Site-Selective Transformation for Preparing Tripod-like NiCo-Sulfides@Carbon Boosts Enhanced Areal Capacity and Cycling Reliability.

Flexible power supply systems for future wearable electronics desperately require high areal capacity (Ca) and robust cycling reliability due to the limited surface area of the human body. Transition metal sulfides are preferred as cathode materials for their improved conductivity and rich redox centers, yet their practical applications are severely hindered by the sluggish charge transport kinetics and unavoidable capacity decay due to the phase transformation during charge/discharge processes. Herein, we develop a site-selective transformation strategy for preparing tripod-like NiCo-sulfides@carbon (T-NCS@C) arrays on carbon cloth. The mass loading of active materials is balanced with charge (electron and ion) transport efficiency. The optimized T-NCS@C delivers a superior Ca of 494 µA h/cm2 (corresponding to 235 mA h/g) at 3 mA/cm2. Due to the protection of the carbon layer that is derived from transformed metal-organic framework (MOF) sheath, the T-NCS@C displays excellent stability with 92% retention over 5000 charge/discharge cycles. The flexible full cell adopting Fe2O3 as the anode and T-NCS@C as the cathode exhibits an improved Ea (areal energy density) of 389 µW h/cm2 at a Pa (areal power density) of 4.22 mW/cm2 together with robust cycling reliability.