Pre-sodiation strategies for constructing high-performance sodium-ion batteries

As a promising energy storage system, sodium-ion batteries (SIBs) have attracted much attention because of the abundant resource of sodium and its relatively low cost. However, the low initial Coulombic efficiency and sodium deficiency (continuous sodium-ion loss or sodium-deficient cathodes) of SIBs result in a low energy density and limited cycle life, which impede their commercial application. Some pre-sodiation strategies have been proposed to address these issues, which can supplement extra sodium ions into the battery system in advance to compensate for its irreversible sodium-ion loss and improve its reversible capacity, energy density and cycling performance. In this review, various pre-sodiation strategies for constructing high-performance SIBs are comprehensively summarized and discussed according to anode pre-sodiation, cathode pre-sodiation, separator pre-sodiation and electrolyte pre-sodiation. Among them, anode pre-sodiation and cathode pre-sodiation are highlighted. In addition, this review provides a fundamental understanding of pre-sodiation principles and the challenges and prospects of these techniques. This review could help researchers to obtain a comprehensive grasp of pre-sodiation strategies and develop new and more effective pre-sodiation techniques for accelerating the commercialization of SIBs.