  We suggest that the lithiation of pristine SnO forms a layered Li$_\text{X}$O
structure while the expelled tin atoms agglomerate into 'surface' planes
separating the Li$_\text{X}$O layers. The proposed lithiation model widely
differs from the common assumption that tin segregates into nano-clusters
embedded in the lithia matrix. With this model we are able to account for the
various tin bonds that are seen experimentally and explain the three volume
expansion phases that occur when SnO undergoes lithiation: (i) at low
concentrations Li behaves as an intercalated species inducing small volume
increases; (ii) for intermediate concentrations SnO transforms into lithia
causing a large expansion; (iii) finally, as the Li concentration further
increases a saturation of the lithia takes place until a layered Li$_2$O is
formed. A moderate volume expansion results from this last process. We also
report a 'zipper' nucleation mechanism that could provide the seed for the
transformation from tin oxide to lithium oxide.
