NaTi2(PO4)3/C‖carbon package asymmetric flexible supercapacitors with the positive material recycled from spent Zn‒Mn dry batteries

Abstract

Spent Zn‒Mn batteries (ZMBs) pose a serious threat on eco-system and human health because of the toxic heavy metal ions released from ZMBs into the environment. In this report, carbon package is recycled from spent ZMBs and used as a positive electrode material for flexible supercapacitors. In a three-electrode system using 1 mol L−1 Na2SO4 as the electrolyte, the recycled carbon package (RCP) can deliver a specific capacitance of 100 F g−1 at 1 A g−1. After 5000 cycles at 1 A g−1, a specific capacitance of 86 F g−1 is retained with nearly 100% coulombic efficiency. Nanocomposite of NaTi2(PO4)3 with nitrogen-doped carbon layer (NTP/C) is prepared through a simple co-precipitation plus annealing method. NTP/C can deliver specific capacity of 320 and 273 F g−1 at 1 and 10 A g−1, using 1 mol L−1 Na2SO4 as the electrolyte. The high rate capability of NTP/C is attributed to the high specific surface area and nitrogen-doped carbon layer. Flexible asymmetric supercapacitors are assembled in configuration of NTP/C‖RCP, using 1 mol L−1 Na2SO4 as the electrolyte and stainless steel foil as the current collector. At 0.5 A g−1, the typical flexible supercapacitor cell can deliver a specific energy of 17.8 W h kg−1 with corresponding specific power of 503 W kg−1, and retain 15 W h kg−1 after 2000 cycles.