Search

Composite electrodes composed of amorphous titanium polysulfide (a-TiSx) and titanium disulfide (TiS2) were designed for application in all-solid-state batteries. The conductivity of the a-TiSx/TiS2-based working electrode was higher than that of the amorphous TiS4 (a-TiS4); the reversible capacity of the cell using a-TiSx/TiS2 electrode was higher than that of the cell using a-TiS4. Designing nanocomposite materials such as the a-TiSx/TiS2 described in this paper is an effective way to improve the performance of all-solid-state batteries.

Graphite–solid electrolyte (SE) composite anode, prepared by spark-plasma-sintering (SPS) process, was applied to all-solid-state lithium secondary batteries with lithium sulfide (Li 2 S) positive electrode. The electrochemical tests demonstrated that the graphite–SE/Li 2 S cells showed the discharge capacity of ca . 750 mAh·g − 1 -Li 2 S with the average voltage of ca . 1.98 V. Although the discharge capacity was lower than that of the In/Li 2 S cells ( ca . 920 mAh·g − 1 -Li 2 S), the estimated energy density was higher than that ( ca . 1490 and 1220 mWh·g − 1 -Li 2 S for graphite–SE/Li 2 S and In/Li 2 S cells, respectively), due mainly to its higher average voltage. The graphite–SE/Li 2 S cells showed improved rate capability as compared with the cells with the graphite + SE blended powder, which was attributable mainly to the reduced interfacial resistance between the graphite and SE particles caused by the SPS process.

Non-graphitizable carbon (hard carbon) as a negative electrode material for lithium-ion batteries is investigated by X-ray photoelectron spectroscopy, and hard X-ray photoelectron spectroscopy (HX-PES). HX-PES spectra have peaks of both the solid electrolyte interphase on the hard carbon surface and the hard carbon itself. The change in spectrum with state of charge is observed by HX-PES. Hard carbon has two types of lithium insertion site; between graphene sheets and into nano-scale voids. These spectroscopic results are consistent with the lithium insertion mechanism into hard carbon.

The new compound LiNaCo[PO(4)]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO(4)]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO(4)]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) Å, and Z = 8. The structure consists of edge-sharing CoO(4)F(2) octahedra forming CoFO(3) chains running along the b axis. These chains are interlinked by PO(4) tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie-Weiss behavior above 60 K with θ = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO(4)]F undergoes a three-dimensional magnetic ordering at T(mag) = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO(3) chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations.

We have investigated the charge-discharge mechanism in the first cycle and the origin of its high charge–discharge capacity for Li1.2Mn0.4Fe0.4O2 (0.5Li2MnO3·0.5LiFeO2) positive electrode material of lithium ion batteries. Results reveal that oxygen loss occurs in the entire region of the Li1.2Mn0.4Fe0.4O2 particles composed of Mn-rich (Fe-substituted Li2MnO3) and Fe-rich (Mn-substituted LiFeO2) nanodomains during the first charge. Nanodomains of Mn-Li ferrites with a spinel structure start to be formed along the particle surfaces. During the first discharge, the extracted oxygen is partially reinserted preferentially into the Fe-rich nanodomains as oxide ions rather than in the Mn-rich nanodomains, and the proportion of the spinel nanodomains decreases. The origin of the high charge–discharge capacity might be ascribed to the participation of the oxide ions and neutral oxygen species in charge compensation by incorporation of the LiFeO2 component into Li2MnO3. Irreversible capacity at the first cycle can be caused by the irreversible loss of oxygen during the charge and irreversible structural changes throughout the cycle: the movements of transition metal ions inducing random cation-site occupation throughout the cycle, associated with the formation and incomplete disappearance of the spinel ferrite nanodomains which is almost electrochemically-inactive under the applied voltage range.

Electrochemically active lithium sulfide–carbon (Li2S–C) composite positive electrodes, applicable for rechargeable lithium-ion batteries, were prepared using spark-plasma-sintering (SPS) process. The electrochemical tests demonstrated that the SPS-treated Li2S–C composites showed the initial charge and discharge capacities of ca. 1200 and 200 mAh g−1, respectively, though Li2S has been reported to show no significant charge capacities when conventionally mixed with carbon powder. Such activation of Li2S was attributed principally to strong bindings between Li2S and carbon powders, formed by the SPS treatment. The ex situ XRD measurements showed that some amounts of Li2S were still remained unchanged and any elemental sulfur was not detected even at fully charged state, which was similar to Li/S cells.

