Reversible lithium insertion into Na2Ti6O13 structure

Pure Na2Ti6O13 phase was successfully prepared from partially washed (Na,H)TiO nanotubes and used as an insertion material for lithium ions. Results show that the structure can accommodate upto 3 mol of lithium per 1 mol of Na2Ti6O13. Accommodation of 0.5 mol of lithium per one titanium atom corresponds to the partial reduction of Ti4+ to Ti3+ and occurs several 100s of millivolts lower than typically encountered for titanium in an octahedral oxygen environment such as Li4Ti5O12. Lithium insertion into this phase was evaluated using especially in situ X-ray. Lithium insertion into Na2Ti6O13 phase includes three domains corresponding to two solid–solutions and a biphasic transition in the potential range between 1.5 V and 1.0 V vs. lithium. The process is very reversible so that after re-oxidation the structure is completely preserved. Capacity fading observed during the cycling is explained by parasitic reactions attributed to a catalytic effect of the exposed bare surface on the electrolyte degradation.