- Email: [email protected]
Structure and electrochemical properties of Mg2SnO4 nanoparticles synthesized by a facile co-precipitation method
Materials Chemistry and Physics 159 (2015) 167e172
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Structure and electrochemical properties of Mg2SnO4 nanoparticles synthesized by a facile co-precipitation method Hao Tang a, *, Cuixia Cheng b, Gaige Yu b, Haowen Liu b, *, Weiqing Chen a a
Institute of Photovoltaics, Nanchang University, Nanchang 330031, PR China Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, Hubei Province, South-Central University for Nationalities, Wuhan 430074, PR China b
h i g h l i g h t s Nanosized Mg2SnO4 has been synthesized by a facile co-precipitation method. We find that Mg2SnO4 sample is very sensitive to the ageing time of the precursor. The single phase Mg2SnO4 nanoparticles with about 23 nm can be obtained by calcining the ageing 35 min percusor at 900 C. The obtained powders show a better electrochemical performance.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 April 2014 Received in revised form 9 February 2015 Accepted 28 March 2015 Available online 8 April 2015
Nanosized Mg2SnO4 has been synthesized by a facile co-precipitation method. The structure and morphology of the as-prepared samples are characterized by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It is found that Mg2SnO4 sample is very sensitive to the aging time of the precursor. The single phase Mg2SnO4 nanoparticles with ~23 nm can be obtained at 900 C using the aging 35 min percusor as source. The electrochemical properties of the powder obtained at 900 C are investigated by galvanostatic discharge-charge tests and cyclic voltammograms (CVs). The initial specific discharge capacity reaches as high as 927.7 mAh g1 at 0.2 mA cm2 in 0.05 e3.0 V, which indicates that Mg2SnO4 nanoparticles could be a promising candidate of anode material for Li-ion batteries. © 2015 Elsevier B.V. All rights reserved.
Keywords: Inorganic compounds Nanostructures Precipitation Sintering Powder diffraction
1. Introduction Recently, Mg2SnO4 has been extensively applied as electronic ceramic, a matrix, humidity sensor and dielectric constant (TCK) [1]. It is also a potential promising alternative anode material to the commercially employed graphite (theory capacity: 370 mAh g1), because of its large theory capacity (theory capacity: 974 mAh g1) at low potentials, as well as its pollution-free, cheap and easy availability of raw materials [2,3]. However, the reversibility of Mg2SnO4 is a problem and it needs to be improved [2]. Tang et al. reported the electrochemical properties of SnO2/Mg2SnO4 mixture [3], and found the initial discharge capacity was only 542 mAh g1,
* Corresponding authors. E-mail addresses: [email protected] (H. Tang), [email protected] (H. Liu). http://dx.doi.org/10.1016/j.matchemphys.2015.03.066 0254-0584/© 2015 Elsevier B.V. All rights reserved.
which is obviously not satisfied. Especially, the report about electrochemical properties of pure phase Mg2SnO4 is scare. The system investigation is required. On the other hand, Mg2SnO4 is mainly synthesized via the conventional solid-state reaction (SSR) method [4e6] and self-heat -sustained (SHS) route [1]. The calcination temperature are acrimonious, 1200 C and 1600 C for SSR and SHS respectively, thus results in many drawbacks, such as consuming great energy, requiring higher standard for device, obtaining powders with large particle sizes. To overcome these disadvantages, wet chemical methods including polymeric precursor method [7], peroxide precursor route [8] and the flux method [9] are developed. However, all these methods are time-consuming and also require harsh reaction conditions and complex pre-treatment procedures. It is highly desirable that a simplified procedure of preparing Mg2SnO4 to alleviate the disadvantages and further improve the potential usage.
168
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
In this work, a novel and facile co-precipitation method was firstly applied to synthesize the pure phase Mg2SnO4 nanoparticles. The effects of aging time of the precursors and calcination temperature on the final products were systematically investigated. The as-prepared samples were characterized by XRD, XPS, SEM, TEM and FT-IR. The electrochemical properties of samples were also studied. 2. Experimental All the chemical reagents were of analytical grade and used without further purification. Mg2SnO4 nanoparticles were synthesized by a facile co-precipitation method. A typical process is as following: MgSO4 (0.1 M), SnCl4 (0.05 M) and NaOH (2 M) -Na2CO3 (0.3 M) mixture were simultaneously added into 100 ml distilled water by a dropwise way. The solution was kept at 65 C and pH value was 9.0. The resulting precipitate was aged at 65 C for a designed period of time (t ¼ 35 min, 1 h, 3 h, 6 h, 12 h, corresponding to sample -FC-A, B, C, D and E) under stirring. After the reaction was finished, the obtained mixture was filtered, rinsed with deionized water for several times and then dried at 70 C overnight. Finally, the white precursor was calcined at different temperatures ranging from 500 C to 900 C in air for 12 h to obtain the final samples. In order to study the effect of the aging temperature of the precursor on the final product, another precursor had also been obtained by aged at 25 C for 35 min. All other conditions were same by following the above general procedure. The obtained sample was signed as sample-AC. The crystallinity and phase purity of the products were examined using a Bruker D8 Advance powder X-ray diffraction (Cu K a, l ¼ 1.5418 Å) in the range of 10 2q 70 . The surface analysis of the sample-FC-A was measured by an X-ray photoelectron spectrometer (Thermo VG Multi Lab2000; USA). Each spectrum was calibrated using the C1s binding energy at 284.6 eV as a standard. Fourier Transform infrared (FT-IR) spectrum was recorded for KBr dilute samples using a PerkineElmer Spectrum GX spectrometer (NEXUS470). The morphology of the sample-FC-A was characterized by field-emission scanning electron microscopy (FESEM, JEOL, JSM-6700F) and transmission electron microscope (TEM, FEI, TECNAI G220 S-Twin; USA). Electrochemical measurements were carried out using the simulate cells. The working electrodes were fabricated by compressing the mixtures of the 80% active materials with 12% acetylene black and 8% polytetrafluoroethylene (PTFE). Lithium metal was used as the counter and reference electrodes. The electrolyte was 1 M LiPF6 in a 1:1 (v/v) mixture of ethylene carbonate (EC) and dimethylcarbonate (DMC), Celgard 2300 membrane was used as the cell separator. The galvanostatic discharge-charge test was carried out at 0.2 mA cm2 in 0.05e3.0 V by a battery testing system (RFT-5 V/10 mA, corporation of Lu Hua electronic equipment, China) at room temperature. Cyclic voltammograms (CV) was performed with a CHI660A electrochemical workstation (CHI Instruments, TN) at a scanning rate of 0.1 mV/s between 0.05 and 3.0 V.
