621 research outputs found
Preparation and magnetoresistance of Ag 2+x Se thin films deposited via Pulsed Laser Deposition
The preparation of Ag 2+x Se thin films with thicknesses between 4 nm and
3000 nm by pulsed laser deposition on single crystalline NaCl and MgO
substrates is reported. The films are perfectly dense and show a good lateral
uniformity with a small number of defects. The microstructure of the films
corresponds to a nanoparquet, being composed of two different phases of silver
selenide. One phase is identified as the Naumannite low temperature phase of
silver selenide, the structure of the other phase has not been reported in
detail before and probably represents a metastable phase. Silver-rich films
contain silver precipitates with typical sizes on the nanoscale. Their presence
and their size appears to be responsible for the large and linear
magnetoresistance effect of silver-rich silver selenide
Challenges for Developing Rechargeable Room-Temperature Sodium Oxygen Batteries
© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The development of high energy-density and low-cost energy storage devices requires new chemistry beyond the horizon of current state-of-the-art lithium-ion batteries. Recently, sodium/oxygen (Na/O2) batteries have attracted great attention as one possible battery type among the new generation of rechargeable batteries. They convince with superior energy density, a relatively simple cell reaction, and abundance of sodium. Research on Na/O2 batteries has progressed quickly in recent years. However, a fundamental understanding underpinning the complex chemical/electrochemical side reactions is still insufficient, and many challenges remain unsolved for real practical applications. Herein, recent achievements and remaining issues for the development of rechargeable Na/O2 batteries are summarized. The discussion focuses on cell reaction mechanisms as well as cathode materials, sodium anodes, and electrolytes as key components of this type of battery. Furthermore, perspectives for future research and technological advances of Na/O2 batteries are outlined
The Effect of Doping Process Route on LiNiO Cathode Material Properties
The pursuit of higher energy density in lithium-ion batteries has driven the increase of the nickel content in lithium nickel cobalt manganese oxide cathode active materials (CAMs), ultimately approaching LiNiO (LNO). The downside of the high specific capacity of LNO is more severe degradation of the CAM during battery operation. A common approach to increase structural stability is the introduction of dopants. Various dopants are discussed and compared with each other when integrated into the CAM and tested against undoped materials in the literature, but little attention is given to the role of the process route of their introduction. In this work, we demonstrate with a series of nominally equally Zr-doped LNO samples that effects on various physico- and electrochemical properties are due not to the dopant itself, as one would assume in comparison to an undoped sample, but to the process route and the resulting particle morphology. Dopant, concentration and process routes (co-precipitation, impregnation and co-calcination) were chosen based on their significance for industrial application
Design Strategies to Enable the Efficient Use of Sodium Metal Anodes in High-Energy Batteries
© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Sodium-based batteries have attracted considerable attention and are recognized as ideal candidates for large-scale and low-cost energy storage. Sodium (Na) metal anodes are considered as one of the most promising anodes for next-generation, high-energy, Na-based batteries owing to their high theoretical specific capacity (1166 mA h g−1) and low standard electrode potential. Herein, an overview of the recent developments in Na metal anodes for high-energy batteries is provided. The high reactivity and large volume expansion of Na metal anodes during charge and discharge make the electrode/electrolyte interphase unstable, leading to the formation of Na dendrites, short cycle life, and safety issues. Design strategies to enable the efficient use of Na metal anodes are elucidated, including liquid electrolyte engineering, electrode/electrolyte interface optimization, sophisticated electrode construction, and solid electrolyte engineering. Finally, the remaining challenges and future research directions are identified. It is hoped that this progress report will shape a consistent view of this field and provide inspiration for future research to improve Na metal anodes and enable the development of high-energy sodium batteries
Silicon nanoparticles with a polymer-derived carbon shell for improved lithium-ion batteries: Investigation into volume expansion, gas evolution, and particle fracture
