Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors

Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer–Emmett–Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5–3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg−1 at a power of 180 W kg−1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg−1 at 180 W kg−1 better, showing 36 Wh g−1 at 3200 W kg−1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0–3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg−1 and 2.5 Wh kg−1 at power densities of 6700 W kg−1 and 14 000 W kg−1, respectively

Continuous Hydrothermal Synthesis of Metal Germanates (M₂GeO₄ ; M = Co, Mn, Zn) for High Capacity Negative Electrodes in Li‐ion Batteries

Nanosized metal germanates (M2GeO4; M = Co, Mn, Zn) were synthesised using a continuous hydrothermal flow synthesis process for the first time. Phase‐pure rhombohedral Zn2GeO4 nanorods, cubic spinel Co2GeO4 nanoparticles, and orthorhombic Mn2GeO4 nanotubes/nanoparticles were obtained. The electrochemical properties of all samples as active materials for negative electrodes in Li‐ion half cells was explored. The galvanostatic and potentiodynamic testing was conducted in the potential range 3.00 to 0.05 V vs. Li/Li+. The results suggest that both alloying and conversion reactions associated with Ge contributed to the stored charge capacity; Zn2GeO4 showed a high specific capacity of 600 mAh g-1 (10 cycles at 0.1 A g -1) due to alloying and conversion reactions for both Ge and Zn. Mn2GeO4 was studied for the first time as a potential negative electrode material in a Li‐ion half‐cell; an excellent specific charge capacity of 510 mAh g-1 (10 cycles / 0.1 A g-1) was obtained with a significant contribution to charge arising from the conversion reaction of Mn to MnO upon delithiation. In contrast, Co2GeO4 only showed a specific capacity of 240 mAh g-1, after 10 cycles at the same current rate, which suggested that cobalt had little or no benefit for enhancing stored charge in the germanate

TiO2/MoO2 nanocomposite as anode materials for high power Li-ion batteries with exceptional capacity

Nanoparticles of molybdenum(IV) oxide (MoO 2 ) and a TiO 2 /MoO 2 nanocomposite were synthesised via a continuous hydrothermal synthesis process. Both powders were analysed using XRD, XPS, TEM, and BET and evaluated as active materials in anodes for Li-ion half-cells. Cyclic voltammetry and galvanostatic charge/discharge measurements were carried out in the potential window of 0.1 to 3.0 V vs. Li/Li+. Specific capacities of ca. 350 mAh g -1 were obtained for both materials at low specific currents (0.1 A g -1 ); TiO 2 /MoO 2 composite electrodes showed superior rate behaviour & stability under cycling (compared to MoO 2 ), with stable specific capacities of ca. 265 mAh g -1 at a specific current of 0.5 A g -1 and ca. 150 mAh g -1 after 350 cycles at a specific current of 2.5 A g -1 . The improved performance of the composite material, compared to MoO 2 , was attributed to a smaller particle size, improved stability to volume changes (during cycling), and lower charge transfer resistance during cycling. Li-ion hybrid electrochemical capacitors using TiO 2 /MoO 2 composite anodes and activated carbon (AC) cathodes were evaluated and showed excellent performance with an energy density of 44 Wh kg -1 at a power density of 600 W kg -1

Organoboron Ion-gel Electrolytes as Lithium Ions Transport Media

Design of organoboron electrolytes has been an attractive approach to produce ion conductive media showing high ionic conductivity and lithium transference number at the same time When silicate matrix formation and radical polymerization of ionic liquid monomer was conducted simultaneously, transparent hybrid ion-gel electrolytes were obtained under a wide range of materials composition. Incorporation of the boron atom as borosilicate glass led to further improved ionic conductivity of resulting ion-gel electrolytes. However, one problem of in-situ polymerization has been long reaction time (at least more than a week) to complete the sol-gel condensation reactions. As a different strategy for efficient preparation of organic-inorganic hybrid type ion-gels, we examined a condensation of cellulose with boric acids in ionic liquid (Scheme 1) The obtained ion-gels exhibited ionic conductivity of 3.6 x 10 -3 ~ 5.4 x 10 -4 Scm -1 at 324K that are comparable to ionic liquids themselves A series of cellulose based ion-gels including boric esters were also prepared by dehydrocoupling of cellulose with hydroboranes in ionic liquid (Scheme 2). The organoboron ion-gels obtained showed ionic conductivity of 6.3 x 10 -4 ~ 1.1 x 10 -4 Scm -1 at 324 K. The desired ion-gels were successfully prepared during the reactions for 1 h. The ion-gels prepared using mesitylborane 12 showed higher ionic conductivity in comparison with iongels prepared from BH 3 -THF complex. Differently from ordinary polymer ion-gels, addition of lithium salt led to further increased ionic conductivity. This should be due to high dissociation degree of LiCl in the presence of boron, as indicated from increased VFT (Vogel-FulcherTammann) parameter corresponding to carrier ion number in the matrices. References Acknowledgement We are grateful to financial support for the present study by New Energy and Industrial Technology Development Organization (NEDO) of Japan

新しいπ-共役系有機ホウ素高分子の創成

京都大学0048新制・課程博士博士(工学)甲第8394号工博第1959号新制||工||1176(附属図書館)UT51-2000-F298京都大学大学院工学研究科高分子化学専攻(主査)教授 中條 善樹, 教授 増田 俊夫, 教授 澤本 光男学位規則第4条第1項該当Doctor of EngineeringKyoto UniversityDA

Boric Ester-Type Molten Salt via Dehydrocoupling Reaction

Novel boric ester-type molten salt was prepared using 1-(2-hydroxyethyl)-3-methylimidazolium chloride as a key starting material. After an ion exchange reaction of 1-(2-hydroxyethyl)-3-methylimidazolium chloride with lithium (bis-(trifluoromethanesulfonyl) imide) (LiNTf2), the resulting 1-(2-hydroxyethyl)-3-methylimidazolium NTf2 was reacted with 9-borabicyclo[3.3.1]nonane (9-BBN) to give the desired boric ester-type molten salt in a moderate yield. The structure of the boric ester-type molten salt was supported by 1H-, 13C-, 11B- and 19F-NMR spectra. In the presence of two different kinds of lithium salts, the matrices showed an ionic conductivity in the range of 1.1 × 10−4–1.6 × 10−5 S cm−1 at 51 °C. This was higher than other organoboron molten salts ever reported

Electrochemical characterization of TiO_2/WO_x nanotubes for photocatalytic application

TiO_2/WO_x nanotubes have unique photo-energy retention properties that have gathered scientific interest. Herein, we report the synthesis, morphological characterization, and the electrochemical characterization of TiO_2/WO_x nanotubes compared with pure TiO_2 nanotubes, prepared by anodization technique. Significant structural differences were not observed in TiO_2/WO_x nanotubes as observed by using scanning electron microscopy and transmission electron microscopy. The charge transfer resistance of TiO_2/WO_x before and after photo irradiation determined by using electrochemical impedance spectroscopy proves the inherent energy retention property which was not observed in pure TiO_2 nanotubes

Lithium ion conductive behavior of TiO_2 nanotube/ionic liquid matrices

A series of TiO_2 nanotube (TNT)/ionic liquid matrices were prepared, and their lithium ion conductive properties were studied. SEM images implied that ionic liquid was dispersed on the whole surface of TNT. Addition of TNT to ionic liquid (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMImTFSA)) resulted in significant increase of ionic conductivity. Furthermore, lithium transference number was also largely enhanced due to the interaction of anion with TNT. Vogel-Fulcher-Tammann parameter showed higher carrier ion number for TNT/BMImTFSA in comparison with BMImTFSA