Elsevier

Journal of Power Sources

Volume 196, Issue 11, 1 June 2011, Pages 5122-5127
Journal of Power Sources

Short communication
Nickel–tin foam with nanostructured walls for rechargeable lithium battery

https://doi.org/10.1016/j.jpowsour.2011.01.110Get rights and content

Abstract

Nickel–tin foams with a graded micro-porous framework and nano-porous walls are created by an electrochemical deposition method for use as the anode in rechargeable lithium batteries. The resulting electrodes react readily with lithium electrochemically and deliver a reversible capacity of more than 470 mAh g−1 for up to 50 cycles. In addition, they show outstanding rate performance: their reversible capacity at a discharging rate of 20 C is about 70% of the capacity at a rate of 1 C, due mainly to their unique structure which allows facile lithium-ion transport and fast surface reactions. The reversible capacity and rate capability show strong dependence on the thickness of the deposit and this is associated with the accessibility of lithium ions inside the porous structure.

Research highlights

► Nickel–tin foams with a graded micro-porous framework and nano-porous walls were created for the first time by an electrochemical deposition method. ► The resulting material delivered a reversible capacity of more than 470 mAh g−1 for up to 50 cycles as the anode in rechargeable lithium battery. ► Its capacity retention at a discharging rate of 20 C was about 70% of the capacity at a rate of 1 C. This is outstanding rate performance exceeding that of the tin-based alloys reported previously. ► The structure presented herein is ideally suited for high-power applications where the rapid transport of lithium ions to the electrode/electrolyte interface and subsequent fast interfacial reaction are required.

Introduction

There has been strong demand for advanced lithium batteries to meet the energy requirements for portable electronic devices with multi-functionality and for eco-friendly transportation systems. With regard to the electrode materials, recent effort has been focused mainly on tin- and silicon-based anodes together with high-voltage cathodes [1], [2], [3]. In spite of the fact that the theoretical capacity of tin is lower than that of silicon, the comparative ease with which various structures and alloy types can be prepared from tin has attracted the attention of researchers. Basically, tin undergoes a large reaction-induced volume change that results in internal mechanical strain. In particular, the tensile strain during the delithiation (or dealloying) process severely affects its structural integrity and results in deterioration of the cycleability.

Among the various useful tin-based compounds that have been developed, those include an inactive element (e.g., nickel, cobalt, copper, and iron) have been considered as promising material types [4], [5], [6], [7], [8], [9]. Their reaction with lithium is described as producing brittle lithium–tin active phases within a ductile inactive matrix that buffers the large volume change of the active phases, leading to improved cycleability. Although, in general, cycling stability and specific capacity are mutually exclusive, tin-based compounds still have good potential for use as next-generation anode materials. In a further attempt to enhance their performance, nano-porous structures were prepared with the intention of accommodating the volume change and also providing a large reaction area. Some of the studies in this area reported notable cycling performances [10], [11].

In this regard, pore gradient copper–tin (η′-Cu6Sn5) foam with a micro-porous framework and nano-porous walls was recently created by an electrochemical deposition process [12]. In addition to the buffering effect of the inactive copper matrix, its porous structure provides the space required for free volume expansion, which might effectively suppress the mechanical disintegration of the electrode during the operation of the cell. Furthermore, since its micro-framework facilitates the rapid transport of lithium ions inside the structure and the nano-porous walls assure a fast interfacial redox reaction, this structure is expected to have the inherently low concentration and activation polarization that are essential for achieving high-rate capability. The resultant porous copper–tin alloy showed superior rate performance, as expected. There were a number of cracks, however, even in the as-prepared sample and this indicates that it had poor mechanical properties, and some aspects of the battery performance (e.g., the cycleability, initial irreversible capacity, and charge–discharge efficiency) were unacceptable.

In this communication, pore gradient nickel–tin micro-foam with nano-structured walls is prepared for use as the anode in rechargeable lithium batteries. The morphology and composition of the as-prepared sample are examined at different deposition times. Its electrochemical properties are investigated by conducting a galvanostatic charge–discharge experiment. In particular, the change in the micro- and nano-porous structure is analyzed in the course of repetitive cycling. Furthermore, its rate capability is evaluated to demonstrate its feasibility for high-power applications.

Section snippets

Experimental details

For the preparation of the porous nickel–tin electrodeposits, a copper foil (Alfa Aesar, 99.8%), pre-treated in diluted sulfuric acid to remove the native surface oxide, was used as the working electrode (the cathode) and platinum wire was adopted for the counter electrode (the anode). The distance between the anode and cathode was kept at 1 cm. A constant cathodic current of 2 A cm−2 was applied for 10, 20 and 30 s to obtain nickel–tin electrodeposits using an EG&G 263A potentiostat/galvanostat.

Results and discussion

The top and cross-sectional views of nickel–tin foams created at different deposition times are presented in Fig. 1. The size of the surface pores increases with increasing deposition time and the foam walls become thicker, which is consistent with previous reports [12]. It is noted that the overall foam structure is well constructed with no evidence of the wall cracking that is usually observed in copper–tin alloys with a similar structure. The absence of cracks indicates that the strength of

Conclusions

Nickel–tin electrodeposits with a graded microporous framework and nanoporous walls have been created and their electrochemical properties have been evaluated for use as the anode in rechargeable lithium batteries. The reversible capacity of a sample prepared for 10 s remains above 470 mAh g−1 for up to 50 cycles, but the capacity falls with increasing thickness, due primarily to the difficulty for the lithium ions to penetrate into the thick walls. During the course of cycling, the overall

Acknowledgements

The research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (KRF-2006-331-D00713). Furthermore, the work was partially supported by the Converging Research Center Program (2010K001091) and the NCRC (National Core Research Center) program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2010-0001-226).

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