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carbon composite used as anode for lithium ion batteries
Materials Chemistry and Physics 115 (2009) 757–760
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Improvement of cycle performance for silicon/carbon composite used as anode for lithium ion batteries Pengjian Zuo a,b,∗ , Geping Yin b , Zhanlin Yang b , Zhenbo Wang b , Xinqun Cheng b , Dechang Jia a , Chunyu Du b a b
Postdoctoral Station of Materials Science and Engineering, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China
a r t i c l e
i n f o
Article history: Received 29 January 2008 Received in revised form 18 July 2008 Accepted 19 February 2009 Keywords: Lithium ion battery Silicon/carbon composite Potassium modification Cycle stability
a b s t r a c t The silicon/carbon composite was prepared by mixing the silicon, graphite and pitch in the tetra-hydrofuran solution followed by pyrolyzing the blends after the evaporation of solvent. The electrochemical performance of the silicon/carbon anode for lithium ion batteries was improved by the treatment of composite powders with KCl aqueous solutions. Scanning electron microscope (SEM) observation and electrochemical impedance spectroscopy (EIS) results showed that the morphology stability of the composite electrodes can be kept during the electrochemical charge/discharge process. The composite electrode of silicon/carbon composite showed an initial reversible capacity of 575 mAh g−1 and still maintained a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of ∼0.3% per cycle. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Recently, metal-based material has been attracted much interest for the purpose of developing the novel lithium ion batteries with high energy density. Si or Sn-based systems, which have very high theoretical capacities in comparison with the traditional carbonaceous materials, possess the potential as alternative anodes for lithium ion batteries [1–4]. However, metal-based materials encounter a large irreversible capacity loss (ICL) during the alloying/de-alloying process of lithium ions with Si, Sn or others, which is mainly caused by the cracking of the electrode and a consequent loss of electronic contact between the bulk particles [5–7]. So far, the electrodes of silicon-based films, which were obtained by deposition of silicon-based materials onto the current collectors, exhibited the excellent properties in the aspects of the reversible capacity and cyclic performance [8–10]. Several other concepts such as “active–inactive” [11–13] and “core–shell” [14,15] have been utilized to relieve the volume changes of the metal-based materials during the charge/discharge process. Much evidence supports that the most attractive structure of Si/C composites is the dispersed silicon in carbon matrix [16–21]. Si-based materials have a long way to put into practice as commercial anodes due to their huge
∗ Corresponding author at: School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China. Tel.: +86 451 86403216; fax: +86 451 86413707. E-mail address: [email protected] (P. Zuo). 0254-0584/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2009.02.036
irreversible capacity loss even though the mechanical and electrochemical characteristics have been increased to some extent. It is believed that the existence of SEI (solid electrolyte interface) layer plays an important role in reversible lithium intercalation into graphite system, and chemical modification of graphite surface favoring the formation of SEI film has attracted extensive attention to improve battery performances. Several additives for the electrolyte solution, such as vinylene carbonate [22,23], metal ions [24,25], have been successfully studied to be effective in order to modify and improve the SEI film. In this paper, the silicon/carbon composites with high capacity and good cycle performance was obtained by pyrolysis of pitch embedded with graphite and silicon powders, and the cycle performance was further improved though the modification of the composite by alkali halide aqueous solution. 2. Experimental The preparation of the silicon/carbon composites was as follows: The silicon powders (−325 mesh, >99.6%) of 2 g and 2 g graphite (D50 = 18 m; Shenzhen BTR Energy Materials Co., Ltd) were added into the tetra-hydrofuran solution containing 8 g pitch and homogeneously mixed. The tetra-hydrofuran solvent was evaporated under stirring to get a solid blend. The mixture was heated at 900 ◦ C in an argon atmosphere for 2 h at a heating rate of 10 ◦ C min−1 and allowed cool down to room temperature naturally. The silicon/carbon composite modified by potassium ions was obtained by simple soaking the silicon/carbon material into the 5 wt.% KCl aqueous solution followed by the filtering and drying in vacuum. The obtained composite powders were characterized by X-ray diffraction (XRD) using a D/max-␥B diffractometer equipped with Cu radiation in the range of 2 = 10–90◦ . The morphology and microstructure of composite materials were observed by the scanning electron microscope (SEM) (Hitachi S-4700).
