Voltage Dependence of Electrolyte Additives for Stabilizing Cathode Electrolyte Interphase

Cathode electrolyte interphases (CEIs) formed with the electrolyte additives of vinylene carbonate (VC) and lithium bis(oxalate)borate (LiBoB) were evaluated after extended cycling up to 4.3 V. At 4.3 V, the Gen2 + LiBoB electrolyte forms a thick fluorine-rich CEI and has poor electrochemical performance (24.4% capacity retention at 460 cycles), while the Gen2 + VC electrolyte forms a thin organic CEI and has superior electrochemical performance (75.0% capacity retention at 1000 cycles). These results demonstrate the superiority of the Gen2 + VC electrolyte-derived CEI at 4.3 V. The poor performance of the Gen2 + LiBoB electrolyte at 4.3 V contradicts the benefits of an HF scavenger above 4.5 V, suggesting voltage-dependent behaviors. To validate the efficacy of the Gen2 + LiBoB electrolyte as an HF scavenger, the higher cycling voltage of 4.5 V was used as a mechanistic probe to evaluate additive efficacy under harsher and HF-rich electrochemical conditions. At 4.5 V, the Gen2 + LiBoB electrolyte demonstrates superior cycling (84.2% capacity retention at 200 cycles) compared to the Gen2 + VC electrolyte (78.5% capacity retention at 200 cycles) and the Gen2 electrolyte system (59.5% capacity retention at 200 cycles).This study demonstrates the voltage-dependent nature of electrolyte additive efficacy and how operating voltage must be a selection criterion for any electrolyte additives to ensure the controlled formation of a robust and high-performance CEI.