Highly Macroporous Polyimide with Chemical Versatility Prepared from Poly(amic acid) Salt-Stabilized High Internal Phase Emulsion Template.

Macroporous polymers have gained significant attention due to their unique mass transport and size-selective properties. In this study, we focused on Polyimide (PI), a high-performance polymer, as an ideal candidate for macroporous structures. Despite various attempts to create macroporous PI (Macro PI) using emulsion templates, challenges remained, including limited chemical diversity and poor control over pore size and porosity. To address these issues, we systematically investigated the role of poly(amic acid) salt (PAAS) polymers as macrosurfactants and matrices. By designing 12 different PAAS polymers with diverse chemical structures, we achieved stable high internal phase emulsions (HIPEs) with >80 vol % internal volume. The resulting Macro PIs exhibited exceptional porosity (>99 vol %) after thermal imidization. We explored the structure-property relationships of these Macro PIs, emphasizing the importance of controlling pore size distribution. Furthermore, our study demonstrated the utility of these Macro PIs as separators in Li-metal batteries, providing stable charging-discharging cycles. Our findings not only enhance the understanding of emulsion-based macroporous polymers but also pave the way for their applications in advanced energy storage systems and beyond.

Long-Range Uniform Deposition of Ag Nanoseed on Cu Current Collector for High-Performance Lithium Metal Batteries.

Uniform lithium deposition is essential to hinder dendritic growth. Achieving this demands even seed material distribution across the electrode, posing challenges in correlating the electrode's surface structure with the uniformity of seed material distribution. In this study, the effect of periodic surface and facet orientation on seed distribution is investigated using a model system consisting of a wrinkled copper (Cu)/graphene structure with a [100] facet orientation. A new methodology is developed for uniformly distributed silver (Ag) nanoparticles over a large area by controlling the surface features of Cu substrates. The regularly arranged Ag nanoparticles, with a diameter of 26.4 nm, are fabricated by controlling the Cu surface condition as [100]-oriented wrinkled Cu. The wrinkled Cu guides a deposition site for spherical Ag nanoparticles, the [100] facet determines the Ag morphology, and the presence of graphene leads to spacings of Ag seeds. This patterned surface and high lithiophilicity, with homogeneously distributed Ag nanoparticles, lead to uniform Li+ flux and reduced nucleation energy barrier, resulting in excellent battery performance. The electrochemical measurements exhibit improved cyclic stability over 260 cycles at 0.5 mA cm-2 and 100 cycles at 1.0 mA cm-2 and enhanced kinetics even under a high current density of 5.0 mA cm-2.

Spherical Sulfur-Infiltrated Carbon Cathode with a Tunable Poly(3,4-ethylenedioxythiophene) Layer for Lithium-Sulfur Batteries.

Li-S batteries have received significant attention owing to their high energy density, nontoxicity, low cost, and eco-friendliness. However, the dissolution of lithium polysulfide during the charge/discharge process and its extremely low electron conductivity hinder practical applications of Li-S batteries. Herein, we report a sulfur-infiltrated carbon cathode material with a spherical morphology and conductive polymer coating. The material was produced via a facile polymerization process that forms a robust nanostructured layer and physically prevents the dissolution of lithium polysulfide. The thin double layer composed of carbon and poly(3,4-ethylenedioxythiophene) provides sufficient space for sulfur storage and effectively prevents the elution of polysulfide during continuous cycling, thereby playing an essential role in increasing the sulfur utilization rate and significantly improving the electrochemical performance of the battery. Sulfur-infiltrated hollow carbon spheres with a conductive polymer layer demonstrate a stable cycle life and reduced internal resistance. The as-fabricated battery demonstrated an excellent capacity of 970 mA h g-1 at 0.5 C and a stable cycle performance, exhibiting ∼78% of the initial discharge capacity after 50 cycles. This study provides a promising approach to significantly improve the electrochemical performance of Li-S batteries and render them as valuable and safe energy devices for large-scale energy storage systems.

Encapsulating lithium at the microscale: selective deposition in carbon-doped graphitic carbon nitride spheres.

For stable lithium deposition without dendrites, three-dimensional (3D) porous structure has been intensively investigated. Here, we report the use of carbon-doped graphitic carbon nitride (C-doped g-C3N4) microspheres as a 3D host for lithium to suppress dendrite formation, which is crucial for stable lithium deposition. The C-doped g-C3N4microspheres have a high surface area and porosity, allowing for efficient lithium accommodation with high accessibility. The carbon-doping of the g-C3N4microspheres confers lithiophilic properties, which facilitate the regulation of Li+flux and dense filling of cavities with nucleated lithium, thereby preventing volume expansion and promoting dendrite-free Li deposition. The electrochemical performance was improved with cyclic stability and high Coulombic efficiency over 260 cycles at 1.0 mA cm-2for 1.0 mAh cm-2, and even over 70 cycles at 5.0 mA cm-2for 3.0 mAh cm-2. The use of C-doped g-C3N4microspheres as a 3D Li host shows promising results for stable lithium deposition without dendrite formation.

