Sb2O3 Nanoparticle Coatings as Anode

Feb 8, 2007 - demonstrated that the co-deposition of 20-25% (w/w) Sb2O3 results from a ... cathode (due to protonation of liberated tartrate) in poorl...
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Chem. Mater. 2007, 19, 1170-1180

Electrodeposited Sb and Sb/Sb2O3 Nanoparticle Coatings as Anode Materials for Li-Ion Batteries Hanna Bryngelsson, Jonas Eskhult, Leif Nyholm,* Merja Herranen, Oscar Alm, and Kristina Edstro¨m Department of Materials Chemistry, The Ångstro¨m Laboratory, Uppsala UniVersity, P.O. Box 538, SE-751 21 Uppsala, Sweden ReceiVed October 17, 2006. ReVised Manuscript ReceiVed December 21, 2006

Galvanostatically electrodeposited coatings of pure Sb or co-deposited Sb and Sb2O3 nanoparticles, prepared from antimony tartrate solutions, were studied as anode materials in Li-ion batteries. It is demonstrated that the co-deposition of 20-25% (w/w) Sb2O3 results from a local pH increase at the cathode (due to protonation of liberated tartrate) in poorly buffered solutions. This causes precipitation of Sb2O3 nanoparticles and inclusion of some of the particles in the deposit where they become coated with a protecting layer of Sb. Chronopotentiometric cycling of the deposits, which also were characterized using, e.g., SEM, TEM, and XRD, clearly showed that the Sb2O3-containing deposits were superior as anode materials. While the Sb/Sb2O3 coatings exhibited a specific capacity close to the Sb theoretical value of 660 mA‚h‚g-1 during more than 50 cycles, the capacity for the Sb coatings gradually decreased to about 250 mA‚h‚g-1. This indicates that the influence of the significant volume changes present upon the formation and oxidation of Li3Sb was much smaller for the Sb/Sb2O3 nanoparticle coatings. The improved performance can be explained by significant formation of Sb2O3 during the reoxidation, the presence of smaller Sb particles in the Sb/Sb2O3 coatings, and the formation of buffering nanoparticles of Li2O in a matrix of Sb during the first reduction cycle for the Sb/Sb2O3 deposits.

1. Introduction The Li-ion battery is well-established on the market and continual studies are made to improve its performance. Graphite is the most commonly used anode material today but efforts are made to find new anode materials with enhanced capacities and improved rate capabilities. There is currently considerable interest in metal-based anode materials (involving elements such as Sb, Sn, Si, and Al) because of their high Li-storage capacities.1,2 The large volume expansion of these anode materials during the lithiation process is, however, a severe problem. This volume change leads to particle loss and pulverization of the anode material, which drastically limits the cycle life. Different approaches have been described to overcome this problem. Glass matrixes have been studied in which the glass network acts as a buffer for the volume changes.3,4 The use of nanoalloys,5,6 active and inactive composite alloy materials, and intermetallic compounds (such as Cu2Sb,7 InSb,8,9 * Corresponding author. Tel.: +46 (0)18 4713742. Fax: +46 (0)18 513548. [email protected].

(1) Besenhard, J. O. Handbook of Battery Materials; Wiley-VCH: Weinheim, 1999. (2) Tarascon, J.-M.; Armand, M. Nature 2001, 414, 359. (3) Courtney, I. A.; Dahn, J. R. J. Electrochem. Soc. 1997, 144, 2045. (4) Gejke, C.; Zanghellini, E.; Bo¨rjesson, L.; Fransson, L.; Edstro¨m, K. J. Phys. Chem. Solids 2001, 62, 1213. (5) Yang, J.; Winter, M.; Besenhard, J. O. Solid State Ionics 1996, 90, 281. (6) Li, H.; Shi, L.; Wang, Q.; Chen, L.; Huang, X. Solid State Ionics 2002, 148, 247. (7) Fransson, L.; Vaughey, J. T.; Benedek, R.; Edstro¨m, K.; Thomas, J. O.; Thackeray, M. M. Electrochem. Commun. 2001, 3, 317.

