Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 3, Issue 2, Fe bruary -2012 1

ISSN 2229-5518

Synthesis and Characterization of C-Ag Nanomaterials for Battery Electrode Application

Ruby Michell e N. Buot, Gil Nonato C. Santos

Abs tract Carbon-Silver composite nanomaterials w ere grow n on the surf ace of a carbon rod using the Horizontal Vapor Phase Crystal Grow th technique. The eff ect of f lame annealing to the source materials bef ore HVPC treatment and the varying ratio of the C-Ag materials w ere studied and w as investigated using the SEM and EDX ana lysis. Results show ed that after subjecting the annealed materials w ith f lame, it produced a high yield of deposited nanomaterials compared to the unannealed ones. The improvement of the battery’s characteristic w as evident w ith the integration of the C-Ag nanomaterial composite and w as conf irmed through a comparative study of a 24 hour-voltage discharge prof ile against the other existing batteries and measurement of its internal resistance using dataStudio and PASCO V-I sensor.

Inde x TermsHVPC, composite materials, nanomaterials, battery electrode, car bon and silver

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1 INTRODUCTION

bundance of car bon in natur e made it an easy tar get as a pr ominent mater ial utilized in differ-
ent fields not only in daily mundane tasks but also in science. It even ser ved a very popular subj ect in r e- sear ch that one author of a book (Har r is 2009) wr ote that “b y the 1980s carb on science w as w idely cons i- der ed to be a matur e discipline, unlikely to yield any maj or sur pr ises, let alone Nob el Pr izes”. How ever, a quick sear ch on the libr ary and on the w or ldw idew eb w ill instantly depict an ir ony of such a statement for it is evident that due to the discovery of carbon nan o- tubes carbon science is once again fashionable.
The bulk of t he r esear ch involves carbon nano- tubes(CNTs) and its similar for m. Though most of the r esear ch focuses on under standing its gr ow th mecha n- isms, some have gear ed towar ds investigating its tec h- nological applications.
Recent studies include investigations of CNTs and its r ole in harvesting and storing ener gy. Though these r esear ches ar e consider ably at their infancy stage, r e- sults show ed an impr oved per for mance in solar cells and better r ever sible cycles in lithium -ion battery w hen CNTs and r elated str uctur es ar e incor por ated in

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Ruby Michele N. Buot, Ma ster of Science in Physics, De La Sa lle Universi- ty -Ma nila Philippines, E-ma il: rubymichelle@gmail.com

Gil Nona to C. Sa ntos, Doctor of Philosophy in Ma teria ls Science a nd E n-

gineering, De La Salle University-Manila , Philippines. E-mail: san-

tosg@dlsu.edu.ph
the system.
All these pr ovide an inter esting avenue of invest i- gation fr om synthesis of car bon nanomater ials to its evaluation for application, and this is what the curr ent invest igation w ill be. Manipulation of par ameter s w ill be carr ied out to lead to a better understanding on the nucleation and gr ow th mechanisms of car bon nanom a- ter ials and to further confir m its r ole in enhancing an electr ode’s electr ochemical per for mance.
This study is focused on the char acter ization of carbon-based nanostr uctur es synthesized thr ough Va- por Phase Crystal (VPC) Gr ow th Technique for elec- tr ode application.
Specifically, the study aims to investigate the ef- fects of the doping o f silver on the graphite pow der in the follow ing char acteristics of car bon-based nano- str uctur es: sur face topogr aphy and mor phology, el e- mental composition, and electr ochemical per formance.

