A long cycle life asymmetric supercapacitor based on advanced nickel-sulfide/titanium carbide (MXene) nanohybrid and MXene electrodes

To enhance rate and cycle performances of nickel sulfide, the two-dimensional (2D) titanium carbide (Ti₃C₂, MXene) with good electrical conductivity and electrochemical stability is chosen as 2D supporting matrix for synthesizing nickel sulfide/delaminated Ti₃C₂ (Ni–S/d-Ti₃C₂) nanohybrids by a solvothermal method. The Ni–S/d-Ti₃C₂ nanohybrids show a coexistence of Ni₃S₂ and NiS with the characteristic peak of d-Ti₃C₂ nanosheets, and have electroactive species-on-sheet structures. The optimal Ni–S/1d-Ti₃C₂ nanohybrid delivers a high specific capacity of 840.4 C g⁻¹ at 1 A g⁻¹ with enhanced capacity retention of 64.3% at 30 A g⁻¹ and an outstanding cycle performance, which are ascribed to an integration of d-Ti₃C₂ nanosheets that can act as electric channels to accelerate electrons transport at interface of the nanohybrid during charge-discharge processes. An increased Ni²⁺ content and BET surface area also contribute to redox reactions of Ni–S/1d-Ti₃C₂ nanohybrid electrode. An asymmetric supercapacitor (ASC) fabricated by using the Ni–S/1d-Ti₃C₂ nanohybrid as positive electrode and d-Ti₃C₂ film as negative electrode exhibits an energy density of 20.0 Wh kg⁻¹ at 0.5 kW kg⁻¹ and a good cycling stability. Our work provides a favorable ingenuity for synthesizing advanced nickel sulfide-based nanohybrids and an alternative strategy of using 2D MXene as capacitive electrode for high-performance supercapacitors.