La(OH) ₃ ‐Based Lithium Ionic Conductor for Quasi‐Solid‐State Lithium Metal Batteries

Quasi-solid-state lithium metal batteries (QSSLMBs) hold great promise for next-generation energy storage but face major challenges for applications, including air instability of electrolytes, high synthesis cost, and poor interfacial compatibility. Here, La(OH)₃-based Li⁺ conductor Li_0.15Sr_0.525La_0.6(OH)₃ (LSLOH) is reported, which is air-stable and cost-effective. LSLOH serves as an ionic conductor exhibiting Li⁺ conductivity of 0.1 mS cm^-1 at 30 °C. To improve interfacial transport, LSLOH is incorporated into a polyethylene oxide (PEO)-LiTFSI polymer electrolyte (PL) to form a quasi-solid-state electrolyte (PL-LSLOH). LSLOH provides additional Li⁺ transport channels, while La³⁺ and Sr²⁺ interact with TFSI^- to promote Li⁺ mobility. Moreover, LSLOH induces the formation of a LiOH and Li₂O-rich solid electrolyte interphase, effectively suppressing Li dendrite growth. As a result, the LiNi_0.6Co_0.1Mn_0.3O₂ | PL-LSLOH | Li pouch cells achieve 2.2 mAh cm^-2 at 0.83 mA cm^-2 (with cathode loading of 19 mg cm^-2) over 200 cycles with 92.5% initial capacity retention, underscoring the potential for scale-up. For the first time, this work demonstrates La(OH)₃-based lithium ionic conductors and electrolyte design that address key barriers to the QSSLMBs.