Fig. 1. XRD patterns of the sample-FC-A under various calcination temperatures. With the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom and the corresponding indexes.
peaks of MgSnO3, which are remarked with the special symbols. When the product was calcined at 900 C, all the diffraction peaks can be indexed to the cubic inverse spinel phase of Mg2SnO4 (PDF No. 24-0723). No peaks delegating impure phases are observed. This temperature is a definite improvement over the calcination temperature reported in the SRS method [1]. The cell parameter obtained from Rietveld refinement with a convincible Rwp value is a ¼ 0.864 nm, which is similar situation as observed for the wet chemical peroxide route for Magnesium orthostannate [8]. The sharp peaks suggest the high crystallinity of the as-prepared powder is obtained. According to Scherer's formula [10], the average particle size has been calculated to be 23 nm. The XRD patters of sample-FC-A, B, C, D and E calcined at 900 C for 12 h are shown in Fig. 2. It demonstrates that all the main phase are the spinel Mg2SnO4 (PDF No. 24-0723) when the aging time ranges from 35 min to 12 h. Increasing the aging time up to 12 h, there are a few of weak peaks corresponding to the SnO2 and MgSnO3. When the aging times are 3 h and 6 h, the weak peaks delegating MgSnO3 disappear, and a small amount of SnO2 is still
3. Results and discussion Fig. 1 shows the diffraction patterns of the sample-FC-A calcined at different temperature for 12 h. The powder obtained at 500 C is amorphous, and only three broad peaks should be attributed to SnO2. When the samples are calcined at higher temperature, the patterns of 700 C and 800 C are similar. Comparing with the standard PDF card (24-0723), stannate phase Mg2SnO4 has been obtained, together with the obvious peaks of SnO2 and a few weak
Fig. 2. XRD patters of sample-FC-A, B,C, D and E after calcined at 900 C, with the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom.
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
detectable. When the aging times are 1 h or 35 min, no other diffraction peaks could be detected except for Mg2SnO4. The results indicate that a short period of aging time is in favor of the formation of pure phase Mg2SnO4. The intensity of the peaks of sample-FC-A is nearly same as that for sample-FC-B. So the optimum aging time could be identified as 35 min. The effect of the aging temperature of the precursor on the final sample has also been investigated. The precursors are aged at 25 and 65 C, respectively. Fig. 3 is XRD patterns of two final products. As seen in Fig. 3a, all the diffraction peaks of sample-FC can be indexed to the pure cubic inverse spinel phase of Mg2SnO4 (PDF#24-0723). However, the high intensity peaks corresponding to the phase of SnO2 (PDF#21-1250) also appear in sample-AC (Fig. 3b), indicating a by-product of SnO2 coexists with Mg2SnO4. It is obvious that the aging temperature plays a key role to the pattern of the final product. The single phase Mg2SnO4 could be obtained when the precursor was aged at 65 C. The precursor aged at 25 C will lead to a mixture of Mg2SnO4 and SnO2. In order to study the effect of aging temperature on the precursors, XRD patterns of the precursors aged at different temperature are represented in Fig. 4. All the diffraction peaks of the precursors of sample-FC-A (Fig. 4a) can be indexed to the pure cubic phase of MgSn(OH)6 (PDF#13-0313). In the XRD of the precursors of sample-AC (Fig. 4b), some minor peaks, designating the orthorhombic SnO2(PDF#03-0439) with asterisks, are also exist with MgSn(OH)6. Higher aging temperature is helpful for the formation of pure MgSn(OH)6. The difference in the precursors may be respond for the different final products. The powder morphologies of sample-FC-A were investigated by SEM and the results are listed in Fig. 5(a) and (b). It seems that the sample is composed of some sponge-like particles, which could be explained by the fundamental mechanisms of the Ostwald ripening [11]. Comparing to large particles, small particles have larger surface area to volume ratio. When small nanoparticles aggregate into large particles, the whole system would attain a lower energy state and higher thermal stability. The TEM and HRTEM images of sample-FC-A are illustrated in Fig. 5(c) and (d), respectively. The particles are irregular shapes with an average diameter between 20 and 30 nm, which are in accordance with the calculated result of the XRD pattern. The interference fringe spacing of Mg2SnO4 is about 0.498 nm
Fig. 3. XRD patters of (a) sample-FC-A (Mg2SnO4) and (b) sample-AC (Mg2SnO4/SnO2). With the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom and the corresponding indexes.
