A smooth interfacial contact between electrode and electrolyte, alleviation of dendrite formation, low internal resistance, and preparation of thin electrolyte (<20 µm) are the key challenging tasks in the practical application of Li7La3Zr2O12 (LLZO)‐based solid‐state batteries (SSBs). This paper develops a unique strategy to reduce interfacial resistance by designing an interface‐based core–shell structure via direct integration of Al‐LLZO ceramic nanofibers incorporated poly(vinylidene fluoride)/LiTFSI on the surface of a porous cathode electrode (HPEIC). This yields an ultrathin solid polymer electrolyte with a thickness of 7 µm. The integrated HPEIC/Li SSB with LiFePO4/C exhibits an initial specific capacity of 166 mAh g−1 at 0.1 C and 159 mAh g−1 with capacity retention of 100% after 120 cycles at 0.5 C (25 °C). The HPEIC/Li SSB with LiNi0.8Mn0.1Co0.1O2 cathode delivers a good discharge capacity of 134 mAh g−1 after 120 cycles at 0.5 C. The rational design of interface‐based core–shell structure outperforms the conventional assembly of solid‐state cells using free‐standing solid electrolytes in specific capacity, internal resistance, and rate performance. The proposed strategy is simple, cost‐effective, robust, and scalable manufacturing, which is essential for the practical applicability of SSBs.

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