Simple preparation of petal-like TiO2 nanosheets as anode materials for lithium-ion batteries

Simple preparation of petal-like TiO2 nanosheets as anode materials for lithium-ion batteries

Available online at CERAMICS INTERNATIONAL Ceramics International 40 (2014) 16805–16810 Shor...

2MB Sizes 0 Downloads 18 Views

Available online at


Ceramics International 40 (2014) 16805–16810

Short communication

Simple preparation of petal-like TiO2 nanosheets as anode materials for lithium-ion batteries Feixiang Wu, Zhixing Wangn, Xinhai Li, Huajun Guo School of Metallurgy and Environment, Central South University, Changsha 410083, PR China Received 16 June 2014; received in revised form 10 July 2014; accepted 11 July 2014 Available online 19 July 2014

Abstract We demonstrate a simple and green approach for the synthesis of one kind of anatase TiO2 nanosheets. The method is based on a hydrothermal method under normal atmosphere without using the complex Teflon-lined autoclave, high concentrations NaOH solution and long reaction time. The as-prepared materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and electrochemical measurements. The obtained anatase TiO2 nanosheets show excellent performance. There is one pair of potential plateaus at 1.7 and 1.9 V in the process of Li insertion and extraction, and the initial Li insertion/extraction capacities are 382 and 326 mA h g  1 at the current density of 20 mA g  1, respectively. After 50 cycles, the TiO2 retains 93% of the initial charge capacity at the current density of 400 mA g  1. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: TiO2; Anode material; Lithium-ion batteries; Nanosheet; Nanostructured

1. Introduction Lithium-ion battery has gained considerable popularity due to its eco-friendly property, in comparison to the environmental damage (global warming and air pollution) caused by petroleum industry, gradual depletion of oil resources and the increasing demands of electronic devices carried by battery energy. For example, the clean energy of rechargeable lithium-ion (Li-ion) cells has been thought of as a next generation motive power for electronic and telecommunication equipment and power tools have paved their way to industrial equipment and transportation markets because of their high energy and high power density, long cycle life, and ambient temperature operation [1–4]. Graphite is widely used as the anode material for Li-ion batteries, which currently cannot meet the requirements in these areas in terms of high power density, long cycle life, and safety. However, the carbon negative electrode used in rechargeable lithium-ion batteries suffers from a number of problems. Firstly, most notably, the potential for lithium intercalation is close to that of the Li þ /Li redox couple, leading to the possibility n

Corresponding author. Tel./fax: þ 86 731 88836633. E-mail address: [email protected] (Z. Wang). 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

of lithium plating during cycling which would cause some safety problems (e.g. short circuit, fire and explosion). Secondly, electrolytes must be consumed to form SEI layer (essential to the operation of the carbon electrode) during the first charge cycle. The stability of the SEI can greatly affect the battery's capacity and power retention as well as cycle life [5–9]. Finally, during full lithium insertion and extraction, the graphite anode undergoes a 9 vol% variation, which may lead to undesirable thickness changes and cause mechanical degradation of the anode, resulting in a poor cycling stability. Titanium oxide (TiO2) has been widely studied as a semiconducting metal oxide due to its great application potential in many fields, such as sensors, photocatalysis, solar cells, and lithium-ion batteries. There has been increasing interest in developing nanoscale titanate-based electrodes for application in electrochemical devices and, in particular, rechargeable lithium batteries, due to growing promise built by the nanostructured systems for future development in Li-ion battery technology [10–12]. TiO2 nanotube, TiO2 nanorod, TiO2 (B) nanowire and hydrogen titanate have been studied by many researchers in order to yield high energy density, large capacity, high rate performance and long cycle life, basically because of their shorter length for both electronic and Li þ ions


