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NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries
Materials Letters 132 (2014) 357–360
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries Ling Cao a,b,n, Dongxiao Wang b, Rong Wang b a Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China b College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 May 2014 Accepted 18 June 2014 Available online 25 June 2014
We reported on NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries. The structural, morphological and electrochemical properties of the films were studied. The results demonstrated that the film exhibits high initial columbic efficiency of 73.6%, high reversible capacity and rather good cycling performance. The discharge specific capacity remained at 687 mA h g 1 at a current density of 100 mA g 1 after 50 cycles. The unique nanoporous structure and enhanced electrical contact between the substrate and active materials could be responsible for the improvement of electrochemical properties. & 2014 Elsevier B.V. All rights reserved.
Keywords: Thin films Semiconductors Physical vapor deposition XPS
1. Introduction Rechargeable lithium-ion batteries (LIBs) have been identified as the most promising power sources for portable electronic devices and hybrid vehicles [1]. Massive efforts have been focused on searching potential materials and fabrication techniques for developing the next-generation LIB electrodes [2]. As novel conversion anode materials, transition-metal oxides, such as Fe3O4 [3], Co3O4 [4], MnO2 [5], CuO [6], and NiO [7], have attracted increasing attention due to their much higher capacity than that of commercial graphite anodes [8]. Among these materials, NiO is one of the most extensively studied anode materials because of its high theoretical energy capacity (718 mA h g 1), earth abundance, chemically and thermally stable, and environmentally benign [9]. To date, many nanostructured NiO with various morphologies, such as nanoflake [10], nanotube [11], nanosheet [12], nanowall [13], and nanoparticle [14], have been investigated. Recently, nanocrystalline thin film anodes grown directly on conducting substrates exhibited excellent electrochemical performance due to its enhanced electrical contact between the substrate and active materials, shortened diffusion lengths for lithium ion, and good structural stability [15]. What is more, the crystallinity and film thickness can be effectively controlled and the intrinsic
n Corresponding author at: Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China. Tel./fax: þ 86 351 6018030. E-mail address: [email protected] (L. Cao).
http://dx.doi.org/10.1016/j.matlet.2014.06.114 0167-577X/& 2014 Elsevier B.V. All rights reserved.
electrochemical properties can be obtained by eliminating the interference from irregular shape and size distribution of active particles as well as from the additives [16]. However, there is no report, to the best of our knowledge, on the NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for LIBs. In this letter, NiO thin films were prepared on Cu foils at room temperature by pulsed laser deposition. The structural, morphological and electrochemical properties of the films were investigated.
2. Experimental details NiO thin films were prepared by pulsed laser deposition using a sintered NiO ceramic target. A KrF excimer laser (Compex102, 248 nm, 25 ns) was employed as a ablation source. The laser repetition rate and the energy per pulse were 5 Hz and 300 mJ, respectively. The deposition was carried out in an oxygen pressure of 5 Pa. All the films were deposited at room temperature for 60 min and had an approximate film thickness of 200 nm. The crystal structures of the films were investigated by X-ray diffraction (XRD) using a XPERT-PRO system with a CuKα (λ ¼1.5406 Å) source. The surface morphology and the film thickness were characterized using field emission scanning electron microscopy (FE-SEM; HITACHIS-4800). The chemical bonding state of the films was analyzed by x-ray photoelectron spectroscopy (XPS) (Thermo ESCALAB 250, AlKα radiation source hν ¼1486.6 eV). The electrochemical performances of the film were measured by two-electrode CR-2025-type coin cells. The cells were assembled in
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an argon-filled glove box using the Cu foil-supported NiO films as working electrodes and lithium foil as counter-electrodes. The electrolyte was 1 M LiPF6 in a 1:1 (w/w) mixture of ethylene carbonate (EC) and dimethyl carbonate (DME). The galvanostatic charge–discharge tests were performed on the LAND battery program-control test system. Cyclic voltammetric (CV) measurements were evaluated on a CHI660C electrochemical workstation with a scan rate of 0.1 mV s 1 between 0 and 3 V (vs. Li/Li þ ).
