In the past ten years, driven by the increasing demand of energy density, metallic Li and silicon become two intriguing choices for next-generation Li batteries. However, graphite still dominates the anode market of the state-of-the-art LIBs because of its superior reversibility and safety. Though ether-based electrolytes show advantages compared to commercial carbonate-based electrolytes in Li metal and Si anodes, their incompatibility with graphite inhibits their practical applications. Traditional ether solvents have strong interaction with Li-ion and co-intercalate into the graphitic structure. High-concentrated electrolytes contribute to improved graphite reversibility while sacrificing economic affordability. Here, we demonstrated a viable strategy for improving the reversibility of ether electrolytes in graphite by tuning Li-solvent interaction ad local Li+ solvation structure in the electrolyte. As Li-solvent interaction decreases, co-intercalation becomes insignificant. Meanwhile, strengthened cation-anion interaction boosts the preferential formation of anion-derived solid electrolyte interface (SEI) enriched with inorganic species. We investigated the thickness, composition, and structural characteristics of the SEI using a combination of X-ray spectroscopy and electron microscopy. Endowed by the rationally designed solvation structure and the robust SEI, we achieved high coulombic efficiency (~99.9%) and excellent capacity retention (&gt;95%) at different current densities after 200 cycles using natural graphite. Since ion desolvation is one of the most energy uphill processes in batteries, such weakened Li-solvent interaction enables fast-charging capability (up to 2 C) and low-temperature performance (0 °C), superior to commercial carbonate electrolytes. Our new ether-based electrolyte can also ensure no Li metal plating on thick graphite electrodes under fast charging conditions. This work has established the design principles for ether electrolytes capable of graphite operation and sheds light on next-generation Li-based batteries using C/Li/Si composite anodes with balanced cyclability, fast-charge, and low-temperature performance.

Weakly solvated electrolytes enable reversible, fast-charge, and low-temperature operation of graphite anode in Li-ion batteries

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ACS Fall 2022

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