Li-rich layered oxide cathodes have attracted extensive attention due to their high energy density. However, due to the low initial Coulombic efficiency and the capacity fading and voltage fading ...during cycling, its practical application is still a great challenge. Here, we report the one-step realization of layered/spinel heterostructures and Na doping by the sodium dodecyl sulfate (SDS)-assisted sol-gel method. The spinel phase provides 3D diffusion channels for Li-ions, and sodium doping changes the layered lattice constant and expands the layer spacing. Therefore, the designed Li1.15Mn0.54Ni0.13Co0.13Na0.05O2 (SDS-2) cathode possesses excellent electrochemical performance such as higher initial Coulombic efficiency and rate capacity and also alleviates voltage decay. The initial discharge-specific capacity of SDS-2 is 298.8 mAh g-1 at 0.1 C, and the discharge-specific capacity can reach 111.7 mAh g-1 at 10 C. This strategy can provide new insights into the design and synthesis of high-performance Li-rich layered oxide cathode materials.Li-rich layered oxide cathodes have attracted extensive attention due to their high energy density. However, due to the low initial Coulombic efficiency and the capacity fading and voltage fading during cycling, its practical application is still a great challenge. Here, we report the one-step realization of layered/spinel heterostructures and Na doping by the sodium dodecyl sulfate (SDS)-assisted sol-gel method. The spinel phase provides 3D diffusion channels for Li-ions, and sodium doping changes the layered lattice constant and expands the layer spacing. Therefore, the designed Li1.15Mn0.54Ni0.13Co0.13Na0.05O2 (SDS-2) cathode possesses excellent electrochemical performance such as higher initial Coulombic efficiency and rate capacity and also alleviates voltage decay. The initial discharge-specific capacity of SDS-2 is 298.8 mAh g-1 at 0.1 C, and the discharge-specific capacity can reach 111.7 mAh g-1 at 10 C. This strategy can provide new insights into the design and synthesis of high-performance Li-rich layered oxide cathode materials.
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IJS, KILJ, NUK, PNG, UL, UM
•LNCM power density is improved by LaF3 modification.•LaF3 modification technique fuses LaF3-decorated with La/F-doping.•A high-power density of 3555 W·kg−1 at 10C is achieved.•The relationship ...between the structures and electrochemical behavior is clarified.
Lithium-rich manganese-based layered oxides, such as Li1.2Mn0.54Co0.13Ni0.13O2 (LNCM), are promising cathodes that possess both ultrahigh-specific capacity and high working voltage, yet they have not been commercialized due to intrinsic challenges. These challenges include sluggish Li-ion diffusion kinetics and structural degradation from the layered structure to a spinel-like form, leading to poor power capability and severe capacity fading. To address these challenges, we have developed a modification technique that involves fusing LaF3-decorated with La/F-doping. Protecting the electrode/electrolyte interface, inert LaF3 particles decorate on the LNCM surface impede interfacial side reactions. La-doping near the surface enlarges the Li layer spacing and facilitates Li-ion diffusion. A stronger TM-F bond is formed when F diffuses into the bulk phase and replaces O, thereby decreasing the migration of TM. The resulting LaF3-modified LNCM exhibits a high capacity of 256.1 mAh g−1 at 0.1C and a high-power capability of 3555 W kg−1 at 10C, which is 2.5 times higher than the pristine sample. We also elucidate the relationship between the structures (i.e., oxidation state of elements, bond energy, mechanical properties, and conductivity) and electrochemical behaviors (i.e., impedance and Li-ion diffusion) to explain why the modification of LaF3 improves the power property of the LNCM.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
LiMn
Fe
PO
(LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO
(LFP) and improved safety features compared to layered oxide ...cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn
Fe
PO
(MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g
, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Understanding energy transfer mechanisms in graphene derivatives is strongly motivated by the unusually interesting electronic properties of graphene, which can provide a template for the creation of ...novel nanostructured derivatives. From a synthetic point of view, it is highly attractive to envision being able to synthesize pristine graphene from precursors such as graphene oxide (GO). While this goal may be challenging over large length-scales, it is possible to generate regions of graphene at the nanoscale, confirmed by Raman spectroscopy or other methods. We describe an in situ method of nucleating gold or palladium nanoparticles in the presence of ethylene glycol as a reducing agent, while simultaneously reducing GO to graphene. The Au nanoparticles aid in spectroscopic characterization by both quenching fluorescence, allowing the graphene D and G bands to be quantified, and yielding a surface enhancement of about two orders of magnitude. We observe the excitation profile (488-785 nm) of the surface enhanced Raman spectrum (SERS) of graphene with Au nanoparticles adsorbed on the surface. Both the D and G bands display a resonance at approximately 593 nm (2.09 eV). This resonance may be interpreted as a combination of the plasmon resonance at 548 nm and a likely contribution from charge transfer as well. In addition, we observe a stiffening of the G band compared with that of graphene. The mechanism of the SERS, whether plasmonic or charge transfer-based, enables insight into the electronic pathways available to the graphene-nanoparticle system. We discuss our results in the context of several existing studies of graphene-based nanostructure derivatives.
