Abstract
A straightforward synthesis of Ti2(SO4)3 and reversible intercalation of 1.7 sodium ions via a two step process with formation of an intermediate phase was reported. The product was then washed with ethyl acetate and dried at 80°C overnight under vacuum. Electrochemical measurements were carried out in Swagelok cells using sodium metal as counter electrode and Whatman GF/D borosilicate glass fiber soaked in the electrolyte as separator. For the sample manually milled, a pseudo-plateau is observed at ca. 1.5 V vs Na+/Na followed by a sloping region to 1.0 V and another pseudo-plateau at ca. 1.0 V. Ball-milled samples exhibit similar profiles but with substantially enhanced capacity, even above 1.5 V. Upon oxidation, two well-defined plateaus at 1.10 and 1.64 V are observed in all samples. The number of electrons exchanged per mol of Ti2(SO4)3 increases with milling time to reach 3.4, which is above the theoretical expected capacity, but only 1.7 are reversible.