Silicon (Si) and composites thereof, preferably with carbon (C), show favorable lithium (Li) storage properties at low potential, and thus hold promise for application as anode active materials in the energy storage area. However, the high theoretical specific capacity of Si afforded by the alloying reaction with Li involves many challenges. In this article, we report the preparation of small-size Si particles with a turbostratic carbon shell from a polymer precoated powder material. Galvanostatic charge/discharge experiments conducted on electrodes with practical loadings resulted in much improved capacity retention and kinetics for the Si/C composite particles compared to physical mixtures of pristine Si particles and carbon black, emphasizing the positive effect that the core−shell-type morphology has on the cycling performance. Using in situ differential electrochemical mass spectrometry, pressure, and acoustic emission measurements, we gain insights into the gassing behavior, the bulk volume expansion, and the mechanical degradation of the Si/C composite-containing electrodes. Taken together, our research data demonstrate that some of the problems of high-content Si anodes can be mitigated by carbon coating. Nonetheless, continuous electrolyte decomposition, particle fracture, and electrode restructuring due to the large volume changes during battery operation (here, ∼170% in the voltage range of 600−30 mV vs Li+/Li) remain as serious hurdles toward practical implementation
Analyzing powers Ayy, Axx, Axz and Ay in the dd->3Hen reaction at 270 MeV
The data on the tensor Ayy, Axx, Axz and vector Ay analyzing powers in the
dd->3Hen obtained at Td= 270 MeV in the angular range 0 - 110 degrees in the
c.m. are presented. The observed negative sign of the tensor analyzing powers
Ayy, Axx and Axz at small angles clearly demonstrate the sensitivity to the
ratio of the D and S wave component of the 3He wave function. However, the
one-nucleon exchange calculations by using the standard 3He wave functions have
failed to reproduce the strong variation of the tensor analyzing powers as a
function of the angle in the c.m.Comment: 8 pages, 7 figures, 4 tables. Submitted to EPJ
Gas Evolution in Operating Lithium-Ion Batteries Studied in Situ by Neutron Imaging
Gas generation as a result of electrolyte decomposition is one of the major issues of highperformance rechargeable batteries. Here, we report the direct observation of gassing in operating lithium-ion batteries using neutron imaging. This technique can be used to obtain qualitative as well as quantitative information by applying a new analysis approach. Special emphasis is placed on high voltage LiNi0.5Mn1.5O4/graphite pouch cells. Continuous gassing due to oxidation and reduction of electrolyte solvents is observed. To separate gas evolution reactions occurring on the anode from those associated with the cathode interface and to gain more insight into the gassing behavior of LiNi0.5Mn1.5O4/graphite cells, neutron experiments were also conducted systematically on other cathode/anode combinations, including LiFePO4/graphite, LiNi0.5Mn1.5O4/Li4Ti5O12 and LiFePO4/Li4Ti5O12. In addition, the data were supported by gas pressure measurements. The results suggest that metal dissolution in the electrolyte and decomposition products resulting from the high potentials adversely affect the gas generation, particularly in the first charge cycle (i.e., during graphite solid-electrolyte interface layer formation)
reaction at intermediate energies
The reaction is considered at the energies between 200 MeV and
520 MeV. The Alt-Grassberger-Sandhas equations are iterated up to the lowest
order terms over the nucleon-nucleon t-matrix. The parameterized wave
function including five components is used. The angular dependence of the
differential cross section and energy dependence of tensor analyzing power
at the zero scattering angle are presented in comparison with the
experimental data
Proteasomes generate spliced epitopes by two different mechanisms and as efficiently as non-spliced epitopes
Proteasome-catalyzed peptide splicing represents an additional catalytic
activity of proteasomes contributing to the pool of MHC-class I-presented
epitopes. We here biochemically and functionally characterized a new melanoma
gp100 derived spliced epitope. We demonstrate that the gp100mel47–52/40–42
antigenic peptide is generated in vitro and in cellulo by a not yet described
proteasomal condensation reaction. gp100mel47–52/40–42 generation is enhanced
in the presence of the β5i/LMP7 proteasome-subunit and elicits a peptide-
specific CD8+ T cell response. Importantly, we demonstrate that different
gp100mel-derived spliced epitopes are generated and presented to CD8+ T cells
with efficacies comparable to non-spliced canonical tumor epitopes and that
gp100mel-derived spliced epitopes trigger activation of CD8+ T cells found in
peripheral blood of half of the melanoma patients tested. Our data suggest
that both transpeptidation and condensation reactions contribute to the
frequent generation of spliced epitopes also in vivo and that their immune
relevance may be comparable to non-spliced epitopes
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