Free-Standing Sb@Rgo Nanocomposite Films for High-Performance Lithium-Ion Battery Anodes
Authors: Zhang Wei , Hu Xianluo , Huang Yunhui 
Published: February 2020

Introduction

Lithium-ion batteries (LIBs) have been overwhelmingly dominant among energy-storage systems1. In particular, they have become indispensable energy-storage devices for intermittent energy conversions, such as solar and wind power2-3. Thanks to the excellent electrochemical performances, LIBs have been successfully integrated into mobile phones, medical and military devices, and have been applied in electrical vehicles (EVs) and stationary storage for renewable energies. Among the various anode materials of LIBs, Sb and its compounds have recently received wide attention as a viable alternative anode material4. Owing to the alloying–dealloying reaction mechanism, these materials have higher theoretical capacities (660 mAh g−1) compared to the intercalation compounds5. However, Sb-based anode materials encounter a large volumetric change during the charge-discharge process, resulting in fast capacity fading.
Here we report on a free-standing nanocomposite made of Sb nanoparticles and reduced graphene oxide (rGO), where Sb nanoparticles were uniformly distributed in the rGO layers by a facile method. The graphene layers can provide the support for anchoring Sb nanoparticles and work as a highly conductive matrix. Importantly, Sb nanoparticles buffered by the graphene matrix can effectively tolerate the massive volume change during the Li alloying/dealloying reaction, which contributes to its highly reversible capacity, excellent cyclic performance and superior rate capability as an anode material for LIBs.

Experimental

Typically, the free-standing Sb@rGO hybrid films were fabricated on a large scale through a facile method in anhydrous ethanol followed by an annealing process. The morphology and structure of the Sb@rGO composite paper was measured by powder X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). For electrochemical tests, the Sb@rGO paper was cut into small pieces as the working electrode in a coin-type cells using lithium metal as reference and counter electrodes and 1 M LiPF6 solution in a mixture of EC and DMC (v/v =1:1) as the electrolyte. The galvanostatic charge-discharge measurements were carried out using a Land Battery Measurement System (Land, China) under various current densities of 100–20000 mA g−1 in the fixed voltage range of 3.00–0.01 V vs. Li/Li+.

Results and Discussion

The crystalline structure of Sb@rGO is revealed by XRD. As shown in Fig. 1a, all the diffraction peaks can be indexed to the typical hexagonal phase of metallic Sb (JCPDS No.35-0732). The Raman spectrum (Fig. 1b) of the Sb@rGO composite shows the peaks at 1348 cm–1 for the D band and 1588 cm−1 for the G band, where the high-intensity G peak suggests a high-graphitization degree. The peak at 657 cm–1 indicates the existence of Sb in the nanocomposite. The TEM images (Fig. 1c and 1d) reveal that Sb nanoparticles in size of 5−10 nm are uniformly embedded in the grapheme nanosheets.
The lithium-storage performance of the Sb@rGO product was evaluated using lithium half-cells. Fig. 1e shows the discharge-charge curves for the Sb@rGO hybrid at 500 mA g−1 between a potential ranging from 3−0.01 V. The Sb@rGO electrode exhibits a high capacity of 575 mAh g−1 after 10 cycles and 584 mAh g−1 after 250 cycles without capacity fading, indicating an outstanding cyclability. In addition, the Sb@rGO electrode also shows excellent high-rate capability, as presented in Fig. 1f. When the current rate increases from 200 mA g−1 to 20 A g−1, a high capacity of 275 mAh g−1can still be achieved, indicating an excellent rate capability.
In conclusion, we have successfully fabricated a hybrid film of ultrasmall Sb nanoparticles uniformly distributed in rGO layers through a convenient route. The Sb@rGO film electrode exhibits an excellent cycling performance, highly reversible capacity, and superior rate capability as an anode material for LIBs.
Figure description: (a) XRD pattern, (b) Raman spectrum, (c,d) TEM images, (e) cycling performance and (f) rate performance of the Sb@rGO electrode.

References

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Figure 1