Internal dynamics of blended Li-insertion electrodes

The blending of different Li-insertion compounds is a successful concept to tailor the properties of electrodes for Li-ion batteries. Recent studies suggest transport phenomena connected with internal redox processes that do not occur in electrodes consisting of a single type of active material. Herein, we report 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. It is shown that the constituents are charged/discharged independent from each other, which can lead to high effective C-rates for an individual constituent although the nominal C-rate is relatively low. At high currents, 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 novel insights are discussed regarding beneficial and unfavorable impacts on the performance of Li-ion batteries with blended insertion electrodes.