Elsevier

Journal of Power Sources

Volume 293, 20 October 2015, Pages 492-497
Journal of Power Sources

SiC@Si core–shell nanowires on carbon paper as a hybrid anode for lithium-ion batteries

https://doi.org/10.1016/j.jpowsour.2015.05.103Get rights and content

Highlights

  • SiC@Si core–shell nanowires on carbon paper.

  • The fabricated electrodes show high specific capacity and good cycling stability.

  • The influence of the growth parameters on the electrode performances has been studied.

Abstract

Silicon has been considered as one of the most promising anode materials for the next generation lithium-ion battery due to its high theoretical capacity, but large volume changes during the electrochemical cycling limit its commercial application. In this study, we report the synthesis of silicon carbide @ silicon core–shell nanowires on carbon paper and their application in lithium-ion batteries. The hybrid nano-structures are fabricated via a two-step chemical vapor deposition method and directly used as the working electrode without any additional binder, exhibiting high specific capacity, high coulombic efficiency and good cycling stability. After 50 cycles, the discharge capacities still remain 2837 and 1809 mAh g−1 at the rates of 0.1C and 0.5C, respectively. Furthermore, we also study the influence of the growth time of SiC NWs and the thickness of Si film on the lithium-ion batteries' performance, and propose the possible method to further improve the battery performance.

Introduction

Recently, with the popularization of electric vehicles and intelligent electronic devices, the demands for lithium-ion batteries with higher energy density and longer service life are increasing rapidly. Silicon has been considered as one of the most promising anode materials for the next generation lithium-ion battery [1], [2], [3], [4], [5], [6], because of its beneficial feature: (i) silicon is the second most abundant element on earth and is widely used in modern electronic industry [7]; (ii) silicon has a low work potential (<0.5 V vs. Li/Li+) for safe use [8]; (iii) silicon has the highest known theoretical capacity (4200 mAh g−1) [6], which is more than 10 times the value of the current commercial graphite anode (372 mAh g−1) [9]. Unfortunately, the poor electronic conductivity and large volume changes (∼400%) during the electrochemical cycling limit its commercial application [6]. The large volume change during lithiation/delithiation results in electrode pulverization and loss of electrical connection, leading to poor reversibility and rapid capacity loss.

Many attempts have been made to overcome the above mentioned shortcomings of silicon electrode. One promising solution is the use of nanostructured silicon, including nanoparticles [10], [11], nanowires [6], [12], nanotubes [13], [14] and thin films [15], [16]. The small structure size alleviates the absolute mechanical stress, and the pores or voids offer free space to accommodate volume expansion. Another promising strategy is to use the composites of silicon and other materials, such as carbon [17], [18], graphene [19], [20], metal [21], [22], [23], other semiconductors [24], [25], etc. In some cases, these materials often enhance the electronic conductivity of silicon electrode, or/and provide shorter electronic pathways, or/and act as a buffering phase for the volume changes of silicon.

Recently, many literature have reported a simple method to enhance the cycling stability by depositing a thin silicon film on a rough or porous substrate [15], [26], [27], [28], since the rough substrates offer the space to buffer volume changes and the thin films usually have better electrical connection with substrates. Moreover, the mass of the active materials per unit area also has been improved, due to the high surface-to-volume ratio of substrates. Inspired by these results, here, we report the synthesis of silicon carbide (SiC) @ Si core–shell nanowires (NWs) on carbon paper (CP) and their application in lithium-ion batteries. The three-dimensional (3D) hierarchical SiC@Si core–shell NWs on CP have a high surface area and short electron collection pathway. Additionally, there are a few reports on the composites of silicon carbide and silicon for lithium-ion batteries [29], [30], and the main advantage of SiC coating on Si nanostructures is preventing Si volume expansions because of its high mechanical strength. In our case, the SiC NWs have been used as the substrates for supporting Si films and transporting the electrons. According to our knowledge, it's the first report about SiC@Si core–shell nanowires for lithium-ion batteries. These structures are directly used as lithium-ion battery anodes without any additional binders or conductive materials, exhibiting high specific capacity, high coulombic efficiency and good cycling stability. Furthermore, The influence of the growth time of SiC NWs and the thickness of silicon film on lithium-ion batteries' performance have been also studied, and the possible method to further improve the battery performance has been proposed.

Section snippets

Synthesis of SiC@Si core–shell NWs on CP

SiC@Si core–shell NWs on CP were fabricated via a two-step chemical vapor deposition (CVD) method. Typically, the CP substrates (N0S1005, Phychemi Company Limited, 2.5 cm × 5.0 cm) were cleaned by sonication sequentially in acetone and alcohol for 10 min respectively. After dried, the cleaned CPs were immersed in 1 M Ni(NO)3 alcohol solution for 20 min. Subsequently, the CPs were dried in oven at 80 °C and transferred into a tube furnace in a quartz boat. In the SiC NWs growth process [31], the

Results and discussions

Fig. 1 shows the schematic illustration of the fabrication process of the SiC@Si core–shell NWs on CP. At first, SiC NWs were grown on CP by a CVD process. Subsequently, a thin film on the surface of SiC NWs was deposited via another CVD process. The morphology of the as-grown products was observed by SEM. As shown in Fig. 2(a), the CP is a woven carbon microfiber matrix without any binder. Compare to the planar metal electrode, CP has a larger surface area for improving the mass of active

Conclusions

In summary, we have fabricated SiC@Si core–shell NWs on CP via a two-step CVD process. The hybrid structures have a high surface area and short electron collection pathway, directly used as electrode without any additional binder. After 50 cycles, the discharge capacities still remain 2837 and 1809 mAh g−1 at the rates of 0.1C and 0.5C, respectively. The core–shell SiC@Si structure is still remained and the morphology of SiC nanowire did not change after 50 cycles, and it has been demonstrated

Acknowledgments

This work was supported by National Natural Science Foundation of China (No. 51272232), Program for New Century Excellent Talents in University, and the Fundamental Research Funds for the Central Universities.

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