169
Fig. 4. XRD patters of (a) precursors of sample-FC-A; (b) precursors of sample-AC; With the reference data (PDF#13-0313) for cubic MgSn(OH)6 on bottom and the corresponding indexes on bottom.
(Fig. 5(d)), which is consistent with the interplanar distance of (111) plane of the spinel structure in the XRD results. XPS was used to study the surface composition of the sampleFC-A and is shown in Fig. 6. All of the peaks are assigned to C, O, Mg and Sn elements, respectively. The high resolution XPS spectra of O, Sn and Mg elements are shown in Fig. 6(b)e(d), respectively. The energy peak located at 530.24 eV corresponds to O1s. The peaks centered at 486.15 eV and 494.7 eV are ascribed to Sn 3d3/2 and Sn 3d5/2, respectively [12]. The value of the Sn 3d5/2 binding energy is lower than that of tin oxide. It may be originated from the oxygen deficiency, which decreases the binding energy of Sn [13]. The peak centered at 49.59 eV is attributed to the Mg 2p. Based on the XPS data, it is concluded that the obtained powder is composed from Mg(II), Sn(IV), and O(II). Combining with the XRD results mentioned above, the pure phase of Mg2SnO4 has been successfully synthesized by this facile co-precipitation method. The synthesis of single phase Mg2SnO4 nanoparticles can be explained by the mechanism of crystal growth in solution. It is well known that precipitation of particles involves nucleation and growth from a super-saturated solution. The relative high temperature of 65 C during the aging process could increase the activity of the reactants, which is favor to the nucleation of MgSn(OH)6. Simultaneously, a short reaction time of 35 min could confine the growth of the crystal, causing the low crystallinity and small crystallite size, as well as avoiding the formation of SnO2. Furthermore, comparing to the conventional solid-state reaction (SSR) method [4e6], the lower calcination temperature of precursor could decrease the degree of the aggregation of the little particles, which is also helpful for the formation of nano-particles. IR spectroscopy is an effective tool to detect the local cation environment of a lattice containing closely packed oxygen array. FTIR signature of sample-FC-A is depicted in Fig. 7. The vibration frequencies at 458.98, 1436.34 and 1633.27 cm1 are attributed to the possible stretching and bending vibrational modes of MgeOeMg and OeMgeO groups [14], respectively. The vibrational band observed at 586.95 cm1 can be ascribed to the stretching vibration of SneO [15]. Fig. 8 shows the charge/discharge curves of the as-prepared sample-FC-A, the electrochemical test was performed between
170
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
Fig. 5. (a) Low-magnification and (b) high-magnification SEM images of sample-FC; (c) TEM and (d) HRTEM images of sample-FC.
0.05 and 3.0 V under a specific current of 0.2 mA cm2 at room temperature. The initial discharge capacity is 927.7 mAh g1. It can be deduced that about 8 Liþ are inserted per Sn atom. In spite of a litter lower than the expected 8.4, this was much higher than that of the Mg2SnO4 synthesized by the SSR method where the capacity of the initial half cycle is just about 6 Liþ per Sn atom [2]. The difference can be explained by the particles size. Since the particle sizes are uniform, and the very small crystallites with a narrow particle size distribution can be recognized easily, the powder is quite reactive. When applied in lithium-ion battery, nanostructure materials shorten Liþ and electronic diffusion distance. In addition, the nanoparticles with a large specific surface area increase the electrodeeelectrolyte contact area, and thus increase transport Liþ number, leading to higher discharge capacity [3,16]. However, the first discharge capacity is lower than that of mixture SnO2/MgSnO4, which may be attributed to the existence of SnO2 [3]. There is a small plateau at ~0.7 V followed by a gradual decrease slope and a wide steady discharging plateau around 0.15 V in the initial discharge curve. The electrochemical mechanism of lithium extraction/reinsertion of the Mg2SnO4 nanoparticles may as follows: Mg2SnO4 þ 4 Liþ þ 4 e / Sn þ 2 Li2O þ 2 MgO
(1)
Liþ þ Sn þ x e 4 LixSn (0 x 4.4)
(2)
The potential of the large plateau around 0.15 V is significantly lower than that of other tin oxides [2], which indicates that Mg2SnO4 could be a promising candidate of anode material for application in Li-ion batteries with high energy density. Starting from the 2nd cycle, the charge/discharge curves are very similar, indicating lithium extraction/reinsertion process is reversible. In additional, all the potential plateaus do not show a wide platform like the initial discharge, but display more inclined
shape. It is obvious that an irreversible reaction happened in the first cycle. The first 100 cycle performances of the as-prepared sample-FCA are presented in Fig. 9. A reversible discharge capacity of 506.7 mAh g1 is retained in the second cycle, which presents an obvious capacity loss. The phenomenon of the large irreversible discharge capacity in the first cycle is also observed by other tin oxide-based systems. It is probably due to: (1) The severe side reactions with the electrolyte on the larger surface area form Li2O and solid electrolyte interphase (SEI) film [17,18]; (2) The formed lithium magnesium oxide matrix is not a good electronic or ionic conductor and so it hinders the formation of the lithiumetin alloy [2]. However, the capacity fade rate is about 1% per cycle after the 2nd cycle, and the reversible capacity reaches 392.2 mAh g1 after 100 cycles. The coulombic efficiency in Fig. 9 also indicates that the process of charge and discharge gradually become stable. It is comparable or even better than the earlier results [2,3]. The discharge capacity was about 350, 123 and 74 mAh g1 for the 50, 70 and 150 nm for SnO2/Mg2SnO4 powders respectively [3]. This should attribute to nano-size of the samples. In general, the smaller of particle sizes are, the better cycling performance [3]. It is not be expected that MgO would be reduced at these potentials, so no Mg metal alloy would be formed, implying MgO worked as a spectator matrix together with Li2O, in which tin can be dispersed, could buffer the volume expansion and contraction during cycling. The cyclic voltammetry of sample-FC-A has been carried out in the potential range of 0.005e3.0 V at slow scan rate of 0.1 mV s1. The obtained results are shown in Fig. 10. Analogous to chargeedischarge profiles, the first-discharge sweep differs significantly from the other of the discharge sweeps. It commences from the open circuit voltage and no cathodic peaks are seen until 1.0 V. A broad shoulder peak at about 0.75 V is observed. It can be ascribed to the onset of reduction of Mg2SnO4 to Sn metal (Eq. (1)). There is another broad peak shown at about 0.1 V, which can be
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
171
Fig. 6. XPS spectra of sample-FC-A: (a) wide scan, (b) O 1s, (c) Sn 3d and (d) Mg 2p.
