Construction Of Turbostratic Titanates And Their Sodium Storage Performance

As the demand for green energy in modern society, lithium-ion batteries(LIB) has been rapidly developed and widely applied in energy storage. However, the wide applications of LIB in electric vehicles and large-scale energy storage will inevitably lead to a relative shortage of lithium resource,thus, the exploration of the sodium-ion batteries(SIB) with excellent electrochemical properties has attracted wide attentions in the field of next generation battery technologies due to its low cost, abundant sodium resource and environment-friendly. Inthis work, we constructed a novel turbostratic titanate/graphene structure via exfoliation and assembly technologies, and disclose the structure-activity relationship and sodium storage mechanisms as anode material in SIB. The main contents and results are as follows.Firstly, K0.8[Ti1.73Li0.27]O4(KTLO) precursor was synthesized through molten salt method, then the H1.08Ti1.73O4·H2O(HTO) nanosheets were prepared by proton exchange and organic amine stripping of KTLO. XRD, SEM and TEM characterizations show that the HTO nanosheets were well exfoliated in the organic amine solution, exhibiting a thickness of several tens of nanometers and a lateral size of several microns. The obtained HTO nanosheets can meet the requirements as building blocks in the construction of turbostratic titanates.The HTO suspension were uniformly mixed with graphene.After freeze-drying and heat treatment, a novel turbostratic titanate/graphene structurewas obtained. The mass ratio of graphene in the composites was adjusted from 0.05/9.5 to 2/8, and the thermal treatments were carried out from 300 to 500 oC. The results show that the TiO2/RGO composite with optimized electrochemical properties can be obtained with 10% reductive graphene mass ratio and thermal treatment temperature of 400 oC, delivering a first coulombic efficiency of 55.2% in the first cycle and a reversible capacity of 187.9 mA h g-1after 30 cycles, the capacity retention was 76.7 %.Charge and discharge at different current densities also demonstrate the excellent rate capability of TiO2/RGO composite.Further investigation shows that the sodium storage of TiO2/RGO composites is mainly contributed by anatase TiO2, graphene and active surface defects. Compared with GO, the RGO presents lower ID/IG and fewer defects, thus demonstrating excellent conductivity. The composite with RGO shows low internal resistance, leading to the improved reversible capacity and rate capability.In this work, we successfully design a novel turbostratic titanate/graphene structure and investigate its sodium storage mechanisms. The TiO2/RGO composite consists of expanded sodium storage space and 3D conductive network, thus significantly improves the sodium storage performance of layered titanates. Our work provide a new strategy to optimize the electrochemical performance of layered titanates as anode in SIB, and will present theoretical and experimental guidance for finding new sodium storage materials.