Design and Synthesis of Three-Dimensional Interconnected Porous Carbon Nanostructure and Its Nanocomposite as Anodes for Li-ion Batteries

Abstract

With ever-increasing fossil fuel consumption and the resulting environmental problems, clean and sustainable energy fuel (such as hydrogen) or energy storage technologies are highly desirable. Rechargeable lithium ion batteries (LIBs) have been one of the most promising energy storage devices owing to their high energy density, no memory effect, and long cycle life. However, their low high-rate capability and limited specific capacity limit their high-energy application such as in electric vehicles (EVs). Improving the energy density of LIBs requires anode materials with higher capacity and faster lithium ion diffusion capability. Carbonaceous materials, especially graphite, have been widely employed as the anode for LIBs. However, their capacity is reaching the theoretical capacity (372 mAh/g) based on the formation of LiC6. Thus, high-capacity anode materials are urgently needed. Tin oxide is a potential anode material owing to its high theoretical specific capacity (783 mAh/g) and has been widely studied in recent years. Unfortunately, this material usually suffers from large volume changes upon lithiation and delithiation, leading to fast capacity decay and poor cycling performance. To address these challenges, this thesis focuses on the engineering and construction of three-dimensional (3D) interconnected-nanoarchitecture advanced carbon materials and tin oxide/carbon nanocomposites. The first part is to design and fabricate 3D interconnected porous carbons. Two different carbon structures are developed: bulk amorphous carbon, which is pyrolyzed through a simple and convenient one-step calcination; and carbon networks, which are developed by using silica as a template. The carbon networks possess a unique three-dimensional structure and a large surface area with promising rate capability. Both carbon materials exhibit ultra-long durability, up to 2000 cycles, without significant capacity fade. The second part of this work is the design and fabrication of 3D interconnected tin oxide/carbon nanocomposites. The tin oxide particles were deposited on both carbon spherules and carbon networks. Tin oxide has a high theoretical capacity, but it also suffers from severe capacity decay due to the large volume change and pulverization during the lithium insertion. Combining the tin oxide with porous carbon, buffer the volume expansion thus enhancing the battery life as well. The SnO2/carbon network possesses an excellent cycling performance and can deliver a capacity of 673.1 mAh/g at 50 mA/g, and after 500 cycles, 210.74 mAh/g at 1000 mA/g with a capacity retention of 95.5%.