Research Progress on Presodiation Strategies for High Energy Sodium-Ion Batteries

Lithium-ion batteries (LIBs) have attracted considerable attention owing to their high energy density and long cycle life. However, lithium resources have become scarcer with the rapid development of electric vehicles and smart grid technologies. Considering the inexpensive and abundant supply of sodium, sodium -ion batteries (SIBs) are expected to replace LIBs for large-scale energy storage systems. However, the development of high-energy SIBs is usually limited by the poor initial Coulombic efficiency (ICE) of the anode materials, although a series of advanced sodium storage electrode materials have been reported. This is because active sodium ions are all provided by the cathode material in a full cell. The low ICE of the anode indicates that numerous active sodium ions are irreversibly consumed during the first cycle, reducing the reversible capacity and shortening the cycle life of the full cell. The significant loss of active sodium ions is attributed to the formation of a solid electrolyte interface (SEI) on the anode side and irreversible sodium capture by defect sites and surface functional groups on the anode material. Consequently, excessive cathode material is required in the full cell, which significantly reduces the utilization rate of the cathode material and the energy density of the full cell. Furthermore, many reported cathode materials, such as Fe2S, are sodium-deficient and cannot be directly matched with anodes, limiting the selection of electrode materials. Presodiation technology is considered the most direct and effective method to solve the state-matching problem of cathode and anode materials by compensating for active sodium-ion loss and increasing the energy density, which are crucial for the commercial application of SIBs. The aim is to eliminate the irreversible capacity loss during the first cycle by incorporating additional active sodium ions to the electrode material in advance. This review comprehensively summarizes the latest research progress on various presodiation strategies, including short circuit with sodium metal, electrochemical presodiation, sodium metal addition, chemical presodiation, and cathode sacrificial additives. The advantages and challenges of existing methods are thoroughly analyzed and discussed from the perspective of their reaction mechanism, safety, compatibility, efficiency, and scalability. Emphasis is placed on the state-of-the-art advancements in chemical presodiation and cathode sacrificial additives, which are considered the two most promising methods for commercial applications. The unresolved scientific problems and technical difficulties are further discussed from a practical perspective. This review may provide guidance for the investigation of advanced presodiation technology and promote further development of high-energy SIBs.