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Construction of symmetric aqueous rechargeable battery with high voltage based on NiFe2O4 hollow microspheres
Electrochemistry Communications 40 (2014) 9–12
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
Short communication
Construction of symmetric aqueous rechargeable battery with high voltage based on NiFe2O4 hollow microspheres Jie Shao 1, Xinyong Li 1, Yuanlei Ding, Zhongming Wan, Hongmei Liu, Jiaojiao Yun, Yang Liu, Qunting Qu ⁎, Honghe Zheng ⁎ School of Energy & College of Chemistry, Chemical Engineering and Material Science, Soochow University, Suzhou, Jiangsu 215006, China
a r t i c l e
i n f o
Article history: Received 1 December 2013 Accepted 9 December 2013 Available online 15 December 2013 Keywords: Aqueous Batteries High voltage Nickel ferrite
a b s t r a c t A new symmetric aqueous rechargeable battery was assembled by utilizing NiFe2O4 hollow microspheres as electrode materials. In this device, the cathode and anode use the same material, but undergo respective redox reaction due to the well-separated redox pairs of NiFe2O4. This new battery possesses a high working voltage of 1.3 V and a capacity of 26 mAh g−1 based on the total mass of active materials. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Aqueous rechargeable batteries possess the advantages of highpower output, low-cost, environmental friendliness, and simple technology for cell assembly [1–7]. They are widely used in a variety of fields such as portable electronic devices, transportation, communication, and military. Especially, Pb-acid batteries are the dominant power sources for the electric bicycles in China. Nonetheless, high toxicity of Pb as well as sulfuric acid electrolyte gives rise to serious environmental problems. Exploration of zero-pollution energy storage systems is becoming urgent to continue a sustainable development of our society. Presently, all of the aqueous rechargeable batteries use different electrode materials for the cathode and anode to achieve a high working voltage [4,5,8–11], which results in tedious technology and high-cost of fabrication of two electrode films. Herein, we intended to construct a cheap and high-voltage symmetric rechargeable battery by employing binary transition-metal (bimetal) oxides as electrode materials. The precondition is that the redox potential windows of two transition-metal elements (MnI + 1 /MnI and MnII + 1/MnII ) are well-separated (Fig. 1a). In this way, the cathode and anode will undergo respective redox reaction, and a high voltage and high energy symmetric rechargeable battery may be achieved. To the best of our knowledge, such a symmetric electrode construction for rechargeable batteries has never been reported before. In this work, NiFe2O4 is first selected as the electrode material to assemble such a symmetric rechargeable battery. This is because iron and ⁎ Corresponding authors. Tel.: +86 051267875503. E-mail addresses: [email protected] (Q. Qu), [email protected] (H. Zheng). 1 These authors contribute equally to this work. 1388-2481/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elecom.2013.12.009
nickel oxides have been widely investigated as the anode and cathode materials [12–16], respectively. Primary results show that the wellseparated redox pairs of NiFe2O4 enable the successful assembly of this new symmetric rechargeable battery. Most importantly, it displays a working voltage of 1.3 V and discharge capacity of 26 mAh g−1 based on the total mass of active materials. 2. Experimental NiFe2O4 was prepared through a hydrothermal route followed by calcination. Briefly, 3 g of glucose, 1.25 mmol of Ni(NO3)2 · 6H2O, and 2.5 mmol of Fe(NO3)3 · 9H2O were dissolved in 30 ml of water, and then the mixture solution was transferred into a 50 ml hydrothermal autoclave and heated at 190 °C for 6 h. The resulted precipitants were collected by centrifuge and repeatedly washed with distilled water. At last, the intermediate products were dried at 60 °C for 5 h and then calcined at 500 °C for 4 h. X-ray diffraction (XRD) patterns were collected using a Rigaku D/MAX-IIA X-ray diffractometer with Cu Kα radiation. Scanning electron microscopy (SEM) images were obtained by Philip XL30 operated at 25 kV. Transmission electron microscopy (TEM) images were obtained using a JEOL JEM-2010 transmission electron microscope. The specific surface area of the obtained material was measured according to the Brunauer–Emmett–Teller (BET) method using Micromeritics ASAP2020 V4.0 apparatus with liquid nitrogen at 77 K. BET surface area of NiFe2O4 was determined to be 48 m2 g−1. For the electrochemical tests, the working electrodes were prepared by pressing a mushy mixture of NiFe2O4, acetylene black (Shanghai Haohua Chemical and Industrial Co. Ltd.), and poly(tetrafluoroethylene) (PTFE, Sigma Aldrich, 60 wt.% dispersion in H2O) with a weight ratio of
J. Shao et al. / Electrochemistry Communications 40 (2014) 9–12
20
NiFe2O4
(440)
JCPDF No. 10-0325
40
(533)
(422)
(511)
(400)
e e e e e e
(220)
e e e e e e
(311)
b Intensity / a. u.
