Rechargeable batteries allow electric energy from intermittent renewable energy sources – such as wind and solar - to be stored until needed. However, important safety concerns limit large-scale use of batteries for electric vehicles and stationary needs. New electrolyte materials with improved safety are needed to enable the next-generation of rechargeable batteries. Electrolytes play the role of conducting ions inside the battery to support the redox reactions at the electrodes. Commercial electrolytes for lithium-ion batteries are based on liquid organic carbonates due to their high ionic conductivity and good wettability with electrodes. Nevertheless, organic carbonates are highly flammable, dry out quickly and can leak out of the battery case. Solid electrolytes have been proposed as an alternative to conventional liquid electrolytes because of their intrinsic safety features. Until now, two main families of materials have been intensively investigated (Figure 1). Inorganic Glass-Ceramics exhibit high ionic conductivities (>1 mS cm-1 for some systems), but with the considerable disadvantage of their rigid interfaces and brittle material properties. On the other hand, Ion-Conductive Polymers show desirable mechanical properties but their ionic conductivity falls short of expectations (<0.1 mS cm-1 for most systems). Recently, a new class of solid electrolytes was proposed by Prof. Maria Forsyth and Prof. Douglas MacFarlane at the Australian ARC Center for Electromaterials Science (ACES). Organic Ionic Plastic Crystals (OIPCs) are crystalline materials entirely composed of small organic ions with short-range molecular motions. This structural feature gives OIPCs several unique properties such as multiple solid-solid phase transitions and plastic mechanical properties, which can greatly improve the interfacial contact with electrodes and - most importantly - facilitate ion diffusion. However, the development of OIPCs as solid electrolytes for rechargeable batteries is still in the early stages. Recent works in Prof. Forsyth’s group showed that composite electrolytes with significantly improved mechanical and ion-transport properties are obtained when OIPCs are combined with polymer fillers. These preliminary studies suggest that chemistry, aspect ratio and size of the fillers affect the structural features of OIPCs matrices at the interface with the polymer. However, a complete understanding of these composite electrolytes is still lacking. The eJUMP action goal is to develop innovative nanocomposites from OIPCs and polymer nanoparticles – which can act both as reinforcement but also add function via a purposely designed nanoparticle interfaces. The fundamental knowledge generated by eJUMP will help to establish specific design criteria for the fabrication of nanocomposite OIPC electrolytes with enhanced safety characteristic and competitive performances with respect to conventional liquid electrolytes.
The specific research objectives of the outgoing stage at ACES are:
1. To synthesize functionalized polymer nanoparticles of sizes between 30-500 nm and controlled surface chemistries as reinforcements for OIPCs nanocomposites,
2. To develop innovative OIPC nanocomposites using the functionalized polymer nanoparticles and last generation OIPCs,
3. To characterize mechanical, thermal and electrochemical properties of the OIPC nanocomposites,
4. To understand ion-transport phenomena in nanocomposite electrolytes using state-of-art characterization methods,
5. To test the most promising materials in sodium/lithium rechargeable battery prototypes.
