All solid state batteries replace conventional flammable liquid electrolytes with solid electrolytes, improving intrinsic safety in applications such as electric vehicles and grid scale energy storage systems. Oxide based systems have attracted interest because they offer high energy density and avoid the toxic gas generation issues associated with sulfide based solid electrolytes.
Garnet type oxide solid electrolytes combine high ionic conductivity with strong chemical stability, but producing dense, defect free membranes typically requires sintering at temperatures above 1,000 C. Under these conditions lithium, an essential constituent of the electrolyte, tends to evaporate during firing, degrading structural integrity, reducing ionic conductivity and increasing interfacial resistance, especially in larger area membranes.
To limit lithium loss, manufacturers have relied on a sintering approach that buries the electrolyte membrane in a large quantity of lithium containing mother powder. This sacrificial material helps maintain lithium activity during sintering but results in more than ten times the amount of mother powder being discarded compared to the mass of usable electrolyte, sharply increasing production costs and hindering large scale adoption.
The KRISS Emerging Material Metrology Group has developed a different approach that coats garnet type solid electrolyte powders with lithium aluminum oxide (Li Al O) based multifunctional compounds before sintering. This thin surface coating supplies lithium locally during high temperature processing and acts as a barrier to lithium evaporation from the membrane.
The coating also promotes a soldering like effect at particle contacts, enhancing interparticle bonding and driving higher densification during sintering. Using this method, the team reports solid electrolyte membranes with a relative density above 98.2 percent without the use of expensive mother powder, producing high strength structures with minimal chemical or mechanical defects.
Ion transport performance improved significantly, with ionic conductivity more than doubling compared to conventionally processed garnet electrolytes. At the same time, electronic conductivity dropped by more than a factor of 20, reducing parasitic internal current leakage and further improving both efficiency and safety in all solid state cell designs that use these membranes.
The process also supports larger format manufacturing. The researchers fabricated solid electrolyte membranes with an area of 16 square centimeters, more than ten times the area of standard laboratory pellets, while achieving a reported yield of 99.9 percent. The combination of high density, large area scalability and very low scrap rates addresses long standing barriers to industrial production.
Dr. Baek Seung Wook, Principal Research Scientist in the Emerging Material Metrology Group at KRISS, said the work resolves materials and process challenges that have persisted for over two decades in garnet solid electrolyte research. He stated that by sharply cutting production costs, the new process is expected to accelerate commercialization of oxide based all solid state batteries and support innovation in energy storage and electric vehicle markets.
Postdoctoral researcher Dr. Kim Hwa Jung noted that Korea currently imports all garnet type solid electrolyte pellets at a unit cost exceeding 550 US dollars for discs with a diameter of only 1 centimeter. The ability to produce high value solid electrolyte membranes domestically using a mother powder free process is expected to strengthen the local supply chain for next generation battery materials.
The research was carried out in collaboration with Professor Park Hyeokjun and colleagues in the Department of Materials Science and Engineering at Korea University. The project received support from the Ministry of Science and ICT and the National Research Foundation of Korea through the Nano and Materials Technology Development Program.
According to KRISS, the results appear in the January issue of the journal Materials Today, which reports an impact factor of 22.0 and a Journal Citation Reports ranking in the top 3.5 percent of its field. The paper is titled "Revitalizing multifunctionality of Li Al O system enabling mother powder free sintering of garnet type solid electrolytes" and documents the development and performance of the coated powder process.
Research Report: Revitalizing multifunctionality of Li Al O system enabling mother powder free sintering of garnet type solid electrolytes
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Korea Research Institute of Standards and Science
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