Search

The surfaces of LiCoO 2 particles were modified to improve the charge-discharge cycling properties of Li-ion batteries containing LiCoO 2 cathodes. The sol-gel technique was used to modify the surface of LiCoO 2 particles with magnesium oxide. Capacity retention during cycling of the magnesium oxide-coated LiCoO 2 cathode was superior to that of a cathode comprising pristine LiCoO 2 . Moreover, results obtained from TEM measurements indicate that the Li concentration was relatively homogeneous in the magnesium oxide-coated LiCoO 2 particles after cycling tests. The crystallographic planes of the coating were found to be coherently oriented with those of the substrate, MgO(111)[1−10]//LiCoO 2 (003)[100]. Therefore, we believe that a thin cover of Mg on the surface of LiCoO 2 stabilizes the surface, contributing to the homogeneity of charge and discharge reactions.

LiNi 1/3 Co 1/3 Mn 1/3 O 2 particles were coated with Al 2 O 3 nanoparticles by means of a mechanochemical bonding process; SEM confirmed that the Al 2 O 3 particles were uniformly coated over the surface of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 powder. During subsequent electrochemical testing using pouch cells, uncoated LiNi 1/3 Co 1/3 Mn 1/3 O 2 exhibited a gradual capacity fading and an increase in area specific impedance (ASI) at a 50% state of charge. Under the same conditions, the increase in ASI of the Al 2 O 3 modified samples was significantly suppressed, although the initial performance (charge/discharge capacity and ASI) slightly deteriorated. The Al 2 O 3 coating was also effective in improving the cyclability of LiNi 1/3 Co 1/3 Mn 1/3 O 2 at elevated temperatures by reducing the extent of cracking.

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.

40%-titanium substituted Li 2 MnO 3 (Li 1+ x (Ti 0.4 Mn 0.6 ) 1− x O 2 , 0 x L -edge energy-loss near-edge structure (ELNES). The morphology change of a primary particle was observed around the Mn reduction phase.

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.

Composite electrodes based on amorphous titanium polysulfide and acetylene black were mechanically prepared, and their performance was investigated. The amorphous TiS4 and acetylene black composites were discharged and charged with a high reversible capacity of 563 mAh g−1 in the 1.9–3.0 voltage range. The Coulombic efficiency of the composite was higher than that of a sulfur electrode because the dissolution of the polysulfide into electrolytes was suppressed. Amorphization and dispersion of carbon inside the particles were effective in improving the performance of the titanium polysulfide electrodes. Keywords: Lithium batteries, Titanium sulfide, Polysulfide, Lithium–sulfur batteries

Li 1.20 − y Ni 0.17 Co 0.10 Mn 0.53 O 2 ( y = 0.1–0.93) were prepared electrochemically and characterized using synchrotron XRD and XAFS measurements. Structural analysis using XRD data demonstrated that the lattice parameters of Li 1.20 Ni 0.17 Co 0.10 Mn 0.53 O 2 are a = 0.285214(7) nm and c = 1.42173(3) nm and that the chemical composition can be expressed referring to the Wyckoff positions 3 a and 3 b as [Li 0.988 Ni 0.012 ] 3 a [Li 0.212 Ni 0.158 Mn 0.53 Co 0.10 ] 3 b O 2 . The M ( M = Ni, Co, and Mn) K and L-edge XAFS results suggested that the Li de-intercalation from Li 1.20 Ni 0.17 Co 0.10 Mn 0.53 O 2 proceeded mainly by the oxidation of Ni and Co ions up to y = 0.4 and then by the removal from oxygen from the lattice up to y = 0.93. On the other hand, the O K-edge XANES results indicated no increase in Li 2 CO 3 or Li 2 O on the surface of the positive electrode materials with Li de-intercalation. These results demonstrate that the XAFS method using a combination of soft and hard X-ray is effective way of clarifying the Li de-intercalation/intercalation of the positive electrode materials.

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.

