Solid Electrolyte Bimodal Grain Structures for Improved Cycling Performance.

The application of solid-state electrolytes in Li batteries has been hampered by the occurrence of Li-dendrite-caused short circuits. To avoid cell failure, the electrolytes can only be stressed with rather low current densities, severely restricting their performance. Since grain size and pore distributions significantly affect dendrite growth in ceramic electrolytes like Li 7 La 3 Zr 2 O 12 and its variants, here we have proposed a "detour and buffer" strategy to bring the superiority of both coarse and fine grains into play. To validate the mechanism, a coarse/fine bimodal grain microstructure was obtained by seeding unpulverized large particles in the green body. The rearrangement of coarse grains and fine pores was fine-tuned through changing the ratio of pulverized and unpulverized powders. The optimized bimodal microstructure, obtained when the two powders are equally mixed, allowed, without extra interface decoration, cycling for over 2000 h as the current density was increased from 1.0 mA·cm -2 gradually up to 2.0 mA·cm -2 . The "detour and buffer" effects was confirmed from postmortem analysis. The complex grain boundaries formed by fine grains discourage the direct infiltration of Li. Simultaneously, the coarse grains further increase the tortuosity of the Li path. Our study sheds light on the microstructure optimization for the polycrystalline solid-state electrolytes. This article is protected by copyright. All rights reserved.