Akihisa Kajiyama

Solid-state lithium battery with graphite anode

Abstract Solid-state lithium batteries with a unique construction are reported in this paper. These batteries contain two kinds of lithium ion-conductive solid electrolytes, LiI–Li2S–P2S5 glass contacted with the anode material and Li3PO4–Li2S–SiS2 glass or Li2S–GeS2–P2S5 crystalline material contacted with the cathode. The former electrolyte was selected as that stable to electrochemical reduction, and the latter two to oxidation. This construction made it possible to use graphite as the anode and LiCoO2 as the cathode in the solid-state lithium battery. The energy density of the battery is 390 W h·l−1 and 160 W h·kg−1 per total volume and weight of the cathode and anode layers, respectively, which are comparable to those of commercialized Li-ion batteries.

Lithium ion conduction in LiTi2(PO4)3

Abstract Li + ion conduction was examined for a mixture of LiTi 2 (PO 4 ) 3 (LTP) and a glassy electrolyte, 0.01Li 3 PO 4 –0.63Li 2 S–0.36SiS 2 . The addition of LTP with 10 wt.% resulted in a significant decrease in activation energy for conduction and little influence on the Li + ion conductivity, although it reduced the conduction path in the glass. The 7 Li NMR spectra of LTP was quite similar to that of Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) with a high conductivity of 10 −3 S cm −1 . These results suggest that Li + ion conduction in LTP is as high as that in the glassy electrolyte and LATP.

Fabrications and properties of composite solid-state electrolytes

Abstract The dry and wet methods of preparation for composite inorganic solid electrolytes including styrene–butadiene copolymer (SBR) or silicone rubber (silicone) as polymer binder are investigated, and their electrochemical properties are analyzed. The SBR composite electrolytes prepared by the dry process showed higher conductivity than the one done by the wet process. For the composite electrolyte prepared by the wet process, the SBR coating on the electrolyte particles blocked lithium-ionic conduction. The electrolytes prepared by the dry process, on the other hand, showed the dispersion of SBR granular domains in the electrolyte matrix, which results in good contact between the electrolyte particles. However, by choosing an adequate polymer such as silicone rubber, the wet-processed composite shows a high Li ion-conductivity.

Electrochemical Reduction of Li2FeS2 in Solid Electrolyte

The nature of the product of the electrochemical reduction of Li 2 FeS 2 has been investigated. This product was completely reoxidized in intimate contact with a lithium ion-conducting solid electrolyte. The product is regarded as α-Fe, although usually, Fe is electrochemically inactive in contact with a solid electrolyte. In order to understand the reason for this discrepancy, the product was investigated by X-ray diffraction and Mossbauer spectroscopy, Its diffraction pattern did not show clear peaks and its Mossbauer spectrum was attributed to superparamagnetic Fe 0 . These results suggest that the reduction product consists of non-crystalline, small particles of Fe dispersed in Li 2 S. Because of the small particle size, most of the Fe atoms are in contact with Li 2 S. This environment is considered to permit the continuous reoxidation to Li 2 FeS 2 . resulting in its electrochemical activity.

Compatibility of Lithium Ion Conductive Sulfide Glass with Carbon-Lithium Electrode

Electrochemical properties of graphite were investigated using SiS 2 -based glass or P 2 S 5 -based glass as a solid electrolyte. Graphite showed reversible electrode reactions in the P 2 S 5 -hased glass while it did not in the SiS 2 -based one. The results of X-ray diffractometry and Raman spectroscopy indicated that the SiS 2 -based glass was reduced as side reactions instead of the intercalation of lithium ions into graphite during the reduction, resulting in the poor reversibility.

Layered Li-Co-Mn Oxide as a High-Voltage Positive Electrode Material for Lithium Batteries

A layered Li-Co-Mn oxide was synthesized from a host layered Na-Co-Mn oxide by ion-exchange technique. Its electrode performance showed anomalous high redox potential of ca. 4.5 V vs. Li/Li for the intercalation and deintercalation of lithium, although the end members of solid solution LiCoO 2 and LiMnO 2 did only 4.0 V. The oxidation state of the cobalt was measured by X-ray photoelectron spectroscopy and was trivalent.

Synthesis and Electrochemical Properties of Lithium Chromium Titanium Oxide with Ramsdellite Structure

A pseudoternary system Li 2 O-Cr 2 O 3 -TiO 2 was investigated in the temperature range from 800 to 1100°C. A new compound with ramsdellite structure was discovered. The ramsdellite-type phase was obtained alone at temperatures above 1000°C in the composition range x ≤ 1.5 of Li 8/7(2-x/3) Cr 8x/7 Ti 8/7(3-2x/3) O 8 . The ramsdellite structure showed reversible extraction and insertion cycles of lithium at the potential of ca. 4.0 V vs. Li/Li + as well as 1.5 V. The former potential was attributed to a redox couple of Cr 3+ /Cr 4+ and the latter to Ti 3+ /Ti 4+ . The crystal structure was maintained against the electrochemical extraction and insertion of lithium, and the cell volume was almost unchanged in the processes.

Research on highly reliable solid-state lithium batteries in NIRIM

Abstract Electrochemical reactions of LiVS2, Li2FeS4, and Li4FeS2 were investigated by using a Li+ ion conductive glass, 0.01Li3PO4–0.63Li2S–0.36SiS2, as an electrolyte. The results showed remarkable differences from that in liquid electrolyte; the redox couples of both Li2VS2/LiVS2 and LiVS2/VS2 were highly reversible, the reduction of Li2FeS2 led to the metastable phase Li4FeS2 that was completely reoxidized to the initial phase, and Li+ ions were extracted from Li2FeCl4 without dissolution of the chloride itself. These improvements by using the solid electrolyte make a large choice of electrode materials.

Lithium iron thio-phosphate: a new 3 V sulfide cathode

Abstract The lithium iron thio-phosphate, Li 2 FeP 2 S 6 , was synthesized, and its electrode property was investigated. The crystal structure was solved as the CdI 2 -type with P 31 m and a =6.0145(4) A, c =6.5600(2) A. Two thirds of the Cd sites were occupied by Li + /Fe 2+ ions with an occupancy of 1/1, and the rest was occupied by (P 4+ ) 2 paired-ion. The residual Li + ions occupy octahedral sites in the van der Waals gap of the CdI 2 structure. Electrochemical oxidation of Li 2 FeP 2 S 6 gave a potential plateau at ca. 3.0 V. This potential was the highest potential among sulfides examined so far.

Application of porous polymer to composite electrodes with inorganic solid electrolytes

The electrochemical performances of composite positive electrodes including polymer materials have been investigated in lithium secondary cells with inorganic solid electrolytes. The polymer added to the electrode generally tends to enlarge the electrode impedance because of its insulating nature. Comparison of charge and discharge characteristics between some composite electrodes in this study revealed that the texture of polymer-coated on the surface of the active materials had a dominant influence on their electrochemical performance. It was found that porous polymer would be promising for the composite electrodes with high performance.