3. Results and discussion Fig. 1 shows the XRD pattern of NiO film grown directly on Cu foil at room temperature. Removing strong peaks of the cubic
crystal Cu, only a broad peak indexed to (111) reflection of the cubic NiO structure can be observed. No extra phases related with nickel and copper compounds can be detected, suggesting that pure NiO film has grown on the Cu foil surface. For comparison, the XRD pattern of NiO film prepared on quartz substrate at the same conditions is also displayed in Fig. 1. It can be seen that the film exhibits well-resolved diffraction peaks indexed as the (111) and (200) reflections of the cubic NiO structure. Fig. 2(a) and (b) shows the surface morphologies of NiO films grown on quartz substrate and Cu foil, respectively. It can be seen that the film on quartz substrate presents a smooth and highly compact surface, which implies a relatively good crystallinity. However, the surface of the film on Cu foil shows higher roughness and less compact, and most of the irregular rounded grains including numerous pores in nanometer scale are separated from each other with nano-voids. Fig. 3 provides the XPS spectra of Ni 2p and O 2p core levels of the NiO film grown on Cu foil. It can be observed from Fig. 3 (a) that the Ni 2p spectrum exhibits the characteristic double peak 2p3/2 and 2p1/2 main lines. The additional peak located at around 855.2 eV is the satellite of Ni 2p3/2 [17]. The double peak structure in the 2p3/2 main line is ascribed to the presence of two types of states, namely Ni2 þ and Ni3 þ for the lower and higher binding energy peaks, respectively [18]. Here, the Ni3 þ only refers to a structure containing Ni2 þ ions with holes and hence does not indicate an existence of Ni2O3 phase in the film [19]. Fig. 3 (b) shows the O 1s spectrum of the film and the O 1s peaks can
Fig. 1. XRD patterns of NiO films grown on quartz substrate and Cu foil.
Fig. 2. Surface morphologies of NiO films grown on (a) quartz substrate and (b) Cu foil.
Fig. 3. XPS spectra of (a) Ni 2p and (b) O 2p core levels of NiO film grown at Cu foil.
L. Cao et al. / Materials Letters 132 (2014) 357–360
359
Fig. 4. (a) Cyclic voltammograms of NiO film at a scan rate of 0.1 mV s 1 for the second cycle. (b) Charge and discharge profiles of NiO film at a current density of 100 mA g 1. (c) Cycling performances and coulombic efficiency of NiO film during cycling. (d) Capacity retention for the NiO film at different current densities.
be fitted by three binding energy curves centered at 529.4 (OI), 531.3 (OII), and 532.5 eV (OIII), which correspond to the oxygen ions in the fully oxidized surrounding, the oxygen ions in oxygen deficient regions, and OH related species or the loosely bound oxygen from chemisorbed H2O on the surface, respectively [20]. The coin-type cell configuration was used to evaluate the electrochemical performance of the NiO film as an anode electrode. Fig. 4(a) displays the cyclic voltammetry (CV) tests of the thin film electrode at a scan rate of 0.1 mV s 1 at the second cycle. During the cathodic/anodic scanning, the reduction peaks located at 0.98 V and 1.35 V correspond to the initial reduction of NiO to metallic Ni and the formation of a partially reversible solid electrolyte interphase (SEI) layer, respectively [21]. The oxidation peaks at around 0.5 V and 1.41 V are associated with the partial decomposition of SEI layer on the NiO surface, while an additional oxidation peak at 2.31 V originates from the decomposition of Li2O and nickel converted back to NiO [22]. The discharge/charge curves of the NiO film electrode at a low current density of 100 mA g 1 are shown in Fig. 4(b). During the discharge process, the voltage decreases rapidly to 0.8 V where a plateau region sets in and continues until a discharge capacity of 1200 mA h g 1 is reached. Then, another slope can be found at 0.6 V with a total first discharge capacity of 1510 mA h g 1, which is higher than the theoretical value. The extra capacity could be ascribed to the formation of SEI in the first discharge process [22]. The first charge capacity is approximately 1112 mA h g 1, which is much less than that of the first discharge. The incomplete decomposition of the SEI and Li2O should be responsible for the irreversible capacity loss between the first discharge and charge [23]. The corresponding initial columbic efficiency is about 73.6%, which is comparable to or even higher than the previous reported values [10,14,21,24].