F. Wu et al. / Ceramics International 40 (2014) 16805–16810

transport, and better accommodation of the strain of Li insertion/ extraction. Recently, nanostructured TiO2 were often prepared by an alkaline–hydrothermal treatment and subsequent acid washing. TiO2 particles and high concentrations NaOH solution were normally mixed together, and then the mixture was added into a Teflon-lined autoclave to be autoclaved at 110–200 1C for 5–72 h [13–22]. In addition, nanostructured TiO2 can be synthesized by a conventional solid-state reaction and ion-exchange process. The solid-state reaction was done between TiO2 and alkali metal carbonates (Na2CO3 or K2CO3) at 800–1000 1C for 20–48 h [23–26]. Especially, TiO2 nanosheets were often obtained in a high-temperature and high-pressure hydrothermal process [27–29]. In our previous paper, the coordination agent of H2O2 was firstly used in leaching of hydrolyzed titania residue decomposed from mechanically activated Panzhihua ilmenite leached by hydrochloric acid [30]. We used the hydrogen peroxide as a coordination agent which can provide a kind of ligand (O2– 2 ion) to dissolve Ti from the hydrolyzed titania precipitate. This method using coordination agent of H2O2 also has been used in our preparation of hydrogen titanate and TiO2 nanowires by using NaOH before boiling process [31–33]. In this paper, we propose a simple, rapid and improved process to synthesize TiO2 nanosheets by using LiOH instead of NaOH. We use a special peroxo-titania ammonium solution to prepare the precursor nanosheets by means of simple boiling of titanium peroxide solution instead of alkaline–hydrothermal treatment of TiO2 and solid-state reaction at high temperature. TiO2 nanosheets with excellent electrochemical performance can be successfully synthesized without using the complex Teflonlined autoclave, high concentrations NaOH solution, high temperature and long reaction time. 2. Experimental 2.1. Synthesis and characterization The precursor nanosheets were prepared according to our previously reported procedure [31–34]. In this experiment, petallike TiO2 nanosheets were fabricated by means of simple boiling of lithium titanium peroxide ammonium solution, followed by a low temperature and short time solid-state calcination. The H2O2 played a very important role in dissolving low cost inorganic Ti resources to yield a special solution at room temperature. Meanwhile, owing to the decomposition of H2O2 in this solution, we got a special nanostructured TiO2. The special lithium titanium peroxide solution was obtained at room temperature according to Eq. (1). Firstly, 5.87 g of H2TiO3 was added into 100 ml deionized water and white slurry was observed. After stirring for 5 min, 37 ml of 30 wt% H2O2 solution and 44 ml of 10 wt% ammonia solution were added into the slurry. After 30 min the white slurry was dissolved, forming a yellow–green solution A. Secondly 10.24 g of 95 wt% LiOH  H2O was added into 50 ml de-ionized water, and then lithium hydroxide solution B was obtained. At last, solutions A and B were mixed in a 1000 ml beaker and then stirred for 10 min. The prepared precursor solution was then boiled to boiling point under vigorous stirring in an oil bath. One hour later, a pale yellow slurry was formed

and filtrated according to Eq. (2). Finally, the pale yellow product was washed by 2 wt% HNO3 several times and then dried at 100 1C for more than 8 h to obtain the precursor nanosheets. The TiO2 nanosheets were produced by calcining the precursor at 300 1C for 3 h in air. H2TiO3 þ H2O2 þ LiOH þ NH3  H2O -Lix(NH4)y(TiOz)(O2)j(OH)k (dissoluble) þ H2O



Lix ðNH4 Þy ðTiOz ÞðO2 Þj ðOHÞk ⟶ ðLix H2  x ÞTi2 O5  2H2 O ↓ðadsorbed NH4 þ and O2 2  Þ þ NH3 ↑ þ H2 O þ O2 ↑


