The Tokyo University of Science has made a significant breakthrough in developing solid-state batteries. In a recent paper published in Materials Today Physics, the researchers have demonstrated unprecedented control over the response speed of these batteries, improving it by two orders of magnitude. This achievement is a significant step towards commercializing all-solid-state batteries with diverse applications, particularly electric vehicles.
Solid-state batteries have been facing a bottleneck in their commercial application due to their low output caused by high surface resistance. The Tokyo University of Science researchers have used a novel technique to investigate and modulate the electric double-layer dynamics at the solid/solid electrolyte interface. The EDL effect, seen in colloidal substances, has been alluded to as the cause of the high surface resistance in these batteries.
Dr Tohru Higuchi, an Associate Professor at Tokyo University of Science, explains that the EDL effect occurs at the solid/solid electrolyte interface and poses a problem in all-solid-state lithium batteries. Dr Higuchi and his colleagues have devised a novel technique to quantitatively evaluate the EDL effect at the solid/solid electrolyte interface to address this issue.
The researchers employed an all-solid-state hydrogen-terminated diamond-based EDL transistor to conduct Hall measurements and pulse response measurements that determined EDL charging characteristics. By inserting a nanometer-thick lithium niobate or lithium phosphate interlayer between the H-diamond and lithium solid electrolyte, the team could investigate the electrical response of the EDL effect at the interface between these two layers.
The electrolyte’s composition did, indeed, influence the EDL effect in a small region around the electrode interface. The EDL effect was reduced when a certain electrolyte was introduced as an interlayer between the electrode/solid electrolyte interface. EDL capacitance for the lithium phosphate/H-diamond interface was much higher than the lithium niobate/H-diamond interface.
The team also explained how they improved the switching response time for charging ASS-EDLs. The EDL has been shown to influence switching properties, so the team considered that the switching response time for charging ASS-EDLs could be greatly improved by controlling the capacitance of the EDL. They used the non-ion-permeable property of diamond in the electron layer of the field-effect transistor and combined it with various lithium conductors. The interlayer accelerated and decelerated the EDL charging speed. The team exhibited control over the EDL charging speed for over two orders of magnitude.
The researchers achieved carrier modulation in all-solid-state devices and improved their charging characteristics. These results are important for improving the interface resistance and may lead to the realization of all solid-state batteries with excellent charge-discharge characteristics in the future. The development of solid-state batteries with these characteristics would have significant implications for the clean energy and carbon neutrality sectors.
While the architecture design of solid-state batteries is not cooperating at present, the problems and challenges are now being defined thanks to the efforts of the Tokyo University of Science researchers. Once these problems are defined and explained, solutions can be worked out. Although solid-state batteries may not be imminent, there is now more confidence that they are inevitable. This is a major stepping stone towards controlling the interface resistance of ASS-LIBs that catalyzes their feasibility for many applications. It will also help design better solid-electrolyte-based devices, including neuromorphic devices.