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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.

Experimental We mechanochemically synthesized the a-NbSx at room tempera- ture. Appropriate amounts of sulfur (S8, 99.9%, Wako Pure Chemical Industries) and niobium disulfide (NbS2, 99%, High Purity Chemi- cals) were weighed and mixed, and the 1.5-g mixture and 500 4-mm- diameter zirconia balls were placed into a 45-mL zirconia pot in a planetary ball mill (P-7, Fritsch GmbH) in an Ar-filled glove box. The mixture was ball-milled at 510 rpm until the amorphous powder was obtained. The X-Ray diffraction (XRD) patterns for the synthesized sam- ples were recorded using an X-ray diffractometer (Rotaflex RU- 200B/RINT, Rigaku). Prior to the measurements, the samples were covered with Kapton film in a glove box to prevent exposure to air. The conductivities of the prepared samples were measured using a two-electrodecell.Thepelletsusedfortheconductivitymeasurements were prepared by pressing powder samples under 360 MPa at 25 ◦ C. A TITAN3 G2 60-300 electron microscope (FEI, Co., Ltd.) was used for the transmission electron microscopy (TEM) measurements. The a-NbS5 powder was directly dispersed on a Cu-mesh-supported carbon film for the TEM measurements. The working electrodes were prepared from a-NbSx (10 mg), acetylene black (1 mg), and polytetrafluoroethylene (PTFE) powder (0.7 mg). A 1 M solution of LiPF6 dissolved in a 1:1 volumet- ric mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (Tomiyama Pure Chemical Industries, Ltd.) was used as the electrolyte. The counter electrode consisted of a 15-mm-diameter, 0.2-mm-thick Li foil disk. A charge-discharge unit (TOSCAT-3100, Toyo System) was used to perform the electrochemical measurements at 30 ◦ C and 100 μ Ac m −2 between 1.5 and 3.0 V.

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.

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

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 (

Ionic liquids (ILs) have been studied as a unique electrolyte for a lithium battery for a past two decades 1). The thermal stability and less-volatility have been expected to improve safety of a conventional lithium ion battery system using flammable non-aqueous electrolytes. For example, using bis(trifluoromethylsulfonyl)imide (TFSA-) –ILs as a electrolyte, LiFePO4 half cell could be charged and discharge over 100 °C 2). In this study, we will report that another unique and important features of a zero-solvent electrolyte like ILs was indicated at a high voltage (> 4.7 V) charging and discharging cycle using a transition metal oxide cathode as a LCO and NMC. A modification of NMC by coating with Al2O3 particle successfully improved the high voltage operation over 4.2 V as already reported 3). However, we found that a LCO and also NMC cathode without any coating could be stable over 4.7 V charging and discharging cycle even in 1-ethyl-3-methylimidezolium bis(fluoromethylsulfonyl)amide ([EMI][FSA]) containing a certain amount of Li[FSA]. This finding indicate that a catalytic site for oxidation decomposition of a conventional organic electrolyte on a transition metal oxide, which was deactivate by a surface coating with Al2O3, did not affect the oxidation of the ionic liquids electrolyte, which did not contain any organic solvents. On the other hand, a cycle stability at a high temperature over 45 °C was effectively stabilized by a surface coating on NMC with ZrO2. The result implies that the surface modification of a transition metal cathode effectively protected the structural disorder of a cathode material by a high temperature condition. These results show that using zero-solvent electrolyte like ILs might be a useful tool to elucidate the effect of surface modification in an organic solvent electrolyte. Acknowledgment This work was supported by the “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING)” project of the New Energy and Industrial Technology Development Organization (NEDO). 1) H. Matsumoto, in Electrolytes for Lithium-ion Batteries, eds. T. R. Jow, K. Xu, O. Borodin and M. Ue, Springer, 2014, ch.4. 2) H. Matsumoto and K. Kubota, ECS Transactions, 64(4), 425 (2014). 3) K. Araki, N. Taguchi, H. Sakaebe, K. tatsumi, Z. Ogumi, J. Power Sources, 269 (2014) 236.

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.

