Energy storage devices are essential to our utilisation of renewable energy and reduction in greenhouse gas emissions. Li-ion batteries face critical safety challenges as flammable electrolytes are employed, and they have low energy density than lithium metal batteries, meaning the technology is not viable for widespread use of electric vehicles (EVs) or for large-scale energy storage. Room temperature ionic liquids (RTILs), often referred to as ‘designer’ solvents, have received substantial attention as electrolytes for lithium batteries due to their intrinsic properties such as low volatility and non-flammability, as well as the flexibility in cation and anion structures that can lead to wide electrochemical windows, wide liquid range, good thermal stability and inertness with other battery materials. However, they suffer from high viscosity compared to organic solvents, leading to poor mass transport.
Organic ionic plastic crystals (OIPCs), considered the solid-state cousins of RTILs, are also gaining popularity for use as solid-state electrolytes that have excellent thermal properties and reduced risk of leakage from batteries. OIPCs are more likely to be formed with small cations. For both OIPCs and ILs, the nature of the cation and anion is important in determining their chemical and physical properties and thus varying these structures is a powerful tool for improving their electrochemical performance.
Working in collaboration with Boron Molecular, a specialist in chemical manufacturing for energy materials, we are exploring synthesis of small organic cations with oxygen functionality, paired with different anions to form new OIPCs with improved conductivity, and new RTILs with lower viscosity. Following on from this, the most promising new materials will be scaled-up for commercialisation.