Despite the extensive investigation on solid‐state lithium‐metal batteries (SSLMBs), their application in flexible electronic devices has been plagued mainly by the physicochemical/mechanical instability of their electrode–electrolyte interfaces. Here, we present a fibrous skeleton‐framed, quasi‐solid‐state LMB (fs‐QSSLMB) as a new cell architecture concept to simultaneously achieve the high‐energy‐density, mechanical flexibility, and safety. The fs‐QSSLMB is fabricated by embedding poly(ethylene terephthalate) (PET) nonwovens, stainless‐steel meshes, and metal‐coated conductive PET nonwovens with a lithiophilic‐gradient morphology as customized fibrous skeletons into quasi‐solid‐state electrolytes (QSSEs), high‐capacity LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes, and Li metal anodes, respectively. The stepwise printing of the NCM811 cathode/QSSE/Li anode assembly and the subsequent one‐pot ultraviolet curing of the gel electrolyte precursors in the assembly enable the formation of seamless interfaces between the electrodes and QSSE, thereby ensuring the electrochemical sustainability and mechanical deformability of the fs‐QSSLMB. In addition, owing to its fibrous skeleton‐based structural uniqueness and seamless interfaces, the fs‐QSSLMB exhibits electrochemical reliability, mechanical flexibility, safety (i.e., electrochemically active after being vertically cut in half and exposed to flame), and high (cell‐based) gravimetric/volumetric energy densities (385 Wh kgcell−1/451 Wh Lcell−1).

Despite extensive studies on lithium‐metal batteries (LMBs) that have garnered considerable attention as a promising high‐energy‐density system beyond current state‐of‐the‐art lithium‐ion batteries, their application to flexible power sources is staggering due to the difficulty in simultaneously achieving electrochemical sustainability and mechanical deformability. To address this issue, herein, a new electrode architecture strategy based on conductive fibrous skeletons (CFS) is proposed. Lithium is impregnated into nickel/copper‐deposited conductive poly(ethylene terephthalate) nonwovens via electrochemical plating, resulting in self‐standing CFS–Li anodes. The CFS–Li anodes exhibit stable Li plating/stripping cyclability and mechanical deformability. To achieve high‐capacity flexible cathodes, over‐lithiated layered oxide (OLO) particles are compactly embedded in conductive heteronanomats (fibrous mixtures of multiwalled carbon nanotubes and functional polymer nanofibers). The conductive heteronanomats, as CFS of OLO cathodes, provide bicontinuous electron/ion conduction pathways without heavy metallic current collectors and chelate metal ions dissolved from OLO, thus improving the areal capacity, redox kinetics, and cycling retention. Driven by the attractive characteristics of the CFS–Li anodes and CFS–OLO cathodes, the resulting CFS–LMB full cells provide improvements in the cyclability, rate performance, and more notably, (cell‐based) gravimetric/volumetric energy density (506 Wh kgcell−1/765 Wh Lcell−1) along with the exceptional mechanical flexibility.

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