Ultrathin conformal coatings of the lithium ion conductor, lithium aluminum oxide (LiAlO2), were evaluated for their ability to improve the electrochemical stability of LiNi0.5Mn1.5O4/graphite Li-ion ...batteries. Electrochemical impedance spectroscopy confirmed the ion conducting character of the LiAlO2 films. Complementary simulations of the activation barriers in these layers match experimental results very well. LiAlO2 films were subsequently separately deposited onto LiNi0.5Mn1.5O4 and graphite electrodes. Increased electrochemical stability was observed, especially in the full cells, which was attributed to the role of the coatings as physical barriers against side reactions at the electrode–electrolyte interface. By comparing data from full cells where the coatings were applied to either electrode, the dominating failure mechanism was found to be the diffusion of transition metal ions from the cathode to the anode. The LiNi0.5Mn1.5O4/graphite full cell with less than 1 nm LiAlO2 on the positive electrode exhibited a discharge capacity of 92 mAh/g at C/3 rate. The chemical underpinnings of stable performance were revealed by soft X-ray absorption spectroscopy. First, both manganese and nickel were detected on the graphite electrode surfaces, and their oxidation states were determined as +2. Second, the ultrathin coatings on the anode alone were found to be sufficient to significantly reduce this deleterious process.
In this study, we investigated the static recrystallization behavior and basal texture change from rolling direction (RD)-split (c-axes of grains toward the RD) to transverse direction (TD)-split ...(c-axes of grains toward the TD) of the cold-rolled Mg-1Al-1Zn-0.1Ca-0.2Y (AZXW1100) alloy during annealing. The cold-rolled AZXW1100 alloy sheet contained highly deformed shear bands (SBs), corresponding to 58 % of the total area, which caused rapid recrystallization at the beginning of annealing. The fine recrystallized grains nucleated in the SBs, and the intersection of the twins grew larger while consuming the deformed matrix grains, which did not recrystallize even at the late stage of annealing and were consumed by the surrounding recrystallized grains nucleated on the SBs. Owing to the difference in the recrystallization initiation time between the SB and deformed matrix grains, the recrystallized grains nucleated in the SBs guided the overall recrystallization behavior. Additionally, quasi-in-situ electron backscattered diffraction analyses clearly showed that among the recrystallized grains nucleated at the SBs, the grains with TD texture components became larger through preferential growth, whereas those with RD texture components did not grow and disappeared. Owing to this preferential grain growth, the texture intensity in the RD decreased and that in the TD was maintained, resulting in the formation of a diamond-like or TD-split texture. In this study, the co-segregation of Al, Zn, and Ca atoms along the grain boundaries and the formation of nanoscale Al8Mn5 particles were found to reduce boundary mobility and, consequently, hinder grain growth. These results can explain the texture change from a strong RD-split to a weak TD-split during annealing.
•Grains recrystallized on shear bands guided the overall static recrystallization behavior.•The deformed matrix grains were only consumed by surrounding recrystallized grains.•The recrystallized grains with TD components grew bigger through preferential growth.•Co-segregation of Al, Zn, and Ca atoms on grain boundaries hindered grain growth.•Prismatic dislocations in deformed grains promote preferential growth of TD grains
Functional electrodes for batteries share a common design rule by which high electronic and ionic conductivity pathways must exist throughout the electrode in its pristine state. Notable amounts of ...conductive carbon additive in the composite electrode are usually included to form an electronically conductive matrix. However, excellent high rate cycling performance has been achieved in electrodes composed of the insulating Li4Ti5O12 without any conductive additives. This behavior opens the possibility of a new paradigm for designing functional electrodes by which high electronic conductivity in the pristine electrode is not required. The mechanism of operation that enables such unexpected electrochemical behavior is evaluated and discussed. Electronically conductive pathways due to the reduction of Ti4+ to Ti3+ form and percolate throughout the Li4Ti5O12 electrode in the early stage of Li insertion, eliminating the need for conductive additives. This work highlights the importance of the mass and charge transport properties of the intermediate states during cycling and of good interparticle ohmic contact in the electrode. This physical behavior can lead to novel system designs with improved battery utilization and energy density.
Li‐ion battery electrodes based on Li4Ti5O12, an electronic insulator, can be successfully cycled without any conducting additives, even at high rates. The mechanisms of phase propagation and origin of such good performance are investigated. The importance of interparticle contact and the transport properties of the intermediate states during cycling are highlighted.
The novel photoelectrochemical cell with very high photocurrent density (>35 mA/cm2) is demonstrated by nanoscale architecturing of TiO2/CdS/CdSe multi-core-shell nanorods. While dimensions of ...constituting layers, i.e. TiO2 nanorod templates, CdS, and CdSe shell layers, are optimized by thorough investigation of optical and photoelectrochemical responses of each layer, high light absorption through the nanorod geometry and facile transport of the photo-generated electrons and holes along the high conduction path of CdSe and CdS result in the high photoelectrochemical performances. In addition, the microscopic model for the electron and hole transport in the core-shell nanorod is elaborated using the energy band diagram. The demonstration of the high performance PEC electrode as well as the platform to optimize PEC electrodes are highlighted in the current work.