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P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
Fig. 1. Reversible capacity and coulomb efficiency vs. cycle number for silicon and silicon/carbon composite.
The composite electrodes were prepared by mixing 85 wt.% active material, 5 wt.% acetylene black and 10 wt.% polyvinylidene fluoride (PVDF) dissolved in Nmethylpyrrolidinone (NMP) to form a slurry which was then coated on the copper foil and dried at 120 ◦ C in vacuum for 14 h. The electrochemical reactions of silicon/carbon composites with lithium were investigated by a simple two-electrode cell using a lithium foil as a reference and counter electrode. The cells were assembled in a glove box filled with argon, and the electrolyte was 1 M LiPF6 in a mixture of EC:DEC:EMC = 1:1:1(v/v/v). The charge/discharge measurements were carried out between 0.01 V and 1.5 V (vs. Li/Li+ ) at 0.15 mA cm−2 using a programmable battery test system (BTS-5V1 mA). Electrochemical impedance spectroscopy (EIS) measurements were conducted using a CHI604 frequency response analyzer. Before the EIS experiments, the cells after a definite cycle at the above constant current density were placed in the delithiated state for 8 h to achieve equilibrium. The impedance spectra were recorded potentiostatically by applying an ac voltage of 5 mV amplitude over the frequency range from 0.1 MHz to 0.01 Hz.
3. Results and discussion Fig. 1 shows the reversible capacity and coulombic efficiency of pristine silicon and silicon/carbon composite prepared by pyrolyzing the blends of silicon, graphite and pitch powders at 900 ◦ C. The silicon/carbon composite shows the satisfying reversible capacity and cycle stability in comparison with the silicon anode, and it possesses an initial discharge capacity of 485 mAh g−1 and coulombic efficiency of 70%. Even though the electrochemical cycle stability of silicon/carbon composite has been improved significantly compared with silicon, the initial reversible efficiency and long-term cycle performance should be concerned further in order to meet the acquirement the possible practicability of silicon-based materials. Fig. 2 shows the XRD pattern of the silicon/carbon composite modified by KCl, in which the diffraction pattern of the pristine silicon/carbon composite is also provided for the purpose of comparison. It can be found the diffraction peak at 2 = 40.6◦ of the KCl crystal in the composite from the curve b in Fig. 2, and the diffraction peak at about 2 = 28.4◦ , 47.3◦ , 56.2◦ , 69.2◦ , 76.3◦ and 87.9◦ are due to the silicon crystal. As shown in the XRD patterns (Fig. 2) of the samples, the broad diffraction peak at about 2 = 22.8◦ could be indexed as diffraction peaks of pyrolyzed carbon from the pitch, and the diffraction peak (0 0 2) of graphite is clearly observed at 26.6◦ from the ex situ X-ray diffraction patterns of these two kinds of composites. The charge/discharge curves of the silicon/carbon composite with and without the modification of KCl are shown in Fig. 3. During the first insertion process, a distinct potential platform, which is mainly attributed to the alloying process of silicon with lithium and the insertion of lithium ions into the carbon host, can be observed at around 0–0.20 V for the silicon/carbon composites. The potential slope at around 0.5–0.7 V in the first discharge process corresponds to the irreversible decomposition of solvent component in electrolyte, which results in the formation of SEI film on the
Fig. 2. X-ray diffraction pattern for silicon/carbon composite (a) without KCl (b) modified by KCl.
