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

The lithium insertion reactions with tin (II) oxide (SnO) and tin-based composite oxide (abbreviated as TBCO) are studied by solid Li-7-NMR Knight shift, T-1 and T-1 rho, relaxation rate, TEM and tn situ XRD methods. By the insertion reaction for SnO, the lithium oxide and beta -tin are produced first at Li/Sn = 2; at Li/Sn = 3 to 6 the products are not simple and a mixture of LiSn2, LiSn, Li5Sn2 and Li7Sn2 alloys is detected during the insertion. For the TBCO, which is revealed as amorphous, mainly constituted by randomly distributed very short-range (order of 10(-9) In) regions by TEM observation, it is found that elsctrochemically inserted lithium forms Li2O and produces metallic tin (Sn) in the first step (Li/Sn < 2), then the highly ionic lithium-tin alloys, Li7Sn2 land Li7Si2), are produced in the second step (Li/Sn > 2). During the second step, the Li/Sn ratio of formed lithium-tin alloy is kept at almost 4. By the analyses of Li-7 NMR Knight shifts, line shape and lit situ XRD, the lithium-inserted TBCOs are characterized as almost amorphous and mixtures of highly ionic components.