Preparation, characterization, and electrochemical performance of Li2CuSnO4 and Li2CuSnSiO6 electrodes for lithium batteries

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1 University of Wollongong Research Online Australian Institute for Innovative Materials - Papers Australian Institute for Innovative Materials Preparation, characterization, and electrochemical performance of LiCuSnO and LiCuSnSiO6 electrodes for lithium batteries Atef Y. Shenouda Central Metallurgical Research and Development Institute Hua-Kun Liu University of Wollongong, hua@uow.edu.au Publication Details Shenouda, AY & Liu, HK, (), Preparation, characterization, and electrochemical performance of LiCuSnO and LiCuSnSiO6 electrodes for lithium batteries, Journal of Electrochemical Society, 57(), pp. A8-A87. Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: research-pubs@uow.edu.au

2 Preparation, characterization, and electrochemical performance of LiCuSnO and LiCuSnSiO6 electrodes for lithium batteries Abstract Lithium copper tin silicon oxide was prepared from their precursor compounds using Brij surfactant and different sources of Si such as SiO, SiC, and Si N. A hydrothermal autoclave method was used in the first stage of the preparation. X-ray diffraction characterization revealed that the crystal structures of these compounds were tetragonal. Scanning electron microscope investigation showed that the particle size morphology of Li CuSnSiO 6 is larger than that of Li CuSnO. Electrochemical impedance spectroscopy explained that the cell prepared from the Li CuSnSiO 6 electrode using Si N precursor had a lower chargetransfer resistance (8 Ω) than that of Li CuSnO (R ct = 96 Ω). Furthermore, the reversible specific discharge capacity of the Li CuSnSiO 6 cell was 87 mah/g in comparison with 78 mah/g for the Li CuSnO cell after cycles. Keywords Preparation, Characterization, Electrochemical, Performance, LiCuSnO, LiCuSnSiO6, Electrodes, for, Lithium, Batteries Disciplines Engineering Physical Sciences and Mathematics Publication Details Shenouda, AY & Liu, HK, (), Preparation, characterization, and electrochemical performance of LiCuSnO and LiCuSnSiO6 electrodes for lithium batteries, Journal of Electrochemical Society, 57(), pp. A8-A87. This journal article is available at Research Online:

3 Journal of The Electrochemical Society, 57 A8-A87-65//57 /A8/5/$8. The Electrochemical Society Preparation, Characterization, and Electrochemical Performance of Li CuSnO and Li CuSnSiO 6 Electrodes for Lithium Batteries Atef Y. Shenouda a, *,z and Hua Kun Liu b, * a Central Metallurgical Research and Development Institute, Tebbin, Helwan P.O. Box 87, Egypt b Institute for Superconducting and Electronic Materials, Australian Research Centre of Excellence for Electromaterials Science, University of Wollongong, New South Wales 5, Australia A8 Lithium copper tin silicon oxide was prepared from their precursor compounds using Brij surfactant and different sources of Si such as SiO,SiC,andSi N. A hydrothermal autoclave method was used in the first stage of the preparation. X-ray diffraction characterization revealed that the crystal structures of these compounds were tetragonal. Scanning electron microscope investigation showed that the particle size morphology of Li CuSnSiO 6 is larger than that of Li CuSnO. Electrochemical impedance spectroscopy explained that the cell prepared from the Li CuSnSiO 6 electrode using Si N precursor had a lower charge-transfer resistance 8 than that of Li CuSnO R ct = 96. Furthermore, the reversible specific discharge capacity of the Li CuSnSiO 6 cell was 87 mah/g in comparison with 78 mah/g for the Li CuSnO cell after cycles. The Electrochemical Society. DOI:.9/.795 All rights reserved. Manuscript submitted January, ; revised manuscript received June 8,. Published September 9,. This was Paper 5 presented at the Vienna, Austria, Meeting of the Society, October 9, 9. * Electrochemical Society Active Member. z ayshenouda@yahoo.com Rechargeable lithium batteries have been considered an attractive power source for a wide variety of applications in popular electronic devices such as mobile telephones, video tape recorders, and laptop computers. Nowadays, these batteries are being scaled-up for prospective use in electric vehicles and energy storage. Therefore, the development of lithium batteries into advanced utilities is considered an important goal to meet a great demand. Different types of active materials have been investigated for both positive and negative electrodes. -8 To develop high capacity anode for lithium-ion batteries, silicon and some metals that can alloy with lithium at a high molar ratio are being exploited and developed as promising anode materials. 