Earth-abundant nanotubes with layered assembly for battery-type supercapacitors

Layer-by-layer assembly has been explored as a versatile bottom-up nanofabrication technique for desired nanostructured composites. We herein report a new class of layer-assembles on earth-abundant clays as potential electrode materials for supercapacitors. The hierarchical structure was constructed by deposition of NiMn layered double hydroxides (NiMn-LDHs) or/and poly(3,4-ethylenedioxythiophene) (PEDOT) onto perforated halloysite nanotubes (H-HNTs) template via growth and polymerization methods. The resulting composites exhibit a three-dimensional architecture with dramatically increased surface area and well-defined core-sheath configuration. NiMn-LDHs/H-HNTs electrode delivers a maximum specific capacitance of 1665 F g(-1) (at 1Ag(-1)), excellent rate capability (74.8% retention at 15 A g(-1)) and cycling stability (89.7% capacitance retention over 2000 cycles), with the performance comparable to those of literature reported NiMn-LDHs composites on artificial templates. NiMn-LDHs/PEDOT/H-HNTs electrode exhibits even higher specific capacitance (1808 F g(-1) at 1 A g(-1)) and cycling stability. Moreover, symmetric device of NiMn-LDHs/PEDOT/H-HNTs exhibit a high specific capacitance of 167.8 F g(-1) (at 1 A g(-1)), a maximum energy density of 59.6Wh kg(-1) and maximum power density of 15.7 kW kg(-1). With a much lower cost than commercial carbon nanotubes, H-HNTs stand out as a promising template for cost-effective capacitive energy storage.