angyu Li

Three-dimensional MoSx (1 < x < 2) nanosheets decorated graphene aerogel for lithium–oxygen batteries

The electrochemical performance of lithium–oxygen (Li–O2) batteries depends largely on the architecture and catalytic effectiveness of the oxygen cathode. Herein, in this study, a graphene aerogel decorated with MoSx nanosheets (MoSx/HRG) with a three-dimensional porous framework synthesized using a one-step hydrothermal reaction followed by freeze-drying is reported. The MoSx/HRG aerogel possesses hierarchical mesopores and micropores, which could facilitate electrolyte impregnation and oxygen diffusion, and provide much more accommodation space for the reaction products. The lithium–oxygen batteries based on this MoSx/HRG aerogel cathode show improved electrochemical performance, with a high initial discharge capacity up to 6678.4 mA h g−1 at a current density of 0.05 mA cm−2 and better cycling capability with a cut-off capacity of 500 mA h g−1 at a current density of 0.1 mA cm−2, compared with the lithium–oxygen batteries based on an HRG aerogel cathode. The enhanced performance is ascribed to the excellent catalytic activity of the MoSx nanosheets and the unique three-dimensional porous architecture.

Three-Dimensional Porous Si and SiO2 with In Situ Decorated Carbon Nanotubes As Anode Materials for Li-ion Batteries

A high-capacity Si anode is always accompanied by very large volume expansion and structural collapse during the lithium-ion insertion/extraction process. To stabilize the structure of the Si anode, magnesium vapor thermal reduction has been used to synthesize porous Si and SiO2 (pSS) particles, followed by in situ growth of carbon nanotubes (CNTs) in pSS pores through a chemical vapor deposition (CVD) process. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy have shown that the final product (pSS/CNTs) possesses adequate void space intertwined by uniformly distributed CNTs and inactive silica in particle form. pSS/CNTs with such an elaborate structural design deliver improved electrochemical performance, with better coulombic efficiency (70% at the first cycle), cycling capability (1200 mAh g-1 at 0.5 A g-1 after 200 cycles), and rate capability (1984, 1654, 1385, 1072, and 800 mAh g-1 at current densities of 0.1, 0.2, 0.5, 1, and 2 A g-1, respectively), compared to pSS and porous Si/CNTs. These merits of pSS/CNTs are attributed to the capability of void space to absorb the volume changes and that of the silica to confine the excessive lithiation expansion of the Si anode. In addition, CNTs have interwound the particles, leading to significant enhancement of electronic conductivity before and after Si-anode pulverization. This simple and scalable strategy makes it easy to expand the application to manufacturing other alloy anode materials.

A new type of cyclic silicone additive for improving the energy density and power density of Li–O2 batteries

In this work, a novel electrolyte additive, octamethylcyclotetrasiloxane (OMTS), is applied to Li–O2 batteries to increase their practical discharge capacity and also their rate capability. By adding OMTS into a tetraethylene glycol dimethoxyethane (TEGDME)-based electrolyte, the solubility of oxygen increases significantly, and the ionic conductivity and viscosity remain the same. 7Li nuclear magnetic resonance (NMR) spectra show that the 7Li peak shifts downfield when adding OMTS to the electrolyte, indicating the increment of the solvation of Li+ in the electrolyte. The electrochemical tests show that, with an optimal OMTS content (10 vol% OMTS), the cell displays a high discharge capacity of 6778 mA h g−1 at 0.05 mA cm−2. Its capacity retention is more than double that of the cell with no OMTS additive at a large current density of 1 mA cm−2. Further NMR and Li2O2 yield measurements during discharge indicate that the OMTS additive does not alter the discharge product, or compromise the stability of the TEGDME electrolyte. The great increment in energy density and power density could be attributed to the high oxygen solubility and increment of solvated Li+, leading to the formation of more nodular products, as observed by scanning electron microscopy (SEM).