A low temperature iron-based phosphate potassium-ion battery

Potassium ion battery (PIB) is considered as a promising candidate for large-scale energy storage due to its abundant element reserves and low-cost. However, the large potassium ion radius and slowing potassium-ion migration kinetics have seriously hindered its rate capability and low temperature performance. In this work, the pyrophosphate phosphate iron potassium (K 3 NaFe 3 (PO 4 ) 2 P 2 O 7 , donate as KNFPP) cathode material is prepared via electrochemical exchange method for PIB. The KNFPP cathode shows a larger reversible specific capacity of 116.4 mAh g −1 at 0.05C under room temperature in PIB. Remarkably, it still exhibits a capacity retention ratio of 92 % after 600 cycles at 5C. Even at − 40 °C, it still maintains 61.9 % specific capacity comparing to room temperature in PIB at 0.1C. After comparing the electrochemical with Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (donate as N 4 FPP) cathode in sodium-ion battery (SIB), the KNFPP cathode exhibits better low-temperature performance particularly in a higher capacity retention ratio of 12 % than N 4 FPP at − 40 °C. Finally, the PIB full cell using KNFPP cathode and hard carbon anode shows a reversible specific capacity of 70.2 mAh g −1 with a maximum specific energy density of 224.64 Wh Kg −1 accompanying with excellent rate capability and cycle stability. The HC||NNFPP full cell shows a reversible specific capacity of 70.2 mAh g −1 with a maximum specific energy density of 224.64 Wh Kg −1 . • The KNFPP is synthesized via electrochemical ion exchange method. • The KNFPP cathode shows an outstanding low-temperature performance in PIBs. • A full cell exhibits excellent low-temperature performance.