Fe-substituted Li2MnO3 including a monoclinic layered rock-salt structure (C2/m), (Li1+x(FeyMn1−y)1−xO2, 0 F m 3 ¯ m ) and monoclinic ones at high Fe content above 30% (y ≥ 0.3), while the sample was assigned as a monoclinic phase (C2/m) at low Fe content less than 20%. In the monoclinic Li2MnO3-type structure, the Fe ion tends to substitute a Li (2b) site, which corresponds to a center position of Mn4+ hexagonal network in Mn–Li layer. The electrochemical properties including discharge characteristics under high current density (

Trends of technology developments of lithium and lithium-ion rechargeable batteries for hybrid electric vehicles (HEVs), plug-in HEVs (PHEVs), and battery electric vehicles (BEVs) in national R&D projects of Japan are reviewed. In addition, roadmap of current status for R&D for improving specific power and specific energy of the batteries in national project in Japan are overviewed.

Lithium sulfide (Li2S)-carbon composite positive electrodes were prepared by the spark-plasma-sintering (SPS) process for use in rechargeable lithium batteries. By the SPS treatment of Li2S and acetylene black (AB) blended powder, the strong binding between the active materials and the carbon powders were formed. Such contact effect improved the electrochemical performance of the cells with liquid electrolytes (1M LiFP6/(EC+DMC)), probably due to the increase in conductivity of the positive electrodes, though the samples prepared by the ball-milling process showed no significant capacity in the electrochemical tests.

We have investigated initial stage of the delithiation of Li1.2-xMn0.4Fe0.4O2 nanoparticles by means of transmission electron microscopy and electron energy-loss spectroscopy. It was found that depletion areas with diameters of less than 10 nm are preferentially formed at Fe-rich regions on the particle surfaces. Correlations between redox reactions of transition metal ions and formation of the depletion areas are discussed.

Layered lithium cobalt oxide (LiCoO2) cathode films were successfully deposited onto an aluminum substrate with a large surface area by electrostatic spray deposition (ESD). Highly porous films were prepared by ESD using cobalt acetate tetrahydrate (CoOAc) and lithium hydroxide monohydrate (LiOH) dissolved ethyl alcohol (15 vol.%) and di(ethylene glycol)butyl ether (85 vol.%) as a precursor solution. An LiCoO2 film, the crystal structure of which contained a combination of layered and spinel regions, was synthesized by heat treatment for 2 h at 400 °C. Charge–discharge curves showed that the capacity of this film was 120 mAh g−1. Heat treatment at 650 °C was shown to be a low enough temperature for the resulting film to be used with an aluminum substrate and to allow the retention of the morphology of the surface on which the film is deposited. The discharge capacity for the layered LiCoO2 region of this film was 140 mA g−1 at a rate of 1C and it achieved a good cycle and a rate performance without the need for auxiliary materials.

The specific capacity of Li 0.44 Mn 1− y Ti y O 2 (0 y 3 –LiOH salt at a low temperature. High-purity specimens of the lithium-inserted Li 0.44+ x Mn 1− y Ti y O 2 have been successfully prepared. We have conducted a systematic experimental study of the structural and electrochemical properties of these compounds. The inserted lithium content, x , in Li 0.44+ x Mn 1− y Ti y O 2 increases together with the substituted Ti content, y . The initial charge capacity increases from 130 mAh g −1 ( y = 0) to 145 mAh g −1 ( y = 0.22) for the Li 0.44+ x Mn 1− y Ti y O 2 compounds. The maximum discharge capacity that has been achieved is 180 mAh g −1 in the case of Li 0.72 Mn 0.78 Ti 0.22 O 2 between 2.5 and 4.8 V with a fixed current density of 30 mA g −1 ( C /6) at 30 °C. The discharge capacity at the 4 V plateau region (about 100 mAh g −1 ) in the lithium-inserted Li 0.55 MnO 2 has been improved to twice that in as-prepared Li 0.44 MnO 2 (about 50 mAh g −1 ). The structural differences between Li 0.44 MnO 2 and Li 0.55 MnO 2 are discussed based on XRD Rietveld analysis results.

