Lithium-rich mixed metal layered oxides constitute a large class of promising high-potential positive electrode materials in which higher specific charges are accessed only by activation of the Li2MnO3 domains. During the activation, oxygen is extracted from the oxide and evolves at the electrode–electrolyte interface. Differential electrochemical mass spectrometry was employed to follow volatile species developed during cycling. Although typical Li-ion aprotic carbonate electrolytes already suffer from oxidative decomposition at high potentials, the presence of O2 is here confirmed to enhance its reactivity. During the first cycle, O2 and CO2 evolve and their respective amounts vary as a function of the cycling conditions. However, for ethylene carbonate-based electrolytes, the amount of O2 and CO2 is found to be independent of the electrolyte composition. Moreover, X-ray photoelectron spectroscopy revealed that carbon-based components of the solid layers are dissolved between 3.0 and 4.0 V versus Li+/Li where no gas is evolving.

In Li-ion batteries, Li 4 Ti 5 O 12 (LTO) has merits of an excellent cycling stability combined with a safe working potential of 1.55 V vs. Li + /Li at which no adverse side-reactions with the electrolyte are expected. Concerns regarding gassing of LTO, especially at elevated temperatures, have however recently been reported. In this work, LTO gassing behavior at 50 • C is investigated by in situ pressure and online electrochemical mass spectrometry (OEMS), allowing for both qualitative and quantitative analysis of evolving gases. H 2 , C 2 H 4 , and CO 2 are the dominantly evolving gases for ethylene carbonate (EC) based electrolytes. H 2 is mainly produced during the first charge step, while C 2 H 4 is observed at lower potentials resulting from the reduction of EC. CO 2 evolution mechanism is complex and is promoted at more anodic potentials. Passivating the LTO surface, e.g. by a proper coating, and/or exchanging the LiPF 6 salt, may effectively reduce gas evolution, thus clearing the way for future use of LTO in energy storage applications at elevated temperatures.

Several Niobium oxides of formula Ba 2 LnFeNb 4 O 15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the "Tetragonal Tungsten Bronze" (TTB) structure have been synthesised by conventional solid-state methods. The Neodymium, Samarium and Europium compounds are ferroelectric with Curie temperature ranging from 320 to 440K. The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300 K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystalchemical analysis we propose some relationships between the introduction of Ln 3+ ions in the TTB framework and the chemical, structural and physical properties of these materials.