Boron-doping enabled multi-site electronegativity enhancement in carbon nitride for high-performance aqueous zinc-ion batteries

• Boron doping achieves enhanced electronegativity of multiple sites in carbon nitride. • Modified carbon nitride strengthens attraction towards Zn 2+ and repulsion towards SO 4 2− . • Functionalized separator suppresses dendrite growth and mitigates side reactions. Aqueous zinc ion batteries (AZIBs) emerge as a viable next-generation energy storage solution, leveraging inherent non-flammability, cost efficiency, and ecological sustainability. Nevertheless, significant hurdles persist at the Zn anode interface, where rampant dendrite proliferation and detrimental side reactions undermine electrochemical durability, which constrain practical deployment. Functional separator modification offers an effective anode protection strategy. Carbon nitride (CN), an economical and robust compound exhibiting intrinsic zincophilicity, serves as an suitable separator-modifying material. Herein, boron-doped CN (BCN) with enhanced properties was synthesized through simple calcination of CN and NaBH 4 mixture. During this process, B-doping not only modulates the charge distribution within CN, increasing the charge density at adjacent N sites, but also facilitates cleavage of C-N bonds at adjacent sites, triggered by reactions between active hydrogen species and CN, thereby promoting the formation of electronegative cyano groups. This synergistic effect concurrently enhances the electronegativity at multiple sites within the CN framework. Consequently, the BCN-functionalized separator not only strengthens Zn 2+ affinity to homogenize ion flux and guide uniform Zn deposition but also electrostatically repels SO 4 2− , suppressing side reactions. Accordingly, symmetric cells employing the BCN-3@GF separator achieve a high Zn 2+ transference number (0.79) and demonstrate remarkable cycling stability exceeding 1200 h at 2 mA cm −2 . Furthermore, full cells paired with a CVO cathode exhibit long-term cyclability, retaining a high specific capacity of 126.8 mAh g −1 after 3000 cycles at 5 A g −1 with a high capacity retention of 86.7 %. This study demonstrates that a simple strategy enhances the intrinsic zincophilicity of CN for functional separators, providing fundamental insights for advanced separator design in AZIBs.