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Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries
Journal of Alloys and Compounds 470 (2009) 75–79
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Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Mn3 O4 doped with nano-NaBiO3 : A high capacity cathode material for alkaline secondary batteries Junqing Pan a,b , Yanzhi Sun a , Zihao Wang b , Pingyu Wan a,∗ , Maohong Fan c,∗ a
College of Science, Beijing University of Chemical Technology, Beijing 100029, China College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China c School of Materials Science and Engineering, Georgia Institute of Technology, GA 40332, USA b
a r t i c l e
i n f o
Article history: Received 11 December 2007 Received in revised form 5 February 2008 Accepted 9 February 2008 Available online 3 June 2008 Keywords: Electrode materials X-ray diffraction Electrochemical reactions
a b s t r a c t In this paper we report a novel Mn3 O4 electrode doped with nano-NaBiO3 . It is demonstrated that doping with nano-NaBiO3 alters the electrochemical inertia of Mn3 O4 , converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn3 O4 electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn3 O4 electrode doped with nano-NaBiO3 can reach and become stable at 372 mAh g−1 under 60 mA g−1 . The doped cathode can also maintain a cycling capacity of 261 mAh g−1 while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g−1 . Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn3 O4 cathode could possibly shorten to as little as 30 min. © 2008 Published by Elsevier B.V.
1. Introduction Nanophase materials feature high surface energy and reactivity resulting from their high specific surfaces. They also demonstrate special electric, magnetic, absorptive, and catalytic properties in many reactions [1–5]. Besides the significant research directed towards new applications for nanophase materials, investigators are reexamining existing applications as well as the widespread use in many fields of nanophase materials to dope other materials for enhanced performance [6,7]. It has been more than 140 years since French scientist Georges Leclanche´ invented the manganese dioxide (MnO2 ) battery in 1865. Since then, the MnO2 battery has continuously been improved, starting with the earliest zinc-manganese dry battery, followed by the high-performance zinc-manganese battery, and up to today’s mercury-free zinc alkaline manganese battery. Because of the maturity of its technology, reliable performance, and competitive price, the MnO2 battery has seen widespread use, with global sales of approximately 60 billion units annually [8,9]. The primary cathode material for zinc-manganese batteries, MnO2 , has various polymorphs, including ␣, , ␥ and ␦ structures. Of these, the superior discharge performance of ␥-MnO2 with more than 92% purity has made it the active material of choice for the cathode of alkaline
∗ Corresponding authors. Tel.: +86 10 64445917; fax: +86 10 64445917. E-mail addresses: [email protected] (P. Wan), [email protected] (M. Fan). 0925-8388/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.jallcom.2008.02.075
MnO2 batteries. Moreover, the elimination of mercury has considerably reduced environmental pollution from alkaline manganese batteries. However, because of the sheer volume of their use worldwide, production of these batteries still results in a serious waste of manganese resources. As for alkaline manganese batteries with zinc anodes, the enhanced electrochemical performance of MnO2 has opened the bottleneck to improve MnO2 battery performance. Moreover, methods for improving MnO2 discharge performance to make these batteries rechargeable may represent an effective approach to conserving manganese resources. Various studies have indicated that doping with bismuth dioxide, lead dioxide, titanium dioxide, and other relevant additives significantly improves discharge performance for MnO2 electrodes, yet without greatly improving their recharge capacity [10–23]. A recent study indicated that a MnO2 electrode doped with bismuth dioxide could be recharged over tens of cycles. Also, further studies have suggested that the reason for the continuous decay in performance of MnO2 electrodes in the charge/discharge cycle is due to the unavoidable formation of Mn3 O4 , an electrochemically inert substance having a sharp crystalline structure different from MnO2 structures in the cycle process [24–26]. Because Mn3 O4 formed upon discharge and deoxidization cannot oxidize into highly valued MnO2 during the charge process, this results in the gradual reduction of MnO2 in the electrode. Therefore, besides avoiding the formation of Mn3 O4 entirely, developing methods for making it act as a charging and cycling substance is critical for making rechargeable alkaline manganese batteries.
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In this paper, following our previous studies on alkaline cathode of high capacity [27,28], we report a novel Mn3 O4 electrode doped with nano-NaBiO3 that offers a high specific capacity of 376 mAh g−1 (at 60 mA g−1 ) and 261 mAh g−1 (at 500 mA g−1 ), as well as a stable reversible capacity over a range of 0.5–1.75 V in 60 charge/discharge cycles. Moreover, the ability of the electrode to accept high charging levels results in a recharge time of only 30 min. 2. Experimental The nano-NaBiO3 was synthesized in a NaOH–NaClO solution as previously reported [10,29]. 0.005 mol of self-prepared NaBiO3 was ground in an agate mortar and added to 2.5 mL of water, followed by ultrasonic dispersion for 15 min. Then, 0.1 mol of Mn3 O4 (Shanghai Regent Plant) was added, followed by ultrasonic dispersion for 30 min. The resulting suspension liquid was moved into an autoclave lined with PTFE, followed by vacuum drying at 373 K for 3 h and at 323 K for 24 h. The resulting solid yellow powder served as the electrode material of Mn3 O4 doped with nano-NaBiO3 (NB–Mn3 O4 ). The phase structures of the prepared samples were analyzed using a Rigaku D/max2500VB2 + /PCX X-ray diffractometer (XRD) with a Cu anticathode. The morphology of samples was examined using a field-emission scanning electron microscope (FESEM). The element analysis was performed using energy-dispersive X-ray spectroscopy (EDS). 80% (wt.) NB–Mn3 O4 sample, 15% (wt.) expansive graphite, and 5% PTFE binder were mixed and pressed on foam nickel to form a NB–Mn3 O4 working electrode. 40% KOH (including 10 g L−1 ZnO) was used as an electrolyte, Ni wire as an auxiliary electrode, and Zn(Hg)/ZnO as a reference electrode. The charge/discharge test was
carried out with a LAND CT2001A cell test instrument, and the cyclic voltammetry measurement was performed using an EG&G Princeton Applied Research 273 potentiostat controlled by M270 electrochemistry software.
