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2016 Volume 74 Issue 2
2016, 74(2): 185-190
doi: 10.6023/A15100658
Abstract:
Commercial graphite anode material for lithium-ion batteries (LIB) with a theoretical specific capacity of 372 mAh·g-1 is unable to satisfy the requirements of increasing mobility and high energy demands. Therefore, it is necessary to develop alternative anode material with high specific capacity. In recent years, a large amount of research has been worked out in the area of high capacity anode materials, for example, silicon (Si) and germanium (Ge). However, the large volume changes of Si and Ge during the charge and discharge process result in the cracking and pulverization of active material and delamination from the current collector, leading to a rapid decay during the cycling. As a semiconductor, Zn2GeO4 possesses a high capacity of 1443 mAh·g-1 which is 90.19% as high as Ge. Nevertheless, the weight rate of germanium element in Zn2GeO4 is only 27.15%, which can effectively cut down the cost of anode material. In this work, Zn2GeO4 nanorods were synthesized through a hydrothermal method by using GeO2 and Zn(CH3COO)2·2H2O and combined with RGO to form a 3D composite. In a typical synthesis, 1.10 g Zn(CH3COO)2·2H2O and 0.52 g GeO2 was added into 15 mL deionized (DI) water and the pH of the mixture was adjusted to 7~8 by using NaOH aqueous solution. Then, the hydrothermal treatment was performed at 140℃ for 24 h in an oven to obtain Zn2GeO4 nanorods. Finally, the Zn2GeO4 nanorods were filtrated with GO to form a uniform membrane and reduced by hydrazine hydrate. The Zn2GeO4 nanorods and Zn2GeO4@RGO composite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, etc. SEM and TEM testified that Zn2GeO4 nanorods were firmly adhered on the surface of graphene sheets, which can effectively avoid the stacking of graphene sheets. The graphene sheets connected with each other to form an electric conductive network, which can improve the electrical conductivity of the composite. Furthermore, the electrodes are fabricated without conductive additive that can improve the weight ratio of the active material in the whole electrodes. The excellent electrochemical performance showed that the 3D architecture electrode which worked as a stable framework to accommodate the volume change of active material during Li+insertion/extraction. It delivers a specific capacity of 1189.5 mAh·g-1 at 500 mA·g-1 after 190 discharge/charge cycles. When at different current densities of 0.8, 1.6, 3.2 A·g-1, the capacities were found to be about 880, 700, 450 mAh·g-1, respectively. Even at a high current density of 6.4 A·g-1, the capacity can maintain about 250 mAh·g-1. These results indicate that the composite possesses outstanding cycling stability and excellent rate performance.
Commercial graphite anode material for lithium-ion batteries (LIB) with a theoretical specific capacity of 372 mAh·g-1 is unable to satisfy the requirements of increasing mobility and high energy demands. Therefore, it is necessary to develop alternative anode material with high specific capacity. In recent years, a large amount of research has been worked out in the area of high capacity anode materials, for example, silicon (Si) and germanium (Ge). However, the large volume changes of Si and Ge during the charge and discharge process result in the cracking and pulverization of active material and delamination from the current collector, leading to a rapid decay during the cycling. As a semiconductor, Zn2GeO4 possesses a high capacity of 1443 mAh·g-1 which is 90.19% as high as Ge. Nevertheless, the weight rate of germanium element in Zn2GeO4 is only 27.15%, which can effectively cut down the cost of anode material. In this work, Zn2GeO4 nanorods were synthesized through a hydrothermal method by using GeO2 and Zn(CH3COO)2·2H2O and combined with RGO to form a 3D composite. In a typical synthesis, 1.10 g Zn(CH3COO)2·2H2O and 0.52 g GeO2 was added into 15 mL deionized (DI) water and the pH of the mixture was adjusted to 7~8 by using NaOH aqueous solution. Then, the hydrothermal treatment was performed at 140℃ for 24 h in an oven to obtain Zn2GeO4 nanorods. Finally, the Zn2GeO4 nanorods were filtrated with GO to form a uniform membrane and reduced by hydrazine hydrate. The Zn2GeO4 nanorods and Zn2GeO4@RGO composite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, etc. SEM and TEM testified that Zn2GeO4 nanorods were firmly adhered on the surface of graphene sheets, which can effectively avoid the stacking of graphene sheets. The graphene sheets connected with each other to form an electric conductive network, which can improve the electrical conductivity of the composite. Furthermore, the electrodes are fabricated without conductive additive that can improve the weight ratio of the active material in the whole electrodes. The excellent electrochemical performance showed that the 3D architecture electrode which worked as a stable framework to accommodate the volume change of active material during Li+insertion/extraction. It delivers a specific capacity of 1189.5 mAh·g-1 at 500 mA·g-1 after 190 discharge/charge cycles. When at different current densities of 0.8, 1.6, 3.2 A·g-1, the capacities were found to be about 880, 700, 450 mAh·g-1, respectively. Even at a high current density of 6.4 A·g-1, the capacity can maintain about 250 mAh·g-1. These results indicate that the composite possesses outstanding cycling stability and excellent rate performance.