Layered oxides, ruthenium-substituted Li 2 MnO 3 , were synthesized at 800 °C and 1200 °C. Their phase relation and electrical and electrochemical properties were investigated. Li 2 Mn 1− x Ru x O 3 synthesized at 800 °C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 ≤ x ≤ 0.05, while Li 2 Mn 1− x Ru x O 3 synthesized at 1200 °C formed two solid solutions in the whole composition range across a structural transition between x = 0.6 and 0.8. The electrical resistivity of Li 2 Mn 1− x Ru x O 3 decreased with increasing ruthenium content. Li 2 Mn 0.2 Ru 0.8 O 3 ( x = 0.8) synthesized at 1200 °C showed the lowest resistivity of 5.7 × 10 2 Ω cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li 2 Mn 0.4 Ru 0.6 O 3 ( x = 0.6) exhibited a discharge capacity of 192 mAh g −1 in the initial cycle and 169 mAh g −1 in the tenth cycle with high and almost constant charge–discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10 C . The ruthenium substitution to Li 2 MnO 3 is quite effective to improve electrical conductivity and charge–discharge performance.

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.

Equal amounts of Fe- and Ni-substituted Li2MnO3 (chemical formula: Li1+x[(Fe1/2Ni1/2)yMn1−y]1−xO2, 0 F m 3 ¯ m ). Electrochemical characterization as a positive electrode shows that the Li2O extraction region disappears above y = 0.6 on initial charging and that the energy density is decreased drastically above the composition on initial discharging. The optimized transition metal ratios are y = 0.4 and 0.5 because the initial average discharge voltage increases with y and the maximum initial cycle efficiency is attained. In the optimized composition, the Fe- and Ni-substituted Li2MnO3 is a 3.5 V class positive electrode, with similar charge and discharge profiles to those of the most attractive active material, NMC positive electrode (chemical formula: Li1+x[(Co1/2Ni1/2)yMn1−y]1−xO2, 0

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.

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.

Cylindrical lithium-ion cells with a lithium–nickel–cobalt–aluminum oxide (LiNi0.8Co0.15Al0.05O2) and a non-graphitizable carbon (hard carbon) as the positive and negative electrodes, respectively, were degraded by the storage tests with 50% state-of-charge (SOC). The degraded cells were disassembled and positive electrodes obtained were examined. The cation distribution of lithium and nickel in the positive electrode was clarified using neutron and synchrotron X-ray diffraction measurements. The degree of lithium and nickel disordering varied with the storage condition. X-ray absorption near-edge structure (XANES) analysis demonstrated that the structural change was mainly located near the surface of the positive electrode and the valence state of Ni and Co ions did not change with the storage test. The disordering of the cations near the surface was closely related to the power fade of the cell. The storage condition is an important factor in the power fade of lithium-ion cells.

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.

Inorganic compounds on the surfaces of the cathode materials LiNi 0.80 Co 0.15 Al 0.05 O 2 and LiCoO 2 were studied using Li and 0 K-edge X-ray absorption near edge structure (XANES) measurements. Rietveld analysis revealed that the LiNi 0.80 Co 0.15 Al 0.05 O 2 sample contained 2% Li 2 CO 3 , while the LiCoO 2 sample was single-phase. The Li and O K-edge XANES spectra indicated that the surface of LiCoO 2 was almost free of residual Li 2 CO 3 . In contrast, the presence of both residual Li 2 CO 3 and an additional cubic phase were observed, respectively, on and near the surface of LiNi 0.80 Co 0.15 Al 0.05 O 2 . These results demonstrate that the XANES technique, using a combination of the total electron yield and fluorescence methods, is an effective tool for probing the surfaces of cathode materials.