3. Results and discussion The FESEM images of Mn3 O4 and the prepared NB–Mn3 O4 are shown in Fig. 1. Fig. 1a reveals that the commercial Mn3 O4 is composed of irregular particles with actual grain sizes of 30–50 m. After hydrothermal treatment and doping of Mn3 O4 with NaBiO3 , we found that the surface of the resulting NB–Mn3 O4 was covered with a layer of fine crystal (Fig. 1b). The EDS analysis was performed in order to determine whether the sample was doped with Bi and Na elements. Fig. 2 represents the EDS analysis diagrams of the Mn3 O4 and NB–Mn3 O4 samples, respectively. It can be seen that only Mn and O elements appear in the Mn3 O4 sample in Fig. 2a. By contrast, Fig. 2b shows that Mn, O, Bi, and Na elements appear simultaneously in the NB–Mn3 O4 sample, which indicates that the Mn3 O4 is evenly doped with NaBiO3 . Fig. 3 shows the XRD plots of NB, Mn3 O4 , and NB–Mn3 O4 samples. Because the NB–Mn3 O4 largely reveals the diffraction peak of Mn3 O4 and no typical diffraction peak of NB, we deduced that this part of nano-NB had been mixed into the crystal lattice of Mn3 O4 . The new diffraction peaks at 23.5 and 56.2◦ might result from the composite peaks of nano-NB and Mn3 O4 . In other words, NaBiO3
Fig. 1. The FSEM pictures of Mn3 O4 (a1, a2) and NB–Mn3 O4 (b1, b2) samples.
J. Pan et al. / Journal of Alloys and Compounds 470 (2009) 75–79
Fig. 2. The EDS analysis diagrams of Mn3 O4 (a) and NB–Mn3 O4 (b) samples.
promotes the birnessite formation reaction independent of the prevention of Mn3 O4 formation [30,31]. Simultaneously, the new diffraction peaks at 28.3 and 30.1◦ corresponding to Bi2 O3 , which might be the redox resultant from a small quantity of Bi(V) and Mn3 O4 could be observed. In addition, NaBiO3 has a certain extent of solubility, which keeps the balance between dissolution and precipitation, and Mn3 O4 itself has potential ion exchange property. Consequently, NaBiO3 is evenly dispersed in Mn3 O4 crystal and its surface. That changes the original electrochemical inertia of Mn3 O4 and activates its potential electrochemical property.
Fig. 3. The X-ray powder patterns of NB, NB–Mn3 O4 and Mn3 O4 samples.
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Fig. 4. Discharge curves of Mn3 O4 (A) and NB–Mn3 O4 (B) electrodes at 60 mA g−1 .
The pure Mn3 O4 electrode and the NB–Mn3 O4 electrode were subjected to galvanostatic charge/discharge cycles at 60 mA g−1 over a potential range of 0.50–1.75 V, respectively. Fig. 4 represents the charge/discharge curves of both electrodes. It can be seen that a pure Mn3 O4 electrode provides a capacity of only 7–11 mAh g−1 , which also decays along with increased cycling and presents almost no reversibility. By contrast, the NB–Mn3 O4 electrode provides an initial capacity of 215 mAh g−1 , which does not decrease as does the ordinary Mn electrode, but instead gradually increases. After 10 cycles, the capacity tends to stabilize at 372 mAh g−1 . The increased capacity might be due to the continuous deep activation of the doped NB from inside to outside. During the first 15 cycles, the average discharge voltage gradually increases, from an initial value of 0.75–0.98 V, with a corresponding decrease in charge voltage from 1.58 to 1.17 V, which reflects not only an increase in energy efficiency but also an increase in reversibility of the material as well. The cycling efficiency is found to be 99.2–100%, calculated in accordance with the capacity ratio of charge and discharge. It is obvious that the reversibility of NB–Mn3 O4 is optimal, with the minor loss in capacity due to the dissolution of the small amount of slightly soluble MnOOH in the electrolyte KOH and oxygen evolution at high voltages. Fig. 4 also reveals that the doped cathode produced a 0.81–0.77 V discharge potential and a 215 mAh g−1 discharge capacity in the first discharge cycle. Calculation under the Faraday principle indicates that, if Mn3 O4 completely deoxidizes into Mn(OH)2 , the capacity is 245 mAh g−1 . Using the electrode data of manganese oxide in an alkaline solution as specified in the electrochemical manual, we
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Fig. 6. The discharge–charge curves of NB–Mn3 O4 electrode at various discharge rates.