A mixture of flammable organic solvent and nonflammable room temperature ionic liquid (RTIL) has been investigated as a new concept electrolyte to improve the safety of lithium-ion cells. This study focused on the use of N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP13-TFSI) as the RTIL for the flame-retardant additive. It was found that a carbon negative electrode, both graphite and hard carbon, could be used with the mixed electrolyte. A 383562-size lithium-ion trial cell made with the mixed electrolyte showed good discharge capacity, which was equivalent to a cell with conventional organic electrolyte up to a discharge current rate of complete discharge in 1 h. Moreover, the mixed electrolyte was observed to be nonflammable at ionic liquid contents of 40 mass% or more. Thus the mixed electrolyte was found to realize both nonflammability and the good discharge performance of lithium-ion cells with carbon negative electrodes. These results indicate that RTILs have potential as a flame-retardant additive for the organic electrolytes used in lithium-ion cells.

A charge–discharge cycling test of a Li/LiCoO 2 cell containing ionic liquids based on bis(fluorosulfonyl)imide ([FSI] − ) as the electrolyte media, revealed significantly better rate properties compared to those of cells using conventional ionic liquids. The use of an 1-ethyl-3-methylimidazolium (EMI + ) salt permitted the retention of 70% of the discharge capacity at a 4 C current rate. In contrast, similar performance of cells containing N -methyl- N -propylpyrrolidinium (Py 13 + ) and N -methyl- N -propylpiperidinium (PP 13 + ) salts of [FSI] − was limited to operation at 2 and 1 C current rates, respectively. However, the charge/discharge cycling stability of the cell with Py 13 [FSI] was much better than that of the cell using EMI[FSI].

Electrochemical characteristics of low crystalline carbonaceous materials and carbonized non-graphitizable carbons as negative electrodes of rechargeable lithium-ion cells are reviewed, particularly from the viewpoint of the relationship linking the electrochemical characteristics and nano-structural features of these materials. These low crystalline materials show very attractive characteristics for negative electrodes of lithium-ion cells, e. g., reversible capacity higher than that of graphite (LiC6, 372mAh/g). In addition, carbonized non-graphitizable carbons display a significant capacity below 0.1V (vs. Li/Li+). These features are very important to improve specific energy of lithium-ion cells. 7Li-nuclear magnetic resonance (7Li-NMR) observation on lithium insertion into those materials suggested that lithium species in those materials are quite different from that in graphite. Lithium species in low crystalline carbonaceous materials have an ionic character. On the other hand, lithium in carbonized non-graphitizable carbons is classified into two species. One of the lithium species is the same as that in graphitizable carbons. However, the other lithium species are inferred to be lithium clusters, which gave 7Li-NMR peaks at 190 and 280ppm (vs. aq. LiCl) at -130°C. The structural characteristics, which form ionic lithium species and lithium clusters, are discussed.

Charge-discharge behaviors for tin-12% iron alloy films on electrolytic copper foils prepared by electroplating, which were low cost and made of environmentally friendly alloy, were investigated for X-ray a diffraction measurement, cyclic voltammetry and charge-discharge tests. Tin-12% iron alloy plating anodes showed a discharge capacity of 374 mAh/g after 50 cycles with metallic lithium as counter electrodes. From the results of cyclic voltammograms for tin-12% iron alloy plating anodes, the current value for lithium deposition increased around 0.26 V in the first cycle and increased around 0.68 V in the second cycle. The current value for lithium deposition in tin plating anodes increased around 0.66 V in the first cycle. These results suggested that iron was separated from tin-iron alloy plating film in the first charge and electric conductivity of tin-lithium intermetallic compounds formed bycharge-discharge reactions was improved by the dispersion of iron particles between these compounds. At a discharge rate of 5C(50 A/m2) tin-12% iron alloy plating anodes showed a discharge capacity of 285 mAh/g after 50 cycles and was applicable for high discharge rate. A coin-type cell(CR 2032) with a tin-12% iron alloy plating anode and a LiCoO2 cathode showed a discharge capacity of 273 mAh/g and coulombic efficiency of 90.4% after 95 cycles in charge-discharge tests at a constant charge capacity of 302 mAh/g. Therefore, tin-12% iron alloy plating anodes can be expected to substitute for carbon as high capacity anodes for advanced lithium secondary batteries.

