Document Type

Thesis - Open Access

Award Date

2016

Degree Name

Master of Science (MS)

Department / School

Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao

Keywords

acidic, basic, charge modified nano fillers, composite gel polymer electrolyte (CGPE), electrochemical, ionic conductivity

Abstract

Batteries have been ubiquitously utilized in enormous applications such as portable electronics, satellites, computers, medical instruments, and electric cars. The development of battery technology has been through a long journey since the 17th century, paving its way to commercialization of lithium ion batteries in 1991 by Sony. Rechargeable lithium ion batteries represent the most favorable type of batteries for portable applications due to their high energy density compared to other alkali metals. In 1997, lithium polymer batteries with solid polymer/composite electrolyte were introduced where the safety drawbacks of the liquid electrolyte were eliminated but the ionic conductivity of the batteries was lower than that of a liquid. In this work, composite gel polymer electrolyte (CGPE) films, consisting of poly (vinylidene fluoridehexafluoropropylene) (PVdF-HFP) as the membrane, dimethylformamide (DMF) and propylene carbonate (PC) as solvents and plasticizing agent, mixture of charge modified TiO2 and SiO2 nano particles as ionic conductors, and LiClO4+LiPF6 as lithium salts were fabricated. CGPE was coated on an O2-plasma treated trilayer polypropylenepolyethylene- polypropylene (PP) membrane separator using solution casting technique. In acidic CGPE, the mixture of acid treated TiO2 and neutral SiO2 nano particles played the role of the charge modified nano fillers with enhanced hydroxyl groups. The mixture of neutral TiO2 nano particles with basic SiO2 prepared through the hydrolization of tetraethyl orthosilicate (TEOS) provided a more basic environment due to the residues of NH4OH (Ammonium hydroxide) catalyst. The CGPE exhibited submicron pore size while the ionic conductivities were in order of 10-3 - 10-5 S.cm-1 with and without modified nano-fillers respectively. Half-cells with graphite anode and Li metal as reference electrode were then assembled and the electrochemical measurements and morphology examinations were successfully carried out. Half-cells demonstrated a considerable change in their electrochemical performance upon the enhancement of acidic properties of the CGPE, gaining the reversible specific capacity of 372 mAh.g-1 in acidic CGPE vs. 270 mAh.g-1 in basic CGPE @ C/20 after 40 cycles.

Library of Congress Subject Headings

Lithium ion batteries

Polyelectrolytes

Polymeric composites

Description

Includes bibliographical references (pages 104-112)

Format

application/pdf

Number of Pages

128

Publisher

South Dakota State University

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Rights Statement

In Copyright