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Electrochemical investigation of SnSb nano particles for lithium-ion batteries
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Electrochemical investigation of SnSb nano particles for lithium-ion batteries P. Nithyadharseni a,b, M.V. Reddy b,c,n, B. Nalini d, B.V.R. Chowdari b a
Department of Physics, Bannari Amman Institute of Technology, Sathyamangalam 638402, India Advanced Batteries Lab, Department of Physics, National University of Singapore, 117542, Singapore c Department of Materials Science and Engineering, National University of Singapore,117546, Singapore d Department of Physics, Avinashilingam Institute for Home Science and Higher Education for Women University, Coimbatore 641043, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 20 November 2014 Accepted 25 February 2015
The nanosized SnSb alloy was synthesized by a reductive co-precipitation method using NaBH4 as a reducing agent. In order to get fine powder with uniformly distributed particles, the final product was sonicated and stirred for 48 h with isopropyl alcohol, dried at 100 1C and characterized by various techniques. Galvanostatic cycling results showed initial reversible capacities of 1300 and 1500 mA h g 1 respectively for Cu foil and Ni mesh current collector, at a constant current density of 60 mA g 1 in the potential range of 0.005–1.5 V. Upon increasing the potential window from 1.5 to 3 V, the initial reversible capacity of Cu foil increased to 1400 mA h g 1 whereas for Ni mesh, the same capacity of 1500 mA h g 1 is obtained. However, the capacity fading is found to be significantly lower in the Ni mesh compared to Cu foil. The coulombic efficiency of the Cu foil and Ni mesh current collector is better maintained at 99% in the potential window between 0.005–1.5 V in comparison with 0.005–3 V. The electrochemical impedance studies imply that the kinetic properties of Li þ are very fast even after 50 cycles. & 2015 Published by Elsevier B.V.
Keywords: SnSb Nanoalloy Ultrasonication Lithium ion batteries Raman spectroscopy
1. Introduction Presently, lithium ion batteries (LIB's) play an important role in portable electronic devices such as cameras, laptops etc., because of their high energy density and long cycle life. In order to meet these requirements new anode materials have emerged to replace commercially used carbonaceous anodes [1–4]. The Sn, Si and Sb based anode materials have been widely studied due to their superior Li-storage and high specific gravimetric and volumetric capacities (Li4.4Sn, 990 mA h g 1 Li/Sb: 660 mA h g 1 and Li22Si5: 4200 mA h g 1 [5–8]. However, alloy anodes have not been commercialized because of their high volume change during alloying and de-alloying reactions with Li þ . Continuous volume change during cycling will cause the mechanical pulverization of the electrode resulting in poor cyclability and cracking of the electrode. In order to overcome this problem, next generation anodes of intermetallic compounds [9], active/inactive nanocomposite materials [10] and single phase instead of multiphase materials [11] have been widely studied. It is to be noted that n Corresponding author at: Department of Materials Science and Engineering, National University of Singapore 117546 Singapore. Tel.: þ65 65162607; fax: þ65 67776126. E-mail address: [email protected] (M.V. Reddy).
nano-composite materials can reduce the volume change during a cycling process due to their small particle size and uniform particle distribution of the compound, which can alleviate the mechanical disintegration of the electrode and thus lead to low capacity fading with good cycling behavior. Hence, in this article, we report SnSb nano-material that was prepared by a reductive co-precipitation method using NaBH4 as a reducing agent. To obtain fine particle size with uniform particle distribution, the final product was ultrasonicated and stirred for 48 h with isopropyl alcohol. In order to improve the stability of the electrode and ensure a good electrical contact during volume expansion and contraction upon cycling, the electrode materials were coated on two different current collectors of Cu foil and Ni mesh. Electrochemical properties of SnSb nano material coated on Cu foil and Ni mesh were studied at two different potential ranges and the results are discussed here.
