Difference in Electrochemical Mechanism of SnO Conversion in Lithium-Ion and Sodium-Ion Batteries: Combined in Operando and Ex Situ XAS Investigations.

Conversion and alloying type negative electrodes attracted huge attention in the present research on lithium/sodium-ion batteries (LIBs/SIBs) due to the high capacity delivered. Among these, SnO is investigated intensively in LIBs due to high cyclability, low reaction potential, cost-effectiveness, and environmental friendliness. Most of the LIB electrodes are explored in SIBs too due to expected similar electrochemical performance. Though several LIB negative electrode materials successfully worked in SIBs, bare SnO shows very poor electrochemical performance in SIB. The reason for this difference is investigated here through combined and X-ray absorption spectroscopy (XAS). For this, the electrodes of SnO (space group 4/ synthesized via one-pot hydrothermal method) were cycled in Na-ion and Li-ion half-cells. The Na/SnO half-cell delivered a much lower discharge capacity than the Li/SnO half-cell. In addition, higher irreversibility was observed for Na/SnO half-cell during electrochemical investigations compared to that for Li/SnO half-cell. XAS investigations on the Na/SnO half-cell confirms incomplete conversion and alloying reactions in the Na/SnO half-cell, resulting in poor electrochemical performance. The difference in the lithiation and sodiation mechanisms of SnO is discussed in detail.