Optical and electrochemical performance of electrospun NiO-Mn3O4 nanocomposites for energy storage applications

NiO-Mn3O4 ribbons were synthesized through electrospinning and subsequently compared with NiO nanoparticles and Mn3O4 octahedral particles to evaluate their optical and electrochemical properties. XRD analysis confirmed the presence of cubic and tetragonal phases of NiO and Mn3O4, respectively, within the nanocomposite. UV-Vis diffuse reflectance spectroscopy (DRS) revealed a bandgap of 3.53 eV for the nanocomposite, while photoluminescence emission quenching indicated an enhancement in surface defects. The ribbons exhibited superior electrochemical performance, achieving a specific capacitance of 372 F g-1 at a current density of 1 A g-1, along with 94% capacitance retention after 3000 cycles at 7 A g-1. Furthermore, the assembled NiO-Mn3O4//AC asymmetric supercapacitor device exhibited a maximum energy density of 40 Wh kg-1 at a power density of 2400 W kg-1. These findings suggest that NiO-Mn3O4 ribbons hold significant promise for high-performance energy storage devices.

Unravelling the effect of crystal lattice compression on the supercapacitive performance of hydrothermally grown nanostructured hollandite α-MnO2 induced by incremental growth time

Manganese oxide (α-MnO2) nanoparticles are highly recognised for their use in supercapacitor applications. This study demonstrates the successful synthesis of flower-like and nanorods hollandite α-MnO2 by a simple one-pot hydrothermal technique at various reaction times. The synthesised nanoparticles were characterised by various physicochemical and electrochemical characterisation techniques. The influence of the various reaction times on the structural and morphological properties was evaluated by X-ray diffraction (XRD) and scanning electron microscope. XRD patterns revealed that the synthesized MnO2 nanoparticles are tetragonal structures with crystallite sizes ranging from 13.69 to 20.37 nm estimated from the Williamson-Hall method. Moreover, the functional groups and surface area were examined by Fourier transform infrared spectroscopy and Bruner-Emmert-Teller, respectively. Furthermore, the compositional elements were studied by X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Finally, the electrochemical performances were studied using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS). The GCD characteristics revealed that the optimised α-MnO2 has a good capacitive behaviour, which predicts the potential application in energy storage. Electrochemical studies revealed that the 3 h-MnO2 sample exhibited a superior electrochemical behaviour and demonstrated a high specific capacitance of 132 F/g at a current density of 1A/g.

A versatile iron [1-(naphthalen-2-ylmethyl)-2-(pyridin-2-yl)-1H-benzo[d]imidazole]3 metal complex redox active material for energy conversion and storage systems

Novel Fe2+/3+ [npbi]3 redox electrolytes contributed to competitive performances in both DSC and SC applications.

In Situ Formed Core-Shell LiZnxMn2-xO4@ZnMn2O4 as Cathode for Li-Ion Batteries

Elemental doping and surface modification are commonly used strategies for improving the electrochemical performance of LiMn₂O₄, such as the rated capacity and cycling stability. In this study, in situ formed core-shell LiZn_xMn_2-xO₄@ZnMn₂O₄ cathodes are prepared by tuning the Zn-doping content. Through comprehensive microstructural analyses by the spherical aberration-corrected scanning transmission microscopy (Cs-STEM) technique, we shed light on the correlation between the microstructural configuration and the electrochemical performance of Zn-doped LiMn₂O₄. We demonstrate that part of Zn²⁺ ions dope into the spinel to form LiZn_xMn_2-xO₄ in bulk and other Zn²⁺ ions occupy the 8a sites of the spinel to form the ZnMn₂O₄ shell on the outermost surface. This in situ formed core-shell LiZn_xMn_2-xO₄@ZnMn₂O₄ contributes to better structural stabilization, presenting a superior capacity retention ratio of 95.8% after 700 cycles at 5 C at 25 °C for the optimized sample (LiZn_0.02Mn_1.98O₄), with an initial value of 80 mAh g^-1. Our investigations not only provide an effective way toward high-performance LIBs but also shed light on the fundamental interplay between the microstructural configuration and the electrochemical performance of Zn-doped spinel LiMn₂O₄.

Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Supercapacitors (SCs) can effectively alleviate problems such as energy shortage and serious greenhouse effect. The properties of electrode materials directly affect the performance of SCs. Rare earth (RE) is known as "modern industrial vitamins", and their functional materials have been listed as key strategic materials. In the past few years, the number of scientific reports on RE-based nanomaterials for SCs has increased rapidly, confirming that adding RE elements or compounds to the host electrode materials with various nanostructured morphologies can greatly enhance their electrochemical performance. Although RE-based nanomaterials have made rapid progress in SCs, there are very few works providing a comprehensive survey of this field. In view of this, a comprehensive overview of RE-based nanomaterials for SCs is provided here, including the preparation methods, nanostructure engineering, compounds, and composites, along with their capacitance performances. The structure-activity relationships are discussed and highlighted. Meanwhile, the future challenges and perspectives are also pointed out. This Review can not only provide guidance for the further development of SCs but also arouse great interest in RE-based nanomaterials in other research fields such as electrocatalysis, photovoltaic cells, and lithium batteries.

