Elsevier

Journal of Power Sources

Volume 196, Issue 20, 15 October 2011, Pages 8669-8674
Journal of Power Sources

Facile synthesis and electrochemical properties of Fe3O4 nanoparticles for Li ion battery anode

https://doi.org/10.1016/j.jpowsour.2011.06.067Get rights and content

Abstract

Nanostructured Fe3O4 nanoparticles were prepared by a simple sonication assisted co-precipitation method. Transmission electron microscopy, X-ray diffraction and BET surface area analysis confirmed the formation of ∼20 nm crystallites that constitute ∼200 nm nanoclusters. Galvanostatic charge–discharge cycling of the Fe3O4 nanoaprticles in half cell configuration with Li at 100 mA g−1 current density exhibited specific reversible capacity of 1000 mAh g−1. The cells showed stability at high current charge–discharge rates of 4000 mA g−1 and very good capacity retention up to 200 cycles. After multiple high current cycling regimes, the cell always recovered to full reversible capacity of ∼1000 mAh g−1 at 0.1 C rate.

Highlights

• A simple and inexpensive ultrasonic assisted co-precipitation route has been followed to make monodisperse Fe3O4 nanoparticles. • Anodes made from the Fe3O4 nanoparticles exhibit specific reversible capacity of ∼1000 mAh g−1. • The anodes could operate at a current density from 100 to 4000 mA gm−1 with coulombic efficiency of almost 100%. • The anodes showed excellent cyclic stability for at least 200 cycles without capacity fade, and returned to specific capacity of 1000 mAh gm−1 at 0.1 C after multiple high current charge–discharge cycles.

Introduction

Li ion batteries (LIB) are, by far, the most promising of all secondary storage devices. Growing demand for high energy density and high power density batteries has shifted the attention from graphitic anodes, with a theoretical capacity of 372 mAh g−1, to many oxides, alloys and hybrid materials with higher specific capacity. Recently, it has been shown that transition metal oxides possessing reversible capacity between 600 and 1000 mAh g−1 can potentially replace graphite based anodes [1]. In particular, Fe3O4 exhibits promise since it possesses high specific capacity, is cheap, abundantly available, and environmentally benign [2], [3]. Magnetite also possesses good electronic conductivity of 2 × 104 S m−1, which is considerably better than other transition metal oxides [4]. Although the results are promising, capacity retention after several cycles and the ability to operate at higher current densities are some of the concerns that need to be bettered. In general, anode materials with higher specific capacity tend to undergo considerable amount of volume dilation between the Li+ inserted and extracted states. For Fe3O4 based anodes the active materials transform from an oxide to metallic iron. Such volume changes result in pulverization of the active materials, disintegration of the anode assembly, poor cycling performance, and capacity fade over several charge discharge cycles [5]. Battery anodes with nanostructured materials have significant advantages [6] because of (i) short Li ion transport distance, (ii) large electrolyte-electrode contact area that provides faster reactions, and (iii) accommodation of the structural strain generated due to Li intercalation. Therefore, to improve the electrochemical properties of LIB anodes, Fe-oxide based nanostructured materials [7], [8], [9], [10], [11], [12], composites and hybrids [13], [14], [15], [16], [17], [18], [19], [20], [21], [22] have been considered. Taberna et al. deposited Fe3O4 on Cu nanorods and obtained 800 mAh g−1 capacity cycling at C/32 rate [3]. Recently, Wang et al. produced sub-micron spheroids of magnetite that delivered 900 mAh g−1 capacity for up to 60 cycles [10]. On the contrary, however, Chen et al. showed that microcrystalline Fe3O4 exhibited better capacity retention (685 mAh g 1 at 50th cycle) than nanocrystalline Fe3O4 [11]. With Fe3O4 and carbon based composites Zhang et al. and Liu et al. obtained capacity in the range of 600 mAh g−1 that were stable over 50 cycles [8], [14]. Some of the very recent literatures have shown graphene–magnetite composites with good cyclic stability and rate capability [16], [17], [18], [19], [20], [21], [22].

Design of an efficient anode configuration can be accomplished in two stages. Crystallinity, morphology, size and the distribution of the active oxide materials have a profound influence on the performance of the battery; it has been shown specifically in the iron oxide system [23], [24]. Therefore, optimization of the nanoparticle parameters can lead to better capacity, rate capability and cyclic stability. Secondly, with the use of new admixtures, including graphene, carbon nanotubes (CNT), core-shell assemblies, etc., the cell performance can be bettered further [15], [20], [21], [22]. The current work underscores the first approach, and describes an easy and inexpensive process for the synthesis of Fe3O4 nanoparticles. Synthesis of oxide materials by co-precipitation process is a very well established and inexpensive technique that has the potential for processing of bulk amounts of nanostructured materials [25]. In the current work, a novel ultrasonic assisted co-precipitation method has been used to synthesize magnetite nanoparticles with controlled size, morphology and distribution. The said magnetite nanoparticles were found to deliver excellent specific reversible capacity of 1000 mAh g−1 at 0.1 C, sustain cycling at extremely high current density (4000 mA g−1), and exhibit stability up to at least 200 cycles without capacity fading.

Section snippets

Nanoparticle synthesis

An inexpensive, sonication assisted co-precipitation method that has been tried in other systems [26] was applied for the synthesis of Fe3O4 nanoparticles. Fe3+ and Fe2+ chlorides (Alfa Aesar) were mixed at the molar ratio of 2:1 in deionized water. The solution was destabilized with the addition of 1 M NaOH solution while maintaining the pH of the system between 8 and 10. The contents in the beaker were irradiated with an ultrasonic horn (20 kHz) for 30 min to yield a blackish suspension. The

Nanoparticles synthesis

The washed nanoparticles were such that they can be peptized with water without the use of any surfactant to make a nanocolloid that remains stable for months. The dried Fe3O4 nanoparticles, however, were powders with a monomodal size distribution, as can be seen from the TEM micrographs (cf. Fig. 1a). The SAD pattern shows well defined concentric rings, indicating that the powders are crystalline and not amorphous (inset of Fig. 1a). Absence of spots in the SAD pattern also indicated that the

Discussion

A few features come out strikingly different in the current set of experiments as compared to the electrochemical behavior of Fe3O4 based conventional anode materials in the literature. Based on Eqs. (2), (3), the theoretical capacity for Fe3O4 is 924 mAh g−1 considering transfer of 8 electrons per formula weight. The specific capacity obtained in the current study (1000 mAh g−1) seems slightly higher than the theoretical value. Although rarely seen for intercalation mechanism based anodes

Summary

A facile bulk synthesis route was followed to produce monomodal magnetite nanoparticles of ∼10 nm. Electrochemical characterization of the nanopowders for Li ion battery anodes showed reversible capacity of ∼1000 mAh g−1 for charge–discharge rates at 0.1 C. Progressive increase in the current showed that the cell can cycle at 4000 mA g−1 current density and deliver reversible capacity of 200 mAh g−1. The cells showed no fading of capacity for at least 200 charge–discharge cycles, and always recovered

Acknowledgements

The author is indebted to Prof. Martin Harmer (Lehigh University) and Prof. Rishi Raj (University of Colorado at Boulder) for their encouragement to pursue independent work. The Fe3O4 nanoparticles were prepared at Lehigh University, and the electrochemical tests were carried out at the University of Colorado at Boulder.

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