Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Copyright copy 2010 American Scientific PublishersAll rights reservedPrinted in the United States of America

Nanoscience andNanotechnology Letters

Vol 2 86ndash88 2010

Electrochemical Characterization of Tin Quantum DotsGrown on a Carbon Nanotube Mat as an Anode of

Batteries for Medical Applications

Zhikan Zhang1 Neelima Dahal1 Ke Xu1 Daniel Choi1lowastEui-Hyeok Yang2 and Jung-Rae Park3

1Nano and Micro Engineering Laboratory Department of Chemical and Materials EngineeringUniversity of Idaho Moscow ID 83844 USA

2Department of Mechanical Engineering Stevens Institute of Technology Castle Point on the HudsonHoboken NJ 07030 USA

3Department of Plastic Engineering University of Massachusetts Lowell MA 01854 USA

Tin (Sn) quantum dots (QDs) were fabricated on carbon nanotube mats by O2 plasma and a subse-quent electrodeposition as anode materials for lithium rechargeable batteries This nanofabricationprocess may be compatible with a complementary metal-oxide-semiconductor (CMOS) processtherefore this anode material can be used for micro-batteries Lithium (Li) can be inserted reversiblywithin most carbonaceous materials Chemical vapor deposition (CVD) by using the precursor ofCH4 were employed for fabrication of carbon nanotube (CNT) mats resulting in high surface areaof anodes Sn QDs grown on the CNT mats is improving cyclic performance of anodes due to highsurface area of CNT matrix with Sn quantum dots and high specific capacity of Sn The electro-chemical characterization reveals that the discharge capacity of about 400 mAg is maintained after20 cycles The microstructure of Sn QDs was investigated by scanning electron microscopy andX-ray diffraction

Keywords Quantum Dots Carbon Nanotube Mat Lithium Rechargeable Batteries

1 INTRODUCTION

The concept of zero-dimensional (0D) material has beenaround for a few decades now and is receiving atten-tion due to its unique features and wide applicationsMuch effort has been made to fabricate nano-materials toimprove the electrochemical performances of the lithium(Li) rechargeable batteries Tin (Sn)-based anodes havehigher gravimetric and volumetric capacities than those ofcommercially available carbon materials and hence havereceived much attention as anodes in Li ion batteries12

The demands for thin film rechargeable batteries with highrate capability and energy density are increasing for var-ious applications including powering implantable medi-cal devices By increasing the surface area of anode andcathode micro-batteries may be able to have high ratecapabilities In this paper we develop a process of growingSn QDs on carbon nanotube (CNT) mats as anodes for Lirechargeable batteries

lowastAuthor to whom correspondence should be addressed

The advantage of Sn QDs grown on CNT as activematerials are as follows (1) The one-dimensional (1-D)geometry of carbon nanotubes increases the surfacearea and also improves the cycle performance of Li-alloy anodes which results in the increased capabilityof batteries3ndash6 (2) Li can be inserted reversibly withinmost carbonaceous materials Electrodepositing Sn QDson CNT allows more increment in surface area whichresults in the better cyclic performance of the battery(3) Sn being recyclable makes the battery environmentfriendly as well Fabrication of anode for coin battery testinvolves vacuum processes chemical vapor deposition forproducing CNT and deposition of Sn QDs on CNT

2 EXPERIMENTAL DETAILS

Several growth and assembly methods have been reportedfor Field Effect Transistor (FET) applications based onlsquoforests of carbon nanotubes (CNTs)rsquo7ndash9 some of whichare commercially being developed However the con-cept proposed in this research requires a growth of uni-formly distributed CNTs on substrates (to achieve the

86 Nanosci Nanotechnol Lett 2010 Vol 2 No 2 1941-490020102086003 doi101166nnl20101062

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Zhang et al Electrochemical Characterization of Sn QDs Grown on a CNT Mat as an Anode of Batteries for Medical Applications

maximum high surface area from CNTs) The technol-ogy necessary to realize lsquoCNT matsrsquo growth on substrateshas been demonstrated by controlling the catalyst structureand amount and the growth conditions has been reportedin previous work10 CNTs are grown by metal-catalyzedchemical vapor deposition (CVD) gaseous hydrocarbonprecursors such as methane (CH4 or ethylene (C2H4are decomposed over nanometer-sized particles of appro-priate catalytic metals typically iron the hydrocarbonsdecompose upon the catalytic metal surface releasing car-bon atoms which under proper conditions will form intoCNTs Typically given CNTs nucleate and grow from asingle metal particle with the size and position of thecatalytic particle determining the size (diameter) and posi-tion of the resulting CNTs First the Ni current collectorsubstrate is coated with nanometer-scale particle catalystmaterials An alumina-supported iron nanoparticle catalystsuspended in methanol is spun onto the substrate followedby a soft baking process to create catalyst islands SecondCNTs are grown from the catalyst using CVD processAn overview of the process of fabricating tin (Sn)

