Materials Letters 246 (2019) 157–160
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
High volumetric capacity Fe2TeO6 as a novel anode material for alkali-ion batteries Biao Shang, Qimeng Peng, Xun Jiao, Guocui Xi, Xuebu Hu ⇑ College of Chemistry and Chemical Engineering, Chongqing University of Technology, Chongqing 400054, China
a r t i c l e
i n f o
Article history: Received 11 December 2018 Received in revised form 13 March 2019 Accepted 18 March 2019 Available online 18 March 2019 Keywords: Fe2TeO6 High volumetric capacity Alkali-ion batteries Nanocrystalline materials Energy storage and conversion
a b s t r a c t Tetragonal Fe2TeO6 (FTO) was successfully synthesized via simple calcination method and evaluated as anode materials of alkali-ion (lithium and sodium ion) batteries for the first time. Its physical properties were investigated by X-ray diffraction, scanning electron microscopy and transmission microscopy. Its electrochemical characteristics were studied via cyclic voltammetry and galvanostatic charge/discharge. The FTO materials exhibit excellent electrochemical performance in LIBs and SIBs. It can deliver a high reversible volumetric capacity of 1901.5 mA h cm3 at 100 mA g1 after 500 cycles as the anode of lithium-ion batteries. Furthermore, FTO shows impressive performance at higher current density. It maintains a discharge capacity of over 311.7 mA h cm3 even at a current density of 2000 mA g1. In addition, it also can deliver a discharge capacity of 574.9 mA h cm3 after 500 cycles at 100 mA g1 as the anode materials of sodium-ion batteries. These results indicate that FTO is a potential anode material for lithium ion and sodium ion batteries. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Rechargeable batteries are an indispensable part of our society and provide electrical energy on demand in a multitude of applications . In particular, lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) are two of the most important types of energy storage systems that have been investigated extensively owing to their advantages of environmental friendliness, high energy/power density and long cycle life . Since rechargeable batteries are the first choice of electrochemical energy storage, improving their cost and performance can greatly expand their applications and enable new technologies which depend on energy storage. Therefore, a great volume of research in energy storage field has thus far been in electrode materials [3,4]. In terms of cost and environmental impact, iron-based electrode materials seem the most ideal choice for large-scale battery systems . Iron chalcogenide (sulfide, selenide) has also attracted considerable attention because of the abundant reserves of iron and its wide range of compositions and phases [6,7]. Tellurium, a VIA group nonmetallic element, can alloy with Li and Na by forming Li2Te and Na2Te (theoretical capacity for LIBs and SIBs: 420 mAh g1), respectively. It has a large volumetric capacity of approximately 2621 mAh cm3 because of its high den-
⇑ Corresponding author. E-mail address: [email protected]
(X. Hu). https://doi.org/10.1016/j.matlet.2019.03.069 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
sity (6.24 g cm3) . In addition, Te shows a better electronic conductivity than S and Se, which have been attracted much attention as a potential research for rechargeable LIBs and SIBs. Herein, combining the abovementioned merits of Fe and Te, Fe2TeO6 have been prepared via solid state reaction and evaluated the electrochemical performance as the anode materials of LIBs and SIBs for the first time.
2. Results and discussion As shown in Fig. 1a, the diffraction peaks in FTO could be wellindexed to standard FTO diffraction peaks (PDF card No. 15-0686), which suggested FTO was successfully synthesized. No any other peaks delegating impure phases could be detected, indicating a high purity of the powder. Strong and sharp peaks revealed that the as-synthesized FTO were higher crystallinity. Fig. 1b and c demonstrated the SEM image of FTO. The morphology of the obtained FTO was bulk, which had a particle size of 50–200 nm but agglomerated significantly due to the high sintering temperature in solid state reaction. Fig. 1d and e displayed their TEM images. As shown in the images, lattice fringes of FTO (1 1 3) plains were observed, and the distance of the fringes was measured as 0.22 nm. Different electrochemical tests were conducted on FTO electrodes for LIBs and SIBs respectively. Firstly, CVs of the electrodes for the first three cycles were performed at a scan rate of
B. Shang et al. / Materials Letters 246 (2019) 157–160
Fig. 1. (a) XRD patterns, (b) low- and (c) high-magnification SEM images, (d) TEM and (e) HRTEM image of FTO.
