- Email: [email protected]
Nanostructured Si–C composite anodes for lithium-ion batteries
Electrochemistry Communications 6 (2004) 689–692 www.elsevier.com/locate/elecom
Nanostructured Si–C composite anodes for lithium-ion batteries G.X. Wang *, J.H. Ahn, Jane Yao, Steve Bewlay, H.K. Liu Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia Received 19 April 2004; accepted 11 May 2004 Available online 2 June 2004
Abstract Nanostructured Si–C composite materials were prepared by dispersing nanocrystalline Si in carbon aerogel and subsequent carbonization. Through this process, nanosize Si was homogeneously distributed in a carbon matrix. The Si–C composites exhibit a reversible lithium storage capacity of 1450 mA h/g when used as anodes in lithium-ion cells. The nanostructured Si–C composite electrodes demonstrated good cyclability. The Si–C composites could provide a novel anode material for lithium-ion batteries. Ó 2004 Published by Elsevier B.V. Keywords: Nanostructured Si–C composite; Carbon aerogel; Nanocrystalline Si; Lithium-ion batteries
1. Introduction Carbonaceous materials are currently used as anode materials in lithium-ion batteries. Carbon anodes have a theoretical lithium storage capacity of 372 mA h/g to form LiC6 intercalation compound [1–3]. The development of a new generation of lithium-ion batteries requires new anode materials with a high lithium storage capacity. Recently, various lithium alloys have attracted worldwide attention as anode materials for lithium-ion batteries. For example, there have been intensive investigations on tin, tin based alloys and tin oxide composites [4–6]. The formation of Li4:4 Sn results in a theoretical capacity of 991 mA h/g for elemental Sn. However, this alloying process is accompanied by a 259% volume increase, causing the disintegration of the electrode. This phenomenon can be partially alleviated by embedding Sn in the inactive M matrix to create a buffering effect. Silicon has the highest theoretical capacity of 4000 mA h/g when forming Li4:2 Si alloys, far greater than that of carbon and Sn. However, this alloying process is associated with a 300% volume dilation, pulverizing the brittle electrode and inducing poor cyclability [7]. *
Corresponding author. Tel.: +61-2-42215726; fax: +61-2-42215731. E-mail address: [email protected] (G.X. Wang).
1388-2481/$ - see front matter Ó 2004 Published by Elsevier B.V. doi:10.1016/j.elecom.2004.05.010
The performance of Si anodes can be significantly improved by preparing nanostructured electrode. This is because the mechanisms of fracture will be changed when the material crystals are in a size of tens of nanometer scale. Nanodispersed Si in carbon has been synthesised by chemical vapour deposition (CVD) and demonstrated a reversible capacity of 500 mA h/g. However, the CVD approach produces SiC and cannot control the morphology of Si and C [8]. A nanostructured thin-film form of Si electrode has been investigated and exhibited a specific capacity of around of 1100 mA h/g [9,10]. Nano Si–C composite prepared by hand mixing has been reported to have a high reversible capacity of 1700 mA h/g [11]. Crystalline Si powders have been dispersed in sol–gel graphite [12], in synthetic graphite [13], and in a TiN matrix [14] by ball milling. Those Si–C composites showed increased specific capacity compared to bare graphite, and improved cyclability compared to bare Si electrodes. In this investigation, we report the synthesis of nanostructured Si–C composites by dispersing nanocrystalline Si in carbon aerogel. The electrochemical properties of nanostructured Si–C were systematically evaluated. The improved electrochemical performance of Si–C could originate from the unique mechanisms of the lithiation and de-lithiation processes in nanostructured Si–C composites.
