Flexible carbon film with local enlarged interlayer spacing for ultrafast and highly durable potassium storage

Abstract

Carbon materials have drawn much attention as a rigid electrode for the reversible intercalation of K+ along with a high surface adsorption capacity for potassium-ion batteries (KIBs). However, it is a challenge to prepare flexible carbon film for freestanding KIBs anodes, which could promote the free transfer of electrolyte and allow sufficient interlayer spacing to relieve the tension generated by K+-intercalation. Herein, a flexible carbon film constructed by honeycomb-like porous nanofibers with local enlarged interlayer spacing is synthesized by an electrospinning method together with a metal-organic frameworks (MOFs)-derived strategy. The flexible carbon film improves the electrical conductivity of freestanding electrode, and the interconnected porous structure with local enlarged interlayer spacing facilitates the transfer of electrolyte to active sites fluently and relieves the K+-intercalation induced tension, which synergistically boosts the reaction kinetics and K+-storage capacity. The freestanding flexible carbon film delivers excellent potassium storage performance of 386.1 mAh g−1 at 0.1 A g−1 after 500 cycles and 190.1 mAh g−1 at 5 A g−1 after 2400 cycles. Moreover, density functional theory (DFT) calculation confirms the advantage of edge-N atoms at graphene defect in adsorbing the K+ with limited volume expansion, which could provide extra capacity beyond K+-intercalated contribution for KIBs.