Ionic liquids and organic ionic plastic crystals utilizing small phosphonium cations

Abstract

The development of new liquid and solid state electrolytes is paramount for the advancement of electrochemical devices such as lithium batteries and solar cells. Ionic liquids have shown great promise in both these applications. Here we demonstrate the use of phosphonium cations with small alkyl chain substituents, in combination with a range of different anions, to produce a variety of new halide free ionic liquids that are fluid, conductive and with sufficient thermal stability for a range of electrochemical applications. Walden plot analysis of the new phosphonium ionic liquids shows that these can be classed as ''good'' ionic liquids, with low degrees of ion pairing and/or aggregation, and the lithium deposition and stripping from one of these ionic liquids has been demonstrated. Furthermore, for the first time phosphonium cations have been used to form a range of organic ionic plastic crystals. These materials can show significant ionic conductivity in the solid state and thus are of great interest as potential solid-state electrolyte materials.

Optimising organic ionic plastic crystal electrolyte for all solid-state and higher than ambient temperature lithium batteries

“…The OIPC materials used in this work were prepared and purified according to published methods [14,15]. Differential scanning calorimetry was performed using a TA-Q100 instrument.…”

A novel organosilicon-based ionic plastic crystal as solid-state electrolyte for lithium-ion batteries

“…According to Timmermans (1961)'s criterion, the entropy of fusion for plastic crystal is considered to be <20 J/(mol·K). However, the entropy of melting can be higher for OIPCs because one of its ion species may exhibit rotational motions (Armel et al, 2011). The decreased entropy of LiODFB/[DTMA] [TFSI] suggests that LiODFB might affect the crystallinity of the plastic crystal, probably owing to the formation of solid solutions as observed in LiTFSI-pyrrolidinium family (Forsyth et al, 2000).…”

“…Recently, research on OIPCs mainly has focused on quaternary ammonium cations such as imidazolium, pyrrolidinium Howlett et al, 2011;Horike et al, 2012), and quaternary phosphonium (Armel et al, 2011). There are many studies on the structure and properties of new cations and anions.…”

“…Moriya et al (2014) reported that new OIPCs, which were produced from cyclic perfluorosulfonylamide anion and cyano-substituted quaternary ammonium cations, had a wide plastic crystal temperature range, from about −30 °C to 250 °C. Armel et al (2011) synthesized a range of OIPCs using phosphonium cations for the first time. To use OIPCs as potential solidstate electrolyte materials in lithium-ion batteries, the ionic conductivity and electrode compatibility of these materials have to be improved.…”

Wireless radio frequency detection of greatly simplified polymeric membranes based on a multifunctional ionic liquid

“…Furthermore, the ease of incorporation of IL's into a polymer support (most commonly via in situ polymerisation of the monomer dissolved in the IL [24] or via polymer swelling [25]) provides the basis for both solid state electrolyte [26][27][28] and sensing templates [29].…”