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Solid composite electrolytes exhibit tremendous potential for practical all-solid-state lithium metal batteries (ASSLMBs), whereas the interfacial contact between cathode and electrolyte remains a long-standing problem. Herein, we demonstrate an integrated design of a double-layer functional composite electrolyte and cathode (ID-FCC), which effectively improves interfacial contact and increases cycle stability. One composite electrolyte layer, PVDFLiFSI@LLZNTO (PL1@L), comes into contact with the LLZNTO (Li6.5La3Zr1.5Nb0.4Ta0.1O12)-containing cathode, while the other layer, PEOLiTFSI@LLZNTO (PL2@L) with a Li anode, is introduced in each. Such a design establishes a continuous network for the transport of Li+ on the interface, and includes the advantages of both PEO and PVDF for improving stability with the electrodes. The Li symmetric cells Li/PL2@L-PL1@L-PL2@L/Li steadily cycled for more than 3800 h under the current density of 0.05 mA cm−2 at 60 °C. Outstandingly, the all-solid-state batteries of LiFePO4-ID-FCC/Li showed an initial specific capacity of 161.5 mA h g−1 at 60 °C, demonstrating a remaining capacity ratio of 56.1% after 1000 cycles at 0.1 C and 74.5% after 400 cycles at 0.5 C, respectively. This work provides an effective strategy for solid-state electrolyte and interface design towards ASSLMBs with high electrochemical performance. [ABSTRACT FROM AUTHOR]