Electrolytes of a room temperature ionic liquid (RTIL), trimethyl(isobutyl)phosphonium (P111i4) bis(fluorosulfonyl)imide (FSI) with a wide range of lithium bis(fluorosulfonyl)imide (LiFSI) salt concentrations (up to 3.8 mol kg(-1) of salt in the RTIL) were characterised using a combination of techniques including viscosity, conductivity, differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), nuclear magnetic resonance (NMR) and cyclic voltammetry (CV). We show that the FSI-based electrolyte containing a high salt concentration (e.g. 1 : 1 salt to IL molar ratio, equivalent to 3.2 mol kg(-1) of LiFSI) displays unusual transport behavior with respect to lithium ion mobility and promising electrochemical behavior, despite an increase in viscosity. These electrolytes could compete with the more traditionally studied nitrogen-based ionic liquids (ILs) in lithium battery applications.

computers and power tools, and emergent energy storage solutions for transport or for storing renewable energy in an ever-evolving 'smart grid'. Each of these products requires diverse battery technologies, with many batteries well-suited for specific cases, e.g., Li-ion batteries for the electrification of vehicles due to their light weight and therefore intrinsic energy density (typically 100-265 Wh kg −1 ). In fact, the adoption and penetration of electric vehicles (EVs) in the transport market is quickly becoming synonymous with battery research, with advanced lithium technologies such as lithium-sulfur (Li-S) and lithium-oxygen (Li-O 2 ) envisaged as the next generation of batteries to power our vehicles (theoretical energy densities of 2567 and 3505 Wh kg −1 respectively). [3] Lithium technologies power many of our modern devices and so are well understood, however sodium chemistries share commonalities. They are also well known because both Li and Na batteries were investigated in tandem near the end of the last century prior to the commercialization of Li-ion by Sony. [2,4] In fact, Sodium battery energy storage systems (ESS) precede Li-ion, with the description of a β-Al 2 O 3 Na + ion conducting solid electrolyte in the 1960s by Kummer and Weber of Ford Motor Co which enabled sodium/sulfur technologies. [5] Since then, sodium technologies have found use in stationary applications and usually consist of one of two battery technologies, these are Na-S and zero emission battery research activities. [6] Both these cell chemistries require operation at elevated temperatures (≈300 °C) which enables the use of a molten sodium Electrolytes composed entirely of salts, namely, ionic liquid solvents paired with a target ion salt, have been studied extensively within lithium batteries and have recently garnered interest as advanced electrolytes for sodium chemistries. In this review, the unique properties of ionic liquid electrolytes and their solid-state analogs, organic ionic plastic crystals, are examined. Structure-property relationships, the effect of salt addition, cation and anion functionalization, and their effect upon physicochemical and thermal character are discussed. The authors discuss the use of ionic liquid electrolytes paired with organic solvents (referred to as hybrids) and briefly present the impact of using water as an additive. The majority of the literature presented herein covers studies of sodium electrolytes at Na + concentrations greater than 50 mol%, labelled as superconcentrated electrolytes, which have recently been investigated for their beneficial device performance and improved target ion mobility. The developing research of ionic liquids toward the oxygen reduction reaction is also presented toward the realization of Na-O 2 chemistries to rival that of conventional Li-ion; gaining fundamental understanding of the active species during discharge, its resultant nucleation and character. Additionally, the properties of the electrode-electrolyte interface resulting from the interaction...

We describe the direct electro-chemical reduction of graphene oxide to graphene from aqueous suspension by applying reduction voltages exceeding -1.0 to -1.2 V. The conductivity of the deposition medium is of crucial importance and only values between 4-25 mS cm(-1) result in deposition. Above 25 mS cm(-1) the suspension de-stabilises while conductivities below 4 mS cm(-1) do not show a measurable deposition rate. Furthermore, we show that deposition can be carried out over a wide pH region ranging from 1.5 to 12.5. The electro-deposition process is characterised in terms of electro-chemical methods including cyclic voltammetry, quartz crystal microbalance, impedance spectroscopy, constant amperometry and potentiometric titrations, while the deposits are analysed via Raman spectroscopy, infra-red spectroscopy, X-ray photoelectron spectroscopy and X-ray diffractometry. The determined oxygen contents are similar to those of chemically reduced graphene oxide, and the conductivity of the deposits was found to be ∼20 S cm(-1).

The chemical composition of the solid electrolyte interphase (SEI) layer formed on the surface of lithium metal electrodes cycled in phosphonium bis(fluorosulfonyl)imide ionic liquid (IL) electrolytes are characterized by magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray photoelectron spectroscopy (XPS), fourier transformed infrared spectroscopy, and electrochemical impedance spectroscopy. A multiphase layered structure is revealed, which is shown to remain relatively unchanged during extended cycling (up to 250 cycles at 1.5 mA·cm, 3 mA h·cm, 50 °C). The main components detected by MAS NMR and XPS after several hundreds of cycles are LiF and breakdown products from the bis(fluorosulfonyl)imide anion including LiS. Similarities in chemical composition are observed in the case of the dilute (0.5 mol·kg of Li salt in IL) and the highly concentrated (3.8 mol·kg of Li salt in IL) electrolyte during cycling. The concentrated system is found to promote the formation of a thicker and more uniform SEI with larger amounts of reduced species from the anion. These SEI features are thought to facilitate more stable and efficient Li cycling and a reduced tendency for dendrite formation.

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