No abstract

The main impediments to the widespread acceptance of electric drive vehicles are the cost, energy-storage capacity, and durability of portable electrical energy sources and, in particular, batteries. In situ experimental techniques that can accurately detect and monitor performance degradation mechanisms on the nanoscale, including the identities of short-lived chemical species and changes in materials properties as a function of cycling rate, temperature, or time, are not widely used. Herein we demonstrate the combination of in situ 1D imaging and slice-selective NMR diffusion measurements as a tool for the spatially and temporally resolved determination of lithium diffusivities in a conventional liquid electrolyte (1.0 M lithium bis(trifluoromethanesulfonyl)imide solution in propylene carbonate) under application of a constant electrical current. All experiments were carried out using standard NMR equipment, so the proposed technique can be easily implemented in any modern R&D facility.

We propose trapping of Mn cations by polymeric crown ethers as a mitigation measure for the consequences of Mn dissolution in Li-ion batteries (LIBs). Mn cations trapping by poly(vinylbenzo-18-crown-6) and poly(undecylenyloxymethyl-18-crown-6) was investigated for 1M LiPF 6 solutions in binary carbonates containing Mn(II) salts and in lithium manganese oxide (LMO) spinelgraphite (GR) cells. Trapping site occupancies by Mn +2 exceeding 90% were measured in bench top experiments. Polyethylene separators coated with poly(vinylbenzo-18-crown-6) trapped Mn cations in LMO -GR cells and decreased capacity fade during 100 cycles at high temperature (60 • C) and C/4 rate, retaining 26% more capacity than the baseline cells. We also address the important distinction between using free (molecular) vs. tethered (polymeric) macrocycles, and its consequences for LIB performance.

A new in situ magic angle spinning (MAS) 7 Li nuclear magnetic resonance (NMR) strategy allowing for the observation of a full lithium-ion cell is introduced. Increased spectral resolution is achieved through a novel jelly roll cell design, which allowed these studies to be performed for the first time under MAS conditions (MAS rate 10 kHz). The state of charge, metallic lithium plating and solid-electrolyte interface (SEI) formation was captured for the first charge/discharge cycle of a full electrochemical cell (LiCoO 2 /graphite). This strategy can be used to monitor both anode and cathode electrodes concurrently, which is valuable for tracking the lithium distribution in a full cell in real time and may also enable identification of causes of capacity loss that are not readily available from bulk electrochemical analyses, or other post-mortem strategies.

Binary PtMn/C alloy catalysts with various atomic ratios (60-90 atomic% Mn) were synthesized and tested for the activity toward ethanol oxidation. The synthesized catalysts were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD studies indicate that a Pt-Mn alloy has formed in all cases. PtMn(19:81)/C and PtMn(10:90)/C exhibited the highest activity toward ethanol oxidation compared to PtMn(39:61)/C and Pt/C. XPS analysis indicates that highest activity occurs for alloys with similar surface and bulk Mn contents.