Effect of Highly Periodic Au Nanopatterns on Dendrite Suppression in Lithium Metal Batteries.

Despite the extremely high energy density of the lithium metal, dendritic lithium growth caused by nonuniform lithium deposition can result in low Coulombic efficiency and safety hazards, thereby inhibiting its practical applications. Here, we report a new strategy for adopting a nanopatterned gold (Au) seed on a copper current collector for uniform lithium deposition. We find that Au nanopatterns enhance lithium metal battery performance, which is strongly affected by the feature dimensions of Au nanopatterns (diameter and height). Ex situ scanning electron microscopy images confirm that this can be attributed to the perfectly selective lithium nucleation and uniform growth resulting from the spatial confinement effect. The spatial arrangement of Au dot seeds homogenizes the Li+ flux and electric field, and the size-controlled Au seeds prevent both seed-/substrate-induced agglomeration and interseed-induced lithium growth, leading to uniform lithium deposition. This dendrite-free lithium deposition results in the improvement of electrochemical performance, and the system showed cyclic stability over 300 cycles at 0.5 mA cm-2 and 200 cycles at 1.0 mA cm-2 (1 mA h cm-2) and a high rate capability. This study provides in-depth insights into the more complicated and diverse seed geometry control of seed materials for the development of high-performance lithium metal batteries.

Understanding the Chemical Composition with Doping Aliovalent Ions, Followed by the Electrochemical Behavior for Surface-Modified Ni-Rich NMC Cathode Materials.

A comparative study of doping aliovalent ions, Zr- or Al-, into Ni-rich Li(Ni,Co,Mn)O2 cathode materials is conducted in terms of the electrochemical properties and chemical analysis, especially on the surface region. The solubility and chemical composition for the given sol-gel treatment matches well with the computational results with which the infinitesimal Zr-coating is identified as exhibiting increased charge capacity with prolonged cycle life. Specifically, the whole process can be understood by the suppressed lithium-ion charge transfer resistance (RCT) during the cycles, which can be facilitated by the decreased NiO formation during the cyclic reactions.

Polyelemental Nanoparticles as Catalysts for a Li-O2 Battery.

The development of highly efficient catalysts in the cathodes of rechargeable Li-O2 batteries is a considerable challenge. Polyelemental catalysts consisting of two or more kinds of hybridized catalysts are particularly interesting because the combination of the electrochemical properties of each catalyst component can significantly facilitate oxygen evolution and oxygen reduction reactions. Despite the recent advances that have been made in this field, the number of elements in the catalysts has been largely limited to two metals. In this study, we demonstrate the electrochemical behavior of Li-O2 batteries containing a wide range of catalytic element combinations. Fourteen different combinations with single, binary, ternary, and quaternary combinations of Pt, Pd, Au, and Ru were prepared on carbon nanofibers (CNFs) via a joule heating route. Importantly, the Li-O2 battery performance could be significantly improved when using a polyelemental catalyst with four elements. The cathode containing quaternary nanoparticles (Pt-Pd-Au-Ru) exhibited a reduced overpotential (0.45 V) and a high discharge capacity based on total cathode weight at 9130 mAh g-1, which was ∼3 times higher than that of the pristine CNF electrode. This superior electrochemical performance is be attributed to an increased catalytic activity associated with an enhanced O2 adsorbability by the quaternary nanoparticles.

Nanoscale Wrinkled Cu as a Current Collector for High-Loading Graphite Anode in Solid-State Lithium Batteries.

Solid-state lithium batteries have been intensively studied as part of research activities to develop energy storage systems with high safety and stability characteristics. Despite the advantages of solid-state lithium batteries, their application is currently limited by poor reversible capacity arising from their high resistance. In this study, we significantly improve the reversible capacity of solid-state lithium batteries by lowering the resistance through the introduction of a graphene and wrinkle structure on the surface of the copper (Cu) current collector. This is achieved through a process of chemical vapor deposition (CVD) facilitating graphene-growth synthesis. The modified graphene/wrinkled Cu current collector exhibits a periodic wrinkled pattern 420 nm in width and 22 nm in depth, and we apply it to a graphite composite electrode to obtain an improved areal loading average value of ∼2.5 mg cm-2. The surface-modified Cu current collector is associated with a significant increase in discharge capacity of 347 mAh g-1 at 0.2 C when used with a solid polymer electrolyte. Peel test results show that the observed enhancement is due to the improved strength of adhesion occurring between the graphite composite anode and the Cu current collector, which is attributed to mechanical interlocking. The surface-modified Cu current collector structure effectively reduces resistance by improving adhesion, which subsequently improves the performance of the solid-state lithium batteries. Our study can provide perspective and emphasize the importance of electrode design in achieving enhancements in battery performance.

