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Currently widely used carbonate-based electrolytes face difficulty in ensuring that the lithium-ion batteries work beyond 4.2 V for the purpose of energy density improvement. Herein, we report a novel electrolyte that emphasizes the synergistic effect of fluoroethylene carbonate (FEC) and 2-(trifluoromethyl) phenyl boric acid (2-TP) as coadditives, enabling the LiCoO 2 cathode to operate stably under high voltages. With the addition of 1% 2-TP and 10% FEC into a carbonate-based electrolyte, LiCoO 2 shows a significantly improved cyclic stability. Spectral characterizations, electrochemical measurements, and theoretical calculations demonstrate that the improved cyclic stability can be attributed to the cathode−electrolyte interphase (CEI) derived from FEC and 2-TP. These two additives are preferentially oxidized on the LiCoO 2 electrode into their oxidation decomposition products to construct a robust and lowimpedance CEI with inorganic LiF uniformly dispersed in the organic B-containing matrix. This unique CEI construction provides a facile solution to the challenges in developing high-energy-density lithium-ion batteries based on high-voltage cathodes, not limited to LiCoO 2 .

The rate capability of lithium-ion batteries is highly dependent on the interphase chemistry of graphite anodes. Herein, we demonstrate an anode interphase tailoring based on a novel electrolyte additive, lithium dodecyl sulfate (LiDS), which greatly improves the rate capability and cyclic stability of graphite anodes. Upon application of 1% LiDS in a base electrolyte, the discharge capacity at 2 C is improved from 102 to 240 mAh g −1 and its capacity retention is enhanced from 51% to 94% after 200 cycles at 0.5 C. These excellent performances are attributed to the preferential absorption of LiDS and the as-constructed interphase chemistry that is mainly composed of organic long-chain polyether and inorganic lithium sulfite. The long-chain polyether possesses flexibility endowing the interphase with robustness, while its combination with inorganic lithium sulfite accelerates lithium intercalation/deintercalation kinetics via decreasing the resistance for charge transfer.

LiF plays an important role in stabilizing solid electrolyte interphases (SEIs) on graphite anodes of commercialized lithium-ion batteries (LIBs) that adopt 1 M LiPF 6 in carbonate solvents as base electrolytes. To construct LiF-rich SEIs, various strategies have been developed, including replacing carbonates with F-containing solvents, applying F-containing additives, and using LiPF 6 with ultrahigh concentrations. However, these efforts add cost to battery manufacturing or are at the expense of battery rate capability. In this work, we propose new strategies based on the insight into the formation mechanism of LiF. It is found that LiPF 6 presents higher reduction activity than carbonate solvents and prefers to be reduced under the coordination of carbonate solvents, generating LiF that contributes to the main component of SEIs on graphite. Among various carbonate solvents, EC is the most beneficial for the formation of LiF because of its strong ability to combine LiPF 6 . Additionally, the content of LiF in SEIs can be controlled by applying pulse potentials. Therefore, LiF-rich SEIs can be achieved by regulating solvent compositions and graphite anode potentials. This new strategy not only provides a facile solution to the construction of stable SEIs but is also beneficial for designing stabler SEIs on graphite anodes to further improve the performances of LIBs.