690
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
2. Experimental Nanocrystalline Si with an average particle size of 80 nm was purchased from Nanostructured and Amorphous Materials Inc., USA, which were prepared by laser driven silane gas reaction. Resorcinol (98%, Sigma–Aldrich) and formaldehyde (37.6% in methanol, Sigma–Aldrich) were used for preparing carbon aerogel. A typical carbon gel was formed by mixing 0.29 M resorcinol and 0.57 M formaldehyde. The pH value was adjusted to be in the range of 6.5–7.4 by adding NH3 H2 O solution. The mixture solution was put in an ampoule, sealed and heated on a hot plate. The temperature was maintained at 85 °C. The solution changed progressively from clear to milk white to yellow to orange as the reaction progressed. When the solution became viscous, nanocrystalline Si powders were added, and dispersed through magnetic stirring. The ampoule was kept at 85 °C for 10 h and then carbon aerogel was formed with Si dispersed inside the gel. The obtained gel was then sintered at 650° under flowing argon to yield Si–C composites, containing 40% by weight in carbon. The carbon content was measured by thermogravimetric analysis (TG). X-ray diffraction was performed on the prepared Si– C composites to determine the phase compositions (MO3xHF22, MacScience, Japan) using Cu Ka radiation. The morphology of the Si–C powders was studied using a high resolution transmission electron microscope (300 KV JEOL JEM-3000F with field emission). The electrochemical evaluation of Si–C composites was accomplished by assembling CR2032 coin cells. The electrodes were made by dispersing 92 wt% active materials and 8 wt% polyvinylidene fluoride (PVDF) binder in n-methyl pyrolidone (NMP) solvent to form a homogeneous slurry. The slurry was then spread onto an Al foil. The coated electrodes were dried in a vacuum oven at 120 °C for 12 h and then pressed to enhance the contact between the active materials and the conductive carbons. The cells were assembled in an argon filled glove-box (Mbraun, Unilab, Germany) using lithium metal foil as the counter electrode. The electrolyte was 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume, provided by MERCK KgaA, Germany). The cells were galvanostatically charged and discharged over a voltage range of 0.02–2.0 V at a C/10 rate. Cyclic voltammetry (CV) measurements were performed using an EG&G Scanning Potentiostat (Model 362) at a scanning rate of 0.1 mV/s.
these then further react with each other to form a crosslinked 3-dimensional net-work (called RF gel). Fig. 1 shows a schematic diagram of the reaction of resorcinol with formaldehyde. In the resorcinol structure, an enhanced electron density exists in the 2, 4, 6 ring positions. However, the number two position is sterically hindered by the adjacent hydroxyl groups. So, the reaction occurs primarily in the four and six positions [15,16]. Through crosslinking, RF gel forms an interconnected bead structure (3 dimensional network). The nanocrystalline Si was homogeneously embedded in this RF gel network. After heat treatment at 650 °C, the gel was carbonized to become amorphous carbon. The final products were Si–C composites. Fig. 2 shows an X-ray diffraction pattern of typical Si–C composites. All diffraction lines are indexed to Si. No diffraction lines from crystalline carbon (graphite) were observed, indicating the amorphous nature of carbon in the composites. A TEM image of nanocrystalline Si is shown in Fig. 3(a). The pristine Si powders contain nanosize Si particles with a spherical shape. The size of individual particles ranges from 20 to 80 nm. Some amorphous Si powders are also present. Fig. 3(b) shows a TEM photo of nano Si–C composite powders. It clearly demonstrates that Si powders are surrounded
Fig. 1. A schematic diagram of the R–F gel reaction.
3. Results and discussion Resorcinol reacts with formaldehyde to form initially chains of hydroxymethyl derivatives of resorcinol, and
Fig. 2. X-ray diffraction pattern of Si–C composites.
