Porous silicon oxide electrodes advance sustainable energy storage solutions

Tokyo, Japan (SPX) Dec 16, 2024 - Lithium-ion batteries (LIBs) are indispensable in modern devices, from smartphones to electric vehicles and renewable energy systems. Yet, challenges such as limited durability and the use of toxic liquid electrolytes necessitate advancements in battery technology. Aiming to address these issues, researchers have been investigating all-solid-state batteries as a potential alternative for over a decade.

Despite their promise, silicon-based all-solid-state batteries have faced significant hurdles. The repetitive expansion and contraction of the silicon electrode during charge/discharge cycles generates mechanical stress, causing the electrode to crack and detach from the solid electrolyte, leading to a decline in performance.

A research team led by Professor Takayuki Doi of Doshisha University has proposed a potential solution. Their recent study, published in *ACS Applied Materials and Interfaces* on October 29, 2024, examines the introduction of pores into silicon oxide (SiOx) electrodes to mitigate these mechanical stresses. Collaborating with Dr. Kohei Marumoto of Doshisha University and Dr. Kiyotaka Nakano from Hitachi High-Tech Corporation, the team explored the performance of porous SiOx electrodes in all-solid-state cells.

The team fabricated the electrodes using radiofrequency sputtering, incorporating Li-La-Zr-Ta-O (LLZTO) as a solid electrolyte. Advanced scanning electron microscopy revealed that porous SiOx electrodes outperformed their non-porous counterparts during repeated charge/discharge cycles.

"Non-porous SiOx 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," says Dr. Doi. "In contrast, though the initially observed pore structure of porous SiOx 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."

A significant achievement of the research is the ability to fabricate thicker SiOx electrodes. While conventional silicon electrodes require thicknesses below one micrometer to prevent cracking, porous SiOx electrodes achieved stable performance at 5 um. This improvement results in an energy density 17 times higher than that of traditional non-porous silicon electrodes, significantly enhancing space efficiency by enabling greater energy storage per unit volume.

The study emphasizes the broader implications of this innovation. Porous silicon oxide electrodes could pave the way for more efficient and safer all-solid-state batteries, benefiting applications ranging from electric vehicles to large-scale energy storage. "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," adds Dr. Doi.

The findings also highlight areas for further exploration, particularly in optimizing the porous structures of SiOx electrodes to achieve peak performance. This progress represents a significant step toward a sustainable future powered by advanced energy storage technologies.

Research Report:Tailored Design of a Nanoporous Structure Suitable for Thick Si Electrodes on a Stiff Oxide-Based Solid Electrolyte