Sandwich‐Structured Quasi‐Solid Polymer Electrolyte Enables High‐Capacity, Long‐Cycling, and Dendrite‐Free Lithium Metal Battery at Room Temperature

Abstract The insufficient ionic conductivity, limited lithium‐ion transference number (t _Li +), and high interfacial impedance severely hinder the practical application of quasi‐solid polymer electrolytes (QSPEs). Here, a sandwich‐structured polyacrylonitrile (PAN) based QSPE is constructedin which MXene‐SiO ₂ nanosheets act as a functional filler to facilitate the rapid transfer of lithium‐ion in the QSPE, and a polymer and plastic crystalline electrolyte (PPCE) interface modification layer is coated on the surface of the PAN‐based QSPE of 3 wt.% MXene‐SiO ₂ (SS‐PPCE/PAN‐3%) to reduce interfacial impedance. Consequently, the synthesized SS‐PPCE/PAN‐3% QSPE delivers a promising ionic conductivity of ≈1.7 mS cm ⁻¹ at 30 °C, a satisfactory t _Li + of 0.51, and a low interfacial impedance. As expected, the assembled Li symmetric battery with SS‐PPCE/PAN‐3% QSPE can stably cycle more than 1550 h at 0.2 mA cm ⁻² . The Li||LiFePO ₄ quasi‐solid‐state lithium metal battery (QSSLMB) of this QSPE exhibits a high capacity retention of 81.5% after 300 cycles at 1.0 C and at RT. Even under the high‐loading cathode (LiFePO ₄ ≈ 10.0 mg cm ⁻² ) and RT, the QSSLMB achieves a superior area capacity and good cycling performance. Besides, the assembled high voltage Li||NMC811(loading ≈ 7.1 mg cm ⁻² ) QSSLMB has potential applications in high‐energy fields.