Degradation mechanisms of layered materials (LiCoO2 and Li2CuO2) captured by an EIS-based graphical reconstruction method

The capacity fade of Lithium-ion batteries (LIB) is related to irreversible degradation processes occurring on one or several cathode components. The development of accessible strategies capable to understand the degradation processes is critical for further advancements. Therefore, this work proposes the practical application of a recently developed graphical approach based on Bode phase diagrams constructed with the successive addition of electric elements obtained with the best fit of EIS using a conventional eec. The graphical approach allows a rapid and thorough analysis of electrodes modified with specific strategies evidencing the degradation processes and the effect of chemical modifications of LiCoO2 and Li2CuO2, respectively. Both samples suffer drastic changes informing about possible defects involving contact, charge transfer resistance, structural distortions, and others; besides, if they are forced to degrade, the effect on the electrochemical properties as LIB cathodes are more remarkable. These effects can be detected from the Bode phase diagrams reconstruction appearing in a specific range of frequencies. Specifically, while LiCoO2 mainly suffers structural changes that affect intercalation, Li2CuO2 main affectations are charge transfer and diffusion through the composite. In this manner, we demonstrated the graphical method based on EIS reconstruction is a powerful and versatile methodology capable to explain the changes occurring in the materials under different operational conditions and as a support tool detecting the effect of electrode modifications.