Cross Talk between Transition Metal Cathode and Li Metal Anode: Unraveling Its Influence on the Deposition/Dissolution Behavior and Morphology of Lithium

Lithium metal batteries (LMBs) combining a Li metal anode with a transition metal (TM) cathode can achieve higher practical energy densities (Wh L−1) than Li/S or Li/O2 cells. Research for improving the electrochemical behavior of the Li metal anode by, for example, modifying the liquid electrolyte is often conducted in symmetrical Li/Li or Li/Cu cells. This study now demonstrates the influence of the TM cathode on the Li metal anode, thus full cell behavior is analyzed in a way not considered so far in research with LMBs. Therefore, the deposition/dissolution behavior of Li metal and the resulting morphology is investigated with three different cathode materials (LiNi0.5Mn1.5O4, LiNi0.6Mn0.2Co0.2O2, and LiFePO4) by post mortem analysis with a scanning electron microscope. The observed large differences of the Li metal morphology are ascribed to the dissolution and crossover of TMs found deposited on Li metal and in the electrolyte by X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, and total reflection X‐ray fluorescence analysis. To support this correlation, the TM dissolution is simulated by adding Mn salt to the electrolyte. This study offers new insights into the cross talk between the Li metal anodes and TM cathodes, which is essential, when investigating Li metal electrodes for LMB full cells. The influence of the cathode materialsLiNi0.5Mn1.5O4 (LNMO), LiNi0.6Mn0.2Co0.2O2 (NMC 622), and LiFePO4 (LFP) on the Li metal electrode is demonstrated to be caused by the crossover of transition metals dissolved in the electrolyte, especially visible for Li/LNMO cells. This revelation supports the need for thorough investigations of Li metal anodes in full cells with a transition metal cathodes.