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Synthesis and characterisation of sponge-like carbon anode materials for lithium ion batteries
Materials Letters 109 (2013) 253–256
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterisation of sponge-like carbon anode materials for lithium ion batteries Jingjing Tang, Juan Yang, Xiangyang Zhou n School of Metallurgy and Environment, Central South University, Changsha 410083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 9 May 2013 Accepted 26 July 2013 Available online 2 August 2013
Micro-sized carbon material with a unique sponge-like morphology has been fabricated by hydrothermal method coordinating etching process. When evaluate its electrochemical properties in lithium ion batteries, the sponge-like carbon structure exhibits very high specific capacity (around 1175 mAh g 1 after 140th cycle tested at the charge/discharge current density of 200 mA g 1) and wonderful cyclability (about 117% retention is available when cycled back from very high current density of 800 mA g 1) during the galvanostatic cycling, indicating it may be a promising candidate as anode material for Li-ion batteries. & 2013 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Hydrothermal method Structural Electrical properties Lithium ion batteries
1. Introduction In the early 1990s, Sony succeeded in realizing the commercial application of the first rechargeable Lithium ion cell based on a carbon anode (petroleum coke) and a LiCoO2 cathode [1]. Since then, lithium ion batteries have been identified as one of the most important and the greenest type of rechargeable batteries. At present, graphitic carbon anodes are often employed in lithium ion batteries which can avoid the problem of Li dendrite formation by the reversible intercalation of Li into the carbon host lattice and guarantee good cyclability and safety [2]. However, the limited theoretical capacity of 372 mAh g 1 drives extensive research focusing on developing alternative anode materials to realize a high specific capacity and good cycling ability. Among them, hard carbons are found promising due to their appealing properties, such as higher specific capacity and long durability [3,4]. In this paper, sponge-like carbon (SPC) anode material has been prepared via template synthesis process. When employed as anode material for lithium ion batteries, the SPC anode material shows high discharge capacity and good cyclic performance.
2. Experimental Material preparation and characterization: First, 2 g of Co (NO3)2 6H2O was dissolved into 100 ml of continuously stirred isopropyl alcohol–water (1:1, v/v) solution at room temperature. n
Corresponding author. Tel./fax: +86 731 8883 6329. E-mail address: [email protected] (X. Zhou).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.07.100
2 ml of ammonia solution (NH3 H2O, 25 wt%) was subsequently added drop by drop at a time interval of 2 h under vigorous stirring. The reaction was allowed to proceed for a further 12 h and the resulting Co3O4 powder was collected and washed with water. Then, silica coating process was carried out to synthesis Co3O4/ SiO2 composites as previously reported [5]. 0.85 g of as-prepared Co3O4/SiO2 products, 4.2 g glucose, 0.28 g polyvinylpyrrolidone (PVP) were dissolved in 220 ml deionized water under stirring and then ultrasonicated for 0.5 h. The mixture was heated at 180 1C for 6 h in a sealed Teflon-lined autoclave. The dark brown products were collected by suction filtration with absolute ethyl alcohol and deionized water, and dried at 80 1C. The assynthesized samples were further annealed in Ar atmosphere at 900 1C for 2 h. After been immersed in dilute hydrofluoric acid for 3 h, SPC powder was finally obtained after filtering, washing and drying. For comparison, hollow carbon spheres (HCS) were synthesized under the same conditions without the addition of Co3O4. Material characterization: The morphologies of the materials were observed by field emission scanning electron microscopy (NOVA NANO SEM230) and field emission transmission electron microscopy (FETEM, JEM-2100 F). Chemical analysis was performance using an EDAX system interfaced to the FETEM. Structure characterizations were performed by X-ray diffraction (XRD, Rigaku-TTRIII, Cu Kα) at a scanning rate of 10 deg min 1 and Raman spectroscopy (LabRAM Hr800). Electrochemical measurement: The working electrodes were prepared by mixing active material, acetylene black and polyvinylidene at a weight ratio of 8:1:1 and pasted on pure copper foil. Standard 2025 coin cell was assembled in an ultra pure argon filled glove box for electrochemical tests by employing a lithium foil as the counter electrode and 1 M LiPF 6 in ethylene
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J. Tang et al. / Materials Letters 109 (2013) 253–256
carbonate/dimethyl carbonate (1:1) as the electrolyte. Galvanostatic charging/discharging was performed on LAND CT2001 A in the potential range of 0.01–3.2 V versus Li/Li + at a current density of 200 mA g 1 .