2 EXPERIMENTAL SECT ION

2.1 Sample Preparation and HVPC Fabrication

Bulk mater ials namely gr aphite pow der , silver pow der and commercial carbon lid w er e subj ected to EDX analysis show ing 99.94%, 98.72% and 98.41% pu r- ity r espectively.
These mater ials w er e pr epar ed by batch, with each batch containing tw o sets of samples. Each set contains
35 mg commer cial car bon lid and a 35 mg gr aphite pow der plus a var ied per cent by mass addition of si l-

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Inte rnatio nal Jo urnal o f Sc ie ntific & Eng inee ring Re se arc h Vo lume 2, Issue 5, May -2011 2

ISSN 2229-5518

ver pow der that is 0.0175 mg(5%) and 0.175 mg (50%). Each of these samples was loaded into an amor phous silica tube with 8.5 mm inner size diameter , 11 mm outer size diameter and 220 mm length.
The fir st batch of samples labeled U-0%, U-5% and U-50% w er e dir ectly subj ected to HVPC tr eatment w ithout having been subj ected to flame annealing w hile the second batch labeled F-0%, F-5% and F-50% w as subj ected to a flame annealing pr ocedur e befor e HVPC tr eatment.Using a pr ogr ammable Ther molyne Tube Fur nace, all samples ar e baked at the optimum gr owth parameter initially deter mined elsew her e [1] that is 1200°C gr owth temperatur e w ith a r amp time of
80 minutes for 8 hour s. The tubes w er e then a llow ed to
gr adually cool to~100°C and ar e then drastically cooled by immer sing their one end in ice cold w ater w ith temperatur e ~10°C.
Applying nanomater ial r etr ieval techniques, the HVPC tr eated mater ials ar e then pr epar ed for SEM and EDX analysis [2] and battery fabr ication.

2.2 Battery Preparation and Fabrication

The fr agments of the HVPC tr eated amor phous s i- lica tube w er e submer ged in a sodium hydr oxide (NaOH) solution and sonicated for 90 minutes. The solution is then filter ed, fir st using a gauze cloth then an ashless filter paper . The filter ed NaOH solution is used as an electr olyte, the HVPC tr eated commer cial carbon lid as an electr ode and the filter paper as the batter y electr ode separator . A single electr ochemical cell is fabr icated out of each HVPC tr eated car bon lid.
The single cell voltage pr ofiling of each electr o-
chemical cell was done at a 24-hour continuous dis- char ge using PASCO V -I sensor and DataStudio soft- w ar e. The cell w ith the best dischar ge pr ofile w as r e- pr oduced for a 3v battery in ter nal r esistance pr ofiling and w as subj ected to an actual load a pplication test using blinking light emitting diodes (L EDs ) as load.

3 R ES ULTS AND DIS CUSS ION

SEM and EDX analyses confir med the HVPC fa- br ication of silver and car bon nanomater ial to be su c- cessful especially on zone 2 and 3. Nanomaterials ar e for med by pr omoting nucleation sites thr ough vapor i- zation and condensation of sour ce mater ial by pr ovi d- ing a thermal gr adient inside the tube as tubes ar e i n- ser ted halfw ay into a fur nace pr ogrammed for in cr eas- ing the temper atur e at very high level.
The optimum sample setup w as found to be the F-
5% follow ed by the U-5% as compar ed to other sample setup pr epar ation.
The maximum r atio of the sour ce mater ial (i.e.
50%) was observed to pr oduce bigger str uctur es of the mater ial which ar e mostly in micr ometer scale w ith lesser nucleation site.
Low er sur face ener gy ensur es stability of mater ial, thus low er ing the sur face ener gy w ould pr omote n a- nomaterial nucleation. Sur face ener gy can be low er ed in an over all sy stem, by using concave sur faces as sub- str ate since concave sur face has a low er sur face ener gy than a convex sur face. Thus Ag nanomater ials w er e found to nucleate best in the concave gr oove of the carbon r od r ather than on the other r egions. [3].

Figure 1. SEM micrographs of nanomaterial formed on flame annealed carbon lid, (a) F-0% (b) F-5% (c) F-50%. Inset shows dist ribut ion of silver on carbon lid.