Introduction Lithium titanium oxides such as spinel-type Li4Ti5O12 and ramsdellite-type Li2Ti3O7 have been extensively investigated as electrode materials for rechargeable Li-ion batteries. In recent, another metastable phase of Li2Ti3O7 with Na2Ti3O7-type layered structure have been reported with the structural details and electrochemical Li-ion insertion properties [1]. On the other hand, NaLiTi3O7 has been investigated as electrode materials for rechargeable Li-ion batteries [2]. This Ti4+/Ti3+ electrode showed lower operating voltage compared to Li4Ti5O12. In addition, NaLiTi3O7 has a three-dimensional tunnel structure which is thought to be favorable for fast Li-ion transfer. This compound can be prepared by a conventional solid state reaction. Li2Ti3O7 with the NaLiTi3O7-type structure may be prepared by ion exchange of NaLiTi3O7 (Fig. 1). Higher Li-ion insertion capacities similar to that observed in Li2Ti3O7 with Na2Ti3O7-type layered structure can be expected. However, to our knowledge, synthesis, the structural details and electrochemical Li-ion insertion reactions in this compound have not been reported yet. In the present study, we have successfully synthesized single-phase sample of Li2Ti3O7 with the NaLiTi3O7-type structure and determined its crystal structure by Rietveld analysis. Furthermore, the Li-ion insertion properties of this compound have been clarified for the first time. Experimental The precursor NaLiTi3O7 was first prepared by a conventional solid state reaction by using a method similar to that reported previously [3]. A mixture of Na2CO3 (99.9% pure), Li2CO3 (99.99% pure) and TiO2 (99.99% pure) in a molar ratio of 1.01:1.03:3 was heated at 950°C for 24 h in air. Then, the lithiated Li2Ti3O7 samples were prepared from NaLiTi3O7 via ion exchange at a low temperature. Sodium/lithium ion exchange experiments were performed using the molten salt of LiNO3. Ion exchange reaction was performed at 400°C for 6h in air. After heat treatment, the reaction mixture was washed with ethanol and then dried at 80°C for 1 day in air. Further Li-ion exchange treatment was accomplished by heating the as prepared Li2Ti3O7 in molten LiNO3at 380°C for 6 h in air. The phase purity and crystal structure of the obtained samples were characterized by powder X-ray diffraction (XRD) using a Bruker AXS D8 ADVANCE diffractometer with Cu Kα radiation source filtered by a Ni thin plate (Cu Kα radiation, operating conditions: 40 kV, 55 mA). The particle morphology and chemical composition were verified by scanning electron microscopy equipped with energy dispersive X-ray spectrometer (SEM-EDX; Keyence VE-8800). The chemical and structural characteristics were evaluated using ICP, DTA and FTIR measurements. Electrochemical lithium insertion/extraction experiments were performed using lithium coin-type cells (CR2032-type). The working electrode were made of 80wt% active materials, 10wt% carbon black (Super-P) as a conductive agent, and 10wt% poly(vinylidene difluoride) as a binder. Copper foil was used as a current collector, and the area of the electrode was a diameter of 14 mm. The counter electrode was a Li foil having a diameter of 16 mm. The separator was a microporous polypropylene sheet. A solution of 1 M LiPF6 in a 1:2 mixture of ethylene carbonate (EC) and dimethycarbonate (DMC) by volume (Mitsubishi Chemical Co., Ltd.) was used as the electrolyte. Cells were constructed in a dry room, and electrochemical measurements were carried out with a current density of 10 mA g−1between 0.5 and 2.0 V at 25°C after standing 6h under an open circuit condition. Results and discussion Figure 2 presents the XRD patterns of the NaLiTi3O7 and Li2Ti3O7 samples. These data suggested that the products were single-phase samples of NaLiTi3O7 and Li2Ti3O7. Chemical analysis confirmed that the removal of Na was not complete at the present experimental condition. The electrochemical measurements revealed that the initial Li insertion capacities were 152 mAh g−1 and 243 mAh g−1 for NaLiTi3O7 and Li2Ti3O7, respectively, which were equivalent to 1.62 and 2.45 electron transfer per each formula unit. In addition, reversible Li-ion insertion and extraction reactions were observed in these samples, although a capacity loss of approximately 50 mAh g−1 and 75 mAh g−1 for the first cycle was observed in NaLiTi3O7 and Li2Ti3O7, respectively. Acknowledgement This work was supported by the “Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING project)” of the New Energy and Industrial Technology Development Organization (NEDO; Japan). References [1] K. Chiba et al., Solid State Ionics, 178, 1725 (2008). [2] S.Y. Yin et al., Electrochem. Commun., 11, 1251 (2009). [3] L.M. Torres-Martínez et al., Solid State Sci. 8, 1281 (2006).

