Electric Field and Nanocontact Effects in Metal–Organic Framework/Li_6.4La₃Zr_1.4Ta_0.6O₁₂ Ionic Conductors for Fast Interfacial Lithium-Ion Transport Kinetics

The slow ion transport kinetics inside or between the nanofillers in composite polymer electrolytes (CPEs) lead to the formation of lithium dendrites for solid-state lithium batteries. To address the critical issues, CPEs (U@UNL) composed of a UIO-66@UIO-66-NH₂ (U@UN) core-shell heterostructure and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) filler is designed. Due to the different band structures of the U@UN heterostructure, a built-in electric field is constructed to promote the transfer kinetics of carriers. Besides, the introduction of LLZTO facilitates the formation of a close nanometer contact interface between U@UN and LLZTO, reducing interface impedance and accelerating the lithium-ion transfer rate. As a benefit from the built-in electric field and the nanometer contact interface, U@UNL exhibits a wide electrochemical window of 5.17 V, a large lithium-ion transference number of 0.76, and a high ionic conductivity of 3.50 × 10^-3 S cm^-1. Consequently, the U@UNL electrolyte possesses excellent interfacial stability against Li metal after 1200 h at 0.1 mA cm^-2 and shows a high specific capacity of 160.2 and 152.6 mAh g^-1 at 0.5 and 1 C, respectively. This work proposes a complete strategy for building high-performance solid-state lithium batteries by a built-in electric field and nanometer contact interface between U@UN and LLZTO.