a
(222)
10
60
80
2-Theta / Degree
c
d
Fig. 1. (a) Configuration and electrochemical mechanism of new symmetric rechargeable battery. (b) XRD pattern of the obtained NiFe2O4 sample. (c) SEM and (d) TEM images of NiFe2O4 microspheres.
8:1:1 onto Ni-grid. The loading of active material on each electrode is about 2 mg cm−2. Cyclic voltammogrammic (CV) behavior of NiFe2O4 electrode was tested in a three-electrode cell, in which Ni-mesh and saturated calomel electrodes (SCE) were used as the counter and reference electrodes, respectively. 1 M KOH aqueous solution was used as electrolyte. The symmetric NiFe2O4 rechargeable battery with a weight ratio of 1/1 for the cathode and anode was assembled using a two-electrode glass-cell. In order to compare the working voltage and capacity of this new symmetric NiFe2O4//NiFe2O4 battery with other aqueous energy storage devices, Activated carbon (AC)//AC symmetric and AC//MnO2 hybrid supercapacitors were also constructed. AC with a specific surface area of about 2800 m2 g− 1 was purchased from Ningde Xinseng Chemical and Industrial Co. Ltd. and used as received without further treatment. MnO2 was prepared through a precipitation method [17], and its BET surface area is 135 m2 g−1. AC and MnO2 electrodes were prepared in the same way as NiFe2O4 electrode. 3. Results and discussion The XRD pattern of the obtained sample (Fig. 1b) corresponds well to the standard diffraction peaks of spinel NiFe2O4 (JCPDF No. 10-0325). SEM image (Fig. 1c) reveals that the as-prepared NiFe2O4 powder is composed of homogeneous microspheres with a diameter ranging from 500 nm to 3 μm. TEM image validates that the interior of these spheres is hollow (Fig. 1d). We think that, glucose can be converted into carbon microspheres during the hydrothermal process [18], while metal ions or the resultant precursors are predominantly situated at the outer surface of carbon spheres owing to the abundant functional groups and highly reactive surfaces of carbon spheres [19,20]. After calcination under air atmosphere, hollow spherical NiFe2O4 can be obtained.
