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 K₃V_3-xLa_x(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 K₃V_3-xLa_x(PO₄)₄/C. Specifically, K₃V_2.98La_0.02(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.