Synthesis and electrochemical performance of Li and Ni 1,4,5,8-naphthalenetetracarboxylates as anodes for Li-ion batteries

Synthesis and electrochemical performance of Li and Ni 1,4,5,8-naphthalenetetracarboxylates as anodes for Li-ion batteries

Electrochemistry Communications 25 (2012) 136–139 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepag...

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Electrochemistry Communications 25 (2012) 136–139

Contents lists available at SciVerse ScienceDirect

Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom

Synthesis and electrochemical performance of Li and Ni 1,4,5,8-naphthalenetetracarboxylates as anodes for Li-ion batteries Xiaoyan Han a, Feng Yi a, Taolei Sun a,⁎, Jutang Sun b a b

State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China College of Chemistry and Molecular Sciences, Wuhan University, 430072, China

a r t i c l e

i n f o

Article history: Received 24 August 2012 Received in revised form 8 September 2012 Accepted 8 September 2012 Available online 17 September 2012

a b s t r a c t Metal-1,4,5,8-naphthalenetetracarboxylates (Metal = Li and/or Ni) were synthesized and investigated as anode materials for lithium ion batteries. These complexes were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetry. Electrochemical tests indicated that these materials exhibited superior electrochemical performance and good cycling stability. © 2012 Elsevier B.V. All rights reserved.

Keywords: Metal-1,4,5,8-naphthalenetetracarboxylates Anode materials Lithium ion batteries

1. Introduction

2. Experimental

In recent years, considerable attention has been paid to lithium ion batteries due in part to their applications in cameras, computers and portable electronics [1–3]. In this technology, energy storage is mainly limited by the positive electrode, which usually has a much lower capacity than the negative electrode [4–6]. Therefore, much effort has been made to find new materials with higher capacity and stability for use in the positive electrode. Among these materials, organic aromatic materials have recently aroused intense interest [7–10]. Interestingly, these compounds also exhibit excellent performance as anode materials [9,10], which contribute extra benefits to their applications in lithium ion batteries. 1,4,5,8-Naphthalenetetracarboxylic dianhydride (NTCDA), a high-performance molecular device, has been used in photocurrent multiplication and organic semi-conductors [11,12]. It contains four carbonyl groups, which can reversibly intercalate 4 Li per unit formula. However, according to our recent study [13], NTCDA can achieve a high discharge capacity by intercalating 18 Li to form a 1:1 Li/C complex. The electron conductivity of NTCDA is significantly increased by the doping of metal atoms [14]. Herein, we synthesized metal-1,4,5,8-naphthalenetetracarboxylates (M-NTC, M = Li and/or Ni) via a rheological phase reaction [15] and investigated its electrochemical properties as anode materials for lithium ion batteries.

NTCDA and LiOH·H2O were mixed in the desired stoichiometric ratio by grinding. An appropriate amount of distilled water was added to obtain a rheological mixture. The mixture was transferred into a Teflon container, which was then sealed in a stainless steel reactor at 100 °C for 12 h. After drying at 120 °C, the precursor was heated at 400 °C for 3 h in air, resulting in Li-NTC. Ni-NTC was synthesized from NTCDA and Ni(OH)2 using a similar procedure, except that the heat treatment was performed at 300 °C. Li-NTC and Ni-NTC were mixed by grinding with a mass ratio of 1:1 to obtain a Li/Ni-NTC mixture. The reaction formulas are expressed as follows:

⁎ Corresponding author. Tel.: +86 27 87858547. E-mail address: [email protected] (T. Sun). 1388-2481/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.elecom.2012.09.014

Fourier transform infrared spectra (FT-IR) of the samples (in KBr pellets) were recorded using a Nicolet AVATAR-360 spectrometer. X-ray diffraction analysis (XRD) was performed using a Shimadzu XRD-6000 diffractometer with a Ni filter and Cu–Kα radiation. The refined crystal lattice parameters were calculated by the JADE5 program. Thermogravimetric analysis (TG) was carried out using a

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The cells were composed of a working electrode and a lithium foil counter electrode separated by a Celgard 2300 microporous membrane using 1 M LiPF6 in EC/DMC (1:1, v/v) as the electrolyte. The working electrode was prepared by mixing the sample, acetylene black and PTFE binder in a weight ratio of 60:35:5 and then pressing the mixture on a stainless steel mesh current collector. Next, 2016 coin-type cells were assembled in an argon-filled glove box. The discharge–charge tests were performed using a Neware battery test system between 0.01 and 3.0 V with a current of 100 mA g −1.

Transmittance (a.u.)

NTCDA

Li-NTC

3. Results and discussion

Ni-NTC

Fig. 1 presents the FT-IR spectra of NTCDA and M-NTC. All spectra showed peaks at 1400–1600 cm−1 for the aromatic C_C stretching vibration. NTCDA showed a distinct peak at 1780 cm−1, resulting from the C_O stretching vibration, and a peak at 1582 cm−1, resulting from the C\O stretching vibration. However, both peaks were weakened in M-NTC; instead, a broad peak at approximately 1606 (Li-NTC) and 1556 cm−1 (Ni-NTC) appeared. The red shift of these two peaks was caused by the interaction of C_O with Li or Ni atoms, which means that the Li or Ni atoms exist near the C_O of NTCDA and thus affect the molecular vibration. Moreover, the strong peak at 1294 cm−1 in NTCDA can be attributed to the C\O\C stretching vibration, which disappeared in M-NTC, indicating that the C\O\C stretching mode was broken. The IR spectrum of Li/Ni-NTC exhibited absorption peaks from both Li-NTC

LiNi-NTC

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Wavenumber (cm-1) Fig. 1. FT-IR spectra of NTCDA and M-NTC.