Fig. 4(c) shows the capacity retention properties of the NiO film electrode. The discharge specific capacity decreases to 1134 mA h g 1 in the 2nd cycle and remains at 687 mA h g 1 after 50 cycles. Moreover, the coulombic efficiency of the electrode keeps over 93% after the 2nd cycle. Fig. 4(d) displays reversible capacities of NiO film at different current densities. It can be seen that the reversible capacity decreases slowly with increase in the discharge/charge current densities. Outstanding capacities of 640 and 382 mA h g 1 could be obtained at the current density of 200 and 800 mA g 1, respectively. When the current density returns to 200 mA g 1, the film can still deliver a reversible capacity of 492 mA h g 1. These results clearly indicate that the NiO film possesses excellent electrochemical performance, which could be related to its unique microstructural characteristics. The nanopores inside the NiO film as well as the nano-voids between adjacent grains can provide structural flexibility for volume change during the charge–discharge process [25]. In addition, the close contact of the film grown directly on the current collector further allows for a fast charge transfer pathway, which efficiently decreases the contact resistance and hence improves the electrode capacity [26].
4. Conclusions In summary, pure NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries have been investigated. The as-prepared NiO film possesses excellent electrochemical performance comparable to or even better than the NiO anodes reported previously, which could be related to its unique microstructural characteristics and enhanced
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L. Cao et al. / Materials Letters 132 (2014) 357–360
electrical contact between the substrate and active materials. We expect that the electrochemical properties of the films could be further improved by applying more optimalized deposition conditions. Therefore, the pulsed laser deposited NiO thin films are promising candidates for the applications in lithium-ion batteries. Acknowledgments This work is supported by the National Natural Science Foundation of China (Grant no. 11347157) and the Qualified Personnel Foundation of Taiyuan University of Technology (Grant no. tyut-rc201247a). References [1] [2] [3] [4] [5] [6] [7]
Ma Y, Ji G, Ding B, Lee JY. J Mater Chem 2012;22:24380–5. Wu HB, Chen JS, Hng HH, Lou XW. Nanoscale 2012;4:2526–42. Wu H, Du L, Wang JZ, Zhang H, Yang DR. J Power Sources 2014;246:198–203. Fang F, Bai L, Liu YG, Cheng SB, Sun HY. Mater Lett 2014;125:103–6. Kundu M, Ng CCA, Petrovykh DY, Liu LF. Chem Commun 2013;49:8459–61. Qiu DF, Zhao B, Lin ZX, Pu L, Pan LJ, Shi Y. Mater Lett 2013;105:242–5. Wang XH, Qiao L, Sun XL, Li XW, Hu DK, Zhang Q, et al. J Mater Chem A 2013;1:4173–6.