Improvement technique of the life of Li-ion batteries has been intensively studied. Modification of the surface of positive electrode material including coating is effective to this purpose. In that process, it is very important to compare the bulk and surface structure of the positive electrode with/without surface modification to understand this effect. For basic information concerning the effect of surface modification, authors have applied Transmission Electron Microscopy (TEM) to visualize the structural distribution inside the positive electrode particles after degradation [1]. As a model material, we synthesized sub-micron size particle of positive electrode such as LiCoO2 by Pechini sol-gel method [2, 3] that could provide the suitable sample for TEM observation without damages from sample preparation like ion-milling or FIB. Analytical TEM measurements by scanning transmission microscopy (STEM) with electron energy-loss spectroscopy (EELS) equipped with monochromator were applied. Li-K EELS peak around 62 eV was clearly found and this peak intensity changed with Li charge-discharge state. The EELS mapping from the spectrum imaging method using this Li-K region spectra showed a distribution of Li in the particle or among particles during the charge discharge cycle. We discuss precisely the change of chemical states at the surface and Li ion distribution inside particles of positive electrode material with/without surface modification using Si, Zr, Al, Mg oxide during charge-discharge cycle. References [1] N. Taguchi, T. Akita, H. Sakaebe, K. Tatsumi, Z. Ogumi, J. Electrochem. Soc., 160, A2293 (2013). [2] Y. Sun, I. Oh, S. Hong, J. Mat. Sci., 31, 3617 (1996).

1. Introduction Lithium sulfide (Li2S) is one of the promising cathode active materials for high-energy rechargeable lithium batteries, because it has a high theoretical capacity (ca. 1170 mAhg-1) and has an advantage that a variety of anode materials without lithium sources are applicable in the practical battery system [1]. However, this material is both electronically and ionically resistive, which gives rise to low active material utilization in the cells [2]. Several attempts have been performed to enhance the conductivity of Li2S, such as forming composites with several metals (Li2S-Fe, Li2S-Cu) [1,2] or carbon [3-5]. Recently, we have tried to prepare the composite with FeS2 (Li2S : FeS2 = 1 : 1 molar ratio) using the spark-plasma-sintering (SPS) process and found that the cells showed the initial charge capacity of ca. 330 mAhg-1 [6]. For improving the charge capacity, preparation of the composite with Li2S-rich composition is required. In the present work, we tried to prepare the Li2S-FeS x -C (x = 1, 2) composites with a Li2S : FeS x = 4 : 1 molar ratio using the combination processes of the SPS and the mechanical milling, and examined their electrochemical properties. 2. Experimental Li2S and FeS2 (or FeS) with a molar ratio of 4 : 1 were mixed thoroughly, and the mixture was then treated by the SPS process [6] at 600oC. The resulting pellet was ground and mixed with carbon (acetylene black) powder with a weight ratio of Li2S-FeS x : C = 9 : 1, and then it was mechanically milled for 8 h to yield the Li2S-FeS x -C composites. All the procedures were carried out in an argon atmosphere, because Li2S is very sensitive to atmospheric moisture. The obtained composite samples were characterized by XRD, as well as Fe and S K-edge XAFS measurements. Electrochemical lithium insertion / extraction reactions were carried out using lithium coin-type cells with 1M LiPF6 / (EC + DMC) electrolyte at a current density of 46.7 mAg-1 (corresponding to 0.04C) initially with charging. For improving the electrochemical performances, we applied pre-cycling treatment to the present Li2S-FeS x -C composite sample cells, whereby cycle capability of some oxide cathode active materials (such as Li(NiCoMn)O2) was successfully improved [7]. 3. Results and Discussion The obtained Li2S-FeS x -C composite samples were black in color, and their XRD patterns showed that they consisted of Li2S (antifluorite structure) with low crystallinity. The atomic ratio, estimated by ICP and atomic absorption spectroscopy, was Li : Fe : S = 7.8 : 1.0 : 4.8 for the Li2S-FeS x -C composite sample with Li2S : FeS = 1 : 4. Since the initial composition was Li : Fe : S = 8 : 1 : 5, this result indicates that negligibly slight amounts of Li and S (ca. 3 – 4%) were lost during the SPS and the following milling processes. The electrochemical tests for the Li2S-FeS x -C sample cells showed that the initial charge capacity was ca. 600 mAhg-1, which was much higher than the previously reported Li2S-FeS2 (1 : 1 molar ratio) sample cells (ca. 330 mAhg-1) [6]. The discharge capacity was ca. 330 mAhg-1 with the normal electrochemical cycling, and it was enlarged to ca. 730 mAhg-1 after the pre-cycling treatment, Fig. 1. This result indicates that the pre-cycling treatment was effective for improving the electrochemical performances of the Li2S-FeS x -C composite cells. Ex-situ XRD measurements showed that the peaks ascribed to Li2S disappeared after the normal electrochemical cycling, while they were still observable after the pre-cycling treatment. Also, ex-situ S K-XAFS measurements showed the reversible changes of the valence states of S atom with the pre-cycling treatment. Therefore, the pre-cycling treatment of the Li2S-FeS x -C sample was effective for maintaining the antifluorite structure, as well as for improving the reversibility of the valence states of S atom, which would be responsible for improving the electrochemical performances of the Li2S-FeS x -C composite sample cells. References [1] A. Hayashi et al., J. Power Sources, 183, 422 (2008). [2] M. N. Obrovac and J. R. Dahn, Electrochem. Solid-State Lett., 5, A70 (2002). [3] T. Takeuchi et al., J. Power Sources, 195, 2928 (2010). [4] J. Hassoun et al., J. Power Sources, 196, 343 (2011). [5] M. Nagao et al., J. Mater. Chem., 22, 10015 (2012). [6] T. Takeuchi et al., J. Electrochem. Soc., 159, A75 (2012). [7] A. Ito et al., J. Power Sources, 183, 344 (2008). Acknowledgment This work was financially supported by R&D project for lithium batteries (RISING Project) by METI and NEDO.

