NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

Structural And Conductivity Studies Of Li4TisOl2N.A. Alias, S.R. Majid and A.K. Arof*

Centre for Ionics University Malaya, Department of Physics,University of Malaya, 50603 Kuala Lumpur, Malaysia

*Corresponding Author: akaroj@um.edu.my

Ab tract

Li4 isO'2 has been successfully synthesized via the sol-gel method. The powders werecalcined at 700 °c, 800 "C, 900 -c and 1000 "C for one hour followed by pellet formationat 500 bars and sintering at 1000 "C for four hours. Electrochemical impedancespectroscopy (EIS) and X-Ray Diffraction (XRD) were employed to characterize theprepared Li4TisO'2. XRD pattern shows that Li4TisO'2 are crystalline and imp rities of theprepared sample pellet can be eliminated by double heat treatment. The conductivityobtained is of the order 10-8 S ern" at room temperature.

Keywords: Li4TisOl2, conductivity, XRD pattern

1. INTRODUCTION

Li4TisO'2 has attracted much attention asanode material for lithium ion batteries dueto its excellent cycling performance [1-4].Li4TisOl2 are zero-strain materials which isdefined as materials undergoing smallchanges in volume expansion duringcharge and discharge when it is cycled inthe voltage range from a v to 3.0 V [5-6].It has charge and discharge plateaus at 1.5V and a theoretical capacity of 175 mAhg'[7-8].

Huang and co-workers [9] havesynthesized Lb.92TisOll.96 via the solidstate reaction which has a conductivity of3.7 x 10-9 S ern" at ambient temperature.Previous works have reported that theconductivity of Li4TisO'2 increased afterwith Mg2+ doping on the u' sites [10] andthe Li4TisOl2 lattice ~arameter dopantswith Ga3+, Co3+ and Al + tend to decrease. he : di h G 3+ C 3+since t e rome ra II sue as a, 0,

Ae+ are smaller than Ti4+ and u' [9].Other techniques to enhance conductivityof Li4TisO'2 is by forming composites witha conductive second phase [11].Wolfenstine and Allen [12] have doped Taelements in Li4Tis012 in order to substitute

T s+ . T·4+. d ha Ion on a I sites an t econductivity obtained is 3 x 10-8 Scm-I.Generally, Li4TisOl2 powders were mainlysynthesized by solid-state reactions [13-14]and sol-gel methods [15-16]. Tosynthesize the material directly by solid-state method requires high calcinationtemperatures which results ininhomogeneity and contamination of thefinal products [17-18]. In the sol-gelmethod, inhomogeneity is overcomeduring mixing at the atomic or molecularlevel, synthesis temperature is low, heatingtime is shorter, and the crystalline particlesare distributed uniformly [19-20]. Duringthe sol-gel preparation process, isopropylalcohol was used to decelerate the sol-gelreaction and avoid the emergence ofprecipitations [21].

In the present work, Li4TisO'2 wasprepared via the sol-gel technique andcharacterized using X-Ray Diffraction(XRD) and electrochemical impedancespectroscopy (EIS). •

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NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 2009

2. EXPERIMENTAL

2.1. Sample Preparation

The prepared powder was synthesized bysol-gel method. Lithium tert-butoxide(LTB) and titanium isopropoxide (TIP)were purchased from Aldrich. 0.05 molLTB was dissolved in ethanol beforemixing with 0.03 mol of TIP. Then, themixture of water and ethanol was addeddropwise to the solution that has LTB andTIP compound. The mixture was thenstored for one week followed by filtration.The white powder was calcined at 700°C,800 DC,900°C and 1000 -c for one hour.0.5 g of calcined powder was ground usingmortar and pestle before pelletization at500 bars. The pellets were sintered at 1000°c for four hours and then stored in adessicator for characterization.

