During charge and discharge cycles, Li+ incorporation in either the cathode or anode electrode of a Li-ion battery is accompanied by the formation of a solid electrolyte interphase (SEI). Understanding the structure of the SEI and its mechanism of formation will enable us to design batteries with higher accessible charge and greater longevity.In this study, we examine the SEI formed on Au and Sn anode surfaces in propylene carbonate (PC) and a 1:1 mixture of ethylene carbonate, dimethyl carbonate (EC:DMC) solvents.  Electrochemical crystal microbalance (EQCM) measurements show that substantial mass is retained on Au electrodes, while much less is retained on Sn following potential cycling.   Matrix assisted laser desorption ionization (MALDI)-time of flight (TOF) mass spectrometry analysis of both Sn and Au surfaces after emersion of electrodes surfaces cycled to 100 mV (vs. Li/Li+), showed regular repeat patterns, which confirm the presence of high molecular weight oligomerized species as a part of SEI. From regular spacing between  peaks in the spectrometry, we find that different subunits form with different solvents and surfaces, the origin of which can be interpreted in terms of a radical initiated polymerization of solvent molecules.  Methods to control this oligimerization will be described.

Solvent oligomerization during SEI formation in Li-ion battery anodes

243rd National Meeting (2012)

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