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Lithium diffusion in a small Li4/3Ti5/3O4 (LTO) particle was investigated from kinetic viewpoints of two-phase transition process based on a core-shell model by means of galvanostatic and potentiostatic measurements of thin LTO composite electrodes. High-rate galvanostatic charge (insertion) – discharge (extraction) properties of the thin LTO composite electrode showed that the insertion into the LTO particle was significantly slower than the extraction. An apparent chemical diffusion coefficient (Dapp ) of lithium in the LTO particle during the insertion and extraction was evaluated from the results of potential step chronoamperometry (PSCA) with a spherical finite diffusion model. The phase-boundary movements between the two phases in the cathodic and the anodic potential steps for a long-time region were controlled by lithium diffusion through Li7/3Ti5/3O4 rock-salt (LTO-rock-salt) and Li4/3Ti5/3O4 spinel (LTO-spinel) shell, respectively. Dapp in the LTO-rock-salt and the LTO-spinel phase were estimated to be approximately 1 × 10−12 cm2/s and 1.6 × 10−11 cm2/s, respectively. The slower insertion was mainly due to a Dapp value one order of magnitude smaller in the LTO-rock-salt than that in the LTO-spinel phase. Electrochemical kinetic properties of the LTO particle with the core-shell structure were interpreted by lithium diffusion through the LTO-rock-salt shell during the insertion and the LTO-spinel shell with the low electron conductivity during the extraction.

Microvoltammograms of a single particle of lithium titanium oxide (LTO, normalLi4∕3normalTi5∕3normalO4 ) spinel were interpreted using a core-shell model in the spinel∕rock-salt two-phase transition process. Lithium insertion into the particle was controlled by the diffusion in LTO rock-salt structure outlayer. The quick charging was effectively enhanced by reducing the LTO particle size. Lithium extraction from the particle was significantly affected by the charge transfer on the LTO spinel outlayer rather than by the diffusion of lithium ions. The discharge speed during the internal short-circuit abuse test connecting with the LTO anode was 3 orders of magnitude slower than that with graphite anode. At the internal short-circuit point, transformation to the low electron-conductive LTO spinel phase will work to suppress the rapid extension of internal short circuit reaction. A 2V class lithium-ion battery system using the LTO anode had a high output and input power density of 4000W∕kg for a 10s pulse condition. Quick-charging performance showed 80% of the full capacity in 1min . It was demonstrated that the 2V class lithium-ion battery system exhibited excellent high power and quick charging with outstanding safety characteristics by using the LTO anode.

We carried out an electron spin resonance (ESR) study on hydrogen ion radicals produced by radiolysis of solid para-H(2). In addition to quartet ESR lines proposed to be H(2) (+)-core H(6) (+) (D(2d)) ions in solid para-H(2) [T. Kumada et al., Phys. Chem. Chem. Phys. 7, 776 (2005)], we newly observed totally more than 50 resolved lines in gamma-ray irradiated solid para-H(2)-ortho-D(2) (1 mol %) and para-H(2)-HD (1 mol %) mixtures. We assigned these lines to be isotope substituents of H(2) (+)-core H(6) (+) ions such as H(5)D(+), H(4)D(2) (+), and H(2)D(4) (+) throughout the comparison of their ESR parameters with theoretical results. These results provide a conclusive evidence that H(2) (+)-core H(6) (+) ions are generated in irradiated solid hydrogens. Analysis of the EPR spectrum and ab initio calculations predicts D(2d) symmetry of the H(6) (+) ions, whereas a lowering symmetry (D(2d)-->C(2v)) induced by asymmetric nuclear wave function is observed in H(5)D(+) and H(4)D(2) (+). We also observed isotope-substitution reactions such as H(6) (+)+D(2)-->H(4)D(2) (+)+H(2) and H(6) (+)+HD-->H(5)D(+)+H(2), which are analogous to the well-known isotope-condensation reactions of H(3) (+) in dark nebula, H(3) (+)+HD-->HD(2) (+)+H(2) and HD(2) (+)+HD-->D(3) (+)+H(2).

Lithium storage in TiO 2 (B) was investigated by 6 Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and exsitu X-ray diffraction (XRD) analysis combined with the entropy ( S) and galvanostatic intermittent titration technique (GITT) measurements. Lithium storage sites in TiO 2 (B) were characterized to be separated from four bands assigned to different lithium storage sites. Band A at 0 ppm vs. LiCl in the 6 Li NMR spectra and S measurements indicated that ionic lithium was stored at surface domain of Li x TiO 2 (B) up to x = 0.18. Band B at 2.5 ppm significantly increased with lithium insertion in the region for 0.25 < x < 0.5, which indicated that lithium was mainly inserted into the site lying between bridging oxygens in Li x TiO 2 (B). Additionally, the site on the lithium diffusion path along b-axis was also occupied by a small amount of lithium. The stepwise change of OCV and S at around x = 0.45 indicated that lithium was inserted at the site in TiO 2 layer in Li x TiO 2 (B). In the region for x > 0.75, Band D was observed at more positive chemical shift than Band B. The lithium at the site distorted the local structure of Li x TiO 2 (B), which leads to decrease of the lithium diffusivity in Li x TiO 2 (B).