Novel electrolyte materials, room temperature ionic liquids (RTILs) were applied to the Li battery system and their characteristics in Li-metal batteries are discussed, partly reviewing authors work in the past. Quaternary ammonium (QA) cation-imide RTIL was focused on because of the excellent stability in cathodic environment of Li. Li/LiCoO2 cell performance and Li cycling efficiency using the selected QA-imide RTIL was almost satisfactory. In addition, thermal stability of selected QA-imide RTIL with the charged positive electrode and Li was the advantage for Li battery. On the other hand, further improvement in the conducting properties is required with balanced approach for both electrochemical stability and thermal stability in order to use the RTIL electrolyte practically in batteries.

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.

X-ray photoemission spectroscopic and high-resolution hard X-ray photoemission spectroscopic studies of positive electrodes in LiNi0.73Co0.17Al0.10O2 and hard carbon based batteries were carried out to elucidate the mechanism of battery degradation. Li2CO3, hydrocarbons, ROCO2Li, polycarbonate-type compounds and LiF were observed on positive electrode surfaces and the amount of carbonates was found to have increased after cycle testing. Above 60 °C, signs of electrolyte decomposition were indicated. Near the surface of the positive electrodes, a Li-deficient cubic phase is present and grows with degradation. Capacity and power fade could be related to the amount of species on the surface and the thickness of the Li-deficient cubic phase near the surface.

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.

Cylindrical lithium-ion (Li-ion) cells with a nickel-cobalt oxide (LiNi0.73Co0.17Al0.10O2) positive electrode and a non-graphitizable carbon (hard carbon) negative electrode were degraded using cycle tests. The degraded cells were disassembled and examined; most attention was paid to the positive electrodes in order to clarify the origin of the power fade of the cells. X-ray absorption near-edge structure (XANES) analysis demonstrated that the crystal structure of the electrode at the surface changed from rhombohedral to cubic symmetry. Furthermore, a film of lithium carbonate (Li2CO3) covered the surface of the positive electrode after the cycle tests. Using a combination of X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and glow discharge optical emission spectrometry (GD-OES) measurements, a schematic model of the changes occurring in the surface structure of the positive electrode during the cycle tests was constructed. The appearance of both an electrochemically inactive cubic phase and lithium carbonate films at the surface of the positive electrode are important factors giving rise to power fade of the positive electrode.

Fe-substituted Li2MnO3 (Li1+x(FeyMn1−y)1−xO2, 0 ≤ x ≤ 1/3, 0.3 ≤ y ≤ 0.7) was synthesized using a combination of coprecipitation, hydrothermal, and heat-treatment methods. It exhibits high initial specific capacity greater than 200 mAh g−1 and small capacity, which fades up to the 50th cycle (>150 mAh g−1 at the 50th cycle) under electrochemical cycle testing at 60 °C. The attractive electrode properties appeared by controlling the chemical composition (x > 0.05, 0.3 ≤ y ≤ 0.5) and high specific surface area (>20 m2 g−1). The Fe-substituted Li2MnO3 is an attractive candidate as a novel 3 V-class positive electrode material.

Li1−yNi0.45Mn0.45Al0.1O2 was synthesized and characterized using both XRD and XANES measurements. The Li/Li1−yNi0.45Mn0.45Al0.1O2 cell showed a discharge capacity of 125 mAh/g in the voltage range 4.5–2.5 V. The Ni K and LII,III-edge XANES results indicated that the Li de-intercalation from LiNi0.45Mn0.45Al0.1O2 proceeded mainly by the valence state change of Ni ions over the whole composition range. Structural analysis clarified that most of the Li ions and a small fraction of the Ni ions migrated from the octahedral 3a site to the tetrahedral 6c site with Li de-intercalation. This observed structural change was similar to that of Li1−yNi0.5Mn0.5O2, indicating that this structural change is characteristic in the Li(NiMn)O2 system.

