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

• Published in: Chemistry of materials 2018-03, Vol.30 (5), p.1505-1516
• Main Authors: Tsiamtsouri, Maria A, Allan, Phoebe K, Pell, Andrew J, Stratford, Joshua M, Kim, Gunwoo, Kerber, Rachel N, Magusin, Pieter C.M.M, Jefferson, David A, Grey, Clare P
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.7b03753

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.