Hot pressing and SPS found equally effective for next-gen batteries

Solid-state lithium metal batteries (SSLMBs) are drawing worldwide attention as a next-generation technology that promises higher energy density and greater safety than today's lithium-ion batteries. Among the most promising candidates for their solid electrolytes is the garnet-type oxide Li₇La₃Zr₂O₁₂ (LLZO), which combines high ionic conductivity with strong chemical stability. However, fabricating thin, dense, and defect-free ceramic membranes has long posed a challenge, limiting large-scale application.

Traditionally, oxide solid electrolytes require prolonged high-temperature sintering, often lasting several hours at temperatures above 1000 °C. These conditions lead to lithium evaporation, higher production costs, and poor scalability. To address this, researchers have turned to pressure-assisted sintering techniques such as hot pressing (HP) and spark plasma sintering (SPS). SPS, in particular, has often been believed to offer unique advantages due to a supposed "plasma effect."

Now, a study led by Eric Jianfeng Cheng and Hidemi Kato from Tohoku University, published in Small, has systematically compared HP and SPS in processing LLZO. The results reveal that both methods achieve nearly full densification (~98%) in under five minutes, with no significant differences in ionic conductivity or microstructure. The team confirmed that densification is driven by applied pressure and heat, just as in hot pressing, not by any special "plasma effect."

"Our findings show that SPS is not inherently superior to hot pressing," said Cheng. "This evidence helps both researchers and manufacturers make informed decisions based on cost, equipment, and scalability, rather than on misconceptions."

This finding challenges a widely held assumption in the field and underscores that either HP or SPS can be selected based on cost, equipment availability, and scalability needs. For manufacturers and researchers working to advance SSLMBs, the message is clear: both approaches are equally effective for oxide solid electrolytes like LLZO.

By dispelling the myth of SPS superiority, this study opens the door to more flexible and cost-effective production strategies, accelerating the path toward safer, high-performance solid-state batteries.

About the World Premier International Research Center Initiative (WPI)

The WPI program was launched in 2007 by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

See the latest research news from the centers at the WPI News Portal: www.eurekalert.org/newsportal/WPI

Main WPI program site:  www.jsps.go.jp/english/e-toplevel

Advanced Institute for Materials Research (AIMR)

Tohoku University

Establishing a World-Leading Research Center for Materials Science

AIMR aims to contribute to society through its actions as a world-leading research center for materials science and push the boundaries of research frontiers. To this end, the institute gathers excellent researchers in the fields of physics, chemistry, materials science, engineering, and mathematics and provides a world-class research environment.