Fluorine-Free Ionic Liquids and Electrolytes : From Synthesis to Energy Storage Applications

• Since their introduction by Sony in 1990, lithium-ion batteries (LIBs) have acquired a sizable market share. They have the best energy densities, a high open circuit voltage, a low self-discharge rate, no memory effect, and a slow loss of charge when not in use. These properties make them the most popular rechargeable batteries for portable gadgets, electric vehicles and aerospace applications. They do, however, pose major safety issues since the conventional electrolytes are made of fluorinated salts dissolved in volatile organic solvents, the former being meta-stable at ambient temperature and the latter being flammable with a high vapour pressure. Thus, there is an urge to develop thermally and electrochemically stable non-fluorinated electrolytes to improve the safety and performance of batteries. Electrolytes based on ionic liquids (ILs) offer a range of advantages over traditional electrolytes including low volatility and high thermal and electrochemical stabilities, and can additionally be made fluorine-free and task-specific. In addition, the transport properties of ILs can be controlled by structural design of chemical functionalities to reduce the ionic interactions and enhance the ion mobilities.This thesis is focussed on the development of new fluorine-free ILs and electrolytes for safer energy storage applications. An overview of synthesis, physicochemical and electrochemical characterizations of six different families of ILs and their structurally analogous electrolytes based on the aromatic heterocyclic rings, oligoether based aromatic and aliphatic carboxylates, oligoether phosphates and aromatic sulfonyl anions coupled with n- tetrabutylphosphonium-, imidazolium-, pyrrolidinium-based and alkali metal cations is presented. The structures and purity of the new anions, their intermediate products and the ILs are characterized by using multinuclear NMR, FTIR and mass spectrometry. These studies are further complemented by using NMR diffusometry to investigate the relative anion and anion mobilities and understand the possible interaction mechanisms between the oppositely charged ions within the ILs and the electrolytes, and especially, the influence of Li+ addition in the IL-based electrolytes. Among the synthesized ILs, the sulfonyl-based ILs revealed highest thermal stabilities, aromatic oligoether-based ILs showed the best electrochemical stabilities and aromatic sulfonyl -based ILs exhibited highest ionic conductivities. Some of the synthesized salts displayed promising performance as electrolytes in energy storage devices.

Ämnesord

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

Nyckelord

Ionic Liquids

Electrolytes

Sustainability

Lithium ion batteries

Flourine-Free

Chemistry of Interfaces

Gränsytors kemi

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