performance in high-voltage LIB cells. Our results point out the importance to thoroughly evaluate the impact of the separator on cell performance, especially when it comes to comparison of electrochemical data within the scientific community. Results and Discussion2.1. Impact of PP Membrane and PP Fiber Separators with Different Thicknesses on the "Rollover" Failure

A hybrid cathode concept that targets combining the specific advantages of Li‐ion batteries and dual‐ion batteries is proposed. LiNi0.5Mn1.5O4 (LNMO), (de)inserting Li+, and graphite, capable to (de)intercalate PF6− present in the electrolyte, are combined in one cathode, aiming for synergy effects due to the presence of two electrochemically active species to overcome rate limitations caused by electrolyte depletion. Hybrid cathodes of different compositions and designs are prepared and investigated regarding their properties and the storage mechanism using electrochemical analyses combined with operando XRD and extensive materials characterization, including scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Finally, hybrid cathodes with higher areal capacity are prepared and investigated regarding rate performance. Model‐based analysis of the results reveals design criteria and material properties required to achieve synergistic effects between the components in hybrid cathodes. These insights lay the foundation for a new type of battery with advantageous properties in terms of cost, environmental friendliness, and electrochemical performance.