3. Results and discussion The crystallinity of carbon materials can be determined by XRD and Raman spectroscopy. Fig. 1a shows the XRD patterns
of SPC and HCS. The characteristic (002) (20–301) and (100) (40–451) peaks of graphite are discernible in both carbon materials, which indicates the amorphous nature of obtained materials. Compared with HCS, SPC exhibits a stronger (002) peak, demonstrating the well-stacked graphene layers in the sample [6]. The d 002 of SPC and HCS is about 0.37 nm and 0.38 nm, respectively. The larger interlayer spacing compared with pure graphite carbon (about 0.33 nm) is thought to be favorable for lithium insertion and extraction, retaining the structural stability of an electrode during cycles [7]. It is
Fig. 1. (a) XRD patterns and (b) Raman spectra of samples. Insert is the EDS of SPC.
Fig. 2. (a) SEM and (b–d) TEM images of SPC, (e) SEM and (f) TEM images of HCS.
J. Tang et al. / Materials Letters 109 (2013) 253–256
demonstrated from the EDS spectrum that there is no existence of Co or Si in the final SPC sample. More convincing evidence of the carbon materials is provided by Raman spectra (Fig. 1b). Both SPC and HCS exhibit two peaks at approximately 1355 and 1578 cm 1, which are usually denoted as D band and G band, respectively. The D band can be explained as structure defects and disorder-induced features of carbon, while the G band corresponds to the stretching vibration mode of graphite crystals. The former mode is forbidden in perfect graphite and only becomes active in the presence of disorder [8]. The peak integrated intensity ratio of the D band to the G band (ID/IG) for SPC and HCS are estimated to be 1.26 and 2.23, disclosing that there are more disorder defective carbons with HCS. Besides, in the region of the higher-order Raman spectrum for SPC, three distinct peaks located at 2690, 2934 and 3220 cm 1 are typical character of highly ordered pyrolytic graphite (HOPG) [9]. Fig. 2 depicts representative SEM and TEM images of samples. From Fig. 2a, it can be seen that SPC sample takes on an irregular shape and the surface is uneven. TEM image as shown in Fig. 2b demonstrates that the obtained sample is porous and exhibits a sponge-like feature, which is similar to the previous report in SnO2 nanoarchitecture [10]. Selected area electron diffraction (SAED) image proves the amorphous nature of SPC, which is in good agreement with XRD. At higher magnification, as shown in Fig. 2c and d, graphitic layers can be seen on the edge of SPC. It is speculated that the existence of cobalt oxide is responsible for the unique sponge-like structure and the higher degree of order. Without the addition of Co3O4, the obtained carbon sample consists of well-dispersed hollow spheres ranged between 200 and 400 nm. Further research is being carried out to confirm the exact formation mechanism of SPC. Fig. 3a shows the first charge/discharge curves of as-prepared SPC and HCS. The curve shape of the two samples in the first discharge process is similar. When Li+ inserts into the anode in the first charge, there are two sloping voltage ranges ( 40.8 V and o0.8 V) that can be detected. The first slope is attributed to the decomposition of the electrolyte and the formation of solid electrolyte interface (SEI) film, while the second corresponds to
255
the insertion of Li+ into the porous of materials [11]. It is also apparent that both SPC and HCS have a large Li+ storage capacity. The charge capacity of SPC and HCS is about 2066 and 873 mAh g 1, respectively. The reductive decomposition of electrolyte and the subsequent formation of SEI are responsible for the low initial Coulombic efficiency. Fig. 3b and c show the cycling performances of SPC and HCS anodes. The results demonstrate that SPC anode delivers good cycle stability and large reversible capacity, which is always larger than that of HCS anodes. Due to the unique structure of SPC, the discharge capacity increased to 1175 mAh g 1 after 140th cycle. A similar capacity increasing phenomenon