Electrolyte additive combinations that enhance performance of high-capacity Li1.2Ni0.15Mn0.55Co0.1O2-graphite cells

The synergistic effects of LiB(C2O4)2 (LiBOB), LiF2B(C2O4) (LiDFOB), triphenylamine (Ph3N), and 1,4-benzodiozane-6,7-diol (BDOD) as functional electrolyte additives in high-energy electrochemical cells is examined. The influence of these additives, individually, and in different combinations, is evaluated using galvanostatic cycling of cells containing Li1.2Ni0.15Mn0.55Co0.1O2 (0.5Li2MnO3·0.5LiMn0.375Ni0.375Co0.25O2)-based positive electrodes, graphite-based negative electrodes, and a LiPF6-based electrolyte. Electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and voltage-hold tests are also used. By itself, LiBOB is a good additive for reducing cell capacity loss, but cell impedance rise is still significant after extended cycling. Similarly, neither Ph3N nor BDOD alone provide desired improvements in cell performance. However, cells containing LiBOB in combination with LiDFOB, Ph3N, or BDOD exhibit enhanced capacity retention, rate capability, and cyclability; probable reaction mechanisms are highlighted here. Combining electrolyte additives that act synergestically is a practical and versatile strategy to improve performance and life of lithium-ion cells.