2. Experimental details Nanosized SnSb powders were fabricated by reductive coprecipitation of the metal chloride salts as follows: raw materials (Merck, AR grade) taken for solution A were 1 mol of SnCl2 2H2O, 1 mol of SbCl3 H2O and 0.5 mol of C6H5Na3O7 (sodium citrates)
http://dx.doi.org/10.1016/j.matlet.2015.02.124 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
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and solution B is made of 1.5 mol of each NaOH and NaBH4 respectively, as reducing agents. These two solutions were titrated (i.e. the solution A is slowly mixed with solution B under continuous stirring). The resultant precipitate was filtered and washed with distilled water, 0.35 M HCl and acetone several times before being dried at ambient temperature. After that, the final products were dissolved in isopropyl alcohol using ultrasonicator and magnetic stirrer for 48 h and then dried at 100 1C for 24 h. The final product was characterized by various techniques. The structure and morphology of the samples were examined by X-ray diffraction (XRD,–SHIMAZDU-6000) using Cu-Kα radiation source. Raman studies were carried out using a Renishaw micro Raman spectrometer (Model-INVIA, λ¼514 nm-Ar ion laser). The slurry was prepared using 70 wt% of SnSb, 15 wt% of super P carbon and 15 wt% of PVDF dispersed in appropriate amount of NMP (N-methyl pyrrolidinone) and the slurry was coated on Cu foil and Ni mesh (16 mm circular diameter). Then the electrodes were kept in vacuum oven for drying at 70 1C for overnight. The batteries were assembled in an Argon filled glove box by using active materials as an anode, Li metal as counter electrode and 1 M LiPF6 in EC/DMC (1:1) as electrolyte. The fabricated coin cells were studied electrochemically by using galvanostatic cycling (GC) (Bitrode battery tester (model SCN, Bitrode, USA)), cyclic voltammetry (CV) (MacPile II, Biologic, France) and electrochemical impedance spectroscopy (EIS). The GC test was carried out at two different potential ranges of 0.005–1.0 V and 0.005– 3.0 V vs. Li, at a current density of 60 mA g 1 and CV was carried out in the potential range of 0.005–3.0 V. The electrochemical impedance measurements were carried out using Solartron/Gain-phase analyzer (model SI 1255) and the plots are recorded by applying an AC signal of 10 mV amplitude over the frequency range from 0.18 MHz to 3 mHz at room temperature and the data was analyzed by Z-view software.
3. Results and discussions XRD pattern of Fig. 1(a) can be indexed to the well-known rhombohedral β-SnSb phase (JCPDS 33-0118) [10,12] with the
space group, R-3m (Space Group: 166). No discrete oxide peak and impurity phases (except a minor peak at 401) were detected in the sample indicating that the elemental Sn and Sb had been completely reduced from their chlorides to form single phase SnSb alloy by a solution reduction method. All the diffraction peaks are sharp, which is an indication of good crystallinity and shows low crystallite size of 11 nm. For further confirmation of SnSb alloy, Raman spectroscopy was carried out. Raman spectrum of Fig. 1(b) shows two specific emission peaks at 440 cm 1 and 680 cm 1 indicating the formation of SnSb nano alloy [13]. TEM image (Fig. 1(c)) shows the agglomerated particles of SnSb. The aggregated particles are spherical and uniformly distributed with lower dimension around 20 nm in diameter. A few selected galvanostatic charge (de-lithiation)–discharge (lithiation) cycling profiles of SnSb nanoparticles are shown in Fig. 2(a and b). Lithium ion insertion–extraction for all potential ranges and coulombic efficiency vs. cycle number are shown in Fig. 2(c–f), respectively. To study the effect of operating voltage on electrochemical properties, the SnSb material was tested in two different potential ranges of 0.005–1.5 V (CSLV) and 0.005– 3 V (CSHV) for Cu foil and 0.005–1.5 V (NSLV) and 0.005–3 V (NSHV) for Ni mesh at a constant current density of 60 mA g 1, respectively. For both potential ranges the Cu foil and Ni mesh electrodes show a first cycle intercalation potential plateau of nearly 1 V. Comparing both potential ranges at after 50 cycles, very mild intercalation potential differences of 0.6–0.8 V is observed in Cu foil and Ni mesh electrodes. This indicates higher stability of SnSb alloy electrodes during the cycling process [14]. The initial reversible capacity of 1500 mA h g 1 is observed for both potential ranges of Ni mesh, whereas Cu foil shows slightly lower capacity of 1300–1400 mA h g 1 for both the ranges. The increased initial reversible capacity of Ni mesh electrode might be due to the increased surface area of the mesh which would contain a higher quantity of active material (20–22 mg), suggesting more solid electrolyte interface (SEI) film formation in Ni mesh electrode than the Cu foil (3–4 mg). The SEI film formation is mainly due to the decomposition of the electrolyte
Fig. 1. (a) XRD diffraction, (b) Raman spectrum and (c) TEM microscope of SnSb alloy, scale bar 200 nm.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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Fig. 2. Charge–discharge curves of SnSb alloys (a) CSLV (V ¼0.005–1.5 V), (b) NSLV (V ¼0.005–1.5 V), capacity vs. cycle number plots and coulombic efficiency of CSLV (c), CSHV (d), NSLV (e) and NSHV(f). Current rate, 60 mA g 1.
