Ammonia Treatment of 0.35Li2MnO3·0.65LiNi0.35Mn0.45Co0.20O2 Material: Insights from Solid-State NMR Analysis

Li-rich cathode materials of the formula xLi2MnO3·yLiNiaCobMncO2 (x + y = 1, a + b + c = 1) boast very high discharge capacity, ca. 250 mAh/g. Yet, they suffer capacity decrease and average voltage fade during cycling in Li-ion batteries that prohibit their commercialization. Treatment of the materials with NH3(g) at high temperatures produces improved electrodes with higher stability of capacity and average voltage. The present study follows the changes occurring in the materials upon treatment with ammonia gas, through 6Li and 7Li solid-state NMR investigations of the untreated and ammonia treated 0.35Li2MnO3·0.65LiNi0.35Mn0.45Co0.20O2 as well as its constituent phases, Li2MnO3 and LiNi0.4Co0.2Mn0.4O2. The NMR analysis demonstrates the biphasic nature of these materials. Furthermore, it shows that the Li2MnO3 component phase in the integrated material is the phase mostly being affected by the gas treatment. A thickening of a protective surface film in the integrated material, with the right exposure tim...