Atsushi Hirano

Li∕Polymer Electrolyte∕Water Stable Lithium-Conducting Glass Ceramics Composite for Lithium–Air Secondary Batteries with an Aqueous Electrolyte

A water-stable Li metal anode with water-stable lithium-conducting glass ceramics, Li 1+x+y Ti 2-x Al x Si y P 3-y O 12 (LTAP), and a lithium-conducting polymer electrolyte, PEO 18 Li(CF 4 SO 2 ) 2 N (PEO 18 LiTFSI), was proposed as the lithium anode for lithium-air batteries with an aqueous solution at the air electrode. LTAP was unstable when in direct contact with Li metal, and the cell resistance of Li/LTAP/Li rapidly increased as a function of the contact time. The Li/PEO 18 LiTFSI/LTAP/PEO 18 LiTFSI/Li symmetrical cell showed no change in the total resistance (around 800 Ω cm 2 at 60°C) over a period of 1 month. The PEO 18 LiTFSI membrane served as a protective interlayer to suppress the reaction between the water-stable glass ceramics LTAP and Li metal effectively. The Li/PEO 18 LiTFSI/LTAP/aqueous LiCl/Pt air cell showed a stable open-circuit voltage of 3.70 V at 60°C for 2 months. The open-circuit voltage was comparable with that calculated from the cell reaction of 2Li + 1/2O 2 + H 2 O = 2LiOH. The cell exhibited a favorable discharge and charge performance at 0.25 mA cm -2 and 60°C.

Ln1−xSrxCo1−yFeyO3−δ (Ln=Pr, Nd, Gd; x=0.2, 0.3) for the electrodes of solid oxide fuel cells

Abstract Promising candidates of intermediate temperature electrodes for solid oxide fuel cells (SOFCs), Ln 1− x Sr x Co 1− y Fe y O 3− δ (LSCF) (Ln=Pr, Nd, Gd; x =0.2, 0.3; 0≦ y ≦1) were studied for their electrical conductivity, thermal expansion rate, cathodic polarization, and reactivity with gadolinia-doped ceria (Ce 0.9 Gd 0.1 O 1.95 , CGO) or yttria-stabilized zirconia (YSZ). Superiorly electrical conductivity has been demonstrated for LSCF electrodes and all samples except Ln=Gd ( y ≧0.8) compositions demonstrate above 200 S/cm at 800 °C. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of Ln 1− x Sr x CoO 3− δ , can be achieved to lower thermal expansion coefficient (TEC) values with more Fe substitution. Using CGO electrolytes, LSCF electrodes over the composition range of y =0.0–0.8 show high cathodic activity for oxygen reduction operating at temperatures from 700 to 900 °C and exhibit no significant dependence on the kind of lanthanide elements. These electrode behaviors are analogous to widely used La 1− x Sr x Co 1− y Fe y O 3− δ , Ln 1− x Sr x Co 1− y Fe y O 3− δ (Ln=Pr, Nd, Gd) systems, however, have potential advantages in reactivity with YSZ. In Ln=Pr, Nd ( y =0.8) compositions, for example, the by-products of Ln 2 Zr 2 O 7 and SrZrO 3 are both suppressed when sintered at 1000 °C for 100 h. LSCF also yield no reaction product with CGO when sintered at 1200 °C for 36 h.

Silicon/Carbon Composites as Anode Materials for Li-Ion Batteries

A silicon/carbon composite has been synthesized by two poly(vinyl chloride) (PVC) pyrolysis reactions, combined with an intervening high-energy mechanical milling (HEMM) step. As lithium storage host, the composite demonstrates high initial coulombic efficiency of 82% and a large capacity at ca. 900 mAh g - 1 over 40 cycles. Controlling Li-insertion level at 600 mAh g - 1 can greatly extend the cycles to over 100. Another composite prepared by ballmilling a mixture of graphite and silicon and followed by a PVC pyrolysis process also shows both good capacity and capacity retention.

Lithium Dendrite Formation in Li/Poly(ethylene oxide)–Lithium Bis(trifluoromethanesulfonyl)imide and N-Methyl-N-propylpiperidinium Bis(trifluoromethanesulfonyl)imide/Li Cells

Lithium metal dendrite growth in Li/poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide (PEO x LiTFSI) and in an ionic liquid, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI) composite solid polymer electrolyte/Li was examined by direct in situ observation. Lithium dendrite formation was observed after 15 h of polarization at 0.5 mA cm ―2 and at 60°C on PEO 18 LiTFSI. The onset time was increased to 35 h at 0.5 mA cm ―2 by the addition of PP13TFSI into PEO 18 LiTFSI up to 1.44 mol. The dendrite onset time decreased with increasing current density and deviated from Sands law in the current density range of 0.1-0.5 mA cm ―2 at 60°C. The electrical conductivity of PEO 18 LiTFSI was enhanced, and the interface resistance between Li and PEO 18 LiTFSI was suppressed by the addition of PP13TFSI. The lithium ion transport number of the composite electrolyte decreased with increasing x in PEO 18 LiTFSI―xPP13TFSI. The suppression of the lithium dendrite formation could be explained by the low resistance of the interface layer between lithium and the composite polymer electrolyte.