9 Tin-based oxides have attracted much attention, as they have been considered as a potential substitute for the current graphite electrode theoretical capacity 7 mah g primarily on the basis of their higher theoretical reversible specific capacity e.g., 78 mah g for SnO., When SnO was used as the anode material of lithium-ion batteries, tin works as the virtual part, and its reversible capacity is based on the formation and decomposition of lithium tin alloys, LiSn, Li 7 Sn,L 5 Sn,Li Sn 5,Li 7 Sn,orLi Sn 5. 8 The practical application of SnO, however, is hampered by poor material cyclability arising from the large specific volume change % in repetitive charging and discharging of the battery, which causes mechanical failure and the loss of electrical contact at the anode. -6 SnO undergoes severe phase changes during the lithiation and delithiation processes with severe volume expansion and contraction. Thin films of a few nanostructured carbon-free anode materials SnO,Li O SnO, CuO SnO, and Li O CuO SnO composite were prepared. Li O was introduced to suppress the aggregation of the Li Sn alloy; CuO was introduced to combine more Li per Sn metal and to improve the discharge capacity by enlarging the voltage range. These novel composites display outstanding cyclability when tested for Li storage in the voltage window. V. The ternary Li O CuO SnO composite electrode has only 7.6% initial capacity loss and nearly % capacity retention after cycles at.5c cycling rate. Fine powders of tin oxide doped with traces of silicon in combination with highly dispersed amorphous silicon oxide have been synthesized by an advanced flame-assisted ultrasonic spray pyrolysis method. 7 Upon addition with enough Si, the irreversible reaction capacity, as well as the oxidation state of Sn, reduces significantly. When the silicon content in the precursor was high enough, some metallic tin appeared in the product. Huang et al. indicated that the addition of some Si OMe to the precursor will reduce the oxygen content of the final product. Because the oxygen bound to Sn is responsible for the observed irreversible capacity, a low oxidation state is highly beneficial for this anode material. 7 Furthermore, a reversible capacity of 9 95 mah/g was found for these composites. This improved performance was explained due to an enhanced interfacial diffusion caused by highly dispersed inert second phases, i.e., SiO and LiSi O. We can also see that the introduction of SiO into the Li O CuO SnO system will improve the specific capacity through the intercalation and deintercalation of Li with Si. This study is an attempt to study the electrochemical performance of this quaternary metal oxide system Li O CuO SnO SiO. Also, the amount of reported literature on this system is small, and more data are needed. Experimental Materials preparation. Stoichiometric amounts of CH COOLi Alfa Aesar, CH CO Cu Aldrich, and stannous oxalate Aldrich were dissolved separately in distilled water to prepare Li CuSnO. Brij CH CH CH OCH CH OH surfactant was added in a weight ratio of 5: wt/wt with respect to the active materials. To prepare Li CuSnSiO 6, we used Si N Nanostructured and Amorphous Materials Inc., US, 5 nm, SiC MTI Corporation, nm and SiO, fumed silica 5 nm, CABOT GambH. The raw material compounds were then mixed together. The mixed solution was stirred and heat-treated at 8 C for h. The mixture was then transferred to an autoclave vessel 5 cm and heat-treated at 5 C for h. Finally, the samples were calcined in air atmosphere at 75 C for h in an alumina crucible. The samples were left to cool down to room temperature inside the furnace. The samples were sintered again for another h at the same temperature in air. Materials characterizations. Powder X-ray diffraction XRD measurements were carried out using a Philips powder diffractometer with Cu K radiation. IR absorption spectra were recorded using an FT/IR-6 type-a Fourier transform infrared FTIR interferometer. Samples were ground to fine powders, mixed, and diluted with KBr. The IR region examined was cm. Elemental compositions of the various tin oxide compounds were Downloaded on -8- to IP.7.8 address. Redistribution subject to ECS license or copyright; see

