Non-flammable liquid electrolytes and solid electrolyte interphases for high-voltage lithium-ion batteries

The rapid and accelerating adoption of lithium-ion batteries worldwide, especially in the transportation sector, has focused attention on their safety. One area of particular interest is finding alternatives for their most flammable component, the liquid electrolyte. Over the past 20 years, a number of non-flammable liquid electrolytes have been identified and tested. However, no proper non-flammable electrolyte has been commercialized yet mainly due to poorer performance. The solid-electrolyte interphase (SEI), a thin interfacial layer at the anode resulting from electrolyte decomposition, is well-known to play an important role in battery performance. Indeed, many of the issues that arise from the use of non-flammable electrolytes are rooted in the SEI properties, which can lead to battery failure. In this thesis project, the SEI is formed in LiNi0.6Mn0.2Co0.2O2 | graphite cells from a state-of-the-art electrolyte (1M LiPF6 in 3:7 v/v mixture of ethylene carbonate and ethyl methyl carbonate) that is offers high performance but is high flammability. Galvanostatic cycling and cell resistance analysis during ageing are used to monitor the performance of the new modified non-flammable electrolytes. Additionally, X-ray photoelectron spectroscopy (XPS) measurements probe the composition of SEIs. Considerable improvements were observed in the stability of cells using the novel electrolytes after pre-formation of the SEI.