[en] Water-based systems are dominating the coating market because of worldwide VOCs regulations. Research is focusing especially on waterborne polyurethane (WPU) because of its unique mechanical and chemical properties. However, commercial WPU consists of linear thermoplastic polymers with polar groups on the main chain, which do not perform as well as solvent-borne PU in a two-pack system. In this study, APTES were used as a chain crosslink agent to overcome commercial WPU's limited performance. WPUs synthesized by using a sol-gel process were evaluated with FT-IR, particle analysis, TGA, tensile tests, pull-off tests, SEM, and EIS. The results showed that WPUs with added APTES had better thermal stability, mechanical properties, and water resistance than did WPUs without added APTES. Consequently, the sol-gel process increased the crosslink density of WPUs and modified the WPU's own properties.

[en] One of the critical issues in the coating specification is the allowable limit of surface contaminant(s) - such as soluble salt(s), grit dust, and rust - after grit blasting. Yet, there is no universally accepted data supporting the relationship between the long-term coating performance and the amount of various surface contaminants allowed after grit blasting. In this study, it was attempted to prepare epoxy coatings applied on grit-blasted steel substrate dosed with controlled amount of surface contaminants - such as soluble salt(s), grit dust, and rust. Then, coating samples were subjected to 4,200 hours of cyclic test(NORSOK M-501), which were then evaluated in terms of resistance to rust creepage, blistering, chalking, rusting, cracking and adhesion strength. Additional investigations on the possible damage at the paint/steel interface were carried out using an Electrochemical Impedance Spectroscopy(EIS) and observations of under-film-corrosion. Test results suggested that the current industrial specifications were well matched with the allowable degree of rust, whereas the allowable amount of soluble salt and grit dust after grit blasting showed a certain deviation from the specifications currently employed for fabrication of marine vessels and offshore facilities

[en] Highlights: • Li₂TiF₆ coating was designed to grow surface lithium conductivity and stability. • We conducted an easy and versatile Li₂TiF₆ lithium conductive coating on cathode. • The coating was performed very simply by ambient-temperature co-precipitation. • After the coating, rate capability, cycleability and thermal stability improved. - Abstract: We demonstrate an easy and versatile approach to modify a cathode-surface with a highly lithium–ion conductive layer by coating it with Li₂TiF₆. The thin and homogeneous Li₂TiF₆ coating is introduced onto an over-lithiated layered oxide (OLO, namely Li_1.17Ni_0.17Co_0.1Mn_0.56O₂) surface via simple co-precipitation at ambient temperature by using Li₂CO₃ and H₂TiF₆ aqueous solutions. The lithium–conductive fluoride coating is expected to effectively suppress the undesired electrochemical and thermal interfacial reactions involving the OLO, which is critical in improving cycle performance and thermal stability. After Li₂TiF₆ surface modification, the coated OLO materials showed high rate capability as well as long cyclability and improved thermal stability. The crystalline structure and surface microstructure of the prepared OLOs were investigated by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Ultimately, the performances of the assembled lithium ion batteries were thoroughly investigated by electrochemical methods and thermal analysis

[en] Size and structure controlled, non-agglomerated nanoparticles are essential for many applications, such as electronics and energy storage. In this study, inductively coupled and square wave modulated RF (13.56 MHz) plasma was used to control the nanoparticle size, and a heater was installed inside the substrate to change the structure of Si nanoparticles from amorphous to crystalline. We found that the size of Si nanoparticles can be controlled by the plasma on-time. The nanoparticles were not agglomerated and grown mainly by surface deposition. The Si nanoparticles generated can be used in energy devices, such as secondary batteries, supercapacitors and solar cells.

[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

[en] The electrochemical lithiation-delithiation reaction was examined for LiMnPO₄ in which different cations were substituted for part of Mn. The X-ray diffraction analysis indicated that LiMnPO₄ is tolerant, to some extent, to substitution of Mg²⁺, Ca²⁺ and Zr⁴⁺. The substitution of Mg²⁺ and/or Zr⁴⁺ led to an increased reversible capacity and a reduced polarization, whereas Ca²⁺ substitution had a detrimental effect on the electrochemical properties. The potential transient analysis showed that LiMn_0.88Mg_0.1Zr_0.02PO₄ has higher lithium diffusivities than pure LiMnPO₄, indicating facilitated diffusion kinetics in the substituted material. Upon the first charge-discharge cycle, LiMn_0.88Mg_0.1Zr_0.02PO₄ suffered less irreversible capacity loss when compared with LiMnPO₄, and smaller amounts of electrolyte salt-based species were detected on the electrode surface of LiMn_0.88Mg_0.1Zr_0.02PO₄.

