Graphene-Based Hybrid Nanostructured Electrodes for Li-Ion Batteries

With the ever-increasing demand for energy storage, lithium ion battery has been an attractive technology that has revolutionized the portable electronic industry [1]. With its large scale applications, such as in hybrid electric vehicles (HEV’s), and plug-in HEVs, there is great interest in developing multifunctional hybrid nanostructured electrode materials for high performance Li-ion batteries [2,3]. Novel architectures of hybrid nanomaterials as both electrodes and electrolytes, have been shown to improve the device performances. New electrode materials with high electrical conductivity and large surface area, resulting in improved electrochemical performances are highly desirable. Though metal oxides with high specific capacity have been extensively studied as advanced Li-ion battery anodes, their structural instability under lithium insertion has been of great concern [4]. Hence, several approaches have been undertaken to improve the electrochemical performance of metal oxides as efficient Li-ion battery anodes. One of the strategies to increase the conductivity is by incorporating the anode material on the conducting carbonaceous matrix including mesoporous carbon, amorphous carbon, carbon nanotubes and graphenes [5].

Here, we report the synthesis of Nb₂O₅ and TiNb₂O₇ -anchored graphene hybrid nanocomposites through simple hydrothermal method and its electrochemical performance studies as advanced anodes for lithium ion battery. The nanocomposite electrodes have been characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Thermo Gravimetric Analysis (TGA). Using these hybrid nanostructures as positive electrodes in 1 M LiPF₆–EC/DMC electrolyte vs. Li metal negative electrodes, Cyclic voltammetry and Galvanostatic charge-discharge cycling measurements have been performed.

The self-supported nanostructured electrodes, with graphene as support with homogenously anchored orthorhombic Nb₂O₅ (T-Nb₂O₅) and monoclinic TiNb₂O₇ nanoparticles, exhibited excellent electrochemical performance with high reversible capacity and enhanced rate capability, arising from the synergistic effect of Nb₂O₅ nanocrystals anchored onto conducting graphene layers. While the presence of three-dimensional structure in Nb₂O₅ and TiNb₂O₇ provides open channels and vacant sites for lithium intercalation, presence of conducting graphene sheets improve the kinetics of lithium ion and electron transport, leading to improved battery performances. The hybrid nanocomposite electrodes showed exceptional power capability, with ~80% of the total capacity sustained at 16C rate (Figure 2). We believe these hybrid nanocomposites, with superior electrochemical performance, can be used as efficient anode for high performance lithium ion battery. 

Figure 1. SEM images of (a) Nb₂O₅ nanocrystals (b) Nb₂O₅/graphene (c) TiNb₂O₇ and (d) TiNb₂O₇/graphene nanocomposite

Figure 2. (a) Galvanostatic cycling of TiNb₂O₇/graphene nanocomposite electrode, (b) Rate capability of Nb₂O₅/graphene nanocomposite electrode.

References

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