Hopping-Phase Ion Bridge Enables Fast Li⁺ Transport in Functional Garnet-Type Solid-State Battery at Room Temperature

Composite polymer electrolytes (CPEs) containing Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) is widely regarded as leading candidate for high energy density solid-state lithium-metal batteries due to its exceptional ionic conductivity and environmental stability. However, Li₂CO₃ and LiOH layers at LLZTO surface greatly hinder Li⁺ transport between LLZTO-polymer and the electrode–electrolyte interface. Herein, the surface of LLZTO is boronized to obtain functionalized LLZTO, and its conversion mechanism is clarified. By dissolving the crystal structure of cellulose to obtain hopping-phase ion bridge (HPIB), which release the Li⁺ transport activity of its oxygen-containing polar functional group (─OH, ─O─). Therefore, a high-throughput ion transporter (HTIT-37) with high ion transfer number (0.86) is prepared by introducing the HPIB into functionalized LLZTO and polyvinylidene fluoride interface by intermolecular hydrogen bond interaction, and it is demonstrated that the HPIB acts as a “highway” for the Li⁺ across this heterogeneous interface. Moreover, the HPIB is found to self-adsorb on the SEI surface, leading to fast Li⁺ transport kinetics at anode–CPE interface. Thus, the lifespan of Li|HTIT-37|Li is over 8000 h, and the critical current density exceeds 2.3 mA cm⁻². The LiNi_0.5Co_0.2Mn_0.3O₂|Li and Li_1.2Ni_0.13Co_0.13Mn_0.54O₂|Li battery remains stable with the HPIB-enhanced electrode process, proving the application potential of LLZTO-based CPE in high energy density SSLMB.