The evolutions of the structure occurring into the lithium rich cobalt free layered cathode material Li 1.2 Mn 0.61 Ni 0.18 Mg 0.01 O 2 upon the first electrochemical cycle were investigated by the means of high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope and electron diffraction in a transmission electron microscope. They are coupled with electron energy loss spectroscopy (EELS) experiments in order to probe the chemical evolutions occurring during the first charge/discharge cycle. In the pristine material, the analysis of the HAADF images and electron diffraction patterns confirmed the ordering between the cations (Li or Ni with Mn) and the existence of disoriented domains stacked along the c axis. Moreover, the partial solid solution of Ni into Li 2 MnO 3 leading to a composite material is evidenced. Upon the first charge, a loss of material is shown to have occurred, and the presence of a defect spinel phase due to the transfer of transition metal cations to the interslab is clearly established. It is localized at the edge of the particles. This defect spinel phase apparition is confirmed by EELS experiments and identified as (Li)Mn (2−x) Ni x O 4 . After the first discharge, the spinel phase is still present, and structural discrepancies from one crystal to another are observed. Also, it seems that all the domains would not have the same behavior upon discharge.

High-voltage spinel oxides combined with Li4Ti5O12 result in 3 V lithium-ion batteries with a high power capability; however, the electrochemical performances are limited by electrode/electrolyte interfacial reactivity at high potential. We have investigated electrode/electrolyte interfaces in LiMn1.6Ni0.4O4/Li4Ti5O12 cells by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectrocopy (EIS). EIS has shown that both electroadsorption and film-formation mechanisms occur at the positive electrode. XPS has revealed that very low amounts of lithiated species are deposited at the surface of the positive electrode, despite the high potential, but that great amounts of organic species are deposited. Interesting results were obtained for the Li4Ti5O12 electrode. Whereas Li4Ti5O12 is usually considered as a passivation-free electrode material, large amounts of organic and inorganic species were deposited at the surface of this electrode. The question of a possible interaction between both electrodes in the formation mechanisms of surface films is discussed.