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

Abstract

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.