Abstract: In this work, graphitic carbon nitride (g-C₃N₄) is employed as a “molecular canvas” to construct a stable reaction platform, aiming to reveal the underlying mechanism by which electronic structure engineering enhances Li⁺ conduction. This platform is expected to clarify the relationship between electronic structure engineering and Li⁺ conduction, which is important for the rational design of advanced polymer electrolytes. Guided by theoretical calculations, we designed a dual-functionalized modified carbon nitride framework material (CN-O-N). In this design, oxygen atoms and amino groups are introduced synergistically to modify the carbon nitride skeleton. This material can act as an efficient ion-conducting “highway” for reconstructing polymer electrolytes, thereby constructing all-solid-state lithium metal batteries with high ionic conductivity and a high lithium-ion transference number. Through the synergistic dual functionalization of oxygen atoms and amino groups, the electronic environment of the CN-O-N framework is precisely modulated. Such modulation endows the material with an optimized band structure and abundant electron-rich active sites. The optimized band structure and electron-rich active sites are considered to be the key factors for the enhanced oxidation resistance, promoted lithium salt dissociation, and suppressed anion migration. These features significantly enhance the oxidation resistance of the material, promote the dissociation of lithium salt ion pairs, and effectively inhibit the migration of anions. Consequently, introducing CN-O-N into a poly(ethylene oxide) (PEO) matrix not only realizes rapid and selective Li⁺ transport but also significantly alleviates the growth of lithium dendrites. Specifically, the constructed PEO composite electrolyte achieves a high ionic conductivity of 0.551 mS cm^-1 and an excellent Li⁺ transference number of 0.78 at 60 ℃. The lithium symmetric cell assembled with this electrolyte exhibits stable lithium plating/stripping cycling performance for more than 1100 h. Notably, when matched with a LiFePO₄ (LFP) cathode, the assembled all-solid-state lithium metal battery stably cycles for more than 1000 cycles at 60 ℃ and 1C, and its capacity retention after 500 cycles is about 80%. Meanwhile, its pouch cell still retains a capacity retention as high as 95% after 200 cycles at 0.2C. These results indicate that the dualfunctionalized CN-O-N framework offers an effective strategy for precisely regulating the electronic structure of carbon nitride and for constructing high-performance all-solid-state lithium metal batteries.

Key words: All-solid-state Li metal battery, Polymer electrolyte, Directional Li-ion transport, Bifunctionally modified carbon nitride, LiF-rich interphase