Search Results (28)

We have investigated for the first time the temperature, size, and ion-doping concentration dependence of the magnetic properties, band-gap energy, and specific heat of CuFeO₂ in both bulk materials and nanoparticles using a microscopic model (the s-d model) and Green’s function theory. Variations in the ionic radii of the dopant elements compared to those of the host ions introduce strain effects, which alter the exchange-interaction constants. Consequently, the influence of ion doping on the various properties of CuFeO₂ nanoparticles has been elucidated at a microscopic level. The magnetization exhibits an increase when CuFeO₂ is doped with Mn at the Fe site or Li and Ca at the Cu site, whereas doping with Sc or Mg at the Fe site leads to a decrease in magnetization. Regarding the band-gap energy, it increases upon doping with Mg and Sc at the Fe site, while doping with Mn at the Fe site or with Li and Ca at the Cu site results in a decrease. The temperature dependence of the specific heat reveals two distinct peaks, corresponding to the two magnetic phase-transition temperatures. The theoretical results show good qualitative agreement with experimental data, confirming the validity of the proposed model. Full article

Transition metal oxides (TMOs) occupy an increasing share in the search for new electrode materials for Li-Ion batteries. Despite promising electrochemical performances (up to 1000 mAh g⁻¹ in the case of conversion), these materials have poor cyclability linked primarily to hysteresis phenomena. To improve their electrochemical performance, one strategy consists of reducing the particle size. A second strategy relies on the incorporation of fluorine directly into electrode materials to limit the solid–electrolyte interface (SEI). Our study focuses on the impact of fluorination on the electrochemical performance of manganese oxide obtained by solid combustion synthesis (SCS). Two fluorinating agents were used: pure gaseous molecular fluorine F₂ and radical fluorine F^• through xenon difluoride XeF₂ decomposition. The use of F₂ results in strong fluorination localized primarily at the particle surface while XeF₂ diffuses deeper into the particle, resulting in the removal of residual carbon from the synthesis by combustion. The electrochemical performance of the oxide fluorinated with XeF₂ reaches more than 750 mAh g⁻¹ after 160 cycles, whereas that of the oxide fluorinated by F₂ barely exceeds that of the non-fluorinated oxide, less than 200 mAh g⁻¹ after 200 cycles. Full article

With the swift advancement of wearable electronics and artificial intelligence, the integration of electronic devices with the human body has advanced significantly, leading to enhanced real-time health monitoring and remote disease diagnosis. Despite progress in developing stretchable materials with skin-like mechanical properties, there remains a need for materials that also exhibit high optical transparency. Supercapacitors, as promising energy storage devices, offer advantages such as portability, long cycle life, and rapid charge/discharge rates, but achieving high capacity, stretchability, and transparency simultaneously remains challenging. This study combines the stretchable, transparent polymer PEDOT:PSS with MnO₂ nanoparticles to develop high-performance, stretchable, and transparent supercapacitors. PEDOT:PSS films were deposited on a PDMS substrate using a spin-coating method, followed by electrochemical deposition of MnO₂ nanoparticles. This method ensured that the nanosized MnO₂ particles were uniformly distributed, maintaining the transparency and stretchability of PEDOT:PSS. The resulting PEDOT:PSS/MnO₂ nanoparticle electrodes were gathered into a symmetric device using a LiCl/PVA gel electrolyte, achieving an areal capacitance of 1.14 mF cm⁻² at 71.2% transparency and maintaining 89.92% capacitance after 5000 cycles of 20% strain. This work presents a scalable and economical technique to manufacturing supercapacitors that combine high capacity, transparency, and mechanical stretchability, suggesting potential applications in wearable electronics. Full article

The integration of heterostructures within electrode materials is pivotal for enhancing electron and Li-ion diffusion kinetics. In this study, we synthesized CoO/MnO heterostructures to enhance the electrochemical performance of MnO using a straightforward electrostatic spinning technique followed by a meticulously controlled carbonization process, which results in embedding heterostructured CoO/MnO nanoparticles within porous nitrogen-doped carbon nanofibers (CoO/MnO/NC). As confirmed by density functional theory calculations and experimental results, CoO/MnO heterostructures play a significant role in promoting Li⁺ ion and charge transfer, improving electronic conductivity, and reducing the adsorption energy. The accelerated electron and Li-ion diffusion kinetics, coupled with the porous nitrogen-doped carbon nanofiber structure, contribute to the exceptional electrochemical performance of the CoO/MnO/NC electrode. Specifically, the as-prepared CoO/MnO/NC exhibits a high reversible specific capacity of 936 mA h g⁻¹ at 0.1 A g⁻¹ after 200 cycles and an excellent high-rate capacity of 560 mA h g⁻¹ at 5 A g⁻¹, positioning it as a competitive anode material for lithium-ion batteries. This study underscores the critical role of electronic and Li-ion regulation facilitated by heterostructures, offering a promising pathway for designing transition metal oxide-based anode materials with high performances for lithium-ion batteries. Full article

