Electrolyte and SEI Decomposition Reactions of Transition Metal Ions Investigated by On-Line Electrochemical Mass Spectrometry

By S. Solchenbach, Gloria Hong, A. Freiberg, Roland Jung, H. Gasteiger. 2018

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We use on-line electrochemical mass spectrometry (OEMS) to elucidate and quantify the electrolyte reduction on graphite caused by transition metal ions. To have a controlled system, we use ethylene carbonate (EC) with 1.5 M LiPF 6 and representative amounts of Ni(TFSI) 2 or Mn(TFSI) 2 as model electrolytes, combined with a 2-compartment cell in which anolyte and catholyte are separated by an impermeable solid lithium ion conductor. Focusing on C 2 H 4 evolution as a marker for EC reduction, we find that both Ni 2 + and Mn 2 + lead to enhanced gas evolution on pristine graphite electrodes once the potential is decreased to below the TM 2 + /TM 0 redox potential, demonstrating that the reduced transition metals are active toward electrolyte reduction. If the electrodes are preformed in a TM-freeelectrolyteandsubsequentlycycledinanelectrolytecontainingeitherMn 2 + orNi 2 + ,theactivityofnickeltowardelectrolyte decomposition is greatly reduced, whereas the electrolyte with manganese still shows a strong ongoing C 2 H 4 generation. The use of vinylene carbonate during formation partially suppresses the gas evolution from manganese. Using OEMS and post-mortem ATR-FTIR, we finally show that reduced manganese can decompose organic SEI components into Li 2 CO 3 , thereby compromising the integrity of the SEI and enabling the additional reduction of electrolyte.

Subfields: Automotive Engineering, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/45a0cb36d071b11eb2b01fc3c036eb57c640e45e