attributed to the formation of Li4.4Sn alloy (Eq. (2)). In the first charge process, there is only one broad anodic shoulder peak at about 0.55 V. In the subsequent scanning cycles, the CV curves are very similar. Only one peak lies at 0.55e0.6 V in the anodic (charge)
and one at 0.65e0.7 V in the cathodic (discharge) sweeps. The intensities of the oxidation-reduction peaks increase, but their positions and shapes do not shift, which further indicates that the electrode is stable.
Fig. 7. Room temperature FT-IR spectra of the sample-FC-A.
Fig. 8. Charge-discharge voltage profiles of sample-FC-A.
172
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
Fig. 9. Charge and discharge capacities as a function of cycle number for sample-FC-A.
927.7 mAh g1. Both the chargeedischarge and cyclic voltammograms results have shown that Mg2SnO4 is a promising candidate of anode material.
Acknowledgment This paper was supported by the Basic Scientific Research of Hubei Normal University (2014F006).
References [1] [2] [3] [4] Fig. 10. Cyclic voltammograms of sample-FC-A in 0.005e3.0 V vs Li at the slow scan rate of 0.1 mV s1. Numbers indicate the cycle number.
4. Conclusions In this paper, single phase Mg2SnO4 nanoparticles have been synthesized by a facile coprecipitation method. The aging time of the precursors and the calcination temperature had a great influence on the final products. It was found that the optimum aging time of the precursor was 35 min and the calcination temperature was 900 C. The structure, composition and the morphology of the sample-FC-A were characterized by XRD, XPS, FT-TR, TEM and SEM. The average crystallite size of sample was 23 nm. The initial discharge capacity of the products reached as high as
[5] [6] [7]
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A.M. Azad, L.J. Min, M.A. Alim, J. Ceram. Int. 27 (2001) 335e341. P.A. Connor, J.T.S. Irvine, J. Power Sources 97e98 (2001) 223e225. T. Xiao, Y. Tang, Z. Ji, S. Feng, Electrochim. Acta 54 (2009) 2396e2401. I.N.S. Jackson, R.C. Liebermann, A.E. Ringwood, Earth Planet Sci. Lett. 24 (1974) 203e208. S. Raghavan, Thermochim. Acta 122 (1987) 389e393. K.T. Jacob, J. Valderrama-N, J. Solid State Chem. 22 (1977) 291e295. M.R.S. Silva, L.C.O. Miranda, M.R. C assia-Santos, S.J.G. Lima, L.E.B. Soledade, E. Longo, C.A. Paskocimas, A.G. Souza, I.M.G. Santos, J. Therm. Anal. Cal. 87 (2007) 753e757. G. Pfaff, Thermochim. Acta 237 (1994) 83e90. S. Shimada, K. Kodaira, T. Matsushita, J. Cryst. Growth 59 (1982) 662e664. H. Liu, H. Zhu, H. Yang, Mater. Res. Bull. 48 (2013) 1587e1592. W.Z. Oswald, Phys. Chem. 34 (1900) 495e499. D. Deng, J.Y. Lee, J. Chem. Mater. 20 (2008) 1841e1846. T. Sugimoto, Adv. Colloid Interf. Sci. 28 (1987) 65e108. Inorganic Library of FT-IR Spectra- Minerals, Nicodom 1, 1998. N. Jayaprakash, N. Kalaiselvi, Y.K. Sun, Electrochem. Commun. 10 (2008) 455e460. H. Liu, L. Tan, Z. Luo, J. Alloy. Comp. 502 (2010) 407e410. J.J. Zhu, Z.H. Lu, S.T. Aruna, D. Aurbach, A. Gedanken, J. Chem. Mater. 12 (2000) 2557e2566. D. Aurbach, B. Markovsky, M.D. Levi, E. Levi, A. Schechter, M. Moshkovich, Y. Cohen, J. Power Sources 81e82 (1999) 95e111.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Structure and electrochemical properties of Mg2SnO4 nanoparticles synthesized by a facile co-precipitation method Hao Tang a, *, Cuixia Cheng b, Gaige Yu b, Haowen Liu b, *, Weiqing Chen a a
Institute of Photovoltaics, Nanchang University, Nanchang 330031, PR China Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, Hubei Province, South-Central University for Nationalities, Wuhan 430074, PR China b
h i g h l i g h t s Nanosized Mg2SnO4 has been synthesized by a facile co-precipitation method. We find that Mg2SnO4 sample is very sensitive to the ageing time of the precursor. The single phase Mg2SnO4 nanoparticles with about 23 nm can be obtained by calcining the ageing 35 min percusor at 900 C. The obtained powders show a better electrochemical performance.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 April 2014 Received in revised form 9 February 2015 Accepted 28 March 2015 Available online 8 April 2015
Nanosized Mg2SnO4 has been synthesized by a facile co-precipitation method. The structure and morphology of the as-prepared samples are characterized by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), fourier Transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It is found that Mg2SnO4 sample is very sensitive to the aging time of the precursor. The single phase Mg2SnO4 nanoparticles with ~23 nm can be obtained at 900 C using the aging 35 min percusor as source. The electrochemical properties of the powder obtained at 900 C are investigated by galvanostatic discharge-charge tests and cyclic voltammograms (CVs). The initial specific discharge capacity reaches as high as 927.7 mAh g1 at 0.2 mA cm2 in 0.05 e3.0 V, which indicates that Mg2SnO4 nanoparticles could be a promising candidate of anode material for Li-ion batteries. © 2015 Elsevier B.V. All rights reserved.
