In-operando vibrational spectroscopy studies on lithium-sulfur batteries

Rhyz Pereira

doi:10.17918/00010901

The industrialization of the developing world and the continued economic growth of the developed world demands energy sources that are economically viable and do not have adverse environmental consequences. Climate change compels us to turn away from conventional fossil fuel sources to renewables such as solar and wind power which are now being more broadly adopted. To effectively utilize such intermittent sources, energy storage systems need to be deployed at scale. Rechargeable batteries represent the most promising option for this and to date have already established themselves as a key player in the transportation sector and a growing player in the grid storage sector. To date the lithium-ion (Li-ion) battery has offered the highest energy density, and major car manufacturers have manufactured battery electric vehicles using Li-ion batteries. However, this technology is quickly reaching its theoretical limit and the continued electrification of various sectors of the economy demands higher energy densities, lower costs, and more secure supply chains. Among the most promising post-Li-ion chemistry has been lithium-sulfur (Li-S) batteries which offer a theoretical energy density of 2600 Whkg⁻¹, 3-5 times higher than the most advanced Li-ion battery. Sulfur is also one of the most abundant elements in Earth's crust, making it a very attractive material. The Li-S chemistry, however, has several critical issues that must first be resolved before it can fully realize its potential: the polysulfide shuttle effect, the insulating nature of sulfur and lithium sulfide (Li₂S), and stability issues inherent to Li metal anodes. The polysulfide shuttle effect leads to an unstable cathode and low cycle life. The insulating nature of sulfur and Li₂S leads to low active material content and low power densities. The use of Li metal leads to dendrites and dangerous short circuiting and thermal runways. All these issues have prevented widescale commercialization of Li-S batteries. Many materials solutions for this issue are being researched to tackle these problems from additives to physical inhibition to catalysis. However, the fundamental mechanisms governing the effectiveness of these solutions during the charge discharge cycle of a battery are rarely explored. Most solutions are evaluated postmortem and must deal with the inherent pitfalls that come with postmortem evaluations: mechanical damage from deconstructing a battery, reactions of air sensitive materials with air, and the inability to capture time and voltage dependent data. The ideal way to investigate the processes that occur in electrochemical systems and the material solutions developed for them would be to use in-situ and in-operando characterization techniques, that is, observe the cell while it is charging and discharging. In this work I present three powerful in-operando techniques that utilize vibrational spectroscopy to understand the fundamental chemistry occurring in Li-S and Li-metal batteries.

In-operando vibrational spectroscopy studies on lithium-sulfur batteries

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In-operando vibrational spectroscopy studies on lithium-sulfur batteries

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