surface of the silicon/carbon composite. The broad platform around 0.3–0.6 V corresponds to the de-intercalation reaction of lithium from the Lix Si phase and the extraction of lithium ions from the carbon materials. From Fig. 3, it can be seen that the initial discharge (816 mAh g−1 ) and charge capacity (575 mAh g−1 ) of silicon/carbon composite modified by KCl is higher than those (692 mAh g−1 and 485 mAh g−1 respectively) of the pristine silicon/carbon composite. The impedance spectra of the silicon/carbon composite anodes in delithiated states after 40 cycles are shown in Fig. 4. In general, the semicircles appeared in the high frequency range of the composites are due to the formation of SEI film caused by the decomposition of electrolyte solution, and the electrochemical reaction process of lithium with silicon or carbon corresponds to the second semicircle in the medium frequency regions. The sloping straight line at low frequency corresponds to diffusion of lithium ions in the bulk electrode [19]. It can be seen that the curves in high frequency range is almost overlapped while the radius of semicircle in the middle frequency for the pristine silicon/carbon composite is larger than that for the composite with KCl, which implies that the electrochemical reaction of silicon/carbon composite with lithium ions has been facilitated due to the modified by KCl. Fig. 5 shows the SEM images of electrodes for silicon/carbon composite modified by KCl before and after 40 cycles. It is clear that the composite electrode exhibits a homogeneous surface morphology and no obvious
Fig. 3. Charge/discharge curves of the silicon/carbon composite (a) with and (b) without modification of KCl.
P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
759
Fig. 6. Reversible capacity and coulomb efficiency vs. cycle number for silicon and silicon/carbon composite modified by KCl. Fig. 4. Nyquist plots of silicon/carbon composite electrodes in delithiated state after 40 cycles.
cracks can be seen even though it has been cycled electrochemically for 40 cycles. Fig. 6 shows the curves of discharge capacity and coulomb efficiency vs. cycle number for silicon/carbon composite with KCl used as anode material for lithium ion batteries. The composite electrode exhibits an initial reversible capacity of 575 mAh g−1 and a coulomb efficiency of 70% and still maintains a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of only ∼0.3% per cycle. The coulomb efficiency of composite electrode becomes constant to be nearly 100% after the fifth cycle even though the initial efficiency is a little lower. Compared with the pristine silicon/carbon composite as shown in Fig. 1, the reversible capacity and cycle performance are improved significantly after the modified of KCl for the silicon/carbon composite. 4. Conclusions In this paper, the silicon/carbon composite were prepared by dispersing the silicon and graphite particles into the tetra-hydrofuran solution containing pitch followed by the pyrolyzing the blends after the evaporation of solvent. The cycle stability silicon/carbon has been improved obviously in comparison with the pure silicon anode, the charge/discharge capacity and electrochemical cycle stability increase significantly through the modification of KCl on the surface of the active silicon-based materials. The composite electrode of silicon/carbon composite shows an initial reversible capacity of 575 mAh g−1 and a coulomb efficiency of 70%, and it still maintains a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of only ∼0.3% per cycle. Acknowledgements This work was partially supported by The Natural Science Foundation of China (no. 20673032), China Postdoctoral Science Foundation funded project (20070420860), Natural Scientific Research Innovation Foundation in Harbin Institute of Technology (HIT.NSRIF. 2008.25) and the Key Scientific & Technological Programme of Heilongjiang Province of China (no. GB06A309). References
Fig. 5. SEM images of electrodes for silicon/carbon composite modified by KCl (a) before and after (b) 40 cycles.
[1] T.D. Hatchard, J.M. Topple, M.D. Fleischauer, J.R. Dahn, Electrochem. Solid-State Lett. 6 (2003) A129. [2] W.J. Weydanz, M. Wohlfahrt-Mehrens, R.A. Huggins, J. Power Sources 81–82 (1999) 237. [3] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276 (1997) 1395. [4] S.D. Beattle, J.R. Dahn, J. Electrochem. Soc. 150 (2003) 894.
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P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
[5] A.N. Dey, J. Electrochem. Soc. 118 (1971) 1547. [6] D. Larcher, C. Mudalige, A.E. George, V. Porter, M. Gharghouri, J.R. Dahn, Solid State Ionics 122 (1999) 71. [7] Z.P. Guo, J.Z. Wang, H.K. Liu, S.X. Dou, J. Power Sources 146 (2005) 448. [8] H. Jung, M. Park, Y.-G. Yoon, G.-B. Kim, S.-K. Joo, J. Power Sources 115 (2003) 346. [9] M. Uehara, J. Suzuki, K. Tamura, K. Sekine, T. Takamura, J. Power Sources 146 (2005) 441. [10] T. Takamura, M. Uehara, J. Suzuki, K. Sekine, K. Tamura, J. Power Sources 158 (2006) 1401. [11] H.Y. Lee, S.W. Jang, S.M. Lee, S.J. Lee, H.K. Baik, J. Power Sources 112 (2002) 8. [12] S.Y. Chew, Z.P. Guo, J.Z. Wang, J. Chen, P. Munroe, S.H. Ng, L. Zhao, H.K. Liu, Electrochem. Commun. 9 (2007) 941. [13] S. Yoon, C.M. Park, H. Kim, H.J. Sohn, J. Power Sources 167 (2007) 520. [14] Y.S. Jung, K.T. Lee, J.H. Ryu, D. Im, S.M. Oh, J. Electrochem. Soc. 152 (2005) A1452. [15] N. Dimov, S. Kugino, M. Yoshio, Electrochim. Acta 48 (2003) 1579. [16] Y. Zheng, J. Yang, J.L. Wang, Y.N. NuLi, Electrochim. Acta 52 (2007) 5863.