In order to verify our new concept of constructing a high-voltage symmetric rechargeable battery based on bimetal oxides, we first investigated the CV behaviors of NiFe2O4 in the positive and negative potential regions (Fig. 2a). In the positive potential region, a couple of highly reversible redox peaks appear at 0.34 and 0.41 V vs. SCE, agreeing well with the characteristic redox potentials of NiO [15,16] or Ni(OH)2 [13] in KOH aqueous electrolyte. Hence, it is deduced that the redox reaction of NiFe2O4 in the positive potential region is ascribed to the electrochemical conversion of Ni2+/Ni3+. In the negative potential region, there exists another couple of distinct redox peaks centered at −1.07 and −0.95 V, approximating to the redox windows of Fe3+/ Fe2+ pairs [12,14]. Such a wide separation between the redox pairs of NiFe2O4 makes us believe that a high voltage of 1.3 V may be achieved for the symmetric NiFe2O4 battery. CV curves of NiFe2O4 electrode at different scan rates are presented in Fig. 2b. Even at the fast scan rate of 200 mV s−1, the redox peaks of NiFe2O4 are maintained quite well for both the Ni3 +/Ni2+ and Fe3 +/ Fe2+ pairs, demonstrating its excellent high-rate capability. Fig. 2c shows the typical discharge curves of the assembled aqueous devices at the current density of 1 A g− 1. A distinct voltage plateau appears at about 1.3 V for the NiFe2O4//NiFe2O4 symmetric battery. The average discharge voltage (average value of voltage during discharge) is considerably higher than that of commercial AC//AC supercapacitors (0.5 V) and even higher than those of the most intensively studied aqueous hybrid devices including AC//MnO2 and graphene//MnO2 systems (0.9 or 0.7 V) [17,21–24]. Reversible capacity of NiFe2O4//NiFe2O4 battery based on the total mass of active materials is 26 mAh g− 1, comparable to that of AC//MnO2 hybrid device. Since the BET surface area of NiFe2O4 is much lower than those of AC and MnO2, the capacity of NiFe2O4 should mainly result from the faradic redox reaction of Ni 2 + /Ni3 + and Fe3 + /Fe2 + couples
J. Shao et al. / Electrochemistry Communications 40 (2014) 9–12
a
b 2+
2+
3+
15
Current / A g-1
Current / A g-1
Fe /Fe
(-)NiFe2O4 // NiFe2O4(+)
O2
2 0 -2
30
3+
Ni /Ni
4
H2
3+
3+
-1 40 mV s -1 50 mV s -1 75 mV s -1 100mV s -1 200mV s
0
2+
Ni /Ni
-4
-15
2+
Fe /Fe -6 -1.2
-0.8
-0.4
0.0
0.4
-1.2
-0.8
Potential / V vs. SCE
c
11
-0.4
0.0
0.4
Potential / V vs. SCE
d
2.0
Separator
(-)NiFe2O4//NiFe2O4(+) Voltage / V
1.5
Ni2+/Ni3+
1.0
Fe3+/Fe2+
0.5 0.0
(-)AC//AC(+)
(-)AC//MnO2(+)
-0.5 0
5
10
15
20
25
NiFe2O4
30
Capacity / mAh g-1
Fig. 2. (a) CV curves of NiFe2O4 electrode at the scan rate of 20 mV s−1 in the positive and negative potential regions. (b) CV curves of NiFe2O4 electrode at different scan rates. (c) The typical discharge curves of the assembled aqueous devices at the current density of 1 A g−1. (d) Schematic illustration of the symmetric NiFe2O4 rechargeable battery that undergoes respective redox pairs in cathode and anode.
gradually during the initial hundreds of cycles, probably owing to the activation process of NiFe2O4. This battery exhibits good cycling performance with above 96% of capacity maintained after 2000 cycles. The XRD analyses on the NiFe2O4 electrodes after electrochemical cycling (Fig. 3b) suggest that the crystalline structure of NiFe2O4 is very stable for both the cathode and anode.
instead of electrical double layer capacitance. Of course, optimization of charge balance on the positive and negative electrodes may help achieve the highest voltage and capacity of NiFe 2 O4 battery [25,26], which however, will lead to a tedious process for the preparation of two NiFe 2O 4 electrode films with different thickness. A schematic is shown in Fig. 2d to illustrate that, the electrochemical reaction of NiFe 2 O4 cathode is based on Ni2 +/Ni3 + redox pairs, while the anode undergoes the Fe3 +/Fe2 + pairs. The NiFe2O4 rechargeable battery was charge/discharged for extended cycles at the current density of 1 A g−1, and the capacity evolution is shown in Fig. 3a. Discharge capacity of NiFe2O4 battery increases
4. Conclusions In conclusion, a new concept of high-voltage and low-cost symmetric rechargeable battery was realized by utilizing NiFe2 O4 as
a
b 30
Ni
Intensity / a. u.
