[en] This study reports the onset of the Jahn-Teller distortion in 4 V LiMn₂O₄ thin film electrodes that was investigated using an in situ bending beam method (BBM). The phase transformation during lithium insertion/extraction could be detected using the BBM technique. The phase transformation between the cubic and tetragonal phases was depicted by the larger value of the compressive or tensile differential strain, which is consistent with a well-known phase transformation between those phases in 3 V LiMn₂O₄. The cyclic deflectograms and cyclic voltammograms were obtained simultaneously. The potential ranges responsible for the Jahn-Teller distortion in 4 V range, which takes place at the electrode surface, was determined by the charge versus. differential strain (dε/dQ) curve. The onset of the Jahn-Teller distortion was observed at the end of the cathodic scan, and the relaxation of the Jahn-Teller distortion was observed at the beginning of anodic scan. Furthermore, the onset of the Jahn-Teller distortion was found to be dependent on the lithium ion insertion rate, which was controlled by the scan rate

[en] A new solution combustion synthesis of layered LiNi_0.5Mn_0.5O₂ involving the reactions of LiNO₃, Mn(NO₃)₂, NiNO₃, and glycine as starting materials is reported. TG/DTA studies were performed on the gel-precursor and suggest the formation of the layered LiNi_0.5Mn_0.5O₂ at low temperatures. The synthesized material was annealed at various temperatures, viz., 250, 400, 600, and 850 deg. C, characterized by means of X-ray diffraction (XRD) and reveals the formation of single phase crystalline LiNi_0.5Mn_0.5O₂ at 850 deg. C. The morphology of the synthesized material has been investigated by means of scanning electron microscopy (SEM) and suggests the formation of sub-micron particles. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) studies on the synthesized LiNi_0.5Mn_0.5O₂ powders indicate that the oxidation states of nickel and manganese are +2 and +4, respectively. Electrochemical galvanostatic charge-discharge cycling behavior of Li//LiNi_0.5Mn_0.5O₂ cell using 1 M LiPF₆ in EC/DMC as electrolyte exhibited stable capacities of ∼125 mAh/g in the voltage ranges 2.8-4.3 V and 3.0-4.6 V and is comparable to literature reports using high temperature synthesis route. The capacity remains stable even after 20 cycles. The layered LiNi_0.5Mn_0.5O₂ powders synthesized by this novel route have several advantages as compared to its conventional synthesis techniques

[en] This study determined the potential range where the dissolution of a surface film on a thin film LiMn₂O₄ electrode, which forms during electrode synthesis, and the formation of a new surface film during cycling at room temperature using an in situ bending beam method (BBM) and an in situ electrochemical quartz crystal microbalance (EQCM) technique with cyclic voltammetry and a galvanostatic charge/discharge cycle. The electrolytes used were LiClO₄/EC-DEC, LiClO₄/PC and LiPF₆/EC-DMC. The deflectogram and massogram showed large peaks during the anodic scan only in the first cycle. These phenomena, were observed regardless of the electrolytes and scan rate used. The tensile strain and the mass reduction in the early stage of the strain peak and the mass peak are related to the dissolution of the initial surface film. In addition, the compressive strain and the mass increase are related to the formation of a new surface film during cycling. The potential ranges where the formation of the new surface film begins ranged from 4.03 to 4.1 V, which appears to terminate at the end of the first anodic scan, and was also observed during the galvanostatic charge/discharge cycle in the same potential range

[en] Effect of electrolyte layer thickness and increase in concentration of electrolyte during electrolyte thining on the atmospheric corrosion of carbon steel were investigated using EIS and cathodic polarization technique. The electrolyte layer thickness was controlled via two methods : one is mechanical method with microsyringe applying a different amount of electrolyte onto the metal surface to give different electrolyte thickness with the same electrolyte concentration. The other is drying method in which water layer thickness decreases through drying, causing increase in concentration of electrolyte during electrolyte thinning. In the region whose corrosion rate is controlled by cathodic reaction, corrosion rate for mechanical method is larger than that for drying method. However, for the electrolyte layers thinner than 20 ∼ 30 m, increase in concentration of electrolyte cause a higher corrosion rate for the case of the mechanical method compared with that of drying method. For a carbon steel covered with 0.1M Na₂SO₄, maximum corrosion rate is found at an electrolyte thickness of 45 ∼ 55 μm for mechanical method. However, maximum corrosion rate is found at an electrolyte thickness of 20 ∼ 35 μm for drying method. The limiting current is inversely proportional to electrolyte thickness for electrolyte thicker than 20 ∼ 30 μm. However, further decrease of the electrolyte thickness leads to an electrolyte thickness-independent limiting current reagion, where the oxygen rate is controlled by the solvation of oxygen at the electrolyte/gas interface. Diffusion limiting current for drying method is smaller compared with that for mechanica control. This can be attributed to decreasing in O₂ solubility caused by increase in concentration of electrolyte during electrolyte thining

