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 0.15 Sr 0.525 La 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 La 3+ and Sr 2+ interact with TFSI − to promote Li⁺ mobility. Moreover, LSLOH induces the formation of a LiOH and Li 2 O‐rich solid electrolyte interphase, effectively suppressing Li dendrite growth. As a result, the LiNi 0.6 Co 0.1 Mn 0.3 O 2 | 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.