Elsevier

Electrochimica Acta

Volume 54, Issue 28, 1 December 2009, Pages 7519-7524
Electrochimica Acta

A facile route to carbon-coated SnO2 nanoparticles combined with a new binder for enhanced cyclability of Li-ion rechargeable batteries

https://doi.org/10.1016/j.electacta.2009.08.006Get rights and content

Abstract

Carbon-coated SnO2 nanoparticles were prepared by a novel facile route using commercial SnO2 nanoparticles treated with concentrated sulfuric acid in the presence of sucrose at room temperature and ambient pressure. The key features of this method are the simple procedure, low energy consumption, and inexpensive and non-toxic source materials. As-prepared core/shell nanoparticles were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The electrochemical measurements showed that the carbon-coated SnO2 nanoparticles with 10% carbon and using carboxymethyl cellulose (CMC) as a binder displayed the best electrochemical performance with the highest specific capacity of 502 mAh g−1 after 50 cycles at a current density of 100 mA g−1. In addition, owing to the water solvability of CMC, the usage of CMC as binder makes the whole electrode fabrication process cheaper and more environmental friendly.

Introduction

Rechargeable lithium-ion batteries are currently the technology of choice for portable electronic devices [1], [2]. In order to meet the requirements of the rapidly increasing portable electronics market, the performance of rechargeable lithium-ion batteries needs to be improved with higher energy density and better rate capability. Currently, the commercial anode material of choice is graphite, which has a relatively low theoretical capacity around 370 mAh g−1 [3]. Materials based on tin oxide have been proposed as promising alternative anode materials for rechargeable lithium batteries owing to their high theoretical capacity (SnO2: 790 mAh g−1) [4], [5], [6], [7], [8], [9]. The severe volume expansion and contraction during the alloying–dealloying cycles with Li+ ions is the main hindrance to the commercial use of SnO2 [10]. In order to alleviate the volume changes, two main methods have been investigated, fabricating SnO2 into nanostructures [11], [12], [13], [14], [15], [16], [17], [18] and adding/coating with buffer materials (such as carbon or other conductive materials), inside or outside the particles [19], [20], [21], [22], [23], [24], [25], [26]. Various types of SnO2 nanostructures, such as nanotubes [11], [12], [13], [14], nanowires [15], [16], and nanorods [17], [18], have been investigated and were found to have enhanced electrochemical performance. They provide more reaction sites, short Li+ diffusion lengths, and considerable kinetic enhancement. However, the high cost for synthesizing the nanostructured materials and the relatively low capacity retention still need to be addressed for future commercial application. On the other hand, surface-coated/composite SnO2 showed better electrochemical performance than the bare material. Among the buffer materials, carbon has to be considered as the best choice because of its cheap, light, and conductive nature. To date, carbon coated onto or added into SnO2 has been prepared by spray pyrolysis, polymer coating and then carbonization, and hydrothermal/solvothermal methods [19], [20], [21], [22], [23], [24], [25]. However, it is still important to explore economical synthesis techniques with low energy consumption for the formation of carbon-coated SnO2.

Recently, the choice of binder has become a very important issue in finding a solution to the problem of the large capacity fade observed for anode materials after cycling [27], [28], [29], [30], [31]. Buqa et al. reported that nano-Si electrode containing 1% sodium carboxymethyl cellulose (CMC) as binder shows the same cycle stability as an identical electrode containing 10% conventional polyvinylidene fluoride (PVdF) binder [27]. Lestriez et al. claimed that the extended conformation of CMC in solution facilitates an efficient networking process between the conductive agent and the Si particles [28]. Hochgatterer et al. reported that the chemical bonding between CMC binder and Si particles contributes to the enhanced capacity retention of Si/C composite electrodes [29]. Li et al. reported that Fe2O3 electrodes using CMC binder and two other new binders show better cycling performance (about 800 mAh g−1 for 100 cycles) compared to electrodes made from conventional PVdF binder [30]. Another advantage of using CMC as the binder is that CMC can be dissolved and processed in water, which makes the whole electrode fabrication process cheaper and more environmental friendly. However, there are still no reports on using CMC binder with SnO2-based anode materials.

Here, carbon-coated SnO2 nanoparticles were prepared by a novel facile route using commercial SnO2 nanoparticles treated with concentrated sulfuric acid in the presence of sucrose at room temperature and ambient pressure. The key features of this method are the simple procedure, low energy consumption, and inexpensive and non-toxic source materials. In addition, CMC was used as a binder to further investigate its effects on the electrochemical performance.

Section snippets

Preparation of carbon-coated SnO2 nanoparticles

The method used here is adopted from the literature [32]. The typical procedure to prepare Sample CS-1 is as follows. A mixture of the SnO2 nanoparticles (1.7193 g, 99.5%, Nanostructured & Amorphous Materials Inc., 61 nm), sucrose (3.0159 g, 98%, Aldrich), and water (1 mL) was ultrasonicated for 30 min at room temperature, and then H2SO4 (5 mL, 98 wt.%, Sigma–Aldrich) was slowly added with stirring. After reacting for about 20 min, the final products were washed with N,N-dimethylformamide three times,

Results and discussion

SEM and TEM images and EDX mapping of carbon-coated SnO2 nanoparticles (CS-1 sample) are shown in Fig. 1. Fig. 1(a) shows that the nanoparticles of the CS-1 sample are agglomerated into big particles several micrometers in diameter. The EDX spectrum in Fig. 1(d) shows that only the elements Sn, O, and C are present in the sample, indicating its high purity. Fig. 1(b) and (c) contains the EDX mapping images for C and Sn, showing the good distribution of carbon in the composite. That is to say,

Conclusions

Carbon-coated SnO2 nanoparticles were prepared by a novel facile route using commercial SnO2 nanoparticles treated with concentrated sulfuric acid in the presence of sucrose at room temperature and ambient pressure. The key features of this method are the simple procedure, low energy consumption, and inexpensive and non-toxic source materials. The electrochemical measurements showed that both the carbon coating and the binder selection affected the electrochemical performance. The carbon-coated

Acknowledgments

Financial support provided by the Australian Research Council (ARC) through ARC Centre of Excellence funding (CE0561616) is gratefully acknowledged. The authors thank Dr. T. Silver for critical reading of the manuscript.

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