Constructing electron-blocking grain boundaries in garnet to suppress lithium dendrite growth

Li₇La₃Zr₂O₁₂ (LLZO) is considered as a promising solid-state electrolyte due to its high ionic conductivity, wide electrochemical window, and excellent electrochemical stability. However, its application in solid-state lithium metal batteries (SSLMBs) is impeded by the growth of lithium dendrites in LLZO due to some reasons such as its high electronic conductivity. In this study, lithium fluoride (LiF) was introduced into Ta-doped LLZO (LLZTO) to modify its grain boundaries to enhance the performance of SSLMBs. A nanoscale LiF layer was uniformly coated on the LLZTO grains, creating a three-dimensional continuous electron-blocking network at the grain boundaries. Benefiting from the electronic insulator LiF and the special structure of the modified LLZTO, the symmetric cells based on LLZO achieved a high critical current density (CCD) of 1.1 mA cm^-2 (in capacity-constant mode) and maintained stability over 2000 h at 0.3 mA cm^-2. Moreover, the full cells combined with a LiFePO₄ (LFP) cathode, demonstrated excellent cycling performance, retaining 97.1% of capacity retention after 500 cycles at 0.5 C. Therefore, this work provides a facile and effective approach for preparing a modified electrolyte suitable for high-performance SSLMBs.