and the reaction of surface oxide Sb2O3 with Li by forming Li2O [15,16]. Moreover, the SEI formations are mainly due to the smaller particle size of the SnSb alloy. CSHV and NSHV shows considerable capacity fading than the CSLV and NSLV, which can be attributed to electrochemical pulverization that leads to the loss of electrical contact between the current collector and the active material of the electrodes. The disintegration of the electrode and capacity fading on long term cycling will be the consequence of the same [14]. Discharge capacities of 510 and 490 mA h g 1 are observed at 50th cycle for SnSb nano alloy coated on Cu foil electrodes, which is higher than the previous reports [10,17–19] prepared by other methods. The increased capacity values could be due to the increase in surface to volume ratio of SnSb achieved during the preparation process. In summary, comparing the samples, CSLV, CSHV and NSHV shows higher capacity fading than the NSLV; this might be due to the small volume changes that occur during lithium insertion and extraction. Moreover, the nanosized particles are very difficult to pulverize in Ni mesh, which can easily reduce the contact loss between the Ni mesh current collector and active materials. However, a low reversible specific capacity of around 300 and 150 mA h g 1 is observed for NSLV and NSHV after 50 cycles respectively. The columbic efficiency of the CSLV and NSLV is 99% and it is maintained even after 50 cycles, but for CSHV and NSHV, only lower efficiency of 95% is observed. It can be concluded that SnSb alloy coated on Cu foil current collector shows higher capacity at lower operating potential range than Ni mesh. However, Ni mesh current collector can alleviate the volume change during long term cycling better than Cu foil current collector.
Fig. 3(a) displays the cyclic voltammogram (CV) of nanosized SnSb on Cu foil current collector for first four cycles at the scan rate of 0.058 mV s 1 in the potential range of 0.005–3 V. The cathodic and anodic plateau of CV scans ascribed to the reactions of both phases of SnSb to Li3Sb and the multistep phase of Li–Sn alloying reaction is observed at 0.6 and 1.12 V respectively. One pair of peaks at 1.12 and 0.5 V corresponds to the reaction of Li-absorption/extraction of Sb and the pair below 0.6 and around 0.2 V belongs to the reaction of Li-insertion/extraction of Sn at different lithiated phase [20]. The electrochemical impedance response of SnSb nanoparticles of fresh cell coated on Cu foil and Ni mesh are shown in Fig. 3(b). Impedance response of fresh cell shows one typical semicircle in higher frequency region which corresponds to charge transfer resistance and Warburg line at low frequency contributed to the diffusion rate of Li þ and the accumulation of Li þ on the anode materials. Compared to the Cu foil coated electrode, Ni mesh shows very low resistance indicating that the Li þ transportation is very high. The Warburg contribution of both fresh cells show no much difference indicating the kinetic properties of Li þ are very fast [20].