[8] Jiang J, Li YY, Liu JP, Huang XT. Nanoscale 2011;3:45–58. [9] Ma JM, Yang JQ, Jiao LF, Mao YH, Wang TH, Duan XC, et al. CrystEngComm 2012;14:453–9. [10] Wu H, Xu M, Wu HY, Xu JJ, Wang YL, Peng Z, et al. J Mater Chem 2012;22:19821–5. [11] Needham SA, Wang GX, Liu HK. J Power Sources 2006;159:254–7. [12] Zhu YQ, Guo HZ, Wu Y, Cao CB, Tao S, Wu ZY. J Mater Chem A 2014;2:7904–11. [13] Cao F, Pan GX, Tang PS, Chen HF. Mater Res Bull 2013;48:1178–83. [14] Kim GP, Nam I, Park S, Park J, Yi J. Nanotechnology 2013;24 (p. 475402-1– 475402-8). [15] Cui ZH, Guo XX, Li H. J Power Sources 2013;244:731–5. [16] Wang Y, Qin QZ. J Electrochem Soc 2002;149:A873–8. [17] Ai L, Fang GJ, Yuan LY, Liu NS, Wang MJ, Li C, et al. Appl Surf Sci 2008;254:2401–5. [18] Yang ZG, Zhu LP, Guo YM, Ye ZZ, Zhao BH. Thin Solid Films 2011;519:5174–7. [19] Yang M, Pu HF, Zhou QF, Zhang Q. Thin Solid Films 2012;520:5884–8. [20] Cao L, Zhu LP, Ye ZZ. J Phys Chem Solids 2013;74:668–72. [21] Zhong J, Wang XL, Xia XH, Gu CD, Xiang JY, Zhang J, et al. J Alloys Compd 2011;509:3889–93. [22] Chen Z, Xiao A, Chen Y, Zuo C, Zhou S, Li L. Mater Res Bull 2012;47:1987–90. [23] Aricò AS, Bruce P, Scrosati B, Tarascon JM, van Schalkwijk W. Nat Mater 2005;4:366–77. [24] Chai H, Chen X, Jia DZ, Bao SJ, Zhou WY. Mater Res Bull 2012;47:3947–51. [25] Chen X, Zhang NQ, Sun KN. Electrochem Commun 2012;20:137–40. [26] Xie D, Yuan WW, Dong ZM, Su QM, Zhang J, Du GH. Electrochim Acta 2013;92:87–92.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries Ling Cao a,b,n, Dongxiao Wang b, Rong Wang b a Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China b College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 May 2014 Accepted 18 June 2014 Available online 25 June 2014
We reported on NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries. The structural, morphological and electrochemical properties of the films were studied. The results demonstrated that the film exhibits high initial columbic efficiency of 73.6%, high reversible capacity and rather good cycling performance. The discharge specific capacity remained at 687 mA h g 1 at a current density of 100 mA g 1 after 50 cycles. The unique nanoporous structure and enhanced electrical contact between the substrate and active materials could be responsible for the improvement of electrochemical properties. & 2014 Elsevier B.V. All rights reserved.
Keywords: Thin films Semiconductors Physical vapor deposition XPS
1. Introduction Rechargeable lithium-ion batteries (LIBs) have been identified as the most promising power sources for portable electronic devices and hybrid vehicles [1]. Massive efforts have been focused on searching potential materials and fabrication techniques for developing the next-generation LIB electrodes [2]. As novel conversion anode materials, transition-metal oxides, such as Fe3O4 [3], Co3O4 [4], MnO2 [5], CuO [6], and NiO [7], have attracted increasing attention due to their much higher capacity than that of commercial graphite anodes [8]. Among these materials, NiO is one of the most extensively studied anode materials because of its high theoretical energy capacity (718 mA h g 1), earth abundance, chemically and thermally stable, and environmentally benign [9]. To date, many nanostructured NiO with various morphologies, such as nanoflake [10], nanotube [11], nanosheet [12], nanowall [13], and nanoparticle [14], have been investigated. Recently, nanocrystalline thin film anodes grown directly on conducting substrates exhibited excellent electrochemical performance due to its enhanced electrical contact between the substrate and active materials, shortened diffusion lengths for lithium ion, and good structural stability [15]. What is more, the crystallinity and film thickness can be effectively controlled and the intrinsic
n Corresponding author at: Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, People's Republic of China. Tel./fax: þ 86 351 6018030. E-mail address: [email protected] (L. Cao).
http://dx.doi.org/10.1016/j.matlet.2014.06.114 0167-577X/& 2014 Elsevier B.V. All rights reserved.
electrochemical properties can be obtained by eliminating the interference from irregular shape and size distribution of active particles as well as from the additives [16]. However, there is no report, to the best of our knowledge, on the NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for LIBs. In this letter, NiO thin films were prepared on Cu foils at room temperature by pulsed laser deposition. The structural, morphological and electrochemical properties of the films were investigated.
