碳包覆Ti2Nb2O9纳米片的制备及其储钠性能

Preparation of Carbon Coated Ti2Nb2O9 Nanosheets and Its Sodium Ion Storage Properties

具有两种不同阳离子的二元金属氧化物在钠离子电池中可发生可逆的多电子反应,是一类非常具有应用前景的高容量负极材料。在本项工作中,通过离子交换法和化学剥离法得到HTiNbO5纳米片,采用水热法将其与蔗糖复合再经由后续热处理得到碳包覆的Ti2Nb2O9纳米片材料。碳包覆的Ti2Nb2O9纳米片可用作钠离子电池的负极材料,具有更高的电子导电性和多的反应活性点以及快速的离子传输通道,在50 mA∙g^−1的电流密度下具有265.2 mAh∙g^−1的可逆容量。在0.5 A∙g^−1的大电流密度下,循环200圈之后比容量为160.9 mAh∙g^−1(容量保持率75.3%)。研究结果表明Ti2Nb2O9/C纳米片在钠离子电池中具有出色的充放电性能和循环稳定性,为钠离子电池负极材料提供了可行的新选择。

In the past few decades, new energy industries have developed rapidly due to the threat of the depletion of non-renewable resources. Among them, the lithium-ion battery has attracted significant attention of various researchers. However, lithium-ion batteries are limited by the uneven distribution of lithium resources and high cost. Sodium, which is in the same periodic group as Lithium, can help alleviate the problems related to the limited development of lithium ion batteries owing to the shortage of lithium resources. Sodium ion batteries are cheap, with varying choice of electrolytes, and have relatively stable electrochemical performances. However, the radius of a sodium ion is larger than that of a lithium ion, leading to slow ion transportation as well as changes in the volume of the host material during the charging and discharging processes. Therefore, compared with existing lithium ion batteries, sodium ion battery anode materials are very limited. Moreover, most sodium ion battery electrode materials have low specific capacities and poor cycle retention rates. Among these, ternary metal oxides, which have two different cations and can reversibly react with sodium ions are promising high-capacity anode materials for sodium ion batteries. In this study, Ti2Nb2O9 nanosheets are obtained by ion-exchange and chemical-delaminate methods. The carbon-coated Ti2Nb2O9 nanosheets are obtained after hydrothermal coating with sucrose and calcination. From the thermogravimetric analysis(TG) curve, the carbon content in the composites is calculated to be approximately 8.0%. Owing to the rich reactive sites and a short ion transport pathway, the Ti2Nb2O9/C electrode delivers a high reversible capacity of 265.2 m Ah·g-1 at a current density of 50 m A·g-1. Even at a high current density of 500 m A·g-1, the electrode exhibits an excellent electrochemical performance with a reversible capacity of 160.9 m Ah·g-1 after 200 cycles(capacity retention of 75.3%). Additionally, the Ti2Nb2O9/C nanosheets exhibit high reversible capacities of 251.3, 224.6, 197.4, 176.3, and 156.5 m Ah·g-1 at the current densities of 100, 200, 500, 1000, and 2000 m A·g-1, respectively. It is demonstrated through the use X-ray photoelectron spectroscopy(XPS) that the following process involving the transfer of four electrons occurs: Ti4+/Ti3+, Nb5+/Nb4+, during the charging and discharging process of the Ti2Nb2O9 electrode in the voltage range of 0.01–3.0 V. The theoretical specific capacity of Ti2Nb2O9 in this process is calculated to be 252 m Ah·g-1, corresponding to the electrochemical data. Overall, this study demonstrates that the Ti2Nb2O9/C anode nanosheets have an excellent chargedischarge performance, cycle stability, and rate performance in sodium ion batteries, thereby providing a feasible choice for sodium ion battery anode materials.