Fig. 5. Cyclic voltammogram of Mn3 O4 electrodes (A) and NB–Mn3 O4 electrodes (B) at a scan rate of 0.5 mV s−1 .
conclude that such discharge capacity comes from the composite discharge of both Mn3 O4 and NB in the doped electrode as follows: Bi(V)0.05 [Mn(II)Mn(III)2 O4 ] → Bi(0)0.05 [Mn(II)(OH)2 ]3
(1)
The theoretical capacity for the above-mentioned calculation is 334 mAh g−1 , but the actual discharge capacity (215 mAh g−1 ) is less than the theoretical value, indicating that some Mn3 O4 has not been fully activated in the first discharge process. In successive charge cycles, we found that discharge capacity in the electrode had gradually increased and stabilized at 370–377 mAh g−1 . At the same time, we also found that the NB–Mn3 O4 electrode produced three discharge platforms in the second discharge process after the first charge. As for platform characteristics, we considered that the formation of Mn(IV) after first charging the electrode (but prior to discharge) might have transferred it into three processes, which also greatly increased the cycling capacity of the electrode, i.e.: Bi0.05 (V)Mn(IV) → Bi0.05 (III)Mn(III) Bi0.05 (III)Mn(III)3 → Bi0.05 (III)Mn(III)2 Mn(II) Bi0.05 (III)Mn(III)2 Mn(II) → Bi(0)0.05 [Mn(II)(OH)2 ]3
(2)
The doped electrode has a solid discharge process that corresponds to the steep discharge process of Mn(IV) → Mn(III) within 1.55–0.80 V, however, the 0.78 V discharge platform should correspond to the solid–liquid discharge process of Mn(III) → Mn(II). The cyclic voltammetry (CV) plots of the Mn3 O4 and NB–Mn3 O4 electrodes for the first 6 cycles are shown in Fig. 5. Using general electrochemical test practices, we first scanned the reduction process. As Fig. 5A indicates, we found that pure Mn3 O4 produced one
deoxidized peak in the 0.90–0.73 V voltage range over one deoxidization process for the cathode; this suggests some Mn in the Mn3 O4 , which corresponds to the discharge curve merging at 0.81 V in the aforementioned Mn3 O4 electrode. We also found that peak current for the pure Mn3 O4 electrode became much smaller (only 57 mA g−1 ) and rapidly attenuated in later cycles. In the course of the oxidation process for the pure Mn3 O4 electrode, we also found a weak oxidation peak at 1.19 V. As for the local area surrounded by peak current at peak oxidation, an integral method using Corrtest CView software reveals that its charge capacity (3.3 mAh g−1 ) was less than that of a deoxidized process (3.8 mAh g−1 ), indicating the production of deoxidized compounds Mn(II) and Mn(III) from the electrode in the course of deoxidization reaction, generating an electrochemically inert compound named Mn3 O4 and thus further reducing the capacity for reversibility. Fig. 5B indicates that the discharge mechanism of an NB–Mn3 O4 electrode is distinct from that of a pure MnO2 electrode. On first deoxidizing the cathode of an NB–Mn3 O4 electrode, we observed that one deoxidization peak occurred at 0.75 V, and that the potential for such reduction corresponded to the discharge performance of the doped cathode platform occurring at 0.76 V. We also considered this deoxidization reaction at Bi(V)Mn(III) → Bi(0)Mn(II), observing in the course of successive cathode scans that the doped electrode would alternately produce three deoxidization peaks at 1.14, 0.92 or 0.69 V. We considered as well that three deoxidization peaks would be generated and that Bi(V) and Mn(IV) would correspondingly be allied in the course of possible oxidization. Careful observation revealed that the three above-mentioned deoxidization peaks actually correspond to the positions for three discharge platforms occurring in the course of the charge/discharge process. As these deoxidization peaks are apparently different expressions of the same deoxidization reaction in the aforementioned discharge/charge process, the deoxidization process at the 1.14 V point should correspond to the process for Bi(V)Mn(IV) → Bi(III)Mn(III). As for the deoxidization peak at 0.92 V, we considered that post-incorporation features a formation peak from Mn3 O4 with electrochemical activation. A deoxidization peak at the 0.69 V point would correspond to a composite deoxidization peak at Bi(III)0.05 Mn(III)2 Mn(II) → Bi(0)0.05 Mn(II)3 . In addition, the deoxidization peak current for a doped Mn3 O4 electrode at first cycle amounted to 382 mA g−1 , well beyond the 57 mA g−1 for a pure Mn3 O4 electrode. This also indicated that a doped electrode greatly improved electrochemical activation for Mn3 O4 , thereby rendering a higher peak current at the same scan rate with a corresponding increase in deoxidizing capacity. This condition also corresponded
J. Pan et al. / Journal of Alloys and Compounds 470 (2009) 75–79
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discharge capacity over the first ten cycles. Moreover, despite the high rate of discharge/charge electric cycles (up to 60 cycles), the doped electrode still maintained a 95.3% reversible capacity. 4. Conclusions
Fig. 7. The cycling ability of NB–Mn3 O4 electrode at 500 mA g−1 .