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
691
Fig. 3. (a) TEM image of nanocrystalline Si powders. (b) TEM image of nanocrystalline Si–C composites.
by amorphous carbon. Spot EDX (energy dispersive Xray) analysis confirmed that the spherical black crystals in Fig. 3(b) are Si. Therefore, nanocrystalline Si particles are uniformly embedded in amorphous carbon matrix through the carbon aerogel synthesis process. The electrochemical performance of the nanostructured Si–C composites was systematically measured. Cyclic voltammograms of Si–C electrodes in a lithiumion cell, in which a lithium foil was used as the counter electrode and reference electrode, are shown in Fig. 4. The initial potential of the Si–C electrode is about 3.0 V in the open-circuit state. In the first scanning cycle, there are two broad cathodic peaks located at 0.60 and 0.38 V, respectively, which disappear from the second cycle. These reduction peaks could be attributed to the formation of a solid-electrolyte interphase (SEI) passivation layer on the surface of the composite electrode, due to the reaction of lithium with electrolyte. Once the SEI layer is formed, it will be stable under subsequent
lithium insertion and extraction, which is evidenced by the disappearance of these two reduction peaks from the second cycle. Two anodic peaks, located at 0.38 and 0.50 V, gradually evolve from the first scanning cycle, and become more distinct after the fourth cycle, which corresponds to the extraction of lithium ions from the Si–C electrode. One additional cathodic peak at 0.20 V appears from the fourth cycle. The two pairs of redox peaks remains stable from the fourth scanning cycle until the twentieth cycle. We suggest that a few cycles are required to activate the Si–C composite electrode under a scanning rate of 0.1 mV/s. The observed two redox peaks should be attributed to the reaction of lithium with Si to form Lix Si alloys as indicated in Eq. (1).
Fig. 4. Cyclic voltammetry of Si–C composite electrode.
Fig. 5. The discharge/charge profiles of Si–C composite electrode.
xLi þ Si $ Lix Si
ð1Þ
This observation in cyclic voltammetry is similar to that for thin-film Si electrodes [9].
692
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
demonstrates a high lithium storage capacity and good cycle life.
4. Conclusions
Fig. 6. The discharge capacity versus cycle number for Si–C electrode.
The specific capacity and cyclability of nanostructured Si–C composite electrodes were measured by constant discharge/charge testing. Fig. 5 shows the discharge/charge profiles of a Si–C electrode at a rate of C/ 10. The Si–C electrode delivered a discharge capacity of about 2000 mA h/g in the first cycle, but with a irreversible capacity of about 550 mA h/g. Part of this irreversible capacity was used to form a SEI passivation layer on the surface of the electrode. The reversible capacity was improved from the second cycle. In the first cycle, there is a discharge plateau in the voltage range of 0.8–0.5 V, which corresponds to the formation of the SEI layer. However, this discharge plateau disappears from the second cycle. This observation is in good agreement with CV measurement. A stable discharge plateau between 0.30–0.02 V is evolved from the second cycle and remains stable. The results of the cycling test are shown in Fig. 6, indicating good cyclability of nanostructured Si–C composite electrodes. It is well known that a 300% volume increase is accompanies to the lithium alloying process with Si to form Li4:4 Si. This dramatic volume variation could pulverize the electrode, inducing poor cyclability. We resolve this problem by utilizing nanosize silicon powders and embedding Si in an amorphous carbon matrix. Through the synthesis of carbon aerogel, Si powders are homogeneously embedded in a three-dimensional carbon network matrix. Since Si particles are nanosize in nature, the volume increase in the local sites is small, and can be easily cushioned by the carbon matrix surrounded the Si nanoclusters. Therefore, the volume change in the macrodomain will be negligibly small for the Si–C composite electrode, which allows the integrity of the electrode to be preserved for repeated lithiation and de-lithiation processes. As a result, the Si–C composite electrode
Nanostructured Si–C composite anode materials were prepared by dispersing nanocrystalline Si powders in carbon aerogel, followed by heat treatment for carbonization. Cyclic voltammetry measurements show two pairs of redox peaks associated with the lithiation and de-lithiation processes of Lix Si alloys. A reversible capacity of 1450 mA h/g for Si–C composite electrodes was achieved. The good cyclability should be attributed to the usage of nanosize Si powders and their homogeneous distribution in an amorphous carbon matrix.
