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The shuttling of polysulfides and uncontrollable growth of lithium dendrites remain the most critical obstacles deteriorating the performance and safety of lithium–sulfur batteries. The separator plays a key role in molecule diffusion and ion transport kinetics; thus, endowing the separator with functions to address the two abovementioned issues is an urgent need. Herein, a protein-based, low-resistance Janus nanofabric is designed and fabricated for simultaneously trapping polysulfides and stabilizing lithium metal. The Janus nanofabric is achieved via combining two functional nanofabric layers, a gelatin-coated conductive nanofabric (G@CNF) as a polysulfide-blocking layer and a gelatin nanofabric (G-nanofabric) as an ion-regulating layer, into a heterostructure. The gelatin coating of G@CNF effectively enhances the polysulfide-trapping ability owing to strong gelatin–polysulfide interactions. The G-nanofabric with exceptional wettability, high ionic conductivity (4.9 × 10 −3 S cm −1 ) and a high lithium-ion transference number (0.73) helps stabilize ion deposition and thus suppresses the growth of lithium dendrites. As a result, a Li/Li symmetric cell with the G-nanofabric delivers ultra-long cycle life over 1000 h with very stable performance. Benefiting from the synergistic effect of the two functional layers of the Janus nanofabric, the resulting Li–S batteries demonstrate excellent capacity, rate performance and cycling stability ( e.g. initial discharge capacity of 890 mA h g −1 with a decay rate of 0.117% up to 300 cycles at 0.5 A g −1 ). 

Structural and compositional diversities of proteins generate a number of functions for fabricating novel and advanced materials. Recent progress in protein engineering endows flexible approaches and new functionalities, which makes the fabricated materials potentially applicable in a broad spectrum of fields. Such engineering strategies by applying proteins alone or together with other molecules derive numerous functional materials such as patterned nanometal materials/nanometallic compounds, well‐designed nanocomposites, etc. Advantages in materials’ tunability, property improvement (e.g., electronic and mechanical properties, etc.), functionalities, and biocompatibility have been demonstrated, thus providing alternatives to existing materials via conventional methods. This review summarizes and discusses the strategies of fabricating functional materials using proteins as the critical contributors. Benefiting from their versatility, proteins find their roles in engineering functional materials via acting as structure‐control agents, reaction agents, and battery components, which are emphasized in this review. The strategies of each group of functions are specifically detailed. Properties of protein‐engineered functional materials and their potential applications in the fields of microelectronics, energy storage and conversion, sensor devices, etc. are also reviewed.