to the current-constant result previously expressed. In the course of the oxidization process for the incorporated electric polar, we also observed a slight oxidization peak at 0.86 V. Based on the electrode potential manual, we predicted that this might be an oxidization process for Bi(0) → Bi(III). Oxidization peaks occurring later at 1.17 and 1.29 V would correspond to two oxidization processes for Bi(III)Mn(II) → Bi(III)Mn(III) and Bi(III)Mn(III) → Bi(III)Mn(IV), with the last oxidization peak at 1.62 V perhaps put into process for Bi(III)Mn(IV) → Bi(V)Mn(IV). The experiments indicated that the NB dopant made the oxidization and deoxidization processes for Mn3 O4 relatively easier, making Mn3 O4 generated by the cycling process no longer electrochemically inert. In other words, Mn3 O4 doped with NB presents greater electrochemical activity. The development of digital products and electric appliances not only requires better cycling characteristics from electrode materials, but also focuses particularly on the charge/discharge performance of batteries under heavy loads. Fig. 6 represents a discharge curve under different discharge rates of doped Mn3 O4 electrodes from 60 to 500 mA g−1 . After tests for current-constant discharge/charge for an NB–Mn3 O4 electrode, we found that the middle-value charge voltage for the doped electrode increased only by 22 mV while its current density ranged from 60 to 500 mA g−1 , indicating an electrode with superior reversible performance. In addition, we also found that the discharge capacity of the doped electrode attenuated from 371 to 261 mAh g−1 along with the increase of current density. However, the electrode still maintained a relatively flat discharge/charge platform, a phenomenon suggesting that, under greater current discharge conditions, some Mn3 O4 does not promptly attend electrode reaction, thus reducing electrode capacity. Viewing from Fig. 6, we also found that charging time for the battery shortened to 30 min when charging current reached 500 mA g−1 , suggesting that charging time for an alkaline battery using doped Mn3 O4 cathode could possibly be reduced to as little as 30 min. For further consideration of discharge performance at high discharge rates, Fig. 7 shows the curve of cycling capacity under 500 mA g−1 for a doped Mn3 O4 electrode. Viewed from the test, we found that over the course of 60 cycles the NB–Mn3 O4 electrode remained stable for at least 50 cycles after a slow increase in
This article examined the electrochemical performance of a Mn3 O4 electrode doped with nano-NaBiO3 . It demonstrated that doping with NaBiO3 alters the electrochemical inertia of Mn3 O4 , converting it into a secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn3 O4 electrode can barely maintain a single charge and discharge cycle, the cycling capacity of a doped NB–Mn3 O4 electrode can reach and become stable at 372 mAh g−1 under 60 mA g−1 . The doped cathode can also maintain a cycling capacity of 261 mAh g−1 while holding a 95.3% reversibility capacity after 60 cycles at a high rate of 500 mA g−1 . Acknowledgments The authors gratefully acknowledge Prof. Y.S. Yang (Academician) for important discussions and support of this research. This work was supported by National Natural Science Foundation of China (No. 20573135). References [1] J.Q. Pan, Y.Z. Sun, Z.H. Wang, P.Y. Wan, X.G. Liu, M.H. Fan, J. Mater. Chem. 17 (2007) 4820. [2] H. Huang, S.C. Yin, T. Kerr, N. Taylor, L.F. Nazar, Adv. Mater. 14 (2002) 1525. [3] X. Wang, Y.D. Li, J. Am. Chem. Soc. 124 (2002) 2880. [4] G. Jain, J. Yang, M. Balasubramanian, J.J. Xu, Chem. Mater. 17 (2005) 3850. [5] W.P. Tang, X.J. Yang, Z.H. Liu, K. Ooi, J. Mater. Chem. 13 (2003) 2989. [6] G. Armstrong, A.R. Armstrong, P.G. Bruce, P. Reale, B. Scrosati, Adv. Mater. 18 (2006) 2597. [7] X.H. Liu, L. Yu, J. Power Sources 128 (2004) 326. [8] R.M. Dell, Solid State Ion. 134 (2000) 139. [9] S. Licht, S. Ghosh, J. Power Sources 109 (2002) 465. [10] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Electrochim. Acta 51 (2006) 3118. [11] V.K. Nartey, L. Binder, A. Huber, J. Power Sources 87 (2000) 205. [12] D. Im, A. Manthiram, J. Electrochem. Soc. 150 (2003) A68. ¨ [13] H. Schlorb, M. Bungs, W. Plieth, Electrochim. Acta 42 (1997) 2619. [14] J.J. Xu, X.L. Luo, Y. Du, H.Y. Chen, Electrochem. Commun. 6 (2004) 1169. [15] A.M. Kannan, S. Bhavaraju, F. Prado, M.M. Raja, A. Manthiram, J. Electrochem. Soc. 149 (2002) A483. [16] F. Beck, P. Ruetschi, Electrochim. Acta 45 (2000) 2467. [17] M. Manickam, P. Singh, T.B. Issa, S. Thurgate, R.D. Marco, J. Power Sources 130 (2004) 254. [18] B. Sajdl, K. Micka, P. Krtil, Electrochim. Acta 40 (1995) 2005. [19] X. Xia, C. Zhang, Z. Guo, H.K. Liu, G. Walter, J. Power Sources 109 (2002) 11. [20] M. Wagemaker, A.P.M. Kentgens, F.M. Mulder, Nature 418 (2002) 397. [21] W. Janscher, L. Binder, D.A. Fiedler, R. Andreaus, K. Kordesch, J. Power Sources 79 (1999) 9. [22] J. Kim, A. Manthiram, Nature 390 (1997) 265. [23] H. Yagi, T. Ichikawa, A. Hirano, N. Imanishi, S. Ogawa, Y. Taked, Solid State Ion. 154 (2002) 273. [24] D. Im, A. Manthiram, B. Coffey, J. Electrochem. Soc. 150 (2003) A1651. [25] L. Bai, D.Y. Qu, B.E. Conway, Y.H. Zhou, G. Chowdhury, W.A. Adams, J. Electrochem. Soc. 140 (1993) 884. [26] D.Y. Qu, J. Appl. Electrochem. 29 (1999) 511. [27] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Chem. Commun. (2005) 3340. [28] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Electrochem. Commun. 7 (2005) 857. [29] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Chem. J. Chin. Univ. 25 (2004) 2204. [30] V. Raghuveer, A. Manthiram, Electrochem. Commun. 7 (2005) 1329. [31] V. Raghuveer, A. Manthiram, J. Power Sources 163 (2006) 598.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Mn3 O4 doped with nano-NaBiO3 : A high capacity cathode material for alkaline secondary batteries Junqing Pan a,b , Yanzhi Sun a , Zihao Wang b , Pingyu Wan a,∗ , Maohong Fan c,∗ a
College of Science, Beijing University of Chemical Technology, Beijing 100029, China College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China c School of Materials Science and Engineering, Georgia Institute of Technology, GA 40332, USA b
a r t i c l e
i n f o
Article history: Received 11 December 2007 Received in revised form 5 February 2008 Accepted 9 February 2008 Available online 3 June 2008 Keywords: Electrode materials X-ray diffraction Electrochemical reactions
a b s t r a c t In this paper we report a novel Mn3 O4 electrode doped with nano-NaBiO3 . It is demonstrated that doping with nano-NaBiO3 alters the electrochemical inertia of Mn3 O4 , converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn3 O4 electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn3 O4 electrode doped with nano-NaBiO3 can reach and become stable at 372 mAh g−1 under 60 mA g−1 . The doped cathode can also maintain a cycling capacity of 261 mAh g−1 while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g−1 . Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn3 O4 cathode could possibly shorten to as little as 30 min. © 2008 Published by Elsevier B.V.