Acknowledgements This work was supported by the Australia Research Council through ARC Centre for Nanostructured Electromaterials.
References [1] K. Sato, M. Noguchi, A. Demachi, N. Oki, M. Endo, Science 264 (1994) 556. [2] J.R. Dahn, T. Zheng, Y.H. Liu, J.S. Xue, Science 270 (1995) 590. [3] R. Yazami, Electrochimica Acta 45 (1999) 87. [4] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276 (1997) 1395. [5] M. Winter, J.O. Besenhard, Electrochimica Acta 45 (1999) 31. [6] O. Mao, R.L. Turner, I.A. Courtney, B.D. Fredericksen, M.I. Buckett, L.J. Krause, J.R. Dahn, Electrochem. Solid-State Lett. 2 (1999) 3. [7] J.O. Besenhard, M. Hess, P. Komenda, Solid State Ionics 40–41 (1990) 525. [8] A.M. Wilson, J.R. Dahn, J. Electrochem. Soc. 142 (1995) 326. [9] J. Gratz, C.C. Ahn, R. Yazami, B. Fultz, Electrochem. Solid-State Lett. 6 (1999) A194. [10] S. Ohara, J. Suzuki, K. Sekine, T. Takamura, J. Power Sources 119–121 (2003) 591. [11] H. Li, X.J. Huang, L.Q. Chen, Z.G. Wu, Y. Liang, Electrochem. Solid-State Lett. 2 (1999) 547. [12] J. Niu, J.Y. Lee, Electrochem. Solid-State Lett. 5 (2002) A107. [13] C.S. Wang, G.T. Wu, X.B. Zhang, Z.F. Qi, W.Z. Li, J. Electrochem. Soc. 145 (1998) 2751. [14] I. Kim, P.N. Kumta, G.E. Blomgren, Electrochem. Solid-State Lett. 3 (2000) 493. [15] R.W. Pekala, J. Mater. Sci. 24 (1989) 3221. [16] D.D. Werstler, Polymer 27 (1986) 757.
Nanostructured Si–C composite anodes for lithium-ion batteries G.X. Wang *, J.H. Ahn, Jane Yao, Steve Bewlay, H.K. Liu Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia Received 19 April 2004; accepted 11 May 2004 Available online 2 June 2004
Abstract Nanostructured Si–C composite materials were prepared by dispersing nanocrystalline Si in carbon aerogel and subsequent carbonization. Through this process, nanosize Si was homogeneously distributed in a carbon matrix. The Si–C composites exhibit a reversible lithium storage capacity of 1450 mA h/g when used as anodes in lithium-ion cells. The nanostructured Si–C composite electrodes demonstrated good cyclability. The Si–C composites could provide a novel anode material for lithium-ion batteries. Ó 2004 Published by Elsevier B.V. Keywords: Nanostructured Si–C composite; Carbon aerogel; Nanocrystalline Si; Lithium-ion batteries
1. Introduction Carbonaceous materials are currently used as anode materials in lithium-ion batteries. Carbon anodes have a theoretical lithium storage capacity of 372 mA h/g to form LiC6 intercalation compound [1–3]. The development of a new generation of lithium-ion batteries requires new anode materials with a high lithium storage capacity. Recently, various lithium alloys have attracted worldwide attention as anode materials for lithium-ion batteries. For example, there have been intensive investigations on tin, tin based alloys and tin oxide composites [4–6]. The formation of Li4:4 Sn results in a theoretical capacity of 991 mA h/g for elemental Sn. However, this alloying process is accompanied by a 259% volume increase, causing the disintegration of the electrode. This phenomenon can be partially alleviated by embedding Sn in the inactive M matrix to create a buffering effect. Silicon has the highest theoretical capacity of 4000 mA h/g when forming Li4:2 Si alloys, far greater than that of carbon and Sn. However, this alloying process is associated with a 300% volume dilation, pulverizing the brittle electrode and inducing poor cyclability [7]. *
Corresponding author. Tel.: +61-2-42215726; fax: +61-2-42215731. E-mail address: [email protected] (G.X. Wang).
