Electrochemical Storage Properties Of Carbon Nanotubes-Nickel Cobalt Sulfide Composites

As a new kind of 1-D material,carbon nanotubes?CNTs?have high specific area,remarkable conductivity and mechanical properties.However,CNTs are limited for the relatively low specific capacity in energy storage field.In this paper,we studied in synthesizing hybrids of transition metal sulfides/oxides and CNTs,with morphology controlling.The composites possess excellent energy storage properties and high specific area,superior conductivity from CNTs.We studied correlation among the morphology,structure and energy storage property of each composite systematically.The CNTs@SiO₂ substrate was obtained by applying hydrolyzed TEOS onto hydroxylated CNTs.Via a two-step hydrothermal synthesis,CNTs@NiCo₂S₄ for supercapacitors was synthesized.The study illustrated that when the concentration of Na2S in the sulfuration procedure was 1.2 g L^-1,the CNTs@NiCo2S4 was obtained with good integrity of the coaxial cable structure.At a discharging rate of 1 A g^-1,the CNTs@NiCo2S4 demonstrated a good specific capacity of 688 F g^-1,and it remained84.3%when the rate increased up to 5 A g^-1.The material retained 80%capacity after1600 cycles at a scanning rate of 50 mV s^-1,showing good cycling stability.The CNTs@SiO_x film prepared by a floating catalyst vapor deposition method was used as the substrate.Through a two-step hydrothermal synthesis,the CNTs@NiCo₂S₄composite film was fabricated.Results indicate that with a sulfuration process in which the concentration of Na2S is 1.2 g L^-1,the film has the best electrochemical properties.The film material has high specific capacity of 1182 F g^-1 at 5.7 A g^-1,with even 77.5%retention at 100 A g^-1.The material possesses excellent cycling stability with a capacitance retention of 86.6%after 4000 cycles at 10 A g^-1.The CNTs@?-Fe₂O₃@C material for lithium ion battery anodes was prepared by a two-step synthesis composed of a hydrothermal reaction and a post heat treatment.It is revealed that the products possess a special coaxial-cable structure.When the glu-cose was added at a concentration of 2.15 g L^-1,the pro-ducts got the best properties.It exhibits an initial reversible capacity of 1360 mAh g^-1 at current density of 50 mA g^-1,with coulombic efficiency of 68.1%.It shows good cycling performance with a reversible capacity of 97.7%after 150 cycles at the current density of 2 A g^-1.