CAS:1513-87-7，bis(2,2,2-trifluoroethyl) carbonate，(DTFEC)

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Increasing the voltage of Li-ion batteries is one of the best ways to increase their energy density. However, there is no commercial electrolyte available for these high voltage cells since state-of-the-art electrolytes containing organic carbonates and typical salts are prone to decompose at high potentials. In this presentation, three electrolyte systems including ethylene carbonate (EC) – ethyl methyl carbonate (EMC), sulfolane (SL) – EMC and fluorinated carbonate mixtures composed of fluoroethylene carbonate (FEC) and bis(2,2,2- trifluoroethyl) carbonate (TFEC) with some selected additive blends were tested in high voltage Li[Ni0.4Mn0.4Co0.2]O2(NMC442)/graphite pouch cells. Figure 1a shows the voltage drop during storage at 40°C (500 h) as a function of initial open circuit voltage for the NMC442/graphite pouch cells with the three different electrolytes. Figure 1a shows that at 4.5 V or above, FEC:TFEC-based electrolytes have significantly smaller potential drops than EC:EMC-based or SL:EMC-based electrolytes, suggesting less electrolyte oxidation occurs in FEC-TFEC-based electrolytes at high potentials. Figure 1b shows the discharge capacity vs cycle number for NMC442/graphite pouch cells with the three different families of electrolytes. Figure 1c shows the difference between average charge and discharge voltage (V) vs cycle number for the same cells shown in Figure 1b. Figures 1b and 1c show that cells using the FEC:TFEC-based electrolyte have the best capacity retention and least impedance growth during long term high-voltage cycling (to 4.5 V) at 40oC.



Figure 1. a) Voltage drop vs. initial open circuit voltage during storage at 40. ± 0.1ºC for 500 h, b) discharge capacity vs cycle number and c) ΔV vs cycle number for NMC442/graphite pouch cells containing EC:EMC, SL:EMC and FEC:TFEC electrolyte systems containing selected additive combinations. The long-term cycling is between 2.8 and 4.5 V at C/2.4 (100 mA) and 40C.