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For better charge storage and rate performance, supercapacitors need unique electrode materials and design architectures. Recent interest in metal–organic frameworks (MOFs) stems from their chemical compatibility with host materials and the abundance of active sites. However, their direct use as electrode materials has been difficult due to their limited electrical conductivity and excessive agglomeration, making them poor electrochemical performers. To solve these problems and boost the performance, we synthesized a nanoporous carbon-based electrode with metallic cobalt nanoparticles and MXenes. The electrode material is a zeolite-imidazole framework (ZIF)-67-derived cobalt-based nanoporous carbon nanotube (CNT) composite produced via in situ growth on Ti3C2Tx MXene flakes by pyrolysis under inert conditions. In situ synthesized porous CNTs add porosity and interconnecting channels to the MXenes providing increased sheet ion transport and diffusion, improving the electrochemical performance. This lowered the charge resistance to 3.73 Ω and enhanced the MXene nanosheet Bode phase angle. In an aqueous acidic electrolyte, the MXene-nanoporous CNT composite exhibited a nominal capacitance of 1605 F/g and 94.5% charge retention after 5000 cycles. [ABSTRACT FROM AUTHOR]

Transition-metal oxide anode materials have been observed to possess an intriguing surplus of capacity beyond the expected values based on conversion reaction. However, the mechanisms behind this phenomenon have remained contentious and elusive. This study focuses on synthesized nanosized molybdenum dioxide and its electrochemical performance as an anode material for Li-ion batteries. Our findings reveal a substantial increase in capacity upon cycling, achieving approximately 1688 mA h g−1, nearly double the theoretical capacity, after 700 cycles at a 1C rate. To elucidate the mechanisms underlying this augmented capacity, a comprehensive analysis employing in situ and ex situ X-ray diffraction, X-ray absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy was conducted at various stages of the Li-ion cell cycling. Our results indicate that no conversion reaction occurs during the initial discharge phase, with Li2O and Mo remaining undetected. Instead, Li0.98MoO2 is generated upon lithiation. Further materials characterization employing electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy on the cycled electrode suggests the potential formation of a metallic Li-rich layer at the interface of the Li-ion intercalated phase subsequent to the formation of Li0.98MoO2, contributing to the surplus Li storage. Moreover, electrochemical impedance spectroscopy coupled with ex situ SEM and TEM analyses reveals that alterations in particle size and morphology, along with changes in the solid electrolyte interphase (SEI) resistance, are instrumental in the capacity variation observed upon cycling. [ABSTRACT FROM AUTHOR]

Green synthesis offers a superior alternative to traditional methods for producing metal and metal oxide nanoparticles. This approach is not only benign and safe but also cost-effective, scalable, and straightforward, operating under ambient conditions. Notable metals and metal oxide nanoparticles, such as manganese oxides, iron oxides, silver, and gold, have been produced using various bio-reductants derived from plant extracts. These biological agents not only expedite the reduction process but also stabilize the nanoparticles, serving dual roles as reducing and capping agents. This review presents the green synthesis of nanoparticles (NPs) obtained from biogenic wastes and plant extracts. The green-synthesized nanostructured MnO2 nanoparticles are evaluated as a potential photocatalyst for water treatment and as an electrode material in lithium-ion batteries and supercapacitors. The green-derived iron oxide nanoparticles are examined as promising antioxidant, anti-inflammatory, and anti-diabetic agents. Additionally, this review discusses the green synthesis of precious metal nanoparticles, specifically silver (Ag NPs) and gold (Au NPs), highlighting their potential medical applications in areas like antiviral treatments and cancer therapy. [ABSTRACT FROM AUTHOR]

Group IV elements and their oxides, such as Si, Ge, Sn and SiO have much higher theoretical capacity than commercial graphite anode. However, these materials undergo large volume change during cycling, resulting in severe structural degradation and capacity fading. Al2O3 coating is considered an approach to improve the mechanical stability of high-capacity anode materials. To understand the effect of Al2O3 coating directly, we monitored the morphology change of coated/uncoated Sn particles during cycling using operando focused ion beam–scanning electron microscopy. The results indicate that the Al2O3 coating provides local protection and reduces crack formation at the early stage of volume expansion. The 3 nm Al2O3 coating layer provides better protection than the 10 and 30 nm coating layer. Nevertheless, the Al2O3 coating is unable to prevent the pulverization at the later stage of cycling because of large volume expansion. [ABSTRACT FROM AUTHOR]

Surface coating has become an effective approach to improve the electrochemical performance of Ni-rich cathode materials. In this study, we investigated the nature of an Ag coating layer and its effect on electrochemical properties of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material, which was synthesized using 3 mol.% of silver nanoparticles by a facile, cost-effective, scalable and convenient method. We conducted structural analyses using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, which revealed that the Ag nanoparticle coating did not affect the layered structure of NCM811. The Ag-coated sample had less cation mixing compared to the pristine NMC811, which could be attributed to the surface protection of Ag coating from air contamination. The Ag-coated NCM811 exhibited better kinetics than the pristine one, which is attributed to the higher electronic conductivity and better layered structure provided by the Ag nanoparticle coating. The Ag-coated NCM811 delivered a discharge capacity of 185 mAh·g−1 at the first cycle and 120 mAh·g−1 at the 100th cycle, respectively, which is better than the pristine NMC811. [ABSTRACT FROM AUTHOR]

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na+/F− co-doping on the structure and electrochemical performance of LiNi1/3Mn1/3Co1/3O2. The co-doped Li1-zNazNi1/3Mn1/3Co1/3O2-zFz (z = 0.025) and pristine LiNi1/3Co1/3Mn1/3O2 materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na+ and F− dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi1/3Mn1/3Co1/3O2 electrode delivered an initial specific capacity of 142 mAh g−1 at a 1C rate (178 mAh g−1 at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate. [ABSTRACT FROM AUTHOR]