As energy storage technology continues to advance, the rapid charging capability enabled by high power density is gradually becoming a key metric for assessing energy storage devices. In this context, ionic hybrid capacitors aim to achieve higher energy density than electric double-layer capacitors (EDLC) and higher power density than ionic batteries by combining the characteristics of EDLC and ionic batteries. Sodium-ion capacitors (SICs) can offer cos. As energy storage technology continues to advance, the rapid charging capability enabled by high power density is gradually becoming a key metric for assessing energy storage devices. In this context, ionic hybrid capacitors aim to achieve higher energy density than electric double-layer capacitors (EDLC) and higher power density than ionic batteries by combining the characteristics of EDLC and ionic batteries. Sodium-ion capacitors (SICs) can offer cost and resource configuration advantages compared to lithium-ion capacitors (LICs). By virtue of the strong redox reaction, metal oxide electrodes have the potential to achieve a higher theoretical specific capacity than traditional carbon-based electrodes, making them potential candidates for SICs. Furthermore, metal oxide electrodes have significant surface pseudocapacitance properties that enable fast ion transport, thereby shortening the power output gap with EDLC. However, when used as electrodes for SICs, most metal oxides encountered compatibility issues with EDLC counter electrodes, in addition to inherent issues such as low conductivity and severe volume expansion. Therefore, the implementation of reasonable modification strategies and adherence to electrode matching rules is crucial for realizing high-performance SICs. This review summarizes the application and research progress of various metal oxides as electrodes for SICs. Additionally, the storage mechanism and structural design of SICs are further discussed. Finally, this review provides a. ••The in-depth classification and analysis of the recent work on metal oxides for sodium-ion capacitors.••The storage mechanism of sodium-ion capacitors in a definite manner have been summarized.••The detailed outlooks on the existing issues of metal oxides as anode materials for sodium-ion capacitors have been proposed.••The optimizations and applications perspectives of sodium-ion capacitors on the emerging field have been delivered.Sodium-ion capacitorsMetal oxidesPseudocapacitanceStorage mechanismAccording to the current energy structure, energy shortage and environmental pollution have become critical challenges with the rapid socioeconomic development,. Increasing the proportion of renewable energy systems based on solar, wind, and tidal energy is vital to improving the current situation and controlling CO2 emissions. However, based on the inherent limitations of renewable energy sources (intermittent output and low conversion efficiencies), developing stable and efficient energy storage systems is essential for achieving a sustainable energy supply. Among various energy storage modes, electrochemical energy storage systems represented by secondary batteries and supercapacitors exhibit apparent advantages in terms of energy densities and power densities, respectively,. Battery systems represented by lithium-ion batteries (LIBs) face challenges in rate and cycling performance due to the slow ion diffusion and high volumetric strains during the charging and discharging process. As another vital component of electrochemical energy storage, supercapacitors can achieve high power densities and fast responsiveness by the rapid reversible accumulation of charge in the physical state. However, traditional electric double-layer capacitors (EDLCs) tend to exhibit lower energy densities than battery systems because they lack Faraday processes. The in-depth research on supercapacitors has led to the discovery of Faraday pseudocapacitors (PCs), which has provided fundamental support. Like sodium-ion batteries (SIBs) systems, the components of SICs contain the electrolyte, separator, current collector, battery shell, and electrode materials (anode and cathode). Compared to SIBs and EDLCs, SICs represent a balanced solution. On the one hand, in comparison to EDLCs, SICs offer significant capacity advantages due to their battery-type electrode materials with high energy density. On the other hand, the EDLC/PCs electrodes in SICs make it easier to achieve superior power density, which is challenging to realize in SIBs. Therefore, by combining the advantages of batteries and supercapacitors, SICs are expected to be developed into a low-cost energy storage system with a demand for energy and power density. As the core components of SICs, developing and matching cathode and anode materials are the main design strategies for achieving high-performance Na+ storage.According to the different electrode reaction mechanisms, SICs can be broadly classified into two categories: battery-type anode/capacitive cathode and capacitive anode/battery-type cathode. The anode materials containing battery-type reactions mainly contain pure and combined battery-capacitor configurations, and the corresponding cathodes are available in pseudocapacitive and EDLC configurations. Furthermore, the matching regime can still be applied when battery-type materials are used as cathodes. Based.
