Pillar strategy enhanced ion transport and structural stability toward ultra-stable KVPO4F cathode for practical potassium-ion batteries

Abstract

KVPO4F (KVPF) is a promising cathode material for potassium-ion batteries (PIBs) because of its high operating voltage, high energy density, and excellent thermal stability. Nevertheless, the low kinetics and large volume change have been the major hurdles causing irreversible structural damage, high inner resistance, and poor cycle stability. Herein, a pillar strategy of Cs+ doping in KVPO4F is introduced to reduce the energy barrier for ion diffusion and volume change during potassiation/depotassiation, which significantly enhances the K+ diffusion coefficient and stabilizes the crystal structure of the material. Consequently, the K0.95Cs0.05VPO4F (Cs-5-KVPF) cathode exhibits an excellent discharge capacity of 104.5 mAh g−1 at 20 mA g−1 and a capacity retention rate of 87.9% after 800 cycles at 500 mA g−1. Importantly, Cs-5-KVPF//graphite full cells attain an energy density of 220 Wh kg−1 (based on the cathode and anode weight) with a high operating voltage of 3.93 V and 79.1% capacity retention after 2000 cycles at 300 mA g−1. The Cs-doped KVPO4F cathode successfully innovates the ultra-durable and high-performance cathode materials for PIBs, demonstrating its considerable potential for practical applications.