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 Li?La?Zr?O?? (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.

Publication Details:

Title: High‐Temperature Sintering of Garnet Solid Electrolyte Li?La?Zr?O??: A Comparative Study of Induction Hot Pressing and Spark Plasma Sintering
Authors: Mikihisa Fukuda, Ying Li, Jing Wei, Koichi Harata, Guoqiang Luo, G. Jeffrey Snyder, Yutaka S. Sato, Hidemi Kato, Eric Jianfeng Cheng
Journal: Small
DOI: 10.1002/smll.202506257