Stabilizing the Solid Electrolyte Interphase Layer and Cycling Performance of Silicon-Graphite Battery Anode by Using a Binary Additive of Fluorinated Carbonates

Stabilization of the solid electrolyte interphase (SEI) layer of the silicon (Si) graphite composite anode for Li-ion batteries leads to an improvement of cycling performance. The SEI stabilization is achieved by utilizing a binary additive of fluoroethylene carbonate (FEC) and a fluorinated linear carbonate, di(2,2,2-trifluoroethyl)carbonate (DFDEC). The SEI composition analyses using attenuated total reflectance Fourier transform infrared (ATR FTIR) and X-ray photoelectron spectroscopy reveal that FEC alone plays a role in producing relatively more and various organic compounds including anhydride but lower concentration of inorganic salts, lowering interfacial resistances than those of conventional electrolyte and other additives. The SEI composition of silicon-graphite composite anode with FEC additive is distinguished from those reported for Si only and graphite only. The role of DFDEC alone, which possessed six fluorine atoms, is found to be the production of plenty of inorganic compounds such as Li2CO3, LiF, and OPF3-y(OR)(y)/LixPFyOz compounds, thickening the SEI layer. Blending of FEC and DFDEC results in the SEI thickening with the formation of mixtures of organic and inorganic compounds, which permits effective surface passivation of the anode, SEI robustness, and structural robustness of the silicon-graphite anode material. The anode with the binary additive of 10 wt % FEC and 1 wt % DFDEC outperforms the one in the conventional electrolyte and with FEC alone, delivering improved initial Coulombic efficiency of 84%, high discharge capacity of 742-601 mAh g(-1) of a whole active material, and 81% capacity retention at the 50th cycle.