With researchers at the Tokyo Institute of Technology, the Iron and Steel Association (AIST) and Yamagata University launching a strategy to restore their low resistance, all-solid-state batteries are now one step closer to becoming the next generation of main batteries. They also explored potential reduction mechanisms, paving the way for a better understanding of the basic working principles of all-solid-state lithium batteries.
All-solid-state lithium battery has become a new craze in the field of material science and engineering, because traditional lithium-ion batteries can no longer meet advanced technical standards, such as electric vehicles requiring high energy density, fast charging and long cycle life. All-solid-state batteries use solid electrolytes instead of liquid electrolytes in traditional batteries, which not only meet these standards, but also can be fully charged in a short time, so it is relatively safer and more convenient.
However, solid electrolytes have their own challenges. The results show that there is a large resistance at the interface between the positive electrode and the solid electrolyte, and its source is not clear. In addition, when the electrode surface is exposed to air, the resistance increases, and the capacity and performance of the battery decrease. Although scientists have tried many ways to reduce the resistance, they have never been able to reduce the resistance to 10 Ω cm2, which is the interface resistance reported when it is not exposed to air.
Recently, a team of researchers from Japan may have finally found a way to solve these problems, which was published in the journal (ACS Applied Materials & Interfaces of the American Chemical Society Applied Materials and Interfaces. The team was able to identify strategies to effectively restore low interface resistance and reveal the mechanism of resistance reduction, providing valuable insights for the manufacture of high-performance all-solid-state batteries.
First, the team prepared a thin film battery consisting of a lithium negative electrode, a LiCoO2 positive electrode and a Li3PO4 solid electrolyte. Before completing the battery production, the team exposed the surface of LiCoO2 to air, nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2) and water vapor (H2O) for 30 minutes.
To their surprise, they found that the performance of batteries exposed to N2, O2, CO2 and H2 did not decline compared with unexposed batteries. Professor Hitosugi said, "only water vapor can strongly degrade the Li3PO4-LiCoO2 interface and significantly increase its resistance, which is more than 10 times higher than that of the unexposed interface."
The team then carried out a process called annealing, in which the sample was heat-treated in the form of a battery at 150 °C for an hour, depositing negative electrodes. Surprisingly, this reduces the resistance to 10.3 Ω cm2, which is comparable to that of an unexposed battery.
Through numerical simulations and cutting-edge measurements, the team then revealed that the reduction may be attributed to the spontaneous removal of protons from the LiCoO2 structure during annealing. "our research shows that protons in the LiCoO2 structure play an important role in the recovery process," the researchers said. We hope that the elucidation of these interface microscopic processes will help to expand the application potential of all-solid-state batteries. "
