Abstract
We report the exfoliation of layered Na2Ti3O7, a promising anode material for Na-ion batteries, and restacking using HNO3 and NaOH to form H-[Ti3O7] and Na(x)-[Ti3O7] compositions, respectively. The materials were characterized by a range of techniques (SEM, TEM, solid-state NMR, XRD, PDF). Although the formation of aggregated nanoparticles is favored under acidic restacking conditions, the use of basic conditions can lead to control over the adherence between the exfoliated layers. Pair distribution function (PDF) analysis confirms that the local TiO6 connectivity of the pristine material is maintained. The lowest sodium-containing phase Na(1)-[Ti3O7], which is the stable product upon Na+ leaching after consecutive washing steps, displays the best performance among the compositions studied, affording a stable reversible capacity of about 200 mAh·g–1 for 20 cycles at a C/20 rate. Washing removes the excess of “free/reactive” Na+, which otherwise forms inactive Na2CO3 in the insufficiently washed compositions.
Highlights
The discovery of atomically thick graphene has recently aroused great interest in the properties and phenomena exhibited by two-dimensional (2D) materials, which in general can be considered as the exfoliation products of layered structures to form either single or few layers
SEM shows that the pristine material comprises well-shaped nanorods of approximately 2.5 μm length and 0.1 μm thickness (Figure 2A)
It should be noted that the existence of Na2CO3 in the Na(2)-[Ti3O7] and Na(6)-[Ti3O7] compositions may have an additional effect on the nature of the solid-electrolyte interphase (SEI) forming during operation, due to its solubility in the electrolytes commonly used for sodium-ion batteries.[51]
Summary
The discovery of atomically thick graphene has recently aroused great interest in the properties and phenomena exhibited by two-dimensional (2D) materials, which in general can be considered as the exfoliation products of layered structures to form either single or few layers. We sought to entirely exfoliate Na2Ti3O7 into nanosheets by complete removal of Na, along with the alkyl ammonium ions used during the process, followed by reinsertion of Na ions to restack the layers in a more disordered fashion. The data were converted to intensity vs Q using the software Data Analysis WorkbeNch (DAWN).[24] Standard corrections (background subtraction, Compton scattering, detector effects) were applied, and the data were Fourier transformed to obtain G(r) using the software PDFGetX2 using a Qmax of 24 Å−1.25 Refinements against known TiO2 phases were performed in PDFGui.[26] Refinements against single-layer models were performed in the Diffpy-CMI complex modeling framework.[27] The starting model was simulated from supercells of the Na2Ti3O7 structure, where all atoms except for a single-layer in the middle of the unit cell were removed.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
