  A high reversible capacity is a key feature for any rechargeable battery. In
the lithium-ion battery technology, tin-oxide anodes do fulfill this
requirement, but a fast loss of capacity hinders a full commercialization.
Using first-principles calculations, we propose a microscopic model that sheds
light on the reversible lithiation/delithiation of SnO and reveals that a
sintering of Sn causes a strong degradation of SnO-based anodes. When the
initial irreversible transformation ends, active anode grains consist of
Li-oxide layers separated by Sn bilayers. During the following reversible
lithiation, the Li-oxide undergoes two phase transformations that give rise to
a Li-enrichment of the oxide and the formation of a layered SnLi composite. We
find that the model-predicted anode volume expansion and voltage profile agree
well with experiment, and a layered anode grain is highly-conductive and has a
theoretical reversible capacity of 4.5 Li atoms per a SnO host unit. The model
suggests that the grain structure has to remain layered to sustain its
reversible capacity and a thin-film design of battery anodes could be a remedy
for the capacity loss.
