Elsevier

Electrochimica Acta

Volume 206, 10 July 2016, Pages 328-336
Electrochimica Acta

Highly stable SiOx/multiwall carbon nanotube/N-doped carbon composite as anodes for lithium-ion batteries

https://doi.org/10.1016/j.electacta.2016.04.161Get rights and content

Abstract

Fabricating high-capacity electrode materials with long cycle life is essential to developing high-power energy storage and conversion systems. SiOx is a very attractive anode material for lithium-ion batteries, but both low electronic conductivity and volume effect severely hamper its practical application. In this work, multiwall carbon nanotube (MWCNT) and N-doped carbon are combined to improve the electrochemical properties of SiOx. The synthesized composite (labeled as SiOx/MWCNT/N-doped C) has a network structure, in which MWCNT serves as a highly conductive and porous scaffold facilitating electron and ion transport, while N-doped C improves electric contact between SiOx/MWCNT particles and prevents the physical and electrochemical agglomeration of SiOx. The electrochemical measurement shows that the SiOx/MWCNT/N-doped C exhibits excellent cyclic stability and rate capability. At a current density of 100 mA g−1, a stable discharge capacity of about 620 mAh g−1 is achieved and the capacity can be preserved up to 450 cycles. The enhanced conductivity and stable electrode structure should be responsible for the excellent electrochemical performance.

Introduction

The rapid development of both electrical vehicles and large-scale energy storage systems has created great demands for lithium-ion batteries with high energy density and long cycle life [1]. Since the electrode materials play predominant part in deciding the energy density of lithium-ion batteries, developing high-capacity electrode materials has been pursued [2], [3]. Silicon is regarded as the most ideal anode material for lithium-ion batteries because of a high specific capacity of about 3600 mAh g−1 at room temperature, satisfying lithium insertion/extraction potentials and abundant resources [4]. However, the exceptional lithium-storage capability is accompanied by a huge volume variation upon cycling, which leads to structural instability of the electrode and becomes the biggest challenge for the application of Si-based materials [5], [6]. In recent two decades, although some important progress has been achieved, the large-scale application of silicon-based materials in lithium-ion batteries still faces many challenges [7], [8], [9], [10]. Especially when a high mass loading of active materials is used per unit area, it is still difficult to achieve stable cycle performance in prolonged cycling. Compared with pure silicon, silicon oxides not only have a relatively small volume change, but also Li2O and silicate salts formed during the initial lithiation severe as the dispersion and buffer media of silicon in subsequent cycles [11], [12], [13]. Overall, silicon oxide electrodes have better cyclic stability than the elemental silicon electrodes. Other than commercial SiO, nonstoichiometric SiOx (x>1) is synthesized readily by simple liquid phase chemical method, which is cost-effective and offers much more choices to improve its electrochemical performance. In the recent several years, SiOx has attracted the researchers’ attention and exhibits promising prospect [14], [15], [16], [17], [18], [19], [20]. For instance, Guo used cellulosic substances as template to prepare SiOx nanotubular materials [21]. The SiOx nanotube exhibited a reversible capacity of 940 mAh g−1 and the capacity retention kept over 91.5% after 50 cycles. SiOx/C composite synthesized by Zhao’ group via a template assisted hydrothermal route and a carbon-coating process demonstrated a specific capacity of 780 mA h g−1 with a 0.02% decay per cycle [20]. Lately, we fabricated graphene nanoplatelets-supported SiOx composite, which showed a stable reversible capacity of about 630 mAh g−1 and the capacity retention could be kept up to 250 cycles [22]. However, the cyclic stability of these materials is still far from the requirement of practical application and thus more advanced material structural design is needed. In this work, network-structural SiOx/MWCNT/N-doped C ternary composite is fabricated. Herein, MWCNT is used as the scaffold of anchoring SiOx. Because of high conductivity, excellent flexibility and large specific area [23], the introduction of MWCNT is expected to effectively improve the conductivity of the electrode and buffer the volume change of SiOx to a large extent. Considering the interface contact between SiOx/MWCNT particles is not good enough because of low conductive SiOx on the surface of MWCNT and the exposed SiOx nanoparticles tend to agglomeration during annealing and cycling, high conductive N-doped carbon is used to coat SiOx/MWCNT. The electrochemical measurement shows that such structural composite exhibits prominent cycle stability with a high reversible capacity.

Section snippets

Material preparation

A certain amount of MWCNT (US Research Nanomaterials, Inc.) was dispersed in a solution composed of 0.2 g of cetyltrimethylammonium bromide (CTAB), 25 mL of ethanol and 58 mL of distilled water via ultrasonication. Next, 2.5 mL of ammonium hydroxide was added and the solution was stirred at room temperature for 15 min. Subsequently, 1.8 mL of (C2H5O)3SiC2H5 was added dropwise to the above dispersion and stirring was continued until the solution completely became clear. The precipitate was collected

Results and discussion

The SiOx/MWCNT/N-doped C is synthesized by self-assembly, in situ polymerization reactions and physical coating, followed by heat treatment. Firstly, CTA+ cations were adsorbed on MWCNT surface by intermolecular interaction. With the help of aqueous ammonia, negatively charged oligomeric silicate species produced by the hydrolysis of (C2H5O)3SiC2H5 were adsorbed on the surface of CTA+-coated MWCNT by electrostatic interaction [24], [25]. The absorbed oligomeric alkyl silicate species

Conclusions

In summary, we successfully fabricate a network-structured SiOx/MWCNT/N-doped C anode composite for lithium-ion batteries. The SiOx/MWCNT/N-doped C composite exhibits excellent cyclic stability with a high capacity. After 450 deep charge–discharge cycles, the discharge capacity is still as high as 621 mAh g−1. The composite also demonstrates good rate capability. The excellent electrochemical performance of the SiOx/MWCNT/N-doped C should be attributed to the combination of MWCNT and N-doped

Acknowledgment

This research was financially supported by Natural Science Foundation of China (51374175 and 21576030), Lithium-ion Battery Innovative Team Project of China West Normal University (CXTD2015-1) and Foundation of enterprises, universities and research institutes of Jiangsu Province (BY2014037-31).

References (36)

Cited by (53)

View all citing articles on Scopus
View full text