0.1 mV s1. As shown in Fig. 2a, one irreversible peak at 1.37 V might be ascribed to the decomposition of FTO after the insertion of Li+, another reduction peak at 0.56 V could be observed in
the first and subsequent cycling that could be attributed to the conversion reaction of Fe2O3 and reversible reaction between TeO2 and Li (the ex-situ XRD data and analysis were given in SI).
Fig. 2. Electrochemical performance of FTO for LIBs. (a) CV curves at 0.1 mV s1; (b) Charge-discharge profiles at 100 mA g1; (c) Cycling performance at 100 mA g1, (d) Rate performance.
B. Shang et al. / Materials Letters 246 (2019) 157–160
On the other hand, oxidation peaks around 0.46 V and 1.50 V appeared in the first three cycle, which was mainly due to the reversible reaction of Fe2O3 and TeO2 with Li. The lithiumstorage properties were illustrated in Fig. 2b. The FTO performed an initial discharge capacity as high as 4357.9 mAh cm3 at 100 mA g1. A sudden fall rised up in the second cycle blame for the irreversible reactions like decomposition of electrolyte. After 200 cycles, FTO still held a reversible capacity of 1915.1 mAh cm3. The long cycling performance of the FTO electrode was characterized, as shown in Fig. 2c. There were still 1901.5 mAh cm3 after 500 cycles at 100 mA g1 with a coulombic efficiency of nearly 100%. Fig. 2d showed the capacity of the FTO under different current densities from 100 to 2000 mA g1, with the discharge capacities of 1789.3, 1447.7, 1039.9, 758.8, 582.1 and 311.7 mAh cm3 respectively. After 60 cycles at different current densities, the reversible capacity recovered up to 1521.1 mAh cm3 when the current returned to 100 mA g1, suggesting the good cycling stability. The electrochemical performances of sample in SIBs were demonstrated in Fig. 3. The CV curves were displayed in Fig. 3a. During the first discharge process, one reduction peak at 1.85 V might be ascribed to the decomposition of FTO after the insertion of Na which was irreversible, one reduction peak at 0.28 V could
be attributed to the conversion reaction of Fe2O3 and reversible reaction between TeO2 and Na, and 0.70 V arose in the first cycling that could be attributed to the formation of SEI. On the other hand, oxidation peaks around 1.60 V showed up in the sequent charge process, which was mainly due to the oxidation of Fe0 to Fe3+. Another reduction peak showed up at about 1.13 V owing to the reversible reaction between TeO2 and Na. (the detailed analysis was given in SI). Fig. 3b describes its cycling performances. The initial discharge capacity of FTO reached 1437.0 mAh cm3, then decreased to 656.5 mAh cm3 in the first charge cycle with a relatively low coulombic efficiency at 45.7%. After 200 cycles, the FTO contained a reversible capacity of 598.4 mA h cm3. Fig. 3c showed long cycle performances of FTO at 100 mA g1, it could be seen that the FTO delivered a reversible discharge capacity of 574.9 mAh cm3 after 500 cycles. Fig. 3d showed the rate performances under different current densities from 50 to 2000 mA g1, FTO reversibly delivered the capacities of 591.2, 470.4, 341.7, 298.0, and 190.1 mAh cm3, respectively. Notably, the electrochemical performance of FTO for SIBs was not as remarkable as that for LIBs, even at low charge/discharge current densities. The relatively low reversible capacity for sodium storage might be mostly attributed to the larger radius of Na+ (1.02 Å) than Li+ (0.59 Å), resulting in sluggish reaction kinetics .
Fig. 3. Electrochemical performance of FTO for SIBs. (a) CV curves at 0.1 mV s1; (b) Charge-discharge profiles at 100 mA g1; (c) Cycling performance at 100 mA g1; (d) Rate performance.
B. Shang et al. / Materials Letters 246 (2019) 157–160
Fig. 4. Kinetic analysis of lithium and sodium storage in FTO electrode: (a, e) CV curves of FTO electrode at various scan rates from 0.4 to 1.0 mV s1. (b, f) Linear plot of the relationship between log (Ip) and log (v) for both the anodic and cathodic scans of the FTO electrode. (c, g) Capacitive (black) and diffusion-controlled contribution at 1.0 mV s1. (d, h) The capacities of derived from capacitive contribution and battery contribution at different scan rates.