The as-prepared materials are characterized by XRD, TG–DTA, SEM, BET and TEM. The precursor was analyzed by using a simultaneous TG–DTA apparatus SDT Q600 (TA instruments). The SEM images of particles were observed with scanning electron microscopy (SEM, Sirion 200). Powder X-ray diffraction (XRD, Rint-2000, Rigaku) using CuKα radiation was employed to identify the crystalline phase of the precursor and TiO2 nanosheets. The TEM images of the prepared powders were measured by a transmission electron microscope (Tecnai G12). 2.2. Electrochemical measurement The electrochemical performance was performed using a twoelectrode coin-type cell (CR2025) of Li|LiPF6 (EC:EMC:DMC¼ 1:1:1 in volume)|TiO2. The working cathode was composed of 80 wt% TiO2 powders, 10 wt% acetylene black as conducting agent, and 10 wt% poly(vinylidene fluoride) as binder. After being blended in N-methyl pyrrolidinone, the mixed slurry was spread uniformly on a thin copper foil and dried in vacuum for 12 h at 120 1C. A metal lithium foil was used as the anode. Electrodes were punched in the form of 14 mm diameter disks, and the typical positive electrode loading was about 1.3 mg cm  2. A polypropylene micro-porous film was used as the separator. The assembly of the cells was carried out in a dry argon-filled glove box. The cells were charged and discharged over a voltage range of 1.0–3.0 V versus Li/Li þ electrode at room temperature. 3. Results and discussion 3.1. Morphology and structure of the materials Fig. 1(a) shows the X-ray diffraction (XRD) patterns of the precursor and as-produced TiO2. The precursor has many peaks, indicating crystalline phase of lithium titanium oxide hydrate ((LixH2  x)Ti2O5  2H2O, JCPDS Card No. 47-0123); however, the Li ions have been washed by aqueous HNO3. As we can see clearly in Fig. 1(b), there is only one distinct step of weight loss. The observed major sharp weight loss of 15.05% occurs from 30 to 450 1C on the TG–DTA curve due to the vaporization of adsorbed water molecules and decomposition of the adsorbed NH4þ and O2– 2 , Ti–OH and Li–OH bonds in the precursor. After calcination at 300 1C for 3 h, the phase of lithium titanium oxide hydrate changes into TiO2 which shows anatase TiO2 (JCPDS Card No. 65-5714). Compared to the precursor, the as-produced TiO2 shows a little higher crystallinity due to the calcination at

F. Wu et al. / Ceramics International 40 (2014) 16805–16810


Fig. 1. (a) X-ray diffraction of the produced samples: produced TiO2 and its precursor; (b) TG–DTA pattern of the precursor; SEM micrographs of (c) the precursor and (d) produced TiO2; (e) the enlarged SEM image of the produced TiO2 nanosheets and (f) BET surface area of produced TiO2 nanosheets powder.

300 1C. However, the produced anatase TiO2 did not show very sharp peaks in XRD result, which is due to little amount of residual bonding water which cannot be fully removed by the calcination at 300 1C from TG–DTA result. Fig. 1(c and d) shows SEM images of the precursor (c) and as-prepared TiO2 (d). When boiling the lithium titanium peroxide solution, the H2O2 is gradually decomposed. Due to the interfacial tension, van der Waals attractive forces, and other factors, the titanate nucleus would aggregate together to form “multi-nuclei.” Subsequently, the titanate “multi-nuclei” gradually grow up and assemble into a micro-spherical shape along with H2O2 decomposition. From Fig. 1(c), porous spherical particles or microspheres with about a diameter of 1 μm and

rough surface are observed obviously in flower-like morphology. As shown in Fig. 1(d), the morphology images of the precursor and as-prepared TiO2 have similar flower-like structure. The produced TiO2 maintains the morphology of the precursor, which is attributed to the low calcined temperature. The enlarged image of the particles of produced TiO2 shows that the spherical particles or microspheres are composed of aggregations of petal-like nanosheets, which are consistent with the TEM images (Fig. 2(a, b and c)). As shown in Fig. 2, the morphology images of produced TiO2 have flower-like structure with aggregations of nanosheets. These nanosheets are petalshaped with the edge length in the range of 20–50 nm and the thickness is about 5 nm in Fig. 2(c). The SAED pattern in Fig. 2


F. Wu et al. / Ceramics International 40 (2014) 16805–16810

Fig. 2. TEM images of (a) the precursor and (b) produced TiO2; (c) the enlarged TEM image of the produced TiO2 nanosheets; (d) SAED image of produced TiO2 and (e) HRTEM image of the produced TiO2 nanosheets.

