Anionic F-doping-induced engineering of P2-type layered cathode materials for high-performance potassium-ion batteries

Abstract

P2-type layered oxides have emerged as promising cathode candidate materials for potassium-ion batteries. Nevertheless, unsatisfactory cycling stability hinders their practical application, chiefly arising from deleterious phase transitions and the Jahn–Teller distortion of Mn³⁺. Herein, an anion-doping strategy where F⁻ is incorporated into P2-K_0.6Zn_0.1Ti_0.05Al_0.05Mn_0.8O₂ (KTMO) cathode materials is proposed. Raman spectroscopy was employed to investigate the local chemical environment of these materials. The results revealed a slight shift to higher wavenumbers in the E_g and A_1g peaks, which was ascribed to the shortening of the average TM–O bond length triggered by the addition of F. Ex situ XRD analysis revealed that the material K_0.6Zn_0.1Ti_0.05Al_0.05Mn_0.8O_1.93F_0.07 effectively suppresses undesirable phase transitions. Moreover, the maximum variation in the lattice parameter c is only 2.2% during potassium insertion/extraction, which fully demonstrates the outstanding performance of this material in terms of structural stability. This strategy brings about excellent cycling stability with a reversible capacity of 131.8 mA h g⁻¹ and capacity retention of 76.8% after 100 cycles, within a voltage range of 2.0–4.0 V. These findings offer novel insights into the design of cathode materials possessing optimized structures and enhanced performance for potassium-ion batteries.