LiMn_0.5Ni_1.5O₂ is one of the most important materials for high voltage Lithium Ion batteries. Due to the high operation voltage, the LiMn_0.5Ni_1.5O₂ – electrolyte interphase suffers high reactivity which limits the cyclability of the electrodes. Several modifications to the electrolyte, cathode material, and inclusion of additives in both phases have been investigated, however although they have provided slight improvements, the reasons behind the stability enhancement still are not fully understood [1]. Additionally, the presence of carbon additives has also been reported to influence the initial capacity and cyclability of the cathodes; however, the great variety of cathode composite compositions, type of carbon additives and experimental conditions makes difficult a fair comparison between them. In this work the influence of carbon additives at two compositions (2 and 10%) is studied by cyclic voltammetry charge and discharge curves and Electrochemical Impedance spectroscopy (EIS), the cyclability in both cases resulted very high with high coulombic efficiency close to 100% with Li anodes. The EIS spectra were adjusted to several equivalent electric circuits, while most of them results in a fair agreement, the explications derived from them are not applicable to all cases, moreover, a phenomenological interpretation was proposing which resulted in excellent xi² adjustment (10^-5) which overpasses by far state of the art results (10^-3) with limited phenomenological information. In this work the EIS was applied at several conditions of the electrode and in general it was observed an enormous increase of charge transfer resistance as cycling goes on. However, the lower carbon content results in an even faster degradation process which is also accelerated by longer times at higher voltages. Therefore, the carbon additive also has a big influence on the reactivity of the electrode-electrolyte interphase and can serve as additional tool to increase the cyclability of the electrodes.

Acknowledgements This work was supported, GR thanks (project seciti/080/2017) IG thanks CONACYT (proyect 237343) for financial support. G. Guzman is grateful to CONACYT for the scholarship granted to pursue his doctoral studies.

[1] Kang-Joon Park,a Byung-Beom Lim,a Moon-Ho Choi,a Hun-Gi Jung, Yang-Kook Sun, Marta Haro, Nuria Vicente, Juan Bisquert and Germá Garcia-Belmonte, J. Mater. Chem. A, 2015, 3, 22183