Electrochemical Evaluation of Titanium Oxide and Tin Oxide as High Power Anode Materials for Lithium-Ion Batteries

Abstract

The development of electric vehicles (EVs) has been stimulated with the advent of the era of clean energy, leading to the commercialization of hybrid electric vehicles (HEVs), powered by an internal combustion engine and an electric motor that utilizes energy stored in lithium-ion batteries (LIBs), and the rapid development of battery electric vehicles (BEVs) using only battery as a power source. The demand for power performance in the battery of EVs is more than 50 times higher than in the small electric devices such as cellular phones and laptop computers. The high power performance is associated with the various factors including electrode material, electrode structure, ion conductivity of electrolyte, etc. For the anode materials at present known, energy density (Watt-hours) and power density (Watt) are trade-off relation, which expedites the following researches for the realization of high power performance from high energy density materials: (1) new material development (2) electrode filming (3) design of integrated electrode (4) understanding of reaction mechanism and design for new electrode material using ab initio quantum chemistry methods. In this dissertation, high power density through the material design and the integrated electrode architecture utilizing the character of thin film electrode potentially will be discussed. Chapter 1 begins with general overview of LIBs and materials of cathode and anode categorized according to structure and reaction mechanism, respectively. In addition, titanium oxide known as a typical anode material with high rate capability and tin oxide having a high theoretical capacity in anode materials are introduced. Chapter 2 describes the electrochemical properties of titanium oxide. In particular, the effect of particle size controlled with three different size groups on the power density is discussed. The structural changes upon cycling were analyzed by in-situ synchrotron X-ray diffraction. The increase of capacity upon cycling like activation was observed in all size groups, which is rarely reported in the stable anode material following intercalation reaction mechanism. As a reason for this phenomena, I propose the enhancement of contact area between active material and electrolyte resulted from lattice expansion upon cycling through in-situ synchrotron X-ray diffraction analysis. Chapter 3 introduces an approach to improve the electrochemical performance of tin oxide. Compared with conventional LIBs electrode in 2-dimensional (2D) laminate structure, electrode design was extended into 3-dimensional (3D) architecture of copper foam applied to template for the deposition of tin oxide. The copper foam, served as a current collector and a template for forming a thin layer of tin oxide, is advantageous for alleviating the large volume changes of tin oxide during cycling by providing void space. The integrated electrode is free of binder and conducting agent, exhibiting a high reversible capacity, good rate capability, and stable cycle retention with maintaining a structural integrity. As another electrode architecture, copper layer-by-layer assembly is introduced. Many pores are developed on the surface of each layer, penetrating the layer and creating an open pore system. Consequently, the copper layer-by-layer assembly with high surface area realizes excellent power performance even at very high current densities from tin oxide of high capacity anode material.