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Li-rich layered oxides (LRLO) with specific energies beyond 900 Wh kg$^{−1}$ are one promising class of high-energy cathode materials. Their high Mn-content allows reducing both costs and the environmental footprint. In this work, Co-free Li$_{1.2}$Mn$_{0.6}$Ni$_{0.2}$O$_{2}$ was investigated. A simple water and acid treatment step followed by a thermal treatment was applied to the LRLO to reduce surface impurities and to establish an artificial cathode electrolyte interface. Samples treated at 300 °C show an improved cycling behavior with specific first cycle capacities of up to 272 mAh g$^{−1}$, whereas powders treated at 900 °C were electrochemically deactivated due to major structural changes of the active compounds. Surface sensitive analytical methods were used to characterize the structural and chemical changes compared to the bulk material. Online DEMS measurements were conducted to get a deeper understanding of the effect of the treatment strategy on O$_2$ and CO$_2$ evolution during electrochemical cycling.

Lithium-rich layered oxides (LRLOs) exhibit specific capacities above 250 mAh g−1, i.e., higher than any of the commercially employed lithium-ion-positive electrode materials. Such high capacities result in high specific energies, meeting the tough requirements for electric vehicle applications. However, LRLOs generally suffer from severe capacity and voltage fading, originating from undesired structural transformations during cycling. Herein, the eco-friendly, cobalt-free Li1.2Ni0.2Mn0.6O2 (LRNM), offering a specific energy above 800 Wh kg−1 at 0.1 C, is investigated in combination with a lithium metal anode and a room temperature ionic liquid-based electrolyte, i.e., lithium bis(trifluoromethanesulfonyl)imide and N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide. As evidenced by electrochemical performance and high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and online differential electrochemical mass spectrometry characterization, this electrolyte is capable of suppressing the structural transformation of the positive electrode material, resulting in enhanced cycling stability compared to conventional carbonate-based electrolytes. Practically, the capacity and voltage fading are significantly limited to only 19% and 3% (i.e., lower than 0.2 mV per cycle), respectively, after 500 cycles. Finally, the beneficial effect of the ionic liquid-based electrolyte is validated in lithium-ion cells employing LRNM and Li4Ti5O12. These cells achieve a promising capacity retention of 80% after 500 cycles at 1 C., publishedVersion

In order to learn more about the effect of H2 fuel starvation on the degradation of Pt anode catalysts and in particular on the role of the support therein, we have investigated the impact of a simulated fuel starvation procedure on three different polymer electrolyte fuel cell anode catalysts, Pt/C, Pt/TiO2 and Pt/TiO2+C, by differential electrochemical mass spectrometry (DEMS) measurements. Monitoring the potential as well as the mass spectrometric signal transients of the possible reaction products CO2 (carbon oxidation reaction – COR) and O2 (oxygen evolution reaction – OER) upon switching from H2-saturated to N2-saturated electrolyte under galvanostatic oxidation conditions, we find a rapid increase of the potential to values at about 1.75 V upon electrolyte exchange, together with the onset of CO2 formation and O2 evolution, where the latter dominates at high potentials. The ratio of O2 evolution and carbon support oxidation differs significantly for different catalyst supports, with the COR contributing more for the carbon-containing catalysts in the initial stage of the fuel starvation period, and the OER prevailing for the Pt/TiO2 catalyst over the whole starvation time. The complex interplay between different catalyst degradation processes during fuel starvation is discussed., publishedVersion