We present electrochemical properties of lithium alanate (LiAlH4) dissolved in aprotic ethers – diethyl ether (Et2O) and tetrahydrofuran (THF) – under an Ar atmosphere of 1 atm at 298 K. Specific conductivities of both LiAlH4–THF and LiAlH4–Et2O solutions are measured by AC four-terminal method. Cyclic voltammetry is performed with using a beaker-type electrochemical cell consisted of a Ni wire, Ni mesh and Li wire as a working, counter and reference electrode, respectively. In order to clarify the electrochemical behavior, anodic polarization of LiAlH4–THF solution is measured. The current density of 1.0 M LiAlH4–THF solution reaches to 1 A cm−2, which is higher than the LiAlH4–Et2O solution. Quantitative analysis of H2 gas generated on the working electrode during the potentiostatic electrolysis tells that the number of electrons involved in the anodic reaction at the limiting current is one in case of the LiAlH4–THF solution. We propose conceivable electrochemical reactions of LiAlH4 in the non-aqueous ethereal solutions.

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].

By combining coprecipitation, hydrothermal, and firing methods under various firing temperatures (500−750 °C), Fe-substituted Li2MnO3 (nominal formula Li1.2Fe0.4Mn0.4O2) samples were prepared. A pure O3 phase was obtained below 700 °C. However, a small amount of spinel ferrite-like LiFe5O8 coexisted as an impurity phase for the sample that was fired at 750 °C. The maximum initial and 10th discharge capacities were obtained at 600−650 °C because of the balance between the development of 3d cation ordering, their primary particle size, and Li content, depending on the iron valence, which is changeable between 3+ and 4+.

The specific capacity of Fe-substituted Li 2 MnO 3 (Li 1.2 Fe 0.4 Mn 0.4 O 2 ) was improved by adjusting the preparation temperature of Fe–Mn co-precipitate below RT in order to suppress the spinel ferrite formation, which hinders the formation of homogeneous and reactive precursor. The degradation of discharge capacity with cycle could be suppressed by nominal 5% Al, Ni and Co doping. This means that Fe-substituted Li 2 MnO 3 will be considered to be one of the near future positive electrodes for practical use by careful optimization of its preparation condition and chemical composition.

LiMn 2 O 4 films with vertically aligned holes were formed by electrostatic spray deposition (ESD) and subsequent annealing. Different surface morphologies, such as dense grains, 1 μm-diameter pores with 1 μm-thick walls, and 5 μm pores with 3 μm walls, were formed by varying the lithium sources in the precursor solution. The randomly oriented pores in the films prepared using ESD were rearranged in vertical stacks after annealing to produce crystalline LiMn 2 O 4 . This process would be suitable for constructing three-dimensional interfaces between active materials and solid-state electrolytes.

The properties of the Li/LiCoO 2 cell containing several RTILs with three different anions were investigated. Introducing the asymmetric nature to anionic species using amide improved the viscosity and conductivity of the RTIL, however, the rate properties of the cell was not enhanced very much. Declined cathodic stability seems to be responsible for the result. In the case of the stable system consisting of quaternary ammonium cation and imide anion, both of cycling properties and Coulombic efficiency during the cycling were satisfactory and the viscosity dominated the rate properties of the cell. The performance of the Li/LiCoO 2 cell in this study was almost consistent with the stability of Li-electrolyte interface evaluated by ac impedance measurement.

The physical and electrochemical properties of room temperature ionic liquids (RTILs) based on asymmetric amide anions (TSAC: 2,2,2-trifluoro- N -(trifluoromethylsulfonyl)acetamide, C1C2: N -(trifluoromethylsulfonyl)pentafluoroethylsulfonamide) and aliphatic onium cations, such as ammonium, phosphonium, and sulfonium, were reported. The melting point of the C1C2 salts decreased compared to the corresponding TFSI salts (TFSI: bis(trifluoromethylsulfonyl)imide), however, the viscosity was about twice that of the TFSI salts. Relatively low viscosity RTILs based on aliphatic onium cations could be prepared using the TSAC anion and tetraalkylammonium cation containing an alkoxy group. The linear sweep voltammogram of these RTILs with and without Li-TFSI were investigated in order to estimate the electrochemical windows and possible use as a lithium battery electrolyte.