Capacity / mAh g
-1
After cycling
(-)NiFe2O4//NiFe2O4(+)
20
cycled between 0.5 and 1.6V 10
NiFe2O4 cathode
NiFe2O4 anode 0 0
500
1000
Cycle Number
1500
2000
20
40
60
2-Theta / Degree
Fig. 3. (a) Cycling performance of the NiFe2O4//NiFe2O4 rechargeable battery. (b) XRD patterns of the NiFe2O4 electrodes after electrochemical cycling.
12
J. Shao et al. / Electrochemistry Communications 40 (2014) 9–12
electrode materials. In this construction, the cathode and anode use the same material, but undergo respective redox reaction due to the well-separated redox pairs of NiFe2O4. Fabrication of the same two electrodes leads to a simple preparation technology and low manufacturing cost for practical application. We believe that, other bimetal oxides such as CoFe2 O 4, NiMoO4 , CoMoO 4 , NiMn2 O4 , and CoMn2O4, can also be attempted to construct the new symmetric rechargeable battery considering that the redox couples of these bimetal oxides may be well-separated. Acknowledgments This work was supported by the National Natural Science Foundation of China (NSFC Nos. 21203133, 21301124, and 51272168) and the Natural Science Foundation of Jiangsu Province (BK2012186). References [1] J.-Y. Luo, W.-J. Cui, P. He, Y.-Y. Xia, Nat. Chem. 2 (2010) 760–765. [2] J. Shao, X. Li, L. Zhang, Q. Qu, H. Zheng, Nanoscale 5 (2013) 1460–1464. [3] Q. Qu, L. Fu, X. Zhan, D. Samuelis, J. Maier, L. Li, S. Tian, Z. Li, Y. Wu, Energy Environ. Sci. 4 (2011) 3985–3990. [4] Y. Wang, J. Yi, Y. Xia, Adv. Energy Mater. 2 (2012) 830–840. [5] W. Li, J.R. Dahn, D.S. Wainwright, Science 264 (1994) 1115–1118. [6] C.D. Wessells, R.A. Huggins, Y. Cui, Nat. Commun. 2 (2011) 550.
[7] R. Ruffo, C. Wessells, R.A. Huggins, Y. Cui, Electrochem. Commun. 11 (2009) 247–249. [8] W. Tang, Y. Hou, F. Wang, L. Liu, Y. Wu, K. Zhu, Nano Lett. 13 (2013) 2036–2040. [9] G. Wang, L. Fu, N. Zhao, L. Yang, Y. Wu, H. Wu, Angew. Chem. Int. Ed. 46 (2007) 295–297. [10] J.Y. Luo, Y.Y. Xia, Adv. Funct. Mater. 17 (2007) 3877–3884. [11] Y.P. Wu, B. Zhang, Y. Liu, X. Wu, Y. Yang, Z. Chang, Z. Wen, Chem. Commun. (2013), http://dx.doi.org/10.1039/C3CC48382G. [12] Q. Qu, S. Yang, X. Feng, Adv. Mater. 23 (2011) 5574–5580. [13] Z. Tang, C.-H. Tang, H. Gong, Adv. Funct. Mater. 22 (2012) 1272–1278. [14] L. Wang, H. Ji, S. Wang, L. Kong, X. Jiang, G. Yang, Nanoscale 5 (2013) 3793–3799. [15] J.-H. Kim, S.H. Kang, K. Zhu, J.Y. Kim, N.R. Neale, A.J. Frank, Chem. Commun. 47 (2011) 5214–5216. [16] Q. Lu, M.W. Lattanzi, Y. Chen, X. Kou, W. Li, X. Fan, K.M. Unruh, J.G. Chen, J.Q. Xiao, Angew. Chem. Int. Ed. 50 (2011) 6847–6850. [17] Q. Qu, P. Zhang, B. Wang, Y. Chen, S. Tian, Y. Wu, R. Holze, J. Phys. Chem. C 113 (2009) 14020–14027. [18] J. Wang, N. Yang, H. Tang, Z. Dong, Q. Jin, M. Yang, D. Kisailus, H. Zhao, Z. Tang, D. Wang, Angew. Chem. Int. Ed. 52 (2013) 6417–6420. [19] M.-M. Titirici, M. Antonietti, A. Thomas, Chem. Mater. 18 (2006) 3808–3812. [20] H.B. Wu, A. Pan, H.H. Hng, X.W. Lou, Adv. Funct. Mater. (2013), http://dx.doi.org/ 10.1002/adfm.201300976. [21] A. Sumboja, C.Y. Foo, X. Wang, P.S. Lee, Adv. Mater. 25 (2013) 2809–2815. [22] L.-F. Chen, Z.-H. Huang, H.-W. Liang, Q.-F. Guan, S.-H. Yu, Adv. Mater. 25 (2013) 4746–4752. [23] H. Gao, F. Xiao, C.B. Ching, H. Duan, ACS Appl. Mater. Interfaces 4 (2012) 2801–2810. [24] H. Jiang, C. Li, T. Sun, J. Ma, Nanoscale 4 (2012) 807–812. [25] T.-H. Wu, Y.-H. Chu, C.-C. Hu, L.J. Hardwick, Electrochem. Commun. 27 (2013) 81–84. [26] T.-H. Wu, C.-T. Hsu, C.-C. Hu, L.J. Hardwick, J. Power Sources 242 (2013) 289–298.