during cycling has also been reported [12,13]. Attractively, SPC anode possesses high specific capacity and cycle stability under high rate charge/discharge processes as shown in Fig. 3d. At the current density of 50 mA g 1, the initial discharge capacity reaches up to 870 mAh g 1. Its specific discharge capacity decreases tardily along with the cycle number and remains 743 mAh g 1 after 10 cycles. When the current density increases to 800 mA g 1 and after 10 cycles, there is a discharge capacity of 405 mAh g 1. A capacity of 800 mAh g 1 was obtained when the current density was returned to 50 mA g 1 after charge/ discharge at a high current density, suggesting the high structural and cyclic stabilities of SPC anode. This rate performance is comparable with the previous reports about hierarchical porous carbon [14]. In the case of HCS, the reversible capacity at 50 and 800 mA g 1 are about 387 and 230 mAh g 1, respectively, which is much lower than that of SPC. However, the reversible capacity retention is almost 100%, indicating an acceptable rate performance, although it is weaker than SPC.
4. Conclusions SPC was synthesized using cobalt oxide and silica as templates. SEM and TEM images demonstrated that the obtained carbon material manifested complex pore structure. The electrochemical tests revealed that SPC anode possessed high reversible capacity,
Fig. 3. Electrochemical performances of SPC and HCS. (a) The first charge/discharge curves of SPC, cycling performances of (b) SPC and (c) HCS, (d) rate capability of SPC and HCS.
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J. Tang et al. / Materials Letters 109 (2013) 253–256
good cycling performance and satisfied rate capability. However, the common disadvantage of hard carbon, such as high first irreversible capacity, needs to be settled by optimizing the condition of material preparation. Acknowledgments
[2] [3] [4] [5] [6] [7] [8] [9]
The research was financially supported by the National Natural Science Foundation of China (51274240, 51204209) and the Hunan Provincial Innovation Foundation for Postgraduate.
[10]
References
[13] [14]
[1] Kraytsberg A, Ein-Eli Y. Advanced Energy Materials 2012;2:922–39.
[11] [12]
Wu YP, Rahm E, Holze R. Journal of Power Sources 2003;114:228–36. Zheng H, Qu Q, Zhang L, Liu G, Battaglia VS. RSC Advances 2012;2:4904–12. Ni J, Huang Y, Gao L. Journal of Power Sources 2013;223:306–11. Zhou X, Tang J, Yang J, Xie J, Ma L. Electrochimica Acta 2013;87:663–8. Fey GTK, Kao YC. Materials Chemistry and Physics 2002;73:37–46. Yi Z, Liang X, Lei X, Wang C, Sun J. Materials Letters 2007;61:4199–203. Kim C, Park SH, Cho JI, Lee DY, Park TJ, Lee WJ, et al. Journal of Raman Spectroscopy 2004;35:928–33. Ni ZH, Fan HM, Feng YP, Shen ZX, Yang BJ, Wu YH. Journal of Physics and Chemistry 2006;124:204703. Wang C, Zhou Y, Ge M, Xu X, Zhang Z, Jiang JZ. Journal of the American Chemical Society 2010;132:46–7. Ji LW, Zhang XW. Nanotechnology 2009;20:155705. Qie L, Chen WM, Wang ZH, Shao QG, Li X, Yuan LX, et al. Advanced Materials 2012;24:2047–50. Xu Y, Guo J, Wang C. Journal of Materials Chemistry 2012;22:9562–7. Song R, Song H, Zhou J, Chen X, Wu B, Yang HY. Journal of Materials Chemistry 2012;22:12369–74.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterisation of sponge-like carbon anode materials for lithium ion batteries Jingjing Tang, Juan Yang, Xiangyang Zhou n School of Metallurgy and Environment, Central South University, Changsha 410083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 9 May 2013 Accepted 26 July 2013 Available online 2 August 2013
Micro-sized carbon material with a unique sponge-like morphology has been fabricated by hydrothermal method coordinating etching process. When evaluate its electrochemical properties in lithium ion batteries, the sponge-like carbon structure exhibits very high specific capacity (around 1175 mAh g 1 after 140th cycle tested at the charge/discharge current density of 200 mA g 1) and wonderful cyclability (about 117% retention is available when cycled back from very high current density of 800 mA g 1) during the galvanostatic cycling, indicating it may be a promising candidate as anode material for Li-ion batteries. & 2013 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Hydrothermal method Structural Electrical properties Lithium ion batteries
