Suppressing the voltage failure by twinned heterostructure for high power sodium-ion capacitor

The voltage failure is a widespread problem in electrochemical energy storage. Nevertheless, uncovering the voltage failure mechanism at the molecular level and further solving this problem are still great challenges. Herein, the voltage failure mechanism of SnSe in the ester-based electrolyte is initially revealed and explained by Hard-Soft-Acid-Base (HSAB) theory. Inspired by theoretical calculations that a CoSe2/SnSe heterostructure with built-in electric field (BEF) can bring the migration of electrons from the CoSe2 to SnSe side and result in the conversion of the boundary acid (Sn2+) into a soft acid, an ultra-homogeneous twinned CoSe2/SnSe heterostructure is fabricated by employing CoSnO3-MOFs as precursor, exhibiting prominent electrochemical performances for sodium-ion capacitors (SICs). Owing to the abundant phase boundaries and BEF, the migration barrier of Na+ decreases from 1.17 eV to 0.39 eV, delivering greatly enhanced charge transport kinetics. Impressively, the SICs assembled by employing this materials as the anode deliver high energy density (146.3 Wh kg(-1)) and high power density (12 kW kg(-1)) as well as excellent cycle lifespan, indicating that the voltage failure phenomenon is solved perfectly by the strategy of constructing heterostructures. The work promotes better fundamental understanding of the voltage failure and provides a new strategy to suppress the voltage failure of electrodes, which may also be extended to other electrochemical energy storage system with similar voltage failure phenomenon.