Exploring KTiPO4F as a robust polyanion anode material for potassium-ion batteries

Abstract

Because of the environmental benignity, abundance, and promising electrochemical properties of Ti-containing materials in batteries, these materials have been attracting the attention of the academic community. Herein, we report on KTiPO₄F as a novel Ti-containing polyanionic negative electrode (anode) material with a robust framework structure, which is obtained via a facile hydrothermal synthesis route. A comprehensive analysis of the chemical composition, particle morphology, and electronic and crystal structure of KTiPO₄F is performed using X-ray powder diffraction, electron microscopy, and spectroscopy methods. When tested against metallic K with a 1 M KPF₆ electrolyte, the carbon-coated KTiPO₄F reveals remarkable K-ion storage properties, delivering around 130 mA h g⁻¹ at 130 mA g⁻¹ with symmetric charge/discharge (1C rate) in the 0.001–3.0 V vs. K/K⁺ potential range with 97% capacity retention after 1000 cycles. This polyanion anode operates at an average potential of only 0.8 V vs. K/K⁺via a solid-solution-like de/insertion mechanism showing a cell volume change of 8.5% – the lowest value among modern benchmark electrode materials for potassium-ion batteries. A full symmetric K-ion KTiPO₄F‖KTiPO₄F cell is for the first time assembled and tested. This work complements the available range of anode materials for K-ion batteries with a new polyanionic representative thus extending the development frontiers.