Impact of High-Nickel Cathodes and Test Conditions on the Coulombic Efficiency of Lithium Metal in Advanced Electrolytes

Uncontrollable Li plating morphology and inferior Coulombic efficiency (CE) are major challenges that limit the practical viability of lithium–metal batteries (LMBs). With the design of advanced electrolytes, promising CEs (∼99.5%) have been shown in Cu | Li cells. However, the impact of cathode materials and their operating conditions in the cells on the CE has not been systematically evaluated. Here, we compare the CE of Li metal in Cu | Li cells and Cu | LiNi 1– x – y Mn x Co y O 2 cells with different Ni contents. We also evaluate the CE with different cutoff charge voltages (4.4 and 4.6 V). The cathode as well as increasing Ni content or cutoff voltage all negatively impact the Li CE in advanced electrolytes. The chemical crossover from the cathode to the anode alters the composition of the solid-electrolyte interphase (SEI) on the surface of Li metal. The crossed over sulfur and nitrogen species and the formation of less inorganic components like LiF in the Li SEI could lead to inferior Li CE. This study highlights the importance of considering the compatibility of advanced electrolytes both with Li metal and cathodes for LMBs.