Professor Taro Ichisugi of Tokyo Institute of Technology and his colleagues, in collaboration with Assistant Professor Hideyuki Kawashita of Tohoku University and Professor Masaru Shiraki of Nippon Institute of Technology, have achieved extremely low interfacial resistance with a high-output all-solid-state battery, and achieved ultra-high-speed charging and discharging. The demonstration was successful.
At present, high-power all-solid-state batteries that generate a higher voltage than ordinary lithium-ion batteries are attracting attention.One of the challenges for practical use is to reduce the resistance of lithium ions at the interface formed by the electrode that generates a high voltage and the solid electrolyte, but there is no clear measure for reducing the interface resistance, and its feasibility is unclear.
The research group uses thin film fabrication technology and an ultra-high vacuum process to fabricate an ideal all-solid-state battery using an electrode material that generates a high voltage of about 5 V.As a result of evaluating the ionic conductivity at the interface between the solid electrolyte and the electrode, the interface resistance was an extremely low value of 7.6 Ωcm2.This is about two orders of magnitude lower than that reported with conventional all-solid-state batteries, and about one order of magnitude lower than that with liquid electrolytes.Furthermore, the activation energy showed a low value (about 2 eV) similar to that of the superionic conductor.
In order to find the stability of such a low resistance interface, we conducted a charge / discharge test and succeeded in stable high-speed charge / discharge even with a large current (14 mA / cm2). No change in battery capacity was observed after 100 ultra-high-speed charges and discharges, demonstrating that the interface between the solid electrolyte and the electrode is stable against the high-speed movement of lithium ions.In addition, as a result of structural analysis of the all-solid-state battery, it was clarified that lithium ions spontaneously move from the solid electrolyte to the electrode immediately after forming the interface between the solid electrolyte and the electrode.
It is expected that this achievement will not only be an important step toward the practical application of high-power all-solid-state batteries, but will also lead to the establishment of the theory of ion transport at the interface between the solid electrolyte and the electrode.
Paper information:[ACS Applied Materials and Interfaces] Extremely low resistance of Li3PO4 electrolyte / Li (Ni0.5Mn1.5) O4 electrode interfaces
