RESUMEN
Defect engineering in NiS nanosheets is an effective method to improve their surface properties and electronic structure for promoting electrochemical properties. However, a tunable, simple, and safe strategy for the introduction of abundant defect sites with a high activity into NiS with a special microstructure is worth developing. Herein, a novel hierarchical micro-flower-like NiS using graphene-like ultra-thin nanosheets with abundant defects as the building blocks was facilely synthesized by an innovative solvent-free compound-direct reaction strategy, which employed cost-efficient NaCl as the friction agent and dispersant to ensure adequate contact between sulfur ions and nickel ions and regulate the growth direction of NiS. Graphene-like ultra-thin NiS nanosheets effectively shorten the transport distance of ions and electrons. Defect engineering in NiS nanosheets provides more adsorption and storage sites for ions and high-activity sites for electrode materials, as well as adjusts the local electronic structure so as to effectively promote ion diffusion and charge transfer. The high performance of the as-obtained N-NiS electrode is illustrated by fabricating an asymmetric supercapacitor, which exhibits a specific capacitance of 351.5 F g-1 and energy density of 71.0 W h kg-1 at a power density of 229.3 W kg-1. The solvent-free compound-direct reaction strategy demonstrated in this study provides a new direction for the synthesis of high-performance nanomaterials for electrochemical energy storage applications.
RESUMEN
Mg2+/Li+ hybrid batteries (MLHBs), which support the rapid insertion and removal of Mg2+/Li+ bimetallic ions, are promising energy storage systems. Inspired by the Kirkendall effect, ball-in-ball bimetallic sulfides with heterostructures were prepared as cathode materials for the MLHBs. First, a nickel-cobalt precursor (NiCo-X precursor) with three-dimensional (3D) nanosheets on its surface was prepared using a solvothermal method based on the association reaction between alkoxide molecules. Subsequently, the NiCo-X precursor was vulcanized at high temperature using the potential energy difference as the driving force to successfully prepare NiS2@CoS2 core-shell hollow spheres. When used as the positive electrode material for the MLHBs, the NiS2@CoS2 hollow spheres exhibited excellent Mg2+/Li+ ion storage capacity, high specific capacity, good rate performance, and stable cyclic stability owing to their tough hierarchical structure. At a current density of 500 mA g-1, a specific capacity of 536 mAh g-1 was maintained after 200 cycles. By explaining the transformation mechanism of Mg2+/Li+ in bimetallic sulfides, it was proven that Mg2+ and Li+ worked cooperatively. This study provides a new approach for developing MLHBs with good electrochemical properties.
RESUMEN
Unordered vacancies engineered in host anode materials cannot well maintain the uniform Na+ adsorbed and possibly render the local structural stress intense, resulting in electrode peeling and battery failure. Here, the indium is first introduced into Cu2Se to achieve the formation of CuInSe2. Next, an ion extraction strategy is employed to fabricate Cu0.54In1.15Se2 enriched with ordered vacancies by spontaneous formation of defect pairs. Such ordered defects, compared with unordered ones, can serve as myriad sodium ion micropumps evenly distributing in crystalline host to homogenize the adsorbed Na+ and the generated volumetric stress during the electrochemistry. Furthermore, Cu0.54In1.15Se2 is indeed proved by the calculations to exhibit smaller volumetric variation than the counterpart with unordered vacancies. Thanks to the distinct ordered vacancy structure, the material exhibits a highly reversible capacity of 428 mAh g-1 at 1 C and a high-rate stability of 311.7 mAh g-1 at 10 C after 5000 cycles when employed as an anode material for Sodium-ion batteries (SIBs). This work presents the promotive effect of ordered vacancies on the electrochemistry of SIBs and demonstrates the superiority to unordered vacancies, which is expected to extend it to other metal-ion batteries, not limited to SIBs to achieve high capacity and cycling stability.