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A novel amorphous Fe2V4O13 as cathode material for lithium secondary batteries
Materials Letters 72 (2012) 145–147
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A novel amorphous Fe2V4O13 as cathode material for lithium secondary batteries Yuchang Si a, b, Lei Zhao a, Zhongbao Yu a,⁎, Weikun Wang a, Jingyi Qiu a, Yusheng Yang a Research Institute of Chemical Defence, Beijing, 100083, PR China Logistics College of Chinese Armed Police Forces, Tianjin, 300162, PR China
a r t i c l e
i n f o
Article history: Received 14 September 2011 Accepted 27 December 2011 Available online 2 January 2012 Keywords: Amorphous materials Energy storage and conversion Fe2V4O13 Cathode material Lithium secondary batteries
a b s t r a c t Amorphous Fe2V4O13 has been synthesized by the liquid precipitation method. The compound showed nanolamellar structure with the average thickness of layer was about 40 nm, which leads to an enhanced lithium ion transport and sustained volume variations. The initial specific capacity is 235 mAh/g, and the specific capacity still remained 201 mAh g− 1 after 40 cycles at the rate of 0.25 C in the range of 2.0–4.0 V, which only brought about an 14% reduction of the capacity. The results show that the amorphous nanostructured Fe2V4O13 is a novel promising cathode material due to its high specific capacity, power density and good cycle performance. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Li-ion batteries represent the promising power sources for advanced electric vehicles and portable electronic devices because of their advantages in energy density and cyclability [1]. The conventional commercialized cathode materials of Li-ion batteries are focused on layered compounds LixMO2 and spinel compounds LixM2O4 (M = Co, Ni, et al.) [2–4]. However, they are obtained from limited mineral resources and synthesized by high temperature reactions. So new generation of cathode materials as alternatives to the presently commercialized electrodes are now being researched. In this field, several vanadium oxides [5–9] have attracted special attention as electrode materials for rechargeable lithium batteries because of low price, open structure and the high specific capacity. Though the LiV3O8 [10] and V2O5 [11] cathode materials have high specific capacity, the bad cyclability and more than one discharge plateaus limit their application. Denis [12] has reported the electrochemical properties of amorphous and crystalline FeVO4 as the anode materials. Either amorphous or crystallized FeVO4 displayed reversible capacities of 900 mAh/g, however, they both showed poor capacity retention. Despite the large initial irreversible capacity, amorphous phase showed better capacity retention than triclinic FeVO4. Richardson [13] used crystallized Fe2V4O13 as the cathode material, the initial specific capacity reached 205 mAh/g at 0.1 C rate. In this paper, amorphous nano-lamellar Fe2V4O13 was successfully synthesized by the liquid precipitation method and investigated firstly as lithium insertion compound, which showed the good electrochemical stability and capacity retention. Here, we discussed the
lithium insertion mechanism of iron(III)-vanadium(V) complex oxides in the range from 4.0 to 2.0 V vs. Li +/Li, in which vanadium was electrochemically active, while iron was totally inactive. 2. Experimental procedure 2.1. Synthesis of the samples The Fe2V4O13 particles were synthesized by liquid precipitation method using Fe(NO3)·H2O and NH4VO3 as the starting materials which were dissolved in distilled water respectively. NH4VO3 solution was slowly added to the Fe(NO3)·H2O solution in molar ratios of Fe:V=1:2. The dark red mixture was stirred for 3 h in the ultrasonic instrument. After that, the precipitate was separated by the centrifugation, washed with
1.2 100 1.0
717.8oC
0.8 96 0.6 0.4 92 0.2 0.0 88 0
325.9oC 200
400
-0.2 600
800
Temperature (oC) ⁎ Corresponding author. Tel./fax: + 86 10 66704313. E-mail addresses: [email protected] (Z. Yu), [email protected] (Y. Si). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.12.104
Fig. 1. TG and DTA curves of the precursor.
DTA /(uV/mg)
b
TG (%)
a
146
Y. Si et al. / Materials Letters 72 (2012) 145–147
(b)
(a)
(c)
Intensity (a.u.)