[en] For preparing spinel Li_4Ti_5O_12 nanofiber, a hydrogen titanate nanofiber precursor was mixed with LiOH·H_2O and then the mixture was treated at 130°C in an autoclave for 24 hrs. The hydrogen titanate nanofiber precursor was made using a TiO_2 and NaOH solution as the starting material. As a result, the diameter of the Li_4Ti_5O_12 nanofiber was 5-10nm and the length was over 100 nm longer fiber. The oleic acid (C_17H_33COOH) coated Li_4Ti_5O_12 nanofiber with different oleic acid contents (5, 7.5, and 10 wt%) was obtained by a simple mixing method and heat treatment at 450°C in a N_2 atmosphere. The results clearly revealed that the surface of the Li_4Ti_5O_12 nanofiber was coated with an amorphous carbon layer (1 nm). The crystallinity of the samples was also enhanced. The oleic acid coated Li_4Ti_5O_12 nanofiber (5 wt% and 7.5 wt%) displayed a much lower impedance than the Li_4Ti_5O_12 nanofiber because of the decreased charge transfer resistance, therefore, it had an improved discharging/charging capacity, c-rate and cycle performance.

[en] Highlights: • Fabrication of Mott–Schottky-type Cu₄SiP₈-CNT hybrid anode for metal-ion batteries. • Role of Cu⁺ and chemical bridges to reform polycrystalline Cu₄SiP₈ during recharging. • Inhibition of formation of unwanted c-Li_3.75Si and LiP phases in Li-ion batteries. • Successful utilization and reversible reaction of Si with Na⁺ ions over many cycles. • Evolution of dense, even, and inorganic-rich SEI films in Li-ion and Na-ion batteries. In the search for new anode materials having a high theoretical capacity, satisfactory redox potentials, and inexpensive, abundant components for use in high-performance metal-ion batteries, ternary copper phosphosilicide (Cu₄SiP₈) is herein explored for the first time as a highly promising anode electrode material for Li-ion and Na-ion batteries (LIBs and NIBs). In a hybrid architecture with a defective carbon network, the nanoparticles can be fully embedded and robust chemical bonds permanently constructed, thus firmly protecting the integrity of the electrode against dramatic changes in volume, boosting electron/ion transport, and regulating the reaction pathways. Specifically, these work to inhibit the formation of undesirable LiP and crystalline Li_3.75Si phases in LIBs, promote the stable reaction of Si with Na⁺ in NIBs, and guarantee the reversible regeneration of Cu₄SiP₈ during recharging. Thus, the electrode delivered a first discharge capacity of 1764 mA h g⁻¹ (Coulombic efficiency; CE: 92.29%) at 0.1 A g⁻¹ and demonstrated superb capacity retention at 5 A g⁻¹ for 1200 cycles in an LIB. In an NIB, the hybrid electrode exhibited a high first discharge capacity and CE (796 mA h g⁻¹ and 81.78% at 0.1 A g⁻¹), outstanding cyclic stability (>700 cycles, >75% retention), and exceptional rate capability under symmetric/asymmetric conditions.

[en] The ruthenium oxide nanoparticles dispersed on multi-wall carbon nanotubes (CNTs) were successfully synthesized via microwave-polyol process combined with forced hydrolysis without additional thermal oxidation or electrochemical oxidation treatment. The HRTEM, Raman spectra and TGA curve indicate that CNTs were uniformly coated with crystalline and partially hydrous RuO₂.0.64H₂O nanoparticles of 2 nm diameter and the loading amount of ruthenium oxide in the composite could be controlled up to 70 wt.%. The specific capacitance was 450 Fg^-1 of ruthenium oxide/CNT composite electrode with 70 wt.% ruthenium oxide at the potential scan rate of 10 mV s^-1 and it decreased to 362 Fg^-1 by 18% at 500 mV s^-1. The specific capacitance of ruthenium oxide in the composite was 620 Fg^-1 of ruthenium oxide at 10 mV s^-1. The ruthenium oxide nanoparticles in ruthenium oxide/CNT nanocomposite electrode had a high ratio of outer charge to total charge of 0.81, which confirmed its high-rate capability of the composite through the preparation of the nano-sized ruthenium oxide particles on the external surface of CNTs.