quantum dots on CNT is as follows The substrate withCNT mats is placed on O2 plasma chamber Reactive ionsinjected into the CNTs with energy about 50 Wndash60 Wbreak up the carbonndashcarbon (CndashC bonds) in the CNTswhich can create certain amount of defect sites on the sur-face of CNTs Once certain density of defects is createdon the surface of CNTs Sn is deposited on the CNTsby electrodeposition The electrolyte for the electrodepo-sition of Sn consists of SnSO4 and H2SO4 in 500 ml ofDI water solution A galvanostatic method was employedfor the electrodeposition at current density of 5 mAcm2

using potentiostatgalvanostat model VMC-4 of Princeton

(a)

(b)

Fig 1 Schematic diagram of defects on carbon nanotubes created byO2 plasma (a) and Sn quantum dots grown on the carbon nanotube mat(b) Those metal quantum dots can be grown on the defect cites of carbonnanotube by electrodeposition

Applied Research During electrodeposition defect citescreated by O2 plasma are played a role as nucleation citeswhere Sn QDs are grown as shown in Figure 1 The den-sity and dimensions of Sn QDs depend strongly on theplasma conditions (power time) and electrodeposition con-ditions (pulse-rate deposition time concentration of bath)The anode for the battery was developed by electrode-

positing Sn on CNT mat The electrolyte used for the pro-cess was Sn bath A current density of 5 mAcm2and avoltage range of minus5 V to 5 V were applied The electrode-position process was carried out with no heating and nostirring After a 30 sec (60 sec) of deposition the samplewas dipped in nanopure water for a minute and then wasallowed to dry naturallyCoin-type test cells were assembled in an Ar-filled glove

box using Celgard 480 as a separator 1 M LiPF6 in ethy-lene carbonate (EC)dimethyl carbonate (DMC) (11 vol-ume ratio Aldrich) as an electrolyte and Li foil (AlfaAesar) as a counter electrode and a reference electrodeThe discharge (Li insertion into the working electrode)-charge (Li removal) experiments were performed gal-vanostatically within the voltage window of 20sim39 V(vs LiLi+

3 RESULTS AND DISCUSSION

In this work a two-step process of growing Sn QDs oncarbon nanotubes mats was developed After the first step

(a)

(b)

500 nm

500 nm

Fig 2 FESEM images of Sn quantum dots grown on the surface ofcarbon nanotubes by O2 plasma and a subsequent electrodeposition ofSn for 30 seconds (a) and 90 seconds (b)

Nanosci Nanotechnol Lett 2 86ndash88 2010 87

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Electrochemical Characterization of Sn QDs Grown on a CNT Mat as an Anode of Batteries for Medical Applications Zhang et al

Fig 3 EDS spectrum of the Sn quantum dots grown on the car-bon nanotubes mat EDS analysis confirmed growth of Sn quantumdots

of producing carbon nanotube by using chemical vapordeposition (CVD) Sn QDs were deposited on the carbonnanotube mats by using electrodeposition Field emissionscanning electron microscope (FESEM) images of Sn QDsgrown on carbon nanotubes are shown in Figure 2 Inthese figures the Sn QDs with 50ndash100 nm in diameter areclearly observed In the FESEM images the Sn QDs arebrighter than carbon nanotubes because atomic number ofSn is much higher than average atomic number of carbonFigure 3 shows the X-ray energy dispersive spectroscopy(EDS) data obtained from the Sn QDs grown on carbonnanotubes The characteristic results using EDS confirmedthe growth of Sn QDsThe cycle performance of the tin quantum dots grown

electrodes cycled at a constant current of 400 mAg isshown in Figure 4 At the high dischargecharge rate of150 mAg it is found that the discharge capacities ofabout 400 mA hg are still maintained during 20 cycleswhich can be attributed to the 0D Sn structure grownon 1D carbon nanotubes having high surface area andhigh surface to volume ratio providing more active sitesfor the contact between the electrode material and elec-trolyte And also the spaces between the carbon nano-tubes give better accommodation for the volume changeswhen the tin active material reacts with Li ions duringdischargecharge processes It is believed that this effectresults in the improved cycle performance of the anodematerial