SnSb,10,11 and AlSb9,12) can likewise be employed to circumvent the problem. This type of intermetallic compound (AxBy) has a strong structural relationship with its lithiated products and reacts with Li+ through a fully reversible displacement process, during which the metallic A element is extruded from the structure during the discharge, but readmitted upon charging. Another approach involves the manufacturing of nanostructured electrodes for which the effects of the volume expansion have been reported to be decreased.13,14 The use of transition metal oxides as anodes involves lithium conversion reactions consisting of an electrochemically driven reversible decomposition of the oxide precursor (MO) electrode into an M/Li2O nanocomposite electrode that can release Li+ upon the following charge.15,16 These Mn+ f M0 conversion reactions can (8) Johnson, C. S.; Vaughey, J. T.; Thackeray, M. M.; Sarakonsri, T.; Hackney, S. A.; Fransson, L.; Edstro¨m, K.; Thomas, J. O. Electrochem. Commun. 2000, 2, 595. (9) Vaughey, J. T.; Johnson, C. S.; Kropf, A. J.; Benedek, R.; Thackeray, M. M.; Tostmann, H.; Sarakonsri, T.; Hackney, S.; Fransson, L.; Edstro¨m, K.; Thomas, J. O. J. Power Sources 2001, 97-98, 194. (10) Trifonova, A.; Wachtler, M.; Winter, M.; Besenhard, J. O. Ionics 2002, 8, 321. (11) Mukaibo, H.; Osaka, T.; Reale, P.; Panero, S.; Scrosati, B.; Wachtler, M. J. Power Sources 2004, 132, 225. (12) Honda, H.; Sakaguchi, H.; Fukuda, Y.; Esaka, T. Mater. Res. Bull. 2003, 38, 647. (13) Li, N.; Martin, C. R.; Scrosati, B. J. Power Sources 2001, 97-98, 240. (14) Li, N.; Martin, C. R.; Scrosati, B. Electrochem. Solid-State Lett. 2000, 3, 316. (15) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J.-M. Nature 2000, 407, 496. (16) Armand, M.; Dalard, F.; Deroo, D.; Mouliom, C. Solid State Ionics 1985, 15, 205.

10.1021/cm0624769 CCC: $37.00 © 2007 American Chemical Society Published on Web 02/08/2007

Sb/Sb2O3 Nanoparticle Coatings for Li-Ion Batteries

Chem. Mater., Vol. 19, No. 5, 2007 1171

involve as many as 2e- (CoO) or 4e- (RuO2) per formula unit as compared to only one for classical insertion/ deinsertion reactions.15,16 In this study, coatings composed of electrodeposited Sb and Sb/Sb2O3 have been studied as anode materials for Liion batteries. Sb compounds exhibit high capabilities of storing Li and have therefore been proposed as potential anode materials for Li-ion batteries7-12,17-19 despite the toxicity of Sb compounds. During the reduction of Sb, a compound containing three Li atoms can be formed,20 as shown in reaction (1) below: 3Li+ + 3e- + Sb T Li3Sb

(1)

The latter reaction corresponds to a theoretical capacity of 660 mA‚h‚g-1, which may be compared to 372 mA‚h‚g-1 for graphite. The expected volume expansion (ca. 150%21) during the lithiation process, however, generally leads to a dramatic capacity loss during cycling of this type of material.20 One possibility to minimize this capacity loss could be to use thin coatings composed of a mixture of Sb and Sb2O3 which are reduced to a Sb/Li2O nanocomposite upon the first cycle, as has previously been described for many 3d metal (Co, Ni, Fe, Cu, and Mn) based oxides.15,16 Such Sb/Sb2O3 materials should be possible to electrodeposit using a similar approach as that described22-26 for the manufacturing of Cu/Cu2O coatings. In a recent report, Xue and Fu27 demonstrated the reversible formation and decomposition of Li2O for crystalline Sb2O3 thin films also containing about 14 mol % Sb. It was demonstrated that the coatings exhibited a high reversible capacity between 691 and 794 mA‚h‚g-1 with good cycling stability. A large irreversible capacity loss (234 mA‚h‚g-1) was, however, seen on the first cycle. While Pralong et al.19 recently studied nanometer thin cobalt antimonide and antimony films prepared by pulsed laser deposition and Xue and Fu27 employed similarly obtained Sb2O3 coatings, we are interested in comparing the properties of electrodeposited Sb and Sb/Sb2O3 coatings. Electrodeposition is an inexpensive and straightforward method which generally is carried out at low temperature. The technique facilitates large-scale production of coatings which makes it interesting for industrial applications. As electrodeposition also offers precise control of the deposition reactions, by controlling either the potential or the current (17) Ionica, C. M.; Aldon, L.; Lippens, P. E.; Morato, F.; Olivier-Fourcade, J.; Jumas, J.-C. Hyperfine Interact. 2004, 156/157, 555. (18) Tarascon, J.-M.; Morcrette, M.; Dupont, L.; Chabre, Y.; Payen, C.; Larcher, D.; Pralong, V. J. Electrochem. Soc. 2003, 150, A732. (19) Pralong, V.; Leriche, J.-B.; Beaudoin, B.; Naudin, E.; Morcrette, M.; Tarascon, J.-M. Solid State Ionics 2004, 166, 295. (20) Tirado, J. L. Mater. Sci. Eng. 2003, R40, 103. (21) Besenhard, J. O.; Hess, M.; Komenda, P. Solid State Ionics 1990, 4041, 525. (22) Golden, T. D.; Shumsky, M. G.; Zhou, Y.; VanderWerf, R. A.; Van Leeuwen, R. A.; Switzer, J. A. Chem. Mater. 1996, 8, 2499. (23) Leopold, S.; Herranen, M.; Carlsson, J.-O. J. Electrochem. Soc. 2001, 148, C513. (24) Leopold, S.; Herranen, M.; Carlsson, J.-O.; Nyholm, L. J. Electroanal. Chem. 2003, 547, 45. (25) Eskhult, J.; Herranen, M.; Nyholm, L. J. Electroanal. Chem. 2006, 594, 35. (26) Ghosh, J. C.; Kappana, A. N. J. Phys. Chem. 1924, 28, 149. (27) Xue, M.-Z.; Fu, Z.-W. Electrochem. Commun. 2006, 8, 1250.

