Electrochemical reduction of natural graphite was carried out in 1M LiClO4 ethylene carbonate (EC)/1,2‐dimethoxyethane (DME) (1:1 by volume) solution at 30°C. Natural graphite was reduced stepwise to LiC6 (golden yellow in color). The staging phenomenon was observed by x‐ray diffraction (XRD). The first stage ( LiC6 ; cL=3.70true3_Å ) and the second stage ( LiC12 ; d2=7.06Å ) compounds were identified as a commensurate structure in which lithium atoms form a close‐packed two‐dimensional array. A second‐stage compound false(LiC18false) with a different in‐plane lithium ordering based on a LiC9 two‐dimensional packing in lithium intercalated sheets also was observed; also third ( LiC27 ; d3=10.4Å ), fourth‐( LiC36 ; d4=13.8Å ), and eighth‐( LiC72 ; d8=27.2Å ) stage compounds were identified. The electrochemical oxidation of the first‐stage compound false(LiC6false) was examined and shown to be reversible over the entire range, i.e., □C6+xnormalLi⇄LixC6 . The reaction mechanism for the reduction of graphite and the oxidation of the first‐stage compound are discussed in relation to the staging phenomenon from the detailed open‐circuit voltage and XRD data. The chemical potential of LiC6 was estimated to be −3.6 kcal · mol−1 from the observed reversible potential. The feasibility of using a lithium‐graphite intercalation compound in lithium ion (shuttlecock) cells is described, and the innovative secondary systems, □C6/LiCoO2 and □C6/LiNiO2 fabricated in discharged states, are demonstrated.

Highly active catalysts for electrochemical reduction of oxygen insensitive to the presence of methanol were prepared from transition metal hexacyanometallate precursors by heat-treatment with carbon black under an inert atmosphere. The catalytic activity for oxygen reduction was examined with the floating electrode technique under an air atmosphere at room temperature. The electrolyte used in most of the measurements was 1 M sodium phosphate buffer solution (pH 7.5), whereas acid and alkaline solutions were also used in addition to the neutral buffer solution to examine the catalytic activity of the prepared catalyst over a wide range of pH. Remarkable enhancements in the catalytic activity were observed for samples heat-treated at temperatures higher than 500°C. Among several 3d-transition metals incorporated in the inorganic precursor, the combination of cobalt and iron incorporated at neighboring sites gave the highest activity, comparable to that of platinum black catalyst (Pt/C). The catalytic activity for oxygen reduction was not affected by the presence of 2.5 M methanol in the electrolyte, while that of Pt/C was severely impaired by the presence of methanol. The catalysts prepared from the inorganic precursors were characterized by X-ray diffraction (XRD), infrared (IR), and X-ray photoelectron spectroscopy (XPS) measurements. The XRD and IR data indicated that the cyanide structure of the inorganic precursor was decomposed when heating beyond 500°C. The XPS data indicated that the oxidation states of cobalt and iron are close to metallic ones and two types of nitrogen forming new bonding are present in the heat-treated samples. The same structural and spectral changes were observed for samples heat-treated without carbon black. From these results, the evolution of the high catalytic activity by heat-treating the inorganic precursors is discussed. © 2004 The Electrochemical Society. All rights reserved.

Charge and discharge of normalLi/MnO2 cells were examined with monitoring of particle fracture of manganese dioxide by acoustic emission. Manganese dioxide used was electrolytic manganese dioxide heat‐treated at 400°C for 24 h in air [HEMD(400)]. The acoustic‐emission technique worked well to monitor events that occurred inside a cell. During the first discharge to prepare a deep‐discharge product, a closely packed series of acoustic events was observed, especially in the latter half of the discharge process, which contained most of the acoustic events. During cycling, acoustic events were concentrated at the end of discharge while no event was observed during charge, indicating that particle fracture took place during lithium‐ion insertion into a solid matrix. Rate‐capability tests showed that the rate of acoustic events was a function of current drain, i.e., a higher discharging current accelerated particle fracture. From these results we discuss the important role of mechanical properties of materials upon the lithium‐insertion scheme. We also discuss the ideal considerations regarding insertion materials for advanced batteries.

Lithium insertion materials have attracted attention among electrochemists and battery researchers because of their potential use for both positive and negative electrodes for lithium-ion (shuttlecock) batteries. 1-3 The negative-electrode materials are usually carbon on which the side reactions of the decomposition of organic solvents due to a catalytic effect of carbon proceed during charge and discharge in addition to lithium-ion insertion and extraction reactions. 4-6 Some of them show anomalous expansion in the negativeelectrode thickness, especially during the first charge and discharge, so-called breaking-in process. These effects can be minimized by selecting appropriate carbon materials together with electrolyte and by optimizing the electrode composition and processing methods, and cycle life can be extended to a quite high level. However, we need to explore new insertion materials in order to advance beyond current lithium-ion batteries. A final goal of our basic research is to design so-called zero-strain insertion materials with which one can expect excellent cycle life and also to control cell chemistry to give ultimate reliability and safety for the next lithium-ion batteries. In order to approach such a final goal, we have planned systematic studies on the effect of partial metal substitution on the crystal structure, electrochemical reactivity, solid-state redox potential, and insertion scheme.In this paper we report the results on Li [CrTi]O 4 , which is isostructural with Li[Li 0.33 Ti 1.67 ]O 4 , 7 and discuss the differences and similarities between the solid-state electrochemistry of Li[Li 0.33 Ti 1.67 ]O 4 and that of Li[CrTi]O 4 . Experimental Li[CrTi]O 4 was prepared from LiOHиH 2 O (Kishida ChemicalCo., Ltd., Japan), Cr 2 O 3 (Wako Pure Chemical Co., Ltd., Japan), and TiO 2 (anatase; Kishida Chemical Co., Ltd.). The reaction mixture was ground in an alumina mortar with a pestle by hand and pressed into pellets (23 mm diam and ca. 5 mm thick.). The pellets were reacted at 800ЊC for 20 h in air. The reaction product was ground and stored in a desiccator over blue silica-gel. The prepared sample was characterized by X-ray diffraction (XRD) using an X-ray diffractometer (XD-3A, Shimadzu Corp., Japan) with Cu K␣ radiation (30 kV, 20 mA). The optical system was adjusted to be a line focus. The system was equipped with a diffracted graphite monochromator to select the copper K␣ line from the diffracted beam. The X-ray system was calibrated using Si (a ϭ 5.4308 Å). Prior to the XRD measurements, the electrode samples (15 ϫ 20 mm) were covered with polyethylene film and heat-sealed to prevent the reactions of the reduced or oxidized samples of Li[CrTi]O 4 with moist air.Details of the electrochemical cells and data acquisition system used in this study were described previously. 8,9 Acoustic events inside the cells were also measured by a method described previously. [10][11][12] The composition of the electrode mix was 85 wt % Li[CrTi]O 4 (or Li[Li 0.33 Ti 1.67 ]O 4 ), 10 wt % acetylene black, a...

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