As the world embraces renewable energy and the electric vehicle revolution, the demand for high-performance, all-solid-state batteries has skyrocketed. Researchers at Sophia University in Japan have leveraged material informatics to explore a promising solution: organic ionic plastic crystals (OIPCs). These materials offer exceptional ionic conductivity, stability, and safety, paving the way for the next generation of rechargeable batteries that could boost the range of electric vehicles and promote their widespread adoption.
Revolutionizing Rechargeable Batteries with OIPCs
The sharp growth of renewable energy and the electric vehicle market is spurring demand for next-generation, high-performance all-solid-state batteries. Solid-state batteries have a number of advantages over traditional liquid electrolyte-based batteries, such as higher energy density, increased safety, longer life, and reliable operation over a broad temperature range.
However, the commercial presence of solid-state batteries has not yet picked up due to numerous hurdles including low ionic conductivity and interfacial resistance and the very existence of particle-particle interfaces within the electrolyte that may further increase resistance and consequently decrease energy density. In this review, the focus has been given to inorganic and organic solid electrolytes because these are two categories that have been highly researched so far along with their advantages and disadvantages are also discussed.
The research team at Sophia University started examining the organic ionic plastic crystals (OIPCs) to counter these grievances Solid electrolytes based on these materials, composed of organic cation and appropriate inorganic anion, together with a lithium salt of the same anion, exhibit high ionic conductivities along with good stability and no fire hazard.
Harnessing Material Informatics to Unlock OIPC Potential
The researchers used material informatics (MI) to investigate the design of highly conductive OIPCs. In a broader sense, MI also uses information science, in particular statistics and machine learning to assist the development of materials.
We trained the MI model based on a training dataset of {[chemical structures],[ OIPC conductivity]} collected from available literature, and validated the model prediction accuracy for two compound tests. The validation results support this by showing that the prediction accuracy is enhanced when the training data is closely related to chemical structures (9). With that insight in mind, the researchers chose pyrrolidinium cations as their candidate molecules, since they were prominently featured in the training data.
In addition, by using empirical knowledge gained from previous studies of pyrrolidinium cation-based OIPCs concerning improving ionic conductivity such as MI, researchers narrowed down candidate compounds (see Fig. The team, therefore, successfully synthesized eight new compounds (Six OIPCs and two ionic liquids). One of them showed excellent ionic conductivities at 25 °C, reaching up to 1.75 × 10−4 S cm−1, which is among the highest values ever reported[].
Unlocking New Insights and Future Potential
The MI model has succeeded in obtaining a high-performance OIPC and uncovered novel knowledge regarding the relationship between ionic radius and ionic conductivity. Empirical rules that have been developed over the past decades indicate that a small ionic radius: ionic conductivity ratio is favorable; however, the new molecules show that some value is optimal.
Furthermore, the MI model predicted steps in the OIPC organization as well as a sharp transition line indicating that higher accuracy may also lead to predicting phase transitions of OIPCs. Taken together, these results showcase the promise of MI for gaining insight into OIPCs and providing guidelines for designing safe, high-performance, and new-generation rechargeable batteries.
Feasible high-performance solid electrolytes (e.g., the OIPCs studied in this work) will contribute to realizing high-safety rechargeable batteries without using liquid cells. Additionally, these improvements will mean higher energy density in batteries, which will make battery-equipped devices smaller and lighter. This might, for example, greatly extend the cars of the future, making electric cars add up to the more commonplace and requiring an additional traditional sustainable energy generation for further widespread use.
