Internal dynamics of blended Li-insertion electrodes. (December 2018) - Heubner, C.
Graphical abstract: Highlights: Investigation of internal dynamics using a model-like blended Li-insertion electrode. Independent (dis)charging of the constituents can lead to high effectives C-rates. Constituent with fast kinetics can serve as internal redox couple at high loads. Li-exchange among the constituents when subjected to temperature changes. Complex tradeoff between benefits and drawbacks of internal dynamics. Abstract: The blending of different Li-insertion compounds is a successful concept to tailor the properties of electrodes for Li-ion batteries. Recent own studies and reports from literature suggest internal redox processes that do not occur in electrodes consisting of a single type of active material. Herein, we summarize recent electrochemical experiments along with theoretical considerations related to internal dynamics in blended insertion electrodes. A special experimental setup and a model-like blend electrode is applied to capture any interactions among the constituents of the blend. In accordance with theoretical considerations from the literature, it is shown experimentally that the constituents are charged/discharged independent from each other, which can lead to high effective C-rates for an individual constituent. At high loads, a constituent with fast reaction kinetics can act as an internal pathway, carrying the current for a more rate-limited constituent. This effect enables very good rate capability but also includes multiple reaction steps, which might reduce the cycle life performance. Furthermore, it is shown that changes in temperature induce a redistribution of Li among the constituents without any active cycling of the cell. These recent insights regarding internal dynamics are discussed with respect to beneficial and unfavorable impacts on the performance of Li-ion batteries with blended insertion electrodes.