Synthesis of different manganese tungstate nanostructures for enhanced charge-storage applications: theoretical support for experimental findings

Due to the dual features of EDLC and pseudocapacitance the low-temperature developed MnWO4 nanostructures with different aspect ratio showed good electrochemical properties. DFT study provided the quantum capacitance value.

Amalgamation of MnWO4 nanorods with amorphous carbon nanotubes for highly stabilized energy efficient supercapacitor electrodes

Enhanced electrochemical performance of supercapacitors can be achieved through optimal hybridization of electroactive nanomaterials, as it effectively increases the overall surface area and ensures greater electrolyte-electrode interaction. This work reports the realization of a manganese tungstate and amorphous carbon nanotube (MnWO4-aCNT) hybrid and its utilization as the electrodes for a solid-state asymmetric supercapacitor. Large-scale synthesis of aCNTs was carried out via an economical solid-state reaction at low temperature and the walls of these nanotubes were decorated with MnWO4 nanorods via a surfactant-free in situ hydrothermal process. The as-fabricated electrode based on this hybrid over nickel foam delivered a high specific capacitance of 542.18 F g-1 at a scan rate of 2 mV s-1, which is much superior to the values of the structural units separately. This MnWO4-aCNT based electrode showed a high-rate capacity with ∼100% capacitance retention and a coulombic efficiency of ∼100% even after operation for 15 000 cycles. A solid-state asymmetric supercapacitor based on this hybrid attained an energy density of 5.6 W h kg-1 and a power density as high as 893.6 W kg-1. Significantly enhanced electrochemical behaviour registered from the hybrid sample is accounted for by its enhanced surface area and thereby greater number of redox reaction sites along with the positive synergetic effect of the building blocks. This study unlocks further exploration possibilities with other types of aCNT-based hybrid materials for the development of highly stable, non-toxic and cost-effective sustainable energy storage systems.

Long-Term Cycling Behavior of Electrospun Separators for Lithium-Ion Batteries: A Comparison with Conventional Separators

This paper considered the electrochemical behavior of new electrospun separators for lithium-ion batteries on the basis of nano- and microfibers of polyvinylidene fluoride (PVDF) and its polymer composition, with polytetrafluoroethylene (PTFE) having advanced electroconductive properties over conventionally used separators based on polypropylene (PP) and glass-fibers (GF). Such advancement is associated with the low density of electrospun material leading to lower mechanical strengths. However, its use in the electrochemical systems with middle-voltage anode materials where dendrite growth is excluded is very prospective. The performance at the operation of the separators were investigated in the three-electrode-containing laboratory half-cells having Li4Ti5O12 as the electrode under investigation. Galvanostatic charge and discharge tests of cells were conducted under variation of the experimental conditions: the current varied in the range 0.1 C–1 C, and 1C cycling was conducted over 100 cycles. The working electrode and separator characteristics at cycling were monitored by the electrochemical impedance spectroscopy (EIS) method. The gradual decrease of Li4Ti5O12 transport characteristics at cycling was noticed for all the types of separators. However, the least degradation rate was associated with the PVDF and the PTFE-based separator. This fact is explained by the better conductivity of an electrospun separator compared to others, with therefore a better current distribution on the electrode surface and a lower concentration perturbation in the electrode.

Study on the Synthesis of Mn3o4 Nanooctahedrons and Their Performance for Lithium Ion Batteries

Among the transition metal oxides, the Mn₃O₄ nanostructure possesses high theoretical specific capacity and lower operating voltage. However, the low electrical conductivity of Mn₃O₄ decreases its specific capacity and restricts its application in the energy conversion and energy storage. In this work, well-shaped, octahedron-like Mn₃O₄ nanocrystals were prepared by one-step hydrothermal reduction method. Field emission scanning electron microscope, energy dispersive spectrometer, X-ray diffractometer, X-ray photoelectron spectrometer, high resolution transmission electron microscopy, and Fourier transformation infrared spectrometer were applied to characterize the morphology, the structure, and the composition of formed product. The growth mechanism of Mn₃O₄ nano-octahedron was studied. Cyclic voltammograms, galvanostatic charge-discharge, electrochemical impedance spectroscopy, and rate performance were used to study the electrochemical properties of obtained samples. The experimental results indicate that the component of initial reactants can influence the morphology and composition of the formed manganese oxide. At the current density of 1.0 A g^-1, the discharge specific capacity of as-prepared Mn₃O₄ nano-octahedrons maintains at about 450 mAh g^-1 after 300 cycles. This work proves that the formed Mn₃O₄ nano-octahedrons possess an excellent reversibility and display promising electrochemical properties for the preparation of lithium-ion batteries.

Electrospun Separation Material for Lithium-Ion Batteries: Synthesis and Study of Physical and Electrochemical Properties

The paper presents a comprehensive study of the physicochemical and electrochemical properties of a new nano-microporous non-woven composite separation material for a lithium-ion battery based on nano- and microfibers of polyvinylidene fluoride (PVDF) and its copolymer with polytetrafluoroethylene (PTFE), obtained by capillary-less electrospinning. A technique for the synthesis of separation material was developed, and the composition of the polymeric solution and the electrospinning conditions were optimized to produce polymer nano-microfibers with the required physicochemical characteristics. The optimal synthesis conditions for the separation material were determined. Higher porosity of the separation material and increased wettability in the most common electrolyte compositions contribute to the higher conductivity of the obtained separation material in comparison with the widely used commercial separation materials based on polypropylene (PP). The working characteristics of the separation material were studied in laboratory half-cells with a working electrode based on Li4Ti5O12, as well as a lithium metal counter electrode and a reference electrode. Charge-discharge tests of cells were performed in a wide range of variation of currents: From 0.1 to 25 C. A decrease in the total polarization of the working electrode and an increase in the cycled capacity at comparable currents in comparison with a cell with a PP-based separator were noted. The state of the electrodes and the separator in the cell was monitored using electrochemical impedance spectroscopy: The polarization resistances of the electrodes in different frequency ranges were determined, and the diffusion coefficient of lithium ions in the Li4Ti5O12 electrode was estimated in various lithiation states and at different stages of electrochemical tests, which were in the interval of 10−10 to 10−9 cm2·s−1.