Enhancement of K storage performance in K3V3-xLax(PO4)4/C cathode materials for potassium-ion batteries via La3+ gradient doping

Abstract

K3V3(PO4)4(KVP) is recognized as a promising cathode material for potassium-ion batteries (PIBs) due to its high capacity and robust cycling performance. However, its practical application is hindered by low electrical conductivity. This study reports on the synthesis of K3V3-xLax(PO4)4/C materials with varying levels of lanthanum doping, using sol-gel method. We conducted a systematic investigation into the effects of La3+ doping on the crystal structure, morphological characteristics, and electrochemical performance through physicochemical characterization, theoretical calculations, and electrochemical testing. Theoretical calculations suggest that La3+ doping reduces the band gap energy. Electrochemical tests demonstrate that appropriate levels of La3+ doping enhance the electrochemical performance of K3V3-xLax(PO4)4/C. Specifically, K3V2.98La0.02(PO4)4/C shows excellent electrochemical performance. After 100 cycles at 200 mA g−1, the discharge specific capacity reaches 59 mAh g−1, and after 300 cycles at 400 mA g−1, the reversible specific capacity maintains at 48 mAh g−1—nearly twice that of the undoped KVP/C. The enhanced electrochemical performance of these materials is attributed to La3+ doping, which appropriately enlarges the unit cell volume while stabilizing the crystal structure, improving K+ diffusion capability, and boosting the intrinsic electronic conductivity of the material. These findings offer new insights for developing cost-effective and high-performance cathode materials for PIBs.