The reversible lithiation of SnO: a three-phase process

TL;DR

This paper presents a microscopic model explaining the reversible lithiation process in SnO anodes, highlighting the importance of layered grain structures for maintaining capacity and proposing thin-film design as a solution.

Contribution

It introduces a first-principles based model detailing the three-phase lithiation process in SnO and its implications for improving anode stability and capacity retention.

Findings

Model predicts anode volume expansion and voltage profile consistent with experiments.

Layered grain structure is crucial for reversible capacity.

Thin-film anode design can mitigate capacity loss.

Abstract

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.