A complex of polymer, plasticizer and lithium salts can be used as a solid gel polymer electrolyte in lightweight and rechargeable lithium batteries. Considerable research has been directed towards the development of a gel polymer with high conductivity at room temperature. In this work, a gel polymer electrolyte using polyvinylidene fluoride (PVdF)-1000 (KF), a plasticizer of 1:1 ethylene carbonate (EC) and propylene carbonate (PC), and LiBF 4 salt is optimized. Gel electrolytes have high ionic conductivity, good mechanical stability, a wide electrochemical stable window, and a stable lithium interface. The results of preliminary charge–discharge of cells are discussed in detail.

Lithium fully inserted into both graphitizable and non-graphitizable carbons has been investigated by 7 Li -NMR spectroscopy at low temperatures. It was found that lithium only in the non-graphitizable carbons heat-treated at ca. 1000°C showed peak separation phenomena at temperatures below −30°C. This peak separation is explained as exchange of lithium nuclei between different kinds of lithium species in the carbons. In addition, an equilibrium relationship between the lithium species in the non-graphitizable carbons was found in the temperature range from −30 to −150°C.

Lithium intercalation of natural graphite and well-graphitized vapor-grown carbon fibers has been investigated by solid-state {sup 7}Li-NMR and by cyclic voltammetry. Chemical shift of {sup 7}Li in Li-graphite intercalation compounds (Li-GICs) of natural graphite occurs in two regions, >40 and

Non-graphitizable carbon fibers heat-treated between 1000 and 1200 °C gave capacity higher than the capacity of LiC6 (372 mAh g−1) with a significant capacity below 0.1 V during oxidation. 7Li nuclear magnetic resonance (7Li-NMR) observation on lithium insertion into the carbon fibers suggested that lithium in the carbons are classified into two species. One of the lithium species was the same as that in graphitizable carbons. However, the other lithium species was quite different from that in graphitizable carbons, because the line shifts in the 7Li-NMR spectra of the carbon fibers fully lithiated to 0 V were between 80–110 ppm (versus LiCl); these shifts are larger than the maximum shift of lithium in graphitizable carbons (∼45 ppm). In particular, a significant capacity below 0.1 V corresponded to the formation of a new lithium species.

Crystallographic and electrochemical characteristics of a carbon as a by-product of a SiC production in an Acheson-style furnace were examined as an anode material of rechargeable lithium-ion batteries. The X-ray diffraction pattern of the carbon indicates that the carbon is highly graphitized. The fine powder (9.4μm in average) of the carbon gave a reversible capacity of ca. 370 mAh g-1 between the cut-off voltages, 0 and 2.5V (vs. Li/Li+), in 1 mol dm-3-LiClO4/ethylene carbonate + diethylcarbonate (50: 50 mixture in volume) electrolyte. Moreover, the potential change of the carbon during the electrochemical intercalation and deintercalation of lithium was almost the same as that of natural graphite showing slopes and plateaus. These results indicate that the carbon is an artificial graphite as well graphitized as natural graphite.

In the last two decades, demand for rechargeable batteries with high specific energy or high energy density has been increasing for applications in portable electronic devices such as mobile phones (feature phones and smartphones), notebook personal computers (PCs), and tablet PCs. Since these electronic devices possess relatively large and bright display panels (liquid-crystal or organic electroluminescence), smaller and lighter rechargeable batteries are required to lengthen the devices’ battery life. Furthermore, the need is rapidly increasing for electrochemical power sources applied to electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in HEVs (PHEVs). In particular, the European Union (EU) CO2 emission regulation proposed for 2020 has made a strong impact on future automotive power trains, and EVs and PHEVs are thought to be indispensable for meeting this regulation.

The stacking order of graphite layers in mesocarbon microbeads (MCMBs) heat-treated between 700 and 3,000 C was examined by analyses of X-ray diffraction measurements, and lithium insertion into the MCMBs has been observed using solid-state {sup 7}Li-nuclear magnetic resonance ({sup 7}Li-NMR) spectroscopy. In MCMBs heat-treated above 2,000 C, the fully lithiated MCMBs showed two bands at ca. 45 ppm (vs. KiCl) and ca. 27 ppm in their {sup 7}Li-NMR spectra. The profile of the band at 45 ppm was very close to that for the first-stage lithium graphite intercalation compound (Li-GIC), though the other band at 27 ppm could not be assigned to any phases of Li-GICs. From these results, it is suggested that the structures of the MCMBs heat-treated above 2,000 C for lithium insertion are classified as graphitic structure, which has the AB stacking order of graphite layers, and turbostatic structure with a random stacking sequence of graphite layers; the fully lithiated compositions of both structures were estimated as LiC{sub 6} and ca. Li{sub 0.2}C{sub 6}, respectively. Although MCMB heat-treated at 700 C gave a higher capacity than LiC{sub 6}, the line shift in the {sup 7}Li-NMR spectra indicated that lithium stored in the MCMB displayed an ionic more » character. Capacity change of the MCMBs during charge-discharge cycling up to 20 cycles and capacity loss at higher current densities (

