Mechanistic Insights into Sodium-ion Storage Differences between Crystalline and Nanomaterial Na2Ti3O7

Sodium titanate (Na2Ti3O7) is an important anode material candidate for next-generation sodium-ion batteries. It displays a theoretical capacity of 177 mA.h g-1 and has been reported to have the lowest insertion voltage of any Na intercalation oxide to date. Other factors like low cost and good cycling stability make this a very attractive anode material for Na-ion batteries. However, its performance at high currents is hampered by poor ionic and electronic conductivity, and multiple methods have been trialled to improve the high-rate performance. This mainly includes its nanostructuration to improve the Na-ion diffusion. DFT studies have shown its maximum theoretical storage is 11 sodium ions stored per unit cell or a structural formula of Na5.5Ti3O7, corresponding to a specific capacity of 311 mAh g-1. Nevertheless, the reasons why the specific capacity of nanostructured Na2Ti3O7 approaches this theoretical limit whereas pristine Na2Ti3O7 does not, are not fully understood. Given the disordered nature of nanostructured Na2Ti3O7, neutron PDF measurements are essential to elucidate differences between the cycling characteristics of nanosheet and crystalline Na2Ti3O7, and in the local structure changes upon insertion/deinsertion of Na ions. This proposal is part of our wider research into investigating the charge/discharge mechanisms of nanomaterial Na2Ti3O7 and using this information to improve the properties of the material as an anode for Na-ion batteries.