Electrochemical properties of a titanium-substituted KVPO4F cathode for K-ion batteries

Polyanionic materials provide a stable framework to reversibly store and release potassium (K) as a cathode for K-ion batteries. KVPO4F which operates at a 4.3 V average redox potential is one of the most energy-dense polyanionic cathodes. Although promising, its electrochemical properties show room for improvement for practical applications. In this work, we have investigated the effects of cation mixing on the electrochemical properties of KVPO4F by introducing titanium to partially substitute vanadium. While low-voltage Ti redox is a compromise from the energy density perspective, 50% Ti-substituted KVPO4F exhibits good capacity retention that compensates for the energy density decrease, delivering 98 mA h g−1 at average 4.1 V upon 50 cycles at C/5. In addition, Ti substitution can promote K diffusion by expanding K diffusion pathways, leading to improved rate capability (71 mA h g−1 at 4C). Our results suggest that judicious selection of cation compositions can be an effective approach to engineer K-ion cathode materials with a desirable electrochemical response.