Takashi Itoh

In Situ Observation of LiNiO2 Single‐Particle Fracture during Li ‐ Ion Extraction and Insertion

Electrochemical lithium‐ion extraction/insertion properties of single particles were investigated by attaching a filament microelectrode to the particle in carbonate + propylene carbonate electrolyte. High‐resolution cyclic voltammograms and galvanostatic chronopotentiograms were recorded. In addition, we observed in situ particle fracture during charge‐discharge using an optical microscope equipped with a charge‐coupled device camera. We found that the particle fractures when it is polarized above vs. . This phenomenon was explained by the change in crystal parameters expected to occur for in . ©2000 The Electrochemical Society

Microvoltammetry for cathode materials at elevated temperatures: electrochemical stability of single particles

Abstract The electrochemical stability of single particles of cathode materials (LiMn 2 O 4 , Li 1.10 Cr 0.048 Mn 1.852 O 4 , LiCoO 2 and LiNi 0.85 Co 0.15 O 2 ) was investigated by means of a microelectrode technique at 25°C and 50°C. The cycle stability was evaluated by multi-cyclic voltammetry. LiMn 2 O 4 showed good cycle stability in LiClO 4 /propylene carbonate (PC)+ethylene carbonate (EC) and LiBF 4 /PC+EC solutions even at 50°C. On the contrary, in LiPF 6 /PC+EC, significant capacity fading during charge–discharge was observed at 50°C. The cycle stability of LiMn 2 O 4 in the latter solution was improved by partial substitution of Mn by Cr and Li. Regarding LiCoO 2 , its cycle life in LiClO 4 /PC+EC at 50°C was unsatisfactory when the potential was scanned between 3.60 and 4.30 V. On the other hand, LiCoO 2 retained 90% of its capacity when the potential scan was limited to 4.00 V. LiNi 0.85 Co 0.15 O 2 showed similar trend at 50°C.

Microvoltammetry of lithium nickel oxide single particle: deterioration of the redox behavior by water molecules

The microelectrode technique was applied to investigate the electrochemical behavior of LiNiO2 which seriously influenced by water molecules. Cyclic voltammograms of humidified LiNiO2 particles were compared to that of as-synthesized. As a result, a significant peak-potential shift was observed, which denotes that the reaction product caused by H2O generates an electrochemical inactive material on the particle which prevents the Li+ insertion/extraction. The reaction product was considered to be NiO, and deterioration property has also been discussed.

Electric-field dependent redox electron transfer in an organic solid: study of carrier photogeneration efficiency

Abstract We have investigated the electric field dependence of the carrier photogeneration efficiency in an organic photoconductor with high sensitivity. The rate-determining step to generate photocarriers was considered to be the electron transfer between the neighboring two-redox molecules, which is influenced by the electric field. The overall carrier photogeneration efficiency was expressed by employing the electron-transfer velocity at the rate-determining step as a function of electric-field-dependent activation energy. This model successfully fits the experimental results for an organic photoconductor over a wide range of field strengths.

IN SITU CONDUCTANCE MEASUREMENT TO INVESTIGATE ROLES OF CONDUCTIVE ADDITIVES IN LITHIUM ION BATTERY ELECTRODES

Abstract Electrical dc conductance of a composite electrode for a lithium-ion battery was monitored in situ during successive charge/discharge cycles, in order to investigate functions of conductive additives. Such measurement was achieved by means of an interdigitated microarray electrode with a bipotentiostat. The composite films of mesocarbon microbeads (MCMBs) heat-treated at 1000°C were studied with conductive additives of acetylene black or a synthetic graphite in a 1 M LiClO 4 non-aqueous carbonate solution. The role of the conductive additives is discussed in connection with their type and content within the composites. In addition, we propose a modified preparation procedure for the composites having a high retention of conductance.

Catalytic Transformation of Cyclohexene Hydroperoxides to Epoxy Alcohols with Vanadyl Acetylacetonate

Cyclohexene hydroperoxide and its methyl derivatives undergo rearrangement in the presence of the vanadyl acetylacetonate catalyst to the corresponding epoxyalcohols with high cis-stereoselectivity in high yields.