Eiichi Iwata

Lithium Aluminum Manganese Oxide Having Spinel-Framework Structure for Long-Life Lithium-Ion Batteries

Lithium aluminum manganese oxide (LAMO) having a spinel-framework structure (a = 8.211 A) was prepared and examined in lithium nonaqueous cells. LAMO shows extremely small irreversible capacity with rechargeable capacity of ca. 105 mAh g -1 in lithium cells operated in voltage of 3 to 5 V. To show durability for long-life applications, a 2.5 V lithium-ion cell of Li[Li 1/3 Ti 5/3 ]O 4 and LAMO was fabricated and accelerated cycle tests were done at room temperature in voltage of 2 to 3 V for 3600 cycles, and an empirical relation between capacity (Q) and number of cycle (n) was obtained to be Q = 102.7 - 0.144 n 1/2 .

Capacity failure on cycling or storage of lithium-ion batteries with Li–Mn–O ternary phases having spinel-framework structure and its possible solution

Instability of Li–Mn–O ternary phases having a spinel-framework structure especially at temperatures above 50°C is a problem in designing lithium-ion batteries with these materials. This paper describes the solubility of manganese ions from these materials in 1 M LiPF6EC/DMC (2/1 by volume), X-ray diffraction (XRD) analysis of these materials after solubility tests, and cycle tests of lithium cells with these materials at room temperature or at temperature higher than 50°C. Severe damage was observed in both solubility and cycle tests when Li–Mn–O ternary phases were operated or stored at temperatures higher than 50°C. The XRD examinations indicated that the spinel-framework structure changed in its line shape and location. In order to cope with this problem, we intensively examined the addition of transition metal elements into Li–Mn–O phases and found possible solution on this problem. One of the possible materials is Li[Cr0.1Mn1.9]O4 (Fd3m) which shows excellent performance on cycling and storage at 50°C.

Structural analysis of lithium-excess lithium manganate cathode materials by 7Li magic-angle spinning nuclear magnetic resonance spectroscopy

Abstract The local structures of lithium-excess lithium manganese spinel oxides were studied by high-resolution solid-state 7 Li magic-angle spinning (MAS) NMR spectroscopy. Two resonance lines at ∼500 and ∼555 ppm were observed for the spinels in 7 Li MAS NMR spectra. Spinel stability tests in which spinel powder was stored in electrolyte solution were performed to analyze the changes in the lithium local structure after manganese dissolution. After the spinel stability test, the intensity of the resonance at ∼500 ppm decreased, whereas new resonance line at 0 ppm was observed. The lithium content of the 0 ppm peak increases with the storage time in electrolyte. SEM and chemical analysis suggested a surface coating of non-spinel lithium compounds, the presence of defects on particles surface and fluorine incorporation into the aged spinel. In addition, about 60–70% of lithium remains in the spinel framework after the storage.