Hikari Sakaebe

N-Methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13–TFSI) – novel electrolyte base for Li battery

A few room temperature ionic liquid containing quaternary ammonium cation and imide anion was prepared and electrochemically evaluated with compared the conventional room temperature ionic liquid system with 1-ethyl-3-methylimidazolium cation. Ability as an electrolyte base of lithium battery system was totally explained with the cathodic stability of the salt, however, another properties might also affect. Among the salts studied here, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide is the most promising candidate as the electrolyte base. Li/LiCoO2 cell containing the salt showed very good performance with a consistent capacity of LiCoO2 and the Coulombic efficiency at entire cycles of more than 97% at C/10 current rate. When cycled at higher rate (C/2), 85% of the discharge capacity was still retained.

The Influence of the Graphitic Structure on the Electrochemical Characteristics for the Anode of Secondary Lithium Batteries

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.

Structure and Electrochemical Properties of LiFe x Mn2 − x O 4 ( 0 ⩽ x ⩽ 0.5 ) Spinel as 5 V Electrode Material for Lithium Batteries

An electroactive spinel solid solution, LiFe x Mn 2-x O 4 (0 ≤ x ≤ 0.5), was prepared and investigated. X-ray Rietveld refinements showed a small amount of transition metal ions in tetrahedral 8a sites in Fe-substituted samples. The 57 Fe Mossbauer spectrum of LiFe 0.5 Mn 1.5 O 4 at 300 K is composed of two doublets and attributed to trivalent Fe. In the voltage range 3.0 and 5.3 V vs. Li/Li + . two reversible plateaus appeared at 4.9 and 3.9 V during discharge. Combined data of X-ray diffraction, Mn K-edge X-ray absorption near-edge structure (XANES), and 57 Fe Mossbauer spectroscopy obtained in situ during charge and discharge demonstrate that the plateau around 4 V on charging is associated with the oxidation of Mn 3+ to Mn 4+ and the plateau around 5 V with the partial oxidation of Fe 3+ to Fe 4+ .

Preparation of AFeO2 (A = Li, Na) by hydrothermal method

Lithium ferrites (LiFeO 2 , LiFe 5 O 8 ) and sodium ferrite (NaFeO 2 ) were prepared at low temperature (130-220°C) by hydrothermal treatment of Fe(III) compounds (FeOOH, FeCl 3 . 6H 2 O, Fe(NO 3 ) 3 . 9H 2 O and Fe 2 (SO 4 ) 3 . nH 2 O) with a large excess of LiOH and NaOH, respectively. One of possible polymorphic LiFeO 2 with superlattice of β-LiFeO 2 are obtained by a low temperature (350°C) heat treatment of the hydrothermally obtained α-LiFeO 2 with a small quantity of β-LiFeO 2 .

Synthesis, Cation Distribution, and Electrochemical Properties of Fe-Substituted Li2MnO3 as a Novel 4 V Positive Electrode Material

LiFeO 2 -Li 2 MnO 3 solid solution was synthesized using solid-state reaction and hydrothermal-postannealing methods and characterized as a positive electrode material for rechargeable lithium batteries. Although the maximum Fe content [Fe/(Fe + Mn)] was limited up to 30% by solid-state reaction, the content can extend up to 75% by the hydrothermal-postannealing method. Neutron and X-ray Rietveld analysis reveal that the basic structure of the sample is a layered rock-salt structure isostructural with LiCoO 2 (R3m) in which Fe ions exist on both Li (3a) and Co (3b) sites. Elemental analysis and 57 Fe Mossbauer spectra show Fe ions exist as 3+/4+ mixed-valence state after the samples were postannealed above 650°C. The initial charge capacity of Li/sample cells was above 100 mAh/g when the upper voltage limit was 4.3 V. The plateau around 4 V was observed for all Li/sample cells on first discharge. The maximum of initial discharge capacity was about 100 mAh/g down to 2.5 V for the Li/(50% Fe-substituted sample) cell, when the positive electrode was obtained by postannealing at 650°C in air. The capacity fading of the 4 V plateau could be suppressed by adjusting the Fe content to less than 50%, postannealing temperature between 600 and 700°C, and by 10% Ni substitution.

Electrochemical Properties of Hydrothermally Obtained LiCo1 − x Fe x O 2 as a Positive Electrode Material for Rechargeable Lithium Batteries

Changes in the crystal structure and transition metal valancy in LiFe{sub x}Co{sub 1{minus}x}O{sub 2}(0 {le} x {le} 0.25) positive electrodes during the charge-discharge of Li/LiFe{sub x}Co{sub 1{minus}x}O{sub 2} cells were examined using ex situ X-ray diffraction measurements, Fe and Co K-X-ray adsorption near edge spectroscopy (XANES) and {sup 57}Fe Mossbauer spectroscopy. An iron-doped host material with rhombohedral symmetry was obtained up to 25% Fe per formula unit in LiCoO{sub 2} by hydrothermal reaction below 300 C from a mixture of Co{sup 3+}-Fe{sup 3+} coprecipitate (iron-doped CoOOH) and LiOH. No symmetry changes were observed during electrochemical charge-discharge tests up to the tenth cycle. The structures of Li-extracted and reinserted samples were determined by a model similar to LiCoO{sub 2} prepared at low temperature in which Li ions are located at the interstitial 6c and octahedral 3a sites. {sup 57}Fe Mossbauer and Fe and Co K-XANES spectra at 293 K indicated the presence of tetravalent Fe ions upon oxidation up to 4.3 V.