4 A8 Journal of The Electrochemical Society, 57 A8-A87 5 The crystal structure of the compounds has tetragonal system with rutile structure. Counts [A A.U.] theta Figure. Color online XRD patterns of Li SnCuO and Li SiCuSnO 6 prepared from different sources of Si: SiC, Si N, and SiO. Figure. Color online SEM of Li SnCuO and Li SiCuSnO 6 prepared from different sources of Si: SiC, Si N, and SiO. analyzed by inductively coupled plasma ICP, Perkin-Elmer Optima DV. Scanning electron microscopy SEM was conducted with a JEOL SEM model 66. Electrochemical measurements. The homogeneous slurry used to form the electrodes was composed of 85 wt % active materials, wt % acetylene black, and 5 wt % poly vinylidene fluoride binder dissolved in N-methyl pyrrolidone solvent. It was then spread onto Cu foil substrates. The area of each coated electrode was cm. The electrodes were dried in a vacuum oven under a vacuum pressure of Torr at C for h. The electrodes were then pressed at a pressure of kg/cm. The active material loading was about mg for each individual electrode. CR coin cells were then assembled in an argon-filled glove box Mbraun, Unilab, Germany, using lithium metal foil as the counter electrode. The electrolyte was M LiPF 6 in a mixture of ethylene carbonate and dimethyl carbonate : by volume, provided by Merck. The cells were galvanostatically charged and discharged over a voltage range of V using a current of A for both processes. Cyclic voltammetry measurements were performed using a Multi-stat CHI66 Electrochemical Workstation at a. mv s scanning rate, and the potential windows were and V vs Li/Li + electrode. The ac impedance measurement amplitude was 5 mv. The frequency range was khz mhz. Results and Discussion Structural characterization. XRD patterns of the Li CuSnO and Li CuSnSiO 6 samples showed suitable crystallinity as shown in Fig.. The samples diffraction peaks exhibited good crystalline structures. Their structures were indexed to the tetragonal system using Rietveld analysis of the XRD pattern data with a standard software package. The refined unit cell parameters are given in Table I. The crystallite sizes of Li SnCuO and Li CuSnSiO 6 prepared from Si N precursor are.86 and 8.95 nm, respectively, according to the Debye Scherrer equation L =.9 /w cos where and w are the Bragg angle and the full width at halfmaximum fwhm peak, measured in radians, of each diffraction peak, respectively. Also, is the X-ray wavelength.556 Å and L is the effective particle or grain size. It is observed that the unit cell parameters of Li SnCuSiO 6 are greater in value than those of Li SnCuO. Figure shows an SEM image of the samples. The powders have average crystal sizes of 5 and nm. In general, the particles have an interconnected network structure in the form of nanoaggregates. Figure illustrates FTIR spectra collected in the wavenumber range from to cm. The bands at, 8, 79, and 95 cm are attributed to different vibrational modes of Si O Si and O Si O groups; the vibration band at 65 cm indicates an interaction between Sn, O, and Si, which is equivalent to a Sn O Si bond in the silicon-doped tin oxide composite. These data are consistent with previous literature. EIS measurements. Electrochemical impedance spectroscopy EIS may be considered as one of the most sensitive tools for the study of differences in electrode behavior due to surface modification. The electrochemical impedance spectra of the cells, as presented in Fig., show an intercept at high frequency on the real axis Z for the resistance of the electrolyte, R e, followed by a semicircle in the high-middle frequency region and a straight line in the low frequency region. The numerical value of the diameter of the semicircle on the Z real axis is approximately equal to the charge-transfer resistance, R ct, and therefore, it can be seen that there is a marked decrease in R ct after the addition of the silicon compound. The straight line in