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Researchers find annealing significantly reduces interface resistance in all-solid-state-batteries

All-solid-state lithium batteries could address a number of the shortcomings of conventional lithium-ion batteries in advanced applications such as in electric vehicles, which demand high energy densities, fast charging, and long cycle lives. However, the solid electrolyte comes with its own challenge; the interface between the positive electrode and solid electrolyte shows a large electrical resistance whose origin is not well understood.

Furthermore, the resistance increases when the electrode surface is exposed to air, degrading the battery capacity and performance. While several attempts have been made to lower the resistance, none have managed to bring it down to 10 Ω cm2—the reported interface resistance value when not exposed to air.

Now, in an open-access paper published in ACS Applied Materials & Interfaces, a research team led by Prof. Taro Hitosugi from Tokyo Institute of Technology (Tokyo Tech) and Shigeru Kobayashi demonstrates that drastic reduction of the resistance is achievable by annealing the entire battery cell.

Exposing the LiCoO2 positive electrode surface to H2O vapor increases the resistance by more than 10 times (to greater than 136 Ω cm2). The magnitude can be reduced to the initial value (10.3 Ω cm2) by annealing the sample in a battery form. First-principles calculations reveal that the protons incorporated into the LiCoO2 structure are spontaneously deintercalated during annealing to restore the low-resistance interface. These results provide fundamental insights into the fabrication of high-performance all-solid-state Li batteries.

—Kobayashi et al.


The team prepared thin film batteries comprising a lithium negative electrode, an LiCoO2 positive electrode, and an Li3PO4 solid electrolyte. Before completing the fabrication of 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 researchers 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 Prof. Hitosugi.

The team next heated the sample at 150°C for an hour in battery form i.e. with the negative electrode deposited. This reduced the resistance down to 10.3 Ω cm2, comparable to that of the unexposed battery.

By performing numerical simulations and advanced measurements, the team then found that the reduction could be attributed to the spontaneous removal of protons from within the LiCoO2 structure during annealing.

The study was the result of a joint research by Tokyo Tech, National Institute of Advanced Industrial Science and Technology (AIST), and Yamagata University.


  • Shigeru Kobayashi, Elvis F. Arguelles, Tetsuroh Shirasawa, Shusuke Kasamatsu, Koji Shimizu, Kazunori Nishio, Yuki Watanabe, Yusuke Kubota, Ryota Shimizu, Satoshi Watanabe, and Taro Hitosugi (2022) “Drastic Reduction of the Solid Electrolyte–Electrode Interface Resistance via Annealing in Battery Form” ACS Applied Materials & Interfaces doi: 10.1021/acsami.1c17945



Having taken note of the pros and cons in this post mainly concerning SSBs in general and in particular to those in this post, I decided to make a reference to Quantumscape's (QS) technology platform. I'm convinced that currently, QS is the leading contender of SSBs. Also, with their latest achievement of packaging 10 cells successfully it is only a matter of time until they can manage to pack multiple combinations of these e. g. 20, 30, 40 etc.. IMO, the most intriguing attributes of QS are the solid electrolyte and the anode-less architecture of the copper electrode constituting the the solid metal anode once fully charged.
If I have interpreted the post of QS correctly, then any viable metal chemistry should be able to be implemented into QS's technology platform enabling greater energy density and enhancing some other features e.g. cycle life, temperature consistency etc. . Why keep on inventing the wheel again and again once it has been optimized.?


anode-less architecture
The ceramic stops the dendrites


If QS would coat their copper electrode with a layer of graphene, that would likely enhance quicker and more evenly deposition of the Li metal anode and prevent growth of dendrites . Graphene is no longer expensive to produce since the discovery of its cheap production.
Graphene is not only an excellent current conductor , it is also the best heat conductor currently known. Such a Graphene-layer on the copper electrode would enable even faster charging without detrimental heat occurrence.


Kevlar stops dendrites

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