Structure of H₂Ti₃O₇and its evolution during sodium insertion as anode for Na ion batteries

Abstract

H2Ti3O7 was prepared as a single phase material by ionic exchange from Na2Ti3O7. The complete ionic exchange was confirmed by (1)H and (23)Na solid state Nuclear Magnetic Resonance (NMR). The atomic positions of H2Ti3O7 were obtained from the Rietveld refinement of powder X-ray diffraction (PXRD) and neutron diffraction experimental data, the latter collected at two different wavelengths to precisely determine the hydrogen atomic positions in the structure. All H(+) cations are hydrogen bonded to two adjacent [Ti3O7](2-) layers leading to the gliding of the layers and lattice centring with respect to the parent Na2Ti3O7. In contrast with a previous report where protons were located in two different positions of H2Ti3O7, 3 types of proton positions were found. Two of the three types of proton are bonded to the only oxygen linked to a single titanium atom forming an H-O-H angle close to that of the water molecule. H2Ti3O7 is able to electrochemically insert Na(+). The electrochemical insertion of sodium into H2Ti3O7 starts with a solid solution regime of the C-centred phase. Then, between 0.6 and 1.2 inserted Na(+) the reaction proceeds through a two phase reaction and a plateau at 1.3 V vs. Na(+)/Na is observed in the voltage-composition curve. The second phase resembles the primitive Na2Ti3O7 cell as detected by in situ PXRD. Upon oxidation, from 0.9 to 2.2 V, the PXRD pattern remains mostly unchanged probably due to H(+) removal instead of Na(+), with the capacity quickly fading upon cycling. Conditioning H2Ti3O7 for two cycles at 0.9-2.2 V before cycling in the 0.05-1.6 V range yields similar specific capacity and better retention than the original Na2Ti3O7 in the same voltage range.

Structural and Electronic Properties of Na2Ti3O7 and H2Ti3O7

“…The structural optimization of H 2 Ti 3 O 7 is performed using a supercell containing 48 atoms. The supercell is obtained by doubling the unit cell in Figure (f) in the direction perpendicular to the Ti‐O layer . One of the two layers is then shifted laterally by half cell, as shown in Figure (g), and Figure (h) shows the lateral view of the double cell where the shift by half cell is clearly visible.…”

A DFT +Ustudy on structural, electronic, vibrational and thermodynamic properties of TiO2polymorphs and hydrogen titanate: tuning the Hubbard ‘U-term’

“…In table 6 bulk modulus and volume variation using DFT and DFT+U at 0 K and 298 K is listed to compare the effect of addition of Hubbard parameter in our calculations [13,45,46].…”

“…The polymorph TiO 2 -B has been studied to a lesser extent and currently, only few theoretical and experimental studies of their properties exist [9][10][11]. Fewer reports are found regarding hydrogen titanate (H 2 Ti 3 O 7 ) [12][13][14].…”

Investigation the sodium storage kinetics of H1.07Ti1.73O4@rGO composites for high rate and long cycle performance

“…5,[38][39][40] As a new 2D material, H 1.07 Ti 1.73 O 4 (HTO) is a kind of insertion type anodes with a large interplanar spacing of 0.904 nm ((020) crystal plane), a much lower sodiation/desodiation plateaus, and a higher theoretical specific capacity than NTO. 41 Although there is one study to use HTO as the anode of SIBs, 42 plenty of works need to be done to investigate sodium ion storage behavior and further improve the performance of HTO, including the electrochemical reactions, phase change during the sodiation/desodiation process and surface kinetics.…”