Fig 4 Cyclic performance of the Sn quantum dots-grown CNT elec-trode cycled at a constant current of 150 mAg

4 CONCLUSIONS

CNTs were grown by metal-catalyzed CVD on which SnQDs were deposited by a subsequent electrodepositionprocess Coin-type test cells were assembled in an Ar-filledglove box with Sn QDs on CNT mat as anode and Li foilas counter electrode The dischagendashcharge experiments onthe battery were performed galvanostatically Sn quantumdots grown on CNT mat as an anode in Li-rechargeablebatteries results in improved cyclic performance of theanode materials

Acknowledgments The authors acknowledge thefinancial support of the University of Idaho New FacultyStart-up Fund University of Idaho Biological Applicationsof Nanotechnology (BANTech) Funds and the Korea Sci-ence and Engineering Foundation thought the Pioneer Pro-gram funded by the Ministry of Education

References and Notes

1 N Li C Martin and B Scrosati J Power Sources 97 240 (2001)2 Y Idota T Kubota A Matsufuji Y Maekawa and T Miyasaka

Science 276 1395 (1997)3 C Sides F Croce V Young C Martin and B Scrosati Elec-

trochem and Solid-State Lett 8 A484 (2005)4 R H Baughman A Zakhidov and W de Heer Science 297 787

(2002)5 G Che B Lakshmi E Fisher and C Martin Nature 393 346

(1998)6 E T Thostensona Z Renb and T Choua Compo Science and

Technol 61 1899 (2001)7 Y Zhang A Chang J Cao Q Wang W Kim Y Li N Morris

J Kong and H Dai Appl Phys Lett 79 3155 (2001)8 N Franklin Q Wang T Tombler A Javey and H Dai Appl Phys

Lett 81 913 (2002)9 A Ural Y Li and H Dai Appl Phys Lett 81 3464 (2002)

Received 31 March 2010 Accepted 4 June 2010

88 Nanosci Nanotechnol Lett 2 86ndash88 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Zhang et al Electrochemical Characterization of Sn QDs Grown on a CNT Mat as an Anode of Batteries for Medical Applications

maximum high surface area from CNTs) The technol-ogy necessary to realize lsquoCNT matsrsquo growth on substrateshas been demonstrated by controlling the catalyst structureand amount and the growth conditions has been reportedin previous work10 CNTs are grown by metal-catalyzedchemical vapor deposition (CVD) gaseous hydrocarbonprecursors such as methane (CH4 or ethylene (C2H4are decomposed over nanometer-sized particles of appro-priate catalytic metals typically iron the hydrocarbonsdecompose upon the catalytic metal surface releasing car-bon atoms which under proper conditions will form intoCNTs Typically given CNTs nucleate and grow from asingle metal particle with the size and position of thecatalytic particle determining the size (diameter) and posi-tion of the resulting CNTs First the Ni current collectorsubstrate is coated with nanometer-scale particle catalystmaterials An alumina-supported iron nanoparticle catalystsuspended in methanol is spun onto the substrate followedby a soft baking process to create catalyst islands SecondCNTs are grown from the catalyst using CVD processAn overview of the process of fabricating tin (Sn)

quantum dots on CNT is as follows The substrate withCNT mats is placed on O2 plasma chamber Reactive ionsinjected into the CNTs with energy about 50 Wndash60 Wbreak up the carbonndashcarbon (CndashC bonds) in the CNTswhich can create certain amount of defect sites on the sur-face of CNTs Once certain density of defects is createdon the surface of CNTs Sn is deposited on the CNTsby electrodeposition The electrolyte for the electrodepo-sition of Sn consists of SnSO4 and H2SO4 in 500 ml ofDI water solution A galvanostatic method was employedfor the electrodeposition at current density of 5 mAcm2

using potentiostatgalvanostat model VMC-4 of Princeton

(a)

(b)

Fig 1 Schematic diagram of defects on carbon nanotubes created byO2 plasma (a) and Sn quantum dots grown on the carbon nanotube mat(b) Those metal quantum dots can be grown on the defect cites of carbonnanotube by electrodeposition

