Enhancing Stability of NMC 111 at High Voltage/High Temperature Using Borylated Aryl Amines as Additive

Abstract

The present study exhibited the use of borylated aryl amines, as an electrolyte additive for high voltage and high-temperature LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) cathode to improve electrochemical performance. The interfacial characteristics of cathode and electrolytes are investigated using electrochemical assessments and physical characterizations. The additive undergoes oxidation at ∼3.8 V vs. Li⁺/Li. Charge discharge at 4.5V vs. Li⁺/Li at varied C-rate shows that 2 mg/ml additive-containing electrolyte (MBA2) has better rate capability than baseline (1.0 M LiPF₆/EC:DEC) and other additive-containing electrolytes. The MBA2 cell exhibits enhanced capacity retention at 0.2C and 1C with 77% and 44% of its initial discharge capacity, respectively at 200 cycles compared to MBA0 (control electrolyte). Electrochemical impedance spectroscopy reveals that the additive helps decrease the charge transfer and CEI resistance when employed at an optimum concentration. High-temperature studies at 60 °C showed better capacity retention of MBA2 with 93 % compared to MBA0 (89%) at the 100^th cycle. The excellent electrochemical performance of MBA2 is attributed to the robust, stable and protective film formation of MBA containing boron and nitrogen species, which is demonstrated by physical characterization. This film mitigates the continuous carbonate-based electrolyte decomposition and prevents the effect of HF in transition metal ions dissolution from the cathode upon cycling at high voltage and temperature, confirming its feasibility in practical applications.