ALBERTO V. PUGA
Instituto de Tecnología Química (UPV-CSIC), avenida de los Naranjos, 46022, Valencia, SpainFormer address: The QUILL Research Centre, School of Chemistry and Chemical Engineering, the Queen’s University of BelfastStranmillis Road, Belfast BT9 5AG, United Kingdom

Abstract

Ionic liquids are reasonable alternatives to electrolytes used in energy storage devices, such as lithium batteries, both lithium-ion and lithium-metal, given the safety advantages they provide. This is due to the favourable properties they often possess, mainly non­flammability and non­volatility. Candidates with alicyclic ammonium cations exhibit high electrochemical stabilities, especially towards lithium, a unique feature which enables the fabrication of reversible lithium-metal batteries. Recent advances in this field are reviewed herein, with emphasis on two new families of ionic liquids, based on either azepanium or 3­methylpiperidinium cations, and having potential windows around or above 6 V.

THE RELEVANCE OF LITHIUM BATTERIES

During the past twenty years, advances in lithium battery technologies have boosted the sector of portable electronic devices (1-3). Currently, devices such as laptop computers, mobile phones, photographic cameras, audio players or electric tools are widely used on a daily basis. The lithium battery market is rapidly growing and an annual global production in excess of several thousand million units has been estimated (3). Therefore, lithium cell technologies are at a certainly advanced stage, at least for relatively small devices.
In brief, batteries are devices composed of one or more electrochemical cells which store electricity as chemical energy. Each of these electrochemical cells consists of a negative electrode (anode) and a positive electrode (cathode) internally connected by an electrolyte through which ions are transported, whereas the generated electric current flows externally through a conducting material. Battery voltage (E) is defined by convention (4) as the difference between the potentials of the positive and negative terminals, (E₊ and E₋, respectively); these are in t ...