Multi-electron nitrobenzothiadiazole sp-conjugated-alkynyl covalent organic frameworks for ammonium-ion batteries.

Abstract

Covalent organic frameworks containing periodic redox-active motifs and conjugation structures are booming as competitive negative electrodes for ammonium-ion batteries. Introducing substantial single-electron active motifs linked by dynamic imine bonds can increase their capacity; however, this design is constrained by suboptimal single-electron redox efficiency and insufficient linkage stability. Here we unlock a multiple two-electron-transfer nitrobenzothiadiazole covalent organic framework via integrating alkynyl benzenes and nitro-functionalized four-electron benzothiadiazoles. The high degree of π-electron sp-conjugation along alkynyl linkages and strong electron-drawing effect of nitrobenzothiadiazole motifs in nitrobenzothiadiazole covalent organic framework promise high NH₄⁺ accessibility of multi-two-electron nitro/thiazole sites (95.2% utilization) with a lower activation energy (25.93 vs. 35.99 kJ mol^-1 of benzothiadiazole covalent organic framework).The fast octadeca-H-bonded NH₄⁺ coordination in nitrobenzothiadiazole units liberates a high specific capacity of 317 mAh g^-1 for nitrobenzothiadiazole covalent organic framework negative electrode. The alkynyl-bridged π-conjugation network establishes structural anti-dissolution to enable a cycling durability of 70,000 cycles. Paired with high-voltage Prussian blue analogue positive electrode, the ammonium-ion full battery delivers a specific energy of 86.1 Wh kg^-1 (based on total active material mass) and a lifespan of 25,000 cycles. This work extends the design landscape of high-performance covalent organic frameworks for advanced ammonium-ion batteries.