Hierarchical Interconnected Hybrid Solid Electrolyte Membrane for All-Solid-State Lithium-Metal Batteries Based on High-Voltage NCM811 Cathodes

Although hybrid solid electrolyte (HSE) membranes containing a small amount of ceramic filler are promising electrolytes for all-solid-state Li-metal batteries (ASSLMBs), they face various challenges while charging at high cut-off voltages. In this study, we prepared a high voltage-friendly flexible hierarchical interconnected hybrid solid electrolyte (HIHSE) membrane through polymer-based solution injection into a three-dimensional (3D) interconnected c-LALZO framework (Li_6.25Al_0.25La₃Zr₂O₁₂, fabricated using a template method). The HIHSE membrane possessed bulk (σ_b), grain boundary (σ_gb), and total ionic conductivities of 4.54, 0.30, and 0.28 mS cm^-1, respectively, with a Li⁺ ion transference number of 0.66 and an electrochemical stability window of up to 4.90 V (vs Li/Li⁺). The HIHSE membrane also displayed desirable Li plating/stripping performance, with very stable voltage hysteresis at a current density of 0.2 mA cm^-2 over 800 h. A Li₂MoO₄@LiN_0.8C_0.1M_0.1O₂ (LMO@NCM811)/HIHSE/Li full cell exhibited an excellent capacity retention of 86.14% after 400 cycles, with an average Coulombic efficiency of 99.27%, when operated at a rate of 0.5C in the voltage range of 2.6-4.2 V at room temperature (RT). Moreover, a cell with similar formulation delivered an excellent capacity output of 197.55 mAh g^-1, with an excellent capacity retention of 89.22% after 100 cycles and an average Coulombic efficiency of 99.11% at a rate of 0.1C in the potential range of 2.6-4.5 V at RT. Surprisingly, the performance of an ASSLMB incorporating our HIHSE membrane maximized at the upper limit potential of 4.5 V. Hence, ASSLMBs featuring such HIHSE membranes have great potential for use in high-voltage cathode materials while also increasing the energy density of Li-metal batteries.