Novel Hierarchical Sandwiched Ni Mn₂O₄/C Arrays For Both High-Efficiency Supercapacitors And Li-ion Batteries

Among the various storage technologies, the supercapacitors and Li-ion batteries, which have conquered the portable electronic market, such as mobile phones, laptops, cameras and other portable electronic devices, have become the prime candidate to power the next generation of Electric Vehicles(EVs) and Plug-in Hybrid Electric Vehicles(PHEVs) due to their high power/energy densities, long cycle life, environmental friendliness and safety. As is known to all, the controllable and selective synthesis of nano-structural materials is gradually becoming more important due to their functionalities and applications in plenty of fields, especially in biomedical, energy related, and electronic areas. The combination of active materials and ancillary materials to form functional systems is highly expected to be a valid approach to achieve the designed synthesis. For the active materials, transition-metal oxides are regarded as the promising candidates since they exhibit unique and irreplaceable properties in optics, magnetism, catalysis, and electricity. Certainly their potential functions in the energy fields such as in electrochemical energy storage may not be neglected either. This paper introduced a novel sandwiched-like composite with NiMn2O4 nanoparticles encapsulated in graphitized carbon sheet as the enhanced supercapacitors electrode and Li ion batteries anode for the first time.In this method, we use ultrathin NiMn Layered Double Hydroxide(NiMn-LDH) arrays as both precursors and sacrificial templates, and glucose molecules serve as the green carbon source. Under the aid of hydrogen bonding interaction between the precursor and carbon source, a polymer layer would be hydrothermally formed and then rationally converted to graphitized carbon sheet upon inert calcinations at elevated temperature. Meanwhile, the NiMn-LDH nanosheet simultaneously turns to NiMn nanoparticles encapsulated in the carbon sheet by undergoing a decomposition and reduction process induced by high temperature and the carbon sheet. Finally the samples were calcined for 200 min in air to oxidize the synthesized NiMn to NiMn2O4 nanoparticles.The obtained sandwich-like composite performs excellently as the supercapacitors electrode and Li ion batteries anode, especially in rate capability and lifespan, which is reasonably believed to originate from the synergistic effect based on the combination of the NiMn2O4 nanoparticles and graphitized carbon sheet. In the paper, there are XRD, EDS, TEM, SEM, BET data and electrochemical testing to analyze the precursor and the final obtained composite. This advanced nanoarchitecture obtained here can not only improve the electronic conductivity due to graphitized carbon coating and conductive substrates, but also prevent NiMn2O4 nanoparticles from agglomeration, pulverization and peeling off from conductive substrates. The as-prepared sandwiched NiMn2O4/C arrays are more desirable to apply in energy storage. When evaluated as supercapacitors(SCs) electrode, it exhibits ultrahigh specific capacitance(2679 F/g at 1 A/g) and superior stability(98% retention after 6000 cycles). On the other hand, due to the unique structure design, it demonstrates excellent specific capacity(1346 mAh/g at 500 mA/g), superior rate performance and cyclability for lithium-ion batteries(LIBs).