Changes in the structure and physical properties of the solid solution LiNi1−xMnxO2 with variation in its composition

The layered oxides LiNi1−xMnxO2 (x = 0.1–0.5) were synthesized and characterized using synchrotron X-ray diffraction, TOF neutron diffraction, SQUID magnetometry, ICP spectroscopy, XAFS, and electrochemical measurements. All the samples were single-phase and adopted the α-NaFeO2 structure; LiNi1−xMnxO2 can be represented as Li(Ni2+xNi3+1−2xMn4+x)O2. Structural analysis using synchrotron and neutron diffraction data demonstrated that the lattice parameters of LiNi0.5Mn0.5O2 are a = 2.892 A and c = 14.302 A and that the chemical composition can be expressed by referring to the Wyckoff positions 3a and 3b as [Li0.91Ni0.09]3a[Li0.09Mn0.5Ni0.41]3bO2. The lattice parameters a and c and the fraction of Ni at the 3a site of LiNi1−xMnxO2 increased with Mn content up to the x = 0.4 composition and then showed little change between x = 0.4 and 0.5. An increase in the Ni–O distance was observed with increasing x. The appearance of ferromagnetism was clearly observed at x = 0.4–0.5 as the Ni2+ and Mn4+ content increased. The discharge capacity of the Li/LiNi1−xMnxO2 cell decreased from 190 mAh g−1 (x = 0.1) to 140 mAh g−1 (x = 0.5).

All-Solid-State Lithium Secondary Battery with Li2S – C Composite Positive Electrode Prepared by Spark-Plasma-Sintering Process

Electrochemically active lithium sulfide-carbon (Li 2 S-C) composite positive electrodes, prepared by the spark plasma sintering process, were applied to all-solid-state lithium secondary batteries with a Li 3 PO 4 -Li 2 S-SiS 2 glass electrolyte. The electrochemical tests demonstrated that In/Li 2 S-C cells showed the initial charge and discharge capacities of ca. 1010 and 920 mAh g -1 -Li 2 S, respectively, which showed higher discharge capacity and coulombic efficiency (ca. 91%) than the Li/Li 2 S-C cells with nonaqueous liquid electrolytes (ca. 200-380 mAh g -1 -Li 2 S and ca. 27%, respectively). The ex situ S K-edge X-ray absorption fine structure measurements suggested the appearance and disappearance of elemental sulfur in the positive electrodes after charging and discharging, respectively, indicating that the ideal electrochemical reaction Li 2 S ⇔ 2Li + S proceeded in the present all-solid-state cells. Such ideal electrochemical reaction, due probably to the suppression of the dissolution of Li 2 S in the form of polysulfides into the electrolytes, would result in higher coulombic efficiency and discharge capacity as compared with those of the liquid-electrolyte cells.

Preparation of LiCoO2 and LiCo1–xFexO2 using hydrothermal reactions

Iron doped/undoped LiCoO 2 powders could be obtained from hydrothermal reactions of either Fe 3+ or Co 3+ containing co-precipitates or a CoCl 2 -NaOH-NaClO 3 (oxidant) mixture with an excess amount of LiOH·H 2 O at 220 °C for 8-48 h. The LiFe x Co 1–x O 2 solid solution maintained a layered rock-salt structure until x=0.25. 57 Fe Mossbauer and Co K-edge XANES spectra and magnetic susceptibility data reveal that iron and cobalt in the solid solution are in high-spin Fe 3+ (S=5/2) and low-spin Co 3+ (S=0) configurations.

Electrochemical and magnetic properties of lithium manganese oxide spinels prepared by oxidation at low temperature of hydrothermally obtained LiMnO2

Cubic and tetragonally distorted lithium manganese oxide spinels (LiMnO2 + x) were obtained by progressive oxidation of LiMnO2 between 300 and 400 °C. Orthorhombic LiMnO2 was prepared by hydrothermal treatment of either γ-MnOOH or Mn(COOCH3)3 · 2H2O with LiOH · H2O in large excess. The reversible specific capacity for LiMnO2 + x was found to be sensitive to average manganese valency changeable by the oxidizing condition. The LiMnO2 + x exhibits the ferromagnetic behavior with Tc = 20–40 K and the occurrence of spontaneous magnetic moment is associated with the decrease in the development of ferromagnetic interaction accompanying the decrease in the average shortest MnMn distance between Mn ions on octahedral 16d sites.