2. Experimental details NiO thin films were prepared by pulsed laser deposition using a sintered NiO ceramic target. A KrF excimer laser (Compex102, 248 nm, 25 ns) was employed as a ablation source. The laser repetition rate and the energy per pulse were 5 Hz and 300 mJ, respectively. The deposition was carried out in an oxygen pressure of 5 Pa. All the films were deposited at room temperature for 60 min and had an approximate film thickness of 200 nm. The crystal structures of the films were investigated by X-ray diffraction (XRD) using a XPERT-PRO system with a CuKα (λ ¼1.5406 Å) source. The surface morphology and the film thickness were characterized using field emission scanning electron microscopy (FE-SEM; HITACHIS-4800). The chemical bonding state of the films was analyzed by x-ray photoelectron spectroscopy (XPS) (Thermo ESCALAB 250, AlKα radiation source hν ¼1486.6 eV). The electrochemical performances of the film were measured by two-electrode CR-2025-type coin cells. The cells were assembled in
358
L. Cao et al. / Materials Letters 132 (2014) 357–360
an argon-filled glove box using the Cu foil-supported NiO films as working electrodes and lithium foil as counter-electrodes. The electrolyte was 1 M LiPF6 in a 1:1 (w/w) mixture of ethylene carbonate (EC) and dimethyl carbonate (DME). The galvanostatic charge–discharge tests were performed on the LAND battery program-control test system. Cyclic voltammetric (CV) measurements were evaluated on a CHI660C electrochemical workstation with a scan rate of 0.1 mV s 1 between 0 and 3 V (vs. Li/Li þ ).
3. Results and discussion Fig. 1 shows the XRD pattern of NiO film grown directly on Cu foil at room temperature. Removing strong peaks of the cubic
crystal Cu, only a broad peak indexed to (111) reflection of the cubic NiO structure can be observed. No extra phases related with nickel and copper compounds can be detected, suggesting that pure NiO film has grown on the Cu foil surface. For comparison, the XRD pattern of NiO film prepared on quartz substrate at the same conditions is also displayed in Fig. 1. It can be seen that the film exhibits well-resolved diffraction peaks indexed as the (111) and (200) reflections of the cubic NiO structure. Fig. 2(a) and (b) shows the surface morphologies of NiO films grown on quartz substrate and Cu foil, respectively. It can be seen that the film on quartz substrate presents a smooth and highly compact surface, which implies a relatively good crystallinity. However, the surface of the film on Cu foil shows higher roughness and less compact, and most of the irregular rounded grains including numerous pores in nanometer scale are separated from each other with nano-voids. Fig. 3 provides the XPS spectra of Ni 2p and O 2p core levels of the NiO film grown on Cu foil. It can be observed from Fig. 3 (a) that the Ni 2p spectrum exhibits the characteristic double peak 2p3/2 and 2p1/2 main lines. The additional peak located at around 855.2 eV is the satellite of Ni 2p3/2 [17]. The double peak structure in the 2p3/2 main line is ascribed to the presence of two types of states, namely Ni2 þ and Ni3 þ for the lower and higher binding energy peaks, respectively [18]. Here, the Ni3 þ only refers to a structure containing Ni2 þ ions with holes and hence does not indicate an existence of Ni2O3 phase in the film [19]. Fig. 3 (b) shows the O 1s spectrum of the film and the O 1s peaks can
Fig. 1. XRD patterns of NiO films grown on quartz substrate and Cu foil.