To investigate the lithium and sodium storage mechanism in FTO electrodes, CV curves at different scan rates were measured in Fig. 4. As shown in previous work, the capacitive contributions on the electrode surface to the total lithium or sodium storage capacity could be qualitatively confirmed by assessing the relationship between the scan rate (v) and recorded current (i) from CV curves measured at different sweep rates .
Log i ¼ b log v þ log a
Here, the slope b determined by the linear relationship between log v and log i described the ionic storage process of the electrode. For a diffusion-controlled process, b approaches 0.5, whereas it approached 1 for a capacitance-dominated process . Therefore, as shown in the Fig. 4b and f, the b values of the LIBs electrode (0.5098 and 0.4519 for peak a and b, respectively) demonstrated its favorable diffusion-controlled capacitive kinetics for LIBs. However, the relatively high b value (0.5489 and 0.7592 for peak a0 and b0 , respectively) of SIBs indicated that the pseudocapacitive characteristics of the electrode, which also explained the huge difference of CV between LIBs and SIBs. Through these analysis, the capacitive contributions at 1.0 mV s1 rates were further quantitatively evaluated in Fig. 4c and g. Typically, the fraction of SIBs of capacitive contribution was 58.5%, a little higher than that of LIBs (55.1%). In addition, the capacitive contribution ratios at other scan rates were also calculated, as shown in Fig. 4d and h. The proportion of capacitive process for LIBs were increasing from 36.4% to 55.1% as the increasing of scan rates from 0.4 mV s1 to 1 mV s1, while increasing from 42.3% to 58.5% for SIBs. 3. Conclusion In this work, tetragonal FTO was synthesized by a facile high temperature solid state method route and evaluated as anode materials for LIBs and SIBs for the first time. As anode materials of LIBs, the FTO delivered a fairly high discharge capacity of 1901.5 mA h cm3 after 500 cycles at 100 mA g1. Meanwhile, it maintained a discharge capacity of over 311.7 mA h cm3 even at a current density of 2000 mA g1. As anode materials of SIBs, it also could deliver a discharge capacity of 574.9 mA h cm3 after 500
cycles at 100 mA g1. Besides, electrochemical kinetics analysis indicated that the pseudocapacitive behavior proceed in the sodium storage which explained the different electrochemical mechanism between LIBs and SIBs. All those results illustrated that the FTO was expected a promising anode material for LIBs and SIBs. Conflict of interest statement All authors of this manuscript have declared no conflict of interest. Acknowledgments This work were supported by key project of science and technology research program of Chongqing Education Commission of China (No. KJZD-K201801103), Scientific and Technological Research Program of Chongqing Municipal Education Commission (KJ1600926) and Chongqing Research Program of Basic Research and Frontier Technology (cstc2016jcyjA0438). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.03.069. References:  P.K. Nayak, L. Yang, W. Brehm, P. Adelhelm, Angew. Chem. Int. Ed. 57 (2018) 102–120.  M. Li, J. Lu, Z. Chen, K. Amine, Adv. Mater. 30 (2018) 1800561.  N. Nitta, F. Wu, J.T. Lee, G. Yushin, Mater. Today 18 (2015) 252–264.  Y. Sun, S. Guo, H. Zhou, Adv. Energy Mater. (2018) 1800212.  J. Ma, X. Guo, Y. Yan, H. Xue, H. Pang, Adv. Sci. 5 (2018) 1700986.  K. Zhang, Z. Hu, X. Liu, Z. Tao, J. Chen, Adv. Mater. 27 (2015) 3305–3309.  Y. Chen, X. Hu, B. Evanko, X. Sun, X. Li, T. Hou, S. Cai, C. Zheng, W. Hu, G.D. Stucky, Nano Energy 46 (2018) 117–127.  A.R. Park, C.M. Park, ACS Nano 11 (2017) 6074–6084.  X. Ma, W. Zhao, J. Wu, X. Jia, Mater. Lett. 188 (2017) 248–251.  V. Augustyn, J. Come, M.A. Lowe, J.W. Kim, P.L. Taberna, S.H. Tolbert, H.D. Abruña, P. Simon, B. Dunn, Nat. Mater. 12 (2013) 518.  J. Wang, J. Polleux, J. Lim, B. Dunn, J. Phys. Chem. C 111 (2007) 14925–14931.