JCPDS 39-893
0
10
20
30
40
50
60
2 theta/degrees Fig. 2. (a) XRD patterns of Fe2V4O13 annealed at 300 °C, 400 °C and standard pattern of crystallized Fe2V4O13(JCPDS 39-893), (b) SEM of Fe2V4O13 annealed at 300 °C, (c) SEM of Fe2V4O13 annealed at 400 °C.
distilled water and ethanol thoroughly, then dried at 50 °C in the overnight. The precursor precipitate was finally calcined at 300 °C and 400 °C for 36 h to get the Fe2V4O13 samples.
2.2. Instruments XRD pattern was recorded on a Rigaku diffractometer using Cu Kα radiation in 2θ range of 10 to 80°. Thermal stability was analysed by TG-DTA experiments using a NETZSCH STA 449 °C apparatus at the heating rate of 5 °C/min under air atmosphere. The morphology of samples was characterized by SEM performed on a FEI HITACHI 4800 microscope operated at 20 kV. The galvanostatic charge/ discharge tests were performed to evaluate the electrochemical capacity and cycle life of electrodes at room temperature under a LAND-BTI-10 instrument. The cutoff potentials for charge and discharge are set at 4.0 and 2.0 V vs. Li +/Li, respectively. The cyclic voltammetry (CV) (scan rate: 0.1 mV·s − 1) was conducted with a Solartron 1280Z electrochemical workstation.
2.3. Electrochemical studies The synthesized Fe2V4O13 powder was mixed homogeneously with 15% acetylene black and 5 wt.% PVDF dissolved in N-Methyl-2Pyrrolidone. The mixtures were ground together in the planetary ball mill for 6 h with excessive NMP at a rate of 500 r/min. The lithium sheet was acted as the counter electrode and the electrolyte was 1 M LiPF6 dissolved in a 1:1 (volume ratio) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The cell was assembled in an argon gas glove box. The charging and discharging voltage was from 2.0 V to 4.0 V at 0.25 C rate.
3. Results and discussion 3.1. Thermal stability of the precursor Fe2V4O13 Fig. 1 showed the TG-DTA curves of the precursor under nitrogen atmosphere which displayed the formation temperature of amorphous and crystallized Fe2V4O13 powders. Two distinct thermal phenomena appeared on the DTA curve. An endothermic peak at 325.9 °C was attributed to a transformation of the amorphous phase and the crystallization of the compound. A strong exothermic peak appeared around 717.8 °C, which ascribed to the decomposition of compound. 3.2. The XRD and morphology of the samples Fig. 2(a) presented the XRD pattern of Fe2V4O13 annealed at different temperature. The compound obtained at 300 °C is amorphous. The compound annealed at 400 °C was crystalline and was identified to the crystallized Fe2V4O13 (JCPDS 39-893). As shown in Fig. 2(b) and (c), Fe2V4O13 annealed at 300 °C showed a uniform nano-lamellar structure with the average thickness of layer was about 40 nm, each lamella consist of nanoparticles. However, the structure collapsed and aggregated when it was annealed at 400 °C. It is well known that the electrochemical behavior of cathode materials strongly depends on the crystallinity and morphology. The nano-lamellar Fe2V4O13 obtained at 300 °C which have larger surface area might have good electrochemical performances. 3.3. Electrochemical characteristics of amorphous Fe2V4O13 The cyclic voltammetry(CV) curve of amorphous Fe2V4O13/Li cell in the range of 2.0–4.0 V and 0.02–4.0 V at a rate of 0.1 mV/s was 4
(a)
5 0 -5
0 1st -2 -4 -6 -8
-10 1st, 2nd, 3rd, 4th, 5th
-15
(b)
2
Current (1e-4A)
Current (1e-4A)
10
2.0
2.5
3.0
Potential (V)
-10 3.5
4.0
0
1
2
3
4
5
Potential ( V)
Fig. 3. Cyclic voltammetry of amorphous Fe2V4O13 at different cutoff votages (a) 2.0–4.0 V; (b) 0.02–4.3 V (scan rate = 0.1 mV/s).
