Elimination of detrimental grain boundary segregation in Garnets
- Kai Yao
- Kwangnam Kim
- Dylan Jennings
- Jan Dippell
- Lei Jin
- Meng Ma
- Xingyu Liu
- Qianli Ma
- Walter Sebastian Scheld
- Christoph Roitzheim
- Yuan Zeng
- Timo Danner
- Olivier Guillon
- Mark Huijben
- Johan E. ten Elshof
- Liwen F. Wan
- Arnulf Latz
- Brandon C. Wood
- Martin Finsterbusch
- Dina Fattakhova-Rohlfing
2026-06-29
Garnet Li 7 La 3 Zr 2 O 12 electrolyte is considered a key enabler of solid-state batteries with Li metal electrodes, but the grain boundaries impair its performance. To date, the understanding of grain boundary structures and its impact on performance remains elusive. Here, we show that element segregation at Li 7 La 3 Zr 2 O 12 grain boundaries critically governs Li transport and nucleation. During conventional sintering, Al, Ta, and La segregate at grain boundaries, locally depleting Li and creating space-charge layers that lower total ionic conductivity. Simultaneously, this segregation leads to higher electronic conductivity along grain boundaries, which promotes Li nucleation at grain boundary edges with increased risk of dendrite formation. The underlying mechanism of segregation is governed by both thermodynamic driving forces and diffusion kinetics. Building on this understanding, we develop a strategy to achieve segregation-free grain boundaries through a rapid sintering protocol that utilizes the onset of solid-state softening. This approach yields transparent, polycrystalline Li 7 La 3 Zr 2 O 12 with negligible grain boundary impedance and enhanced dendrite tolerance. By elucidating the structural origins and electrochemical consequences of grain boundary segregation, this work provides a guidance for the rational optimization of solid electrolytes.