Synthesis of monodisperse hollow carbon spheres and their electrochemical performance as anodes in potassium-ion batteries

To explore high-performance carbon anodes for potassium-ion batteries, monodisperse novel hollow carbon spheres (MHCSs) were synthesized via a combination of hydrothermal reactions and high-temperature pyrolysis using 2,4-dihydroxybenzoic acid and hexamethylenetetramine as the main raw materials. The synthesized MHCSs range from 140 to 260 nm in size with a large specific area of 466 m² g^-1. The potassium storage performance and dynamics of MHCSs in KN(SO₂F)₂ (KFSI) and KPF₆ electrolytes were systematically investigated. In the KFSI electrolyte, the MHCSs have a higher reversible capacity, better cycling stability, better rate performance, and faster electrode process dynamics than in the KPF₆ electrolyte. The excellent electrochemical performance of MHCSs in the KFSI electrolyte is attributed to the hollow structure of the material and the formation of a KF-rich and uniform solid-electrolyte interface film.