Keywords: Inorganic compounds Nanostructures Precipitation Sintering Powder diffraction
1. Introduction Recently, Mg2SnO4 has been extensively applied as electronic ceramic, a matrix, humidity sensor and dielectric constant (TCK) [1]. It is also a potential promising alternative anode material to the commercially employed graphite (theory capacity: 370 mAh g1), because of its large theory capacity (theory capacity: 974 mAh g1) at low potentials, as well as its pollution-free, cheap and easy availability of raw materials [2,3]. However, the reversibility of Mg2SnO4 is a problem and it needs to be improved [2]. Tang et al. reported the electrochemical properties of SnO2/Mg2SnO4 mixture [3], and found the initial discharge capacity was only 542 mAh g1,
* Corresponding authors. E-mail addresses: [email protected] (H. Tang), [email protected] (H. Liu). http://dx.doi.org/10.1016/j.matchemphys.2015.03.066 0254-0584/© 2015 Elsevier B.V. All rights reserved.
which is obviously not satisfied. Especially, the report about electrochemical properties of pure phase Mg2SnO4 is scare. The system investigation is required. On the other hand, Mg2SnO4 is mainly synthesized via the conventional solid-state reaction (SSR) method [4e6] and self-heat -sustained (SHS) route [1]. The calcination temperature are acrimonious, 1200 C and 1600 C for SSR and SHS respectively, thus results in many drawbacks, such as consuming great energy, requiring higher standard for device, obtaining powders with large particle sizes. To overcome these disadvantages, wet chemical methods including polymeric precursor method [7], peroxide precursor route [8] and the flux method [9] are developed. However, all these methods are time-consuming and also require harsh reaction conditions and complex pre-treatment procedures. It is highly desirable that a simplified procedure of preparing Mg2SnO4 to alleviate the disadvantages and further improve the potential usage.
168
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
In this work, a novel and facile co-precipitation method was firstly applied to synthesize the pure phase Mg2SnO4 nanoparticles. The effects of aging time of the precursors and calcination temperature on the final products were systematically investigated. The as-prepared samples were characterized by XRD, XPS, SEM, TEM and FT-IR. The electrochemical properties of samples were also studied. 2. Experimental All the chemical reagents were of analytical grade and used without further purification. Mg2SnO4 nanoparticles were synthesized by a facile co-precipitation method. A typical process is as following: MgSO4 (0.1 M), SnCl4 (0.05 M) and NaOH (2 M) -Na2CO3 (0.3 M) mixture were simultaneously added into 100 ml distilled water by a dropwise way. The solution was kept at 65 C and pH value was 9.0. The resulting precipitate was aged at 65 C for a designed period of time (t ¼ 35 min, 1 h, 3 h, 6 h, 12 h, corresponding to sample -FC-A, B, C, D and E) under stirring. After the reaction was finished, the obtained mixture was filtered, rinsed with deionized water for several times and then dried at 70 C overnight. Finally, the white precursor was calcined at different temperatures ranging from 500 C to 900 C in air for 12 h to obtain the final samples. In order to study the effect of the aging temperature of the precursor on the final product, another precursor had also been obtained by aged at 25 C for 35 min. All other conditions were same by following the above general procedure. The obtained sample was signed as sample-AC. The crystallinity and phase purity of the products were examined using a Bruker D8 Advance powder X-ray diffraction (Cu K a, l ¼ 1.5418 Å) in the range of 10 2q 70 . The surface analysis of the sample-FC-A was measured by an X-ray photoelectron spectrometer (Thermo VG Multi Lab2000; USA). Each spectrum was calibrated using the C1s binding energy at 284.6 eV as a standard. Fourier Transform infrared (FT-IR) spectrum was recorded for KBr dilute samples using a PerkineElmer Spectrum GX spectrometer (NEXUS470). The morphology of the sample-FC-A was characterized by field-emission scanning electron microscopy (FESEM, JEOL, JSM-6700F) and transmission electron microscope (TEM, FEI, TECNAI G220 S-Twin; USA). Electrochemical measurements were carried out using the simulate cells. The working electrodes were fabricated by compressing the mixtures of the 80% active materials with 12% acetylene black and 8% polytetrafluoroethylene (PTFE). Lithium metal was used as the counter and reference electrodes. The electrolyte was 1 M LiPF6 in a 1:1 (v/v) mixture of ethylene carbonate (EC) and dimethylcarbonate (DMC), Celgard 2300 membrane was used as the cell separator. The galvanostatic discharge-charge test was carried out at 0.2 mA cm2 in 0.05e3.0 V by a battery testing system (RFT-5 V/10 mA, corporation of Lu Hua electronic equipment, China) at room temperature. Cyclic voltammograms (CV) was performed with a CHI660A electrochemical workstation (CHI Instruments, TN) at a scanning rate of 0.1 mV/s between 0.05 and 3.0 V.