Y. Si et al. / Materials Letters 72 (2012) 145–147
Specific capacity (mAh.g-1)
300
147
lower than the experimental capacity, this may result from the attribution of amorphous structure, and more detailed work on discharge/ charge mechanism and high capacity characterization is still going on.
250 200
4. Conclusions
150 100 50 0
0
5
10
15
20
25
30
35
40
Cycle number Fig. 4. The cyclability of amorphous Fe2V4O13 for 40 cycles at cutoff voltage of 2.0–4.0 V and 0.25 C.
shown in Fig. 3, respectively. In Fig. 3(a), there was a pair of redox peaks of amorphous Fe2V4O13 near 2.50 and 2.85 V, which should be associated with redox couple(V 5+/V 4+)[13]. In order to study the discharge mechanism of amorphous Fe2V4O13, we expanded the voltage range of CV (0.02–4.3 V). As shown in Fig. 3(b), the two obvious reduction peaks appeared at 2.30 V and 1.77 V, which were corresponding to the reduction peaks for V 5+/V 4+ and Fe 3+/Fe 2+, respectively. However, there were no oxidation peaks corresponding to oxidation of V 4+ to V 5+ and Fe 2+ to Fe 3+, respectively, indicating the redox is irreversible during the deep discharging. Therefore amorphous Fe2V4O13 might have good cyclability and capability at cutoff voltage of 2.0–4.0 V. The further detailed studies such as XPS, FTIR, ex-XRD at different cutoff voltages are in progress. The galvanostatic charge/discharge cycle performance of the amorphous Fe2V4O13 was illustrated in Fig. 4. At the rate of 0.25 C, the initial specific capacity was 235 mAh/g, after 40 cycles, the specific capacity remained 201 mAh·g − 1with the capacity retention of 86%. However, for the crystallized Fe2V4O13, the theoretical number of e − moles exchanged was proposed to be 4 for the V 5+/V 4+ and the theoretical capacity (mAh/g per e - mole) was 205 mAh/g, which was
In this paper, amorphous Fe2V4O13 was successfully synthesized by the liquid precipitation method. The electrochemical properties of amorphous Fe2V4O13 showed good capacity retention, high specific capacity and power density. To our knowledge, this amorphous material was never reported being used as cathode materials for lithium secondary batteries.
Acknowledgements This study is supported by Natural Science Foundation of China (no.20973200, 20801059) and the Natural Science Fund of Tianjin (no.10JCYBJC08000).
References [1] Zhao L, Wang WK, Wang AB, Yu ZB, Chen S, Yang YS. J Electrochem Soc 2011;158: A991–6. [2] Guo J, Jiao LF, Yuan HT, Wang LQ, Li HX, Zhang M, et al. Electrochim Acta 2006;51: 6275–80. [3] Cho J, Kim Y, Kim MG. J Phys Chem C 2007;111:3192–6. [4] Chen H, Liu L, Li Z, Wei YJ, Meng X, Wang CZ, et al. J Alloys Compd 2010;506: 488–91. [5] Amdouni N, Zarrouk H, Soulette F, Julien CM. J Mater Chem 2003;13:2374–80. [6] Yang T, Xia DG, Wang ZL, Chen Y. Mater Lett 2009;63:5–7. [7] Vuk AS, Orel B, Drazic G. J Solid State Electrochem 2001;5:437–49. [8] Hayasgubara M, Eguchi M, Miura T, Kishi TA. Solid State Ionics 1997;98:119–25. [9] Melghit K, AL-Mungi AS. Mater Sci Eng B 2007;136:177–81. [10] Si YC, Jiao LF, Yuan HT, Li HX, Wang YM. J Alloys Compd 2009;486:400–5. [11] Li HX, Jiao LF, Yuan HT, Zhao M, Zhang M, Wang YM. Mater Lett 2007;61:101–4. [12] Denis S, Baudrin E, Touboul M, Iarascon JM. J Electrochem Soc 1997;144: 4099–109. [13] Patoux S, Richardson TJ. Electrochem Commun 2007;9:485–91.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A novel amorphous Fe2V4O13 as cathode material for lithium secondary batteries Yuchang Si a, b, Lei Zhao a, Zhongbao Yu a,⁎, Weikun Wang a, Jingyi Qiu a, Yusheng Yang a Research Institute of Chemical Defence, Beijing, 100083, PR China Logistics College of Chinese Armed Police Forces, Tianjin, 300162, PR China
a r t i c l e
i n f o
