Boosting the fast electrochemical kinetics of Na4Fe3(PO4)2(P2O7) via a 3D graphene network as a cathode material for potassium-ion batteries

Abstract

The structural deformation during the embedding/de-embedding of K⁺ with a large ionic size is an important factor limiting the development of potassium-ion batteries (PIBs). The iron-based mixed polyanionic material Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) makes an excellent cathode material for PIBs due to its low cost, non-toxicity, suitable theoretical capacity, and stable structure. Here, a 3D reduced graphene oxide network wrapped NFPP (NFPP@rGO) was synthesized using a freeze-drying and subsequent annealing treatment. The NFPP@rGO material as a PIB cathode achieves a high discharge specific capacity of 119.1 mA h g⁻¹ at 0.1C and 80.3 mA h g⁻¹ even at 2C current density, and retains 82.1% of its initial capacity after 500 cycles. Ex situ XPS and XRD are utilized to understand the K⁺ storage mechanism of NFPP@rGO in PIBs. The superior electrochemical properties are due to the 3D reduced graphene oxide network, which improves the material's electrical conductivity and K⁺ diffusion rate, and stabilizes structural deformation during charge and discharge. These results indicate the feasibility of the NFPP@rGO cathode material for PIBs.