Asymmetric ion transfer orchestration in mechanically self-adaptive stratified solid electrolytes enabling bipolar interface compatibility for solid-state lithium metal batteries

The compatibility of solid-state electrolyte (SSE) with high-voltage cathode and lithium metal anode in terms of transfer kinetics and mechanical properties is crucial for the performance of high-energy-density solid-state lithium metal battery (SSLMB). However, monophase polymer and ceramic, as well as their composites, often fail to meet the disparate requirements of both electrodes due to inadequate ion transfer and mechanical confinement. Herein, a novel bilayer SSE composed of fast-ion-transfer layer (poly (vinylidene fluoride)/succinonitrile/UiO-66-NH₂/LiFSI, PSUL) and ion-transfer-rectifying layer (ITRL) is designed to accommodate the differentiated requirements of electrodes. We demonstrate that UiO-66-NH₂ additive disrupts the symmetry of poly (vinylidene fluoride) chains, increasing polarity and further lowering the migration barrier of complexed [Li (DMF)_x]⁺. The preferential coordination of succinonitrile with Li-ion facilitates the desolvation process, creating more transfer pathways. Additionally, the enhanced adhesion of PSUL favors the stability of interfacial Li-ion transport and assists in mitigating the interfacial resistance. These synergistically enable fast and stable Li-ion flux in obtained electrolyte. Meanwhile, ITRL dominated by UiO-66-NH₂ triggers satisfactory Li-ion transference number and homogeneous flux, combined with outstanding Young's modulus against punctures, imparting the electrolyte with uniform Li plating/stripping behavior. Therefore, compatible bilayer solid electrolyte enables the realization of high-energy-density SSLMB with excellent cycling stability when being assembled as LiNi_0.8Mn_0.1Co_0.1O₂/Li cell.