4. Conclusion In this work, the nanosized SnSb alloy was prepared by reductive co-precipitation method using NaBH4 as a reducing agent. Rhombohedral β-SnSb phase was observed from X-ray diffraction and transmission electron microscopy shows spherical and uniformly distributed particle size of 20 nm in diameter.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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Fig. 3. (a) Cyclic voltammogram of SnSb at first 4 cycles and (b) Nyquist plots (Z0 vs. Z″) of SnSb fresh cell coated on Cu foil and Ni mesh electrodes.
Raman spectrum exhibits the SnSb alloy formation due to the respective emission peaks. Cyclic voltammogram shows cathodic and anodic plateaus corresponding to both the phase of Li–Sn and Li–Sb on reaction. Galvanostatic cycling studies showed lower capacity fading for nanosized SnSb on Ni mesh than the Cu foil at a lower potential range of 0.005–1.5 V. Electrochemical Impedance spectroscopy studies reveal very good kinetic properties of Li þ even after 50 cycles. Acknowledgments Dr. Nithya thanks National University of Singapore (NUS) and India Research Initiatives (IRI) for partial financial support. References [1] Guo Q, Chen S, Qin X. Preparation of graphene/SnO2 composite as high capacity anode material for lithium ion batteries. Mater Lett 2014;119:4–7. [2] Reddy MV, Subba Rao GV, Chowdari BVR. Metal oxides and oxysalts as anode materials for Li ion batteries. Chem Rev 2013;113:5364–457. [3] Reddy MV, Khai VH, Chowdari BVR. Facile one pot molten salt synthesis of nano (M1/2Sb1/2Sn)O4 (M¼ V, Fe, In). Mater Lett 2015;140:115–8. [4] Nithyadharseni P, Nalini B. The best route to synthesis SnSb nanoparticle with low distribution of size. Int J Nanosci Nanotech 2011;2:217–24. [5] Kasavajjula U, Wang C, Appleby AJ. Nano-and bulk silicon-based insertion anodes for lithium-ion secondary cells. J Power Sources 2007;163:1003–39. [6] Wang K, He X, Ren J, Wang L, Jiang C, Wan C. Preparation of Sn2Sb alloy encapsulated carbon microsphere anode materials for Li-ion batteries by carbothermal reduction of the oxides. Electrochim Acta 2006;52:1221–5. [7] Park CM, Kim JH, Kim H, Sohn HJ. Li-alloy based anode materials for Li secondary batteries. Chem Soc Rev 2010;39:3115–41.
[8] Yanna N, Jun Y, Mingshan J. Synthesis and characterization of Sn/CNT and Bi/CNT composites as anode materials for lithium-ion batteries. Mater Lett 2007;62:2092–5. [9] Zhang J, Wang Z, Hong Y, Shengxian L, Xianbo J, Chen GZ. Electrochemical fabrication of porous Sn/SnSb negative electrodes from mixed SnO2–Sb2O3. Electrochem Commun 2014;38:36–9. [10] Fei W, Mingshu Z, Xiaoping S. The improved electrochemical performance of SnSb-based alloy anode materials for Li-ion batteries. J Alloy Compd 2009;472:55–8. [11] Leigang X, Xin X, Telpriore T, Kun F, Shu Z, Shuli L, et al. A simple method to encapsulate SnSb nanoparticles into hollow carbon nanofibers with superior lithium-ion storage capability. J Mater Chem A 2013;1:13807–13. [12] Nithyadharseni P, Reddy MV, Nalini B, Kalpana M, Chowdary BVR. Sn-based intermetallic alloy anode materials for the application of Lithium ion batteries. Electrochim Acta 2015. [13] Seng KH, Guo ZP, Chen ZX, Liu HK. SnSb/graphene composite as anode materials for lithium ion batteries. Adv Sci Lett 2011;4:18–23. [14] Juan L, Qiang R, Shejun H, Dawei S, Beibei Z, Xianhua H. Spherical nano-SnSb/ MCMB/carbon core-shell composite for high stability lithium ion battery anodes. Electrochim Acta 2013;113:505–13. [15] Reddy MV, Tse LY, Bruce WZ, Chowdari BVR. Low temperature molten salt of nano-SnO2 as anode for lithium-ion batteries. Mater Lett 2015;138:231–4. [16] Jian X, Wentao S, Yunxiao Z, Shuangyu L, Tiejun Z, Gaoshao C, et al. Preparation and Li-storage properties of SnSb/graphene hybrid nanostructure by a facile one-step Solvothermal route. Int J Smart Nanomater 2011;2:261–71. [17] Shufen F, Ting S, Xianhong R, Qingyu Y, Huey