A lithium-ion rechargeable battery based on carbon anode, a viable replacement for lithium metal anode, has been developed. Lithium-ion rechargeable batteries are considered to have high capacity and high safety. For this reason, we have investigated rechargeable batteries with higher energy density, and studied host carbon materials for the anode, in particular. In this investigation, the vapour-grown carbon fibre was used as the anode material. This carbon fibre after graphitization showed high capacity (363 mAh/g carbon) and low potential (versus Li Li + ). It showed good stability during cycling, and is expected to be a suitable anode material in lithium-ion rechargeable batteries. Further, a coin-type cell was prepared with this carbon anode and LiCoO2 cathode, and the performance during galvanostatic charge/discharge cycling observed. This coin-type battery has a high energy density.

Chopped vapor-grown carbon fibers (VGCFS) were studied as anodes for secondary lithium ion batteries using a 1 mol/dm{sup 3} LiClO{sub 4} in a 1:1 (by volume) mixture of ethylene carbonate (EC) and diethylcarbonate (DEC) electrolyte. VGCFs were prepared from hydrocarbons by a vapor-grown method and chopped to ca. 10 {mu}m length. Three different diameters of the VGCFS, 1, 2, and 3 {mu}m (1GWH, 2GWH, and 3GWH, respectively) were used. The VGCFs chopped after graphitization (the 2A method-VGCFs) displayed a higher capacity than those chopped before (the 1A method-VGCFs). In particular, 2GWH-2A gave a capacity of 363 mAh/g carbon, 1.6-fold higher than the capacity of 2GWH-1A; this is almost equal to the theoretical intercalation capacity of an ideal graphite (LiC{sub 6}). The cyclic voltammogram of 2GWH-2A showed the most significantly different profile from that of natural graphite among all of the VGCFs. It is suggested that a new structural change is induced in the well-graphitized VGCFs during the chopping process that affects the lithium storage reaction.

Graphite whiskers, produced by Nikkiso Co., Ltd., (sample code 2GWH-2A) have been investigated with respect to their electrochemical characteristics in different types of liquid electrolytes: LiClO4, LiPF6, LiAsF6, LiBF4, LiCF3SO3 in ethylene carbonate-diethyl carbonate and in solid electrolytes. A high capacity (363 mAh/g) is obtained when a liquid electrolyte was used and 330 mAh/g at 80 °C in the case of a polymer electrolyte. The coulombic efficiency during the first cycle is lower when polymer electrolyte is used. 2GWH-2A shows very different performances in LiClO4 and in LiPF6 electrolytes. The degree of intercalation depends upon of the nature of the binder, composition of the electrode and electrolyte. The color of the carbon electrode also changed from black to gold in the presence of some lithium salt electrolytes, when lithium was fully intercalated into the electrode. The galvanostatic charge/discharge tests show a large plateau near 0 V. On measuring the slow cyclic voltammogram of the 2GWH-2A, five cathodic peaks were observed.

Carbon is one of the best candidate materials for the negative electrode of rechargeable lithium batteries; however, the electrochemical characteristics are not fully understood in terms of the structure of the materials. The relationship linking the volume ration of the graphitic structure (P{sub 1}) of mesocarbon microbeads (MCMBS) and the electrochemical characteristics has been examined, and it was found that the capacity in the range between 0 to 0.25 V (vs. Li/Li{sup +}) in 1 mol/dm{sup 3} LiClO{sub 4}/ethylene carbonate (EC) + 1,2-diethoxyethane (DEE) electrolyte increased with an increase of the P{sub 1} of the MCMBs. This result shows that the lithium storage mechanism in this potential range is the lithium-intercalation reaction into the graphitic layers with the AB or ABC stacking. On the other hand, MCMB heat-treatment temperature (HTT) 1,000 C showed much larger capacity in the range between 0.25 to 1.3 V than higher HTT MCMBs, and it is suggested the interaction among each graphite layer is weaker in nongraphitized carbon than that in well-graphitized ones.

