The development of sustainable materials for lithium-ion batteries is of paramount significance with the ever-growing demand of energy storage for the transportation sector. Lithium- and manganese-rich oxides are of great interests because of inherently high capacities/energies and the potential economic benefits associated with earth-abundant manganese-based compositions. With several challenges hindering the commercialization of these cathodes, there have been many studies on understanding the mechanisms of voltage fade, hysteresis, and oxygen activity. However, relatively little attention has been given to understanding the impedance of these materials. In particular, the drastic rise in area specific impedance at lower states of charge, and the overall impedance rise on extended cycling due to surface issues, are critical barriers that need to be understood and addressed to accelerate deeper market penetration.

This poster will present a detailed study of the impedance behavior in cobalt-free, lithium- and manganese-rich cathodes. A combined surface-treatment/electrolyte-additive has been used to probe the behavior over long-term cycling in the absence of (i.) surface issues, (ii.) the impedance rise due to electrolyte interactions, and (iii.) capacity loss. The results presented in the poster support the hypothesis that the anomalous rise in impedance at lower states of charge is directly associated with the bulk processes of voltage fade and voltage hysteresis. Furthermore, a preliminary conceptual model is presented for understanding the impedance behavior of these activated materials, which can be described as layered-type, ordered-domain network with facile Li diffusion, where interspersed, disordered, low-voltage sites within this network hinder the Li insertion.