Contents lists available at ScienceDirect
Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom
Short communication
Construction of symmetric aqueous rechargeable battery with high voltage based on NiFe2O4 hollow microspheres Jie Shao 1, Xinyong Li 1, Yuanlei Ding, Zhongming Wan, Hongmei Liu, Jiaojiao Yun, Yang Liu, Qunting Qu ⁎, Honghe Zheng ⁎ School of Energy & College of Chemistry, Chemical Engineering and Material Science, Soochow University, Suzhou, Jiangsu 215006, China
a r t i c l e
i n f o
Article history: Received 1 December 2013 Accepted 9 December 2013 Available online 15 December 2013 Keywords: Aqueous Batteries High voltage Nickel ferrite
a b s t r a c t A new symmetric aqueous rechargeable battery was assembled by utilizing NiFe2O4 hollow microspheres as electrode materials. In this device, the cathode and anode use the same material, but undergo respective redox reaction due to the well-separated redox pairs of NiFe2O4. This new battery possesses a high working voltage of 1.3 V and a capacity of 26 mAh g−1 based on the total mass of active materials. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Aqueous rechargeable batteries possess the advantages of highpower output, low-cost, environmental friendliness, and simple technology for cell assembly [1–7]. They are widely used in a variety of fields such as portable electronic devices, transportation, communication, and military. Especially, Pb-acid batteries are the dominant power sources for the electric bicycles in China. Nonetheless, high toxicity of Pb as well as sulfuric acid electrolyte gives rise to serious environmental problems. Exploration of zero-pollution energy storage systems is becoming urgent to continue a sustainable development of our society. Presently, all of the aqueous rechargeable batteries use different electrode materials for the cathode and anode to achieve a high working voltage [4,5,8–11], which results in tedious technology and high-cost of fabrication of two electrode films. Herein, we intended to construct a cheap and high-voltage symmetric rechargeable battery by employing binary transition-metal (bimetal) oxides as electrode materials. The precondition is that the redox potential windows of two transition-metal elements (MnI + 1 /MnI and MnII + 1/MnII ) are well-separated (Fig. 1a). In this way, the cathode and anode will undergo respective redox reaction, and a high voltage and high energy symmetric rechargeable battery may be achieved. To the best of our knowledge, such a symmetric electrode construction for rechargeable batteries has never been reported before. In this work, NiFe2O4 is first selected as the electrode material to assemble such a symmetric rechargeable battery. This is because iron and ⁎ Corresponding authors. Tel.: +86 051267875503. E-mail addresses: [email protected] (Q. Qu), [email protected] (H. Zheng). 1 These authors contribute equally to this work. 1388-2481/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elecom.2013.12.009
