Strong electron push–pull effect and low transition barrier boosting non-metallic COFs photoelectrode for ultrahigh-rate photo-assisted Li–air batteries

Abstract

Photo-assisted Li–gas batteries have been recognized as one of the most effective strategies for reducing charge/discharge overpotential by incorporating photoelectrodes into conventional gas cathodes. However, the current photo-electrodes have still faced several issues, including narrow solar absorption, inadequate charge carrier separation, etc., which seriously restricted their rate capability and application in complicated Li–Air batteries. Herein, a series of the functionalized D–A configuration COF-n compounds with tunable built-in electric field and low charge-carrier recombination rates were designed and synthesized by optimizing the intramolecular electron distribution. The optimized benzoquinone-based COF-2 exhibited the lowest transition barrier of photon-generated carriers for impressive light absorption, exciton dissociation and charge separation, meanwhile its large D–A potential difference constructed ultra-strong electron push–pull effect, resulting in the strongest and even-distributed built-in electric field. Therefore, the assembled COF-2 based photo-assisted Li–Air battery delivered a record round-trip efficiency of 98% with discharge potential up to 3.34 V at 200 mA g⁻¹. Remarkably, the battery maintained prominent rate capability with a round-trip efficiency of 72% even at a high current density of 1000 mA g⁻¹, demonstrating reversible conversion of Li₂O₂, Li₂CO₃ and Li₃N. These findings highlight the significance of ultra-strong electron push–pull effect and low transition barrier in photo-assisted Li–Air batteries.