Dynamic Gradient Oxygen Layer Enables Stable Sn Anode for Lithium Storage

Sn-based anodes are of significant interest due to their high capacity and resource abundance for lithium-ion batteries. However, incomplete lithiation and severe volume expansion result in their low capacity and electrode pulverization. Here, a rationally designed coating layer, composed of disordered SnO_x (x = 1, 2) lamellar structures, on the Sn particles surface (Sn@SnO_x) is proposed. This coating effectively mitigates volume expansion and minimizes lithium consumption owing to the intercalation behaviors of SnO_x. During lithiation and delithiation, a dense, amorphous, mechanical coating with a dynamic gradient of oxygen forms in situ, providing excellent protection against continuous pulverization of the Sn particles. The intercalation-type dynamic gradient oxygen with high ionic conductivity enables rapid exchange of lithium ions, thus promoting the deep lithiation of Sn to form Li_4.4Sn. Such gradient oxygen protection mechanism of the oxide layer in Sn@SnO_x brings a high reversible capacity after 900 cycles with a capacity retention of 84%. This work offers a new strategy to design a protective coating layer on alloy-based anodes for high-performance lithium storage.