Fully sp2-carbon connected polymeric frameworks with rotatable conformation-enhanced lithium-storage performance

Abstract

Conjugated porous polymers are emerging as sustainable and reliable electrode materials for lithium-ion batteries, owing to their versatile chemical modification, environmental-friendliness, and low cost, but still suffer from insufficient redox-active sites and sluggish ion/electron transport. Here, two new kinds of porous polymers (denoted as TPT-CMP and BFT-CMP), comprising full sp²-carbon skeletons connected through vinylidene linkages, are synthesized by acid-catalyzed Knoevenagel condensation of ethene-1,1,2,2-tetrayl-tetrakis-1,1′-biphenyl-4-carbaldehyde and 9,9′-bifluorenylidene-3,3′,6,6′-tetrayl-tetrabenzaldehyde with s-indacene-1,3,5,7-(2H,6H)-tetraone, respectively. Such porous polymers were readily composited with carbon nanotubes to form freestanding thin films upon a simple vacuum-assisted filtration. As the anode, the TPT-CMP-based film delivered a much higher capacity of 550 mA h g⁻¹ at 100 mA g⁻¹ than the BFT-CMP-based one (407 mA h g⁻¹), although TPT-CMP exhibits a much lower surface area of 535.92 m² g⁻¹ than that (934.41 m² g⁻¹) of BFT-CMP. This phenomenon might be attributed to the idea that the conformationally rotatable tetraphenylethylene moieties in the case of TPT-CMP might improve rapid mass transport. Both composite electrodes can sustain 500 cycles without any significant decay. These results set new capacity records among porous polymer-based lithium-ion batteries and suggest a new method for achieving promising anode materials by rationally designing the main backbones of conjugated porous polymers.