[en] Mechanochemically coating over-lithiated layered oxide with the multi-functional VOPO₄ is studied by using that VOPO₄ is capable of accommodating lithium ions that are reversibly inserted/extracted at 3.8 V vs. Li/Li⁺ and exerts a surface-stabilizing effect. The impregnation with VOPO₄ relieves the characteristic irreversible problems of over-lithiated layered oxide, since the initial fully delithiated structure of VOPO₄ provides extra lithium storage sites and thus compensates for the unavoidable loss of irreversible charging capacity of VOPO₄ during the first cycle. Interestingly, VOPO₄ loadings below 1 wt. % improves cycleability, whereas higher loadings result in unfavorable kinetic hindrance. Additionally, VOPO₄-coated samples exhibit enhanced thermal stability due to featuring reduced decomposition exothermicity and increase thermal runaway onset temperature.

[en] Highlights: • To suppress the voltage depression, Ga ions were doped into the host lattice of Li-rich layered oxide using site-specific doping process. • Results of TEM and EXAFS spectroscopy revealed that the Ga ions were predominantly located at tetrahedral site in Li layer of Li₂MnO₃-like component. • The modified Li-rich layered oxide showed greatly reduced voltage depression due to increased structural stability of Li₂MnO₃-like component. • First principal calculations and Ex-situ XRD analyses imply that the formation of GaO₄ structural unit increased activation barrier for cation migration into Li layer. Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lithium-ion batteries. However, their energy densities are considerably reduced upon cycling due to a voltage depression originated from the layered-to-spinel phase transition. In this study, the influence of site-specific Ga-doping on the electrochemical properties of Li-rich layered oxide is investigated. A powder of Li-rich layered oxide is treated in acid, and then annealed with a Ga source at low temperature (300 °C) to insert Ga ions into the powder. Transmission electron microscopy and extended X-ray absorption fine structure analyses indicate that the Ga ions are predominantly doped into the tetrahedral sites of Li₂MnO₃-like nano-domains in Li-rich layered oxide. Cyclability tests with 18650 full cells clearly reveal that the voltage depression is suppressed by the treatment. Ex-situ X-ray diffraction and first principles calculation results imply that the formation of tetrahedral GaO₄ unit in the Li₂MnO₃-like domain improves the structural stability of Li-rich layered oxide upon cycling.

[en] Highlights: • Degradation mechanism of layered LiNi_0.87Co_0.09Mn_0.04O₂ (NCM) cathode was studied. • Dissolution of TMs on the Ni-rich cathode was probed by ICP-AES, EPMA, IC, and XEDS. • TEM coupled with XEDS was used for high-precision particle compositional analysis. • TM dissolution mostly occurred for broken and pulverized particles. • TM dissolution and side reactions lead to Li-ion battery performance degradation. -- Abstract: The dissolution of transition metals (TMs) from LiMO₂ (M = Ni, Co, Mn) cathodes and their subsequent side reactions on the anode and in the electrolyte result in Li-ion battery capacity and power losses. Despite the importance of this process, the lack of adequate analysis methods for tracking the subtle compositional changes at specific locations with nano-meter spatial resolution has prevented the elucidation of its microstructural origin and mechanism. Herein, we studied the dissolution of TMs from a Ni-rich layered cathode and investigated their deposition on a graphite anode and reactions with the electrolyte, with focus on the microstructural aspects. Changes in TM and oxygen contents in Ni-rich LiNi_0.87Co_0.09Mn_0.04O₂ (NCM) cathode materials were two-dimensionally visualized on a micro-scale gathering by nano-scale analysis, which enabled high-resolution particle analysis, through transmission electron microscopy coupled with X-ray energy dispersive spectroscopy. Degraded (capacity retention < 80%) NCM particles featuring grain-boundary cracking caused by repeated volume expansion/contraction upon charge/discharge exhibited compositions similar to that of pristine particles, whereas sectionalized chemical composition mapping revealed that broken and pulverized NCM particles, i.e., those very heavily fractured and broken in such a way as to directly expose the particle surface to the electrolyte, exhibited decreased TM contents. Therefore, TM dissolution was concluded to occur at the cathode material–electrolyte interface and be one of the main reasons of electrode material degradation.