spectrum 2 (irradiated Li 4 Ti 5 O 12 ) was similar to the feature of spectrum 4 (β-Li 2 TiO 3 ), which estimated that its oxygen–cation coordination was octahedral. The structural damage of the Li 4 Ti 5 O 12 phase induced by electron irradiation was explained by the formation of a disordered rock-salt phase by Ti-cation mixing at the spinel 16c and 16d sites. ,, The above cation disordered rock-salt phase formation via electron beam irradiation has also been confirmed in other spinel-type oxide materials such as MgAl 2 O 4 , and MgCo 2 O 4 . The oxygen–cation coordination was altered from the tetrahedral form to an octahedral form by the above cation-site mixing; thus, the shape of the O K-edge ELNES of spectrum 2 (irradiated Li 4 Ti 5 O 12 ) clearly showed the formation of a disordered rock-salt phase via electron irradiation.…”

“…According to the above reaction, the Li 4 Ti 5 O 12 phase mostly alters its structure from spinel to disordered rock salt, which is well known to be the result of electron beam damage for specimens in transmission electron microscopy (TEM) observations. − In the same manner, the β-Li 2 TiO 3 phase is also affected by the reduction reaction with oxygen desorption. , However, the oxygen desorption durability would be different from that of the Li 4 Ti 5 O 12 phase because of the different crystal structure and chemical formula. Comparing the oxygen desorption durabilities between β-Li 2 TiO 3 and Li 4 Ti 5 O 12 phases can assist in understanding the difference in material stability with respect to the crystal structure and chemical formula; however, this topic has not been thoroughly discussed in the literature.…”

In Situ TEM Investigations on the Controlled Phase Transformation of Vertically Aligned WS2 at Designated Locations on an Atomic Scale

“…In addition, it is of interest to find that there is a latent time for the conversion from WS 2 to W under the action of electron beam irradiation and heating treatment. This could be related to the fact that radiolysis needs a latent time to store enough internal energy through the inelastic electron momentum transfer. − Note that the latent time here is defined as the inverse of time required to begin the transformation. Extensive in situ TEM experiments are performed to understand the factors that influence the latent time, and the results are summarized in Figure .…”

Atomistic Phase Transition Mechanism of Zero-Strain Electrode Material: Transmission Electron Microscopy Investigation of Li4Ti5O12 Spinel Lattice Upon Lithiation

“…18 However, the damaged phase formed by electron-beam irradiation is difficult to distinguish from the lithiated phase on the <110> zone axis imaging. [19][20][21][22][23] Furthermore, high-quality STEM imaging requires several seconds and has an insufficient frame rate to capture the phase transition process.…”