Synthesis and Defect Structure Analysis of Complex Oxides for Li-Ion Battery Electrodes.

Abstract

Lithium-ion batteries have attracted increased attention for energy storage development due to the vast demand from portable electronics, (hybrid) electric vehicles and future power grids. The research in this dissertation is focused on the development of oxide electrodes for lithium-ion batteries with high power density and improved stability. One of the promising cathodes for lithium-ion batteries is lithium manganospinel (LiMn2O4). However, this compound suffers from manganese dissolution and a Jahn-Teller distortion due to Mn3+, especially in oxygen deficient LiMn2O4–δ. Hydrothermal based synthesis methods were developed to eliminate oxygen vacancies to enable high power in cathodes composed of nano-sized spinel particles. The relationship between oxygen defects and the capacity fading mechanism was demonstrated, and collapse of the mechanical structure was identified in defect-rich LiMn2O4-δ. Next, the nickel substituted manganospinel, LiNi0.5Mn1.5O4 shows unexpected high voltage side reactions. To overcome this drawback, a thin and chemically inert titanate was used as an artificial SEI (solid electrolyte interface) coating to prohibit transition-metal dissolution and parasitic side reactions, which led to a 200% improvement of the capacity retention at 55°C and negligible polarization losses.

Finally, the spinel-structured lithium titanate (Li4Ti5O12) is introduced as an anode material for lithium-ion batteries due to its higher operating potential and excellent structural stability compared to current graphite anodes. However, the poor electronic conductivity and low lithium diffusion coefficient hinder its wide application. Given these advantages, a facile, low-cost solution method is explored to synthesize nano-sized titanates. Rapid charge/ discharge was achieved up to rates of 100 C (36 second charge/ discharge) due to a shorter lithium mean-free path and better contact between the active material and conductive agents.