SHAHABODDIN Shamshiran ALIREZA Baghan NARJES Naipour MEYSAM Najafi

a (Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam)

b (Faculty of Information Technology, Ton Duc Thang University, Ho Chi Minh City, Vietnam)

c (Department for Chemical Engineering, Amirkabir University of Technology, Mahshahr Campus, Mahshahr, Iran)

d (Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam)

e (Medical Biology Research Center, Health Technology Institute, Kermanshah University of Medical Sciences, Kermanshah 67149-67346, Iran)

ABSTRACT Performance of carbon nanotube (CNT) and their attached metal oxides (manganese oxide (MnO) and cadmium dioxide (CdO2)) structures as anode electrodes in lithium-ion battery (LIB) and potassium-ion battery (KIB) are investigated. The Gibbs free energy of adsorption of Li and K atoms/ions on surfaces of CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2 are calculated. The cell voltages (Vcell) of Li and K atoms/ions adsorption on studied surfaces are examined. The Vcell of LIBs with metal-oxides attached to CNT (8, 0) as anode electrodes are higher than those KIBs. The adsorbed metal oxides (MnO and CdO2) on CNT (8, 0) increased the charges, electronic conductivity and Vcell of LIB and KIB, efficiently. The CNT (8, 0)-CdO2 as anode electrodes in LIB and KIB is proposed.

Keywords: nanotube, metal ion battery, metal oxide, cell voltage, DFT;

1 INTRODUCTION

Nanostructures have increased the electrical con- ductance and improved the capacity of metal-ion battery[1-5]. The nanostructures have high area surfaces and beneficent electrical properties to use as electrode in metal-ion battery. The metal dioxides have been employed in electrochemistry and they have high capacity and performance than gra- phite[6-9]. Researchers have described that nanotubes have great capacity as anode electrodes in metal-ion batteries[10-13].

The experimental researchers have demonstrated the carbon nanotubes have high application in industry due to excellent thermal, electrical and mechanical properties. The experimental researchers have used the composite structures of carbon nanotubes with metal oxides and metal dioxides in order to exploit the applications of carbon nano- tubes[14-16].

The experimental researchers have considered the metal oxides and metal dioxides for energy storage devices due to particular physical and chemical properties. The experimental researchers have confirmed that metal oxides and metal dioxides have high electrical conductivities used in metal-ion batteries[17-19].

The experimental researchers have assembled the framework of metal oxides and metal dioxides on carbon nanotubes and these frameworks increased the heat conduction and surface. The experimental researchers confirmed that these frameworks enhanced the electron and ion transport from within and outside of carbon nanotubes which have applica- tions in metal-ion batteries[20-22].

The experimental researchers have assayed to use layer-by-layer assembly to aid the growth of metal oxides and metal dioxides on carbon nanotubes. They have applied gel polymers to enforce the addition of various metals to create the composites of metal oxides and metal dioxides and carbon nanotubes[23-26].

In this study, potential of carbon nanotube (8, 0) and attached metal oxides (manganese oxide (MnO) and cadmium dioxide (CdO2)) to carbon nanotube (8, 0) as materials of anode electrodes in metal- ion batteries are investigated. The main aims of this study are (a) to compare the potential of MnO and CdO2as anode electrodes in metal-ion batteries and (c) to compare the performance of LIB and KIB.

2 COMPUTATIONAL DETAILS

Geometries of CNT (8, 0), MnO-CNT (8, 0) and CdO2-CNT (8, 0) are calculated via DFT/M06-2X and 6-311+G (2d, 2p) in GAMESS package. The frequency calculations of complexes (MnO-CNT (8, 0) and CdO2-CNT (8, 0)) are done to confirm these optimized complexes are real minima structures[27-32]. The Gibbs free energies of adsorption of metal oxides (MnO and CdO2) on CNT (8, 0) are calcula- ted as follows:

The geometries of MnO-CNT (8, 0) and CdO2-CNT (8, 0) with Li and K are calculated by DFT/M06-2X and 6-311+G (2d, 2p). The Gibbs free energies of adsorption of metals (Li and K) on surfaces of MnO-CNT (8, 0) and CdO2-CNT (8, 0) are calculated as below:

The reactions in cathode of Li-ion and K-ion batteries are: (Li++e-? Li and K++e-? K). The thorough reaction of Li-ion and K-ion batteries are:

In metal-ion battery, cell voltage (Vcell) is:Vcell=- ΔGcell/zF, whereFas Faraday constant is 96,500 C/mol,zis the charge on Li+and K+ions in electro- lyte and ΔGcellwas the Gibbs free energy change ofstudied cells[33-37]. The band gap energy (EBG) of studied nanostructures isELUMO-EHOMO[38-40].

