Researchers in Japan have established a strategy for restoring the low interface resistance in all-solid-state batteries that could bring the next-generation lithium-ion technology to wider commercial adoption.
By establishing a strategy for restoring the low interface resistance as well as unravelling the mechanism underlying this reduction, the team has provided valuable insights into the manufacturing of high-performance all-solid-state batteries.
A stumbling block to full commercialisation has previously been the failure to lower the electrical resistance to 10 Ω cm2 (ohm centimeter-squared), the reported interface resistance value when not exposed to air.
The challenge is the interface between the positive electrode and solid electrolyte shows a large resistance, which increases when the electrode surface is exposed to air, degrading the battery capacity and performance.
That may have changed thanks to the research team led by professor Taro Hitosugi from Tokyo Institute of Technology (pictured), and Shigeru Kobayashi, a doctoral student at Tokyo Tech.
The study was published in the peer-reviewed journal ACS Applied Materials & Interfaces.
The study is the result of a joint research by Tokyo Tech, National Institute of Advanced Industrial Science and Technology (AIST), and Yamagata University.
The team prepared thin film batteries comprising a lithium negative electrode, an LiCoO2 positive electrode, and an Li3PO4 solid electrolyte.
Before building a battery, the team exposed the LiCoO2 surface to air, nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and water vapor (H2O) for 30 minutes.
The team found that exposure to N2, O2, CO2, and H2, did not degrade the battery performance compared to a non-exposed battery.
Only H2O vapor strongly degrades the Li3PO4 – LiCoO2 interface and increases its resistance drastically to a value more than 10 times higher than that of the unexposed interface, said Hitosugi.
The next step included annealing, in which the sample underwent a heat treatment at 150°C for an hour in battery form, which reduced the resistance to 10.3 Ω cm2.
By performing numerical simulations and measurements, the team revealed the reduction could be attributed to the spontaneous removal of protons from within the LiCoO2 structure during annealing.
Hitosugi said: “Our study shows that protons in the LiCoO2 structure play an important role in the recovery process. We hope that the elucidation of these interfacial microscopic processes would help widen the application potential of all-solid-state batteries.”