Fig. 2. Surface morphologies of NiO films grown on (a) quartz substrate and (b) Cu foil.
Fig. 3. XPS spectra of (a) Ni 2p and (b) O 2p core levels of NiO film grown at Cu foil.
L. Cao et al. / Materials Letters 132 (2014) 357–360
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Fig. 4. (a) Cyclic voltammograms of NiO film at a scan rate of 0.1 mV s 1 for the second cycle. (b) Charge and discharge profiles of NiO film at a current density of 100 mA g 1. (c) Cycling performances and coulombic efficiency of NiO film during cycling. (d) Capacity retention for the NiO film at different current densities.
be fitted by three binding energy curves centered at 529.4 (OI), 531.3 (OII), and 532.5 eV (OIII), which correspond to the oxygen ions in the fully oxidized surrounding, the oxygen ions in oxygen deficient regions, and OH related species or the loosely bound oxygen from chemisorbed H2O on the surface, respectively [20]. The coin-type cell configuration was used to evaluate the electrochemical performance of the NiO film as an anode electrode. Fig. 4(a) displays the cyclic voltammetry (CV) tests of the thin film electrode at a scan rate of 0.1 mV s 1 at the second cycle. During the cathodic/anodic scanning, the reduction peaks located at 0.98 V and 1.35 V correspond to the initial reduction of NiO to metallic Ni and the formation of a partially reversible solid electrolyte interphase (SEI) layer, respectively [21]. The oxidation peaks at around 0.5 V and 1.41 V are associated with the partial decomposition of SEI layer on the NiO surface, while an additional oxidation peak at 2.31 V originates from the decomposition of Li2O and nickel converted back to NiO [22]. The discharge/charge curves of the NiO film electrode at a low current density of 100 mA g 1 are shown in Fig. 4(b). During the discharge process, the voltage decreases rapidly to 0.8 V where a plateau region sets in and continues until a discharge capacity of 1200 mA h g 1 is reached. Then, another slope can be found at 0.6 V with a total first discharge capacity of 1510 mA h g 1, which is higher than the theoretical value. The extra capacity could be ascribed to the formation of SEI in the first discharge process [22]. The first charge capacity is approximately 1112 mA h g 1, which is much less than that of the first discharge. The incomplete decomposition of the SEI and Li2O should be responsible for the irreversible capacity loss between the first discharge and charge [23]. The corresponding initial columbic efficiency is about 73.6%, which is comparable to or even higher than the previous reported values [10,14,21,24].
Fig. 4(c) shows the capacity retention properties of the NiO film electrode. The discharge specific capacity decreases to 1134 mA h g 1 in the 2nd cycle and remains at 687 mA h g 1 after 50 cycles. Moreover, the coulombic efficiency of the electrode keeps over 93% after the 2nd cycle. Fig. 4(d) displays reversible capacities of NiO film at different current densities. It can be seen that the reversible capacity decreases slowly with increase in the discharge/charge current densities. Outstanding capacities of 640 and 382 mA h g 1 could be obtained at the current density of 200 and 800 mA g 1, respectively. When the current density returns to 200 mA g 1, the film can still deliver a reversible capacity of 492 mA h g 1. These results clearly indicate that the NiO film possesses excellent electrochemical performance, which could be related to its unique microstructural characteristics. The nanopores inside the NiO film as well as the nano-voids between adjacent grains can provide structural flexibility for volume change during the charge–discharge process [25]. In addition, the close contact of the film grown directly on the current collector further allows for a fast charge transfer pathway, which efficiently decreases the contact resistance and hence improves the electrode capacity [26].