1. Introduction In the early 1990s, Sony succeeded in realizing the commercial application of the first rechargeable Lithium ion cell based on a carbon anode (petroleum coke) and a LiCoO2 cathode [1]. Since then, lithium ion batteries have been identified as one of the most important and the greenest type of rechargeable batteries. At present, graphitic carbon anodes are often employed in lithium ion batteries which can avoid the problem of Li dendrite formation by the reversible intercalation of Li into the carbon host lattice and guarantee good cyclability and safety [2]. However, the limited theoretical capacity of 372 mAh g 1 drives extensive research focusing on developing alternative anode materials to realize a high specific capacity and good cycling ability. Among them, hard carbons are found promising due to their appealing properties, such as higher specific capacity and long durability [3,4]. In this paper, sponge-like carbon (SPC) anode material has been prepared via template synthesis process. When employed as anode material for lithium ion batteries, the SPC anode material shows high discharge capacity and good cyclic performance.
2. Experimental Material preparation and characterization: First, 2 g of Co (NO3)2 6H2O was dissolved into 100 ml of continuously stirred isopropyl alcohol–water (1:1, v/v) solution at room temperature. n
Corresponding author. Tel./fax: +86 731 8883 6329. E-mail address: [email protected] (X. Zhou).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.07.100
2 ml of ammonia solution (NH3 H2O, 25 wt%) was subsequently added drop by drop at a time interval of 2 h under vigorous stirring. The reaction was allowed to proceed for a further 12 h and the resulting Co3O4 powder was collected and washed with water. Then, silica coating process was carried out to synthesis Co3O4/ SiO2 composites as previously reported [5]. 0.85 g of as-prepared Co3O4/SiO2 products, 4.2 g glucose, 0.28 g polyvinylpyrrolidone (PVP) were dissolved in 220 ml deionized water under stirring and then ultrasonicated for 0.5 h. The mixture was heated at 180 1C for 6 h in a sealed Teflon-lined autoclave. The dark brown products were collected by suction filtration with absolute ethyl alcohol and deionized water, and dried at 80 1C. The assynthesized samples were further annealed in Ar atmosphere at 900 1C for 2 h. After been immersed in dilute hydrofluoric acid for 3 h, SPC powder was finally obtained after filtering, washing and drying. For comparison, hollow carbon spheres (HCS) were synthesized under the same conditions without the addition of Co3O4. Material characterization: The morphologies of the materials were observed by field emission scanning electron microscopy (NOVA NANO SEM230) and field emission transmission electron microscopy (FETEM, JEM-2100 F). Chemical analysis was performance using an EDAX system interfaced to the FETEM. Structure characterizations were performed by X-ray diffraction (XRD, Rigaku-TTRIII, Cu Kα) at a scanning rate of 10 deg min 1 and Raman spectroscopy (LabRAM Hr800). Electrochemical measurement: The working electrodes were prepared by mixing active material, acetylene black and polyvinylidene at a weight ratio of 8:1:1 and pasted on pure copper foil. Standard 2025 coin cell was assembled in an ultra pure argon filled glove box for electrochemical tests by employing a lithium foil as the counter electrode and 1 M LiPF 6 in ethylene
254
J. Tang et al. / Materials Letters 109 (2013) 253–256
carbonate/dimethyl carbonate (1:1) as the electrolyte. Galvanostatic charging/discharging was performed on LAND CT2001 A in the potential range of 0.01–3.2 V versus Li/Li + at a current density of 200 mA g 1 .
