Solid-state batteries based on nonflammable inorganic solid electrolytes provide a promising technical solution that can resolve the safety issues of current lithium-ion batteries. Biphasic solid electrolytes comprising Li₇La₃Zr₂O₁₂ (LLZO) garnet and polymer have been attracting significant interest for solid-state Li batteries because of their mechanical robustness and enhanced Li⁺ conductivity, compared to conventional polymer electrolytes. Furthermore, the hybridization allows for the fabrication of thin and large-area electrolyte membranes without the need for high-temperature sintering of LLZO. However, the non-uniform distribution of LLZO particles and polymer species in biphasic electrolytes may cause uneven Li⁺ conduction, which results in poor interfacial stability with electrodes during repeated charge–discharge cycling.

In this study, we report a biphasic solid electrolyte with homogeneous Li⁺ transport pathway achieved by a metal–organic framework (MOF) layer. To regulate and homogenize the Li⁺ flux across the interface between the electrolyte and electrode, a free-standing, biphasic solid electrolyte membrane is integrated with the MOF nanoparticle layer. A mixture of plastic crystal (PC) and polymeric phase is infused into porous networks of the MOF-integrated electrolyte membrane, producing the percolating Li⁺ conduction pathways. The MOF-integrated electrolyte membrane is found to form the smooth and uniform interface with nanoporous channels in contact with the electrodes, effectively facilitating homogeneous Li⁺ transport. A solid-state battery with the MOF-integrated electrolyte membrane shows the enhanced rate-capability and cycling stability in comparison to the battery with the unmodified biphasic electrolyte. This study demonstrates that the proposed electrolyte design provides an effective approach to improving the interfacial stability of biphasic electrolytes with electrodes for long-cycling solid-state batteries.

[1] H.-S. Shin, W. Jeong, M.-H. Ryu, S.W. Lee, K.-N. Jung, J.-W. Lee, Electrode-to-electrode monolithic integration for high-voltage bipolar solid-state batteries based on plastic-crystal polymer electrolyte, Chem. Eng. J, published online.

[2] T. Jiang, P. He, G. Wang, Y. Shen, C.-W. Nan, L.-Z. Fan, Solvent-free synthesis of thin, flexible, nonflammable garnet-based composite solid electrolyte for all-solid-state lithium batteries, Adv. Energy Mater. 10 (2020) 1903376.