4. Conclusions In summary, pure NiO thin films grown directly on Cu foils by pulsed laser deposition as anode materials for lithium ion batteries have been investigated. The as-prepared NiO film possesses excellent electrochemical performance comparable to or even better than the NiO anodes reported previously, which could be related to its unique microstructural characteristics and enhanced
360
L. Cao et al. / Materials Letters 132 (2014) 357–360
electrical contact between the substrate and active materials. We expect that the electrochemical properties of the films could be further improved by applying more optimalized deposition conditions. Therefore, the pulsed laser deposited NiO thin films are promising candidates for the applications in lithium-ion batteries. Acknowledgments This work is supported by the National Natural Science Foundation of China (Grant no. 11347157) and the Qualified Personnel Foundation of Taiyuan University of Technology (Grant no. tyut-rc201247a). References [1] [2] [3] [4] [5] [6] [7]
Ma Y, Ji G, Ding B, Lee JY. J Mater Chem 2012;22:24380–5. Wu HB, Chen JS, Hng HH, Lou XW. Nanoscale 2012;4:2526–42. Wu H, Du L, Wang JZ, Zhang H, Yang DR. J Power Sources 2014;246:198–203. Fang F, Bai L, Liu YG, Cheng SB, Sun HY. Mater Lett 2014;125:103–6. Kundu M, Ng CCA, Petrovykh DY, Liu LF. Chem Commun 2013;49:8459–61. Qiu DF, Zhao B, Lin ZX, Pu L, Pan LJ, Shi Y. Mater Lett 2013;105:242–5. Wang XH, Qiao L, Sun XL, Li XW, Hu DK, Zhang Q, et al. J Mater Chem A 2013;1:4173–6.
[8] Jiang J, Li YY, Liu JP, Huang XT. Nanoscale 2011;3:45–58. [9] Ma JM, Yang JQ, Jiao LF, Mao YH, Wang TH, Duan XC, et al. CrystEngComm 2012;14:453–9. [10] Wu H, Xu M, Wu HY, Xu JJ, Wang YL, Peng Z, et al. J Mater Chem 2012;22:19821–5. [11] Needham SA, Wang GX, Liu HK. J Power Sources 2006;159:254–7. [12] Zhu YQ, Guo HZ, Wu Y, Cao CB, Tao S, Wu ZY. J Mater Chem A 2014;2:7904–11. [13] Cao F, Pan GX, Tang PS, Chen HF. Mater Res Bull 2013;48:1178–83. [14] Kim GP, Nam I, Park S, Park J, Yi J. Nanotechnology 2013;24 (p. 475402-1– 475402-8). [15] Cui ZH, Guo XX, Li H. J Power Sources 2013;244:731–5. [16] Wang Y, Qin QZ. J Electrochem Soc 2002;149:A873–8. [17] Ai L, Fang GJ, Yuan LY, Liu NS, Wang MJ, Li C, et al. Appl Surf Sci 2008;254:2401–5. [18] Yang ZG, Zhu LP, Guo YM, Ye ZZ, Zhao BH. Thin Solid Films 2011;519:5174–7. [19] Yang M, Pu HF, Zhou QF, Zhang Q. Thin Solid Films 2012;520:5884–8. [20] Cao L, Zhu LP, Ye ZZ. J Phys Chem Solids 2013;74:668–72. [21] Zhong J, Wang XL, Xia XH, Gu CD, Xiang JY, Zhang J, et al. J Alloys Compd 2011;509:3889–93. [22] Chen Z, Xiao A, Chen Y, Zuo C, Zhou S, Li L. Mater Res Bull 2012;47:1987–90. [23] Aricò AS, Bruce P, Scrosati B, Tarascon JM, van Schalkwijk W. Nat Mater 2005;4:366–77. [24] Chai H, Chen X, Jia DZ, Bao SJ, Zhou WY. Mater Res Bull 2012;47:3947–51. [25] Chen X, Zhang NQ, Sun KN. Electrochem Commun 2012;20:137–40. [26] Xie D, Yuan WW, Dong ZM, Su QM, Zhang J, Du GH. Electrochim Acta 2013;92:87–92.