nickel oxides have been widely investigated as the anode and cathode materials [12–16], respectively. Primary results show that the wellseparated redox pairs of NiFe2O4 enable the successful assembly of this new symmetric rechargeable battery. Most importantly, it displays a working voltage of 1.3 V and discharge capacity of 26 mAh g−1 based on the total mass of active materials. 2. Experimental NiFe2O4 was prepared through a hydrothermal route followed by calcination. Briefly, 3 g of glucose, 1.25 mmol of Ni(NO3)2 · 6H2O, and 2.5 mmol of Fe(NO3)3 · 9H2O were dissolved in 30 ml of water, and then the mixture solution was transferred into a 50 ml hydrothermal autoclave and heated at 190 °C for 6 h. The resulted precipitants were collected by centrifuge and repeatedly washed with distilled water. At last, the intermediate products were dried at 60 °C for 5 h and then calcined at 500 °C for 4 h. X-ray diffraction (XRD) patterns were collected using a Rigaku D/MAX-IIA X-ray diffractometer with Cu Kα radiation. Scanning electron microscopy (SEM) images were obtained by Philip XL30 operated at 25 kV. Transmission electron microscopy (TEM) images were obtained using a JEOL JEM-2010 transmission electron microscope. The specific surface area of the obtained material was measured according to the Brunauer–Emmett–Teller (BET) method using Micromeritics ASAP2020 V4.0 apparatus with liquid nitrogen at 77 K. BET surface area of NiFe2O4 was determined to be 48 m2 g−1. For the electrochemical tests, the working electrodes were prepared by pressing a mushy mixture of NiFe2O4, acetylene black (Shanghai Haohua Chemical and Industrial Co. Ltd.), and poly(tetrafluoroethylene) (PTFE, Sigma Aldrich, 60 wt.% dispersion in H2O) with a weight ratio of
J. Shao et al. / Electrochemistry Communications 40 (2014) 9–12
20
NiFe2O4
(440)
JCPDF No. 10-0325
40
(533)
(422)
(511)
(400)
e e e e e e
(220)
e e e e e e
(311)
b Intensity / a. u.
a
(222)
10
60
80
2-Theta / Degree
c
d
Fig. 1. (a) Configuration and electrochemical mechanism of new symmetric rechargeable battery. (b) XRD pattern of the obtained NiFe2O4 sample. (c) SEM and (d) TEM images of NiFe2O4 microspheres.
8:1:1 onto Ni-grid. The loading of active material on each electrode is about 2 mg cm−2. Cyclic voltammogrammic (CV) behavior of NiFe2O4 electrode was tested in a three-electrode cell, in which Ni-mesh and saturated calomel electrodes (SCE) were used as the counter and reference electrodes, respectively. 1 M KOH aqueous solution was used as electrolyte. The symmetric NiFe2O4 rechargeable battery with a weight ratio of 1/1 for the cathode and anode was assembled using a two-electrode glass-cell. In order to compare the working voltage and capacity of this new symmetric NiFe2O4//NiFe2O4 battery with other aqueous energy storage devices, Activated carbon (AC)//AC symmetric and AC//MnO2 hybrid supercapacitors were also constructed. AC with a specific surface area of about 2800 m2 g− 1 was purchased from Ningde Xinseng Chemical and Industrial Co. Ltd. and used as received without further treatment. MnO2 was prepared through a precipitation method [17], and its BET surface area is 135 m2 g−1. AC and MnO2 electrodes were prepared in the same way as NiFe2O4 electrode. 3. Results and discussion The XRD pattern of the obtained sample (Fig. 1b) corresponds well to the standard diffraction peaks of spinel NiFe2O4 (JCPDF No. 10-0325). SEM image (Fig. 1c) reveals that the as-prepared NiFe2O4 powder is composed of homogeneous microspheres with a diameter ranging from 500 nm to 3 μm. TEM image validates that the interior of these spheres is hollow (Fig. 1d). We think that, glucose can be converted into carbon microspheres during the hydrothermal process [18], while metal ions or the resultant precursors are predominantly situated at the outer surface of carbon spheres owing to the abundant functional groups and highly reactive surfaces of carbon spheres [19,20]. After calcination under air atmosphere, hollow spherical NiFe2O4 can be obtained.
