Open‐Shell Resonance of Germanium‐Alkyne Porous Organic Radical Polymer for Boosting Sodium‐Ion Storage

Abstract

AbstractPorous organic polymers (POPs) as electrode materials for sodium‐ion batteries (SIBs) are attracting increasing attention. However, the application of porous organic radical polymers (PORPs) with unique properties in SIBs is still in an infancy. Herein, two 3D germanium‐based POPs with conjugated diacetylene units (Ge‐DA) and acetylene units (Ge‐A) are designed and synthesized. Carbon radicals in Ge‐DA are verified by electron paramagnetic resonance and the resonance structure is calculated by density functional theory, showing a lower lowest unoccupied molecular orbital (LUMO) energy level (−5.46 eV) and a narrow energy gap (ca. 1.64 eV). In contrast, Ge‐DA as an anode for SIBs shows superior electrochemical properties to that of Ge‐A counterpart, including a higher specific discharge capacity of 349 mAh g−1 at 200 mA g−1, excellent cyclability with a capacity of 112 mAh g−1 at 5 A g−1 for at least 5000 cycles and high rate performance of 135 mAh g−1 at 20 A g−1, proving that the different electronic structures of the diacetylene and monoacetylene units affect the properties of materials.