Coupling donor doping and anion vacancy in Ni3Se4 battery-type cathode for large-capacity and high-rate charge storage

Transition metal selenides (TMSs) as battery-type cathode materials for hybrid supercapacitors (HSCs) are becoming increasingly attractive. Nevertheless, as an intractable bottleneck, the serious capacity attenuation and inferior rate capability derived from the deficient active sites and sluggish reaction/diffusion kinetics hinder their large-scale applications in HSCs. Herein, driven by the dual supports of Mn donor doping and Se vacancy engineering, the flower-like Ni3Se4 structures with the moderate dopant/vacancy concentration (VSe(M)–Mn(M)–Ni3Se4) are developed, which endows more electron release from Mn and primely collects these electrons around the vacancy, maximizing electron transfer level in the subsequent charge–discharge process. Meanwhile, the electroactive sites and OH− diffusion kinetics are intrinsically enhanced, and the ion chemisorption–desorption equilibrium is also effectively pledged as confirmed by the first-principle calculations. Specifically, the as-prepared cathode presents ultrahigh capacity and rate capability (342 and 269 mAh g−1 at 1 and 100 A g−1, respectively), and an assembled HSC with the cathode delivers superior energy density up to 55.9 Wh kg−1 at 0.83 kW kg−1 and remarkable cycle life. Additionally, the charge/discharge single-phase transition mechanism is detailedly unveiled through ex situ techniques. This work offers a new guideline to realize high-performance battery-type cathodes for next-generation supercapacitors.