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 Li 2 CO 3 , LiF, and OPF 3−y (OR) y /Li x PF y O z 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.

Artificial graphite anode materials are promising for high-performance Li-ion batteries for electric vehicles. Battery cycle-life and performance are known to rely on the formation and stability of solid electrolyte interphase (SEI) layer, particularly, of the anode. Herein, we report the investigation of material characteristics-dependent SEI formation behavior and stability of model artificial graphite anodes in conventional electrolyte with vinylene carbonate additive, and their correlation to performance. Surface analysis results reveal that artificial graphite composite of Cokes and binder pitch in a relatively smaller particle size at 100% graphitization degree and with higher surface area of edges provides promoted interfacial reactivity and formation of more stable, thinner and softer SEI layer that includes plenty of organic compounds, leading to high structural robustness and improved cycling performance. By contrast, aggregated larger particles and/or lower graphitization degree results in inferior performance. A full-cell with the optimized artificial graphite anode and LiCoO 2 cathode delivers initial discharge capacity of 161 mAhg −1 at 0.2C, respectively, and initial coulombic efficiency of 89%, and capacity retention of 91% at the 100 th cycle. The data give an insight into the principles of material design, the SEI layer stabilization and performance enhancement of artificial graphite anode for high-energy Li-ion batteries.

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Utilization of high-voltage electrolyte additive(s) at a small fraction is a cost-effective strategy for a good solid electrolyte interphase (SEI) formation and performance improvement of a lithium-rich layered oxide-based high-energy lithium-ion cell by avoiding the occurrence of metal-dissolution that is one of the failure modes. To mitigate metal-dissolution, we explored fluorinated dual-additives of fluoroethylene carbonate (FEC) and di(2,2,2-trifluoroethyl)carbonate (DFDEC) for building-up of a good SEI in a 4.7 V full-cell that consists of high-capacity silicon-graphite composite (15 wt% Si/C/CF/ C-graphite) anode and Li 1.13 Mn 0.463 Ni 0.203 Co 0.203 O 2 (LMNC) cathode. The full-cell including optimum fractions of dualadditives shows increased capacity to 228 mAhg −1 at 0.2C and improved performance from the one in the base electrolyte. Surface analysis results find that the SEI stabilization of LMNC cathode induced by dual-additives leads to a suppression of soluble Mn 2+ -O formation at cathode surface, mitigating metal-dissolution event and crack formation as well as structural degradation. The SEI and structure of Si/C/CF/C-graphite anode is also stabilized by the effects of dual-additives, contributing to performance improvement. The data give insight into a basic understanding of cathode-electrolyte and anodeelectrolyte interfacial processes and cathode-anode interaction that are critical factors affecting full-cell performance.

Lithium diffusivity of fluorine-free and -doped tin-nickel (Sn-Ni) film model electrodes with improved interfacial (solid electrolyte interphase (SEI)) stability has been determined, utilizing variable rate cyclic voltammetry (CV). The method for interfacial stabilization comprises fluorine-doping on the electrode together with the use of electrolyte including fluorinated ethylene carbonate (FEC) solvent and trimethyl phosphite additive. It is found that lithium diffusivity of Sn is largely dependent on the fluorine-doping on the Sn-Ni electrode and interfacial stability. Lithium diffusivity of fluorinedoped electrode is one order higher than that of fluorine-free electrode, which is ascribed to the enhanced electrical conductivity and interfacial stabilization effect.