1. Introduction Nanophase materials feature high surface energy and reactivity resulting from their high specific surfaces. They also demonstrate special electric, magnetic, absorptive, and catalytic properties in many reactions [1–5]. Besides the significant research directed towards new applications for nanophase materials, investigators are reexamining existing applications as well as the widespread use in many fields of nanophase materials to dope other materials for enhanced performance [6,7]. It has been more than 140 years since French scientist Georges Leclanche´ invented the manganese dioxide (MnO2 ) battery in 1865. Since then, the MnO2 battery has continuously been improved, starting with the earliest zinc-manganese dry battery, followed by the high-performance zinc-manganese battery, and up to today’s mercury-free zinc alkaline manganese battery. Because of the maturity of its technology, reliable performance, and competitive price, the MnO2 battery has seen widespread use, with global sales of approximately 60 billion units annually [8,9]. The primary cathode material for zinc-manganese batteries, MnO2 , has various polymorphs, including ␣, , ␥ and ␦ structures. Of these, the superior discharge performance of ␥-MnO2 with more than 92% purity has made it the active material of choice for the cathode of alkaline
∗ Corresponding authors. Tel.: +86 10 64445917; fax: +86 10 64445917. E-mail addresses: [email protected] (P. Wan), [email protected] (M. Fan). 0925-8388/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.jallcom.2008.02.075
MnO2 batteries. Moreover, the elimination of mercury has considerably reduced environmental pollution from alkaline manganese batteries. However, because of the sheer volume of their use worldwide, production of these batteries still results in a serious waste of manganese resources. As for alkaline manganese batteries with zinc anodes, the enhanced electrochemical performance of MnO2 has opened the bottleneck to improve MnO2 battery performance. Moreover, methods for improving MnO2 discharge performance to make these batteries rechargeable may represent an effective approach to conserving manganese resources. Various studies have indicated that doping with bismuth dioxide, lead dioxide, titanium dioxide, and other relevant additives significantly improves discharge performance for MnO2 electrodes, yet without greatly improving their recharge capacity [10–23]. A recent study indicated that a MnO2 electrode doped with bismuth dioxide could be recharged over tens of cycles. Also, further studies have suggested that the reason for the continuous decay in performance of MnO2 electrodes in the charge/discharge cycle is due to the unavoidable formation of Mn3 O4 , an electrochemically inert substance having a sharp crystalline structure different from MnO2 structures in the cycle process [24–26]. Because Mn3 O4 formed upon discharge and deoxidization cannot oxidize into highly valued MnO2 during the charge process, this results in the gradual reduction of MnO2 in the electrode. Therefore, besides avoiding the formation of Mn3 O4 entirely, developing methods for making it act as a charging and cycling substance is critical for making rechargeable alkaline manganese batteries.
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In this paper, following our previous studies on alkaline cathode of high capacity [27,28], we report a novel Mn3 O4 electrode doped with nano-NaBiO3 that offers a high specific capacity of 376 mAh g−1 (at 60 mA g−1 ) and 261 mAh g−1 (at 500 mA g−1 ), as well as a stable reversible capacity over a range of 0.5–1.75 V in 60 charge/discharge cycles. Moreover, the ability of the electrode to accept high charging levels results in a recharge time of only 30 min. 2. Experimental The nano-NaBiO3 was synthesized in a NaOH–NaClO solution as previously reported [10,29]. 0.005 mol of self-prepared NaBiO3 was ground in an agate mortar and added to 2.5 mL of water, followed by ultrasonic dispersion for 15 min. Then, 0.1 mol of Mn3 O4 (Shanghai Regent Plant) was added, followed by ultrasonic dispersion for 30 min. The resulting suspension liquid was moved into an autoclave lined with PTFE, followed by vacuum drying at 373 K for 3 h and at 323 K for 24 h. The resulting solid yellow powder served as the electrode material of Mn3 O4 doped with nano-NaBiO3 (NB–Mn3 O4 ). The phase structures of the prepared samples were analyzed using a Rigaku D/max2500VB2 + /PCX X-ray diffractometer (XRD) with a Cu anticathode. The morphology of samples was examined using a field-emission scanning electron microscope (FESEM). The element analysis was performed using energy-dispersive X-ray spectroscopy (EDS). 80% (wt.) NB–Mn3 O4 sample, 15% (wt.) expansive graphite, and 5% PTFE binder were mixed and pressed on foam nickel to form a NB–Mn3 O4 working electrode. 40% KOH (including 10 g L−1 ZnO) was used as an electrolyte, Ni wire as an auxiliary electrode, and Zn(Hg)/ZnO as a reference electrode. The charge/discharge test was
carried out with a LAND CT2001A cell test instrument, and the cyclic voltammetry measurement was performed using an EG&G Princeton Applied Research 273 potentiostat controlled by M270 electrochemistry software.
