Advancements in All-Solid-State Battery Research

A study published in ACS Applied Materials & Interfaces, led by Professor Takayuki Doi from Doshisha University, explored a potential approach for advancing all-solid-state batteries.

Batteries are integral to modern electronics, with lithium-ion batteries (LIBs) powering devices ranging from small electronics and electric vehicles to large-scale renewable energy storage systems. However, LIBs face significant limitations, including limited durability and the use of hazardous liquid electrolytes.

For over a decade, researchers have been investigating all-solid-state batteries as a way to address these challenges. While silicon-based all-solid-state batteries offer theoretical advantages over traditional LIBs, significant obstacles remain.

One major issue is the repeated expansion and contraction of the silicon (Si) negative electrode during charge and discharge cycles. This mechanical stress weakens the interface between the electrode and the rigid solid electrolyte, eventually causing the electrode to crack, detach, and experience a permanent loss of performance.

The researchers investigated whether introducing pores to a silicon oxide (SiO_x) electrode could mitigate cracking and peeling caused by the expansion and contraction of silicon electrodes. The study was conducted in collaboration with Dr. Kiyotaka Nakano of Hitachi High-Tech Corporation and Dr. Kohei Marumoto of Doshisha University in Japan.

To test this approach, the team used radiofrequency sputtering to fabricate porous SiO_x electrodes. It incorporated them into all-solid-state cells with Li-La-Zr-Ta-O (LLZTO) as the solid electrolyte. Advanced scanning electron microscopy was used to analyze the pore structures in detail and evaluate their impact on cell performance over multiple charge/discharge cycles.

The results showed that highly porous SiO_x electrodes significantly outperformed their non-porous counterparts, which exhibited a marked reduction in capacity after cycling. Microscopy observations provided clear insights into the nanoscale processes influencing this improvement.

Non-porous SiO_x partially exfoliated from the LLZTO electrolyte by the 20th cycle, which was consistent with the drastic decline in capacity and rise in internal resistance we observed. In contrast, though the initially observed pore structure of porous SiO_x collapsed through repeated expansion and contraction, the remaining pores still served as a buffer against the internal and interfacial stresses. This ultimately helped maintain the interfacial joint between the electrode and the electrolyte.

Takayuki Doi, Professor, Doshisha University

A key limitation of both Si and SiO_x electrodes in all-solid-state batteries is that their thickness must be kept below one micron to prevent cracking and exfoliation. However, introducing pores into SiO_x enabled stable charge-discharge cycles even in films as thick as 5 µm, significantly enhancing space efficiency by increasing the energy stored per unit volume.

Dr. Doi added, “The thicker SiO_x films we achieved resulted in an energy density of the negative electrode approximately 17 times higher than that of conventional non-porous silicon electrodes.”

The study highlights how porous architectures can optimize the performance of all-solid-state batteries. These advancements hold promise for applications in residential and industrial-scale energy generation, potentially playing a vital role in supporting sustainable societies. Additionally, the improved safety and extended lifespan of all-solid-state batteries could make electric vehicles a more attractive option for consumers.

“We expect the results of our research to make a multifaceted contribution towards sustainable development goals, not only in terms of climate change countermeasures based on the reduction of carbon emissions but also in terms of economic growth and urban development,” Dr. Doi concluded.

Further research is needed to fine-tune the porous structure of SiO_x electrodes to maximize their performance in all-solid-state batteries. Continued exploration in this field could pave the way for a significant breakthrough in energy storage technology.

The study was funded by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) 22H04624 and the Grant-in-Aid for Scientific Research on Innovation Areas “Interface Ionics.”

Journal Reference:

Marumoto, K., et. al. (2024) Tailored Design of a Nanoporous Structure Suitable for Thick Si Electrodes on a Stiff Oxide-Based Solid Electrolyte. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.4c15894