Tadaaki Matsumura

Synthesis, Structure, and Electrochemical Properties of a New Cathode Material, LiFeO2 , with a Tunnel Structure

A new lithium iron oxide, LiFeO 2 , with a tunnel structure was synthesized by an ion exchange reaction between the host material, β-FeOOH, with LiOH H 2 O, and its cathodie properties for lithium cells were examined. The ion exchange reaction was carried out by solvothermal reactions using various alcohols and the new phase was obtained for the reaction at 110°C Its structure, determined by X-ray diffraction measurements using Rietveld analysis, has the hollandite-type tunnel structure. Lithium cells consisting of the new LiFeO 2 cathodes and lithium anodes showed good charge and discharge reversibility in the voltage range, 1.5 to 4.5 V. The lithium intercalation and deinterealation mechanism Was characterized using X-ray diffraction results, Mossbauer spectroscopy, and electrochemical measurements.

Lithiation mechanism of new electrode material for lithium ion cells—the α-Fe2O3–SnO2 binary system

Abstract New electrode material for lithium ion cells using surface and intercalation reactions was found for the α-Fe 2 O 3 –SnO 2 binary system. The solid solution was synthesized by a wet preparation method using a precipitation from alkaline solutions containing Fe 3+ , Sn 4+ and SO 4 2− ions. The lithium cells with α-(Fe 2 O 3 ) 0.7 –(SnO 2 ) 0.3 cathode showed the discharge–charge capacity of 300 mA h g −1 . The reaction mechanism was examined by X-ray diffraction (XRD) and the 57 Fe and 119 Sn Mossbauer spectroscopy. Both the intercalation and the surface reactions participate in the charge–discharge process.

Novel Composite Anodes Consisting of Lithium Transition-Metal Nitrides and Transition Metal Oxides for Rechargeable Li-Ion Batteries

Lithium transition-metal nitrides are promising anode candidates for Li-ion batteries. However, lithium must be extracted from the nitrides in an initial anodic oxidation, indicating these compounds cannot directly combine with the current cathodes to constitute cells. This deterrent can be overcome by introducing a certain amount of Co 3 O 4 , which shows large capacities and relatively high oxidation/reduction potentials, into the electrodes containing the above nitrides. A thermodynamically spontaneous reaction between these two active hosts results in a delithiated state of lithium metal nitrides. Under cycling within 1.4-0 V vs Li/Li + Co 3 O 4 is relatively inert to lithium and the nitrides become electrochemically active. The composite electrodes show high first-cycle efficiency of 100%, large capacities of 500 mAh g - 1 , and excellent cyclability. Furthermore, research revealed that the composite electrodes demonstrated high cycling stability operating with polyethylene oxide (PEO) electrolytes at the elevated temperature. The reaction heating of the composite electrode under high Li utilization with PEO electrolytes via differential scanning calorimetry measurement was found to be extremely low compared with those of the lithium metal and the Li-alloy-based systems. suggesting that the composite electrodes could be promising anode candidates for all-solid-state PEO Li-ion batteries in terms of capacity, first-cycle charge efficiency, and thermal reliance.

Synthesis, structure and electrochemical properties of layered material, Li2/3[Mn1/3Fe2/3]O2, with mixed stacking states

Abstract The layered material, Li 2/3 [Mn 1/3 Fe 2/3 ]O 2 , was prepared by Li ion exchange reactions in alcohols from the host, Na 2/3 [Mn 1/3 Fe 2/3 ]O 2 . The structure of the stacking sequence was determined via the simulation of X-ray diffraction patterns and its electrochemical properties were characterized. The stacking sequence of the products depended on the reaction temperature and time. The structure of Li 2/3 [Mn 1/3 Fe 2/3 ]O 2 obtained at 85 °C has stacking faults including the O3, O2 and P2 type with the ratio of 4:4:2. The electrochemical properties of Li 2/3 [Mn 1/3 Fe 2/3 ]O 2 were studied using lithium cells.

Synthesis, structure and physical properties of LixNa1-xNiO2

Solid solutions of Li x -Na 1-x NiO 2 were synthesized and their structures were determined by Rietveld analysis using time-of-flight (TOF) neutron diffraction data. Three phases were observed: monoclinic (C2/m) phase with x=0.00, rhombohedral(I) (R3m) phase with 0.13 <x<0.15, rhombohedral(II) (R3m) phase with 0.70<x<1.00. Rietveld analysis of the rhombohedral(I) phase indicated no Ni disordering at the Li/Na (3a) site, and the disappearance of the cooperative Jahn-Teller ordering corresponds to the distance changes between the adjacent Ni layers. Magnetic properties were also measured for these phases.

La2MgGeO6: a novel Ge based perovskite synthesised under ambient pressure.

In this communication we report the synthesis and structural characterisation of the new perovskite phase La2MgGeO6, which is the first example of a Ge based perovskite phase synthesised at ambient pressure.

Structural Changes and Electrochemical Properties of Chemically oxidized Na_xFeO_2

NaxFeO2 was obtained by chemical oxidization method using NO2BF4 and Br2 which shows the redox potential of ca. 5.1 V and ca. 4.1 V vs Li/Li+, respectively. The oxidized products showed different X-ray diffraction patterns depending on the oxidizing species. In case of NO2BF4, as soaking time progressed, new phase increased with decreasing of NaFeO2 as stating material. The oxidized NaxFeO2 was possible to be inserted the Li ion electrochemically, and resulted in the crystal structure similar to the layered LiFeO2 synthesized by the Li-ion-exchange method from NaFeO2. Reversible discharge-charge reactions were progressed for NaxFeO2 // Li cell, and ac. 150-200 mAh/g of initial capacities were achieved although the capacities decreased with cycle numbers.