Applied Research During electrodeposition defect citescreated by O2 plasma are played a role as nucleation citeswhere Sn QDs are grown as shown in Figure 1 The den-sity and dimensions of Sn QDs depend strongly on theplasma conditions (power time) and electrodeposition con-ditions (pulse-rate deposition time concentration of bath)The anode for the battery was developed by electrode-

positing Sn on CNT mat The electrolyte used for the pro-cess was Sn bath A current density of 5 mAcm2and avoltage range of minus5 V to 5 V were applied The electrode-position process was carried out with no heating and nostirring After a 30 sec (60 sec) of deposition the samplewas dipped in nanopure water for a minute and then wasallowed to dry naturallyCoin-type test cells were assembled in an Ar-filled glove

box using Celgard 480 as a separator 1 M LiPF6 in ethy-lene carbonate (EC)dimethyl carbonate (DMC) (11 vol-ume ratio Aldrich) as an electrolyte and Li foil (AlfaAesar) as a counter electrode and a reference electrodeThe discharge (Li insertion into the working electrode)-charge (Li removal) experiments were performed gal-vanostatically within the voltage window of 20sim39 V(vs LiLi+

3 RESULTS AND DISCUSSION

In this work a two-step process of growing Sn QDs oncarbon nanotubes mats was developed After the first step

(a)

(b)

500 nm

500 nm

Fig 2 FESEM images of Sn quantum dots grown on the surface ofcarbon nanotubes by O2 plasma and a subsequent electrodeposition ofSn for 30 seconds (a) and 90 seconds (b)

Nanosci Nanotechnol Lett 2 86ndash88 2010 87

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Electrochemical Characterization of Sn QDs Grown on a CNT Mat as an Anode of Batteries for Medical Applications Zhang et al

Fig 3 EDS spectrum of the Sn quantum dots grown on the car-bon nanotubes mat EDS analysis confirmed growth of Sn quantumdots

of producing carbon nanotube by using chemical vapordeposition (CVD) Sn QDs were deposited on the carbonnanotube mats by using electrodeposition Field emissionscanning electron microscope (FESEM) images of Sn QDsgrown on carbon nanotubes are shown in Figure 2 Inthese figures the Sn QDs with 50ndash100 nm in diameter areclearly observed In the FESEM images the Sn QDs arebrighter than carbon nanotubes because atomic number ofSn is much higher than average atomic number of carbonFigure 3 shows the X-ray energy dispersive spectroscopy(EDS) data obtained from the Sn QDs grown on carbonnanotubes The characteristic results using EDS confirmedthe growth of Sn QDsThe cycle performance of the tin quantum dots grown

electrodes cycled at a constant current of 400 mAg isshown in Figure 4 At the high dischargecharge rate of150 mAg it is found that the discharge capacities ofabout 400 mA hg are still maintained during 20 cycleswhich can be attributed to the 0D Sn structure grownon 1D carbon nanotubes having high surface area andhigh surface to volume ratio providing more active sitesfor the contact between the electrode material and elec-trolyte And also the spaces between the carbon nano-tubes give better accommodation for the volume changeswhen the tin active material reacts with Li ions duringdischargecharge processes It is believed that this effectresults in the improved cycle performance of the anodematerial

Fig 4 Cyclic performance of the Sn quantum dots-grown CNT elec-trode cycled at a constant current of 150 mAg

4 CONCLUSIONS

CNTs were grown by metal-catalyzed CVD on which SnQDs were deposited by a subsequent electrodepositionprocess Coin-type test cells were assembled in an Ar-filledglove box with Sn QDs on CNT mat as anode and Li foilas counter electrode The dischagendashcharge experiments onthe battery were performed galvanostatically Sn quantumdots grown on CNT mat as an anode in Li-rechargeablebatteries results in improved cyclic performance of theanode materials

Acknowledgments The authors acknowledge thefinancial support of the University of Idaho New FacultyStart-up Fund University of Idaho Biological Applicationsof Nanotechnology (BANTech) Funds and the Korea Sci-ence and Engineering Foundation thought the Pioneer Pro-gram funded by the Ministry of Education

References and Notes

1 N Li C Martin and B Scrosati J Power Sources 97 240 (2001)2 Y Idota T Kubota A Matsufuji Y Maekawa and T Miyasaka

Science 276 1395 (1997)3 C Sides F Croce V Young C Martin and B Scrosati Elec-

trochem and Solid-State Lett 8 A484 (2005)4 R H Baughman A Zakhidov and W de Heer Science 297 787