In order to verify our new concept of constructing a high-voltage symmetric rechargeable battery based on bimetal oxides, we first investigated the CV behaviors of NiFe2O4 in the positive and negative potential regions (Fig. 2a). In the positive potential region, a couple of highly reversible redox peaks appear at 0.34 and 0.41 V vs. SCE, agreeing well with the characteristic redox potentials of NiO [15,16] or Ni(OH)2 [13] in KOH aqueous electrolyte. Hence, it is deduced that the redox reaction of NiFe2O4 in the positive potential region is ascribed to the electrochemical conversion of Ni2+/Ni3+. In the negative potential region, there exists another couple of distinct redox peaks centered at −1.07 and −0.95 V, approximating to the redox windows of Fe3+/ Fe2+ pairs [12,14]. Such a wide separation between the redox pairs of NiFe2O4 makes us believe that a high voltage of 1.3 V may be achieved for the symmetric NiFe2O4 battery. CV curves of NiFe2O4 electrode at different scan rates are presented in Fig. 2b. Even at the fast scan rate of 200 mV s−1, the redox peaks of NiFe2O4 are maintained quite well for both the Ni3 +/Ni2+ and Fe3 +/ Fe2+ pairs, demonstrating its excellent high-rate capability. Fig. 2c shows the typical discharge curves of the assembled aqueous devices at the current density of 1 A g− 1. A distinct voltage plateau appears at about 1.3 V for the NiFe2O4//NiFe2O4 symmetric battery. The average discharge voltage (average value of voltage during discharge) is considerably higher than that of commercial AC//AC supercapacitors (0.5 V) and even higher than those of the most intensively studied aqueous hybrid devices including AC//MnO2 and graphene//MnO2 systems (0.9 or 0.7 V) [17,21–24]. Reversible capacity of NiFe2O4//NiFe2O4 battery based on the total mass of active materials is 26 mAh g− 1, comparable to that of AC//MnO2 hybrid device. Since the BET surface area of NiFe2O4 is much lower than those of AC and MnO2, the capacity of NiFe2O4 should mainly result from the faradic redox reaction of Ni 2 + /Ni3 + and Fe3 + /Fe2 + couples
J. Shao et al. / Electrochemistry Communications 40 (2014) 9–12
a
b 2+
2+
3+
15
Current / A g-1
Current / A g-1
Fe /Fe
(-)NiFe2O4 // NiFe2O4(+)
O2
2 0 -2
30
3+
Ni /Ni
4
H2
3+
3+
-1 40 mV s -1 50 mV s -1 75 mV s -1 100mV s -1 200mV s
0
2+
Ni /Ni
-4
-15
2+
Fe /Fe -6 -1.2
-0.8
-0.4
0.0
0.4
-1.2
-0.8
Potential / V vs. SCE
c
11
-0.4
0.0
0.4
Potential / V vs. SCE
d
2.0
Separator
(-)NiFe2O4//NiFe2O4(+) Voltage / V
1.5
Ni2+/Ni3+
1.0
Fe3+/Fe2+
0.5 0.0
(-)AC//AC(+)
(-)AC//MnO2(+)
-0.5 0
5
10
15
20
25
NiFe2O4
30
Capacity / mAh g-1
Fig. 2. (a) CV curves of NiFe2O4 electrode at the scan rate of 20 mV s−1 in the positive and negative potential regions. (b) CV curves of NiFe2O4 electrode at different scan rates. (c) The typical discharge curves of the assembled aqueous devices at the current density of 1 A g−1. (d) Schematic illustration of the symmetric NiFe2O4 rechargeable battery that undergoes respective redox pairs in cathode and anode.