(d), with several marked rings corresponding to TiO2 (1 0 1), (0 0 4), (2 0 0) and (2 1 1) planes, can be indexed to anatase TiO2. Fig. 2(e) shows the HRTEM images of produced TiO2 nanoparticles. Obvious lattice fringe with a lattice spacing of anatase TiO2 (d101 ¼ 3.511 Å) is found, which confirms the single-anatase phase in the obtained TiO2 particles prepared from relatively low temperature heat treatment. Besides, we can easily see the marked nanocrystallite which shows the size of 12 nm. The Brunauer–Emmett–Teller (BET) specific surface area (SSA) of the electrode particles is an important parameter that determines their electrochemical properties. Fig. 1(f) shows nitrogen sorption curves collected at 77 K on produced TiO2 nanosheets. The result shows that its BET SSA is 28.4 m2/g, which should provide shorter diffusion distance for Li ions and be beneficial for electrochemical performance of the electrode. Fig. 3(a) shows the initial three potential–capacity profiles of anatase TiO2 at the current density of 20 mA g  1. The charge/ discharge curves exhibit one pair of visible and flat voltage plateaus at about 1.7 and 1.9 V for discharging and charging, respectively. In the first discharge process, anatase TiO2 shows 382 mA h g  1 at a current density of 20 mA g  1. The subsequent Li þ extraction of anatase TiO2 shows a capacity of 326 mA h g  1. It displays a relative low coulombic efficiency of 85.3% (ratio of extraction to insertion capacity) and a large irreversible capacity. However, in the subsequent two cycles, the discharge/charge curves gradually coincided with each other, indicating a lower irreversible capacity and a higher coulombic efficiency of 95%. The fade of the curve between

the first and subsequent cycles shows the large irreversible process after the insertion of Li into TiO2 anatase structure. This phenomenon is tentatively ascribed to the side reaction of trace surface adsorbed water because of the large specific surface area. The trace water in the anatase TiO2 could react irreversibly with lithium forming Li2O on inside the interlayers or on surface, which is the major reason for the larger capacity loss. The discharging/charging tends to be stabilized in the following cycles, because the binding water is consumed gradually during the first several cycles [35,36]. Fig. 3(b) shows the discharge and charge capacities of TiO2 at the different current densities. At all current densities, the charge/ discharge curves exhibit visible voltage plateaus. The initial discharge capacities of TiO2 are 381, 273, 236 and 194 mA h g  1 at the current densities of 20, 100, 200 and 400 mA g  1, respectively. Moreover, the cycling performance of TiO2 is shown in Fig. 3(c). As shown, the TiO2 shows an excellent cycling performance. After 50 cycles, the TiO2 retains 81%, 78% and 93% of the initial charge capacity at the current densities of 100, 200 and 400 mA g  1, respectively. 4. Conclusions In conclusion, the nanostructured petal-like TiO2 nanosheets are successfully synthesized by a very facile and green method through a special solution system. Owing to the special lithium titanium peroxide solution the produced petal-like TiO2 nanosheets show 0.5–1 mm microspheres with high BET

F. Wu et al. / Ceramics International 40 (2014) 16805–16810


Fig. 3. (a) First three potential–capacity profiles of anatase TiO2 nanosheets at the charge/discharge current density of 20 mA g  1; (b) the initial charge/discharge curves of anatase TiO2 at the different current densities in the voltage range of 1.0–3.0 V and (c) cycling performance of anatase TiO2 at different current densities.

SSA of 28.4 m2/g, which are composed of aggregations of petal-like nanosheets with the edge length in the range of 20– 50 nm and the thickness of 5 nm, and which shows excellent electrochemical performance. As mentioned above, this simple and ultrafast method is a promising technique to prepare TiO2 nanoparticles. This high-performance petal-like and nanostructured anode material coupled with the simple, relatively low temperatures, low cost, and environmentally benign nature of the preparation method may make this material attractive for large applications in high-performance rechargeable Li-ion batteries and high-power electrochemical supercapacitors. Acknowledgment Supported by Hunan Provincial Innovation Foundation for Postgraduate (CX2012A004), China Scholarship Council (201206370083), Young Scholarship Award for doctoral candidate funded by Ministry of Education (134376140000019) and the National Basic Research Program of China (Grant no. 2014CB643406). References [1] N. Nitta, G. Yushin, High-capacity anode materials for lithium-ion batteries: choice of elements and structures for active particles,, Part. Part. Syst. Charact. 4 (2014) 317–336. [2] N.S. Choi, Z. Chen, S.A. Freunberger, X. Ji, Y.K. Sun, K. Amine, G. Yushin, L.F. Nazar, J. Cho, P.G. Bruce, Challenges facing lithium batteries and electrical double-layer capacitors, Angew. Chem. Int. Ed. 51 (2012) 9994.

