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RISS 인기검색어
- 검색키워드
- 저자 : ThiruvengadamSubburaj (검색결과 1 건)
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ThiruvengadamSubburaj Kyung Hee University 대학원 2015 국내박사
In recent years, incredible consideration has been paid to the development of high-power lithium-ion batteries for electric vehicles (EVs) and hybrid electric vehicles (HEVs) to satisfy the energy and environmental concerns. Unfortunately, the presently used materials cannot meet the high-power demand due to their (i) expensive synthesis, (ii) old chemistry, (iii) thermal instability, (iv) safety hazards, and (v) poor rate performances. My works have been focused on finding the solution of above mentioned problems. High capacity layered Li[Lix(Ni0.3Co0.1Mn0.6)1-x]O2(x = 0.11) cathode and high voltage Li4Ti5O12 spinel anode for the full cell systems have been studied. With combined this cathode and anode materials in an advanced lithium ion battery, a new electrochemical reaction has been demonstrated. It exhibited the initial discharge capacity of 173 mAh g-1 and also was maintained at the average specific capacity of 170 mAh g-1 and more than 90% capacity retention. In addition, the battery can cycle at C/10 rate up to 30 cycles with a very stable capacity delivery. Taking an average voltage of 2.5 V, a specific energy density value of 400 Wh kg-1 was obtained. These environmentally benign Mn-rich layered cathode and spinel Li4Ti5O12 anode materials are going to be future electrodes for Li-ion rechargeable batteries in hybrid electric vehicle applications. The conventional electrolyte system has been compared with the ionic liquid (IL) additive containing electrolyte system at room temperature as well as elevated temperature. In this work, two types of monocationic ILs such as 1-butyl-3-methylpyrrolidinium hexafluorophosphate (Pyr IL) and 1-ethyl-3-methylimidazolium hexafluorophosphate (IMI IL) are added as an additive at two different weight ratios in 1.15 M LiPF6 (EC/EMC=3/7 v/v) electrolyte solution, the structural, electrochemical and thermal characteristics of LiNi0.80Co0.15Al0.05O2 (NCA)/carbon full-cell in different electrolyte formulations have been reconnoitered. X-ray diffraction (XRD) studies have proved that IL as an electrolyte additive does not alter the structural stability of cathode materials after cycling. Under room temperature, Pyr IL additives at 1wt% and 3wt% deliver better cycleability than others, with the retention ratios of 93.62% and 92.8%, respectively. At elevated temperature, only 1wt% Pyr IL additive is giving stable capacity retention ratio of 80.74%. Ionic conductivity and self-extinguishing time (SET) values are increasing with respect to the amount of additive added to the electrolyte. Thermal studies reveal that 3wt% Pyr IL is favorable regarding the safety of the battery as it shows shifting of peak to higher temperature of 272.10°C. Among the IL additives evaluated in this study, addition of 1wt% Pyr IL is the most desirable additive for achieving the best cycling performance as well as thermal behavior of Li-ion batteries. TiO2 nanofibers (NFs) are prepared by electrospinning method and they are decorated over the surafce of Ni-rich Li[Ni0.8Co0.15Al0.05]O2 (LNCA) cathodes at three different ratios namely 0.5 wt%, 1 wt%, and 1.5 wt%, respectively. The structrual, morphological, electrochemical, and thermal characteristics of TiO2 NFs decorated LNCAs are compared with pristine LNCA. From the X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM) investigation, it is evident that the TiO2 NFs are decorated over the surface of cathode powder particles and the NFs are acting like a connecting bridge between the LNCA particles. The TiO2 NFs decorated LNCA electrodes are giving better cycleability and charge-discharge capacity than the pristine LNCA. Under room temperature at C/10 rate, 1 wt% TiO2 NFs decorated LNCAs is giving the capacity retention of 89.2%. Whereas at elevated temperature, it is delivering 81.4% of capacity retention. The onset of thermal decomposition temperature is also shifted towards the higher temperature for TiO2 NFs decorated LNCA electrodes than pristine LNCA electrodes. The improved electrochemical and thermal behaviors of the Ni-rich LNCA is achieved by decorating TiO2 NFs over the LNCA surface. Micro-sized Li4Ti5-xBixO12 (0 ≤ x ≤ 0.15) materials are synthesized using a simple solid state method in air. The structural, morphological, and electrochemical characteristics of Bi-doped lithium titanates and pristine samples are methodically analyzed by X-ray diffraction (XRD), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), and electrochemical impedance spectroscopy (EIS). The XRD and Raman spectroscopy results demonstrate that bismuth-doping do not alter the spinel structure and good crystalline materials are synthesized. The FE-SEM images show that all samples possess the same morphological characteristics, with a particle size distribution of 0.5-1 μm. The electrochemical cycling testing reveals that the Li4Ti4.9Bi0.10O12 sample exhibits discharge capacities of 205.4 mAh g-1, 160.8 mAh g-1, and 135.4 mAh g-1 after 50 cycles at 1C, 5C, and 10C-rates, respectively. The differential capacity curves suggest that the Li4Ti4.9Bi0.10O12 sample has a weaker polarization effect than the other samples. The EIS measurements imply that the Li4Ti4.9Bi0.10O12 sample possesses a high electronic conductivity and lithium ion diffusivity, which demonstrate that this new Li4Ti4.9Bi0.10O12 material would be a good candidate as an anode for lithium ion batteries. A nano-ribbon-like Cu/Cu0.85V2O5 hybrid composite material with a width of 100 nm has been synthesized via a simple, one-step hydrothermal method. The structural and morphological characteristics of the hybrid composite confirm the phase arrangement, composition, and nano-ribbon-like morphology. The formation reaction mechanism has been investigated via hydrothermal reaction time dependent variables, and the electrochemical characterization demonstrates good cyclical behavior. The hybrid composite delivered approximately ~190 mAh g-1 of the specific discharge capacity at a current density of 50 mA g-1 as a cathode, and approximately ~600 mAh g-1 of the specific discharge capacity at a current density of 100 mA g-1 as an anode. These enhanced electrochemical properties can be ascribed to an increase in electronic conductivity via the presence of metallic copper in the hybrid structure and the facilitation of better intercalation-deintercalation of lithium ions due to the porous nano-ribbon-like structure.
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