the low frequency region is attributed to the diffusion of the lithium ions into the bulk of the electrode material, or the so-called Warburg diffusion. The plot of the real part of the impedance, Z re, vs the reciprocal root square of the lower angular frequencies is displayed in Fig. 5. The straight lines are attributed to the diffusion of the lithium ions into the bulk of the electrode material, Table I. Unit cell parameters of tetragonal Li CuSnO and Li CuSnSiO 6 samples. Sample no. Samples a Å c Å Cell volume, V Å Selected fwhm Crystallite size nm Li CuSnO Li CuSnO 6 /SiC Li CuSnO 6 /Si N Li CuSnO 6 /SiO Downloaded on -8- to IP.7.8 address. Redistribution subject to ECS license or copyright; see

5 Journal of The Electrochemical Society, 57 A8-A87 A85 % Transm mittance 6 5 sym O-Si-O O 95 cm - asy O-Si-O 79 cm - Li CuSnO Li CuSnSiO 6 sm Si O Si Si O Si Sn O Si sym O asy 8 cm 65 cm - cm W ave number cm - Figure. Color online FTIR spectra of the prepared Li SnCuO and Li SiCuSnO 6 prepared from Si N. [ohm] -Z`` Z` [ohm] Figure. Color online EIS spectroscopy of Li CuSnO and Li CuSnSiO 6 from SiC, Si N, and SiO cells. ] Z`[ohm] LiCuSnO LiCuSnSiO 6 from SiC LiCuSnSiO 6 from Si N 9 LiCuSnSiO 6 from SiO Figure 5. Color online Relationship between real impedance with the low frequencies for Li CuSnO and Li CuSnSiO 6 from SiC, Si N, and SiO. or the so-called Warburg diffusion. This relation is governed by Eq.. It is observed that the Warburg impedance coefficient, w,is 65.8 s.5 for the Li SnCuSiO 6 cell, and it has a lower value than in Li SnCuO 5.89 s.5. The parameters of the equivalent circuit are presented in Table II. Also, the diffusion coefficient values of the lithium ions for diffusion into the bulk electrode materials have been calculated using Eq. and are recorded in Table II. Z re = R e + R ct + w.5 D =.5 RT/AF w C Z re = R e + R ct + w C dl The double layer capacitance is given by =/R ct C dl 5 where R ct is the charge-transfer resistance, R e is the electrolyte resistance, is the angular frequency in the low frequency region, D is the diffusion coefficient, R is the gas constant, T is the absolute temperature, F is Faraday s constant, A is the area of the electrode surface, and C is the molar concentration of Li + ions. The obtained diffusion coefficient 8. cm s for the Li SnCuSiO 6 cell prepared from the Si N precursor explains the higher mobility for Li + ion diffusion than in the other cell, which lacked Si. Furthermore, the exchange current density is given by the following formula i = RT/nFR ct 6 where n is the number of electron involved in the electrochemical reaction. Li SnCuSiO 6 cell b is higher than for the other cell. Therefore, the charge-transfer reaction of the Li SnCuSiO 6 electrode prepared from Si N is stronger than in the other electrode prepared for the Li SnCuO cell. It is observed that C dl of cell also has a higher value:.95 5 F. Cyclic voltammetry measurements were carried out between and V as shown in Fig. 6. The cyclic voltammograms of the investigated samples show a cathodic reduction peak in the range of.5.6 V. This peak is attributed to the intercalation of lithium into tin to form Li x Sn compound x. as observed in the reported papers., As we have Li SnCuO and Li SnCuSiO 6 as the starting materials, therefore the reduced forms are Li SnCu and Li SnCuSi compounds and their intercalation with Li + are as follows 5,6 LiSnCu +. x Li + +e Li. xsn + Cu 7 Li SnCuSi +. x Li + +e Li. x Sn + Cu + Si Si + xli + + xe Li x Si Li SnCuO shows three anodic oxidation peaks at.,.85, and.7 V, respectively, for the following reactions 5,7,5,6 Li. x Sn + Cu Li SnCu +. x Li + +e Li SnCu +.5 O Li SnCuO +e E =. V E =.85 V 8 9 Table II. Electrochemical impedance parameters of Li CuSnO and Li CuSnSiO 6 cell samples. No. Samples R e R ct s.5 D i cm s C dl ma/cm Li CuSnO Li CuSnO 6 /SiC Li CuSnO 6 /Si N Li CuSnO 6 /SiO Downloaded on -8- to IP.7.8 address. Redistribution subject to ECS license or copyright; see

