Introducing a 0.2 V sodium-ion battery anode: The Na2Ti3O7 to Na3 − xTi3O7 pathway

• A new stable intermediate phase has been discovered during discharge of Na2Ti3O7.
• This Na2Ti3O7 ⇋ Na3 − xTi3O7 pathway elicits a charge plateau at 0.2 V.
• This is the lowest voltage plateau of any non-carbon sodium-ion anode ever reported.
• It shows an ultra-fast response at 80 C with a cycle life of 1500 cycles.
• The Na2Ti3O7 ⇋ Na3 − xTi3O7 pathway is a distinct two-phase reaction mechanism.

A new sodium storage pathway is unveiled for the anode Na2Ti3O7 which involves the newly discovered intermediate phase of Na3 − xTi3O7. Details about this Na2Ti3O7 ⇋ Na3 − xTi3O7 sodium storage pathway and how it relates to the conventional Na2Ti3O7 ⇋ Na4Ti3O7 pathway are mentioned. This Na2Ti3O7 ⇋ Na3 − xTi3O7 pathway has the lowest redox voltage of 0.2 V vs Na/Na+ ever reported for any non-carbon based sodium-ion battery anode along with moderately high capacity approaching 89 mAh/g, negligible polarization, excellent rate performance (up to 80 C, or 45 s response) and good cycle life till 1500 cycles. These results indicate this pathway's potential as an anode for sodium-ion batteries meant for diverse applications.

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