Fig. 1. XRD patterns of the sample-FC-A under various calcination temperatures. With the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom and the corresponding indexes.
peaks of MgSnO3, which are remarked with the special symbols. When the product was calcined at 900 C, all the diffraction peaks can be indexed to the cubic inverse spinel phase of Mg2SnO4 (PDF No. 24-0723). No peaks delegating impure phases are observed. This temperature is a definite improvement over the calcination temperature reported in the SRS method [1]. The cell parameter obtained from Rietveld refinement with a convincible Rwp value is a ¼ 0.864 nm, which is similar situation as observed for the wet chemical peroxide route for Magnesium orthostannate [8]. The sharp peaks suggest the high crystallinity of the as-prepared powder is obtained. According to Scherer's formula [10], the average particle size has been calculated to be 23 nm. The XRD patters of sample-FC-A, B, C, D and E calcined at 900 C for 12 h are shown in Fig. 2. It demonstrates that all the main phase are the spinel Mg2SnO4 (PDF No. 24-0723) when the aging time ranges from 35 min to 12 h. Increasing the aging time up to 12 h, there are a few of weak peaks corresponding to the SnO2 and MgSnO3. When the aging times are 3 h and 6 h, the weak peaks delegating MgSnO3 disappear, and a small amount of SnO2 is still
3. Results and discussion Fig. 1 shows the diffraction patterns of the sample-FC-A calcined at different temperature for 12 h. The powder obtained at 500 C is amorphous, and only three broad peaks should be attributed to SnO2. When the samples are calcined at higher temperature, the patterns of 700 C and 800 C are similar. Comparing with the standard PDF card (24-0723), stannate phase Mg2SnO4 has been obtained, together with the obvious peaks of SnO2 and a few weak
Fig. 2. XRD patters of sample-FC-A, B,C, D and E after calcined at 900 C, with the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom.
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
detectable. When the aging times are 1 h or 35 min, no other diffraction peaks could be detected except for Mg2SnO4. The results indicate that a short period of aging time is in favor of the formation of pure phase Mg2SnO4. The intensity of the peaks of sample-FC-A is nearly same as that for sample-FC-B. So the optimum aging time could be identified as 35 min. The effect of the aging temperature of the precursor on the final sample has also been investigated. The precursors are aged at 25 and 65 C, respectively. Fig. 3 is XRD patterns of two final products. As seen in Fig. 3a, all the diffraction peaks of sample-FC can be indexed to the pure cubic inverse spinel phase of Mg2SnO4 (PDF#24-0723). However, the high intensity peaks corresponding to the phase of SnO2 (PDF#21-1250) also appear in sample-AC (Fig. 3b), indicating a by-product of SnO2 coexists with Mg2SnO4. It is obvious that the aging temperature plays a key role to the pattern of the final product. The single phase Mg2SnO4 could be obtained when the precursor was aged at 65 C. The precursor aged at 25 C will lead to a mixture of Mg2SnO4 and SnO2. In order to study the effect of aging temperature on the precursors, XRD patterns of the precursors aged at different temperature are represented in Fig. 4. All the diffraction peaks of the precursors of sample-FC-A (Fig. 4a) can be indexed to the pure cubic phase of MgSn(OH)6 (PDF#13-0313). In the XRD of the precursors of sample-AC (Fig. 4b), some minor peaks, designating the orthorhombic SnO2(PDF#03-0439) with asterisks, are also exist with MgSn(OH)6. Higher aging temperature is helpful for the formation of pure MgSn(OH)6. The difference in the precursors may be respond for the different final products. The powder morphologies of sample-FC-A were investigated by SEM and the results are listed in Fig. 5(a) and (b). It seems that the sample is composed of some sponge-like particles, which could be explained by the fundamental mechanisms of the Ostwald ripening [11]. Comparing to large particles, small particles have larger surface area to volume ratio. When small nanoparticles aggregate into large particles, the whole system would attain a lower energy state and higher thermal stability. The TEM and HRTEM images of sample-FC-A are illustrated in Fig. 5(c) and (d), respectively. The particles are irregular shapes with an average diameter between 20 and 30 nm, which are in accordance with the calculated result of the XRD pattern. The interference fringe spacing of Mg2SnO4 is about 0.498 nm
Fig. 3. XRD patters of (a) sample-FC-A (Mg2SnO4) and (b) sample-AC (Mg2SnO4/SnO2). With the reference data (PDF#24-0723) for cubic Mg2SnO4 on bottom and the corresponding indexes.
