Crossover Effects of Transition-Metal Ions on Lithium-Metal Anode in Localized High Concentration Electrolytes

The stability of the solid–electrolyte interphase (SEI) is critical to the cycle life of lithium-metal batteries (LMBs). While the crossover effect of transition-metal ions from cathode to anode is extensively studied in lithium-ion batteries with graphite anodes, its impact on LMBs remains largely unexplored. Herein, this study investigates the electrochemical and chemical properties of SEI layers formed on lithium-metal anodes in localized high-concentration electrolytes (LHCEs) containing dissolved transition-metal ions (Ni²⁺, Mn²⁺, and Co²⁺). It is demonstrated that transition-metal ions in LHCEs reduce the coulombic efficiency (CE) and significantly degrade the cycle life of LMBs. Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) reveals that SEI structures differ depending on the dissolved TM ion, with Mn²⁺ and Co²⁺ inducing severe destabilization, and Ni²⁺ exhibiting a less severe impact. These findings underscore the detrimental effects of transition-metal crossover effects in LMB systems.