[17] M. Yoshio, H. Wang, K. Fukuda, T. Umeno, N. Dimov, X. Ogumi, J. Electrochem. Soc. 149 (2002) A1598. [18] Z.S. Wen, J. Yang, B.F. Wang, K. Wang, Y. Liu, Electrochem. Commun. 5 (2003) 165. [19] Z.P. Guo, E. Milin, J.Z. Wang, J. Chen, H.K. Liu, J. Electrochem. Soc. 152 (2005) A2211. [20] M.K. Datta, P.N. Kumta, J. Power Sources 158 (2006) 557. [21] V.G. Khomenko, V.Z. Barsukov, J.E. Doninger, I.V. Barsukov, J. Power Sources 165 (2007) 598. [22] D. Aurbach, J.S. Gnanaraj, W. Geissler, M. Schmidt, J. Electrochem. Soc. 151 (2004) A23. [23] L.B. Chen, K. Wang, X.H. Xie, J.Y. Xie, J. Power Sources 174 (2007) 538. [24] S. Komaba, T. Itabashi, T. Kimura, H. Groult, N. Kumagai, J. Power Sources 146 (2005) 166. [25] S. Komaba, T. Itabashi, B. Kaplan, H. Groult, N. Kumagai, Electrochem. Commun. 5 (2003) 962.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Improvement of cycle performance for silicon/carbon composite used as anode for lithium ion batteries Pengjian Zuo a,b,∗ , Geping Yin b , Zhanlin Yang b , Zhenbo Wang b , Xinqun Cheng b , Dechang Jia a , Chunyu Du b a b
Postdoctoral Station of Materials Science and Engineering, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China
a r t i c l e
i n f o
Article history: Received 29 January 2008 Received in revised form 18 July 2008 Accepted 19 February 2009 Keywords: Lithium ion battery Silicon/carbon composite Potassium modification Cycle stability
a b s t r a c t The silicon/carbon composite was prepared by mixing the silicon, graphite and pitch in the tetra-hydrofuran solution followed by pyrolyzing the blends after the evaporation of solvent. The electrochemical performance of the silicon/carbon anode for lithium ion batteries was improved by the treatment of composite powders with KCl aqueous solutions. Scanning electron microscope (SEM) observation and electrochemical impedance spectroscopy (EIS) results showed that the morphology stability of the composite electrodes can be kept during the electrochemical charge/discharge process. The composite electrode of silicon/carbon composite showed an initial reversible capacity of 575 mAh g−1 and still maintained a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of ∼0.3% per cycle. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Recently, metal-based material has been attracted much interest for the purpose of developing the novel lithium ion batteries with high energy density. Si or Sn-based systems, which have very high theoretical capacities in comparison with the traditional carbonaceous materials, possess the potential as alternative anodes for lithium ion batteries [1–4]. However, metal-based materials encounter a large irreversible capacity loss (ICL) during the alloying/de-alloying process of lithium ions with Si, Sn or others, which is mainly caused by the cracking of the electrode and a consequent loss of electronic contact between the bulk particles [5–7]. So far, the electrodes of silicon-based films, which were obtained by deposition of silicon-based materials onto the current collectors, exhibited the excellent properties in the aspects of the reversible capacity and cyclic performance [8–10]. Several other concepts such as “active–inactive” [11–13] and “core–shell” [14,15] have been utilized to relieve the volume changes of the metal-based materials during the charge/discharge process. Much evidence supports that the most attractive structure of Si/C composites is the dispersed silicon in carbon matrix [16–21]. Si-based materials have a long way to put into practice as commercial anodes due to their huge
