Takeshi Yao

Relaxation Phase Analysis of LiMn2O4 Cathode for Secondary Li Ion Battery

Li-Mn-O system is expected to perform as a favorable electrode material for lithium ion battery due to its low cost, low toxicity and high electric capacity. We firstly extracted all amount of Li electrochemically and inserted Li till =0.1 at a rate of 1C in terms of LixMn2O4 electrochemically then stopped the insertion. We measured X-ray diffraction as a function of elapsed time after termination of Li insertion process and investigated phase change of LiMn2O4 material after termination of Li insertion process. From the asymmetric Lorentz peak fitting result of the XRD pattern, it was found that the two phases, Li-rich phase and Li-lean phase, coexist. It is found that the lattice constants of both phases were almost constant and that the amount of Li-lean phase decreased and Li-rich phase increased with the elapsed time.

Relaxation Analysis of Li Inserted γ-Fe2O3 at Various Rates

Lithium was electrochemically inserted into γ-Fe2O3 with different current densities and its crystal structure was analyzed by X-ray Rietveld method. Iron migrated from 8a site to 16c site in the process of lithium insertion and from 16c site to 8a site gradually at relaxation process after the lithium insertion. It was considered that lithium was inserted at 8a site during the lithium insertion process and migrated to 16c site with relaxation time. Iron occupancy of 8a site just after lithium insertion increased with the decrease of insertion rate. It was considered that lithium migrated from 8a site to 16c site even during lithium insertion process at low insertion rate. These results were very well consistent with the site preference that lithium prefers 8a site to occupy kinetically and prefers 16c site thermodynamically.