Hybridization of nanostructured carbon with phosphate-based materials for high performance Li-ion batteries

Abstract

Since the Sony Corporation has first commercialized lithium ion batteries, it has dominated the batteries market due to their light weight, high energy and power densities. These properties make the batteries ideal for portable electronic devices and electric vehicles. $LiCoO_2$ was the first material used as a cathode and together with other transition metal oxides still dominates today market. The main concern of transition metal oxides are occurrence oxygen evolution during cycling at high temperature. Safety becomes an issue for transition met-al. Recently, $LiFePO_4$ is recognized as a promising cathode material due to its strong covalent bonding of P-O, which allows it to stable at high temperature without oxygen evolution. Other phosphate-based materials, such as $LiT_2(PO_4)_3$, $Li_3V_2(PO_4)_3$, $Na_3V_2(PO_4)_3$, and $Na_2FeP_2O_7$, have been studied as alternative cathode materials. However, phosphate-based materials have suffered low electronic conductivity and render poor electrochemical performance. Thus, various carbonaceous materials have been developed to overcome this challenge. In this work, the role of graphene as conducting material is studied after hybridized with aforementioned phosphate-based materials using various synthesis strategies to enhance electrochemical per-formance. Along with hybridization processing, the relationships between the physico-chemical properties and the electrochemical performance of the hybrid cathode materials are also scrutinized in this work.

In 3^{rd} chapter, the $LiTi_2(PO_4)_3$ (LTP) with NASICON structure was grown on reduced graphene oxide (rGO) as a cathode material for lithium ion batteries and for high power applications, such as hybrid electric vehicles and electric grid systems. LTP has a low electronic conductivity and require effective material design and strategies. Therefore, a two steps approach was employed by first growing TiO_2 nanoparticles on graphene oxide to prevent graphene re-stack...