[3] F.X. Wu, J.T. Lee, A. Magasinski, H. Kim,, G. Yushin, Solution-based processing of graphene–Li2S composite cathodes for lithium-ion and lithium–sulfur batteries, Part. Part. Syst. Charact. 31 (2014) 639. [4] L.W. Ji, Z. Lin, M. Alcoutlabi, X.W. Zhang, Recent developments in nanostructured anode materials for rechargeable lithium-ion batteries, Energy Environ. Sci. 4 (2011) 2682. [5] H. Yang, H. Bang, K. Amine, Investigations of the exothermic reactions of natural graphite anode for Li-ion batteries during thermal runaway, J. Electrochem. Soc. 152 (2005) A73. [6] H. Yang, S. Amiruddin, H. Bang, A review of Li-ion cell chemistries and their potential use in hybrid electric vehicles, J. Ind. Eng. Chem. 12 (2006) 12. [7] H. Yang, X.D. Shen, Dynamic TGA–FTIR studies on the thermal stability of lithium/graphite with electrolyte in lithium-ion cell, J. Power Sources 167 (2007) 515. [8] M. Lu, H. Cheng, Y. Yang, A comparison of solid electrolyte interphase (SEI) on the artificial graphite anode of the aged and cycled commercial lithium ion cells, Electrochim. Acta 53 (2008) 3539. [9] R. Fong, U. von Sacken, Studies of lithium intercalation into carbons using nonaqueous electrochemical cells, J. Electrochem. Soc. 137 (1990) 2009. [10] L. Kavan, M. Gr̈atzel, S.E. Gilbert, C. Klemenz, H.J. Scheel, Electrochemical and photoelectrochemical investigation of single-crystal anatase, J. Am. Chem. Soc. 118 (1996) 6716. [11] I. Exnar, L. Kavan, S.Y. Huang, M. Gr̈atzel, Novel 2 V rocking-chair lithium battery based on nano-crystalline titanium dioxide, J. Power Sources 68 (1997) 720. [12] Y.S. Hu, L. Kienle, Y.G. Guo, J. Maier, High lithium electroactivity of nanometer-sized rutile TiO2, Adv. Mater. 18 (2006) 1421. [13] J.W. Xu, C.H. Jia, B. Cao, W.F. Zhang, Electrochemical properties of anatase TiO2 nanotubes as an anode material for lithium-ion batteries, Electrochim. Acta 52 (2007) 8044. [14] H. Zhang, X.P. Gao, G.R. Li, Electrochemical lithium storage of sodium titanate nanotubes and nanorods, Electrochim. Acta 53 (2008) 7061. [15] G. Armstrong, A.R. Armstrong, J. Canalesb, P.G. Bruce, TiO2(B) nanotubes as negative electrodes for rechargeable lithium batteries, Electrochem. Solid-State Lett. 9 (2006) A139.