H. Cooperative enhancement of capacities in nanostructured SnSb/carbon nanotube network nanocomposite as anode for lithium ion batteries. J Power Sources 2012;201:288–93. [18] Mukaibo H, Osaka T, Reale P, Panero S, Scrosati B, Wachtler M. Optimized Sn/SnSb lithium storage materials. J Power Sources 2004;132:225–8. [19] Needham SA, Wang GX, Liu HK. Electrochemical performance of SnSb and Sn/SnSb nanosize powders as anode materials in Li-ion cells. J Alloy Compd 2005;400:234–8. [20] Chaoli Y, Hailei Z, Hong G, Xianliang H, Weihua Q. Effect of the synthesis method of SnSb anode materials on their electrochemical properties. J Univ Sci Tech Beijing 2007;14:345–9.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Electrochemical investigation of SnSb nano particles for lithium-ion batteries P. Nithyadharseni a,b, M.V. Reddy b,c,n, B. Nalini d, B.V.R. Chowdari b a
Department of Physics, Bannari Amman Institute of Technology, Sathyamangalam 638402, India Advanced Batteries Lab, Department of Physics, National University of Singapore, 117542, Singapore c Department of Materials Science and Engineering, National University of Singapore,117546, Singapore d Department of Physics, Avinashilingam Institute for Home Science and Higher Education for Women University, Coimbatore 641043, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 20 November 2014 Accepted 25 February 2015
The nanosized SnSb alloy was synthesized by a reductive co-precipitation method using NaBH4 as a reducing agent. In order to get fine powder with uniformly distributed particles, the final product was sonicated and stirred for 48 h with isopropyl alcohol, dried at 100 1C and characterized by various techniques. Galvanostatic cycling results showed initial reversible capacities of 1300 and 1500 mA h g 1 respectively for Cu foil and Ni mesh current collector, at a constant current density of 60 mA g 1 in the potential range of 0.005–1.5 V. Upon increasing the potential window from 1.5 to 3 V, the initial reversible capacity of Cu foil increased to 1400 mA h g 1 whereas for Ni mesh, the same capacity of 1500 mA h g 1 is obtained. However, the capacity fading is found to be significantly lower in the Ni mesh compared to Cu foil. The coulombic efficiency of the Cu foil and Ni mesh current collector is better maintained at 99% in the potential window between 0.005–1.5 V in comparison with 0.005–3 V. The electrochemical impedance studies imply that the kinetic properties of Li þ are very fast even after 50 cycles. & 2015 Published by Elsevier B.V.
Keywords: SnSb Nanoalloy Ultrasonication Lithium ion batteries Raman spectroscopy
1. Introduction Presently, lithium ion batteries (LIB's) play an important role in portable electronic devices such as cameras, laptops etc., because of their high energy density and long cycle life. In order to meet these requirements new anode materials have emerged to replace commercially used carbonaceous anodes [1–4]. The Sn, Si and Sb based anode materials have been widely studied due to their superior Li-storage and high specific gravimetric and volumetric capacities (Li4.4Sn, 990 mA h g 1 Li/Sb: 660 mA h g 1 and Li22Si5: 4200 mA h g 1 [5–8]. However, alloy anodes have not been commercialized because of their high volume change during alloying and de-alloying reactions with Li þ . Continuous volume change during cycling will cause the mechanical pulverization of the electrode resulting in poor cyclability and cracking of the electrode. In order to overcome this problem, next generation anodes of intermetallic compounds [9], active/inactive nanocomposite materials [10] and single phase instead of multiphase materials [11] have been widely studied. It is to be noted that n Corresponding author at: Department of Materials Science and Engineering, National University of Singapore 117546 Singapore. Tel.: þ65 65162607; fax: þ65 67776126. E-mail address: [email protected] (M.V. Reddy).