(2002)5 G Che B Lakshmi E Fisher and C Martin Nature 393 346

(1998)6 E T Thostensona Z Renb and T Choua Compo Science and

Technol 61 1899 (2001)7 Y Zhang A Chang J Cao Q Wang W Kim Y Li N Morris

J Kong and H Dai Appl Phys Lett 79 3155 (2001)8 N Franklin Q Wang T Tombler A Javey and H Dai Appl Phys

Lett 81 913 (2002)9 A Ural Y Li and H Dai Appl Phys Lett 81 3464 (2002)

Received 31 March 2010 Accepted 4 June 2010

88 Nanosci Nanotechnol Lett 2 86ndash88 2010

Delivered by Ingenta toStevens Institute of Technology

IP 15524615220Wed 05 Jan 2011 153450

Electrochemical Characterization of Sn QDs Grown on a CNT Mat as an Anode of Batteries for Medical Applications Zhang et al

Fig 3 EDS spectrum of the Sn quantum dots grown on the car-bon nanotubes mat EDS analysis confirmed growth of Sn quantumdots

of producing carbon nanotube by using chemical vapordeposition (CVD) Sn QDs were deposited on the carbonnanotube mats by using electrodeposition Field emissionscanning electron microscope (FESEM) images of Sn QDsgrown on carbon nanotubes are shown in Figure 2 Inthese figures the Sn QDs with 50ndash100 nm in diameter areclearly observed In the FESEM images the Sn QDs arebrighter than carbon nanotubes because atomic number ofSn is much higher than average atomic number of carbonFigure 3 shows the X-ray energy dispersive spectroscopy(EDS) data obtained from the Sn QDs grown on carbonnanotubes The characteristic results using EDS confirmedthe growth of Sn QDsThe cycle performance of the tin quantum dots grown

electrodes cycled at a constant current of 400 mAg isshown in Figure 4 At the high dischargecharge rate of150 mAg it is found that the discharge capacities ofabout 400 mA hg are still maintained during 20 cycleswhich can be attributed to the 0D Sn structure grownon 1D carbon nanotubes having high surface area andhigh surface to volume ratio providing more active sitesfor the contact between the electrode material and elec-trolyte And also the spaces between the carbon nano-tubes give better accommodation for the volume changeswhen the tin active material reacts with Li ions duringdischargecharge processes It is believed that this effectresults in the improved cycle performance of the anodematerial

Fig 4 Cyclic performance of the Sn quantum dots-grown CNT elec-trode cycled at a constant current of 150 mAg

4 CONCLUSIONS

CNTs were grown by metal-catalyzed CVD on which SnQDs were deposited by a subsequent electrodepositionprocess Coin-type test cells were assembled in an Ar-filledglove box with Sn QDs on CNT mat as anode and Li foilas counter electrode The dischagendashcharge experiments onthe battery were performed galvanostatically Sn quantumdots grown on CNT mat as an anode in Li-rechargeablebatteries results in improved cyclic performance of theanode materials

Acknowledgments The authors acknowledge thefinancial support of the University of Idaho New FacultyStart-up Fund University of Idaho Biological Applicationsof Nanotechnology (BANTech) Funds and the Korea Sci-ence and Engineering Foundation thought the Pioneer Pro-gram funded by the Ministry of Education

References and Notes

1 N Li C Martin and B Scrosati J Power Sources 97 240 (2001)2 Y Idota T Kubota A Matsufuji Y Maekawa and T Miyasaka

Science 276 1395 (1997)3 C Sides F Croce V Young C Martin and B Scrosati Elec-

trochem and Solid-State Lett 8 A484 (2005)4 R H Baughman A Zakhidov and W de Heer Science 297 787

(2002)5 G Che B Lakshmi E Fisher and C Martin Nature 393 346

(1998)6 E T Thostensona Z Renb and T Choua Compo Science and

Technol 61 1899 (2001)7 Y Zhang A Chang J Cao Q Wang W Kim Y Li N Morris

J Kong and H Dai Appl Phys Lett 79 3155 (2001)8 N Franklin Q Wang T Tombler A Javey and H Dai Appl Phys

Lett 81 913 (2002)9 A Ural Y Li and H Dai Appl Phys Lett 81 3464 (2002)

Received 31 March 2010 Accepted 4 June 2010

88 Nanosci Nanotechnol Lett 2 86ndash88 2010