∗ Corresponding author at: School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China. Tel.: +86 451 86403216; fax: +86 451 86413707. E-mail address: [email protected] (P. Zuo). 0254-0584/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2009.02.036
irreversible capacity loss even though the mechanical and electrochemical characteristics have been increased to some extent. It is believed that the existence of SEI (solid electrolyte interface) layer plays an important role in reversible lithium intercalation into graphite system, and chemical modification of graphite surface favoring the formation of SEI film has attracted extensive attention to improve battery performances. Several additives for the electrolyte solution, such as vinylene carbonate [22,23], metal ions [24,25], have been successfully studied to be effective in order to modify and improve the SEI film. In this paper, the silicon/carbon composites with high capacity and good cycle performance was obtained by pyrolysis of pitch embedded with graphite and silicon powders, and the cycle performance was further improved though the modification of the composite by alkali halide aqueous solution. 2. Experimental The preparation of the silicon/carbon composites was as follows: The silicon powders (−325 mesh, >99.6%) of 2 g and 2 g graphite (D50 = 18 m; Shenzhen BTR Energy Materials Co., Ltd) were added into the tetra-hydrofuran solution containing 8 g pitch and homogeneously mixed. The tetra-hydrofuran solvent was evaporated under stirring to get a solid blend. The mixture was heated at 900 ◦ C in an argon atmosphere for 2 h at a heating rate of 10 ◦ C min−1 and allowed cool down to room temperature naturally. The silicon/carbon composite modified by potassium ions was obtained by simple soaking the silicon/carbon material into the 5 wt.% KCl aqueous solution followed by the filtering and drying in vacuum. The obtained composite powders were characterized by X-ray diffraction (XRD) using a D/max-␥B diffractometer equipped with Cu radiation in the range of 2 = 10–90◦ . The morphology and microstructure of composite materials were observed by the scanning electron microscope (SEM) (Hitachi S-4700).
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P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
Fig. 1. Reversible capacity and coulomb efficiency vs. cycle number for silicon and silicon/carbon composite.
The composite electrodes were prepared by mixing 85 wt.% active material, 5 wt.% acetylene black and 10 wt.% polyvinylidene fluoride (PVDF) dissolved in Nmethylpyrrolidinone (NMP) to form a slurry which was then coated on the copper foil and dried at 120 ◦ C in vacuum for 14 h. The electrochemical reactions of silicon/carbon composites with lithium were investigated by a simple two-electrode cell using a lithium foil as a reference and counter electrode. The cells were assembled in a glove box filled with argon, and the electrolyte was 1 M LiPF6 in a mixture of EC:DEC:EMC = 1:1:1(v/v/v). The charge/discharge measurements were carried out between 0.01 V and 1.5 V (vs. Li/Li+ ) at 0.15 mA cm−2 using a programmable battery test system (BTS-5V1 mA). Electrochemical impedance spectroscopy (EIS) measurements were conducted using a CHI604 frequency response analyzer. Before the EIS experiments, the cells after a definite cycle at the above constant current density were placed in the delithiated state for 8 h to achieve equilibrium. The impedance spectra were recorded potentiostatically by applying an ac voltage of 5 mV amplitude over the frequency range from 0.1 MHz to 0.01 Hz.
