Synergistically Engineering Grains and Grain Boundaries toward Li Dendrite-Free LiLaZrO.

Cation-doped cubic LiLaZrO is regarded as a promising solid electrolyte for safe and energy-dense solid-state lithium batteries. However, it suffers from the formation of LiCO and high electronic conductivity, which give rise to an unconformable Li/LiLaZrO interface and lithium dendrites. Herein, composite AlF-LiLaZrTaO solid electrolytes were created based on thermal AlF decomposition and F/O displacement reactions under a high-temperature sintering process. When the AlF is thermally decomposed, it leaves AlO/AlF meliorating the grain boundaries and F ions partially displacing O ions in the grains. Due to the higher electronegativity of F in the grains and the grain-boundary modification, these AlF-LiLaZrTaO deliver optimized electronic conduction and chemical stability against the formation of LiCO. The Li/AlF-LiLaZrTaO/Li cell exhibits a low interfacial resistance of ∼16 Ω cm and an ultrastable long-term cycling behavior for 800 h under a current density of 200 μA/cm, leading to Li//LiCoO solid-state batteries with good rate performance and cycling stability.