1388-2481/$ - see front matter Ó 2004 Published by Elsevier B.V. doi:10.1016/j.elecom.2004.05.010
The performance of Si anodes can be significantly improved by preparing nanostructured electrode. This is because the mechanisms of fracture will be changed when the material crystals are in a size of tens of nanometer scale. Nanodispersed Si in carbon has been synthesised by chemical vapour deposition (CVD) and demonstrated a reversible capacity of 500 mA h/g. However, the CVD approach produces SiC and cannot control the morphology of Si and C [8]. A nanostructured thin-film form of Si electrode has been investigated and exhibited a specific capacity of around of 1100 mA h/g [9,10]. Nano Si–C composite prepared by hand mixing has been reported to have a high reversible capacity of 1700 mA h/g [11]. Crystalline Si powders have been dispersed in sol–gel graphite [12], in synthetic graphite [13], and in a TiN matrix [14] by ball milling. Those Si–C composites showed increased specific capacity compared to bare graphite, and improved cyclability compared to bare Si electrodes. In this investigation, we report the synthesis of nanostructured Si–C composites by dispersing nanocrystalline Si in carbon aerogel. The electrochemical properties of nanostructured Si–C were systematically evaluated. The improved electrochemical performance of Si–C could originate from the unique mechanisms of the lithiation and de-lithiation processes in nanostructured Si–C composites.
690
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
2. Experimental Nanocrystalline Si with an average particle size of 80 nm was purchased from Nanostructured and Amorphous Materials Inc., USA, which were prepared by laser driven silane gas reaction. Resorcinol (98%, Sigma–Aldrich) and formaldehyde (37.6% in methanol, Sigma–Aldrich) were used for preparing carbon aerogel. A typical carbon gel was formed by mixing 0.29 M resorcinol and 0.57 M formaldehyde. The pH value was adjusted to be in the range of 6.5–7.4 by adding NH3 H2 O solution. The mixture solution was put in an ampoule, sealed and heated on a hot plate. The temperature was maintained at 85 °C. The solution changed progressively from clear to milk white to yellow to orange as the reaction progressed. When the solution became viscous, nanocrystalline Si powders were added, and dispersed through magnetic stirring. The ampoule was kept at 85 °C for 10 h and then carbon aerogel was formed with Si dispersed inside the gel. The obtained gel was then sintered at 650° under flowing argon to yield Si–C composites, containing 40% by weight in carbon. The carbon content was measured by thermogravimetric analysis (TG). X-ray diffraction was performed on the prepared Si– C composites to determine the phase compositions (MO3xHF22, MacScience, Japan) using Cu Ka radiation. The morphology of the Si–C powders was studied using a high resolution transmission electron microscope (300 KV JEOL JEM-3000F with field emission). The electrochemical evaluation of Si–C composites was accomplished by assembling CR2032 coin cells. The electrodes were made by dispersing 92 wt% active materials and 8 wt% polyvinylidene fluoride (PVDF) binder in n-methyl pyrolidone (NMP) solvent to form a homogeneous slurry. The slurry was then spread onto an Al foil. The coated electrodes were dried in a vacuum oven at 120 °C for 12 h and then pressed to enhance the contact between the active materials and the conductive carbons. The cells were assembled in an argon filled glove-box (Mbraun, Unilab, Germany) using lithium metal foil as the counter electrode. The electrolyte was 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume, provided by MERCK KgaA, Germany). The cells were galvanostatically charged and discharged over a voltage range of 0.02–2.0 V at a C/10 rate. Cyclic voltammetry (CV) measurements were performed using an EG&G Scanning Potentiostat (Model 362) at a scanning rate of 0.1 mV/s.