nano-composite materials can reduce the volume change during a cycling process due to their small particle size and uniform particle distribution of the compound, which can alleviate the mechanical disintegration of the electrode and thus lead to low capacity fading with good cycling behavior. Hence, in this article, we report SnSb nano-material that was prepared by a reductive co-precipitation method using NaBH4 as a reducing agent. To obtain fine particle size with uniform particle distribution, the final product was ultrasonicated and stirred for 48 h with isopropyl alcohol. In order to improve the stability of the electrode and ensure a good electrical contact during volume expansion and contraction upon cycling, the electrode materials were coated on two different current collectors of Cu foil and Ni mesh. Electrochemical properties of SnSb nano material coated on Cu foil and Ni mesh were studied at two different potential ranges and the results are discussed here.
2. Experimental details Nanosized SnSb powders were fabricated by reductive coprecipitation of the metal chloride salts as follows: raw materials (Merck, AR grade) taken for solution A were 1 mol of SnCl2 2H2O, 1 mol of SbCl3 H2O and 0.5 mol of C6H5Na3O7 (sodium citrates)
http://dx.doi.org/10.1016/j.matlet.2015.02.124 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
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and solution B is made of 1.5 mol of each NaOH and NaBH4 respectively, as reducing agents. These two solutions were titrated (i.e. the solution A is slowly mixed with solution B under continuous stirring). The resultant precipitate was filtered and washed with distilled water, 0.35 M HCl and acetone several times before being dried at ambient temperature. After that, the final products were dissolved in isopropyl alcohol using ultrasonicator and magnetic stirrer for 48 h and then dried at 100 1C for 24 h. The final product was characterized by various techniques. The structure and morphology of the samples were examined by X-ray diffraction (XRD,–SHIMAZDU-6000) using Cu-Kα radiation source. Raman studies were carried out using a Renishaw micro Raman spectrometer (Model-INVIA, λ¼514 nm-Ar ion laser). The slurry was prepared using 70 wt% of SnSb, 15 wt% of super P carbon and 15 wt% of PVDF dispersed in appropriate amount of NMP (N-methyl pyrrolidinone) and the slurry was coated on Cu foil and Ni mesh (16 mm circular diameter). Then the electrodes were kept in vacuum oven for drying at 70 1C for overnight. The batteries were assembled in an Argon filled glove box by using active materials as an anode, Li metal as counter electrode and 1 M LiPF6 in EC/DMC (1:1) as electrolyte. The fabricated coin cells were studied electrochemically by using galvanostatic cycling (GC) (Bitrode battery tester (model SCN, Bitrode, USA)), cyclic voltammetry (CV) (MacPile II, Biologic, France) and electrochemical impedance spectroscopy (EIS). The GC test was carried out at two different potential ranges of 0.005–1.0 V and 0.005– 3.0 V vs. Li, at a current density of 60 mA g 1 and CV was carried out in the potential range of 0.005–3.0 V. The electrochemical impedance measurements were carried out using Solartron/Gain-phase analyzer (model SI 1255) and the plots are recorded by applying an AC signal of 10 mV amplitude over the frequency range from 0.18 MHz to 3 mHz at room temperature and the data was analyzed by Z-view software.
