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Synthesis and Characterization of Organic/Inorganic Hybrid Materials for Uses in Electrochemical Devices

Title
Synthesis and Characterization of Organic/Inorganic Hybrid Materials for Uses in Electrochemical Devices
Authors
최일영
Date Issued
2016
Publisher
포항공과대학교
Abstract
Lithium-ion batteries (LIBs) are one of the most popular energy storage systems for portable electronic devices due to high energy densities, no memory effect, and slow self-discharge rate when not in use. Although LIBs have already been widely used, developing new electrode and electrolyte materials with enhanced capacity and safety are still important issues in LIBs research. Herein, in this thesis, the novel strategies to develop the advanced polymer electrolytes and electrodes based on organic/inorganic composite materials are presented. In chapter 1, I described a brief overview about LIBs system and current challenges. Firstly, the development of high energy density and capacity of LIBs is a key challenge. To meet that, significant efforts have been devoted to replace commercial graphite anode and transition metal based cathode by using new active materials such as Si, Li, and S elements due to their high theoretical capacities. Secondly, the safety is becoming the important issue in current LIBs system. The organic liquid electrolytes are usually used in current LIBs system. However, these liquid electrolytes are volatile, flammable, and decomposed at high cell potential. Therefore, replacing the liquid by a solid polymer electrolyte has been a long-standing goal of the battery field, due to the promise of better safety and flexible design. In chapter 2, I investigated new Li-polymer batteries composed of surface functionalized Si nanoparticles (SiNPs) as anode active materials and nanostructured block copolymers as solid electrolytes. Surface protection layer of SiNPs with poly(ethylene oxide) (PEO) chains successfully prevents aggregation of SiNPs during cycling and also helps fast Li+ transport to the active centers in the anodes. The self-assembled block copolymer electrolytes in ca. 50 nm periodicity is aimed to restrain the formation of macroscopic ionic clusters during Li insertion/desertion. To decouple the electrical and mechanical properties of polymer electrolytes, two different nonvolatile additives (ionic liquid and non ionic plasticizer) were incorporated and remarkably different cycle performances have been observed. The results suggest that the structural retention of both polymer electrolytes and SiNPs during cycling attributes to the improved battery performance. In chapter 3, I developed new type of organic/inorganic composite gel polymer electrolytes (CPEs) to enhance the ion conductivity and mechanical strength. Firstly, a new methodology for resolving the long-standing obstacles of Li–S batteries by the synthesis of a CPE with a unique internal structure. The Li–S cells was composed in this novel electrolyte system exhibit high discharge capacities (1140 mA h g-1 during the 1st cycle and reversible capacity of 970 mA h g-1 at the 100th cycle) and improved cycle life. In second section, I designed the CPEs uisng the mesoporous inorganic nanoparticles that have the nitrile functional group. The free volume in mesoporous particles facilitated huge amount lithium conducting moiety and increase the activation level of nitrile groups. As a result, CPEs with a mesoporous nanoparticles achieved the high ion conductivy around 2 x 10-3 S cm-1 while retaining the mechanical and thermal stability. In chapter 4, as a new conducting materials, I investigated a new method to develop two-dimensional PANI nanosheets using ice template. Distinctly high current flows of 5.5 mA at 1 V and a high electrical conductivity of 35 S cm−1 were obtained for the polyaniline (PANI) nanosheets, which marked a significant improvement from previously values on other PANIs reported over the past decades. These improved electrical properties of ice-templated PANI nanosheets were attributed to the long-range ordered edge-on π-stacking of the quinoid ring, ascribed to the ice surface-assisted vertical growth of PANI. The unprecedented advantages of the ice-templated PANI nanosheets are two-fold. First, the PANI nanosheet can be easily transferred onto various types of substrates via float-off from the ice surfaces. Second, PANI can be patterned into any shape using predetermined masks, and this is expected to facilitate the eventual convenient and inexpensive application of conducting polymers in versatile electronic device forms.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000002227919
https://oasis.postech.ac.kr/handle/2014.oak/93457
Article Type
Thesis
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