Improved cycling stability and lithium utilization in trilayer Al-LLZO revealed by Electrochemical cycling performance

Abstract

Garnet-type Li${}_{6.25}$Al${}_{0.25}$La${}_3$Zr${}_2$O${}_{12}$ (Al-LLZO) solid electrolytes are promising for all-solid-state batteries but are limited by interfacial resistance. In this work, dense and graded tri-layer Al-LLZO electrolytes were fabricated and tested in Li/Al-LLZO/NMC(111) full cells. After 25 cycles, the tri-layer cell delivered discharge capacity of $\sim$55 mAhg${}^{-1}$, nearly twice that of the dense Al-LLZO ($\sim$27 mAhg${}^{-1}$). EIS showed lower initial interfacial resistance ($\sim$373 $\Omega$) and improved stability. SEM confirmed a porous-dense-porous structure, while NRA revealed enhanced near-surface lithium ($\sim$75%) compared to dense Al-LLZO ($\sim$48%). These results highlight the role of microstructural grading in improving lithium distribution and cell performance.