Phytic acid controlled in situ synthesis of amorphous cobalt phosphate/carbon composite as anode materials with a high mass loading for symmetrical supercapacitor: amorphization of the electrode to boost the energy density

Abstract

Transition metal phosphate (TMPi)-based composites as anode electrode materials in supercapacitor applications are less reported. Herein, we report a phytic acid (PA)-assisted in situ-formed amorphous cobalt phosphate/carbon (CoPi/C) composite grown on a flexible woven carbon cloth (CC) via a simple one-step carbonization approach. The tunable synthesis of amorphous and crystalline composites is shown by simply controlling the concentration of the cobalt salts. The strategy for high mass loading to 12 mg cm^-2 is also shown in this report. Importantly, the resulting amorphous electrode materials exhibit electric double-layer capacitance (EDLC) behavior that works over a wide potential range from -1.4 to +0.5 V in an aqueous solution of potassium hydroxide (2 M KOH) and from -1.5 to +1.5 V in sodium sulfate (1 M Na₂SO₄). The amorphous electrode as an anode is capable of delivering an areal capacitance up to 2.15 F cm^-2 at a current density of 4 mA cm^-2 (gravimetric capacitance up to 606.1 F g^-1 at 1 Ag^-1) and has a retention of 94.2% at 10 000 cycles. The flexible solid-state symmetric device fabricated shows an energy density of approximately 620.0 μW h cm^-2 at a power density of 4.7 mW cm^-2 (31.1 W h kg^-1 at 476.0 W kg^-1). This study offers a novel route for the generation of metal phosphate-based anode materials with high capacitance for symmetrical supercapacitor device with high energy density.