A Swiss research team has developed a low-temperature sintering and interface coating process that significantly improves the durability of argyrodite-based solid-state batteries. The approach delivers high ionic conductivity and long life, with 75% of capacity retained after 1,500 cycles.
A research team from Switzerland’s Paul Scherrer Institute (PSI) has developed a new approach to improve the stability and longevity of all-solid-state batteries (ASSBs). The work focuses on the argyrodite-type solid electrolyte Li₆PS₅Cl (LPSCl), which is widely considered one of the most promising materials for sulfide-based solid-state batteries.
The researchers combined a new sintering technique with the application of an ultra-thin passivation layer to both densify the electrolyte and stabilize the interface with lithium metal.
“We combined two approaches that together densify the electrolyte and stabilize the interface with the lithium,” said corresponding author Mario El Kazzi in a statement. “Our approach is a practical solution for the industrial production of argyrodite-based, all-solid-state batteries. With a few more adjustments, it could be ready for production.”
According to lead author Jinsong Zhang, the optimized battery cell showed strong electrochemical performance. During testing, the cell retained approximately 75% of its initial capacity after 1,500 charge-discharge cycles. “The cycle stability at high voltage was remarkable,” said Zhang. “These values are among the best reported to date.”
LPSCl is a solid sulfide electrolyte consisting of lithium, phosphorus and sulfur. Despite its high ionic conductivity, its commercial development is limited by the difficulty in achieving sufficient densification to prevent the formation of voids that can be penetrated by lithium dendrites.
Previous studies relied on very high pressure at room temperature or a combination of pressure and temperatures above 400 C to compact the material. However, these methods often resulted in porous microstructure, excessive grain growth, and degradation of the solid electrolyte, undermining battery performance and stability.
Image: Paul Scherrer Institute PSI, Advanced Science, CC BY 4.0
To address these challenges, the team developed a low-temperature, low-pressure sintering process. The LPSCl powder was first pressed uniaxially at 380 MPa at room temperature in a glove box. The resulting cold-pressed pellets were then transferred under vacuum to a chamber connected to the glove box and pressed at 50 MPa for six hours at temperatures of 60 C, 80 C and 100 C.
Sintering at 80 °C was found to be optimal, improving the surface uniformity and densification of the LPSCl pellets while reducing porosity and increasing ionic conductivity.
In a second step, ultrathin lithium fluoride (LiF) layers were deposited on 50 µm thick lithium metal foils at room temperature using electron beam evaporation. The LiF coating has two functions: it suppresses the electrochemical decomposition of the solid electrolyte upon contact with lithium and acts as a physical barrier against lithium dendrite penetration.
The researchers evaluated LiF thicknesses of 40 nm, 65 nm, 100 nm and 130 nm. A thickness of 65 nm was found to be optimal, providing uniform coverage that improved interfacial contact and stabilized solid electrolyte interphase (SEI) formation.
“This double adjustment doubles the critical current density of lithium symmetrical cells from 1.1 mA cm⁻² to 2.2 mA cm⁻²,” the researchers said. “In full cells with LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) cathodes, stable cycling was achieved for more than 2,700 cycles at 1 mA cm⁻² and 1.5 mAh cm⁻², with 75% of capacity retained after 1,500 cycles.”
The system was presented in “Synergistic Effects of Solid Electrolyte, Mild Sintering, and Lithium Surface Passivation for Enhanced Lithium Metal Cycling in All-Solid State Batteries”, published in Advanced science.
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