Fig. 2: Electrochemical and computational characterization of KTiPO₄F.

a CVs at 100 µV s^–1 scan rate in the 2.0–4.2 V vs. K⁺/K range. b First and second charge-discharge cycles at a C/20 rate. Inset: dQ/dE differential plot for the second galvanostatic cycle at C/20. c Galvanostatic discharge curves at rate capabilities measurements, 1C is equal to 133 mA g⁻¹ (C/2 charge rate was applied in all cycles starting from C/2). d Discharge capacities during extended cycling at 2C and 5C charge/discharge rate for 100 cycles and coulombic efficiency. e Formation energies calculated using DFT + U method in the K_1-xTiPO₄F system coupled with the clusters expansion method to predict possible ground state structures at intermediate concentrations. Crosses and arrows mark stable phases. f Theoretical voltage profile based on the ground state phases obtained from the convex hull (solid line), experimental charge curve (dashed line) and “gedanken” pure solid-solution voltage profile with no phase separation or charge ordering (dotted line).