Effect of Choices of Positive Electrode Material, Electrolyte, Upper Cut-Off Voltage and Testing Temperature on the Life Time of Lithium-Ion Cells

The impact of the choices of positive electrode material, coating types, electrolyte (varied electrolyte additive combinations), upper cutoff voltage and testing temperature on the lifetime of various NMC/graphite cells were systematically studied in this work. Ultra-high precision coulometry (UHPC) and long term cycling tests between 3–4.1, 4.2 and 4.3 V were conducted using pouch type cells (∼250 mAh). Cells with ∼90% capacity retention between 3–4.3 V after ∼2500 cycles (∼1.8 years of testing) at 20°C, and cells with ∼81% capacity retention between 3–4.3 V after ∼2200 cycles at 40°C were developed. The correlation between UHPC and long term cycling data was also explored. The major outcome of this work is that NMC622/graphite cells, with appropriate electrolyte additives, can outperform NMC532/graphite cells, demonstrating that cells with NMC grades having higher nickel content need not have shorter lifetime.