3. Results and discussion The FESEM images of Mn3 O4 and the prepared NB–Mn3 O4 are shown in Fig. 1. Fig. 1a reveals that the commercial Mn3 O4 is composed of irregular particles with actual grain sizes of 30–50 m. After hydrothermal treatment and doping of Mn3 O4 with NaBiO3 , we found that the surface of the resulting NB–Mn3 O4 was covered with a layer of fine crystal (Fig. 1b). The EDS analysis was performed in order to determine whether the sample was doped with Bi and Na elements. Fig. 2 represents the EDS analysis diagrams of the Mn3 O4 and NB–Mn3 O4 samples, respectively. It can be seen that only Mn and O elements appear in the Mn3 O4 sample in Fig. 2a. By contrast, Fig. 2b shows that Mn, O, Bi, and Na elements appear simultaneously in the NB–Mn3 O4 sample, which indicates that the Mn3 O4 is evenly doped with NaBiO3 . Fig. 3 shows the XRD plots of NB, Mn3 O4 , and NB–Mn3 O4 samples. Because the NB–Mn3 O4 largely reveals the diffraction peak of Mn3 O4 and no typical diffraction peak of NB, we deduced that this part of nano-NB had been mixed into the crystal lattice of Mn3 O4 . The new diffraction peaks at 23.5 and 56.2◦ might result from the composite peaks of nano-NB and Mn3 O4 . In other words, NaBiO3
Fig. 1. The FSEM pictures of Mn3 O4 (a1, a2) and NB–Mn3 O4 (b1, b2) samples.
J. Pan et al. / Journal of Alloys and Compounds 470 (2009) 75–79
Fig. 2. The EDS analysis diagrams of Mn3 O4 (a) and NB–Mn3 O4 (b) samples.
promotes the birnessite formation reaction independent of the prevention of Mn3 O4 formation [30,31]. Simultaneously, the new diffraction peaks at 28.3 and 30.1◦ corresponding to Bi2 O3 , which might be the redox resultant from a small quantity of Bi(V) and Mn3 O4 could be observed. In addition, NaBiO3 has a certain extent of solubility, which keeps the balance between dissolution and precipitation, and Mn3 O4 itself has potential ion exchange property. Consequently, NaBiO3 is evenly dispersed in Mn3 O4 crystal and its surface. That changes the original electrochemical inertia of Mn3 O4 and activates its potential electrochemical property.
Fig. 3. The X-ray powder patterns of NB, NB–Mn3 O4 and Mn3 O4 samples.
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Fig. 4. Discharge curves of Mn3 O4 (A) and NB–Mn3 O4 (B) electrodes at 60 mA g−1 .
The pure Mn3 O4 electrode and the NB–Mn3 O4 electrode were subjected to galvanostatic charge/discharge cycles at 60 mA g−1 over a potential range of 0.50–1.75 V, respectively. Fig. 4 represents the charge/discharge curves of both electrodes. It can be seen that a pure Mn3 O4 electrode provides a capacity of only 7–11 mAh g−1 , which also decays along with increased cycling and presents almost no reversibility. By contrast, the NB–Mn3 O4 electrode provides an initial capacity of 215 mAh g−1 , which does not decrease as does the ordinary Mn electrode, but instead gradually increases. After 10 cycles, the capacity tends to stabilize at 372 mAh g−1 . The increased capacity might be due to the continuous deep activation of the doped NB from inside to outside. During the first 15 cycles, the average discharge voltage gradually increases, from an initial value of 0.75–0.98 V, with a corresponding decrease in charge voltage from 1.58 to 1.17 V, which reflects not only an increase in energy efficiency but also an increase in reversibility of the material as well. The cycling efficiency is found to be 99.2–100%, calculated in accordance with the capacity ratio of charge and discharge. It is obvious that the reversibility of NB–Mn3 O4 is optimal, with the minor loss in capacity due to the dissolution of the small amount of slightly soluble MnOOH in the electrolyte KOH and oxygen evolution at high voltages. Fig. 4 also reveals that the doped cathode produced a 0.81–0.77 V discharge potential and a 215 mAh g−1 discharge capacity in the first discharge cycle. Calculation under the Faraday principle indicates that, if Mn3 O4 completely deoxidizes into Mn(OH)2 , the capacity is 245 mAh g−1 . Using the electrode data of manganese oxide in an alkaline solution as specified in the electrochemical manual, we
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Fig. 6. The discharge–charge curves of NB–Mn3 O4 electrode at various discharge rates.