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IJS, KILJ, NUK, UL, UM, UPUK
In this work, polyaniline nanowires and nanorods are synthesized through adjusting and controlling the concentration of D‐camphor‐10‐sulfonic acid (CSA) and NaF salt under the application of an ...electric field. The morphologies and structures of as‐synthesized polyaniline (PANI) are characterized through various methods, including transmission electron microscopy, UV–vis, Fouier transform infrared spectroscopy, and X‐ray diffraction. The results demonstrate that the introduction of an electric field can improve the crystallinity of PANI, and PANI nanowires/nanorods are fabricated through changing the amount of NaF or CSA in the presence of the electric field. Besides, the 1H NMR experiments are executed to investigate the structures of final products.
Polyaniline nanowires and nanorods are synthesized through adjusting the concentration of NaF or/and D‐camphor‐10‐sulfonic acid (CSA) under the application of the electric field (30 V), when inorganic salt NaF is introduced into the initial solution containing aniline and CSA. The different morphologies of as‐prepared polyaniline are characterized by transmission electron microscopy and displayed as follows.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A mechanistic study on the nucleation of aggregates exhibiting a weak intermolecular coupling and high molecular mobility for major components, exampled by an entity of aniline and salicylic acid in ...the preparation of polyaniline microspheres (PANI-NS) and interconnected structures (PANI-NC), is explored by in situ 1H NMR experiments. Three different procedures, namely, hydration of the aniline–salicylic acid (SA) entity, removal of the extra charges to the surroundings, and sphere-to-rod transitions, afford the smooth nucleation of products in characteristic morphologies. At the beginning, water plays a fundamental role in attenuating the high chemical potential system by hydrating both the aniline–SA entity and the in situ formed protons in the reaction, and removing the latter to bulk water when the chemical potential increment from the in situ produced proton is at a low initially. The driving force for this process is the increased intermolecular distances between aniline and SA induced by the electrostatic repulsions between positively charged protons in the entity, which paves the pathway for water in bulk to diffuse into the system. When a large amount of protons have been released in the reaction, the high chemical potential can be lowered down by repulsing both large and small sized positive charges to the external surroundings through electrostatic interactions or a sphere-to-rod structural transition initiated by continuously formed oligomers sheathed at the exterior of the spheres, which affords the formation of PANI-NS and PANI-NC, respectively. The competition of the two depends on the relative amplitude between the releasing rate of the protons and the mechanical strength of the aniline–SA entity in the reaction. Our work demonstrates that in situ dynamic NMR experiments such as measurements of NOE and spin–lattice relaxation times, and line shape analysis, provide new perspective powers for resolving the formation profile and more importantly the driving forces for each procedure at the molecular scale.
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Li-rich cathode material Li1.2Mn0.54Co0.13Ni0.13O2 is an important candidate material for Li-ion batteries. However, due to its low initial coulombic efficiency, poor cycle performance and rate ...performance, its development has been limited. In order to stabilize the crystal structure and improve the electrochemical performance, CeO2 was coated on the surface of Li1.2Mn0.54Co0.13Ni0.13O2 by surface engineering strategy while doping trace amount of Ce. The results show that this modification method greatly reduced the Li/Ni mixing level in the material and mitigated the oxygen loss, which was beneficial to improve the electrochemical performance of the material. As expected, the initial cycle coulombic efficiency of the modified sample (4wt % - CeO2) increased by 27.5% at 1 C, and the discharge capacity increased by 28.4% after 50 charge-discharge cycles at 0.2 C in the voltage range of 2.0 V to 4.8 V. In particular, the discharge specific capacity increased by 90.4% at a high rate of 10 C. This strongly proves that the strategy has great prospects in improving the electrochemical performance of Li-ion battery electrode materials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To explore the influence of CuO additive on the thermal kinetics and combustion performance of thermite, Al/MoO3 thermite composites with different mass fractions of CuO were prepared by ball ...milling. Field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), and differential scanning calorimeter (DSC) were used to test the samples. From the DSC results, Al/MoO3 thermite and Al/CuO thermite released 1066 J/g and 849 J/g heat, respectively. The peak temperature of the exothermic reaction was 560.22 °C and 609.43 °C. Interestingly, the Al/MoO3 thermite with 5% CuO released higher heat, about 1747 J/g. The temperature of the exothermic peak was also greatly advanced to 526 °C. Thermodynamic analysis results showed that the activation energy (Ea) of Al/MoO3/5% CuO thermite was merely 184.75 kJ mol−1, which was a decrease of 18.3% and 20.8% of the Al/MoO3 and Al/CuO thermite. The reaction mechanism function of Al/MoO3 thermite, Al/MoO3/5% CuO and Al/CuO thermite can be set as f(α)=1−α. The fast electric heating wire ignition experiment showed that the flame brightness of the Al/MoO3/5% CuO thermite was the brightest and the burning time was the longest. Surprisingly, when the mass fraction of CuO additives in Al/MoO3 thermite reached 10% and 20%, the thermal kinetics and combustion performance of the thermite were completely changed. There was a violent and sharp exothermic peak accompanied by a large amount of heat release of 2042 J/g and 2252 J/g, respectively. The reaction mechanism of Al/MoO3 thermite with 10% and 20% CuO addition can be set as f(α)=3/2∗(1−α)−ln(1−α)1/3. The burning speed became faster and the flame was bright with sparks. This work lays the foundation for the further study of the thermite mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