Achieving high capacity by making use of multi electron processes has been desired to enhance the energy density of lithium-ion batteries. Recently, layered lithium metal oxides with more than one equivalent of lithium per transition metal have been actively researched and developed as new positive-electrode materials with capacities of more than 200 mAh g−1. However, it is still difficult to achieve reversible capacity of more than 300 mAh g−1. To achieve the high capacity, the redox reaction of anions in addition to that of transition metals is needed to be used; that is, the charge and discharge with processes involving more than two-electrons should be required in materials. Therefore, the challenging is development of new electrode active materials which can show redox reactions with more than two electron processes. Metal sulfides are attractive candidates for positive-electrode materials [1, 2]. Their high capacities originate from charge and discharge processes that involve more than one electron; for example, crystalline TiS3 charges and discharges with high reversible capacities of greater than 300 mAh g−1, which corresponds to ca.1.5 electron redox reaction. In this study, amorphous titanium polysulfides a-TiSx (x = 3, 4) and niobium polysulfides a-NbSy(y = 3, 4, 5) were prepared by a mechanical milling process and their electrochemical properties were examined using the cells with carbonate-based electrolytes. Amorphous titanium and niobium polysulfides were mechanochemically synthesized at room temperature using a planetary ball mill apparatus. Sulfur (S8) and titanium disulfide (TiS2) or niobioum disulfide (NbS2) were used as starting materials. The XRD measurements indicated that the diffraction peaks attributable to S8 and TiS2 or NbS2disappeared by mechanical milling, suggesting that the samples became amorphous. Fig. 1 shows charge-discharge curves of the cells using crystalline NbS2 reagent, amorphous NbS3, NbS4, and NbS5. The capacity increases with increasing sulfur/metal ratio and the cell using amorphous NbS5 shows a high capacity of ca 600 mAh g-1. The amorphous TiS4 discharged and charged with a high reversible capacity of ca. 700 mAh g-1in the 1.5–3.0 voltage range [3]. The cell using the amorphous metal polysulfides charged and discharged despite of the use of a carbonate-based electrolyte. Coulombic efficiency of the composite was higher than that of a sulfur electrode because the dissolution of the polysulfide into electrolytes was suppressed. Designing amorphous polysulfides is an effective way to develop novel sulfide-based electrode materials with high capacity. References [1] M. S. Whittingham, Prog. Solid State Chem. 12 (1978)41–99. [2] M.H. Lindic, H. Martinez, A. Benayad, B. Pecquenard, P. Vinatier, A. Levasseur, D. Gonbeau, Solid State Ionics, 176 (2005) 1529–1537. [3] A. Sakuda, N. Taguchi, T. Takeuchi, H. Kobayashi, H. Sakaebe, K. Tatsumi, Z. Ogumi, Electrochem. Commun. 31 (2013) 71–75.

