Slow‐Moving Phase Boundary in Li_4/3+xTi_5/3O₄

Abstract

the material was first explored by Murphy et al. in 1983, [3] but only in 1995 Ohzuku et al. demonstrated its use in lithium-ion battery application and reported a nearly constant dis-/charge voltage of 1.55 V versus Li/Li + . [4] The constant voltage for de-/intercalation is indicative of a phase transformation during lithium insertion/ removal. However, the existence of a twophase reaction at room temperature and on a macroscopic scale has been debated in the past, with reports suggesting solidsolution [5] and/or nano-domains [6] in an equilibrium condition. Nevertheless, the existence of the two phases was confirmed by direct imaging individual phases using high-resolution transmission electron microscopy (TEM). [7] A cubic unit-cell of Li 4/3 Ti 5/3 O 4 has 8 formula units with 32 oxygen atoms located at the 32e sites, 1/3rd of the lithium and all of the titanium atoms are occupying 16d sites (octahedral positions) and the remaining 8 atoms of lithium are at 8a sites (tetrahedral positions). [8] During the phase transformation to Li 7/3 Ti 5/3 O 4 upon lithium insertion, the atoms of lithium at the 8a sites shift to the neighboring 16c position (octahedral position) and the insertion of eight additional lithium atoms takes place in the remaining 16c positions thus filling up all of the octahedral sites. [4,8] This reordering and insertion of lithium atoms, is accompanied by a huge change in the electronic [8] and the optical properties. [9] However, structurally, there is a mere 0.2% change in the volume of the unit-cell (hence the term "zero-strain" phase transformation was coined). [4] The fast dis-/charge ability of LTO (practically achieved by surface modification and reducing particle size) [2] must be governed by the transport properties of lithium and the kinetics of phase propagation in the electrode, provided, the electronic conductivity is sufficient. Ganapathy et al., [16] using first-principle calculations, addressed the migration across the phase boundary and its movement during the phase transformation to explain the fast dis-/charging ability of this material. Their calculation suggests that a fast migration in and out of the phase boundary enables the phase boundary to move almost like a "liquid." This would be in contrast to some silicon-based [10][11][12] and hydrogen-based systems [13,14] where the interface between structurally different phases is known to hinder the migration of atoms. Such hindrance at the phase boundary would lead to a deviation from a normal diffusion-controlled parabolic growth to a slower interface-controlled linear growth of the silicide or hydride phase in the initial stages of atomic transport. This study is aimed at experimentally determining the migration of Lithium titanate is one of the most promising anode materials for high-power demands but such applications desire a complete understanding of the kinetics of lithium transport. The poor diffusivity of lithium in the completely lithiated and delithiated (pseudo spinel) phases challenges to explain the highr...

Thickness-Controllable Electrode of Lithium Titanium Oxide Nanowire Sheets with Multiple Stacked Morphology for Ultrahigh Areal Capacity and Stability of Lithium-Ion Batteries

“…Furthermore, the SAED patterns of each sample were also examined to confirm the crystalline structure of typical LTO materials (Figure S3). In addition, high-resolution TEM (HRTEM) images of LNSB_H3 and LNSB_L3 were collected by the same equipment to measure the particle size of LTO (Figure S4). The thickness of the electrode and the mass of the LNSB samples are summarized in Table .…”

“…). 34 In addition, high-resolution TEM (HRTEM) images of LNSB_H3 and LNSB_L3 were collected by the same equipment to measure the particle size of LTO (Figure S4). The thickness of the electrode and the mass of the LNSB samples are summarized in Table 1.…”

Advantages of a Solid Solution over Biphasic Intercalation for Vanadium-Based Polyanion Cathodes in Na-Ion Batteries

“…The reason for the pronounced concentration polarization observed for Na 3 V 2 (PO 4 ) 2 F 3 must be related to the diffusive motion during the phase transformation, i.e., slow phase boundary propagation, as this is the only source of concentration polarization under the given experimental conditions. However, the diffusivity of a phase boundary can only be strictly quantified by means of in situ observation of phase boundary propagation, which requires sophisticated microscopic techniques for single-particle measurements. − To estimate the rate of phase boundary propagation, an alternative approach could be numerical modeling of the electrochemical data obtained from experiments. This method has been described in refs , .…”

Optical Modulation and Phase Distribution in LiCoO2 upon Li-Ion De/Intercalation

“…Sadly, the German Science foundation refused several times funding of this and our other works on optical properties and light switching with battery materials. 11,12,28 ORCID Yug Joshi https://orcid.org/0000-0001-7920-5890…”

“…These properties, in principle, can be used to probe the phase propagation using a dense, geometricallydefined thin film of LCO. [11][12][13][14][15] But one may also envision a technical function in optical switching, e.g. by coating a LCO layer onto a silicon or silicon nitride waveguide for producing signal modulation by insertion/removal of lithium).…”