Fig. 5. Cyclic voltammogram of Mn3 O4 electrodes (A) and NB–Mn3 O4 electrodes (B) at a scan rate of 0.5 mV s−1 .
conclude that such discharge capacity comes from the composite discharge of both Mn3 O4 and NB in the doped electrode as follows: Bi(V)0.05 [Mn(II)Mn(III)2 O4 ] → Bi(0)0.05 [Mn(II)(OH)2 ]3
(1)
The theoretical capacity for the above-mentioned calculation is 334 mAh g−1 , but the actual discharge capacity (215 mAh g−1 ) is less than the theoretical value, indicating that some Mn3 O4 has not been fully activated in the first discharge process. In successive charge cycles, we found that discharge capacity in the electrode had gradually increased and stabilized at 370–377 mAh g−1 . At the same time, we also found that the NB–Mn3 O4 electrode produced three discharge platforms in the second discharge process after the first charge. As for platform characteristics, we considered that the formation of Mn(IV) after first charging the electrode (but prior to discharge) might have transferred it into three processes, which also greatly increased the cycling capacity of the electrode, i.e.: Bi0.05 (V)Mn(IV) → Bi0.05 (III)Mn(III) Bi0.05 (III)Mn(III)3 → Bi0.05 (III)Mn(III)2 Mn(II) Bi0.05 (III)Mn(III)2 Mn(II) → Bi(0)0.05 [Mn(II)(OH)2 ]3
(2)
The doped electrode has a solid discharge process that corresponds to the steep discharge process of Mn(IV) → Mn(III) within 1.55–0.80 V, however, the 0.78 V discharge platform should correspond to the solid–liquid discharge process of Mn(III) → Mn(II). The cyclic voltammetry (CV) plots of the Mn3 O4 and NB–Mn3 O4 electrodes for the first 6 cycles are shown in Fig. 5. Using general electrochemical test practices, we first scanned the reduction process. As Fig. 5A indicates, we found that pure Mn3 O4 produced one
deoxidized peak in the 0.90–0.73 V voltage range over one deoxidization process for the cathode; this suggests some Mn in the Mn3 O4 , which corresponds to the discharge curve merging at 0.81 V in the aforementioned Mn3 O4 electrode. We also found that peak current for the pure Mn3 O4 electrode became much smaller (only 57 mA g−1 ) and rapidly attenuated in later cycles. In the course of the oxidation process for the pure Mn3 O4 electrode, we also found a weak oxidation peak at 1.19 V. As for the local area surrounded by peak current at peak oxidation, an integral method using Corrtest CView software reveals that its charge capacity (3.3 mAh g−1 ) was less than that of a deoxidized process (3.8 mAh g−1 ), indicating the production of deoxidized compounds Mn(II) and Mn(III) from the electrode in the course of deoxidization reaction, generating an electrochemically inert compound named Mn3 O4 and thus further reducing the capacity for reversibility. Fig. 5B indicates that the discharge mechanism of an NB–Mn3 O4 electrode is distinct from that of a pure MnO2 electrode. On first deoxidizing the cathode of an NB–Mn3 O4 electrode, we observed that one deoxidization peak occurred at 0.75 V, and that the potential for such reduction corresponded to the discharge performance of the doped cathode platform occurring at 0.76 V. We also considered this deoxidization reaction at Bi(V)Mn(III) → Bi(0)Mn(II), observing in the course of successive cathode scans that the doped electrode would alternately produce three deoxidization peaks at 1.14, 0.92 or 0.69 V. We considered as well that three deoxidization peaks would be generated and that Bi(V) and Mn(IV) would correspondingly be allied in the course of possible oxidization. Careful observation revealed that the three above-mentioned deoxidization peaks actually correspond to the positions for three discharge platforms occurring in the course of the charge/discharge process. As these deoxidization peaks are apparently different expressions of the same deoxidization reaction in the aforementioned discharge/charge process, the deoxidization process at the 1.14 V point should correspond to the process for Bi(V)Mn(IV) → Bi(III)Mn(III). As for the deoxidization peak at 0.92 V, we considered that post-incorporation features a formation peak from Mn3 O4 with electrochemical activation. A deoxidization peak at the 0.69 V point would correspond to a composite deoxidization peak at Bi(III)0.05 Mn(III)2 Mn(II) → Bi(0)0.05 Mn(II)3 . In addition, the deoxidization peak current for a doped Mn3 O4 electrode at first cycle amounted to 382 mA g−1 , well beyond the 57 mA g−1 for a pure Mn3 O4 electrode. This also indicated that a doped electrode greatly improved electrochemical activation for Mn3 O4 , thereby rendering a higher peak current at the same scan rate with a corresponding increase in deoxidizing capacity. This condition also corresponded
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discharge capacity over the first ten cycles. Moreover, despite the high rate of discharge/charge electric cycles (up to 60 cycles), the doped electrode still maintained a 95.3% reversible capacity. 4. Conclusions
Fig. 7. The cycling ability of NB–Mn3 O4 electrode at 500 mA g−1 .