The self-dischar ge r ate is a measur e of how quic k- ly a cell w ill lose its ener gy w hile sitting on the shelf due to unw anted chemical actions w ithin the cell. The r ate depends on the cell chemistry and the temper a- tur e. How ever , a battery dischar ge pr ompted by a connection of a load depends on the load the battery has to supply. The load w as ther efor e held fixed upon compar ison of dischar ge per for mance among cells.
A flat dischar ge cur ve depicts the ideal dischar ge per for mance of a battery since the supply voltage stays r easonably constant thr oughout the dischar ge cycle. A sloping cur ve facilitates the estim ation of the state of char ge of the batter y since the cell voltage can be used as a measur e of the r emaining char ge in the cell. Figur e
2a shows the cur ves of the differ ent voltage dischar ge pr ofile of a battery. The X axis was based on dischar ge time; the length of each dischar ge cur ve w ould be pr o- por tional to the nominal capacity of the cell thus the F5% single cell set up w hich is r epr esented by the r ed line show s a better dischar ge pr ofile than the U-5% cell r epr esented by blue line.

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Figure 2. (a) 24-hour single cell voltage profile at const ant discharge wit h constant load (b) Graph of t erminal volt age vs. current of three batt ery set up- commercial, U5% and F5%.

An electr ochemical cell’s inter nal r esistance de- ter mines the oper ating curr ent it delivers. A compar i- son on the inter nal r esistance of a batter y w ith nan o- mater ial to that of a ba ttery w ithout a nanomaterial w as ther efor e under taken.
Figur e 2b illustrates the compar ison of the slopes of the thr ee batter ies show ing the pr ototype battery w ith nanomater ial to have the smallest inter nal r esi s- tance which is 8 MΩ as compar ed to b oth batter ies l a- beled as commer cial and r aw w hich ar e found to have an inter nal r esistance of 10 MΩ. The b lue color r epr esented the r aw battery, r ed the commer cial ba t- tery and gr een the batter y w ith nanomater ial.
In the actual load testing, the ~3V battery w ith n a- nomaterial w as able to pow er all colors of the tw o blinking RGB LEDs connected in par allel while the
~3V batter y without nanomater ial w as limited to ligh t- ing up only one r ed LED. This confir ms that battery w ith nanomater ial has a better voltage sour ce than those w ithout nanomater ial since the blue LEDs have a higher forw ar d voltage than the r ed ones. The battery w ith nanomater ial w as also observed to have a lon ger shelf life than the battery w ithout nanomater ial.

4 CONCLUSION

Flame annealing befor e HVPC tr eatment pr omotes nucleation of mater ial r ather than gr owth thus Carbon and silver nanomater ial composite of high pur ity can
be successfully synthesized using HV P C technique w hen optimum gr owth parameters and flame annea l- ing tr eatment ar e applied.
The HVPC technique is effective in dir ect sur face modification of batter y electr ode. How ever, a r od w ith concave gr ooves should be used as a substr ate to en a- ble dir ect deposition of nanomater ial.

ACKNOWLEDGEM ENT

This w or k w as funded by the Depar tment of Science and Technology and Science Education Inst i- tute thr ough its ASTHR D pr ogr am and suppor ted by the Solid State Physics Resear ch Gr oup.

REFERENCES

[1] J. Fer aer, Fabr ication of Car bon Nanomater ials us- ing Hor izontal Vapor Phase Gr owth Technique

2009.
[2] W. Espulgar, Char acter ization of Silver Nanomat e- r ials, Synthesized by the Hor izontal Vapor Phase Cr ystal (HVPC) Gr ow th Technique, for Antim i- cr obial Pur poses 2010.
[3] G. Cao, Na nostructures & Nano mnate rials Synth esis,

Pro pe rtie s and Applications , Imper ial College Pr ess, London 2004.

[4] D. Linden, T. Reddy Handbook of Batte rie s, McGr aw - Hill, Tw o Penn Plaza, New Yor k 2002.

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