density, the structure, phase composition, and thickness of the deposited coatings can likewise be controlled. An additional advantage of using electrodeposition is that the anode materials can be directly deposited on a metallic substrate later serving as the current collector. In these cases, there is hence no need for the use of additional components such as binders and electron-conducting materials (e.g., carbon black), the presence of which may make the interpretation of the results more complex. The absence of binders etc. naturally also leads to a higher density of the active material in the anode materials. Although a number of reports on the electrodeposition of antimony can be found in the literature,26,28-35 the possibility of carrying out co-deposition of Sb and Sb2O3 by use of a local pH increase has to our knowledge not been investigated previously. The corresponding co-deposition of copper and Cu2O from lactate, tartrate, or citrate solutions has, however, been described.22-25 In the latter cases, it has been found24,25 that Cu2O is formed as a result of the local pH increase caused by the protonation of the ligand released from the copper(II) complexes upon their reduction. If antimony is electrodeposited from a solution containing antimony tartrate, it is reasonable to assume that a corresponding local pH effect should be present, which could result in a co-deposition of Sb and Sb2O3. Such co-depositions were most likely obtained already by Ghosh and Kappana26 who studied the electrodeposition of antimony from tartrate baths in the presence and absence of hydrochloric acid. The latter authors noted that black deposits were obtained upon deposition from a tartrate solution in the absence of added acid while brilliant white deposits were found after adding HCl (or another acid) to the electrolyte. The compositions of the deposits were, however, not investigated. Ghosh and Kappana26 also found that the quality of the deposit was improved when the acid strength and/or the quantity of the acid was increased. Increased current densities were, on the other hand, found to result in inhomogeneous black and spongy deposits. The aim of the present work is to electrodeposit and characterize coatings of Sb and Sb/Sb2O3, respectively, and to study the electrochemical behavior of these coatings, particularly the influence of the presence of Sb2O3 in the coatings on the electrochemical behavior of the materials when used as anodes in Li-ion batteries. Since the limited cycle life has been found to be the main problem for Sbbased anode materials, our main interest is the cycle stability and the general electrochemical performance of the anode materials in the presence and absence of Sb2O3. The influence of the electrolyte composition used in the electrodeposition (28) Past, V. In Encyclopedia of Electrochemistry of the Elements; Bard, A. J., Ed.; Marcel Dekker: New York, 1975; Vol. IV, Chapter IV-I. (29) Sadana, Y. N.; Singh, J. P.; Kumar, R. Surf. Techn. 1985, 24, 319. (30) Paolucci, F.; Mengoli, G.; Musiani, M. M. J. Appl. Electrochem. 1990, 20, 868. (31) Jung, C.; Rhee, C. K. J. Electroanal. Chem. 2004, 566, 1. (32) Yan, J. W.; Wu, Q.; Shang, W. H.; Mao, B. W. Electrochem. Commun. 2004, 6, 843. (33) Hara, M.; Inukai, J.; Yoshimoto, S.; Itaya, K. J. Phys. Chem. 2004, 108, 17441. (34) Ward, L. C.; Stickney, J. L. Phys. Chem. Chem. Phys. 2001, 3, 3364. (35) Yang, M.-H.; Sun, I.-W. J. Appl. Electrochem. 2003, 33, 1077.