Nanoparticles have many advantages as active materials, such as a short diffusion length, low charge transfer resistance, or a reduced probability of cracking. However, their low packing density makes them unsuitable for commercial battery applications. Hierarchically structured microparticles are synthesized from nanoscale primary particles by targeted aggregation. Due to their open accessible porosity, they retain the advantages of nanomaterials but can be packed much more densely. However, the intrinsic porosity of the secondary particles leads to limitations in processing properties and increases the overall porosity of the electrode, which must be balanced against the improved rate stability and increased lifetime. This is demonstrated for an established cathode material for lithium-ion batteries (LiNi_0.33Co_0.33Mn_0.33O₂, NCM111). For active materials with low electrical or ionic conductivity, especially post-lithium systems, hierarchically structured particles are often the only way to produce competitive electrodes. Full article

The lignin-based mesoporous hollow carbon@MnO₂ nanosphere composites (L-C-NSs@MnO₂) were fabricated by using lignosulfonate as the carbon source. The nanostructured MnO₂ particles with a diameter of 10~20 nm were uniformly coated onto the surfaces of the hollow carbon nanospheres. The obtained L-C-NSs@MnO₂ nanosphere composite showed a prolonged cycling lifespan and excellent rate performance when utilized as an anode for LIBs. The L-C-NSs@MnO₂ nanocomposite (24.6 wt% of MnO₂) showed a specific discharge capacity of 478 mAh g⁻¹ after 500 discharge/charge cycles, and the capacity contribution of MnO₂ in the L-C-NSs@MnO₂ nanocomposite was estimated ca. 1268.8 mAh g⁻¹, corresponding to 103.2% of the theoretical capacity of MnO₂ (1230 mAh g⁻¹). Moreover, the capacity degradation rate was ca. 0.026% per cycle after long-term and high-rate Li⁺ insertion/extraction processes. The three-dimensional lignin-based carbon nanospheres played a crucial part in buffering the volumetric expansion and agglomeration of MnO₂ nanoparticles during the discharge/charge processes. Furthermore, the large specific surface areas and mesoporous structure properties of the hollow carbon nanospheres significantly facilitate the fast transport of the lithium-ion and electrons, improving the electrochemical activities of the L-C-NSs@MnO₂ electrodes. The presented work shows that the combination of specific structured lignin-based carbon nanoarchitecture with MnO₂ provides a brand-new thought for the designation and synthesis of high-performance materials for energy-related applications. Full article

Manganese dioxide (MnO₂) exists in a variety of polymorphs and crystallographic structures. The electrochemical performance of Li storage can vary depending on the polymorph and the morphology. In this study, we present a new approach to fabricate polymorph- and aspect-ratio-controlled α-MnO₂ nanorods. First, δ-MnO₂ nanoparticles were synthesized using a solution plasma process assisted by three types of sugars (sucrose, glucose, and fructose) as reducing promoters; this revealed different morphologies depending on the nucleation rate and reaction time from the molecular structure of the sugars. Based on the morphology of δ-MnO₂, the polymorphic-transformed three types of α-MnO₂ nanorods showed different aspect ratios (c/a), which highly affected the transport of Li ions. Among them, a relatively small aspect ratio (c/a = 5.1) and wide width of α-MnO₂-S nanorods (sucrose-assisted) induced facile Li-ion transport in the interior of the particles through an increased Li-ion pathway. Consequently, α-MnO₂-S exhibited superior battery performance with a high-rate capability of 673 mAh g⁻¹ at 2 A g⁻¹, and it delivered a high reversible capacity of 1169 mAh g⁻¹ at 0.5 A g⁻¹ after 200 cycles. Our findings demonstrated that polymorphs and crystallographic properties are crucial factors in the electrode design of high-performance Li-ion batteries. Full article

