Structural and electrochemical studies in aged layered Li1+x(Ni0.33Mn0.33Co0.33)(1-x)O2 as cathode materials for rechargeable lithium ion batteries

M. GAMBA; S. REAL; G. SUAREZ; M. ORTIZ

Bolgna

Congreso; The 69th Annual Meeting of the International Society of Electrochemistry; 2018

The layered transition-metal oxide Li(1+x)(Mn1/3Co1/3Ni1/3)(1-x)O2 (NMC) have become a very promising alternative to LiCoO2 in rechargeable Li-ion batteries. Lithiated layered compounds are hygroscopic to some degree due to the high reactivity of Li towards H2O. Then, it is very important to study the effect of air and/or humidity during storage of these cathode active materials.Layered oxide cathode materials were prepared by solid state reactions from a stoichiometric mixture of Li2CO3, NiO, Co2O3 and MnO2. Starting materials were well mixed in a non-liquid state in an agate ball milling tank at 800 rpm for 270 min. The milled powder was heated at 10 ºC/min heating rate under air atmosphere first up to 400 ºC for 4 h and then up to 800 ºC for 12 h. The obtained materials were left at room temperature and ground using an agate mortar up to smaller than mesh #325.In our contribution, we investigate the ageing process of NMC in a humid atmosphere employing electrochemical analysis: charge and discharge curves, rate capability (showed in the figure) and impedance spectroscopy. Structural studies as infrared and Raman spectroscopies along with X-ray diffraction were performed to characterize changes at the surface and in the bulk, respectively. These experiments were carried out using a fresh sample and that exposed for six months to air and humidity. It is apparent that exposure to a humid atmosphere yield to a rapid chemical attack that is responsible for the drop in the capacity values along with impedance modulus increase. These facts were assigned to Li2CO3 formation at the surface [1], in good agreement with our FTIR experiment results and Rietveld refinement analysis. Consequently, our effort is focused in new material composition designs, such as core-shell structures.