Critical Barriers to Successful Implementation of Earth-Abundant, Mn-Rich Cathodes: Low SOC Impedance

Abstract

The ever-growing demand for electric vehicles and grid storage systems has pushed the development of sustainable cathode materials for Li-ion batteries. Lithium- and manganese-rich (LMR) oxides are a promising class of cathode materials in this regard because of their high capacities/energies and reliance on low-cost, earth-abundant manganese (>50%). However, several outstanding issues remain that hinder the performance of these cathodes. While the mechanisms of the now well-known phenomena of voltage fade, hysteresis, and oxygen activity have been intensively studied, relatively little attention has been given to understanding the impedance characteristics of LMR electrodes. Specifically, the anomalous rise in area specific impedance (ASI) at low states-of-charge (SOCs), and the overall impedance rise on extended cycling due to surface issues, are critical barriers to implementation that still need to be further understood and mitigated.This presentation will discuss a comprehensive study at Argonne National Laboratory on understanding impedance behavior in cobalt-free, LMR cathode-electrodes. In this study, we use a unique surface-treatment/electrolyte-additive combination that allows us to separate the major contributions of bulk and surface to the impedance behavior over long-term cycling. The results indicate that the anomalous rise in impedance at lower SOCs is directly associated with the correlated, bulk processes of voltage fade and voltage hysteresis. A conceptual model is presented to understand the impedance behavior of these complex materials.