KVPO4F/carbon nanocomposite with highly accessible active sites and robust chemical bonds for advanced potassium-ion batteries

Abstract

KVPO4F (KVPF) has been extensively investigated as the potential cathode material for potassium-ion batteries (PIBs) owing to its high theoretical capacity, superior operating voltage, and three-dimensional K+ conduction pathway. Nevertheless, the electrochemical behavior of KVPF is limited by the inherent poor electronic conductivity of the phosphate framework and unstable electrode/electrolyte interface. To address the above issues, this work proposes an infiltration-calcination method to confine the in-situ grown KVPF into the mesoporous carbon CMK-3 (denoted KVPF@CMK-3). The assembled KVPF@CMK-3 nanocomposite features three-dimensional interconnected carbon channels, which not only offer abundant active sites and significantly accelerate K+/electron transport, but also prevent the growth of KVPF nanoparticle agglomerates, hence stabilizing the structure of the material. Additionally, V–F–C bonds are created at the interface of KVPF and CMK-3, which reduce the loss of F and stabilize the electrode interface. Thus, when tested as a cathode material for PIBs, the KVPF@CMK-3 nanocomposite delivers superior reversible capacitiy (103.2 mAh g−1 at 0.2 C), outstanding rate performance (90.1 mAh g−1 at 20 C), and steady cycling performance (92.2 mAh g−1 at 10 C and with the retention of 88.2% after 500 cycles). Moreover, its potassium storage mechanism is further examined by ex-situ XRD and ex-situ XPS techniques. The above synthetic strategy demonstrates the potential of KVPF@CMK-3 to be applied as the cathode for PIBs.