Enhanced high-voltage cyclability of LiNi0.5Co0.2Mn0.3O2-based pouch cells via lithium difluorophosphate introducing as electrolyte additive

To meet the electrolyte requirements for high-voltage cathode materials, lithium difluorophosphate (LiDFP) is evaluated as a lithium salt additive for the conventional carbonate-based electrolyte system. The LiNi0.5Co0.2Mn0.3O2/graphite pouch cells containing 1 wt% LiDFP delivers a discharge capacity retention of 93.8% over 100 cycles operated at a cut-off voltage of 4.5 V, which is higher than the 43.2% of that without additive; and its average discharge capacity can reach around 118.9 mAh g−1 at 5 C, while the reference cell only achieves 93.4 mAh g−1. Herein, the electrochemical impedance spectroscopy results obtained from the two- and three-electrode pouch cells indicate that LiDFP can respectively suppress impedance growth of two electrodes during cycling. The spectroscopic analysis demonstrates that the cathode surface can be modified by the additive and a stable solid electrolyte interface (SEI) is also formed on the anode surface by the presence of LiDFP in the electrolyte. Additionally, the capacity retention for the LiNi0.5Co0.2Mn0.3O2/Si-C pouch cell is also noticeably enhanced from ∼3.5% to 67.2% by adding 1 wt% LiDFP into the electrolyte over 200 cycles operated at 4.5 V.