Dual Modulation Strategy of Mn Donor Doping and Se Vacancy Endows Large Capacity and High-Rate Charge Storage in a Ni3Se4 Battery-Type Cathode

Transition metal selenides (TMSs) have been extensively explored as the most attractive battery-type supercapacitor cathodes. However, TMSs usually exhibit elusive active sites, sluggish reaction/diffusion kinetics, and poor conductivity, which severely degrade their capacity and rate performance. To overcome these shortcomings of TMSs, herein, we employ a synchronous strategy of Mn donor doping and Se vacancy in a flower-like Ni3Se4 cathode and optimize the dopant/vacancy concentration (VSe(M)–Mn(M)–Ni3Se4) to maximize electron release from Mn and effectively accumulate the electrons around the vacancy, resulting in maximum electron transfer during the charge–discharge process. Moreover, the proposed strategy can intrinsically tune electronic structure, increase electroactive sites, accelerate OH− diffusion kinetics, and pledge the ion chemisorption–desorption equilibrium verified based on first-principle calculations. Thus, the fabricated cathode exhibits ultrahigh capacity and rate capability (357 and 275 mAh g−1 at 1 and 100 A g−1, respectively), and a hybrid supercapacitor with the cathode exhibits sufficient energy density of 118 Wh kg−1 at 0.8 kW kg−1 and exceptional durability, which is considerably greater than that exhibited by supercapacitors comprising other cathodes. Moreover, the charge–discharge mechanism is elaborated in detail via ex situ techniques. This study provides fundamental guidelines for constructing high-performance battery-type cathodes, which can be used in next-generation supercapacitors.