to the current-constant result previously expressed. In the course of the oxidization process for the incorporated electric polar, we also observed a slight oxidization peak at 0.86 V. Based on the electrode potential manual, we predicted that this might be an oxidization process for Bi(0) → Bi(III). Oxidization peaks occurring later at 1.17 and 1.29 V would correspond to two oxidization processes for Bi(III)Mn(II) → Bi(III)Mn(III) and Bi(III)Mn(III) → Bi(III)Mn(IV), with the last oxidization peak at 1.62 V perhaps put into process for Bi(III)Mn(IV) → Bi(V)Mn(IV). The experiments indicated that the NB dopant made the oxidization and deoxidization processes for Mn3 O4 relatively easier, making Mn3 O4 generated by the cycling process no longer electrochemically inert. In other words, Mn3 O4 doped with NB presents greater electrochemical activity. The development of digital products and electric appliances not only requires better cycling characteristics from electrode materials, but also focuses particularly on the charge/discharge performance of batteries under heavy loads. Fig. 6 represents a discharge curve under different discharge rates of doped Mn3 O4 electrodes from 60 to 500 mA g−1 . After tests for current-constant discharge/charge for an NB–Mn3 O4 electrode, we found that the middle-value charge voltage for the doped electrode increased only by 22 mV while its current density ranged from 60 to 500 mA g−1 , indicating an electrode with superior reversible performance. In addition, we also found that the discharge capacity of the doped electrode attenuated from 371 to 261 mAh g−1 along with the increase of current density. However, the electrode still maintained a relatively flat discharge/charge platform, a phenomenon suggesting that, under greater current discharge conditions, some Mn3 O4 does not promptly attend electrode reaction, thus reducing electrode capacity. Viewing from Fig. 6, we also found that charging time for the battery shortened to 30 min when charging current reached 500 mA g−1 , suggesting that charging time for an alkaline battery using doped Mn3 O4 cathode could possibly be reduced to as little as 30 min. For further consideration of discharge performance at high discharge rates, Fig. 7 shows the curve of cycling capacity under 500 mA g−1 for a doped Mn3 O4 electrode. Viewed from the test, we found that over the course of 60 cycles the NB–Mn3 O4 electrode remained stable for at least 50 cycles after a slow increase in
This article examined the electrochemical performance of a Mn3 O4 electrode doped with nano-NaBiO3 . It demonstrated that doping with NaBiO3 alters the electrochemical inertia of Mn3 O4 , converting it into a secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn3 O4 electrode can barely maintain a single charge and discharge cycle, the cycling capacity of a doped NB–Mn3 O4 electrode can reach and become stable at 372 mAh g−1 under 60 mA g−1 . The doped cathode can also maintain a cycling capacity of 261 mAh g−1 while holding a 95.3% reversibility capacity after 60 cycles at a high rate of 500 mA g−1 . Acknowledgments The authors gratefully acknowledge Prof. Y.S. Yang (Academician) for important discussions and support of this research. This work was supported by National Natural Science Foundation of China (No. 20573135). References [1] J.Q. Pan, Y.Z. Sun, Z.H. Wang, P.Y. Wan, X.G. Liu, M.H. Fan, J. Mater. Chem. 17 (2007) 4820. [2] H. Huang, S.C. Yin, T. Kerr, N. Taylor, L.F. Nazar, Adv. Mater. 14 (2002) 1525. [3] X. Wang, Y.D. Li, J. Am. Chem. Soc. 124 (2002) 2880. [4] G. Jain, J. Yang, M. Balasubramanian, J.J. Xu, Chem. Mater. 17 (2005) 3850. [5] W.P. Tang, X.J. Yang, Z.H. Liu, K. Ooi, J. Mater. Chem. 13 (2003) 2989. [6] G. Armstrong, A.R. Armstrong, P.G. Bruce, P. Reale, B. Scrosati, Adv. Mater. 18 (2006) 2597. [7] X.H. Liu, L. Yu, J. Power Sources 128 (2004) 326. [8] R.M. Dell, Solid State Ion. 134 (2000) 139. [9] S. Licht, S. Ghosh, J. Power Sources 109 (2002) 465. [10] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Electrochim. Acta 51 (2006) 3118. [11] V.K. Nartey, L. Binder, A. Huber, J. Power Sources 87 (2000) 205. [12] D. Im, A. Manthiram, J. Electrochem. Soc. 150 (2003) A68. ¨ [13] H. Schlorb, M. Bungs, W. Plieth, Electrochim. Acta 42 (1997) 2619. [14] J.J. Xu, X.L. Luo, Y. Du, H.Y. Chen, Electrochem. Commun. 6 (2004) 1169. [15] A.M. Kannan, S. Bhavaraju, F. Prado, M.M. Raja, A. Manthiram, J. Electrochem. Soc. 149 (2002) A483. [16] F. Beck, P. Ruetschi, Electrochim. Acta 45 (2000) 2467. [17] M. Manickam, P. Singh, T.B. Issa, S. Thurgate, R.D. Marco, J. Power Sources 130 (2004) 254. [18] B. Sajdl, K. Micka, P. Krtil, Electrochim. Acta 40 (1995) 2005. [19] X. Xia, C. Zhang, Z. Guo, H.K. Liu, G. Walter, J. Power Sources 109 (2002) 11. [20] M. Wagemaker, A.P.M. Kentgens, F.M. Mulder, Nature 418 (2002) 397. [21] W. Janscher, L. Binder, D.A. Fiedler, R. Andreaus, K. Kordesch, J. Power Sources 79 (1999) 9. [22] J. Kim, A. Manthiram, Nature 390 (1997) 265. [23] H. Yagi, T. Ichikawa, A. Hirano, N. Imanishi, S. Ogawa, Y. Taked, Solid State Ion. 154 (2002) 273. [24] D. Im, A. Manthiram, B. Coffey, J. Electrochem. Soc. 150 (2003) A1651. [25] L. Bai, D.Y. Qu, B.E. Conway, Y.H. Zhou, G. Chowdhury, W.A. Adams, J. Electrochem. Soc. 140 (1993) 884. [26] D.Y. Qu, J. Appl. Electrochem. 29 (1999) 511. [27] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Chem. Commun. (2005) 3340. [28] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Electrochem. Commun. 7 (2005) 857. [29] J.Q. Pan, Y.Z. Sun, P.Y. Wan, Z.H. Wang, X.G. Liu, Chem. J. Chin. Univ. 25 (2004) 2204. [30] V. Raghuveer, A. Manthiram, Electrochem. Commun. 7 (2005) 1329. [31] V. Raghuveer, A. Manthiram, J. Power Sources 163 (2006) 598.