Exfoliation of Layered Na-Ion Anode Material Na₂Ti₃O₇ for Enhanced Capacity and Cyclability

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 characterised by a range of techniques (SEM, TEM, solid-state NMR, XRD, PDF). Although the formation of aggregated nanoparticles is favoured 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 Na(1)-[Ti3O7] phase, 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.

Anomalous Phase Transition of Layered Lepidocrocite Titania Nanosheets to Anatase and Rutile

“…Titanium oxides with various kinds of polymorphs, such as anatase, rutile, brookite and lepidocrocite-type layered structure, have been among the most studied material systems in energy relevant applications such as photoelectrochemical solar cells, photocatalysis and electrode materials for Li/Na-ion batteries. [1][2][3][4][5][6][7] To meet the ever-increasing energy demand, intensive efforts have been devoted to develop the titanium oxides with tunable compositions, morphologies and structures. [8][9][10][11] Understanding the properties of the materials as a function of the crystallographic structure and the phase transition amongst these polymorphs, e.g.…”

Sodium Ion Microscale Electrochemical Energy Storage Device: Present Status and Future Perspective

“…[ 60 ] For instance, low sodium‐containing phase Na(1)‐[Ti 3 O 7 ] nanosheets exfoliated from layered NTO maintained capacity of 200 mAh g −1 . [ 61 ] These nanosheets formed by top‐down approach accelerated the Na ions diffusion kinetics and also promoted the wettability of microelectrodes. Similarly, a 3D flower‐like structure constructed by NTO nanosheet exhibited excellent rate performance with satisfactory capacity of 73.8 mAh g −1 even at 800 mA g −1 .…”

Na2Ti3O7 Nanotubes as Anode Materials for Sodium‐ion Batteries and Self‐powered Systems

“…Titanate materials have a layered structure, which has a large space for sodium ion insertion and extraction . So far, Na 2 Ti 3 O 7 (NTO) is widely used as anode material due to its high theoretical specific capacity of 200 mAh g −1 and low voltage, nevertheless, the structure and properties of the material tend to change to some extent due to the surface side reactions and volume change distortion during the insertion and extraction of sodium ions, which result in poor cycling performance …”

“…[14] So far, Na 2 Ti 3 O 7 (NTO) is widely used as anode material due to its high theoretical specific capacity of 200 mAh g À 1 and low voltage, [15] nevertheless, the structure and properties of the material tend to change to some extent due to the surface side reactions and volume change distortion during the insertion and extraction of sodium ions, which result in poor cycling performance. [16] In this work, Na 2 Ti 3 O 7 nanotubes were prepared by a hydrothermal method and used as an anode for SIBs with high specific capacity and excellent cycling performance up to 2000 cycles. Solid-state sodium batteries with Na 2 Ti 3 O 7 nanotubes anode and Na 3 Zr 2 Si 2 PO 12 electrolyte show comparable performance to the batteries with liquid electrolyte.…”