these then further react with each other to form a crosslinked 3-dimensional net-work (called RF gel). Fig. 1 shows a schematic diagram of the reaction of resorcinol with formaldehyde. In the resorcinol structure, an enhanced electron density exists in the 2, 4, 6 ring positions. However, the number two position is sterically hindered by the adjacent hydroxyl groups. So, the reaction occurs primarily in the four and six positions [15,16]. Through crosslinking, RF gel forms an interconnected bead structure (3 dimensional network). The nanocrystalline Si was homogeneously embedded in this RF gel network. After heat treatment at 650 °C, the gel was carbonized to become amorphous carbon. The final products were Si–C composites. Fig. 2 shows an X-ray diffraction pattern of typical Si–C composites. All diffraction lines are indexed to Si. No diffraction lines from crystalline carbon (graphite) were observed, indicating the amorphous nature of carbon in the composites. A TEM image of nanocrystalline Si is shown in Fig. 3(a). The pristine Si powders contain nanosize Si particles with a spherical shape. The size of individual particles ranges from 20 to 80 nm. Some amorphous Si powders are also present. Fig. 3(b) shows a TEM photo of nano Si–C composite powders. It clearly demonstrates that Si powders are surrounded
Fig. 1. A schematic diagram of the R–F gel reaction.
3. Results and discussion Resorcinol reacts with formaldehyde to form initially chains of hydroxymethyl derivatives of resorcinol, and
Fig. 2. X-ray diffraction pattern of Si–C composites.
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
691
Fig. 3. (a) TEM image of nanocrystalline Si powders. (b) TEM image of nanocrystalline Si–C composites.
by amorphous carbon. Spot EDX (energy dispersive Xray) analysis confirmed that the spherical black crystals in Fig. 3(b) are Si. Therefore, nanocrystalline Si particles are uniformly embedded in amorphous carbon matrix through the carbon aerogel synthesis process. The electrochemical performance of the nanostructured Si–C composites was systematically measured. Cyclic voltammograms of Si–C electrodes in a lithiumion cell, in which a lithium foil was used as the counter electrode and reference electrode, are shown in Fig. 4. The initial potential of the Si–C electrode is about 3.0 V in the open-circuit state. In the first scanning cycle, there are two broad cathodic peaks located at 0.60 and 0.38 V, respectively, which disappear from the second cycle. These reduction peaks could be attributed to the formation of a solid-electrolyte interphase (SEI) passivation layer on the surface of the composite electrode, due to the reaction of lithium with electrolyte. Once the SEI layer is formed, it will be stable under subsequent
lithium insertion and extraction, which is evidenced by the disappearance of these two reduction peaks from the second cycle. Two anodic peaks, located at 0.38 and 0.50 V, gradually evolve from the first scanning cycle, and become more distinct after the fourth cycle, which corresponds to the extraction of lithium ions from the Si–C electrode. One additional cathodic peak at 0.20 V appears from the fourth cycle. The two pairs of redox peaks remains stable from the fourth scanning cycle until the twentieth cycle. We suggest that a few cycles are required to activate the Si–C composite electrode under a scanning rate of 0.1 mV/s. The observed two redox peaks should be attributed to the reaction of lithium with Si to form Lix Si alloys as indicated in Eq. (1).
Fig. 4. Cyclic voltammetry of Si–C composite electrode.
Fig. 5. The discharge/charge profiles of Si–C composite electrode.
xLi þ Si $ Lix Si
ð1Þ
This observation in cyclic voltammetry is similar to that for thin-film Si electrodes [9].
692
G.X. Wang et al. / Electrochemistry Communications 6 (2004) 689–692
demonstrates a high lithium storage capacity and good cycle life.
4. Conclusions
Fig. 6. The discharge capacity versus cycle number for Si–C electrode.