3. Results and discussion The crystallinity of carbon materials can be determined by XRD and Raman spectroscopy. Fig. 1a shows the XRD patterns
of SPC and HCS. The characteristic (002) (20–301) and (100) (40–451) peaks of graphite are discernible in both carbon materials, which indicates the amorphous nature of obtained materials. Compared with HCS, SPC exhibits a stronger (002) peak, demonstrating the well-stacked graphene layers in the sample [6]. The d 002 of SPC and HCS is about 0.37 nm and 0.38 nm, respectively. The larger interlayer spacing compared with pure graphite carbon (about 0.33 nm) is thought to be favorable for lithium insertion and extraction, retaining the structural stability of an electrode during cycles [7]. It is
Fig. 1. (a) XRD patterns and (b) Raman spectra of samples. Insert is the EDS of SPC.
Fig. 2. (a) SEM and (b–d) TEM images of SPC, (e) SEM and (f) TEM images of HCS.
J. Tang et al. / Materials Letters 109 (2013) 253–256
demonstrated from the EDS spectrum that there is no existence of Co or Si in the final SPC sample. More convincing evidence of the carbon materials is provided by Raman spectra (Fig. 1b). Both SPC and HCS exhibit two peaks at approximately 1355 and 1578 cm 1, which are usually denoted as D band and G band, respectively. The D band can be explained as structure defects and disorder-induced features of carbon, while the G band corresponds to the stretching vibration mode of graphite crystals. The former mode is forbidden in perfect graphite and only becomes active in the presence of disorder [8]. The peak integrated intensity ratio of the D band to the G band (ID/IG) for SPC and HCS are estimated to be 1.26 and 2.23, disclosing that there are more disorder defective carbons with HCS. Besides, in the region of the higher-order Raman spectrum for SPC, three distinct peaks located at 2690, 2934 and 3220 cm 1 are typical character of highly ordered pyrolytic graphite (HOPG) [9]. Fig. 2 depicts representative SEM and TEM images of samples. From Fig. 2a, it can be seen that SPC sample takes on an irregular shape and the surface is uneven. TEM image as shown in Fig. 2b demonstrates that the obtained sample is porous and exhibits a sponge-like feature, which is similar to the previous report in SnO2 nanoarchitecture [10]. Selected area electron diffraction (SAED) image proves the amorphous nature of SPC, which is in good agreement with XRD. At higher magnification, as shown in Fig. 2c and d, graphitic layers can be seen on the edge of SPC. It is speculated that the existence of cobalt oxide is responsible for the unique sponge-like structure and the higher degree of order. Without the addition of Co3O4, the obtained carbon sample consists of well-dispersed hollow spheres ranged between 200 and 400 nm. Further research is being carried out to confirm the exact formation mechanism of SPC. Fig. 3a shows the first charge/discharge curves of as-prepared SPC and HCS. The curve shape of the two samples in the first discharge process is similar. When Li+ inserts into the anode in the first charge, there are two sloping voltage ranges ( 40.8 V and o0.8 V) that can be detected. The first slope is attributed to the decomposition of the electrolyte and the formation of solid electrolyte interface (SEI) film, while the second corresponds to
255
