Optimizing Lithium Nucleation Overpotential in Anode-Free Garnet-Based Hybrid Solid-State Batteries

Anode-free solid-state lithium batteries promise high-energy-density storage but remain limited by unstable interfaces between the solid electrolyte and in situ-formed lithium. In this work, a hybrid solid–liquid electrolyte strategy is developed using a localized high-concentration electrolyte containing AlCl₃ and LiPO₂F₂, a trilayer garnet-type Li_6.4Ga_0.1La_2.9Ba_0.1Zr_1.6Ta_0.4O₁₂ solid electrolyte. This configuration forms a mechanically stable and ionically conductive solid-liquid electrolyte interphase, enabling 81% Coulombic efficiency after 300 cycles at 2 mA cm⁻² and 1 mAh cm⁻² in Cu/Li half-cells. A single-layer anode-free hybrid solid-state pouch cell demonstrated excellent long-term cycling performance, retaining 75% of its initial capacity after 400 cycles at 1C (1.25 mA cm⁻²), with a Coulombic efficiency of 99% without external pressure and at room temperature. At the lab scale, this hybrid electrolyte approach shows both scalability and performance, providing a potential practical pathway to next-generation anode-free hybrid solid-state lithium batteries.