title: Gas Evolution in LiNi0.5Mn1.5O4/Graphite Cells Studied In Operando by a Combination of Differential Electrochemical Mass Spectrometry, Neutron Imaging, and Pressure Measurements.
abstract: The cycling performance and in operando gas analysis of LiNi0.5Mn1.5O4 (LNMO)/graphite cells with reasonably high loading, containing a "standard" carbonate-based electrolyte is reported. The gas evolution over the first couple of cycles was thoroughly investigated via differential electrochemical mass spectrometry (DEMS), neutron imaging and pressure measurements. The main oxidation and reduction products were identified as CO2, H2 and C2H4. In different sets of experiments graphite was substituted with delithiated LiFePO4 (LFP) and LNMO with LFP to distinguish between processes occurring at either anode or cathode and gain mechanistic insights. Both C2H4 and H2 were found to be mainly formed at the anode side, while CO2 is generated at the cathode. The results from DEMS analysis further suggest that the Ni redox couples play a profound role in the evolution of CO2 at the LNMO/electrolyte interface. Lastly, it is shown that the cycling stability and capacity retention of LNMO/graphite cells can be considerably improved by a simple cell formation procedure.
authors.forename: Barbara
authors.initials: B
authors.lastname: Michalak
authors.forename: Balázs B
authors.initials: BB
authors.lastname: Berkes
authors.affiliation: BASF SE, 67056 Ludwigshafen, Germany.
authors.forename: Heino
authors.initials: H
authors.lastname: Sommer
authors.forename: Thomas
authors.initials: T
authors.lastname: Bergfeldt
authors.forename: Torsten
authors.initials: T
authors.lastname: Brezesinski
authors.affiliation: Institute of Physical Chemistry, Justus-Liebig-University Giessen , Heinrich-Buff-Ring 17, 35392 Giessen, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Janek