Dual-Carbon Engineering of Nanosized (Ni_0.28Co_0.72)_1-xS for Li⁺ Storage with Enhanced Rate Capability and Stability

The poor conductivity and large volume swelling of transition-metal sulfides are still big challenges to overcome for high-performance energy storage. Herein, the flexibility of MOF precursors offers remarkable versatility in tailoring the chemical composition of NiCo sulfides with a highly desirable porous structure, and then dual-carbon-confined (Ni_0.28Co_0.72)_1-xS nanoparticles are designed, in which an inner sulfur-doped porous carbon (SC) matrix (derived from the organic ligands of metal-organic frameworks (MOFs)) and an outer wrapped S-doped reduced graphene oxide (SG)-co-engineered (Ni_0.28Co_0.72)_1-xS are constructed ((Ni_0.28Co_0.72)_1-xS/SC/SG)) to enhance the rate capability and stability of Li⁺ storage. For the dual carbons, the inner SC can elastically realize the anti-aggregation of nanosized (Ni_0.28Co_0.72)_1-xS and improve their conductivity, while the outer SG could further promote the reaction kinetics, stabilize the structure, and ensure the structural integrity. As expected, the optimized (Ni_0.28Co_0.72)_1-xS/SC/0.7SG exhibits an outstanding rate capability of 640.1 mAh g^-1 at 5.0 A g^-1 and ultrahigh cycling stability of 134.7% at 1 A g^-1 after 1000 cycles. The assembled lithium-ion capacitor (LIC) also shows a high energy density of 125.8 Wh kg^-1 at the power density of 200 W kg^-1, as well as excellent stability (98.8% after 6000 cycles). This work highlights the significance of dual-carbon engineering in enhancing the energy storage performance of active materials, and the fabricated nanosized (Ni_0.28Co_0.72)_1-xS by dual-carbon engineering can be applied in high-performance electrochemical energy storage and beyond.