Solid 7Li-NMR and in situ XRD studies of the insertion reaction oflithium with tin oxide and tin-based amorphous composite oxide

Abstract

The lithium insertion reactions with tin (II) oxide (SnO) andtin-based composite oxide (abbreviated as TBCO) are studied by solid7Li-NMR Knight shift, T1 and T1ρ relaxation rate, TEM and in situ XRD methods. By the insertion reaction for SnO, the lithium oxide andβ-tin are produced first at Li/Sn = 2; at Li/Sn = 3 to 6the products are not simple and a mixture of LiSn2, LiSn,Li5Sn2 and Li7Sn2 alloys is detected during the insertion. For theTBCO, which is revealed as amorphous, mainly constituted by randomlydistributed very short-range (order of 10-9 m) regions by TEMobservation, it is found that electrochemically inserted lithium forms Li2Oand produces metallic tin (Sn) in the first step (Li/Sn <2), thenthe highly ionic lithium-tin alloys, Li7Sn2 (and Li7Si2), areproduced in the second step (Li/Sn >2). During the second step, theLi/Sn ratio of formed lithium-tin alloy is kept at almost 4. By the analysesof 7Li NMR Knight shifts, line shape and in situ XRD, thelithium-inserted TBCOs are characterized as almost amorphous and mixtures ofhighly ionic components.