169
Fig. 4. XRD patters of (a) precursors of sample-FC-A; (b) precursors of sample-AC; With the reference data (PDF#13-0313) for cubic MgSn(OH)6 on bottom and the corresponding indexes on bottom.
(Fig. 5(d)), which is consistent with the interplanar distance of (111) plane of the spinel structure in the XRD results. XPS was used to study the surface composition of the sampleFC-A and is shown in Fig. 6. All of the peaks are assigned to C, O, Mg and Sn elements, respectively. The high resolution XPS spectra of O, Sn and Mg elements are shown in Fig. 6(b)e(d), respectively. The energy peak located at 530.24 eV corresponds to O1s. The peaks centered at 486.15 eV and 494.7 eV are ascribed to Sn 3d3/2 and Sn 3d5/2, respectively [12]. The value of the Sn 3d5/2 binding energy is lower than that of tin oxide. It may be originated from the oxygen deficiency, which decreases the binding energy of Sn [13]. The peak centered at 49.59 eV is attributed to the Mg 2p. Based on the XPS data, it is concluded that the obtained powder is composed from Mg(II), Sn(IV), and O(II). Combining with the XRD results mentioned above, the pure phase of Mg2SnO4 has been successfully synthesized by this facile co-precipitation method. The synthesis of single phase Mg2SnO4 nanoparticles can be explained by the mechanism of crystal growth in solution. It is well known that precipitation of particles involves nucleation and growth from a super-saturated solution. The relative high temperature of 65 C during the aging process could increase the activity of the reactants, which is favor to the nucleation of MgSn(OH)6. Simultaneously, a short reaction time of 35 min could confine the growth of the crystal, causing the low crystallinity and small crystallite size, as well as avoiding the formation of SnO2. Furthermore, comparing to the conventional solid-state reaction (SSR) method [4e6], the lower calcination temperature of precursor could decrease the degree of the aggregation of the little particles, which is also helpful for the formation of nano-particles. IR spectroscopy is an effective tool to detect the local cation environment of a lattice containing closely packed oxygen array. FTIR signature of sample-FC-A is depicted in Fig. 7. The vibration frequencies at 458.98, 1436.34 and 1633.27 cm1 are attributed to the possible stretching and bending vibrational modes of MgeOeMg and OeMgeO groups [14], respectively. The vibrational band observed at 586.95 cm1 can be ascribed to the stretching vibration of SneO [15]. Fig. 8 shows the charge/discharge curves of the as-prepared sample-FC-A, the electrochemical test was performed between
170
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
Fig. 5. (a) Low-magnification and (b) high-magnification SEM images of sample-FC; (c) TEM and (d) HRTEM images of sample-FC.
0.05 and 3.0 V under a specific current of 0.2 mA cm2 at room temperature. The initial discharge capacity is 927.7 mAh g1. It can be deduced that about 8 Liþ are inserted per Sn atom. In spite of a litter lower than the expected 8.4, this was much higher than that of the Mg2SnO4 synthesized by the SSR method where the capacity of the initial half cycle is just about 6 Liþ per Sn atom [2]. The difference can be explained by the particles size. Since the particle sizes are uniform, and the very small crystallites with a narrow particle size distribution can be recognized easily, the powder is quite reactive. When applied in lithium-ion battery, nanostructure materials shorten Liþ and electronic diffusion distance. In addition, the nanoparticles with a large specific surface area increase the electrodeeelectrolyte contact area, and thus increase transport Liþ number, leading to higher discharge capacity [3,16]. However, the first discharge capacity is lower than that of mixture SnO2/MgSnO4, which may be attributed to the existence of SnO2 [3]. There is a small plateau at ~0.7 V followed by a gradual decrease slope and a wide steady discharging plateau around 0.15 V in the initial discharge curve. The electrochemical mechanism of lithium extraction/reinsertion of the Mg2SnO4 nanoparticles may as follows: Mg2SnO4 þ 4 Liþ þ 4 e / Sn þ 2 Li2O þ 2 MgO
(1)
Liþ þ Sn þ x e 4 LixSn (0 x 4.4)
(2)
The potential of the large plateau around 0.15 V is significantly lower than that of other tin oxides [2], which indicates that Mg2SnO4 could be a promising candidate of anode material for application in Li-ion batteries with high energy density. Starting from the 2nd cycle, the charge/discharge curves are very similar, indicating lithium extraction/reinsertion process is reversible. In additional, all the potential plateaus do not show a wide platform like the initial discharge, but display more inclined
shape. It is obvious that an irreversible reaction happened in the first cycle. The first 100 cycle performances of the as-prepared sample-FCA are presented in Fig. 9. A reversible discharge capacity of 506.7 mAh g1 is retained in the second cycle, which presents an obvious capacity loss. The phenomenon of the large irreversible discharge capacity in the first cycle is also observed by other tin oxide-based systems. It is probably due to: (1) The severe side reactions with the electrolyte on the larger surface area form Li2O and solid electrolyte interphase (SEI) film [17,18]; (2) The formed lithium magnesium oxide matrix is not a good electronic or ionic conductor and so it hinders the formation of the lithiumetin alloy [2]. However, the capacity fade rate is about 1% per cycle after the 2nd cycle, and the reversible capacity reaches 392.2 mAh g1 after 100 cycles. The coulombic efficiency in Fig. 9 also indicates that the process of charge and discharge gradually become stable. It is comparable or even better than the earlier results [2,3]. The discharge capacity was about 350, 123 and 74 mAh g1 for the 50, 70 and 150 nm for SnO2/Mg2SnO4 powders respectively [3]. This should attribute to nano-size of the samples. In general, the smaller of particle sizes are, the better cycling performance [3]. It is not be expected that MgO would be reduced at these potentials, so no Mg metal alloy would be formed, implying MgO worked as a spectator matrix together with Li2O, in which tin can be dispersed, could buffer the volume expansion and contraction during cycling. The cyclic voltammetry of sample-FC-A has been carried out in the potential range of 0.005e3.0 V at slow scan rate of 0.1 mV s1. The obtained results are shown in Fig. 10. Analogous to chargeedischarge profiles, the first-discharge sweep differs significantly from the other of the discharge sweeps. It commences from the open circuit voltage and no cathodic peaks are seen until 1.0 V. A broad shoulder peak at about 0.75 V is observed. It can be ascribed to the onset of reduction of Mg2SnO4 to Sn metal (Eq. (1)). There is another broad peak shown at about 0.1 V, which can be
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
171
Fig. 6. XPS spectra of sample-FC-A: (a) wide scan, (b) O 1s, (c) Sn 3d and (d) Mg 2p.
