UNDERSTANDING AND MODIFYING ACTIVE MATERIAL STRUCTURES FOR LI-ION BATTERIES

Abstract

This thesis focuses on improving the structural properties of active materials used in lithium-ion batteries to enhance their performance. It focuses on aspects of Ni-rich and mid-Ni cathode materials, as well as silicon-based anodes. One part of the research examines the effects of coating nickel-rich materials (with over 95% nickel) with tungsten. These materials are also doped with elements like magnesium, manganese, and aluminum. The study investigates how the tungsten coating works and how it impacts the structure and performance of these materials. This knowledge is further used to prevent interdiffusion in core-shell structures, where the core is consists of nickel based layered oxide and the shell includes nickel mixed with manganese or aluminum in the transition metal layer. Another focus of the work is on mid-nickel NMC materials, such as NMC550 and NMC640. The thesis addresses the poor rate capability of NMC550 by adding excess lithium and analyzing its effects on performance across different voltage ranges. Additionally, it explores the impact of reintroducing cobalt into NMC640 to improve performance, with comparisons made between stoichiometric and lithium-excess conditions. The research also looks at using Li-excess NMC550 materials to prelithiate silicon-based anodes, improving their energy density and cycling performance. These improvements are demonstrated in full coin cells and single layer pouch cells, with lithium inventory tracked throughout cycling. Finally, the thesis characterizes advanced silicon-carbon composite structures, analyzing their size, morphology, porosity, and density, and how these features affect the material’s volume expansion during electrochemical cycling. Overall, this work provides insights into optimizing Li-ion battery materials, for better performance and higher energy density in present and future batteries.