gradually during the initial hundreds of cycles, probably owing to the activation process of NiFe2O4. This battery exhibits good cycling performance with above 96% of capacity maintained after 2000 cycles. The XRD analyses on the NiFe2O4 electrodes after electrochemical cycling (Fig. 3b) suggest that the crystalline structure of NiFe2O4 is very stable for both the cathode and anode.
instead of electrical double layer capacitance. Of course, optimization of charge balance on the positive and negative electrodes may help achieve the highest voltage and capacity of NiFe 2 O4 battery [25,26], which however, will lead to a tedious process for the preparation of two NiFe 2O 4 electrode films with different thickness. A schematic is shown in Fig. 2d to illustrate that, the electrochemical reaction of NiFe 2 O4 cathode is based on Ni2 +/Ni3 + redox pairs, while the anode undergoes the Fe3 +/Fe2 + pairs. The NiFe2O4 rechargeable battery was charge/discharged for extended cycles at the current density of 1 A g−1, and the capacity evolution is shown in Fig. 3a. Discharge capacity of NiFe2O4 battery increases
4. Conclusions In conclusion, a new concept of high-voltage and low-cost symmetric rechargeable battery was realized by utilizing NiFe2 O4 as
a
b 30
Ni
Intensity / a. u.
Capacity / mAh g
-1
After cycling
(-)NiFe2O4//NiFe2O4(+)
20
cycled between 0.5 and 1.6V 10
NiFe2O4 cathode
NiFe2O4 anode 0 0
500
1000
Cycle Number
1500
2000
20
40
60
2-Theta / Degree
Fig. 3. (a) Cycling performance of the NiFe2O4//NiFe2O4 rechargeable battery. (b) XRD patterns of the NiFe2O4 electrodes after electrochemical cycling.
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electrode materials. In this construction, the cathode and anode use the same material, but undergo respective redox reaction due to the well-separated redox pairs of NiFe2O4. Fabrication of the same two electrodes leads to a simple preparation technology and low manufacturing cost for practical application. We believe that, other bimetal oxides such as CoFe2 O 4, NiMoO4 , CoMoO 4 , NiMn2 O4 , and CoMn2O4, can also be attempted to construct the new symmetric rechargeable battery considering that the redox couples of these bimetal oxides may be well-separated. Acknowledgments This work was supported by the National Natural Science Foundation of China (NSFC Nos. 21203133, 21301124, and 51272168) and the Natural Science Foundation of Jiangsu Province (BK2012186). References [1] J.-Y. Luo, W.-J. Cui, P. He, Y.-Y. Xia, Nat. Chem. 2 (2010) 760–765. [2] J. Shao, X. Li, L. Zhang, Q. Qu, H. Zheng, Nanoscale 5 (2013) 1460–1464. [3] Q. Qu, L. Fu, X. Zhan, D. Samuelis, J. Maier, L. Li, S. Tian, Z. Li, Y. Wu, Energy Environ. Sci. 4 (2011) 3985–3990. [4] Y. Wang, J. Yi, Y. Xia, Adv. Energy Mater. 2 (2012) 830–840. [5] W. Li, J.R. Dahn, D.S. Wainwright, Science 264 (1994) 1115–1118. [6] C.D. Wessells, R.A. Huggins, Y. Cui, Nat. Commun. 2 (2011) 550.
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