Introduction In order to enhance cycleability of positive electrode materials, coating of metal oxides [1], phosphates [2], and fluorides [3] have been reported to be effective on depressing degradation of positive electrode materials. However, so far, mechanisms of surface modification by coatings have not been clarified well. In recent, we have reported that Al oxides coating significantly suppressed the increase of cracks in LiNi1/3Co1/3Mn1/3O2 particle, and that both capacity and area specific impedance retentions of LiNi1/3Co1/3Mn1/3O2during charge-discharge cycles were improved by the coating [4]. In this paper, effect of coating of various metal oxides on electrochemical characteristics and cycleability enhancement of LiNi1/3Co1/3Mn1/3O2 particles during high voltage charge higher than 4.5 V (vs. Li+/Li) have been examined. Furthermore, effects of coating of various metal oxides on crystal structure deformation at the surface of LiNi1/3Co1/3Mn1/3O2during the charge-discharge cycles were investigated by s-TEM/EELS. Experiments Precursors of metal oxides (Al oxides, Zr oxides, etc.) were coated on LiNi1/3Co1/3Mn1/3O2 particles by sol-gel methods. The precursors coated LiNi1/3Co1/3Mn1/3O2 particles were calcined at 500°C to obtain metal oxides coated LiNi1/3Co1/3Mn1/3O2. Coat layers of metal oxides and surface area of LiNi1/3Co1/3Mn1/3O2 were observed by high resolution s-TEM. Electrochemical characteristics of bare and metal oxides coated LiNi1/3Co1/3Mn1/3O2 were examined in pouch cells with using Li metal counter electrode. The electrolyte used was 1M-LiPF6/EC+DMC +EMC (1:1:1 by volume). The cells were cycled between discharge cutoff voltage of 2.5 V and charge cutoff voltages of 4.5, 4.6 and 4.7 V. Results and discussion Figure 1 shows an s-TEM image and EDX mappings (Al, Ni, and Co) of cross section of Al oxides coated LiNi1/3Co1/3Mn1/3O2. The high resolution s-TEM/EDX observation revealed that coated Al oxides exist as a solid solution (LiTMO2-LiAlO2) from the surface to depth of several nm. Figure 2 shows effect of Al oxides coating on capacity retention of LiNi1/3Co1/3Mn1/3O2 during the charge-discharge cycles. Bare LiNi1/3Co1/3Mn1/3O2 electrodes displayed clear capacity fading during the charge-discharge cycles under the high voltage charge conditions. On the other hand, LiNi1/3Co1/3Mn1/3O2 coated by Al oxides of 0.5 w/o showed enhanced cycleability even in charge cutoff voltages of 4.5 and 4.6 V, while capacity fading of the Al coated LiNi1/3Co1/3Mn1/3O2was not negligible in charge cutoff voltage of 4.7 V. AC impedance analysis showed that capacity fading of LiNi1/3Co1/3Mn1/3O2 was attributed to increases of polarization resistance of LiNi1/3Co1/3Mn1/3O2 electrodes. Since crystal structure deformation was observed at the surface of degraded LiNi1/3Co1/3Mn1/3O2 particles by s-TEM/EELS, increase of polarization is thought to be attributed to this crystal structure deformation. Al oxides coating effects on the crystal structure deformation at the surface of LiNi1/3Co1/3Mn1/3O2will be discussed in comparison with Zr oxides coating effects. Acknowledgements This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING) project of NEDO, Japan. References 1) L. A. Riley et al., J. Power Sources, 196, 3317 (2011). 2) J. Y. Shi et al., J. Power Sources, 195, 6860 (2010). 3) S.-U. Woo et al., J. Electrochem. Soc., 154, A1005 (2007). 4) K. Araki et al., J. Power Sources, to be submitted.

