Exploring Hollandite-Type KVTiO (0.25 ≤ ≤ 2) as Electrode Materials in Potassium-Ion Batteries (KIBs).

Hollandite-type oxides, KVTiO, = 0.25, 0.5, 0.75, 1, 1.25, 1.5, and 2, are synthesized via the citrate method and evaluated as potential electrode materials for potassium-ion batteries (KIBs). Neutron powder diffraction (NPD) confirms an undistorted 4/ structure, uniform K content (1.4 ≤ ≤ 1.6), and high potassium isotropic displacement parameter (B). This decreases significantly for ≥ 1, correlating with tunnel narrowing and vanadium's stronger polarization. Transmission electron microscopy (TEM) techniques, including selected area electron diffraction (SAED), annular bright field (ABF), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) identify superstructure reflections assigned to potassium/vacancy short-range order along the axis with disorder between tunnels. Magnetic studies reveal paramagnetic behavior down to 2 K, with antiferromagnetic interactions at low temperature except for = 0.25 composition, which exhibits ferromagnetic interactions. The experimental magnetic moment suggests a low Ti content, with notable deviations at = 1.25. The electrochemical performance is assessed via galvanostatic cycling using 2.5 M potassium bis(fluorosulfonyl)imide (KFSI) in triethyl phosphate (TEP) as electrolyte. At a rate of C/10, 2 K are reversibly de/inserted per formula unit, comparable to KTiO. At C/5, KVTiO demonstrates a reversible de/insertion of 1 K/f.u., highlighting its potential for rechargeable KIBs.