Mitsuharu Tabuchi

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+ .

All-solid-state lithium secondary battery with ceramic/polymer composite electrolyte

Abstract Dense lithium lanthanum titanate, (Li,La)TiO 3 , pellets were prepared using a spark-plasma sintering (SPS) method. The obtained (Li,La)TiO 3 pellets showed relatively high lithium ion conductivity, typically 10 −3 S cm −1 at 22 °C, with an activation energy of 30.1 kJ mol −1 . Lithium manganese oxide, LiMn 2 O 4 , was deposited on (Li,La)TiO 3 pellets by an electrostatic spray deposition (ESD) method at 400 °C without significant formation of by-products at the interface (Li,La)TiO 3 /LiMn 2 O 4 . An all-solid-state battery system, LiMn 2 O 4 /(Li,La)TiO 3 /SPE/Li, where a solid polymer electrolyte (SPE) was sandwiched between (Li,La)TiO 3 and Li, showed good charge/discharge characteristics over 100 cycles at 60 °C.

5 V Class All-Solid-State Composite Lithium Battery with Li3 PO 4 Coated LiNi0.5Mn1.5 O 4

A 5 V class ceramic/polymer composite all-solid-state lithium battery was prepared. The cell configuration was [Li 3 PO 4 coated LiNi 0.5 Mn 1.5 O 4 |solid polymer electrolyte| Li]. The total cell impedance was 4 kΩ at 333 K and the discharge capacity was 100 mAh g -1 with a discharge voltage plateau in both 4.7 and 4.1 V regions. X-ray absorption near-edge structure results indicated that both transition metal ions, Ni and Mn, involved in the oxidation/reduction processes. The cell without Li 3 PO 4 showed a lower discharge voltage plateau (<3.5 V) than the composite one. Although the Li 3 PO 4 film was so thin that it could be nearly removed with only 2 min of Ar etching in X-ray photoelectron spectroscopy, Li 3 PO 4 is thought to have a function as a solid electrolyte interface between LiNi 0.5 Mn 1.5 O 4 and SPE to prevent the degradation of solid polymer electrolyte.

Crystal chemistry and physical properties of complex lithium spinels Li2MM′3O8 (M=Mg, Co, Ni, Zn; M′=Ti, Ge)

The spinels Li2MM′3O8 (MM′=MgTi, CoTi, CoGe, NiGe and ZnGe) are cubic with space group P4332 . Simple crystal field theory qualitatively explains the distribution of M over tetrahedral and octahedral sites: Ni occupies only octahedral sites, whereas Zn, Mg and Co show strong preference for tetrahedral sites. 1:3 cation ordering of Li/M and M′ occurs on the octahedral sites. The titanates undergo an order–disorder phase transition involving the octahedral cations at high temperatures, whereas the ordered phase is maintained until melting for the germanates. Solid solutions Li2–2XM1+3XM′3–XO8 form at both sides of the Li2MM′3O8 stoichiometry for the titanates; but there is no substantial range of solid solution for Li2ZnGe3O8 and Li2NiGe3O8 . The occurrence of order–disorder phenomena and solid solutions in the titanates is attributed to the similarity in size of Li, M and Ti, whereas the smaller Ge is less able to disorder with Li/M. M is shown to be divalent from magnetic susceptibility measurements (for Co and Ni) with the support of conductivity data. The samples containing Co and Ni are paramagnetic down to 5 K. From impedance measurements on pellets with blocking electrodes, the main conductive species is deduced to be Li+ : the activation energies for conduction are high, 0.55<ΔH/eV<2.14. Cyclic voltammograms show a set of reversible peaks at ca. 1.5 V vs. Li/Li+ for the titanates, attributed to the Ti3+/4+ couple, but no Li could be electrochemically extracted from either titanates or germanates up to 5 V vs. Li/Li+ .

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.

Preparation of LiFeO2 with Alpha‐ NaFeO2‐Type Structure Using a Mixed‐Alkaline Hydrothermal Method

A metastable form of LiFeO 2 with α-NaFeO-type structure (layered LiFeO) was synthesized directly from α-FeOOH or FeCl 3 . 6H 2 O by hydrothermal reaction at 230°C using aqueous mixed-alkaline solutions such as LiOH HO-KOH or LiOH HO-NaOH. Highly crystallized samples could be obtained by a one-step process. The yield of the layered LiFeO strongly depends on the composition of the starting mixture. Preliminary tests on electrochemical lithium deintercalation/intercalation show poor performance between 4.5 and 1.5 V.

Improvement of Degradation at Elevated Temperature and at High State-of-Charge Storage by ZrO2 Coating on LiCoO2

A uniform ZrO 2 coating on LiCoO 2 cathode materials for rechargeable lithium batteries was applied by a spray coating technique. The cells showed improved cycle performance and better durability of storing the cell (calendar life) under a high-voltage charging condition (4.2 V-313 K). X-ray diffraction and calorimetric study revealed that no marked change was observed in the bulk properties, such as crystal structure and phase transition, in the cathode during charge and discharge. The suppression of the increase of cathode/electrolyte interfacial impedance was observed by ZrO 2 coating. Thus, the improved electrochemical performance in the higher voltage region (>4.2 V) is ascribed to the stabilization of the interface between the cathode and electrolyte materials.

Grain size dependence of dielectric properties of ultrafine BaTiO3 prepared by a sol-crystal method

Ultrafine BaTiO3 prepared by a decomposition of an organometallic crystal with unity of Ba/Ti ratio (sol-crystal method) has been characterized. While the as-prepared product resulting from the decomposition of the organometallic crystal at room temperature was BaTiO3 with pseudo-cubic structure, the well-crystallized tetragonal polymorph was obtained by firing the as-prepared product above 1000°C. Residual organic compounds, CO2-3 and OH- ions in the samples prevent the grain growth and tetragonal distortion of BaTiO3. We obtained quite higher room temperature permittivity (3700) at 1 kHz for the sample fired at 1200°C than that (630) prepared by conventional solid-state reaction starting from BaCO3 and TiO2. Such a high value was probably due to the accomplishment of homogeneous cation stoichiometry, which was achieved by this preparation method via the organometallic crystal with stoichiometric Ba/Ti ratio.

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.