Cobalt–manganese-zinc ternary phosphate for high performance supercapattery devices

Abstract

State of the art supercapatteries have received considerable attention for their significant electrochemical performance; however, electrode materials with enhanced charge storage capabilities are desired. Here, we report the synthesis of mixed metal phosphate nanomaterials with different concentrations via a sonochemical approach. Initially, binary metal phosphates based on zinc, cobalt, and manganese were synthesized. Then, the composition of zinc and cobalt was optimized in ternary metal phosphates. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques were utilized to examine the surface morphology, elemental analysis and crystal structure of as-synthesized nanomaterials. The electrochemical characterizations were performed in a three cell configuration. Zn_0.50Co0₀.₅₀Mn(PO₄)₂ delivers the optimum performance with a specific capacity of 1022.52 C g⁻¹ (specific capacitance of 1704.21 F g⁻¹) at 1.2 A g⁻¹. This optimized material was further engaged in an asymmetric device (supercapattery) as a positive electrode material to explore the real device performance. The supercapattery device was found to have an impressive specific energy of 45.45 W h kg⁻¹ at 0.5 A g⁻¹ and provide a remarkable specific power of 4250 W kg⁻¹ at 5 A g⁻¹ current density. The device exhibits excellent capacity preservation of 93% examined after 1500 charge discharge cycles. In addition, to scrutinize the supercapattery performance in terms of capacitive and diffusion controlled processes, a simulation approach was adopted. The real device comprises a capacitive contribution of 8.42% at 3 mV s⁻¹ and 66.56% at 100 mV s⁻¹. This novel progress in ternary metal phosphates results in a fine electrode material for high performance supercapattery applications.