Unique nanocomposite material key to safer electric vehicle batteries
Reliable battery technology is key for mass market adoption of electric vehicles. However, new classes of solid electrolyte materials are needed to eliminate safety concerns and drive the next generation of rechargeable batteries.
From liquid to solid-state electrolytes
In conventional lithium-ion batteries, an electrolyte solution allows lithium ions to shuttle back and forth between the anode and cathode when the battery is used and when it recharges. Ions are typically moved by a liquid electrolyte. Efforts towards the development of liquid electrolytes have repeatedly foundered on safety concerns. If the organic carbonate that is widely used in lithium-ion batteries leaks out of the battery case, it could easily lead to explosion or fire. These safety concerns have turned the industry’s attention to solid-state batteries, which can be made using inorganic glass-ceramic materials or organic polymers. “Inorganic glass-ceramics demonstrate high ionic conductivities but have rigid interfaces and are brittle,” notes David Mecerreyes, coordinator of the eJUMP project that received funding under the Marie Skłodowska-Curie Actions programme. “Conversely, organic polymers have desirable mechanical properties, but their ionic conductivity falls short of expectations.”
Novel structure combines the best of both worlds
Recently, researchers at the Institute of Frontier Materials at Deakin University in Australia proposed a new class of solid-state, organic electrolytes as a prime candidate for more reliable solid-state batteries. “Organic ionic plastic crystals (OIPCs) are crystalline materials composed of small organic ions with short-range molecular motions. This structure lends 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 importantly, facilitate ion diffusion,” explains Mecerreyes. Their work also showed that this type of electrolytes demonstrates improved mechanical and ion-transport properties in conjunction with polymer fillers. Research on the underlying mechanism of these composite electrolytes is still in its very early stage. “Until now, research has focused on nanocomposite structures consisting of ionic liquids, inorganic nanoparticles and polymers. We were the first to combine ionic plastic crystals with a novel type of polymer nanoparticles for solid-state electrolytes,” notes Mecerreyes. The team synthesised functionalised polymer nanoparticles between 30 and 500 nm in size and with controlled surface chemistries to reinforce OIPCs. After nanoparticle synthesis, researchers focused on the morphological and ion-transport properties.
The prominence of polymer nanoparticles
The use of polymer nanoparticle fillers represents a paradigm shift in composite solid-state electrolytes. Most nanoparticle fillers are usually based on inorganic materials, such as alumina or silica. The surface modification of inorganic nanoparticles is a complex, multistep process. “eJUMP’s approach greatly simplifies the nanoparticle synthesis process; polymerisation in dispersed media is a one-step process and allows controlling not only the nanoparticle size but also the functional groups attached to its surface. In addition, the low density of polymers allows better filler dispersion into the OIPC matrix,” explains Mecerreyes. Recent developments in solid polymer electrolytes are reported here. Another paper outlines how different nanoparticle surfaces affect the thermal behaviour and ion-transport properties of the OIPCs here.
Keywords
eJUMP, batteries, polymer nanoparticles, electric vehicle, solid-state electrolyte, organic polymer electrolytes, organic ionic plastic crystals
