α-Ni(OH)2 is an ideal candidate material for a
supercapacitor except for its low conductivity and poor stability.
In this work, BO2
–-intercalated α-Ni
x
Co(1–x)(OH)2 is synthesized by a hydrothermal method at a low
cost. The Co dopant can decrease the charge-transfer resistance and
enhance the cyclic stability. The special unsaturated electronic state
of BO2
– enhances the bonding with metal
ions and attracts water molecules. Thus, the BO2
– ions support the hydroxide layers as pillars and create efficient
paths for proton transportation, optimizing the utilization of α-Ni(OH)2. The three-dimensional (3D) flowerlike morphology supplies
an enormous number of active sites, and r-GO is added to improve the
conductivity. As a result, the modified α-Ni(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g–1 at 1, 20, and 40 A·g–1, respectively,
showing improved rate performance. Matching with the commercial activated
carbon (AC) as an anode, the asymmetric capacitor delivers an energy
density of 40.66 W·h·kg–1 when its power
density is 187.06 W·kg–1. Meanwhile, it retains
81.5% capacitance of the initial cycle at 5 A·g–1 after 3000 cycles. With conductivity enhanced and structure stabilized,
the modified α-Ni(OH)2 confronts broader fields of
application.
The key means to improve the performance of lithium-sulfur batteries (LSBs) is to reduce the internal resistance by building an electronic/ionic pathway and to accelerate the conversion kinetics of lithium polysulfides (LiPSs) through modulation of interface functions. Herein, inspired by a grass root system, a flexible hierarchical CNF-CNT (carbon nanofiber-carbon nanotube) membrane decorated with Co-doped NiS 2 nanoparticles (Co-NiS 2 @CNF-CNT) is designed as an interlayer for LSBs, in which the in situ grown CNTs (root hairs) are wound on CNF (roots). Density functional theory (DFT) calculations show that Co doping introduces electron-deficient regions at the doping sites in NiS 2 , thus improving chemical adsorption and catalytic activities toward LiPSs. The cell pairs with the Co-NiS 2 @CNF-CNT interlayer exhibit a high rate performance of 951.4 mAh g −1 at 3 C, a reversible capacity of 944.1 mAh g −1 after 500 cycles at 0.2 C, and a prolonged cycle life of 3000 cycles at 5 C. More importantly, an areal capacity of 7.96 mAh cm −2 is achieved with a sulfur loading of 9.6 mg cm −2 . This work provides a strategy for enhancing the electrochemical performance of LSBs by combining 3D hierarchical conductive skeletons and electron-deficient functional adsorption and catalysis materials.
The low conductivity of sulfur and the shuttle effect of lithium polysulfides (LiPSs) are the two intrinsic obstacles that limit the application of lithium–sulfur batteries (LSBs). Herein, a sulfur vacancy introduced NiCo2S4 nanosheet array grown on carbon nanofiber (CNF) membrane (NiCo2S4‐x/CNF) is proposed to serve as a self‐supporting and binder‐free interlayer in LSBs. The conductive CNF skeleton with a non‐woven structure can effectively reduce the resistance of the cathode and accommodate volume expansion during charge–discharge process. The bonding between CNF matrix and NiCo2S4 nanosheet is enhanced by in situ growth, ensuring fast electron transfer. Besides, the sulfur vacancies in NiCo2S4 enhance the chemisorption of LiPSs, and the highly active sites at vacancies can accelerate the LiPSs conversion kinetics. LSB paired with NiCo2S4‐x/CNF interlayer achieved improved stability in 500 cycles at 0.2 C and long life of 3000 cycles at 3 C. More importantly, a high areal capacity of 9.69 mAh cm−2 is achieved with a sulfur loading of 10.8 mg cm−2 and a low electrolyte to sulfur (E/S) ratio of 4.8. This work provides insight into the sulfur vacancy in catalysis design for LiPSs conversion and demonstrates a promising direction for electronic defect engineering in material design for LSBs.
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