Hideyuki Noguchi

Studies on an LiMnO spinel system (obtained by melt-impregnation) as a cathode for 4 V lithium batteries part 1. Synthesis and electrochemical behaviour of LixMn2O4

Abstract An Li x Mn 2 O 4 spinel phase is used as a cathode for 4 V lithium batteries and is prepared by the melt-impregnation method, in which melted LiOH or LiNO 3 is impregnated into MnO 2 pores, then reacted with MnO 2 at higher temperature. The effect of synthesis conditions on the electrochemical properties is investigated extensively. For optimum synthesis, the spinel Li x Mn 2 O 4 should be prepared in an N 2 atmosphere at a low temperature of less than 750 °C and for a short time of less than 48 h. The optimum LiMn 2 O 4 delivers an initial charge capacity of 135 mAh/g, and exhibits good rechargeability. The average specific capacity during first 50 cycles is about 120 mAh/g or more.

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

Abstract The preparation of LiCoyMnxNi1−x−yO2 from LiOH·H2O, Ni(OH)2 and γ-MnOOH in air was studied in detail. Single-phase LiCoyMnxNi1−x−yO2 (0≦y≦0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1≦z≦1.11 for y=0.2) and the Co doping level (0.05≦y≦0.2) do not significantly affect the discharge capacity of LizCoyMn0.2Ni0.8−yO2. The doping of Co into LiMn0.2Ni0.8O2 accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn0.2Ni0.8O2 is determined to be 4, the formation of a solid solution between LiCoyNi1−yO2 and Li2MnO3 is confirmed.

Preparation of LiyMnxNi1-xO2 as a cathode for lithium-ion batteries

Abstract The preparation of LiyMnxNi1−xO2 from LiOH·H2O, Ni(OH)2 and γ-MnOOH under oxygen and flowing air is studied. Single phases of LiyMnxNi1−xO2 (0

Crown Ethers for Chemical Analysis: A Review

Abstract Natural macrocvclic compounds, such as valinomycin, are attractive to analysts who have interest in the high selectivity of potassium ion as compared to sodium ion. This selectivity in alkali metal ions was not found in other ligands. Pedersen synthesized many crown ethers [1] and published his result that dibenzo-18-crown-6 (DB18C6) had a larger affinity to potassium than other alkali metals. Since then, these ligands and related compounds have held great interest for physical, inorganic and biochemists.

Synthesis of LiCoO2 from cobalt—organic acid complexes and its electrode behaviour in a lithium secondary battery

Abstract Well-crystallized, layered LiCoO2 has been prepared by heating cobalt—organic acid complexes (such as malic acid and succinic acid) at 900 °C in air after preheating at 400 °C (2 h) and at 650 °C (6 h). LiCoO2 obtained by this method shows a high (003) peak intensity and low (104) or (101) intensities in X-ray diffraction (XRD). The first discharge capacity of LiCoO2 obtained from this method in ester-based electrolyte is 132 mA h g−1 on cycling between 4.3 and 3.7 V. The value is larger than that obtained by the conventional method. X-ray diffraction studies and open-circuit voltage curves show the presence of at least two types of reaction. A two-phase reaction occurs in the region of 0.71

Synthesis and electrochemical properties of layered Li–Ni–Mn–O compounds

Abstract An attempt to prepare solid solutions in the system of LiNiO 2 , LiMnO 2 and Li 2 MnO 3 was performed by heating metal acetates. The solid solutions between end members LiNiO 2 and Li 2 MnO 3 can be successfully prepared in the overall compositional ranges. Both the structure and capacity were compared based on Rietveld analysis and electrochemical investigation on solid solutions between LiNiO 2 and Li 2 MnO 3 . The result showed that the cationic disorder as well as capacity was closely related to the ratio of Li, Mn and Ni in formula. The investigation of chronopotentiogram and ex situ XRD on the solid solutions indicated that the complex phase transitions in LiNiO 2 during delithiation were strongly suppressed with low Mn content (Mn/(Mn+Ni) ratio was 0.1 or 0.2) and completely suppressed with the ratio more than 0.5.

Differences in electrochemical behavior of LiMn2O4 and Li1+xMn2O4 as 4-V Li-cell cathodes

Abstract Stoichiometric spinel LiMn 2 O 4 delivers a large initial capacity of 140 mA hr/g and has unstable rechargeability. The capacity fading of the cell on cycling occurs only in the higher charge voltage range of x x Mn 2 O 4 . Nonstoichiometric spinel Li 1+ x Mn 2 O 4 has a slightly lower capacity of 110 mA hr/g and has an excellent cycling behavior.

Three V or 4 V LiMn composite as cathode in Li batteries prepared by LiNO3 method as Li source

Abstract Four types of lithium-containing manganese oxide obtained by the LiNO3 method, namely (i) Li0.3MnO2 obtained from 1 3 mixture of Li Mn molar ratio heated at 320–350 °C; (ii) LixMn2Oy obtained from the mixture with 1.2–1.8 molar ratio of LiNO 3 MnO 2 heated at 300 °C; (iii) the spinel LiMn2O4 by 1 2 mixture of LiNO 3 MnOOH and (iv) non-stoichiometric spinel Li1+xMn2O4, will be reported and their electrochemical behaviour in lithium cells will be described.

Determination of theoretical capacity of metal ion-doped LiMn2O4 as the positive electrode in Li-ion batteries

The theoretical capacity and cation vacancy of metal ion (M)-doped LiMn2−xMxO4 spinel compounds serving as positive electrodes in a 4-V lithium ion batteries are calculated. The capacity depends strongly on the mole fraction of doped metal ion and vacancies. The theoretical capacity increases with increasing oxidation number of the doped metal ion in the 16d site of LiMn2O4 at the same doping fraction. The validity of the proposed equation for calculation of the capacity has been initially confirmed using a metal ion with well-known valence, such as the Al ion. The oxidation state of Co, Ni and Cr ions in the spinel structure is found to be trivalent, divalent and trivalent, respectively. Analysis shows that metal ion-doped spinel compounds with low vacancy content promote high capacity.

Novel layered Li-Cr-Ti-O cathode materials for lithium rechargeable batteries

Abstract New cathode materials of Li–Cr–Ti–O compounds were synthesized using conventional solid-state reaction at different conditions in air. XRD patterns for these materials indicated that they are isostructure with Li 2 MnO 3 or Li 2 TiO 3 , which have a layered structure with a monoclinic symmetry (space group C2/m). The sample with the best electrochemical properties can deliver initial discharge capacities of 152 and 202 mAh/g for cycling between 2.0 and 4.8 V at a constant current density of 0.44 mA / cm 2 (32 mA/g) at room temperature (about 30 °C) and 60 °C, respectively. The excellent cycling performance was also observed, even at the elevated temperature. These materials demonstrated that Cr 3+ /Cr 6+ could reversibly cycle with a considerably high capacity in a Li 2 TiO 3 -like framework after a significant irreversible capacity loss during the initial cycle.