Constructing FePSe3–FeSe2 heterojunctions uniformly in a Ketjen black carbon matrix for superior potassium ion batteries

Abstract

Layered heterostructures have gained significant attention as potential platforms for energy storage because of their unique electronic and interfacial characteristics. Engineering heterojunctions in a rational, efficient, and effective manner is critical to well-defined battery systems. Herein, FePSe₃–FeSe₂ heterojunctions uniformly dispersed in a Ketjen black carbon matrix (FePSe₃–FeSe₂/C) were prepared by a one-step phosphorization–selenization method. The conductive carbon matrix can prevent the aggregation of FePSe₃–FeSe₂ hexagonal nanoplatelets. Moreover, theoretical calculations demonstrate that FePSe₃–FeSe₂ heterostructures with a strong asymmetric electric field can facilitate K⁺ intercalation. Notably, FePSe₃–FeSe₂/C with rich active sites would undergo negative fading, which results in a capacity increase upon cycling. As an anode for potassium ion batteries (PIBs), FePSe₃–FeSe₂/C can deliver high capacities of 352 mA h g⁻¹ at 0.1 A g⁻¹ after 100 cycles and 224 mA h g⁻¹ at 1.0 A g⁻¹ after 3700 cycles. The strategy of fabricating FePSe₃–FeSe₂ heterojunctions can be extended to other metal phosphorus trichalcogenides to improve their performance in energy storage. Furthermore, the obtained results provide important insights into hetero-nanostructure design toward fast reaction kinetics for PIBs.