3. Results and discussion Fig. 1 shows the reversible capacity and coulombic efficiency of pristine silicon and silicon/carbon composite prepared by pyrolyzing the blends of silicon, graphite and pitch powders at 900 ◦ C. The silicon/carbon composite shows the satisfying reversible capacity and cycle stability in comparison with the silicon anode, and it possesses an initial discharge capacity of 485 mAh g−1 and coulombic efficiency of 70%. Even though the electrochemical cycle stability of silicon/carbon composite has been improved significantly compared with silicon, the initial reversible efficiency and long-term cycle performance should be concerned further in order to meet the acquirement the possible practicability of silicon-based materials. Fig. 2 shows the XRD pattern of the silicon/carbon composite modified by KCl, in which the diffraction pattern of the pristine silicon/carbon composite is also provided for the purpose of comparison. It can be found the diffraction peak at 2 = 40.6◦ of the KCl crystal in the composite from the curve b in Fig. 2, and the diffraction peak at about 2 = 28.4◦ , 47.3◦ , 56.2◦ , 69.2◦ , 76.3◦ and 87.9◦ are due to the silicon crystal. As shown in the XRD patterns (Fig. 2) of the samples, the broad diffraction peak at about 2 = 22.8◦ could be indexed as diffraction peaks of pyrolyzed carbon from the pitch, and the diffraction peak (0 0 2) of graphite is clearly observed at 26.6◦ from the ex situ X-ray diffraction patterns of these two kinds of composites. The charge/discharge curves of the silicon/carbon composite with and without the modification of KCl are shown in Fig. 3. During the first insertion process, a distinct potential platform, which is mainly attributed to the alloying process of silicon with lithium and the insertion of lithium ions into the carbon host, can be observed at around 0–0.20 V for the silicon/carbon composites. The potential slope at around 0.5–0.7 V in the first discharge process corresponds to the irreversible decomposition of solvent component in electrolyte, which results in the formation of SEI film on the
Fig. 2. X-ray diffraction pattern for silicon/carbon composite (a) without KCl (b) modified by KCl.
surface of the silicon/carbon composite. The broad platform around 0.3–0.6 V corresponds to the de-intercalation reaction of lithium from the Lix Si phase and the extraction of lithium ions from the carbon materials. From Fig. 3, it can be seen that the initial discharge (816 mAh g−1 ) and charge capacity (575 mAh g−1 ) of silicon/carbon composite modified by KCl is higher than those (692 mAh g−1 and 485 mAh g−1 respectively) of the pristine silicon/carbon composite. The impedance spectra of the silicon/carbon composite anodes in delithiated states after 40 cycles are shown in Fig. 4. In general, the semicircles appeared in the high frequency range of the composites are due to the formation of SEI film caused by the decomposition of electrolyte solution, and the electrochemical reaction process of lithium with silicon or carbon corresponds to the second semicircle in the medium frequency regions. The sloping straight line at low frequency corresponds to diffusion of lithium ions in the bulk electrode [19]. It can be seen that the curves in high frequency range is almost overlapped while the radius of semicircle in the middle frequency for the pristine silicon/carbon composite is larger than that for the composite with KCl, which implies that the electrochemical reaction of silicon/carbon composite with lithium ions has been facilitated due to the modified by KCl. Fig. 5 shows the SEM images of electrodes for silicon/carbon composite modified by KCl before and after 40 cycles. It is clear that the composite electrode exhibits a homogeneous surface morphology and no obvious
Fig. 3. Charge/discharge curves of the silicon/carbon composite (a) with and (b) without modification of KCl.
P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
759
Fig. 6. Reversible capacity and coulomb efficiency vs. cycle number for silicon and silicon/carbon composite modified by KCl. Fig. 4. Nyquist plots of silicon/carbon composite electrodes in delithiated state after 40 cycles.
cracks can be seen even though it has been cycled electrochemically for 40 cycles. Fig. 6 shows the curves of discharge capacity and coulomb efficiency vs. cycle number for silicon/carbon composite with KCl used as anode material for lithium ion batteries. The composite electrode exhibits an initial reversible capacity of 575 mAh g−1 and a coulomb efficiency of 70% and still maintains a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of only ∼0.3% per cycle. The coulomb efficiency of composite electrode becomes constant to be nearly 100% after the fifth cycle even though the initial efficiency is a little lower. Compared with the pristine silicon/carbon composite as shown in Fig. 1, the reversible capacity and cycle performance are improved significantly after the modified of KCl for the silicon/carbon composite. 4. Conclusions In this paper, the silicon/carbon composite were prepared by dispersing the silicon and graphite particles into the tetra-hydrofuran solution containing pitch followed by the pyrolyzing the blends after the evaporation of solvent. The cycle stability silicon/carbon has been improved obviously in comparison with the pure silicon anode, the charge/discharge capacity and electrochemical cycle stability increase significantly through the modification of KCl on the surface of the active silicon-based materials. The composite electrode of silicon/carbon composite shows an initial reversible capacity of 575 mAh g−1 and a coulomb efficiency of 70%, and it still maintains a high reversible capacity of 506 mAh g−1 after 40 cycles with the capacity loss of only ∼0.3% per cycle. Acknowledgements This work was partially supported by The Natural Science Foundation of China (no. 20673032), China Postdoctoral Science Foundation funded project (20070420860), Natural Scientific Research Innovation Foundation in Harbin Institute of Technology (HIT.NSRIF. 2008.25) and the Key Scientific & Technological Programme of Heilongjiang Province of China (no. GB06A309). References
Fig. 5. SEM images of electrodes for silicon/carbon composite modified by KCl (a) before and after (b) 40 cycles.
