Research On The Application Of Helical Carbon Nanofibers In The Anode Of Lithium-ion Batteries

Lithium-ion batteries have been widely used in many fields due to many advantages such as high open circuit voltage, high capacity, safe and environmentally friendly, long cycle life. But high performance Lithium-ion batteries are demanded because of high power types be widely used. Conventional carbon materials have been unable to meet the requirements of high performance Lithium-ion batteries, It is necessary to explore new energy storage materials to break through bottleneck of Lithium-ion batteries. Helical carbon nanofibers as Lithium-ion batteries cathode have good performance in charge and discharge capacity, cycle stability and rate performance, because it have good conductive properties, high surface area and graphite layers structure is highiy disordered, so helical carbon nanofibers can provide more channel for Lithium-ion insertion and removal. This paper was mainly research the preparation of helical carbon nanofibers, microstructure and the electrochemical properties.(1) In this paper, with copper trihydrate tartaric acid as catalyst precursor, acetylene was as a source of carbon gases, helical carbon nanofibers were prepared by chemical vapor deposition method.In 250-380℃, helical carbon nanofibers were 100-300 nm in diameter and irregular; In 480-680℃, helical carbon nanofibers were around 100 nm in diameter and with the same structure morphology. Under the condition of low temperature in 480℃, the helical carbon nanofibers with same structure morphology were produced successfully. The experimental method has the advantages of simple process, convenient operation, the good reproducibility, low energy consumption and cost, so it can be extended to the industrialization.(2) Helical carbon nanofibers as anode material for Lithium-ion batteries in 480℃,580℃,680℃ were showed good cycle performance and high rate performance. Its initial discharge capacity were 811 m Ah/g, 702 m Ah/g, 613 m Ah/g, after 40 cycles, the discharge capacity were 503 m Ah/g, 443 m Ah/g, 439 m Ah/g capacity, coulombic efficiency were 97.8%, 98.6%, 97%. In a certain temperature range, with the increase of the preparation temperature, the capacity of Lithium-ion batteries was decrease, because of the graphite layer of helical carbon nanofibers were more order.(3) Helical carbon nanofibers with DNA shape, spring shape and braid shape as anode material for Lithium-ion batteries. Its initial discharge capacity were 1066 m Ah/g, 834 m Ah/g, 702 m Ah/g; after 40 cycles, the discharge capacity were 584 m Ah/g, 501 m Ah/g, 443 m Ah/g capacity, coulombic efficiency were 98.5%, 99%, 98.6%. The charge and discharge capacity of helical carbon nanofibers with DNA shaped was the highest, the spring shape was the second, the braid shape was the lowest. Helical carbon nanofibers with DNA shape can provide more channels for Lithium-ion insertion and extraction, because of a lot of "overlapping holes" or "crack" was appeared in order to maintain the DNA helix structure, so its carbon deposition irregularly. The structure was conducive to the charge and discharge capacity, Lithium-ion can be embedded into the surface of carbon nanofibers and the edge of graphite crystallite.