3. Results and discussions XRD pattern of Fig. 1(a) can be indexed to the well-known rhombohedral β-SnSb phase (JCPDS 33-0118) [10,12] with the
space group, R-3m (Space Group: 166). No discrete oxide peak and impurity phases (except a minor peak at 401) were detected in the sample indicating that the elemental Sn and Sb had been completely reduced from their chlorides to form single phase SnSb alloy by a solution reduction method. All the diffraction peaks are sharp, which is an indication of good crystallinity and shows low crystallite size of 11 nm. For further confirmation of SnSb alloy, Raman spectroscopy was carried out. Raman spectrum of Fig. 1(b) shows two specific emission peaks at 440 cm 1 and 680 cm 1 indicating the formation of SnSb nano alloy [13]. TEM image (Fig. 1(c)) shows the agglomerated particles of SnSb. The aggregated particles are spherical and uniformly distributed with lower dimension around 20 nm in diameter. A few selected galvanostatic charge (de-lithiation)–discharge (lithiation) cycling profiles of SnSb nanoparticles are shown in Fig. 2(a and b). Lithium ion insertion–extraction for all potential ranges and coulombic efficiency vs. cycle number are shown in Fig. 2(c–f), respectively. To study the effect of operating voltage on electrochemical properties, the SnSb material was tested in two different potential ranges of 0.005–1.5 V (CSLV) and 0.005– 3 V (CSHV) for Cu foil and 0.005–1.5 V (NSLV) and 0.005–3 V (NSHV) for Ni mesh at a constant current density of 60 mA g 1, respectively. For both potential ranges the Cu foil and Ni mesh electrodes show a first cycle intercalation potential plateau of nearly 1 V. Comparing both potential ranges at after 50 cycles, very mild intercalation potential differences of 0.6–0.8 V is observed in Cu foil and Ni mesh electrodes. This indicates higher stability of SnSb alloy electrodes during the cycling process [14]. The initial reversible capacity of 1500 mA h g 1 is observed for both potential ranges of Ni mesh, whereas Cu foil shows slightly lower capacity of 1300–1400 mA h g 1 for both the ranges. The increased initial reversible capacity of Ni mesh electrode might be due to the increased surface area of the mesh which would contain a higher quantity of active material (20–22 mg), suggesting more solid electrolyte interface (SEI) film formation in Ni mesh electrode than the Cu foil (3–4 mg). The SEI film formation is mainly due to the decomposition of the electrolyte
Fig. 1. (a) XRD diffraction, (b) Raman spectrum and (c) TEM microscope of SnSb alloy, scale bar 200 nm.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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Fig. 2. Charge–discharge curves of SnSb alloys (a) CSLV (V ¼0.005–1.5 V), (b) NSLV (V ¼0.005–1.5 V), capacity vs. cycle number plots and coulombic efficiency of CSLV (c), CSHV (d), NSLV (e) and NSHV(f). Current rate, 60 mA g 1.
and the reaction of surface oxide Sb2O3 with Li by forming Li2O [15,16]. Moreover, the SEI formations are mainly due to the smaller particle size of the SnSb alloy. CSHV and NSHV shows considerable capacity fading than the CSLV and NSLV, which can be attributed to electrochemical pulverization that leads to the loss of electrical contact between the current collector and the active material of the electrodes. The disintegration of the electrode and capacity fading on long term cycling will be the consequence of the same [14]. Discharge capacities of 510 and 490 mA h g 1 are observed at 50th cycle for SnSb nano alloy coated on Cu foil electrodes, which is higher than the previous reports [10,17–19] prepared by other methods. The increased capacity values could be due to the increase in surface to volume ratio of SnSb achieved during the preparation process. In summary, comparing the samples, CSLV, CSHV and NSHV shows higher capacity fading than the NSLV; this might be due to the small volume changes that occur during lithium insertion and extraction. Moreover, the nanosized particles are very difficult to pulverize in Ni mesh, which can easily reduce the contact loss between the Ni mesh current collector and active materials. However, a low reversible specific capacity of around 300 and 150 mA h g 1 is observed for NSLV and NSHV after 50 cycles respectively. The columbic efficiency of the CSLV and NSLV is 99% and it is maintained even after 50 cycles, but for CSHV and NSHV, only lower efficiency of 95% is observed. It can be concluded that SnSb alloy coated on Cu foil current collector shows higher capacity at lower operating potential range than Ni mesh. However, Ni mesh current collector can alleviate the volume change during long term cycling better than Cu foil current collector.