The specific capacity and cyclability of nanostructured Si–C composite electrodes were measured by constant discharge/charge testing. Fig. 5 shows the discharge/charge profiles of a Si–C electrode at a rate of C/ 10. The Si–C electrode delivered a discharge capacity of about 2000 mA h/g in the first cycle, but with a irreversible capacity of about 550 mA h/g. Part of this irreversible capacity was used to form a SEI passivation layer on the surface of the electrode. The reversible capacity was improved from the second cycle. In the first cycle, there is a discharge plateau in the voltage range of 0.8–0.5 V, which corresponds to the formation of the SEI layer. However, this discharge plateau disappears from the second cycle. This observation is in good agreement with CV measurement. A stable discharge plateau between 0.30–0.02 V is evolved from the second cycle and remains stable. The results of the cycling test are shown in Fig. 6, indicating good cyclability of nanostructured Si–C composite electrodes. It is well known that a 300% volume increase is accompanies to the lithium alloying process with Si to form Li4:4 Si. This dramatic volume variation could pulverize the electrode, inducing poor cyclability. We resolve this problem by utilizing nanosize silicon powders and embedding Si in an amorphous carbon matrix. Through the synthesis of carbon aerogel, Si powders are homogeneously embedded in a three-dimensional carbon network matrix. Since Si particles are nanosize in nature, the volume increase in the local sites is small, and can be easily cushioned by the carbon matrix surrounded the Si nanoclusters. Therefore, the volume change in the macrodomain will be negligibly small for the Si–C composite electrode, which allows the integrity of the electrode to be preserved for repeated lithiation and de-lithiation processes. As a result, the Si–C composite electrode
Nanostructured Si–C composite anode materials were prepared by dispersing nanocrystalline Si powders in carbon aerogel, followed by heat treatment for carbonization. Cyclic voltammetry measurements show two pairs of redox peaks associated with the lithiation and de-lithiation processes of Lix Si alloys. A reversible capacity of 1450 mA h/g for Si–C composite electrodes was achieved. The good cyclability should be attributed to the usage of nanosize Si powders and their homogeneous distribution in an amorphous carbon matrix.
Acknowledgements This work was supported by the Australia Research Council through ARC Centre for Nanostructured Electromaterials.
References [1] K. Sato, M. Noguchi, A. Demachi, N. Oki, M. Endo, Science 264 (1994) 556. [2] J.R. Dahn, T. Zheng, Y.H. Liu, J.S. Xue, Science 270 (1995) 590. [3] R. Yazami, Electrochimica Acta 45 (1999) 87. [4] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, Science 276 (1997) 1395. [5] M. Winter, J.O. Besenhard, Electrochimica Acta 45 (1999) 31. [6] O. Mao, R.L. Turner, I.A. Courtney, B.D. Fredericksen, M.I. Buckett, L.J. Krause, J.R. Dahn, Electrochem. Solid-State Lett. 2 (1999) 3. [7] J.O. Besenhard, M. Hess, P. Komenda, Solid State Ionics 40–41 (1990) 525. [8] A.M. Wilson, J.R. Dahn, J. Electrochem. Soc. 142 (1995) 326. [9] J. Gratz, C.C. Ahn, R. Yazami, B. Fultz, Electrochem. Solid-State Lett. 6 (1999) A194. [10] S. Ohara, J. Suzuki, K. Sekine, T. Takamura, J. Power Sources 119–121 (2003) 591. [11] H. Li, X.J. Huang, L.Q. Chen, Z.G. Wu, Y. Liang, Electrochem. Solid-State Lett. 2 (1999) 547. [12] J. Niu, J.Y. Lee, Electrochem. Solid-State Lett. 5 (2002) A107. [13] C.S. Wang, G.T. Wu, X.B. Zhang, Z.F. Qi, W.Z. Li, J. Electrochem. Soc. 145 (1998) 2751. [14] I. Kim, P.N. Kumta, G.E. Blomgren, Electrochem. Solid-State Lett. 3 (2000) 493. [15] R.W. Pekala, J. Mater. Sci. 24 (1989) 3221. [16] D.D. Werstler, Polymer 27 (1986) 757.