Difference in Electrochemical Mechanism of SnO2 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, SnO2 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 SnO2 shows very poor electrochemical performance in SIB. The reason for this difference is investigated here through combined in operando and ex situ X-ray absorption spectroscopy (XAS). For this, the electrodes of SnO2 (space group P42/mnm synthesized via one-pot hydrothermal method) were cycled in Na-ion and Li-ion half-cells. The Na/SnO2 half-cell delivered a much lower discharge capacity than the Li/SnO2 half-cell. In addition, higher irreversibility was observed for Na/SnO2 half-cell during electrochemical investigations compared to that for Li/SnO2 half-cell. In operando XAS investigations on the Na/SnO2 half-cell confirms incomplete conversion and alloying reactions in the Na/SnO2 half-cell, resulting in poor electrochemical performance. The difference in the lithiation and sodiation mechanisms of SnO2 is discussed in detail.