Nitrogen-doped banana peel–derived porous carbon foam (N-BPPCF) successfully prepared from banana peels is used as a binder-free electrode for supercapacitors. The N-BPPCF exhibits superior performance including high specific surface areas of 1357.6 m2/g, large pore volume of 0.77 cm3/g, suitable mesopore size distributions around 3.9 nm, and super hydrophilicity with nitrogen-containing functional groups. It can easily be brought into contact with an electrolyte to facilitate electron and ion diffusion. A comparative analysis on the electrochemical properties of BPPCF electrodes is also conducted under similar conditions. The N-BPPCF electrode offers high specific capacitance of 185.8 F/g at 5 mV/s and 210.6 F/g at 0.5 A/g in 6 M KOH aqueous electrolyte versus 125.5 F/g at 5 mV/s and 173.1 F/g at 0.5 A/g for the BPPCF electrode. The results indicate that the N-BPPCF is a binder-free electrode that can be used for high performance supercapacitors.

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A series of microspherical LiFexV2/3−2x/3PO4/C (0<x<1) composites are successfully prepared using spray drying and the carbothermal reduction method. Compared with Li3V2(PO4)3/C and LiFePO4/C, LiFe0.4V0.4PO4/C is a solid solution and has a microspherical morphology. The LiFe0.4V0.4PO4/C microspheres with an essentially log‐normal distribution around 18.2 μm consist of nanosized LiFe0.4V0.4PO4/C particles as building blocks, which have an average size of around 50 nm, a specific surface area of 11.3 m2 g−1, and a Barrett–Joyner–Halenda pore diameter of 21.9 nm. Moreover, LiFe0.4V0.4PO4/C delivers a discharge capacity of 144.8 mAh g−1 at C/10, which is close to the theoretical discharge capacity of 148.2 mAh g−1 in the insertion/extraction process at 2.5–4.3 V. Even at 10C and 20C, LiFe0.4V0.4PO4/C shows excellent specific capacities of 125.2 and 119.6 mAh g−1, respectively, corresponding to excellent rate capacity retentions of close to 86.5 % and 82.6 %, respectively.

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