Lithium Difluorophosphate As a Promising Electrolyte Lithium Additive for High-Voltage Lithium-Ion Batteries

Lithium difluorophosphate (LiDFP), the decomposition product of LiPF6, was evaluated in high-voltage LiNi1/3Co1/3Mn1/3O2/graphite pouch cells. We report that conventional carbonate-based electrolytes containing 1 wt % LiDFP can notably enhance the cyclability and rate capability of the battery at 4.5 V. Its capacity retention maintained 92.6% after 100 cycles, whereas it is only 36.0% for the additive-free battery. Even after 200 cycles, the capacity retention remained 78.2%. The EIS measurements performed by three-electrode graphite/Li/LiNi1/3Co1/3Mn1/3O2 pouch batteries indicate that LiDFP can efficiently restrain the breakdown of the electrolyte on the LiNi1/3Co1/3Mn1/3O2 electrode surface and relieve the increase of cathode resistance. Additionally, a uniform and stable SEI film modified by LiDFP on the anode can effectively remit the electrode/electrolyte interfacial reaction and relieve the increase of anode resistance during cycling. Further evidence for the beneficial effect of LiDFP in inhibiting the dissolution of transition metal from the cathode under a high operating voltage is also found. On the basis of electrochemical methods and spectroscopic techniques, the enhancement in the high-voltage performance of the cell attributed to the LiDFP component can simultaneously modify the cathode and anode surfaces. Consequently, LiDFP is a promising electrolyte lithium additive for practical applications in high-energy lithium-ion cells.