Hydrothermally synthesized zinc phosphate-rGO composites for supercapattery devices

Supercapattery, a newly emerged energy storage device, that merges the characteristics of supercapacitor and rechargeable battery. This technology not only has the properties of fast charging-discharging and power density of supercapacitor, but also has the features of high energy storage of battery. Here, we have synthesized zinc phosphate (ZnP) through facile hydrothermal technique. The electrochemical analysis of intrinsic zinc phosphate shows low specific capacity of 41.87 C/g, and to enhance the electrochemical properties of this material, ZnP was mixed with reduced graphene oxide (rGO) powder in different mass ratios. The three electrode assembly tests for ZnP_rGO with the percentage ratio of 70:30% shows an enhancement in the specific capacity to 167.2 C/g and specific capacitance reaches up to 278.7 F/g at the current density of 0.6 A/g. Besides, this composition exhibits remarkable rate capability by sustaining 66% of its initial specific capacity even at 3.0 A/g. Furthermore, ZnP_rGO (70/30%) have been successfully applied to develop supercapattery (rGO//ZnP_rGO) device by sandwiching it with rGO. This device depicts a high energy density of 24.26 W.h/kg and outstanding power density of 2550 W/kg along with the specific capacity 102.78 C/g. In order to probe the durability, the device is faced for 2000 charge-discharge cycles, and the satisfactory results were achieved indicating 71% capacity retention after 2000 cycles. Our study reveals that ZnP_rGO with percentage weight ratio of 70/30% can be an interesting electrode material for promising supercapattery applications.