Abstract
In the search for high-capacity anode materials, a facile hydrothermal route has been developed to synthesize phase-pure NiC2O4·2H2O nanorods, which were crystallized into the orthorhombic structure without using templates. To ensure the electrical conductivity of the nanorods, the produced NiC2O4·2H2O nanorods were attached to reduced graphene oxide (rGO) sheets via self-assembly layer-by-layer processes that utilize the electrostatic adsorption that occurs in a poly(diallyldimethylammonium chloride) solution. The high electrical conductivity aided by the presence of rGO significantly improved the electrochemical properties: 933 mAh g−1 for the charge capacity (oxidation), which showed 87.5% efficiency at the first cycle with a retention of approximately 85% for 100 cycles, and 586 mAh g−1 at 10 C-rates (10 A g−1) for the NiC2O4·2H2O/rGO electrode. The lithium storage processes were involved in the conversion reaction, which were fairly reversible via a transformation to Ni metal accompanied by the formation of a lithium oxalate compound upon discharge (reduction) and restoration to the original NiC2O4·2H2O upon charging (oxidation); this was confirmed via X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy and time-of-flight secondary ion mass spectroscopy. We believe that the high rate capacity and rechargeability upon cycling are the result of the unique features of the highly crystalline NiC2O4·2H2O nanorods assisted by conducting rGOs.
Highlights
The demand for sustainable and green-energy sources is rising because of increasing concerns regarding fast population growth and industrialization worldwide
Synthesis of the self-assembly layer-by-layer (SA-LBL) NiC2O4·2H2O/reduced graphene oxide (rGO) composite Hydrothermal reactions under various conditions resulted in phasepure products crystallized into an orthorhombic structure with the Cccm space group (Figure 1b of the XRD pattern, Figures 1c and d of the scanning electron microscopic and transmission electron microscopy (TEM) images, Supplementary Figure S1), the resulting crystallinity varied depending on the reaction conditions
The similarity in the crystal structure that showed the two crystal systems was observed in FeC2O4·2H2O,39 which was synthesized at room temperature and consecutive drying at 60 °C
Summary
The demand for sustainable and green-energy sources is rising because of increasing concerns regarding fast population growth and industrialization worldwide. The high electrical conductivity aided by the presence of rGO significantly improved the electrochemical properties: 933 mAh g− 1 for the charge capacity (oxidation), which showed 87.5% efficiency at the first cycle with a retention of approximately 85% for 100 cycles, and 586 mAh g − 1 at 10 C-rates (10 A g − 1) for the NiC2O4·2H2O/rGO electrode.
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