2.2. Sample Characterizations

The prepared sample was characterized byX-Ray Diffractogram (XRD) andelectrochemical impedance spectroscopy(EIS). The phase purity and crystalstructure of the obtained samples werecharacterized by XRD. The XRD scananalysis was collected over a 29 rangefrom 5° to 80°. The surface of the pelletswere painted with silver paste. Then, thepellets were sandwiched between stainlesssteel electrodes. The measurements werecarried out from 25°C to 110°C. Therange of frequency is from 50 Hz to 100MHz. Conductivity (0') of the pellet wascalculated using Equation (1).

ta=--

RbA (1)

Here t (em) is the thickness of the preparedpellet, Rb is bulk resistance in ohms thatcan be obtained directly from the Cole-Cole plot and A is area of pellet-electrodecontact.

3. RESULTS AND DISCUSSION

Fig. 1 shows the XRD pattern of Li4TisOncalcined at different temperatures (700°C,

8000C 900 "C and 1000 "C for one hour), °followed by heat-treatment at 1000 C forfour hours. The prepared samples arecrystalline. A peak at 28=--20°corresponding to LbTi03 [22-23] wasobserved in the diffractogram for samplecalcined at 700°C and 800 DC.This peakwas successfully eliminated when thesamples were calcined at 900°C and 1000DC.Hence using the above heat-treatment,a pure compound as reported by Kim andco-workers [24] can be obtained. The otherpeaks are due to Li4TisOra compound [25-27].

- _----- -_._----_.-- - ---r--I

~--- 1000 -c (1 hour)

900 ·c (1 hour)

800 ·C (1 hour)

700 ·C (1 hour)

I

_-1-' "T__,--,--r-,---r--r --.,-,-1

5 1015202530354045505560657029 (degree)

F. 1 XRD pattern of Li4Tis012 calcined oatIg. f . t d at 1000 C

different temperatures be ore Sin erefor four hours

Fig 2 shows the complex impedance pl?tsa: ~mbient temperature of Li4TisOl2 whichwere calcined at different temperaturesranging from 700°C to .1 ?OO DC.The Co.le-Cole plots exhibit se~lcI~cle hape whl~hmaybe due to mixed IOnIC and ell:;\"tromcconduction [28].

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NATIONAL WORKSHOP ON FUNCTIONAL MATERIALS 200910

700°C (1 hour)

....... ••• • I

---,---- -~ -~_Jo._--.12~O---__~~~- 10

800°C (1 hour)

oh'Q,.-;:::6c:.__, ........N • ••

~00 6 12

z; (11) (lOs)2

900°C (1 hour)~,-..Q...;::: 1-c:.._,N ...~ ... I•-~-J••

0

o 1 2z, (11)(106)

Fig. 2 C mplex impedance plot at r~omtemperature of Li4TisOl2 calcined at varioustemperatures

Shown in Fig. 3 is the plot of conductivityversus calcined temperatures. Theconductivity of the samples does not differ

significantly although samples calcined at700°C and 800 "C for one hour andsintered at 1000 -c four hours containedimpurities that can be identified as LizTi03[22-23]. The conductivity value ofLi4Tis012 obtained in this work is greaterthan that in previous literature for similarcondition [9-12].

1.00E-07 ~ -.. -- ---------

~ 0.--.-<), ..0:~ '-',A"'t y

="0=QU

1.00E-08 -r--'--~"-;T----,----

600 700 800 900 1000 I 100

Temperature (''C)

Fig. 3 Plot conductivity versus calcinationtemperature for one hour at room temperature

Fig. 4 displays the plot of conductivityversus lOOOff (K'I) of Li4Tis012 fordifferent heat-treatments. It was found thatthe conductivity is increased astemperature increased.

2.6 3.2 3.42.8 3

lOOOrr (KI)

Fig. 4 Plot of lOOOff (K-1) versus conductivity ofLi4TisOl2 calcined at (a) 700°C, (b) 800 -c, (c) 900"C and (d) 1000 °c for one hour

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NATIONAL WORKSHOP ON FUNCTIONAL MATERlALS 2009

4. CONCLUSIONS

Li4Ti50l2 compound has been obtained viathe sol-gel method. XRD profile showsthat Li4Ti50l2 obtained is crystalline andtwo times heat-treatment may eliminateimpurity compounds. The conductivityobtained is of the order 10-8 S cm-I •

ACKNOWLEDGEMENT

Authors would like to thank to Universityof Malaya for the financial support.

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