Recent Advances in Cathode Materials with Core-Shell Structures and Concentration Gradients for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) offer excellent potential for meeting the urgent need to develop low-cost and durable large-scale electrical energy storage systems. However, the electrochemical performance of currently available SIBs requires substantial improvement to enable their practical deployment. The cathode material is one of the greatest factors impacting SIB performance. The recent development of cathodes with core-shell structures and concentration gradients offers considerable promise for addressing these issues limiting the implementation of SIBs. Therefore, this review presents the primary factors affecting the development of these advanced cathode materials. First, the study discusses recently developed methods for preparing these materials, including precipitation reactions, ion-exchange reactions, and doping induction. The study further summarizes recent advances in developing layered transition-metal oxides, poly-anionic compounds, Prussian blue analogs, organic molecules, and other cathodes with core-shell structures and concentration gradients. Moreover, the state of understanding regarding the Na storage mechanisms of these heterogeneous cathodes is also presented. Finally, the remaining major challenges restricting the development of these cathode structures are discussed and possible solutions are provided. This review also enables the heterogeneous concepts to be expanded to high-capacity anodes employed in alkali metal ion batteries. This review summarizes recent advances in developing high-performance cathodes with core-shell structures and concentration gradients, presents the state of understanding regarding the sodium storage mechanisms of these heterogeneous cathodes, discusses the remaining major challenges restricting the development of these cathode structures, and provides possible solutions. image