Grain Boundary Engineering Enabled High-Performance Garnet-Type Electrolyte for Lithium Dendrite Free Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are attracting increasing attentions as one of the promising next-generation technologies due to their high-safety and high-energy density. Their practical application, however, is hindered by lithium dendrite growth and propagation in solid-state electrolytes (SSEs). Herein, an in situ grain boundary modification strategy relying on the reaction between Li₂ TiO₃ (LTO) and Ta-substituted garnet-type electrolyte (LLZT) is developed, which forms LaTiO₃ along with lesser amounts of LTO/Li₂ ZrO₃ at the grain boundaries (GBs). The second phases of LTO/Li₂ ZrO₃ inhibit abnormal grain growth. The presence of LaTiO₃ at the GBs reduces electronic conductivity and improves mechanical strength, which can hinder dendrite formation and block lithium dendrite penetration through the LLZT. Moreover, the adjacent grains by LaTiO₃ build a continuous Li⁺ transport path, providing a homogeneous Li⁺ flux throughout the whole LLZT-4LTO. As a result, symmetric cells of Li | LLZT-4LTO | Li shows a high critical current density of 1.8 mA cm^-2 and a long cycling stability up to 2000 h at 0.3 mA cm^-2 . Moreover, the high-voltage full cells demonstrate remarkable cycling stability and rate performance. It is believed that this novel grain boundary modification strategy can shed light on the constructing of high-performance SSEs for practical SSLMBs.