Shunichi Higuchi

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.

Anode characteristics of non-graphitizable carbon fibers for rechargeable lithium-ion batteries

Abstract Non-graphitizable carbon fibers heat-treated between 1000 and 1200 °C gave capacity higher than the capacity of LiC6 (372 mAh g−1) with a significant capacity below 0.1 V during oxidation. 7Li nuclear magnetic resonance (7Li-NMR) observation on lithium insertion into the carbon fibers suggested that lithium in the carbons are classified into two species. One of the lithium species was the same as that in graphitizable carbons. However, the other lithium species was quite different from that in graphitizable carbons, because the line shifts in the 7Li-NMR spectra of the carbon fibers fully lithiated to 0 V were between 80–110 ppm (versus LiCl); these shifts are larger than the maximum shift of lithium in graphitizable carbons (∼45 ppm). In particular, a significant capacity below 0.1 V corresponded to the formation of a new lithium species.

Characterization of sputtered vanadium oxide films for lithium batteries

Abstract Orthorhombic V2O5 crystal thin films have been prepared by radio frequency sputter deposition in an argon atmosphere containing 20% oxygen and a V2O5 target. The film can undergo reversible charge–discharge cycling. The mass change that takes place during charge–discharge cycling is in good agreement with the lithium value from measurement of the resonance frequency changes of a quartz crystal microbalance. However, during the first few cycles, the amount of mass change differs a little from the lithium value, which may be caused by creation of a surface film on V2O5. During subsequent cycling, the electrode mass continues to increase which that means some part of the inserted lithium can not be extracted. This mass accumulation is clearly related to the origins of the reduced charging capacity of the V2O5 films for cathode material of lithium batteries.

A modification in the preparation process of a carbon whisker for the anode performance of lithium rechargeable batteries

In general, a carbon whisker is prepared from hydrocarbons using a vapor-grown method and chopped to a suitable length. Two procedures were examined to prepare the whiskers: in the normal procedure (1A), whiskers were graphitized after the chopping process, and in the other process (2A), they were chopped after the graphitization. The carbon whisker of 2 μm in length by the 1A procedure (2GWH-1A) showed an average capacity of 248 mAh g−1. On the other hand, the whisker of the same diameter by the 2A process (2GWH-2A) showed a much higher capacity of 363 mAh g−1: this value is 1.6 times of that of 2GWH-1A. This modification method may open a new probability to higher performance carbon materials for the anode.

Discharge and Charge Characteristics of Amorphous FeOOH Including Aniline ( aan ‐ FeOOH ) Influence of Preparation Conditions on Discharge and Charge Characteristics

The effect of the preparation conditions for amorphous FeOOH including aniline (a an -FeOOH) on its discharge and charge characteristics as a cathode material for a rechargeable lithium battery was investigated to improve the discharge and charge characteristics. The a an -FeOOH was prepared in solutions containing different concentrations of aniline, or in solutions with different pH. From the discharge and charge characteristics of these products, it can be seen that the discharge capacity depends on the pH of the reaction solution rather than the concentration of aniline

Electrochemical and quartz microbalance technique studies of anode material for secondary lithium batteries

Abstract The lithium metal anode for secondary lithium batteries was studied using the electrochemical and the quartz crystal microbalance (QCM) techniques. The solutions studied were: (i) propylene carbonate (PC) containing LiClO 4 , and (ii) γ -butyrolactone ( γ -BL) containing LiPF 6 . Surface film formation on the electrodes in these solutions was investigated during galvanostatic electrodeposition of lithium. Moreover, the influence of the surface films upon the electrodeposition of lithium and the electrodeposited lithium through surface films were investigated in these solutions. The molecular weights of the species precipitated on the electrode surface were estimated from the QCM data. The deposited lithium on the electrodes made surface films instantaneously in both solutions. The surface films grew continuously in LiClO 4 /PC even after the electrodeposition of lithium stopped. By contrast, the surface film made in LiPF 6 / γ -BL was thin and close, and prevented the decomposition of electrolyte and consumption of deposited lithium.

Preparation of a FeOCl derivative with pyrrole and its performance as a cathode material in a secondary lithium battery system

Abstract A FeOCl derivative is prepared in water using pyrrole (a py -FeOOH). The X-ray diffraction pattern of the product is similar to γ-FeOOH. From chemical analyses and the FT-IR spectrum, it is found that pyrrole remains in the product with an atomic ratio of Fe:N = 3:1. From discharge/charge cycling tests, it is confirmed that a py -FeOOH is rechargeable and has a specific capacity of 60 mAh g −1 between 2.0 and 4.5 V on the 20th discharge. When N -methylpyrrole (which has similar structure) is used instead of pyrrole, the derivative yields larger capacity during ten cycles.

Cycleability of Ni-Fe hydroxides in nonaqueous electrolyte

Abstract Ni–Fe hydroxides were prepared and cycled in 1.0 mol dm −3 LiClO 4 /propylene carbonate in order to investigate an effect of Ni substitution of iron hydroxides on their cycleability in nonaqueous electrolyte. Ni3Fe1 sample in which mole ratio Ni/Fe was 0.738/0.262 had Ni–Fe–CO 3 LDH (layered double hydroxide) like structure. In the voltage range 2.0–4.0 and 1.5–4.0 V vs. Li/Li + , Ni3Fe1 showed smaller discharge capacity than iron-rich samples (β-FeOOH like structure). Discharge–charge voltage range, Fe content, and structure seem to affect the discharge capacity.

Electrochemical properties of FeOCl derivatives prepared by the reaction of FeOCl intercalated with 2,2-bithiophene and H2O

Abstract A FeOCl derivative was prepared from FeOCl intercalated by 2,2-bithiophene (Bth). This product shows an X-ray diffraction pattern similar to γ-FeOOH and contains the organic substances originating from Bth. Thus we conclude that the product resulting by the means of reaction is “FeOOH including Bth”. As a result of the galvanostatic discharge—charge cycling test, it was revealed that the specific discharge capacity of FeOOH including Bth was 80 mAh · g −1 at 10th discharge.