Browsing by Author "Chang, Jian-Chia"

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Carbon nanobeads as an anode material on high rate capability lithium ion batteries
(2009-11-30)
Chang, Jian-Chia
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Tzeng, Yu-Fen
;
Chen, Jin-Ming
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Chiu, Hsin-Tien
;
Lee, Chi-Young
Carbon nanobeads (CNBs) were prepared by reacting cyclohexachlorobenzene with dispersed sodium metal at 200 degrees C for 4 h. The CNBs prepared in this manner formed uniform nanobeads, with sizes ranging from 100 to 300 nm. Heating resulted in a reduction in the size of the CNBs, and improvements in their degree of crystallinity. The nanosized carbon materials considerably increased the surface area of the powder, reducing the distance of the intercalation/deintercalation pathway, substantially improving the charge capacity of the lithium ion battery at a high charging rate. The charge capacity of CNBs was found to be 238 mAh g(-1), while that of commercial MCMB reached only 36 mAh g(-1), when the charging rate was 1C (372 mAh g(-1)). As the charging rate was further increased to 2C (744 mAh g(-1)) and 3C (1116 mAh g(-1)), the charge capacities of CNBs dropped to 173 and 111 mAh g(-1), respectively. The cyclic performance of the CNBs was measured and found to be significantly improved in comparison to other carbonaceous materials, for up to 100 cycles. Although cyclic performance did result in a gradual reduction in capacity, the CNBs still greatly exceeded the capacity of MCMB. These results clearly demonstrate the potential role of CNBs as anodes for high capacity Li ion batteries for use in the automobile industry. (C) 2009 Elsevier Ltd. All rights reserved.
Lithium Ion Intercalation Performance of Porous Laminal Titanium Dioxides Synthesized by Sol-Gel Process
(2009-02-10)
Tsai, Min-Chiao
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Chang, Jian-Chia
;
Sheu, Hwo-Shuenn
;
Chiu, Hsin-Tien
;
Lee, Chi-Young
We have synthesized novel mesoporous titanate nanosheets by reacting titanium isopropoxide (TTIP) with formic acid. The porous nanosheets were characterized as a new titanate structure with intercalation of formate groups and protons, in the form of HCOOH-intercalated titanate. Most interestingly, TiO(2)-B, a well-known but unusual titanium dioxide phase with great potential in applications in Li-ion batteries, was obtained after the nanosheets were heated above 250 degrees C. Mesoporous nanosheets of HCOOH-intercalated titanate, titanium dioxide with mostly TiO(2)-B and titanium dioxide with traces of TiO(2)-B were obtained by heating the as prepared mesoporous titanate nanosheets at 200, 300, and 550 degrees C, respectively. The method reported here is the first to utilize the sol-gel process to synthesize TiO(2)-B. In addition, different anodes were made from HCOOH-intercalated titanate and titanium dioxide with different ratios of TiO2-B to examine the performance of the charging/discharging capacity in Li ion intercalation. The discharging capacity of titanium dioxide with major TiO2-B can reach 357 mA h/g at the first charging cycle and is highest among TiO(2)-B reports so far.