Optimisation of sodium-based energy storage cells using pre-sodiation: a perspective on the emerging field

Rechargeable sodium-based energy storage cells (sodium-ion batteries, sodium-based dual-ion batteries and sodium-ion capacitors) are currently enjoying enormous attention from the research community due to their promise to replace or complement lithium-ion cells in multiple applications. In all of these emerging sodium-based systems, their performances are worsened by a range of undesired complications, including insufficient initial content of sodium ions in a cell, poor initial coulombic efficiencies of electrode materials, loss of sodium ions during long-term cycling, and the lack of practical possibility to optimise potential ranges in negative and positive electrodes. Pre-sodiation has emerged as an appealing technique to alleviate these problems and, therefore, to increase the practical energy densities of these devices. Nevertheless, the concept of pre-sodiation appears to be under-appreciated within the community, despite the fact that parallel methods of pre-lithiation find more and more uses in the established lithium-based energy storage cells. The intent of this timely perspective is to educate the community on the important benefits of pre-sodiation for a broad range of sodium-based energy storage cells and provide an up-to-date overview of this emerging field. A detailed summary of various situations where pre-sodiation is needed is provided, followed by the critical analysis of electrochemical and chemical techniques used for this purpose. An emphasis is made on the commercialisation potential of the optimal pre-sodiation procedures, and suggestions are provided for the areas of future advancement in the field. This perspective provides important insights of a broad interest to a multidisciplinary community of energy scientists, materials chemists and engineers working at the interface of new energy storage chemistries, device engineering and relevant materials science.