6 A86 Journal of The Electrochemical Society, 57 A8-A87. 8 Li SnCuO 6.x - Li SnCuSiO 6 from SiC.x - Current [I] 6 I[A].x - -.x x E[mV]vs.Li E [ Li SnCuSiO from Si N E[mV]vs.Li + LiSnCuSiO 6 from SiO Figure 6. Color online Cyclic voltammograms of Li CuSnO and Li CuSnSiO 6 from SiC, Si N,and SiO cells; scan rate:. mv s. I[A].5 I [A] E [mv] vs. Li E [mv] vs. Li + [V] vs. Li Voltage..5. Sn + Sn Li SnCuO Li SnCu Sn + Sn () Li SnCuSiO Li SiSnCu 6 8 Specific discharge capacity [mah g - ] Figure 7. Color online First discharge voltage capacity profile of Li CuSnO and Li CuSnSiO 6 from SiC, Si N, and SiO cells. Li SnCuO +.5 O Li SnCuO +e E =.7 V Li SnCuSiO 6 prepared from Si N shows three anodic oxidation peaks at.68,.5, and.85 V for the deintercalation of Li + from Li. x Sn, and the oxidation of Li SnCuSi to Li SnCuSiO and Li SnCuSiO 6, respectively. It is observed that there is a shift in the anodic peaks to more positive potentials. This can be attributed to the change of Si to Si x + and Si +. 6 The first discharge capacity plateaus vs the working voltage between and V are shown in Fig. 7. The profiles for the first reduction look fairly similar for all the samples. There is a plateau that falls in the range between.5 and.7 V vs Li + for the reduction of Sn + to metallic Sn. The first discharge curve of cell delivers the highest specific discharge capacity of about mah g. Similar results have been observed in the literature in spite of using different methods of preparation. 7,,7 Also, the charge discharge profile for the followed cycles for cell is recorded in Fig. 8. The second discharge voltage started from V; furthermore, the th discharge one began at.8 V. The drop in voltage from to.5 V was observed in a different literature. 8 The cycling performance of these cells, as shown in Fig. 9, remained good for cycles with a gradual decrease. The specific discharge capacity of the Li SnCuSiO 6 cell prepared from Si N is about. 5 Volta age [V] city [mah h g - ] arge capa ific Discha Speci Li CuSnO Li CuSnSiO 6 from SiN Li CuSnSiO from SiO 6 Li CuSnSiO 6 from SiC Specific dischargecapacity [mahg - ] C y cle Number Figure 8. Color online Charge discharge voltage capacity profile of Li CuSnSiO 6 cell prepared from Si N. Figure 9. Color online Cycling performance of Li CuSnO and Li CuSnSiO 6 from SiC, Si N,and SiO cells. Downloaded on -8- to IP.7.8 address. Redistribution subject to ECS license or copyright; see

7 Journal of The Electrochemical Society, 57 A8-A87 A87 9 mah g and it is higher than that of the other cells. The higher capacity of the quaternary oxide can be explained on the concept of using mixed types of metal oxide. They can react reversibly with a larger amount of lithium and exhibit improved electrode performance compared to single oxides, and therefore provide benefits from maintaining the structural stability, leading to a good cycling performance. Conclusions The addition of Si to Li SnCuO compound improves the electric conductivity as the charge-transfer resistance of Si compounds decreased. The specific discharge capacity of the cell prepared from Li SnCuSi 6 was improved by % in comparison with one prepared from the Li SnCuO compound. Central Metallurgical Research and Development Institute assisted in meeting the publication costs of this article. References. A. Y. Shenouda, Electrochim. Acta, 5, A. Y. Shenouda and K. R. Murali, J. Power Sources, 76, 8.. A. Y. Shenouda and H. K. Liu, J. Power Sources, 85, A. Y. Shenouda and H. K. Liu, J. Alloys Compd., 77, C. Li, W. Wei, S. Fang, H. Wang, Y. Zhang, Y. Gui, and R. Chen, J. Power Sources, 95, Z. Wen, K. Wang, L. Chen, and J. Xie, Electrochem. Commun., 8, H. Huang, E. M. Kelder, L. Chen, and J. Schoonman, J. Power Sources, 8 8, J. L. Shui, G. S. Jiang, S. Xie, and C. H. Chen, Electrochim. Acta, 9, Y. Yu, C. H. Chen, J. L. Shui, and S. Xie, Angew. Chem., Int. Ed.,, Y. Yu C.-H.Chen, and Y. Shi, Adv. Mater., 9, J. Hasson, S. Panero, P. Reale, and B. Scrosati, Int. J. Electrochem. Sci.,, 6.. C. Matei Ghimbeu, R. C. van Landschoot, J. Schoonman, and M. Lumbreras, J. Eur. Ceram. Soc., 7, Y. Liang, J. Fan, X. Xia, Y. Luo, and Z. Jia, Electrochim. Acta, 5, A. J. Bard and L. R. Faulkner, Electrochemical Methods, nd ed., p., John Wiley & Sons, New York. 5. D. G. Kim, H. Kim, H. J. Sohn, and T. Kang, J. Power Sources,,. 6. Q. Sun, B. Zhang, and Z.-W. Fu, Appl. Surf. Sci., 5, Y. I. Kim, W. H. Lee, H. S. Moon, K. S. Ji, S. H. Seong, and J. W. Park, J. Power Sources,, X. Wang, Z. Wen, Y. Liu, and X. Wu, Electrochim. Acta, 5, Downloaded on -8- to IP.7.8 address. Redistribution subject to ECS license or copyright; see