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An electrochemical energy profile on the charge-discharge cycle model of Li/pyrite-MS 2 (M = Fe, Ni) secondary battery cells was simulated using density functional theory. For a full-discharge reaction of MS 2 under enough Li-ion concentration, the calculated results indicate that the final products are Li 2 S and M metal via the intermediate compound of commonly suggested Li 2 MS 2 (unknown for M = Ni), which is the intermediate product that continues the self-decomposition as Li 2 MS 2 → MS + Li 2 S. For a full-charge reaction Li 2 S + M metal at the cathode, the reproduction of the initial pyrite FeS 2 is a more favorable scheme than the production of other iron sulfides (FeS and Fe 3 S 4 ), indicating the capability of the reversible charge-discharge cycle of Li/FeS 2 cell. However, for Li/NiS 2 , there is difficulty in the reproduction of the initial pyrite NiS 2 due to a closer formation enthalpy between NiS 2 and the other nickel sulfides (NiS, Ni 3 S 2 , and Ni 3 S 4 ). This is one of the reasons that the Li/FeS 2 cell shows an experimentally better charge-discharge cycle performance than Li/NiS 2 . The temperature dependence of the open-circuit voltage (OCV) was also estimated using the Nernst's equation, namely, the change in the Gibbs free energy derived from the enthalpy and entropy obtained by phonon calculations for the crystal lattices by applying the density functional perturbation theory. There is little temperature dependence of the OCV in the temperature range 0-100°C, and the maximum OCVs at the thermodynamic standard state (1.67 V for Li/FeS 2 and 1.84 V for Li/NiS 2 ) are consistent with the experimental results.

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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.

The authors investigated the changes in local structures and magnetic property of the Li 1.2 Mn 0.4 Fe 0.4 O 2 positive electrode material for lithium-ion batteries during the first charge―discharge cycle. Although Li 1.2 Mn 0.4 Fe 0.4 O 2 has a composite structure of the layered and disordered cubic rocksalt before the electrochemical testing, nanometer-sized grains with spinel structures are formed during the extraction of Li ions up to Li 1.2 Mn 0.4 Fe 0.4 O 2 (0 ≤ x ≤ 0.99). The spinel nanograins have weak spontaneous magnetization (ca. 0.3 G cm 3 /g), which is associated with the movements of Fe ions from the octahedral to the tetrahedral sites in both the layered and disordered rocksalt structures. The fraction of spinel nanograins decreased after the subsequent insertion of Li ions.

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In this study, all-solid-state In/LiCoO 2 cells were assembled using 0.01Li3P04-0.63Li2S-0.36SiS2 sulfide glass electrolytes. The cells showed high initial charge and discharge capacities of 194 and 169 mAh/g, with 87% efficiency at a fixed current density, 9.5 mA/g, between 2.0 and 4.1 V. The average discharge voltage was low, 3.22 V, but the energy density was 542 mWh/g: higher than the 462 mWh/g of liquid C/LiCoO 2 cells. An In/LiCoO 2 cell was discharged at -40°C (39 mAh/g at 2.4 mA/g) from 3.9 to 1.5 V. Although the suppression of capacity fading is required, its attractive electrochemical properties resemble lithium-ion batteries.

Single-phase NiS 2 , which was hardly prepared by conventional processes such as mechanical milling or precipitation reaction, was prepared using the spark plasma sintering (SPS) process. Using porous Ni (porosity 95%) as a starting material, similar-shaped porous NiS 2 (porosity 89%), containing trace amounts (ca. 3%) ofNiS, and finally single-phase NiS 2 powder were obtained by the SPS process. The electrochemical tests demonstrated that the present NiS 2 samples showed the initial discharge capacity of ca. 820 mAh g -1 , which was ∼94% of the theoretical value. The capacity retention after 10 cycles was ca. 19%, and such rapid degradation was mainly attributable to the irreversibility of the Li extraction from the lithiated (discharged) NiS 2 electrodes and the electrical disconnections among the active materials, carbon powders, and/or current collectors.

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