Biphasic solid electrolytes with homogeneous Li-ion transport pathway enabled by metal–organic frameworks

Solid-state lithium batteries (SSLBs) based on non-flammable inorganic solid electrolytes have been proposed as promising technical solutions to resolve safety issues caused by flammable organic liquid electrolytes of current Li-ion batteries. Biphasic solid electrolytes (BSEs) comprising Li+-conducting oxides and polymers have garnered significant interest for SSLBs because of their mechanical robustness and high Li+ conductivity. However, the non-uniform distribution of oxide particles and polymer species in BSEs may cause inhomogeneous Li+ conduction, thereby resulting in poor interfacial stability with electrodes during repeated charge–discharge cycles. Herein, we report a Li7La3Zr2O12-based BSE with homogeneous Li+ transport pathways achieved by a metal–organic framework (MOF) layer. To regulate and homogenize the Li+ flux across the interface between the BSE and electrode, a free-standing BSE is integrated with the MOF layer. The MOF-integrated BSE forms smooth and uniform interfaces with nanoporous channels in contact with the electrodes, effectively enhancing the interfacial solid–solid contact and facilitating homogeneous Li+ transport. An SSLB with the MOF-BSE membrane shows enhanced cycling stability and rate-capability compared to the battery with bare BSE. This study demonstrates that the proposed electrolyte design provides an effective approach for improving the conducting properties and interfacial stability of BSEs for high-performance and long-cycling SSLBs.