LiFeO₂-Incorporated Li₂MoO₃ as a Cathode Additive for Lithium-Ion Battery Safety

Li₂MoO₃, with a Mo­(IV)/Mo­(VI) redox couple, has been tested as a cathode additive to make lithium-ion batteries safe under abnormal discharge conditions. Its high charging capacity and sloping discharge voltage below 3.4 V vs Li⁺/Li effectively prevents the Cu anode current collector from oxidative dissolution at the overdischarge condition. However, molybdenum dissolution from the electrochemically charged Li₂MoO₃ quickly deteriorates the battery performance at 45 °C. A solid solution of Li₂MoO₃ with LiFeO₂ has stabilized the crystalline structure at the charged states and suppressed the Mo­(VI) dissolution. The addition of 10 wt % 0.9Li₂MoO₃–0.1LiFeO₂ to LiCoO₂ electrode enables long-term, high-temperature cycling in the operating voltage range of 0.0–4.3 V vs graphite

CO₂ Enhanced Chemical Vapor Deposition Growth of Few-Layer Graphene over NiO_<i>x</i>

The use of mild oxidants in chemical vapor deposition (CVD) reactions has proven enormously useful. This was also true for the CVD growth of carbon nanotubes. As yet though, the use of mild oxidants in the CVD of graphene has remained unexplored. Here we explore the use of CO₂ as a mild oxidant during the growth of graphene over Ni with CH₄ as the feedstock. Both our experimental and theoretical findings provide in-depth insight into the growth mechanisms and point to the mild oxidants playing multiple roles. Mild oxidants lead to the formation of a suboxide in the Ni, which suppresses the bulk diffusion of C species suggesting a surface growth mechanism. Moreover, the formation of a suboxide leads to enhanced catalytic activity at the substrate surface, which allows reduced synthesis temperatures, even as low as 700 °C. Even at these low temperatures, the quality of the graphene is exceedingly high as indicated by a negligible D mode in the Raman spectra. These findings suggest the use of mild oxidants in the CVD fabrication as a whole could have a positive impact

Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study

We report the results of a VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study on the measurement of composition in organic depth profiling. Layered samples with known binary compositions of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-l-phenylalanine in each layer were manufactured in a single batch and distributed to more than 20 participating laboratories. The samples were analyzed using argon cluster ion sputtering and either X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS) to generate depth profiles. Participants were asked to estimate the volume fractions in two of the layers and were provided with the compositions of all other layers. Participants using XPS provided volume fractions within 0.03 of the nominal values. Participants using ToF-SIMS either made no attempt, or used various methods that gave results ranging in error from 0.02 to over 0.10 in volume fraction, the latter representing a 50% relative error for a nominal volume fraction of 0.2. Error was predominantly caused by inadequacy in the ability to compensate for primary ion intensity variations and the matrix effect in SIMS. Matrix effects in these materials appear to be more pronounced as the number of atoms in both the primary analytical ion and the secondary ion increase. Using the participants’ data we show that organic SIMS matrix effects can be measured and are remarkably consistent between instruments. We provide recommendations for identifying and compensating for matrix effects. Finally, we demonstrate, using a simple normalization method, that virtually all ToF-SIMS participants could have obtained estimates of volume fraction that were at least as accurate and consistent as XPS