F. Wu et al. / Ceramics International 40 (2014) 16805–16810

[16] M.D. Wei, Z.M. Qi, M. Ichihara, I. Honma, H.S. Zhou, Ultralong singlecrystal TiO2–B nanowires: synthesis and electrochemical measurements, Chem. Phys. Lett. 424 (2006) 316. [17] A.R. Armstrong, G. Armstrong, J. Canales, P.G. Bruce, TiO2–B nanowires as negative electrodes for rechargeable lithium batteries, J. Power Sources 146 (2005) 501. [18] S.J. Bao, Q.L. Bao, C.M. Li, Z.L. Dong, Novel porous anatase TiO2 nanorods and their high lithium electroactivity, Electrochem. Commun. 9 (2007) 1233. [19] B. Zhao, F. Chen, W.W. Qu, J.L. Zhang, The evolvement of pits and dislocations on TiO2–B nanowires via oriented attachment growth, J. Solid State Chem. 182 (2009) 2225. [20] J.R. Li, Z.L. Tang, Z.T. Zhang, H-titanate nanotube: a novel lithium intercalation host with large capacity and high rate capability, Electrochem. Commun. 7 (2005) 62. [21] K.V. Baiju, S. Shukla, S. Biju, M.L.P. Reddy, K.G.K. Warrier, Hydrothermal processing of dye-adsorbing one-dimensional hydrogen titanate, Mater. Lett. 63 (2009) 923. [22] M.D. Wei, K.W. Wei, M. Ichihara, H.S. Zhou, High rate performances of hydrogen titanate nanowires electrodes, Electrochem. Commun. 10 (2008) 1164. [23] G.N. Zhu, C.X. Wang, Y.Y. Xia, Structural transformation of layered hydrogen trititanate (H2Ti3O7) to TiO2(B) and its electrochemical profile for lithium-ion intercalation, J. Power Sources 196 (2011) 2848. [24] M. Plodinec, I. Friščić, N. Tomašić, D.S. Su, J. Zhang, A. Gajović, The mechanochemical stability of hydrogen titanate nanostructures, J. Alloys Compd. 499 (2010) 113. [25] T.P. Feist, P.K. Davies, The soft chemical synthesis of TiO2 (B) from layered titanates, J. Solid State Chem. 101 (1992) 275. [26] M. Inaba, Y. Oba, F. Niina, Y. Murota, Y. Ogino, A. Tasaka, K. Hirota, TiO2(B) as a promising high potential negative electrode for large-size lithium-ion batteries, J. Power Sources 189 (2009) 580.

[27] J.S. Chen, X.W. Lou, Anatase TiO2 nanosheet: an ideal host structure for fast and efficient lithium insertion/extraction, Electrochem. Commun. 11 (2009) 2332. [28] Y.F. Tang, L. Yang, Z. Qiu, J.S. Huang, Preparation and electrochemical lithium storage of flower-like spinel Li4Ti5O12 consisting of nanosheets, Electrochem. Commun. 10 (2008) 1513. [29] J.Z. Chen, L. Yang, S.H. Fang, Y.F. Tang, Synthesis of sawtooth-like Li4Ti5O12 nanosheets as anode materials for Li-ion batteries, Electrochim. Acta 55 (2010) 6596. [30] F.X. Wu, X.H. Li, Z.X. Wang, Hydrogen peroxide leaching of hydrolyzed titania residue prepared from mechanically activated Panzhihua ilmenite leached by hydrochloric acid, Int. J. Miner. Process. 98 (2011) 106. [31] F.X. Wu, X.H. Li, Z.X. Wang, A novel method to synthesize anatase TiO2 nanowires as an anode material for lithium-ion batteries, J. Alloys Compd. 509 (2011) 3711. [32] F.X. Wu, Z.X. Wang, X.H. Li, Hydrogen titanate and TiO2 nanowires as anode materials for lithium-ion batteries, J. Mater. Chem. 21 (2011) 12675. [33] F.X. Wu, X.H. Li, Z.X. Wang, Inexpensive synthesis of anatase TiO2 nanowires by a novel method and its electrochemical characterization, Mater. Lett. 65 (2011) 1514. [34] F.X. Wu, X.H. Li, Z.X. Wang, Petal-like Li4Ti5O12–TiO2 nanosheets as high-performance anode materials for Li-ion batteries, Nanoscale 5 (2013) 6936. [35] J.R. Li, Z. Tang, Z.T. Zhang, Preparation and novel lithium intercalation properties of titanium oxide nanotubes, Electrochem. Solid-State Lett. 8 (2005) A316. [36] Y.F. Wang, M.Y. Wu, W.F. Zhang, Preparation and electrochemical characterization of TiO2 nanowires as an electrode material for lithiumion batteries, Electrochim. Acta 53 (2008) 7863.