Rational design of a heterogeneous double-layered composite solid electrolyte via synergistic strategies of asymmetric polymer matrices and functional additives to enable 4.5 V all-solid-state lithium batteries with superior performance

High-voltage all-solid-state lithium batteries (ASSLBs) are one of the very promising energy storage devices for future high performance energy storage and conversion, but their development faces multiple interfacial challenges at present. In this work, a novel strategy of asymmetric polymer matrices design combined with the using of functional additives is developed to meet the distinctive requirements on cathode and anode sides for high-voltage ASSLBs simultaneously. A composite solid electrolyte (CSE) consisting of blended polymer matrices (PEO + PVDF) is employed as the cathode side CSE (CSC) due to its high electrochemical stability, while PEO-based CSE with high stability against Li metal is used as the anode side CSE (ASC). Meanwhile, lithium bisoxalatodifluorophosphate (LiBODFP) is incorporated into the CSC to stabilize the cathode-electrolyte interface due to its ability to be oxidized to form the stable LiPxOyFz-rich cathode electrolyte interphase (CEI) film, and LiNO3 in the ASC as the solid electrolyte interphase (SEI) former to effectively suppress the lithium dendrites formation. The assembled high-voltage LiFe0.5Mn0.5PO4-based ASSLB using the as-prepared asymmetric CSE (CSC/ASC) exhibits superior electrochemical behaviors in the voltage range of 2.5 ∼ 4.5 V, with specific capacities of 161.7 and 103.5 mAh g−1 at 0.1 and 2 C, respectively, and a super high capacity retention of 90.6% after 1000 cycles at 1 C. Additionally, respective mechanisms of the addition of LiBODFP in the CSC and LiNO3 in the ASC to prolong the cycle stability of the ASSLB are systematically revealed through detailed characterization of the cycled electrodes.