3 RESULTS AND DISCUSSION

The structures of CNT (8, 0), and MnO and CdO2on CNT (8, 0) are presented in Fig. 1. The top and bridge of carbon atoms are possible sites of adsorption of MnO and CdO2on CNT (8, 0). TheGadof CNT (8, 0)-MnO and CNT (8, 0)-CdO2are reported in Table 1. The top positions of CNT (8, 0)-MnO and CNT (8, 0)-CdO2are more stable than bridge positions by 0.28 and 0.24 eV, respectively.

The CNT (8, 0)-MnO in top and bridge positions are more stable than CNT (8, 0)-CdO2by 0.55 and 0.51 eV, respectively. The top positions of CNT (8, 0)-MnO and CNT (8, 0)-CdO2have lower binding distance than bridge positions 0.13 and 0.12 ?, respectively. The CNT (8, 0)-MnO in top and bridge positions have lower binding distance than CNT (8, 0)-CdO2by 0.91 and 0.92 ?, respectively.

Fig. 1. Structures of CNT, CNT-MnO and CNT-CdO2 and their complexes with metals

Table 1. Gad, Band Gap Energy, q and Vcell of CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2

The band gap energies of CNT (8, 0)-CdO2and CNT (8, 0)-MnO are calculated and reported in Table 1. The band gap energies of CNT (8, 0)-MnO and CNT (8, 0)-CdO2are 0.05～0.15 eV. The CNT (8, 0)-MnO in top and bridge positions have lower band gap energies than CNT (8, 0)-CdO2by 0.06 and 0.07 eV, respectively.

The top positions of CNT (8, 0)-MnO and CNT (8, 0)-CdO2have lower band gap energies bridge positions 0.03 and 0.04 eV, respectively. The addition of MnO and CdO2molecules to the surface of CNT (8, 0) can decrease the band gap energies of CNT (8, 0) from 1.23 to 0.05～0.15 eV.

The potentials of CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2as anode in metal-ion batteries (Li-ion and K-ion battery) are investigated. In Fig. 1, the binding distances of metal ions and CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2are 1.55, 1.67 and 1.74 ?, respectively.

The charge (q) values of metal atoms on CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2surfaces are reported in Table 1. Theqof CNT (8, 0)-MnO and CNT (8, 0)-CdO2of Li and K atoms/ions are higher than CNT (8, 0). The CNT (8, 0)-CdO2has higher charges than CNT (8, 0)-MnO and CNT (8, 0).

The Gibbs free energy (Gad) values of metal atoms on CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2are reported in Table 1. The cell voltages (Vcell) of CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2as anode electrodes are calculated and reported in Table 1. The |Gad| of CNT (8, 0)-MnO and CNT (8, 0)-CdO2for Li and K atoms/ions are higher than CNT (8, 0). The |Gad| of CNT (8, 0)-CdO2for Li and K atoms/ions are higher than CNT (8, 0)-MnO.

TheVcellvalues of CNT (8, 0), CNT (8, 0)-MnO and CNT (8, 0)-CdO2as anode electrodes in LIB are 1.97, 5.13 and 5.99 V, respectively, while those in KIB are 1.71, 4.84 and 5.70 V correspondingly.

The Vcellof CNT (8, 0)-MnO and CNT (8, 0)-CdO2as anode electrodes in KIB are higher than CNT (8, 0) 3.13 and 4.00 V, respectively. The CNT (8, 0)-CdO2has the best potential as an anode electrode in LIB and KIB and it can be proposed as a novel material in electricity storage machines.

4 CONCLUSION

The top positions of CNT (8, 0)-MnO and CNT (8, 0)-CdO2have higher binding distances than bridge positions by 0.13 and 0.12 ?, respectively. The top positions of CNT (8, 0)-MnO and CNT (8, 0)-CdO2are 0.28 and 0.24 eV more stable than the bridge ones, respectively. The CNT (8, 0)-MnO on top and bridge positions are more stable than CNT (8, 0)-CdO2by 0.55 and 0.51 eV, respectively. The CNT (8, 0)-CdO2can have higher charges than CNT (8, 0)-MnO and CNT (8, 0). TheVcellof CNT (8, 0)-MnO and CNT (8, 0)-CdO2as anode electrodes in LIB and KIB are higher than CNT (8, 0) by 3.15 and 4.01 V, respectively. TheVcellvalues of CNT (8, 0)-CdO2as an anode electrode in LIB and KIB are higher than CNT (8, 0)-MnO by 0.85 and 0.86 V, respectively. Finally, the CNT (8, 0)-CdO2has the best potential as an anode electrode in LIB and KIB and it can be proposed as a novel material in electricity storage machines.