Composite positive electrodes LiFePO 4 /C, applicable for rechargeable lithium-ion batteries cycled at high current density, were prepared using spark-plasma-sintering (SPS) technique. LiFePO 4 /C composite positive electrodes with carbon content of 20 wt.% was synthesized at 600 °C in the SPS process, and it was found that LiFePO 4 particles were covered with fine carbon particles and they formed agglomerates with the size of about 10 μm. It resulted in higher electrode density. Charge/discharge tests for the cell using LiFePO 4 /C composite positive electrodes showed superior cycle performance at the rates of 17–850 mAh g −1 (0.1–5 C) compared with the cell using the conventionally blended LiFePO 4 + C composite positive electrodes. The improvement of the cell performance was attributed to strong binding between LiFePO 4 and carbon powders. Consequently, the electrical network remained almost unchanged during electrochemical redox cycling, even at high current rates.

A new series of low-melting, low-viscosity hydrophilic ionic liquids, which comprise 1-ethyl-3-methylimidazolium ([EMI] + ) and alkyl(alkenyl)trifluoroborate anions ([RBF 3 ] - , R=n-C m H 2m+1 (m=1-5), CH 2 CH), were prepared and characterized. The phase-transition behavior, thermal stability, density, viscosity, conductivity, and surface tension of these salts were measured. The influence of the structural variations, such as changing the length and fluorination of the alkyl chain (R) in the anion [RBF 3 ] - , on the above properties was extensively investigated. The low viscosity of these [RBF 3 ] - salts suggests that a high degree of freedom and/or a somewhat flat-shaped feature in the anion make an important contribution to reducing the viscosity. The Walden products for each spit are not constant and vary with temperature, which suggests that the ions in these salts are not completely dissociated.

Structural changes in Li 1− y Ni 0.5 Mn 0.5 O 2 with Li de-intercalation were studied using X-ray diffraction, XAFS, and magnetic measurements. The Li de-intercalation from LiNi 0.5 Mn 0.5 O 2 proceed mainly by a valence state change of Ni ions from Ni 2+ to Ni 3+ up to y =0.5 from the XANES and magnetic results. Structural analysis clarified that a second order phase transition from trigonal to monoclinic was observed between y =0.2 and 0.3 and that a small fraction of the Li ions start to migrate from the octahedral 2 a site to the tetrahedral 4 i site at y =0.3 and most of the Li ions occupied the tetrahedral 4 i site at y =0.5 with Li de-intercalation. The EXAFS analysis clarified the valence state change and the range of phase transition during the Li de-intercalation, from the changes in the bond distance of the first neighbor for each transition metal. This Li de-intercalation mechanism is characteristic of this system and has not been reported for Li 1− y MO 2 (M=Co and Ni).

A novel class of low-melting, hydrophobic ionic liquids based on relatively small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), wherein R(1), R(2), R(3) = CH(3) or C(2)H(5), R = n-C(3)H(7), n-C(4)H(9), CH(2)CH(2)OCH(3)) and perfluoroalkyltrifluoroborate anions ([R(F)BF(3)](-), R(F) = CF(3), C(2)F(5), n-C(3)F(7), n-C(4)F(9)) have been prepared and characterized. The important physicochemical and electrochemical properties of these salts, including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and comparatively studied with those based on the corresponding [BF(4)](-) and [(CF(3)SO(2))(2)N](-) salts. The influence of the structure variation in the quaternary ammonium cation and perfluoroalkyltrifluoroborate ([R(F)BF(3)](-)) anion on the above physicochemical properties is discussed. Most of these salts are liquids at 25 degrees C and exhibit low viscosities (58-210 cP at 25 degrees C) and moderate conductivities (1.1-3.8 mS cm(-1)). The electrochemical windows of these salts are much larger than those of the corresponding 1,3-dialkyimidazolium salts. Additionally, a number of [R(F)BF(3)](-) salts exhibit plastic crystal behavior.