Exfoliation of layered Na-ion anode material Na2Ti3O7 for enhanced capacity and cyclability

TL;DR

This study demonstrates the exfoliation and restacking of Na2Ti3O7 to improve Na-ion battery anode performance, achieving stable capacities through controlled synthesis and washing procedures.

Contribution

It introduces a novel exfoliation and restacking method for Na2Ti3O7, optimizing its electrochemical properties for Na-ion batteries.

Findings

Na(1)-Ti3O7 shows the best reversible capacity (~200 mAh/g)

Basic restacking controls layer adherence and maintains TiO6 connectivity

Washing removes inactive Na2CO3, enhancing performance

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 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.