Phosphorene as Cathode Material for High-Voltage, Anti-Self-Discharge Zinc Ion Hybrid Capacitors

Output voltage and self-discharge rate are two important performance indices for supercapacitors, which have long been overlooked, though these play a very significant role in their practical application. Here, a zinc anode is used to construct a zinc ion hybrid capacitor. Expanded operating voltage of the hybrid capacitor is obtained with novel electrolytes. In addition, significantly improved anti-self-discharge ability is achieved. The phosphorene-based zinc ion capacitor exploiting a "water in salt" electrolyte with a working potential can reach 2.2 V, delivering 214.3 F g^-1 after 5000 cycles. The operating voltage is further extended to 2.5 V through the use of an organic solvent as the electrolyte; the solvent is prepared by adding 0.2 m ZnCl₂ into the tetraethylammonium tetrafluoroborate in propylene carbonate (Et₄NBF₄/PC) solvent, and it exhibits 105.9 F g^-1 even after 9500 cycles. More importantly, the phosphorene-based capacitors possess excellent anti-self-discharge performance. The capacitors retain 76.16% of capacitance after resting for 300 h. The practical application of the zinc ion capacitor is demonstrated through a flexible paper-based printed microcapacitor. It is believed that the developed zinc ion capacitor can effectively resolve the severe self-discharge problem of supercapacitors. Moreover, high-voltage zinc ion capacitors provide more opportunities for the application of supercapacitors.