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Good sintering strategy for densifying LLZO garnets

Good sintering strategy for densifying LLZO garnets

Cubic-Li7La3Zr2O12 (LLZO) is regarded as one of the most promising solid electrolytes for the construction of inherently safe, next generation all-solid-state Li batteries. Unfortunately, sintering these materials to full density with controlled grain sizes, mechanical and electrochemical properties relies on energy and equipment intensive processes. In this work, we elucidate key parameters dictating LLZO densification by tracing the compositional and structural changes during processing calcined and ball-milled Al3+ doped LLZO powders. We find that the powders undergo ion (Li+/H+) exchange during room temperature processing, such that on heating, the protonated LLZO lattice collapses and crystallizes to its constituent oxides, leading to reaction driven densification at < 1000 °C, prior to sintering of LLZO grains at higher temperatures. It is shown that small particle sizes and protonation cannot be decoupled, and actually aid densification. We conclude that using fully ecomposed nanoparticle mixtures, as obtained by liquid-feed flame spray pyrolysis, provides an ideal approach to use high surface and reaction energy to drive densification, resulting in pressureless sintering of Ga3+ doped LLZO thin films (25 μm) at 1130 °C/0.3 h to ideal microstructures (95 ± 1% density, 1.2 ± 0.2 μm average grain size) normally accessible only by pressure-assisted sintering.  Such films offer both high ionic conductivity(1.3 ± 0.1 mS cm−1) and record low ionic area specific resistance (2 Ω cm2).

Original title: key parameters governing the densification of cubic-Li7La3Zr2O12  Li+ conductors


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This work is truly remarkable, the authors achieve exceptional densification without pressing the material. Though the sintering time of 20 minutes is good, the work can be emulated to reduce the sintering temperature as much as possible.

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