Structural transformation of Na2Mn2(SO4)3 alluaudite into orthorhombic Li2Mn2(SO4)3 induced after lithium intercalation

Double sulfate salts of sodium and manganese, Na2Mn2(SO4)(3), with an alluaudite-type of structure has been shown to intercalate Li+ ions reversibly, but the mechanism is still unclear. This study aims to exam-ine the structure transformation of the alluaudite sodium manganese sulfate Na2Mn2(SO4)(3) after Li+ intercalation by means of ex-situ transmission electron microscopy. We demonstrate that lithium inter-calation into alluaudite Na2Mn2(SO4)(3) proceeds at a nano-scale and leads to a formation of orthorhombic phase Li2Mn2(SO4)(3). Although the alluaudite and orthorhombic structures possess common Mn2O10 enti-ties, they are completely different. Because of the nano-structure, in-situ generated phase Li2Mn2(SO4)(3) displays better capacity in comparison with the phase obtained before the electrochemical experiment. The orthorhombic Li2Mn2(SO4)(3) is obtained by freeze-drying method, followed by thermal treatment at 500 C. The revised electrochemical property shows that orthorhombic Li2Mn2(SO4)(3) is able to intercalate reversible at least 1 mol of Li only in the case when electrolyte based on ionic liquid is used. Copyright (C) 2022 Elsevier Ltd. All rights reserved.