Insight into the Improved Performances of Ni-Rich/Graphite Cells by 1,3,5-Trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) Cyclotrisiloxane as an Electrolyte Additive

A Ni-rich cathode is one of the representatives for lithium-ion batteries that can deliver a higher energy density with lower cost than any other counterparts, but its cyclic stability is unsatisfactory. 1,3,5-Trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) cyclotrisiloxane (D3F) as an electrolyte additive is effective for performance improvement of the Ni-rich cathode. Evaluated in a cell based on the Ni-rich cathode (LiNi0.8Co0.1Mn0.1O2, NCM811) and a graphite anode in 1 M LiPF6-EMC/EC/DEC (3/5/2 in weight) between 3.0 and 4.35 V, the application of 5% D3F without any co-contribution of other electrolyte additives enhances the capacity retention of the cell from 38 to 76% after 300 cycles at 1C. The underlying mechanism is understood by combining theoretical calculation with physical characterization and electrochemical measurements. D3F can be electrochemically oxidized and reduced preferentially compared to the electrolyte components, creating robust interphases simultaneously on the cathode and anode. Additionally, it can scavenge HF and eliminates its detrimental effect on battery performances. This understanding helps to further enhance the performance of Ni-rich/graphite cells via designing electrolyte additives.