Setaram Labsys Evo S60/58458 thermal analyzer with a heating rate of 10 °C min −1.

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Fig. 2. The XRD patterns for NTCDA, Li-NTC and Ni-NTC (a), b is the molecular packing diagram of Li-NTC and Ni-NTC in the unit cell, c and d are the XRD patterns for Li-NTC and Ni-NTC before and after heat treatment, respectively. The insets are the TG curves of the precursors, respectively.

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1st

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Fig. 3. The voltage profiles of Li-NTC (a), Ni-NTC (b) and LiNi-NTC (c) for various cycles, d is the voltage profile of Ni-NTC in the initial cycle.

and Ni-NTC. These results indicated that there was no chemical reaction between Li-NTC and Ni-NTC during the mixing process. The XRD patterns for NTCDA, Li-NTC and Ni-NTC are shown in Fig. 2a. NTCDA showed a sharp peak at 2θ = 12.0°, which was in accordance with a previous report [16]. All peaks for Li-NTC could be indexed to a triclinic phase with the P1 (No. 2) space group. The lattice parameters were calculated as follows: a = 9.8820 (41) Å, b = 5.3478 (42) Å, c = 6.7839 (10) Å, α = 74.579 (71)°, β = 100.507 (51)°, γ = 104.126 (57)° and Dcala = 1.6379 g·cm − 3. Ni-NTC can be indexed as exhibiting an orthorhombic phase with the Pbam (No. 55) space group. The lattice parameters a, b, c and Dcala of the sample were determined to be 9.7473 (6), 6.9593 (4), 9.8271 (4) Å and 2.0804 g·cm − 3, respectively. The XRD patterns for Li-NTC and Ni-NTC did not exhibit any peaks for elemental Li or Ni. Thus, it can be concluded that the Li or Ni atoms in the M-NTC are interconnected with NTCDA molecules. For Ni-NTC, one Ni atom was intercalated with four O atoms in a plane. For Li-NTC, one Li atom was intercalated with five O atoms (Fig. 2b). The XRD patterns for the precursors before and after the heat treatment are shown in Fig. 2c and d, respectively. The XRD patterns for the precursors were consistent with the products after heat treatment. The insets are the TG curves of the precursors without heat treatment, which indicate that the samples are stable at high temperatures. Fig. 3a–c shows the voltage profiles of the electrodes for various cycles. The samples exhibit similar discharge and charge properties. There are three clear discharge plateaus in the first discharge curve, whereas the first discharge plateau gradually disappears in the second cycle. The three plateaus in the first discharge curve suggest different reaction mechanisms. According to our previous calculation method [13], the actual Li intercalation reaction of M-NTC can be divided into three steps. Fig. 3d is the voltage profile of Ni-NTC in the initial cycle. Ni-NTC shows three discharge ranges in the first

discharge curve: 1.29–0.93 V, 0.93–0.35 V and 0.35–0.01 V. The Li intercalation reaction of Ni-NTC can be expressed as follows:

ð1Þ

ð2Þ

ð3Þ As shown in the reaction formula provided above, the intercalation of the first 8 Li to C_O is irreversible, disappearing in the following cycles and resulting in a capacity reduction. Fig. 4 compares the cycling properties of these materials. The inset shows the voltage profiles of the samples in the initial cycle. As observed from the inset, the initial voltage profile of Li/Ni-NTC exhibits

X. Han et al. / Electrochemistry Communications 25 (2012) 136–139

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4. Conclusions

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In conclusion, metal-1,4,5,8-naphthalenetetracarboxylates (M-NTC, M = Li and/or Ni) were synthesized by a rheological phase reaction. Li-NTC and Ni-NTC composites exhibit good electrochemical performance as anode materials. The mixing of these materials can effectively improve both the electrochemical capacity and the cycling stability. These results provide important insights for developing a new generation of metal–organic negative materials with high capacities and good stabilities by designing and optimizing the molecular structures [17] of the aromatic derivative.

Cycle numbers Fig. 4. Cycling properties of Li-NTC, Ni-NTC and LiNi-NTC, the inset is the voltage profile of the samples in the initial cycle.

a combination of the properties of Li-NTC and Ni-NTC. As shown in Fig. 4, Ni-NTC delivers initial discharge and charge capacities of 1823 and 982 mAh g −1, respectively, which decrease to 248 and 246 mAh g −1 after 80 cycles. Interestingly, although there is still a remarkable capacity reduction in the first 5 cycles of Li-NTC, the discharge and charge capacities increase gradually to 568 and 554 mAh g −1, respectively, by the 74th cycle and then slowly decrease, reaching 468 and 458 mAh g −1, respectively, after 80 cycles. The initial capacity reduction may be related to the electrode activation process. Li/Ni-NTC delivers initial discharge and charge capacities of 1084 and 601 mAh g −1, respectively, which become 482 and 475 mAh g −1 after 80 cycles. These values indicate a good cycling stability that is much better than that of Li-NTC and Ni-NTC. The larger initial capacity of Ni-NTC is attributed to the existence of an unpaired electron in the Ni atoms (for Li atoms, there is no unpaired electron), which results in good electronic conductivity, promoting the intercalation of Li. For Li/Ni-NTC, the Ni-NTC component can increase the electronic conductivity and the Li-NTC component can improve the structure's stability. Therefore, Li/Ni-NTC delivers both a larger initial capacity and a better cycling stability compared with Li-NTC and Ni-NTC. The above results show that the mixing of Li-NTC and Ni-NTC combines the respective advantages of these materials and thus greatly enhances the overall electrochemical capacity and cycling stability of materials.

Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 51073123) and China Postdoctoral Science Foundation (No. 2011M500900).

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