Mixed ionic/electronic conducting framework enabled by transition metal-ion reduction in Li-LLTO composite anodes for ultrafast lithium diffusion

The development of Li₇La₃Zr₂O₁₂ (LLZO) solid electrolytes is challenged by the unstable Li/LLZO interface during lithium stripping and plating processes, which impedes interfacial charge transport and accelerates lithium dendrite growth. Here, a freestanding ultrathin Li-Li_0.3La_0.5TiO₃ (LLTO) composite anode with a three-dimensional interconnected mixed ionic/electronic conducting LLTO framework was developed. The mixed ionic/electronic conduction of LLTO arises from the in-situ reduction of transition metal ions (Ti⁴⁺) by metallic lithium. The Li-LLTO composite anode possesses good affinity toward LLZO solid electrolytes, achieving a low interfacial resistance of 11.7 Ω cm², and a high lithium self-diffusion coefficient reaching 4.5×10⁻¹¹ cm²/s, about one order of magnitude higher than that of pure lithium anode. These features collectively enhance the Li-LLTO/LLZO interfacial stability, increasing the critical current density fourfold and enabling a 1300-h symmetrical cell cycling life. It delivers high-performance solid-state lithium batteries with an 80% capacity retention after 220 cycles. This advancement not only improves the performance of lithium metal anodes in solid-state batteries but also offers promising insights for next-generation high-energy-density electrochemical energy storage systems.