State-Independent Electrolytes for Energy Storage and Spin Wave Interference-Based Reservoir Computing

Liquids lend themselves to high ionic conductivities because of the inherent positional and orientational disorder of their constituent molecules, which enables the free movement of ions. Currently, however, there are no general strategies to avoid steep drops in ionic conductivity upon phase transitions from a liquid state to the more ordered solid state. This project will develop new organic materials that overcome this fundamental hurdle in materials design by developing organic salts that maintain the same ionic conductivity mechanism across transitions between three states of matter—from isotropic liquid to liquid crystal, then crystalline solid. This unprecedented property of 'state-independent ionic conductivity' (SIIC) in organic materials will be engineered by designing organic salts that (1) minimise the ion-pairing interactions between mobile ions and highly diffuse counterions, and (2) assemble in a stepwise manner to preserve conformational flexibility across phase transitions. Exciting prelimary data using new materials based on triarylcyclopropeniums show that SIIC can indeed be achieved. The ionic conductivity brought about by movement of the halide counterions in these 'state-independent electrolytes' (SIEs) is unaffected by phase transitions. The proposed research will extend the scope of the materials that exhibit this property by designing and synthesising new organic salts that meet criteria (1) and (2) above. In so doing, we will refine our understanding of the structural features necessary for SIIC. We will also be able to optimise physical properties, overcoming the shortcomings of the first-generation SIEs, such as their low absolute values of ionic conductivity, the relatively narrow phase-transition temperature ranges in which the materials can be processed in the solid or liquid state, and improving their stability towards degradation. Concurrently, as these new SIEs are prepared, we will assess their suitability for applications in electronic devices, using the performance of prototypical devices to guide further materials development by optimising the SIE structures. We will investigate SIEs in the contexts of energy storage (batteries), acting as a unique solid-state organic electrolyte that can be processed and assembled as in the liquid state, before being operated as a solid, then if desired, recovered from the device and recycled as a liquid. By doing so, we can take advantage of the improved safety and thermal cycling of solid state materials, while also benefitting from the easier handling and recovery of liquids, as well as the better interfacial contacts liquids form with electrodes, getting the best of both worlds. Working with team members at the National Institute of Materials Science, Japan, we will also develop SIEs bearing paramagnetic ions as the mobile component of the salts to investigate their performance in computer memory devices. We hypothesise that SIEs will improve the performance of reservoir computing devices, which utilise the chaotic interference of spin waves inside ferromagnetic thin films as a form of memory. Reservoir computing devices of this kind require far less energy to operate than current computer memory technologies, but the materials used to prepare them until now fail to give devices with sufficiate accuracy or storage density to compete with other technologies. Adding thin-film coatings of magnetic SIEs to the ferromagnetic reservoir computing devices will allow us to fine-tune and optimise the magnetic properties of the ferromagnet to overcome these drawbacks.