the insertion of Li+ into the porous of materials [11]. It is also apparent that both SPC and HCS have a large Li+ storage capacity. The charge capacity of SPC and HCS is about 2066 and 873 mAh g 1, respectively. The reductive decomposition of electrolyte and the subsequent formation of SEI are responsible for the low initial Coulombic efficiency. Fig. 3b and c show the cycling performances of SPC and HCS anodes. The results demonstrate that SPC anode delivers good cycle stability and large reversible capacity, which is always larger than that of HCS anodes. Due to the unique structure of SPC, the discharge capacity increased to 1175 mAh g 1 after 140th cycle. A similar capacity increasing phenomenon during cycling has also been reported [12,13]. Attractively, SPC anode possesses high specific capacity and cycle stability under high rate charge/discharge processes as shown in Fig. 3d. At the current density of 50 mA g 1, the initial discharge capacity reaches up to 870 mAh g 1. Its specific discharge capacity decreases tardily along with the cycle number and remains 743 mAh g 1 after 10 cycles. When the current density increases to 800 mA g 1 and after 10 cycles, there is a discharge capacity of 405 mAh g 1. A capacity of 800 mAh g 1 was obtained when the current density was returned to 50 mA g 1 after charge/ discharge at a high current density, suggesting the high structural and cyclic stabilities of SPC anode. This rate performance is comparable with the previous reports about hierarchical porous carbon [14]. In the case of HCS, the reversible capacity at 50 and 800 mA g 1 are about 387 and 230 mAh g 1, respectively, which is much lower than that of SPC. However, the reversible capacity retention is almost 100%, indicating an acceptable rate performance, although it is weaker than SPC.
4. Conclusions SPC was synthesized using cobalt oxide and silica as templates. SEM and TEM images demonstrated that the obtained carbon material manifested complex pore structure. The electrochemical tests revealed that SPC anode possessed high reversible capacity,
Fig. 3. Electrochemical performances of SPC and HCS. (a) The first charge/discharge curves of SPC, cycling performances of (b) SPC and (c) HCS, (d) rate capability of SPC and HCS.
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J. Tang et al. / Materials Letters 109 (2013) 253–256
good cycling performance and satisfied rate capability. However, the common disadvantage of hard carbon, such as high first irreversible capacity, needs to be settled by optimizing the condition of material preparation. Acknowledgments
[2] [3] [4] [5] [6] [7] [8] [9]
The research was financially supported by the National Natural Science Foundation of China (51274240, 51204209) and the Hunan Provincial Innovation Foundation for Postgraduate.
[10]
References
[13] [14]
[1] Kraytsberg A, Ein-Eli Y. Advanced Energy Materials 2012;2:922–39.
[11] [12]
Wu YP, Rahm E, Holze R. Journal of Power Sources 2003;114:228–36. Zheng H, Qu Q, Zhang L, Liu G, Battaglia VS. RSC Advances 2012;2:4904–12. Ni J, Huang Y, Gao L. Journal of Power Sources 2013;223:306–11. Zhou X, Tang J, Yang J, Xie J, Ma L. Electrochimica Acta 2013;87:663–8. Fey GTK, Kao YC. Materials Chemistry and Physics 2002;73:37–46. Yi Z, Liang X, Lei X, Wang C, Sun J. Materials Letters 2007;61:4199–203. Kim C, Park SH, Cho JI, Lee DY, Park TJ, Lee WJ, et al. Journal of Raman Spectroscopy 2004;35:928–33. Ni ZH, Fan HM, Feng YP, Shen ZX, Yang BJ, Wu YH. Journal of Physics and Chemistry 2006;124:204703. Wang C, Zhou Y, Ge M, Xu X, Zhang Z, Jiang JZ. Journal of the American Chemical Society 2010;132:46–7. Ji LW, Zhang XW. Nanotechnology 2009;20:155705. Qie L, Chen WM, Wang ZH, Shao QG, Li X, Yuan LX, et al. Advanced Materials 2012;24:2047–50. Xu Y, Guo J, Wang C. Journal of Materials Chemistry 2012;22:9562–7. Song R, Song H, Zhou J, Chen X, Wu B, Yang HY. Journal of Materials Chemistry 2012;22:12369–74.