Hollow Porous Co0.85Se/ZnSe@MXene Anode with Multilevel Built-in Electric Fields for High-Performance Sodium Ion Capacitors.

Sodium ion capacitors (SICs) are promising candidates in energy storage for their remarkable power and energy density. However, the inherent disparity in dynamic behavior between the sluggish battery-type anodes and the rapid capacitor-type cathodes constrained their performance. To address this, we fabricated a hollow porous Co_0.85Se/ZnSe@MXene anode featuring multiheterostructure, utilizing facile etching and electrostatic self-assembly strategies. The hollow porous structure and multiple heterointerfaces stabilize the anode by mitigating the volume changes. Density functional theory (DFT) calculations further revealed that induced multilevel built-in electric fields facilitate the formation of rapid ion diffusion pathways and reduce the Na⁺ adsorption energy, thereby boosting Na⁺/electron transport kinetics. The fabricated TA-Co_0.85Se/ZnSe@MXene anode demonstrates outstanding long-term cycling stability of 406 mA h g^-1 after 1000 cycles at 1 A g^-1, with an ultrahigh rate performance of 288 mA h g^-1 at 10 A g^-1. When paired with the active carbon (AC) cathode, the SICs deliver extraordinary energy/power densities of 144 W h kg^-1 and 12000 W kg^-1, maintaining over 80% capacity retention at 1 A g^-1 after 10000 cycles. This innovative strategy of engineering multiheterostructured anode with the induced multilevel built-in electric fields holds significant promise for advancing high-energy and high-power energy storage systems.