Article history: Received 14 September 2011 Accepted 27 December 2011 Available online 2 January 2012 Keywords: Amorphous materials Energy storage and conversion Fe2V4O13 Cathode material Lithium secondary batteries
a b s t r a c t Amorphous Fe2V4O13 has been synthesized by the liquid precipitation method. The compound showed nanolamellar structure with the average thickness of layer was about 40 nm, which leads to an enhanced lithium ion transport and sustained volume variations. The initial specific capacity is 235 mAh/g, and the specific capacity still remained 201 mAh g− 1 after 40 cycles at the rate of 0.25 C in the range of 2.0–4.0 V, which only brought about an 14% reduction of the capacity. The results show that the amorphous nanostructured Fe2V4O13 is a novel promising cathode material due to its high specific capacity, power density and good cycle performance. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Li-ion batteries represent the promising power sources for advanced electric vehicles and portable electronic devices because of their advantages in energy density and cyclability [1]. The conventional commercialized cathode materials of Li-ion batteries are focused on layered compounds LixMO2 and spinel compounds LixM2O4 (M = Co, Ni, et al.) [2–4]. However, they are obtained from limited mineral resources and synthesized by high temperature reactions. So new generation of cathode materials as alternatives to the presently commercialized electrodes are now being researched. In this field, several vanadium oxides [5–9] have attracted special attention as electrode materials for rechargeable lithium batteries because of low price, open structure and the high specific capacity. Though the LiV3O8 [10] and V2O5 [11] cathode materials have high specific capacity, the bad cyclability and more than one discharge plateaus limit their application. Denis [12] has reported the electrochemical properties of amorphous and crystalline FeVO4 as the anode materials. Either amorphous or crystallized FeVO4 displayed reversible capacities of 900 mAh/g, however, they both showed poor capacity retention. Despite the large initial irreversible capacity, amorphous phase showed better capacity retention than triclinic FeVO4. Richardson [13] used crystallized Fe2V4O13 as the cathode material, the initial specific capacity reached 205 mAh/g at 0.1 C rate. In this paper, amorphous nano-lamellar Fe2V4O13 was successfully synthesized by the liquid precipitation method and investigated firstly as lithium insertion compound, which showed the good electrochemical stability and capacity retention. Here, we discussed the
lithium insertion mechanism of iron(III)-vanadium(V) complex oxides in the range from 4.0 to 2.0 V vs. Li +/Li, in which vanadium was electrochemically active, while iron was totally inactive. 2. Experimental procedure 2.1. Synthesis of the samples The Fe2V4O13 particles were synthesized by liquid precipitation method using Fe(NO3)·H2O and NH4VO3 as the starting materials which were dissolved in distilled water respectively. NH4VO3 solution was slowly added to the Fe(NO3)·H2O solution in molar ratios of Fe:V=1:2. The dark red mixture was stirred for 3 h in the ultrasonic instrument. After that, the precipitate was separated by the centrifugation, washed with
1.2 100 1.0
717.8oC
0.8 96 0.6 0.4 92 0.2 0.0 88 0
325.9oC 200
400
-0.2 600
800
Temperature (oC) ⁎ Corresponding author. Tel./fax: + 86 10 66704313. E-mail addresses: [email protected] (Z. Yu), [email protected] (Y. Si). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.12.104
Fig. 1. TG and DTA curves of the precursor.
DTA /(uV/mg)
b
TG (%)
a
146
Y. Si et al. / Materials Letters 72 (2012) 145–147
(b)
(a)
(c)
Intensity (a.u.)