Due to the low capacity, low working potential, and lithium coating at fast charging rates of graphite material as an anode for Li-ion batteries (LIBs), it is necessary to develop novel anode materials for LIBs with higher capacity, excellent electrochemical stability, and good safety. Among different transition-metal oxides, AB₂O₄ spinel oxides are promising anode materials for LIBs due to their high theoretical capacities, environmental friendliness, high abundance, and low cost. In this work, a novel, porous Zn_0.5Mg_0.5FeMnO₄ spinel oxide was successfully prepared via the sol–gel method and then studied as an anode material for Li-ion batteries (LIBs). Its crystal structure, morphology, and electrochemical properties were, respectively, analyzed through X-ray diffraction, high-resolution scanning electron microscopy, and cyclic voltammetry/galvanostatic discharge/charge measurements. From the X-ray diffraction, Zn_0.5Mg_0.5FeMnO₄ spinel oxide was found to crystallize in the cubic structure with Fd$\overline{3}$m symmetry. However, the Zn_0.5Mg_0.5FeMnO₄ spinel oxide exhibited a porous morphology formed by interconnected 3D nanoparticles. The porous Zn_0.5Mg_0.5FeMnO₄ anode showed good cycling stability in its capacity during the initial 40 cycles with a retention capacity of 484.1 mAh g⁻¹ after 40 cycles at a current density of 150 mA g⁻¹, followed by a gradual decrease in the range of 40–80 cycles, which led to reaching a specific capacity close to 300.0 mAh g⁻¹ after 80 cycles. The electrochemical reactions of the lithiation/delithiation processes and the lithium-ion storage mechanism are discussed and extracted from the cyclic voltammetry curves. Full article

A composite electrode of carbon nanotube CNT@Mn₃O₄ nanocable was successfully synthesized via direct electrophoretic deposition onto a copper foil, followed by calcination. By uniformly depositing Mn₃O₄ nanoparticles on CNTs, a nanocable structure of CNT@Mn₃O₄ can be formed, where the CNT acts as a “highway” for electrons and ions to facilitate fast transportation. Moreover, capacitive energy storage processes play a crucial role in lithium (Li) storage, especially during high scan rates. The significant contribution of capacitance is highly advantageous for the rapid transfer of Li⁺ ions, which ultimately results in an improved reversible capacity and prolonged cycle stability of the battery. A high specific capacity of 1367 mAh g⁻¹ was maintained over 300 charge–discharge cycles at a current density of 1 A g⁻¹, indicating excellent capacity retention and an extended cycle life. Furthermore, the synthesis process was facile and cost-effective, obviating the need for complex procedures such as mixing and pasting. Additionally, no binder was required, thereby enhancing battery quality efficiency. Full article

Separators play an essential role in lithium (Li)-based secondary batteries by preventing direct contact between the two electrodes and providing conduction pathways for Li-ions in the battery cells. However, conventional polyolefin separators exhibit insufficient electrolyte wettability and thermal stability, and in particular, they are vulnerable to Li dendritic growth, which is a significant weakness in Li-metal batteries (LMBs). To improve the safety and electrochemical performance of LMBs, Al₂O₃ nanoparticles and nanocellulose (NC)-coated non-woven poly(vinylidene fluoride)/polyacrylonitrile separators were fabricated using a simple, water-based blade coating method. The Al₂O₃/NC-coated separator possessed a reasonably porous structure and a significant number of hydroxyl groups (-OH), which enhanced electrolyte uptake (394.8%) and ionic conductivity (1.493 mS/cm). The coated separator also exhibited reduced thermal shrinkage and alleviated uncontrollable Li dendritic growth compared with a bare separator. Consequently, Li-metal battery cells with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode and an Al₂O₃/NC-coated separator using either liquid or solid polymer electrolytes exhibited improved rate capability, cycle stability, and safety compared with a cell with a bare separator. The present study demonstrates that combining appropriate materials in coatings on separator surfaces can enhance the safety and electrochemical performance of LMBs. Full article

Surface coating has become an effective approach to improve the electrochemical performance of Ni-rich cathode materials. In this study, we investigated the nature of an Ag coating layer and its effect on electrochemical properties of the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material, which was synthesized using 3 mol.% of silver nanoparticles by a facile, cost-effective, scalable and convenient method. We conducted structural analyses using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, which revealed that the Ag nanoparticle coating did not affect the layered structure of NCM811. The Ag-coated sample had less cation mixing compared to the pristine NMC811, which could be attributed to the surface protection of Ag coating from air contamination. The Ag-coated NCM811 exhibited better kinetics than the pristine one, which is attributed to the higher electronic conductivity and better layered structure provided by the Ag nanoparticle coating. The Ag-coated NCM811 delivered a discharge capacity of 185 mAh·g⁻¹ at the first cycle and 120 mAh·g⁻¹ at the 100th cycle, respectively, which is better than the pristine NMC811. Full article