[en] LiMn₂O₄ powders were prepared by a simple soft-chemical technique at different temperatures. X-ray diffraction and thermogravimetric analysis suggested that the material prepared at 800 deg. C was stoichiometric LiMn₂O₄, whereas those prepared at 600 and 700 deg. C were Li[Mn_0.77³⁺Mn_1.23⁴⁺]O_4.115 and Li[Mn_0.85³⁺Mn_1.15⁴⁺]O_4.075. Several typical XRD peaks of the compounds were investigated with an aim to elucidate (i) the Li immigration to the 16d octahedral sites, (ii) the partial tetragonal phase transition of the material and (iii) the mean coherent domain size and microstrain. SEM study showed that the particle size of the materials increased with heating temperature. The activation energy for the material particle growth was determined as 30.4 kJ mol^-1

[en] In this study, we intend to revisit oxide/nanocarbon composites for a systematic study of oxide particle size, chemical bonding between oxide and carbon, electrical conductivity and ion transport in the composites on the electrochemical properties of NaTi₂(PO₄)₃@nanocarbon microsphere composites prepared using zero-dimensional carbon black, one-dimensional carbon nanotubes, and two-dimensional graphene as anode materials for high-rate sodium-ion batteries. In the solution-based synthesis of the composites, oxide precursor nanoparticles deposited on nanocarbons are converted into final oxide nanoparticles through heat treatment. We demonstrate that growth of the NaTi₂(PO₄)₃ particles in the NaTi₂(PO₄)₃@nanocarbon composites occurs during heat treatment when the concentration of oxygen functional groups per unit specific area of nanocarbons is high. Growth of oxide precursor nanoparticles is observed for carbon black with a high concentration of oxygen functional groups during heat treatment owing to the proximity between precursor particles. On the other hand, growth of precursor nanoparticles is effectively prevented for carbon nanotubes and graphene with a low concentration of oxygen functional groups. Rate capability increases in the order of NaTi₂(PO₄)₃@carbon black < NaTi₂(PO₄)₃@graphene < NaTi₂(PO₄)₃@carbon nanotubes mainly due to the smaller sizes of oxide particles and more efficient Na⁺ transport across carbon nanotubes compared to other nanocarbons.

[en] Graphical abstract: Electrochemically active Li₂MnO₃ nanoparticle dispersed on carbon nanotube (CNT) network has been successfully synthesized by microwave-assisted hydrothermal (MAH) process for advanced lithium ion battery. Highlights: • LMO/CNT nanocomposite is synthesized by microwave-assisted hydrothermal method. • Formation of electrochemically active Li₂MnO₃ nanoparticle on CNT network. • Structure evolution from spinel LiMn₂O₄ to layered-type Li₂MnO₃ nanocrystallites. -- Abstract: Electrochemically active Li₂MnO₃ nanoparticle dispersed on carbon nanotube (CNT) network has been successfully synthesized by microwave-assisted hydrothermal (MAH) process. To the best of our knowledge, this is the first report showing the formation of Li₂MnO₃ nanoparticle on CNT network using MnO₂-coated CNT composite. Appearance of superlattice peak in X-ray diffraction (XRD) pattern and Raman-active modes near the lower wavelength region of Raman spectra reveals the structure transition from spinel LiMn₂O₄ to layered-type Li₂MnO₃ phase. The X-ray absorption near edge spectra (XANES) shows increase in average oxidation state of Mn ion from 3.5+ to 4+, and Mn–O and Mn–Mn peak intensity variations observed from extended X-ray absorption fine structure (EXAFS) are well evidenced for the formation of ordered Li₂MnO₃ structure. Electrochemical performance of Li₂MnO₃ nanocomposite electrode material prepared from higher LiOH concentration shows much higher capacity than spinel component alone. This synthetic strategy opens a new way for effective synthesis of electrochemically active Li₂MnO₃ on CNT network, making it suitable for advanced lithium ion battery