Synthesis of Tin and Cobalt Oxide-Carbon Nanocomposites for Lithium Ion Battery Anodes

Abstract

Developing lithium ion battery (LIB) electrodes with high-energy-density and improved stability is of primary importance to meet the challenges in electronics and automobile industries in the near future. High-capacity anode materials, including transition metal oxides, Si, Sn, and SnO2, generally suffer from a huge volume expansion during cycling, resulting in poor stability. For commercialization, the development of a facile and scalable synthetic method should be also considered. This dissertation includes the facile fabrication of functional hybrid nanomaterials that effectively reduce mechanical stress-induced electrode degradation. Firstly, I report a simple synthetic method of carbon-based hybrid cellular nanosheets that exhibit outstanding electrochemical performance for many key aspects of lithium ion battery electrodes. The hybrid cellular nanosheets consisted of carbon cellular nanosheets loaded with SnO2 nanoparticles. The as-synthesized carbon nanosheets have well-ordered empty cubic cells encapsulated by carbon walls. I loaded SnO2 nanoparticles in the carbon cellular nanosheets by ship-in-a-bottle vapor deposition method and tested the performance of the resulting SnO2-carbon nanosheets as LIB anode materials. When the hybrid nanosheets are cycled, the volume expansion of SnO2 is confined in the cells and the mechanical integrity is maintained, resulting in superior cycling stability. The sheet-like structure of the carbon nanosheets contributes to the short lithium ion diffusion length and facilitates electron transport through the carbon networks. As a result, the hybrid cellular nanosheet exhibited excellent battery performance, 914 mAh g-1 of average capacity over 300 cycles and a capacity reduction of only 20% at a high current density of 3000 mA g-1.

Secondly, various metal (oxy)hydroxide nanoplates with hexagonal shapes were fabricated by a simple and straightforward synthetic method. For their application as LIB anodes, polydopamine is coated on the nanoplates and the resulting hybrid materials are converted to mesoporous CoO@carbon core–shell nanoplates. Through evaluation of the carbon-thickness-dependent electrochemical performance, it is concluded that a proper amount of carbon coating is necessary for preventing conversion-induced degradation and improving battery performance.