In this report, the synergetic sonoelectrochemical method was utilized to produce magnetite nanoparticles was doped with MnO₂ with the assistance of ultrasound to form nanoarchitectonic magnetic crystals with a mesoporous magnetite @ manganese dioxide (m-Fe₃O₄@MnO₂) hybrid nanostructure. The hybrid nanocomposite was rapidly produced based on the nucleation and growth of pure iron-oxide nanocrystals in the electrochemical system. The nanocomposite was pure, highly amorphous, and mesoporous in nature; the magnetite was spherical in shape, with an average diameter of 45 ± 10 nm and a MnO₂-plane length of 420 ± 30 nm. The stability of the pure m-Fe₃O₄ was enhanced from 89.61 to 94.04% with negligible weight loss after adding manganese dioxide and the stable formation of the hybrid nanostructure. Based on the superior results of the material, it was utilized as an anode material in Li-ion batteries. The m-Fe₃O₄@MnO₂ hybrid nanostructure had a highly active surface area, which enhanced the interfacial interaction between the Li-ion and the metal surface; it delivered 1513 mAh g⁻¹ and 1290 mAh g⁻¹ as the first specific discharge and charge capacity, respectively, with 85% coulombic efficiency, and it showed an excellent cyclic reversibility of 660 mAh g⁻¹ with a coulombic efficiency of almost 99% at current density of 1.0 A g⁻¹. Full article

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn₂O₄/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn₂O₄/MWCNTs preparation involved initial synthesis of Mn₃O₄ and CuMn₂O₄ precursors followed by an energy efficient reflux growth method for the CuMn₂O₄/MWCNTs. The CuMn₂O₄/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g⁻¹ at 0.5 A g⁻¹ current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g⁻¹ at 0.5 A g⁻¹ current load. Stability studies showed that after 6000 cycles, the CuMn₂O₄/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte. Full article

To reduce surface contamination and increase battery life, MoO₃ nanoparticles were coated with a high-voltage (5 V) LiNi_0.5Mn_1.5O₄ cathode material by in-situ method during the high-temperature annealing process. To avoid charging by more than 5 V, we also developed a system based on anode-limited full-cell with a negative/positive electrode (N/P) ratio of 0.9. The pristine LiNi_0.5Mn_1.5O₄ was initially prepared by high-energy ball-mill with a solid-state reaction, followed by a precipitation reaction with a molybdenum precursor for the MoO₃ coating. The typical structural and electrochemical behaviors of the materials were clearly investigated and reported. The results revealed that a sample of 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode exhibited an optimal electrochemical activity, indicating that the MoO₃ nanoparticle coating layers considerably enhanced the high-rate charge–discharge profiles and cycle life performance of LiNi_0.5Mn_1.5O₄ with a negligible capacity decay. The 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode could achieve high specific discharge capacities of 131 and 124 mAh g⁻¹ at the rates of 1 and 10 C, respectively. In particular, the 2 wt.% MoO₃-coated LiNi_0.5Mn_1.5O₄ electrode retained its specific capacity (87 mAh g⁻¹) of 80.1% after 500 cycles at a rate of 10 C. The Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ full cell based on the electrochemical-cell (EL-cell) configuration was successfully assembled and tested, exhibiting excellent cycling retention of 93.4% at a 1 C rate for 100 cycles. The results suggest that the MoO₃ nano-coating layer could effectively reduce side reactions at the interface of the LiNi_0.5Mn_1.5O₄ cathode and the electrolyte, thus improving the electrochemical performance of the battery system. Full article

Lithium-rich manganese oxide is a promising candidate for the next-generation cathode material of lithium-ion batteries because of its low cost and high specific capacity. Herein, a series of xLi₂MnO₃·(1 − x)LiMnO₂ nanocomposites were designed via an ingenious one-step dynamic hydrothermal route. A high concentration of alkaline solution, intense hydrothermal conditions, and stirring were used to obtain nanoparticles with a large surface area and uniform dispersity. The experimental results demonstrate that 0.072Li₂MnO₃·0.928LiMnO₂ nanoparticles exhibit a desirable electrochemical performance and deliver a high capacity of 196.4 mAh g⁻¹ at 0.1 C. This capacity was maintained at 190.5 mAh g⁻¹ with a retention rate of 97.0% by the 50th cycle, which demonstrates the excellent cycling stability. Furthermore, XRD characterization of the cycled electrode indicates that the Li₂MnO₃ phase of the composite is inert, even under a high potential (4.8 V), which is in contrast with most previous reports of lithium-rich materials. The inertness of Li₂MnO₃ is attributed to its high crystallinity and few structural defects, which make it difficult to activate. Hence, the final products demonstrate a favorable electrochemical performance with appropriate proportions of two phases in the composite, as high contents of inert Li₂MnO₃ lower the capacity, while a sufficient structural stability cannot be achieved with low contents. The findings indicate that controlling the composition through a dynamic hydrothermal route is an effective strategy for developing a Mn-based cathode material for lithium-ion batteries. Full article