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

TL;DR

This study demonstrates that microstructural grading in trilayer Al-LLZO electrolytes significantly enhances cycling stability, lithium utilization, and reduces interfacial resistance in solid-state batteries.

Contribution

The paper introduces a novel graded tri-layer Al-LLZO electrolyte that improves electrochemical performance and stability over traditional dense electrolytes.

Findings

Tri-layer Al-LLZO achieves nearly double capacity after 25 cycles.

Lower initial interfacial resistance in tri-layer compared to dense Al-LLZO.

Enhanced near-surface lithium content in graded electrolytes.

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.