JCPDS 39-893
0
10
20
30
40
50
60
2 theta/degrees Fig. 2. (a) XRD patterns of Fe2V4O13 annealed at 300 °C, 400 °C and standard pattern of crystallized Fe2V4O13(JCPDS 39-893), (b) SEM of Fe2V4O13 annealed at 300 °C, (c) SEM of Fe2V4O13 annealed at 400 °C.
distilled water and ethanol thoroughly, then dried at 50 °C in the overnight. The precursor precipitate was finally calcined at 300 °C and 400 °C for 36 h to get the Fe2V4O13 samples.
2.2. Instruments XRD pattern was recorded on a Rigaku diffractometer using Cu Kα radiation in 2θ range of 10 to 80°. Thermal stability was analysed by TG-DTA experiments using a NETZSCH STA 449 °C apparatus at the heating rate of 5 °C/min under air atmosphere. The morphology of samples was characterized by SEM performed on a FEI HITACHI 4800 microscope operated at 20 kV. The galvanostatic charge/ discharge tests were performed to evaluate the electrochemical capacity and cycle life of electrodes at room temperature under a LAND-BTI-10 instrument. The cutoff potentials for charge and discharge are set at 4.0 and 2.0 V vs. Li +/Li, respectively. The cyclic voltammetry (CV) (scan rate: 0.1 mV·s − 1) was conducted with a Solartron 1280Z electrochemical workstation.
2.3. Electrochemical studies The synthesized Fe2V4O13 powder was mixed homogeneously with 15% acetylene black and 5 wt.% PVDF dissolved in N-Methyl-2Pyrrolidone. The mixtures were ground together in the planetary ball mill for 6 h with excessive NMP at a rate of 500 r/min. The lithium sheet was acted as the counter electrode and the electrolyte was 1 M LiPF6 dissolved in a 1:1 (volume ratio) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The cell was assembled in an argon gas glove box. The charging and discharging voltage was from 2.0 V to 4.0 V at 0.25 C rate.
3. Results and discussion 3.1. Thermal stability of the precursor Fe2V4O13 Fig. 1 showed the TG-DTA curves of the precursor under nitrogen atmosphere which displayed the formation temperature of amorphous and crystallized Fe2V4O13 powders. Two distinct thermal phenomena appeared on the DTA curve. An endothermic peak at 325.9 °C was attributed to a transformation of the amorphous phase and the crystallization of the compound. A strong exothermic peak appeared around 717.8 °C, which ascribed to the decomposition of compound. 3.2. The XRD and morphology of the samples Fig. 2(a) presented the XRD pattern of Fe2V4O13 annealed at different temperature. The compound obtained at 300 °C is amorphous. The compound annealed at 400 °C was crystalline and was identified to the crystallized Fe2V4O13 (JCPDS 39-893). As shown in Fig. 2(b) and (c), Fe2V4O13 annealed at 300 °C showed a uniform nano-lamellar structure with the average thickness of layer was about 40 nm, each lamella consist of nanoparticles. However, the structure collapsed and aggregated when it was annealed at 400 °C. It is well known that the electrochemical behavior of cathode materials strongly depends on the crystallinity and morphology. The nano-lamellar Fe2V4O13 obtained at 300 °C which have larger surface area might have good electrochemical performances. 3.3. Electrochemical characteristics of amorphous Fe2V4O13 The cyclic voltammetry(CV) curve of amorphous Fe2V4O13/Li cell in the range of 2.0–4.0 V and 0.02–4.0 V at a rate of 0.1 mV/s was 4
(a)
5 0 -5
0 1st -2 -4 -6 -8
-10 1st, 2nd, 3rd, 4th, 5th
-15
(b)
2
Current (1e-4A)
Current (1e-4A)
10
2.0
2.5
3.0
Potential (V)
-10 3.5
4.0
0
1
2
3
4
5
Potential ( V)
Fig. 3. Cyclic voltammetry of amorphous Fe2V4O13 at different cutoff votages (a) 2.0–4.0 V; (b) 0.02–4.3 V (scan rate = 0.1 mV/s).
