High-performance solid-solution potassium-ion intercalation mechanism of multilayered turbostratic graphene nanosheets

Abstract The solid-solution reaction between an alkali cation and an active host material is known as a single-phase redox mechanism, and it is typically accompanied by a continuous voltage change. It is distinct from the typical alkali cation intercalation reaction at an equivalent site of the active host material, which exhibits a voltage plateau. Herein, we report an unusual solid-solution potassium-ion intercalation mechanism with a low-voltage plateau capacity on multilayered turbostratic graphene nanosheets (T-GNSs). Despite the disordered graphitic structure with a broad range of d-spacings (3.65-4.18 A), the T-GNSs showed a reversible plateau capacity of ∼200 mA h g-1, which is higher than that of a well-ordered graphite nanoplate (∼120 mA h g-1). In addition, a sloping capacity of ∼220 mA h g-1 was delivered with the plateau capacity, and higher rate capabilities, better reversibility, and a more stable cycling performance were confirmed on the turbostratic microstructure. First-principles calculations suggest that the multitudinous lattice domains of the T-GNSs contain diverse intercalation sites with strong binding energies, which could be the origin of the high-performance solid-solution potassium-ion intercalation behavior when the turbostratic graphene stacks have a d-spacing smaller than that of equilibrium potassium–graphite intercalation compounds (5.35 A).