Lithium intercalation of natural graphite and well-graphitized vapor-grown carbon fibers has been investigated by solid-state {sup 7}Li-NMR and by cyclic voltammetry. Chemical shift of {sup 7}Li in Li-graphite intercalation compounds (Li-GICs) of natural graphite occurs in two regions, >40 and

In general, a carbon whisker is prepared from hydrocarbons using a vapor-grown method and chopped to a suitable length. Two procedures were examined to prepare the whiskers: in the normal procedure (1A), whiskers were graphitized after the chopping process, and in the other process (2A), they were chopped after the graphitization. The carbon whisker of 2 μm in length by the 1A procedure (2GWH-1A) showed an average capacity of 248 mAh g−1. On the other hand, the whisker of the same diameter by the 2A process (2GWH-2A) showed a much higher capacity of 363 mAh g−1: this value is 1.6 times of that of 2GWH-1A. This modification method may open a new probability to higher performance carbon materials for the anode.

The new compounds Li(2-x)Na(x)Ni[PO(4)]F (x = 0.7, 1, and 2) have been synthesized by a solid state reaction route. Their crystal structures were determined from single-crystal X-ray diffraction data. Li(1.3)Na(0.7)Ni[PO(4)]F crystallizes with the orthorhombic Li(2)Ni[PO(4)]F structure, space group Pnma, a = 10.7874(3), b = 6.2196(5), c = 11.1780(4) Å and Z = 8, LiNaNi[PO(4)]F crystallizes with a monoclinic pseudomerohedrally twinned structure, space group P2(1)/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90° and Z = 4, and Na(2)Ni[PO(4)]F crystallizes with a monoclinic twinned structure, space group P2(1)/c, a = 13.4581(8), b = 5.1991(3), c = 13.6978(16) Å, β = 120.58(1)° and Z = 8. For x = 0.7 and 1, the structures contain NiFO(3) chains made up of edge-sharing NiO(4)F(2) octahedra, whereas for x = 2 the chains are formed of dimer units (face-sharing octahedra) sharing corners. These chains are interlinked by PO(4) tetrahedra forming a 3D framework for x = 0.7 and different Ni[PO(4)]F layers for x = 1 and 2. A sodium/lithium disorder over three atomic positions is observed in Li(1.3)Na(0.7)Ni[PO(4)]F structure, whereas the alkali metal atoms are well ordered in between the layers in the LiNaNi[PO(4)]F and Na(2)Ni[PO(4)]F structures, which makes both compounds of great interest as potential positive electrodes for sodium cells.

TiO 2 - and ZrO 2 -coated nickel sulfide (NiS) were prepared for the improvement of cycle capability in rechargeable lithium batteries with liquid electrolytes. The cells with the TiO 2 -coated NiS showed improved cycle performance as compared with those of the noncoated NiS. This improvement was attributable to the improved structural reversibility of the active materials with Li + insertion/extraction reactions, which might be due to the stabilization of the active materials by TiO 2 , and also attributable to the suppression of sulfur dissolution in the liquid electrolytes. ZrO 2 coating on the NiS surface was not effective for improving the cyclability of the cells, which was attributable to the increase in the amount of metallic Ni clusters, not contributing to the electrochemical redox reactions, when charging.

We have used a self-reaction process, called the JMC (Japanese Metal and Chemical Co., Ltd.) method, to prepare a series of defect spinels Li 8n/n+4 Mn 8 / n+4 O 4 , Li 2 Mn 5 O 12-δ (n = 0.8), Li 2 Mn 3 O 7-δ (n = 0.65), and Li 2 Mn 4 O 9-δ (n = 0.5). We found that it is easy to oxidize a defect spinel with a higher lithium content (Li/Mn ratio of 0.8) during synthesis. At the same time, however, the defect spinel easily becomes oxygen deficient. By contrast, a defect spinel with a smaller lithium content, especially Li/Mn of 0.5, is difficult to fully oxidize. The defect spinels deliver at initial capacity of 160 mAh/g both in the liquid-electrolyte and solid-state polymer-electrolyte-based cells. Li 2 Mn 3 O 7-δ shows the best battery performance; the capacity loss rate is 0.18% per cycle for a lithium-polymer cell during the first 100 cycles at 65°C, and the cell gives a specific energy of 360 Wh/kg based on the pure oxide. All compounds are thermally stable up to 200°C when they are in contact with polymer electrolytes, but undergo thermal runaway over 200°C. The exothermic reaction proceeds via a redox reaction among Mn 4+ , Mn 3+ , and the polymer electrolyte.