Stability of a Water-Stable Lithium Metal Anode for a Lithium–Air Battery with Acetic Acid–Water Solutions

The stability of water-stable lithium metal in aqueous acetic acid solution was examined as an anode in a lithium-air rechargeable battery. The water-stable lithium anode consisted of a water-stable glass-ceramic Li 1+x+y Ti 2-x Al x Si y P 3-y O 12 (LTAP), a poly(ethylene oxide) (PEO)-based electrolyte with Li(CF 3 SO 2 ) 2 N (LiTFSI), and lithium metal. The LTAP immersed in CH 3 COOH (HAc)-H 2 O-saturated CH 3 COOLi (LiAc) solutions at 50°C for several weeks showed no change in the X-ray diffraction pattern and showed a slight decrease in the electrical conductivity. The water-stable lithium anode, Li/PEO 18 LiTFSI/LTAP, showed a total resistance of 164 Ω cm 2 at 60°C after being immersed in HAc (90 vol %)-H 2 O (10 vol %)-saturated LiAc for 1 week. The Li/PEO 18 LiTFSI/LTAP/HAc-H 2 O-LiAc/Pt black air cell had a low polarization for lithium dissolution and deposition at a current density of 1 mA cm -2 . A prototype lithium-air cell using a carbon air electrode with a platinum catalyst showed a good charge and discharge cycle performance, and about 30% of acetic acid in the cell was consumed and recovered in the charge and discharge process.

Water-Stable Lithium Anode with the Three-Layer Construction for Aqueous Lithium–Air Secondary Batteries

A water-stable multilayer Li-metal electrode consisting of a lithium metal, a PEO 18 LiN(SO 2 CF 3 ) 2 ―BaTO 3 composite polymer, and a lithium-conducting glass ceramic Li 1.3S Ti 1.7S Al 0.25 P 0.9 Si 0.1 O 12 (LTAP) was proposed as the lithium anode for aqueous lithium―air secondary batteries. The addition of finely dispersed nanosize BaTiO 3 in the polymer electrolyte greatly reduced the interfacial resistance between the Li anode and the polymer electrolyte. A Li/PEO 18 LiN(SO 2 CF 3 ) 2 ―10 wt % BaTiO 3 /LTAP electrode showed a total resistance of 175 Ω cm 2 in a 1 M aqueous LiCl solution at 60°C, with no change in the electrode resistance over a month. The Li/PEO 18 LiN(SO 2 CF 3 ) 2 ―10 wt % BaTiO 3 /LTAP/aqueous 1 M LiCl/Pt air cell had a stable open-circuit voltage of 3.80 V, which was equivalent to that calculated from the cell reaction of 2Li + 1/2O 2 + H 2 O = 2LiOH. The cell exhibited a stable and reversible discharge/charge performance of 0.5 mA cm ―2 at 60°C, suggesting excellent reversibility of the lithium oxidation reduction reaction for the Li/PEO 18 LiN(SO 2 CF 3 ) 2 ―10 wt % BaTiO 3 /LTAP electrode.

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.

All solid lithium polymer batteries with a novel composite polymer electrolyte

Abstract A composite polymer electrolyte based on polyethylene oxide (PEO) with a hyperbranched polymer poly[bis(triethylene glycol)benzoate] capped with an acetyl group (HBP) and a ceramic filler, BaTiO 3 , was examined as the electrolyte in rechargeable lithium polymer batteries. The conductivity of the composite polymer electrolyte PEO–10 wt.% HBP with Li(CF 3 SO 2 ) 2 N–10 wt.% LiPF 6 as a lithium salt and 10 wt.% BaTiO 3 was found to be 1.6×10 −4 S/cm at 25 °C and 1.5×10 −3 S/cm at 60 °C in a O/Li ratio of 10. The lithium rechargeable batteries consisted of this highly conductive composite polymer electrolyte and the 4 V class cathode, LiNi 0.8 Co 0.2 O 2 , showed excellent charge–discharge cycling performance. The initial cathode discharge capacity of 154 mA h/g declined only 0.1%/cycle during the first 30 cycles at 60 °C.

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.