Luminescence Quenching Behavior of Hydrothermally Grown YVO4:Eu3+ Nanophosphor Excited under Low Temperature and Vacuum Ultra Violet Discharge.

The luminescence quenching behavior and energy transfer process in hydrothermally grown Eu3+-doped YVO4 nanophosphors were studied using low temperature photoluminescence spectroscopy. The luminescence efficiency of nanophosphor is dependent on the acidity of its solution media and the post annealing condition after hydrothermal processing. The overall results suggest that the abnormal luminescence behavior of Eu3+-doped nanocrystalline YVO4 under low temperature photoexcitation is due to the incorporated non-radiative hydroxyl groups often encountered in hydrothermal synthesis as well as to the inefficient energy transfer to luminescent ions from vanadate groups.

Understanding Reaction Pathways in High Dielectric Electrolytes Using ß-Mo2C as a Catalyst for Li-CO2 Batteries.

The rechargeable Li-CO2 battery has attracted considerable attention in recent years because of its carbon dioxide (CO2) utilization and because it represents a practical Li-air battery. As with other battery systems such as the Li-ion, Li-O2, and Li-S battery systems, understanding the reaction pathway is the first step to achieving high battery performance because the performance is strongly affected by reaction intermediates. Despite intensive efforts in this area, the effect of material parameters (e.g., the electrolyte, the cathode, and the catalyst) on the reaction pathway in Li-CO2 batteries is not yet fully understood. Here, we show for the first time that the discharge reaction pathway of a Li-CO2 battery composed of graphene nanoplatelets/beta phase of molybdenum carbide (GNPs/ß-Mo2C) is strongly influenced by the dielectric constant of its electrolyte. Calculations using the continuum solvents model show that the energy of adsorption of oxalate (C2O42-) onto Mo2C under the low-dielectric electrolyte tetraethylene glycol dimethyl ether is lower than that under the high-dielectric electrolyte N,N-dimethylacetamide (DMA), indicating that the electrolyte plays a critical role in determining the reaction pathway. The experimental results show that under the high-dielectric DMA electrolyte, the formation of lithium carbonate (Li2CO3) as a discharge product is favorable because of the instability of the oxalate species, confirming that the dielectric properties of the electrolyte play an important role in the formation of the discharge product. The resulting Li-CO2 battery exhibits improved battery performance, including a reduced overpotential and a remarkable discharge capacity as high as 14,000 mA h g-1 because of its lower internal resistance. We believe that this work provides insights for the design of Li-CO2 batteries with enhanced performance for practical Li-air battery applications.

Formation of toroidal Li2O2 in non-aqueous Li-O2 batteries with Mo2CT x MXene/CNT composite.

Due to the growing demand for high energy density devices, Li-O2 batteries are considered as a next generation energy storage system. The battery performance is highly dependent on the Li2O2 morphology, which arises from formation pathways such as the surface growth and the solution growth models. Thus, controlling the formation pathway is important in designing cathode materials. Herein for the first time, we controlled the Li2O2 formation pathway by using Mo2CT x MXene on a catalyst support. The cathode was fabricated by mixing the positively charged CNT/CTAB solution with the negatively charged Mo2CT x solution. After introducing Mo2CT x , important battery performance metrics were considerably enhanced. More importantly, the discharge product analysis showed that the functional groups on the surface of Mo2CT x inhibit the adsorption of O2 on the cathode surface, resulting in the formation of toroidal Li2O2 via the solution growth model. It was supported by density functional theory (DFT) calculations that adsorption of O2 on the Mo2CT x surface is implausible due to the large energy penalty for the O2 adsorption. Therefore, the introduction of MXene with abundant functional groups to the cathode surface can provide a cathode design strategy and can be considered as a universal method in generating toroidal Li2O2 morphology.

Characterization of Ti3+-doped TiO2 based composite electrode for lithium polymer secondary batteries.

Ti3+-doped TiO2 nanoparticles were synthesized and fabricated into a composite electrode as an anode material for lithium polymer batteries. The composite electrode contained polymer electrolyte (PE) to reduce interfacial resistance between the solid PE and electrode. The effect of PE content on the composite electrodes was analyzed by GITT, and it was found that PE significantly influenced lithium storage as well as internal resistance. A composite electrode was fabricated into a pouch type cell and exhibited a capacity of 160 mAh g-1 in the bent state, demonstrating the applicability of the Ti3+-doped TiO2 based composite electrode in lithium polymer secondary batteries.

