The solid electrode interphase (SEI) on graphite electrodes is important to the performance, calendar life, and safety characteristics of lithium-ion cells. This article examines the SEI formed on binder-free graphite electrodes prepared by electrophoretic deposition. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis data were obtained on electrodes cycled in cells containing four electrolytes comprising ethylene carbonate: ethylmethyl carbonate (3:7 by weight) solvent and 1.2M LiPnormalF6 , 1M LinormalF2BnormalC2normalO4 , 1M LiBnormalF4 , or 0.7M LiB(normalC2normalO4)2 salt. Our observations suggest that, in addition to solvent reduction, the reduction of electrolyte salts plays an important role in SEI formation. Mechanisms to account for the formation of these SEI constituents are included in the article.

In this work, structural and morphological changes in composite sulfur electrodes were studied due to their cycling in rechargeable Li–S cells produced by Sion Power Inc. Composite sulfur cathodes, comprising initially elemental sulfur and carbon, undergo pronounced structural and morphological changes during discharge–charge cycles due to the complicated redox behavior of sulfur in nonaqueous electrolyte solutions that contain Li ions. Nevertheless, Li–S cells can demonstrate prolonged cycling. To advance this technology, it is highly important to understand the evolution of the structure and morphology of sulfur cathodes as cycling proceeds. High resolution scanning and tunneling microscopy, scanning probe microscopy, and Raman spectroscopy were used in conjunction with the electrochemical measurements. A special methodology for slicing composite sulfur electrodes and their cross sectioning and depth profiling was developed. The gradual changes in the structure of sulfur cathodes due to cycling is described and discussed herein. Important phenomena include changes in the surface electrical conductivity of sulfur electrodes and pronounced morphological changes due to the irreversibility of the sulfur redox reactions. Based on the observations presented in this work, it may be possible to outline guidelines for improving Li–S battery technology and extending its cycle life.

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The effects of electrolyte additives singly or in combination on Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells have been systematically investigated and compared using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), an automated storage system, gas evolution measurements and selected long-term cycling experiments. The results of testing Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells with different electrolyte additives singly or in combination were measured and the results for over 110 additive sets are compared. A "Figure of Merit" approach is used to rank the effectiveness of the additives and their combinations. The combination of vinylene carbonate (VC) and/or prop-1-ene-1,3 sultone (PES), a sulfur containing additive, such as methylene methane disulfonate (MMDS), as well as either tris(-trimethly-silyl)-phosphate (TTSP) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) as additives in the electrolyte can give cells with extremely high coulombic efficiency, excellent storage properties, low impedance and superior long term cycling at 55 • C. Additive mixtures such as 2% PES + 1% MMDS + 1% TTSPi are especially excellent in all respects. It is hoped that this comprehensive report sets a benchmark for future studies by others and can be used as a guide and reference for the comparison of other electrolyte additives singly or in combination.

Wound LiCoO 2 /graphite and Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite cells with 1M LiPF 6 EC:EMC electrolyte containing either 0, 1 or 2 wt.% vinylene carbonate were studied using the High Precision Charger at Dalhousie University, automated cell storage and AC impedance. Vinylene carbonate (VC) was found to improve the coulombic efficiency of the cells, decrease charge endpoint capacity slippage and decrease self discharge, in all cases primarily by slowing electrolyte oxidation at the positive electrode. The beneficial impacts of VC are greater in LiCoO 2 cells than in Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 cells. One percent VC is enough to derive the benefits without causing an impedance rise in the cells.

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