Salt-assisted in-situ formation of N-doped porous carbons for boosting K⁺ storage capacity and cycling stability

Potassium-ion batteries (PIBs) have the potential to be used in future large-scale energy storage devices because of the abundance of potassium resources and their relatively high energy density. However, low reversible capacity and poor cycling stability caused by the large size of the potassium ions limit their practical application. N-doped bacterial cellulose-derived carbons (NBCCs) were prepared by impregnating bacterial cellulose with Mg(NO₃)₂ solutions (0.03, 0.05 and 0.07 mol L⁻¹) as a pore template and nitrogen source, followed by carbonization and acid washing. The effects of the Mg(NO₃)₂ concentration on the morphology, porosity, N doping level and electrochemical performance of the NBCCs were investigated. NBCC (0.05) is the best of the three because it has an interconnected pore network structure with a homogeneous distribution of N at a concentration of 3.38 at% and a high specific surface area of 1 355 m² g⁻¹. It delivers an excellent rate capability of 134 mAh g⁻¹ at 5 A g⁻¹ and a capacity of 307 mAh g⁻¹ after 2 500 cycles at 2 A g⁻¹. A NBCC (0.05)-based anode in a potassium ion hybrid capacitor has a high energy density of 166 W h kg⁻¹ at a power density 493 W kg⁻¹ and excellent cyclability with a capacity retention of nearly 95% after 2 000 cycles. This simple synthesis strategy for fabricating carbon anode materials with an excellent electrochemical performance should promote the development of green and large-scale energy storage devices.