We have used a lithiated MnO 2 , Li 0 33 MnO 2 , with ordered alternating one-dimensional [1 × 2] and [1 × 1] channels as a cathode material in solid-state lithium/polymer cells. An optimized cell can operate at moderate temperatures (40-80°C). Li 0.33 MnO 2 delivers a rechargeable capacity of 160 mAh/g with a flat potential plateau at ca. 3.0 V vs. Li/Li + at the C/3 rate and 65°C, corresponding to a specific energy of 450 Wh/kg of the pure oxide. Cells show good rate capability and excellent cyclability when cycled between 2.7 and 3.5 V at 80% depth of discharge, whereas a capacity decline was observed when cycled between 2.0 and 3.5 V. Capacity fading upon cycling is believed to be due to the formation of a thin layer of spinel phase (transformation to Li 0.5 MnO 2 from Li 0.33 MnO 2 ) on the particle surfaces, as well as to increased cell resistance during charge/discharge cycling. The cell self-discharge at high temperature and the thermal stability of Li 0.33 MnO 2 in contact with the polymer electrolyte are also discussed.

Stage 2 FeCl3-graphite intercalation compound (GIC) was chemically reduced with lithium-naphthalene complex in THF and 1-MB. The GIC was also reduced electrochemically in THF, PC and EC+DEC, containing 1 mol/dm3 of LiClO4. When the reduction was performed in THF chemically or electrochemically, fine iron particles were obtained in the graphite matrix. The mean diameter of the particles is in the range of 11-13nm in this case, while 4nm for 1-MB. For PC and EC+DEC, no iron particle was observed in the product. The difference would be related to the co-intercalation of the solvent. In the reduction process, THF is incorporated together with lithium in the interlayer spacing of FeCl3-GIC. The co-intercalated THF molecules facilitate the reduction of FeCl3 by lithium in the graphite gallery probably because FeCl3 is soluble in THF, and relatively large iron particles are obtained.

The reduction of metal chloride in the interlayer spacing of graphite has been a subject of interest during recent years [1-5]. However, few studies of the reaction mechanism have been described in the literature. In a previous letter [6], we discussed factors determining the size of fine metallic particles formed in the graphite matrix. Atoms of zero-valent metal generated by the reduction of metal chloride at respective sites in the graphite intercalation compound (GIC) start moving in the interlayer spacing of graphite to aggregate. The aggregate of metallic atoms also moves in the interlayer spacing of graphite and coalesces with other aggregates or metallic atoms. The activity to move decreases with increasing size. After this aggregate grows to a certain size and its spontaneous movement is restricted, its growth is carried out by coalescence with other aggregates or atoms, which can move actively due to smaller size and coalesce into this immobile aggregate. As the activity of particle precursors (i.e. metal atoms or their aggregates) to move in the graphite gallery is determined by the bulk melting point of the metal, the lower the bulk melting point, the better the chance the precursor has of growing to a great size, which explains the order of the particle size Fe < Ni < Cu. The dependence of the stage number of starting GICs on the particle size is explicable, assuming the mechanism described above. In this letter, we discuss temperature dependence on the size of fine metallic particles and the form of particles. The preparation method of stage 2 FeC13, NiC12 and CuC12 GICs was shown in the previous letter [6]. Each metal chloride GIC ( -10 rag) was immersed in 2 ml tetrahydrofuran (THF) in the presence of 50 mg naphthalene and 200 mg lithium. The mixture was sealed in a Pyrex glass tube and allowed to stand for 21 days at various temperatures: -70 °C, 0 °C, 25 °C and 50 °C. The size of metallic particles, obtained in the graphite matrix, was estimated from the line width of the X-ray diffraction (XRD) profiles, based on Scherrer's formula. The estimated size is listed in Table I. When atoms of zero-valent metal or their aggregates move in the interlayer spacing of graphite, the activity to move is expected to be