[1] T.D. Hatchard, J.M. Topple, M.D. Fleischauer, J.R. Dahn, Electrochem. Solid-State Lett. 6 (2003) A129. [2] W.J. Weydanz, M. Wohlfahrt-Mehrens, R.A. Huggins, J. Power Sources 81–82 (1999) 237. [3] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276 (1997) 1395. [4] S.D. Beattle, J.R. Dahn, J. Electrochem. Soc. 150 (2003) 894.
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P. Zuo et al. / Materials Chemistry and Physics 115 (2009) 757–760
[5] A.N. Dey, J. Electrochem. Soc. 118 (1971) 1547. [6] D. Larcher, C. Mudalige, A.E. George, V. Porter, M. Gharghouri, J.R. Dahn, Solid State Ionics 122 (1999) 71. [7] Z.P. Guo, J.Z. Wang, H.K. Liu, S.X. Dou, J. Power Sources 146 (2005) 448. [8] H. Jung, M. Park, Y.-G. Yoon, G.-B. Kim, S.-K. Joo, J. Power Sources 115 (2003) 346. [9] M. Uehara, J. Suzuki, K. Tamura, K. Sekine, T. Takamura, J. Power Sources 146 (2005) 441. [10] T. Takamura, M. Uehara, J. Suzuki, K. Sekine, K. Tamura, J. Power Sources 158 (2006) 1401. [11] H.Y. Lee, S.W. Jang, S.M. Lee, S.J. Lee, H.K. Baik, J. Power Sources 112 (2002) 8. [12] S.Y. Chew, Z.P. Guo, J.Z. Wang, J. Chen, P. Munroe, S.H. Ng, L. Zhao, H.K. Liu, Electrochem. Commun. 9 (2007) 941. [13] S. Yoon, C.M. Park, H. Kim, H.J. Sohn, J. Power Sources 167 (2007) 520. [14] Y.S. Jung, K.T. Lee, J.H. Ryu, D. Im, S.M. Oh, J. Electrochem. Soc. 152 (2005) A1452. [15] N. Dimov, S. Kugino, M. Yoshio, Electrochim. Acta 48 (2003) 1579. [16] Y. Zheng, J. Yang, J.L. Wang, Y.N. NuLi, Electrochim. Acta 52 (2007) 5863.
[17] M. Yoshio, H. Wang, K. Fukuda, T. Umeno, N. Dimov, X. Ogumi, J. Electrochem. Soc. 149 (2002) A1598. [18] Z.S. Wen, J. Yang, B.F. Wang, K. Wang, Y. Liu, Electrochem. Commun. 5 (2003) 165. [19] Z.P. Guo, E. Milin, J.Z. Wang, J. Chen, H.K. Liu, J. Electrochem. Soc. 152 (2005) A2211. [20] M.K. Datta, P.N. Kumta, J. Power Sources 158 (2006) 557. [21] V.G. Khomenko, V.Z. Barsukov, J.E. Doninger, I.V. Barsukov, J. Power Sources 165 (2007) 598. [22] D. Aurbach, J.S. Gnanaraj, W. Geissler, M. Schmidt, J. Electrochem. Soc. 151 (2004) A23. [23] L.B. Chen, K. Wang, X.H. Xie, J.Y. Xie, J. Power Sources 174 (2007) 538. [24] S. Komaba, T. Itabashi, T. Kimura, H. Groult, N. Kumagai, J. Power Sources 146 (2005) 166. [25] S. Komaba, T. Itabashi, B. Kaplan, H. Groult, N. Kumagai, Electrochem. Commun. 5 (2003) 962.