The influence of compact and ordered carbon coating on solid-state behaviors of silicon during electrochemical processes

To address the issues of large volume change and low conductivity of silicon (Si) materials, carbon coatings have been widely employed as surface protection agent and conductive medium to encapsulate the Si materials, which can improve the electrochemical performance of Si-based electrodes. There has been a strong demand to gain a deeper understanding of the impact of efficient carbon coating over the lithiation and delithiation process of Si materials. Here, we report the first observation of the extended two-phase transformation of carbon-coated Si nanoparticles (Si/C) during electrochemical processes. The Si/C nanoparticles were prepared by sintering Si nanoparticles with polyvinylidene chloride precursor. The Si/C electrode underwent a two-phase transition during the first 20 cycles at 0.2 C, but started to engage in solid solution reaction when the ordered compact carbon coating began to crack. Under higher current density conditions, the electrode was also found to be involved in solid solution reaction, which, however, was due to the overwhelming demand of kinetic property rather than the breaking of the carbon coating. In comparison, the Si/C composites prepared with sucrose possessed more disordered and porous carbon structures, and presented solid solution reaction throughout the entire cycling process

Polyisoprene Captured Sulfur Nanocomposite Materials for High-Areal-Capacity Lithium Sulfur Battery

A polyisoprene-sulfur (PIPS) copolymer and nano sulfur composite material (90 wt % sulfur) is synthesized through inverse vulcanization of PIP polymer with micrometer-sized sulfur particles for high-areal-capacity lithium sulfur batteries. The polycrystalline structure and nanodomain nature of the copolymer are revealed through high-resolution transmission electron microscopy (HRTEM). PIP polymer is also used as binders for the electrode to further capture the dissovlved polysulfides. A high areal capacity of ca. 7.0 mAh/cm2 and stable cycling are achieved based on the PIPS nanosulfur composite with a PIP binder, crucial to commercialization of lithium sulfur batteries. The chemical confinement both at material and electrode level alleviates the diffusion of polysulfides and the shuttle effect. The sulfur electrodes, both fresh and cycled, are analyzed through scanning electron microscopy (SEM). This approach enables scalable material production and high sulfur utilization at the cell level

Tensor coupling effects on spin symmetry in anti-Lambda spectrum of hypernuclei

The effects of $\bar\Lambda\bar\Lambda\omega$-tensor coupling on the spin symmetry of $\bar{\Lambda}$ spectra in $\bar{\Lambda}$-nucleus systems have been studied with the relativistic mean-field theory. Taking $^{12}$C+$\bar{\Lambda}$ as an example, it is found that the tensor coupling enlarges the spin-orbit splittings of $\bar\Lambda$ by an order of magnitude although its effects on the wave functions of $\bar{\Lambda}$ are negligible. Similar conclusions has been observed in $\bar{\Lambda}$-nucleus of different mass regions, including $^{16}$O+$\bar{\Lambda}$, $^{40}$Ca+$\bar{\Lambda}$ and $^{208}$Pb+$\bar{\Lambda}$. It indicates that the spin symmetry in anti-lambda-nucleus systems is still good irrespective of the tensor coupling.Comment: 12 pages, 3 figures

Off-shell effects in dilepton production from hot interacting mesons

The production of dielectrons in reactions involving a_1 mesons and pions is studied. We compare results obtained with different phenomenological Lagrangians that have been used in connection with hadronic matter and finite nuclei. We insist on the necessity for those interactions to satisfy known empirical properties of the strong interaction. Large off-shell effects in dielectron production are found and some consequences for the interpretation of heavy ion data are outlined. We also compare with results obtained using experimentally-extracted spectral functions.Comment: 14 pages, LaTeX2e, 2 figure