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•Design of the TiO2/CdS/CdSe double-sheath core-shell nanorod array.•Superior photoelectrochemical properties (high photocurrent density).•Fundamental understanding about the charge transport mechanism of the core-shell nanorod.
Various redox-active organic molecules can serve as ideal electrode materials to realize sustainable energy storage systems. Yet, to be more appropriate for practical use, considerable architectural ...engineering of an ultrathick, high-loaded organic electrode with reliable electrochemical performance is of crucial importance. Here, by utilizing the synergetic effect of the non-covalent functionalization of highly conductive non-oxidized graphene flakes (NOGFs) and introduction of mechanically robust cellulose nanofiber (CNF)-intermingled structure, a very thick (≈ 1 mm), freestanding organic nanohybrid electrode which ensures the superiority in cycle stability and areal capacity is reported. The well-developed ion/electron pathways throughout the entire thickness and the enhanced kinetics of electrochemical reactions in the ultrathick 5,10-dihydro-5,10-dimethylphenazine/NOGF/CNF (DMPZ-NC) cathodes lead to the high areal energy of 9.4 mWh·cm
−2
(= 864 Wh·kg
−1
at 158 W·kg
−1
). This novel ultrathick electrode architecture provides a general platform for the development of the high-performance organic battery electrodes.
SnO2 nanoparticles with different sizes of ∼3, ∼4, and ∼8 nm were synthesized using a hydrothermal method at 110, 150, and 200 °C, respectively. The results showed that the ∼3 nm-sized SnO2 ...nanoparticles had a superior capacity and cycling stability as compared to the ∼4 and ∼8 nm-sized ones. The ∼3 nm-sized nanoparticles exhibited an initial capacity of 740 mAh/g with negligible capacity fading. The electrochemical properties of these nanoparticles were superior to those of thin-film analogues. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed that the ∼3 nm-sized SnO2 nanoparticles after electrochemical tests did not aggregate into larger Sn clusters, in contrast to those observed with the ∼4 and ∼8 nm-sized ones.
Tin sulfide (SnS) is known for its effective gas-detecting ability at low temperatures. However, the development of a portable and flexible SnS sensor is hindered by its high resistance, low ...response, and long recovery time. Like other chalcogenides, the electronic and gas-sensing properties of SnS strongly depend on its surface defects. Therefore, understanding the effects of its surface defects on its electronic and gas-sensing properties is a key factor in developing low-temperature SnS gas sensors. Herein, using thin SnS films annealed at different temperatures, we demonstrate that SnS exhibits n-type semiconducting behavior upon the appearance of S vacancies. Furthermore, the presence of S vacancies imparts the n-type SnS sensor with better sensing performance under UV illumination at room temperature (25 °C) than that of a p-type SnS sensor. These results are thoroughly investigated using various experimental analysis techniques and theoretical calculations using density functional theory. In addition, n-type SnS deposited on a polyimide substrate can be used to fabricate high-stability flexible sensors, which can be further developed for real applications.
Four types of slip systems (basal , prismatic , pyramidal , and pyramidal <a + c>) and two types of twinning (extension twinning {101–2} and contraction twinning {101–1}) could be identified in ...magnesium alloys using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In addition, the Schmid factors (SF) of these slip systems were systematically calculated on the basis of the Euler angle which was obtained in EBSD. The identification of slip systems and calculation of SF can help us to understand the contribution made by each type of slip in the plastic deformation of the material, which is important for understanding the deformation mechanism.
In this study, the double hydrothermal method is proposed as a facile approach to the synthesis of ZnTe/ZnO core–shell nanorods. The coating thickness of the p-type ZnTe is varied to adjust the ...junction depth in the n-type ZnO nanorods, and the conductance measurements reveal the change in the conduction path in the heterojunction structures. Structural and chemical investigations conducted using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy confirm the hetero-nanostructure formation of ZnTe/ZnO. The role of ZnTe in H2S-gas sensing by the ZnO nanorods is discussed. The enhanced sensing performance observed with a thin ZnTe coating confirms the importance of the base resistance of the nano-transducer in achieving high response characteristics. The composite structure also demonstrates a superior sensing performance of good repeatability, stability, linearity, and gas selectivity at temperatures greater than 200 °C.
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•Hydrothermal processing for ZnTe coated ZnO-nanorod structures synthesis.•A nano-composite gas sensor whose response is purely controlled by pn junction.•Nano-sensor principle showing the maximum response at the depletion depth scale.•Supporting the depletion model for the conduction type gas sensor device.
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