Origin of the High‐Rate Energy Storage for Vacancy‐Rich Chalcogenides: Reinforced d‐p Orbital Hybridization Induced by Strain Field

Abstract The atomic‐level structure manipulation toward transition metal chalcogenides (TMCs) is a promising route to promote the kinetics and rate capability in hybrid supercapacitors (HSCs). Nevertheless, the mechanism of such a strategy remains ambiguous, which inhibits the rational design of cathodes. Herein, the d‐p orbital hybridization descriptor induced by the strain field is proposed to substantially decipher the high‐rate property of the sulfur vacancy‐rich CoNi ₂ S ₄ . The concentrative atomic tensile strain obviously reduces Co‐d orbital energy level and elevates its d‐band center, then specifically boosts the degree of orbital hybridization owing to the formation of stronger σ bonds, further facilitating the charge transfer and fast redox kinetics. Thus, the constructed CoNi ₂ S ₄ with tailored sulfur vacancies (M _SV ‐CoNi ₂ S ₄ ) delivers a large capacity of 352.8 mAh g ⁻¹ at 1 A g ⁻¹ and an exceptional rate capability with 244.4 mAh g ⁻¹ even at 200 A g ⁻¹ , which is four times higher than the maximum tested current density of previously reported TMCs. A fabricated HSC also presents superior energy/power density of 58.1 Wh kg ⁻¹ /13 kW kg ⁻¹ , and outstanding durability (94.1% capacity retention after 10 000 cycles). Such a fundamental understanding of the high rate from electronic structure optimization aspects provides an ingenious perspective to develop desired cathodes.