Synthesis And Electrochemical Properties Of Multiwall Carbon Nanotubes (MWCNTS) Composites As Anode Material For Lithium Ion Batteries

Syed Mustansar, Abbas (2013) Synthesis And Electrochemical Properties Of Multiwall Carbon Nanotubes (MWCNTS) Composites As Anode Material For Lithium Ion Batteries. Doctoral thesis, Quaid-i-Azam University, Islamabad.

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Abstract

Rechargeable lithium ion batteries have been extensively applied in various portable electronic and electric devices.Currently, graphite (LiC6, 372 mAh g-1; about 840 mAh cm-3) is used as an anode material in lithium ion batteries. However, many other higher capacity alternatives have been actively researched.Nanostructured transition metal oxides (TMOs) have been the focus of a large number of studies because they show high capacity and rapid rate capability.Carbon nanotubes (CNTs) with superior electrical conductivity, high surface-to-volume ratio, structural flexibility and chemical stability are recently expected to be an advanced anode material in lithium ion batteries.More importantly, CNTs can also be used in composites with metallic or oxide nanoparticles to improve the electrochemical performance of these particles.CNTs can not only provide a support for anchoring well-dispersed nanoparticles and work as a highly conductive matrix for enabling good contact between them but also can effectively prevent the volume expansion/contraction and aggregation of nanoparticles during the charge/discharge process.Therefore, it is believed that the composite of flexible and electrically conductive CNTs anchored with nanostructured TMO particles can efficiently utilize the combinative merits of nanosized TMOs and CNTs to afford lithium ion batteries with superior performance.The research work here includes the synthesis and characterization of six categories of TMO/CNT composites.CNTs prepared through chemical vapor deposition method are covalently functionalized prior to composite fabrication using wet chemical oxidants. Surface functionality groups and morphology of CNTs were analyzed by XRD, RBS, FTIR, BET, TGA, SEM and TEM. The results consistently confirmed the formation of carboxyl functionalities on CNTs, with the structure of CNTs remaining relatively intact. Functionalized CNTs showed better dispersion in aqueous media than untreated CNTs.A series of Fe3O4/CNT composites are successfully synthesized by a facile chemical co-precipitation method. The electrochemical properties are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy.The Fe3O4-7%CNT composite displays the optimized electrochemical performance, with a discharge capacity of 1093 mAh g-1 and columbic efficiency of 98.4% after 50 cycles at a current density of 100 mA g-1. Furthermore, this composite exhibits good cycling stability and rate performance at higher current densities.CNTs are anchored with mesoporous Co3O4 nano particles and their electrochemical characterizations show that Co3O4-7%CNT composite delivers a capacity of 873 mAh g-1 after 50 cycles at a current density of 100 mA g-1. When the current density is increased to 250, 350 and 500 mA g-1, it still maintains a capacity of 895, 834 and 757 mAh g-1, respectively. The high capacity, rate capability and good cycling ability of Co3O4/CNT composites are attributed to the intimate interaction between the CNTs and Co3O4 nano particles.NiO nanocrystals anchored on CNTs were fabricated and at a current density of 100 mA g-1, the composite anode delivers an initial reversible capacity of 962 mAh g-1 and retains the capacity to 601 mAh g-1 after 50 cycles. In contrast, the reversible capacity of the pure NiO particles faded to 380 mAh g-1 immediately and then gradually decreased to 278 mAh g-1 after 50 cycles. Nanospheres of CuO are synthesized by a facile solution reaction of CuCl2 in the presence of CNTs, yielding a composite material. Electrochemical tests demonstrate high rate capability and superior cycling stability for CuO-5%CNT composite with a high specific capacity of 638 mAh g-1 for up to 50 cycles.Hexagonal disk shaped ZnO are synthesized by a facile solution reaction in the presence of CNTs. The as prepared ZnO-5%CNT composite demonstrates that the conversion reactions in ZnO and ZnO/CNT electrodes enable reversible capacity of 478 mAh g-1 and 602 mAh g-1, respectively for up to 50 cycles. Our investigation highlights the importance of anchoring of small ZnO particles on CNTs for maximum utilization of electrochemically active ZnO and CNTs for energy storage application in lithium ion batteries.CuO-doped NiO (CuNiO) with porous hexagonal morphology is fabricated via a modified in-situ co-precipitation method and its composite is prepared with CNTs. Since Cu can both act as conductor and a catalyst, the CuNiO/CNT composite exhibits higher initial coulombic efficiency (82.7% of the 2nd cycle) and better capacity retention (78.6% on 50th cycle) than bare CuNiO (78.9% of the 2nd cycle), CuO/CNT (76.8% of the 2nd cycle) and NiO/CNT (77.7% of the 2nd cycle) at the current density of 100 mAh g-1. This high capacity and good cycling ability is attributed to the partial substitution of Cu+2 for Ni+2, resulting in an increase of holes concentration, and therefore improved p-type conductivity along with an intimate interaction with CNTs providing large surface area, excellent conduction, mechanical strength and chemical stability.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Lithium, Synthesis, Batteries, Electrochemical, Material, Properties, Ion, Carbon, Nanotubes, Composites, Anode, Multiwall
Subjects: Q Science > QD Chemistry
Depositing User: Muhammad Khan Khan
Date Deposited: 19 Sep 2016 06:24
Last Modified: 19 Sep 2016 06:24
URI: http://eprints.hec.gov.pk/id/eprint/1297

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