Understanding the Effect of Al Doping on the Electrochemical Performance Improvement of the LiMn2O4 Cathode Material

It is well known that the electrochemical performance of spinel LiMn₂O₄ can be improved by Al doping. Herein, combining X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) with in situ electron-beam (E-beam) irradiation techniques, the influence of Al doping on the structural evolution and stability improvement of the LiMn₂O₄ cathode material is revealed. It is revealed that an appropriate concentration of Al³⁺ ions could dope into the spinel structure to form a more stable LiAl_xMn_2-xO₄ phase framework, which can effectively stabilize the surface and bulk structure by inhibiting the dissolution of Mn ions during cycling. The optimized LiAl_0.05Mn_1.95O₄ sample exhibits a superior capacity retention ratio of 80% after 1000 cycles at 10 C (1 C = 148 mA h g^-1) in the voltage range of 3.0-4.5 V, which possesses an initial discharge capacity of 90.3 mA h g^-1. Compared with the undoped LiMn₂O₄ sample, the Al-doped sample also shows superior rate performance, especially the capacity recovery performance.

In Situ Fabrication of Activated Carbon from a Bio-Waste Desmostachya bipinnata for the Improved Supercapacitor Performance

Herein, we demonstrate the fabrication of highly capacitive activated carbon (AC) using a bio-waste Kusha grass (Desmostachya bipinnata), by employing a chemical process followed by activation through KOH. The as-synthesized few-layered activated carbon has been confirmed through X-ray powder diffraction, transmission electron microscopy, and Raman spectroscopy techniques. The chemical environment of the as-prepared sample has been accessed through FTIR and UV-visible spectroscopy. The surface area and porosity of the as-synthesized material have been accessed through the Brunauer-Emmett-Teller method. All the electrochemical measurements have been performed through cyclic voltammetry and galvanometric charging/discharging (GCD) method, but primarily, we focus on GCD due to the accuracy of the technique. Moreover, the as-synthesized AC material shows a maximum specific capacitance as 218 F g^-1 in the potential window ranging from - 0.35 to + 0.45 V. Also, the AC exhibits an excellent energy density of ~ 19.3 Wh kg^-1 and power density of ~ 277.92 W kg^-1, respectively, in the same operating potential window. It has also shown very good capacitance retention capability even after 5000th cycles. The fabricated supercapacitor shows a good energy density and power density, respectively, and good retention in capacitance at remarkably higher charging/discharging rates with excellent cycling stability. Henceforth, bio-waste Kusha grass-derived activated carbon (DP-AC) shows good promise and can be applied in supercapacitor applications due to its outstanding electrochemical properties. Herein, we envision that our results illustrate a simple and innovative approach to synthesize a bio-waste Kusha grass-derived activated carbon (DP-AC) as an emerging supercapacitor electrode material and widen its practical application in electrochemical energy storage fields.

Role of Al-doping with different sites upon the structure and electrochemical performance of spherical LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Al-doped spinel LiNi0.5Mn1.5O4 materials with different sites and contents were synthesized by rapid precipitation combined with hydrothermal treatment and calcination. The roles of Al on structural stability and electrochemical performance were studied by utilizing a series of techniques. XRD patterns indicated lower ion diffusion and no impure phased in doped samples. FT-IR and CV results reveal that Al-doped materials possess a Fd3̄m space group with increased disorder and increasing amounts of Mn3+. SEM and TEM equipped with EDS were used to characterize the regular morphology accompanied by a complete crystal structure and homogeneous distribution of elements. The Al content at the Ni, Mn, and Ni/Mn sites was optimized to be 5%, 3% and 5% (in total), respectively. The cycling stability was considerably enhanced at an ambient temperature (25 °C) and high temperature (55 °C). A typical Al dual-doped sample at Ni/Mn sites with 5% content delivered a reversible capacity of 113.5 mA h g-1 after 200 cycles at 0.5C. The discharge capacity at 5, 10 and 20C was 127.3, 125.5 and 123.1 mA h g-1, respectively. The discharge capacity remained at 126 mA h g-1 after 50 cycles (55 °C, 0.5C). Subsequent EIS and analytical results of the cycled electrode showed improved structural stability with a lower resistance, stable cathode/electrolyte interface, and reduced dissolution of Mn. These data further demonstrated the feasibility and reliability of preparing high-performance spinel LiNi0.5Mn1.5O4 cathode materials by doping with a suitable amount of Al.

In situ grown nickel selenide on graphene nanohybrid electrodes for high energy density asymmetric supercapacitors

Nickel selenide (NiSe) nanoparticles uniformly supported on graphene nanosheets (G) to form NiSe-G nanohybrids were prepared by an in situ hydrothermal process. The uniform distribution of NiSe on graphene bestowed the NiSe-G nanohybrid with faster charge transport and diffusion along with abundant accessible electrochemical active sites. The synergistic effect between NiSe nanoparticles and graphene nanosheets for supercapacitor applications was systematically investigated for the first time. The freestanding NiSe-G nanohybrid electrode exhibited better electrochemical performance with a high specific capacitance of 1280 F g-1 at a current density of 1 A g-1 and a capacitance retention of 98% after 2500 cycles relative to that of NiSe nanoparticles. Furthermore, an asymmetric supercapacitor device assembled using the NiSe-G nanohybrid as the positive electrode, activated carbon as the negative electrode and an electrospun PVdF membrane containing 6 M KOH as both the separator and the electrolyte delivered a high energy density of 50.1 W h kg-1 and a power density of 816 W kg-1 at an extended operating voltage of 1.6 V. Thus, the NiSe-G nanohybrid can be used as a potential electrode material for high-performance supercapacitors.

Facile synthesis of electrostatically anchored Nd(OH)3 nanorods onto graphene nanosheets as a high capacitance electrode material for supercapacitors

Nd(OH)₃/G hybrid is prepared by a solvothermal reduction process and used as an electrode material for asymmetric supercapacitors.