Y. Si et al. / Materials Letters 72 (2012) 145–147
Specific capacity (mAh.g-1)
300
147
lower than the experimental capacity, this may result from the attribution of amorphous structure, and more detailed work on discharge/ charge mechanism and high capacity characterization is still going on.
250 200
4. Conclusions
150 100 50 0
0
5
10
15
20
25
30
35
40
Cycle number Fig. 4. The cyclability of amorphous Fe2V4O13 for 40 cycles at cutoff voltage of 2.0–4.0 V and 0.25 C.
shown in Fig. 3, respectively. In Fig. 3(a), there was a pair of redox peaks of amorphous Fe2V4O13 near 2.50 and 2.85 V, which should be associated with redox couple(V 5+/V 4+)[13]. In order to study the discharge mechanism of amorphous Fe2V4O13, we expanded the voltage range of CV (0.02–4.3 V). As shown in Fig. 3(b), the two obvious reduction peaks appeared at 2.30 V and 1.77 V, which were corresponding to the reduction peaks for V 5+/V 4+ and Fe 3+/Fe 2+, respectively. However, there were no oxidation peaks corresponding to oxidation of V 4+ to V 5+ and Fe 2+ to Fe 3+, respectively, indicating the redox is irreversible during the deep discharging. Therefore amorphous Fe2V4O13 might have good cyclability and capability at cutoff voltage of 2.0–4.0 V. The further detailed studies such as XPS, FTIR, ex-XRD at different cutoff voltages are in progress. The galvanostatic charge/discharge cycle performance of the amorphous Fe2V4O13 was illustrated in Fig. 4. At the rate of 0.25 C, the initial specific capacity was 235 mAh/g, after 40 cycles, the specific capacity remained 201 mAh·g − 1with the capacity retention of 86%. However, for the crystallized Fe2V4O13, the theoretical number of e − moles exchanged was proposed to be 4 for the V 5+/V 4+ and the theoretical capacity (mAh/g per e - mole) was 205 mAh/g, which was
In this paper, amorphous Fe2V4O13 was successfully synthesized by the liquid precipitation method. The electrochemical properties of amorphous Fe2V4O13 showed good capacity retention, high specific capacity and power density. To our knowledge, this amorphous material was never reported being used as cathode materials for lithium secondary batteries.
Acknowledgements This study is supported by Natural Science Foundation of China (no.20973200, 20801059) and the Natural Science Fund of Tianjin (no.10JCYBJC08000).
References [1] Zhao L, Wang WK, Wang AB, Yu ZB, Chen S, Yang YS. J Electrochem Soc 2011;158: A991–6. [2] Guo J, Jiao LF, Yuan HT, Wang LQ, Li HX, Zhang M, et al. Electrochim Acta 2006;51: 6275–80. [3] Cho J, Kim Y, Kim MG. J Phys Chem C 2007;111:3192–6. [4] Chen H, Liu L, Li Z, Wei YJ, Meng X, Wang CZ, et al. J Alloys Compd 2010;506: 488–91. [5] Amdouni N, Zarrouk H, Soulette F, Julien CM. J Mater Chem 2003;13:2374–80. [6] Yang T, Xia DG, Wang ZL, Chen Y. Mater Lett 2009;63:5–7. [7] Vuk AS, Orel B, Drazic G. J Solid State Electrochem 2001;5:437–49. [8] Hayasgubara M, Eguchi M, Miura T, Kishi TA. Solid State Ionics 1997;98:119–25. [9] Melghit K, AL-Mungi AS. Mater Sci Eng B 2007;136:177–81. [10] Si YC, Jiao LF, Yuan HT, Li HX, Wang YM. J Alloys Compd 2009;486:400–5. [11] Li HX, Jiao LF, Yuan HT, Zhao M, Zhang M, Wang YM. Mater Lett 2007;61:101–4. [12] Denis S, Baudrin E, Touboul M, Iarascon JM. J Electrochem Soc 1997;144: 4099–109. [13] Patoux S, Richardson TJ. Electrochem Commun 2007;9:485–91.