Understanding the Critical Role of the Ag Nanophase in Boosting the Initial Reversibility of Transition Metal Oxide Anodes for Lithium-Ion Batteries.

The initial reversible capacity, a critical impediment in transition metal oxide-based anodes, is augmented in conversion-reaction-involved CoO anodes for lithium-ion batteries, by incorporating a chemically synthesized Ag nanophase. With an increase in the added amount of Ag nanophase from 5 to 15 wt %, the initial capacity loss decreases linearly up to 31.7%. The Ag nanophase maintains its pristine metallic nature without undergoing phase transformations, even during repeated vigorous electrochemical reactions of the active CoO phase. Complementary ex situ chemical/physical analyses suggest that the Ag nanophase promotes the catalytic generation of reversible gel-like/polymeric films wherein lithium ions are stored capacitively in the low-voltage region below 0.7 V during discharging. These scientific findings would provide a heretofore unrecognized pathway to resolving a major issue associated with the critical irreversibility in conversion-type transition metal oxide anodes.

Mesoporous amorphous binary Ru-Ti oxides as bifunctional catalysts for non-aqueous Li-O2 batteries.

Mesoporous amorphous binary Ru-Ti oxides were prepared as bifunctional catalysts for non-aqueous Li-O2 batteries, and their electrochemical performance was investigated for the first time. A Li-O2 battery with mesoporous amorphous binary Ru-Ti oxides exhibited a remarkably high capacity of 27100 mAh g-1 as well as a reduced overpotential. A GITT analysis suggested that the introduction of amorphous TiO2 to amorphous RuO2 was responsible for the enhanced kinetics toward both the oxygen reduction reaction and oxygen evolution reaction. Excellent cyclic stability up to 230 cycles was achieved, confirming the applicability of the new bifunctional catalyst in non-aqueous Li-O2 batteries.

High-rate performance of Ti(3+) self-doped TiO2 prepared by imidazole reduction for Li-ion batteries.

Ti(3+) self-doped TiO2 nanoparticles were prepared via a simple imidazole reduction process and developed as an anode material for Li-ion batteries. Introducing the Ti(3+)-state on TiO2 nanoparticles resulted in superior rate performances that the capacity retention of 88% at 50 C. The enhanced electrochemical performances were attributed to the resulting lower internal resistance and improved electronic conductivity, based on galvanostatic intermittent titration technique and electrochemical impedance spectroscopy analyses.

Temperature variable luminescence and color tuning of Eu2+/Mn2+-codoped strontium magnesium phosphates as promising red-emitting phosphors for light emitting diodes.

Eu(2+) and Mn(2+) codoped violet-/red-emitting strontium magnesium phosphates, SrMgP2O7, SrMg2P2O8 and Sr2Mg3P4O15, were prepared and their emission properties, especially for color tuning with temperature variable luminescence, were investigated. Simply by changing the host composition of the SrO-MgO-P2O5 ternary system, we can control the Eu(2+)-sensitized Mn(2+) emission efficiency as well as the thermal quenching of incorporated activators. We can realize that the overall luminescence behavior is induced by the Mn(2+) center positioned at different coordination states with intermixed Sr(2+)/Mg(2+) sites in various hosts, which resulted in widely tunable colors from violet-red through orange-red to pure red. Finally, bright and stable reddish color illuminated light emitting diodes (LEDs) can be obtained by combining the proposed phosphates with ultraviolet LEDs, demonstrating the potential red-emitting phosphors for ultraviolet-pumped phosphor converted white-LEDs.

Crystallinity-controlled titanium oxide-carbon nanocomposites with enhanced lithium storage performance.

Nanocomposites of crystalline-controlled TiO(2) -carbon are prepared by a novel one-step approach and applied in anodes of lithium ion batteries. In our nanocomposite anodes, the Li(+) capacity contribution from the TiO(2) phase was enormous, above 400 mAh g(-1) (Li(1+x) TiO(2) , x>0.2), and the volumetric capacity was as high as 877 mAh cm(-3) with full voltage utilization to 0 V versus Li/Li(+) , which resulted in higher energy density than that of state-of-the-art titania anodes. For the first time, it was clearly revealed that the capacity at 1.2 and 2.0 V corresponded to Li(+) storage at amorphous and crystalline TiO(2) , respectively. Furthermore, improvements in the rate capability and cycle performance were observed; this was attributed to resistance reduction induced by higher electrical/Li(+) conduction and faster Li(+) diffusion.