attributed to the formation of Li4.4Sn alloy (Eq. (2)). In the first charge process, there is only one broad anodic shoulder peak at about 0.55 V. In the subsequent scanning cycles, the CV curves are very similar. Only one peak lies at 0.55e0.6 V in the anodic (charge)
and one at 0.65e0.7 V in the cathodic (discharge) sweeps. The intensities of the oxidation-reduction peaks increase, but their positions and shapes do not shift, which further indicates that the electrode is stable.
Fig. 7. Room temperature FT-IR spectra of the sample-FC-A.
Fig. 8. Charge-discharge voltage profiles of sample-FC-A.
172
H. Tang et al. / Materials Chemistry and Physics 159 (2015) 167e172
Fig. 9. Charge and discharge capacities as a function of cycle number for sample-FC-A.
927.7 mAh g1. Both the chargeedischarge and cyclic voltammograms results have shown that Mg2SnO4 is a promising candidate of anode material.
Acknowledgment This paper was supported by the Basic Scientific Research of Hubei Normal University (2014F006).
References [1] [2] [3] [4] Fig. 10. Cyclic voltammograms of sample-FC-A in 0.005e3.0 V vs Li at the slow scan rate of 0.1 mV s1. Numbers indicate the cycle number.
4. Conclusions In this paper, single phase Mg2SnO4 nanoparticles have been synthesized by a facile coprecipitation method. The aging time of the precursors and the calcination temperature had a great influence on the final products. It was found that the optimum aging time of the precursor was 35 min and the calcination temperature was 900 C. The structure, composition and the morphology of the sample-FC-A were characterized by XRD, XPS, FT-TR, TEM and SEM. The average crystallite size of sample was 23 nm. The initial discharge capacity of the products reached as high as
[5] [6] [7]
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A.M. Azad, L.J. Min, M.A. Alim, J. Ceram. Int. 27 (2001) 335e341. P.A. Connor, J.T.S. Irvine, J. Power Sources 97e98 (2001) 223e225. T. Xiao, Y. Tang, Z. Ji, S. Feng, Electrochim. Acta 54 (2009) 2396e2401. I.N.S. Jackson, R.C. Liebermann, A.E. Ringwood, Earth Planet Sci. Lett. 24 (1974) 203e208. S. Raghavan, Thermochim. Acta 122 (1987) 389e393. K.T. Jacob, J. Valderrama-N, J. Solid State Chem. 22 (1977) 291e295. M.R.S. Silva, L.C.O. Miranda, M.R. C assia-Santos, S.J.G. Lima, L.E.B. Soledade, E. Longo, C.A. Paskocimas, A.G. Souza, I.M.G. Santos, J. Therm. Anal. Cal. 87 (2007) 753e757. G. Pfaff, Thermochim. Acta 237 (1994) 83e90. S. Shimada, K. Kodaira, T. Matsushita, J. Cryst. Growth 59 (1982) 662e664. H. Liu, H. Zhu, H. Yang, Mater. Res. Bull. 48 (2013) 1587e1592. W.Z. Oswald, Phys. Chem. 34 (1900) 495e499. D. Deng, J.Y. Lee, J. Chem. Mater. 20 (2008) 1841e1846. T. Sugimoto, Adv. Colloid Interf. Sci. 28 (1987) 65e108. Inorganic Library of FT-IR Spectra- Minerals, Nicodom 1, 1998. N. Jayaprakash, N. Kalaiselvi, Y.K. Sun, Electrochem. Commun. 10 (2008) 455e460. H. Liu, L. Tan, Z. Luo, J. Alloy. Comp. 502 (2010) 407e410. J.J. Zhu, Z.H. Lu, S.T. Aruna, D. Aurbach, A. Gedanken, J. Chem. Mater. 12 (2000) 2557e2566. D. Aurbach, B. Markovsky, M.D. Levi, E. Levi, A. Schechter, M. Moshkovich, Y. Cohen, J. Power Sources 81e82 (1999) 95e111.