In-situ Transformation Constructs CoTe/Co/CoO Nanosheet Arrays with Rich Grain Boundaries to Enhance Electrochemical Performance

Nickel telluride nanoparticles@hollow porous carbon sphere confined within carbon fibers for fast stable sodium storage

For sodium-ion batteries, nickel telluride (NiTe2) is an excellent anode material. However, significant volume changes and slow kinetics compromise its structural stability and its capacity for high-current reactions. To increase sodium storage performance, NiTe2 nanoparticles are synthesized in situ within hollow porous carbon spheres (NiTe2@HPCS) through a "drop-dry" process, vacuum-assisted adsorption, and vapor tellurization. Then, a large number of NiTe2@HPCS particles are densely encapsulated in carbon fibers (CFs) via electrospinning and carbonization (NiTe2@HPCS/CF). In coin-type half cells, NiTe2@HPCS/CF exhibits a high and stable capacity of 432 mAh g-1 after 500 cycles at 1.0 A g-1. When half cells are operated at 5.0 and 10.0 A g-1, the lifespan reaches 1000 cycles and the capacities sustain at 332 and 195 mAh g-1. The cycled electrode materials preserve the intact composite structure, demonstrating remarkable robustness. Kinetic investigation affirms swift electron and Na+ conduction within NiTe2@HPCS/CF. Furthermore, in Na3V2(PO4)3//NiTe2@HPCS/CF full cells, NiTe2@HPCS/CF also exhibits favorable cycling stability. At 1.0 and 5.0 A g-1 after 300 and 500 cycles, reversible capacities reach 299 and 172 mAh g-1, respectively. The outstanding performance is associated with the unique dual carbon encapsulation structure: HPCSs effectively confine NiTe2 nanoparticles, maintaining their high electrochemical activity and promoting the sodiation/de-sodiation reactions. CFs further reinforce structural stability and electron conduction of NiTe2.

Cationic and anionic defect decoration of CoO through Cu dopants and oxygen vacancy for a High‑Performance supercapacitor

CoO has attracted increasing attention as an electrochemical energy storage owing to its excellent redox activity and high theoretical specific capacitance. However, its low inherent electrical conductivity results in sluggish reaction kinetics, and the poor rate capability of CoO limits its widespread applications. Herein, a multiple-defect strategy of engineering oxygen vacancies and Cu-ion dopants into the low-crystalline CoO nanowires (Ov-Cu-CoO) is successfully applied. Because of the advantage of the dual defect synergetic effect, the electronic structure and charge distribution are effectively modulated, thus enhancing the electrical conductivity and enriched redox chemistry. The obtained Ov-Cu-CoO electrode exhibits a high specific capacity of 1388.6 F⋅g-1 at a current density of 1 A⋅g-1, an ultrahigh rate performance (81.2% of the capacitance retained at 20 A⋅g-1) and excellent cycling stability (101.1% after 10,000 cycles). Moreover, an asymmetric supercapacitor device with Ov-Cu-CoO as the positive electrode having a high energy density of 44.1 W⋅h⋅kg-1 at a power density of 800 W⋅kg-1, and can still remain 27.2 W⋅h⋅kg-1 at a power density of 16 kW⋅kg-1. This study demonstrates an effective strategy to enhance electrochemical performance of CoO that can be easy applied to other transition metal oxides.

Mesoporous Cobalt Oxide (CoOx) Nanowires with Different Aspect Ratios for High Performance Hybrid Supercapacitors

Cobalt oxide (CoOx) nanowires have been broadly explored as advanced pseudocapacitive materials owing to their impressive theoretical gravimetric capacity. However, the traditional method of compositing with conductive nanoparticles to improve their poor conductivity will unpredictably lead to a decrease in actual capacity. The amelioration of the aspect ratio of the CoOx nanowires may affect the pathway of electron conduction and ion diffusion, thereby improving the electrochemical performances. Here, CoOx nanowires with various aspect ratios were synthesized by controlling hydrothermal temperature, and the CoOx electrodes achieve a high gravimetric specific capacity (1424.8 C g-1) and rate performance (38% retention at 100 A g-1 compared to 1 A g-1). Hybrid supercapacitors (HSCs) based on activated carbon anode reach an exceptional specific energy of 61.8 Wh kg-1 and excellent cyclic performance (92.72% retention, 5000 cycles at 5 A g-1). The CoOx nanowires exhibit great promise as a favorable cathode material in the field of high-performance supercapacitors (SCs).