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step on the morphology and composition of the coatings is discussed based on scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoelectron spectroscopy (XPS), and Raman spectroscopic investigations. The electrodeposition reactions and possible reasons for the influence of the Sb2O3 content on the electrochemical performance of the anode materials are also discussed. 2. Experimental Section 2.1. Electrodeposition. The electrodeposition was carried out using mainly two electrolytes with different pH but with the same concentration of Sb(III). The first electrolyte had a pH of 1.3 and contained 0.075 M potassium antimony tartrate trihydrate (K2(Sb2(C4H2O6)2)‚3H2O, Fluka, reagent grade) as well as 0.090 M KCl (Merck, pro analysi) and 0.110 M HCl (Fluka, Purum). The pH of the second electrolyte, containing only 0.075 M potassium antimony tartrate trihydrate dissolved in deionized water, was 4.1. In the depositions, pieces of Ni foil (Goodfellow, thickness 0.0125 mm, purity level 99.9%) were used as working electrodes. A platinum wire served as the counter electrode while a saturated calomel electrode (SCE) was used as the reference electrode. A laboratorydesigned combined sample holder and electrochemical cell consisting of a polyvinyl chloride (PVC) cylinder, in which the Ni foil served as the bottom section, was used during the electrodepositions. The Ni foil was placed on a 3 mm thick copper plate, used as the current collector, on top of a 10 mm thick PVC plate. The area of the working electrode, and hence the electrodeposited material, was 31.2 cm2. From this original sample, smaller samples with an area of 3.14 cm2 were punched out for electrochemical characterization. The electrodepositions were performed at 23 °C in quiescent solution using a constant cathodic current density of either 1.94 or 4.0 mA/cm2, unless stated otherwise. The experiments were performed with an EG&G model 273 potentiostat/galvanostat (EG&G Princeton Applied Research, Princeton, New Jersey). Two different pretreatment approaches were used to clean the surface of the Ni substrate prior to the depositions. In the first approach, the nickel foil was etched with 4 M HNO3 at 40 °C, mainly to facilitate the electrodeposition of Sb on the Ni electrodes. In the second approach, the Ni electrodes were instead cleaned in acetone for 15 min in an ultrasonic bath. After both pretreatments, and prior to the electrodepositions, the Ni substrates were rinsed with deionized water. The electrodepositions in the presence of 0.110 M HCl were carried out for 100 s using a current density of 4.0 mA/cm2 on both the HNO3-etched Ni electrodes and the Ni electrodes cleaned in acetone. In the electrolyte not containing HCl, the latter deposition parameters were also used for the etched Ni electrodes while a current density of 1.94 mA/cm2 for 120 s was used for the Ni electrodes cleaned in acetone. 2.2. Characterization of the Electrodeposits. The morphology of the coatings was studied with a scanning electron microscope (LEO 1550) while the composition and structure of the deposits were investigated using X-ray diffraction (T2T Siemens D5000 diffractometer with Cu KR radiation). Transmission electron microscopy (TEM) micrographs of powders scratched off from the deposited coatings were also obtained using a JEOL 2000 FXII instrument. The Sb2O3 was identified with Raman spectroscopy employing a Renishaw 2000 Raman spectrometer equipped with a near-infrared diode laser (783 nm, 20 mW). The Raman measurements were also made on scratched off powder. X-ray photoelectron spectroscopy (XPS) was used to examine the oxidation state of the

Bryngelsson et al. antimony in the coatings prepared in the presence and absence of HCl, respectively. These experiments were performed with a PHI 5500 system using monochromatic Al KR (1486.6 eV) radiation. To enable calculations of the specific capacity of the coatings used as the anode materials, it is crucial to determine the mass of active material of the electrode. Since the masses of the samples used for the electrochemical characterization (which had an area of 3.14 cm2) were too small (i.e., of the order of 0.5 mg) to weigh reliably, these masses were instead calculated from the mass of the deposited larger sample (which had an area of 31.2 cm2) assuming uniform electrodeposition. The mass increase of the working electrode during the electrodeposition experiments was also studied with the electrochemical quartz crystal microbalance (EQCM) technique. In these experiments, the electrodeposited masses were compared with those obtained as a result of the bulk depositions onto the Ni-foil electrodes. In the EQCM experiments, 9 MHz AT-cut gold-coated quartz crystals (Seiko EG&G model QA-A9M-Au-50) were utilized as working electrodes. Prior to the antimony electrodepositions, the gold-coated quartz crystals were coated with a 45 nm thick layer of metallic nickel by electrodeposition from a 0.4 Ni(II) (sulfate), 0.8 M tartrate solution (pH 6.1) at a potential of -1.1 V vs SCE during 100 s. A PTFE dip cell holder was used to mount the quartz crystals to expose only one side of the crystal to the deposition solution. The changes in the frequency were monitored with a quartz crystal analyzer (SEIKO EG&G model QCA 922) and data were sampled under computer control employing WinEchem (EG&G). The gate time was set to 0.1 s. 2.3. Electrochemical Characterization of the Coatings. Prior to the cell preparation, the electrodeposited coatings were cut into circular electrodes (A ) 3.14 cm2) and dried at 120 °C overnight in a vacuum furnace in an argon-filled glovebox (