Fig. 3(a) displays the cyclic voltammogram (CV) of nanosized SnSb on Cu foil current collector for first four cycles at the scan rate of 0.058 mV s 1 in the potential range of 0.005–3 V. The cathodic and anodic plateau of CV scans ascribed to the reactions of both phases of SnSb to Li3Sb and the multistep phase of Li–Sn alloying reaction is observed at 0.6 and 1.12 V respectively. One pair of peaks at 1.12 and 0.5 V corresponds to the reaction of Li-absorption/extraction of Sb and the pair below 0.6 and around 0.2 V belongs to the reaction of Li-insertion/extraction of Sn at different lithiated phase [20]. The electrochemical impedance response of SnSb nanoparticles of fresh cell coated on Cu foil and Ni mesh are shown in Fig. 3(b). Impedance response of fresh cell shows one typical semicircle in higher frequency region which corresponds to charge transfer resistance and Warburg line at low frequency contributed to the diffusion rate of Li þ and the accumulation of Li þ on the anode materials. Compared to the Cu foil coated electrode, Ni mesh shows very low resistance indicating that the Li þ transportation is very high. The Warburg contribution of both fresh cells show no much difference indicating the kinetic properties of Li þ are very fast [20].
4. Conclusion In this work, the nanosized SnSb alloy was prepared by reductive co-precipitation method using NaBH4 as a reducing agent. Rhombohedral β-SnSb phase was observed from X-ray diffraction and transmission electron microscopy shows spherical and uniformly distributed particle size of 20 nm in diameter.
Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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Fig. 3. (a) Cyclic voltammogram of SnSb at first 4 cycles and (b) Nyquist plots (Z0 vs. Z″) of SnSb fresh cell coated on Cu foil and Ni mesh electrodes.
Raman spectrum exhibits the SnSb alloy formation due to the respective emission peaks. Cyclic voltammogram shows cathodic and anodic plateaus corresponding to both the phase of Li–Sn and Li–Sb on reaction. Galvanostatic cycling studies showed lower capacity fading for nanosized SnSb on Ni mesh than the Cu foil at a lower potential range of 0.005–1.5 V. Electrochemical Impedance spectroscopy studies reveal very good kinetic properties of Li þ even after 50 cycles. Acknowledgments Dr. Nithya thanks National University of Singapore (NUS) and India Research Initiatives (IRI) for partial financial support. References [1] Guo Q, Chen S, Qin X. Preparation of graphene/SnO2 composite as high capacity anode material for lithium ion batteries. Mater Lett 2014;119:4–7. [2] Reddy MV, Subba Rao GV, Chowdari BVR. Metal oxides and oxysalts as anode materials for Li ion batteries. Chem Rev 2013;113:5364–457. [3] Reddy MV, Khai VH, Chowdari BVR. Facile one pot molten salt synthesis of nano (M1/2Sb1/2Sn)O4 (M¼ V, Fe, In). Mater Lett 2015;140:115–8. [4] Nithyadharseni P, Nalini B. The best route to synthesis SnSb nanoparticle with low distribution of size. Int J Nanosci Nanotech 2011;2:217–24. [5] Kasavajjula U, Wang C, Appleby AJ. Nano-and bulk silicon-based insertion anodes for lithium-ion secondary cells. J Power Sources 2007;163:1003–39. [6] Wang K, He X, Ren J, Wang L, Jiang C, Wan C. Preparation of Sn2Sb alloy encapsulated carbon microsphere anode materials for Li-ion batteries by carbothermal reduction of the oxides. Electrochim Acta 2006;52:1221–5. [7] Park CM, Kim JH, Kim H, Sohn HJ. Li-alloy based anode materials for Li secondary batteries. Chem Soc Rev 2010;39:3115–41.
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Please cite this article as: Nithyadharseni P, et al. Electrochemical investigation of SnSb nano particles for lithium-ion batteries. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.124i
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