At high potential, lithium-ion battery electrolyte solvent will decompose to some extent under different voltages due to their intrinsic instability as well as the catalytic effects on the electrode material surface. The generated gas increases internal pressure of lithium ion battery, namely flatulence phenomenon, and the batteries was prone to explode. Investigating the influence of electrolyte composition, electrolyte salts, electrolyte electrode material during the charging and discharging process, drawing the electrolyte decomposition law will be beneficial to optimize the electrolyte component. In this work, the gas evolution behavior in EC/DMC (volume ratio 1:1) electrolyte system was carried out investigation during the first charging process at high voltage with LiNi_0.5Mn_1.5O₂ material as working cathode. The transmission infrared spectrum testing equipment was shown in Figure 1.

The coin cell for transmission infrared spectrum test was prepared and the test scheme was shown as follows: constant current charging, current density of 20 mA/g; voltage range of 3.5-5.0 V. The infrared spectra is collected every interval 0.1V. The infrared spectra collected in different electrolytes at different voltages during the charging process was given in Figure 2. As seen, the wave number corresponding to different functional groups are listed: absorption peak around 3000 cm^-1 corresponds to the -CH symmetrical stretching vibration, absorption peak at 2360, 2340cm^-1 corresponds to CO₂ gas, absorption peak around 1802, 1770 cm^-1 corresponds to C=C bond stretching vibration, the peak around 1282 and 1165 cm^-1 corresponds to C-H bending and CF₃ degenerate stretching of CHF₃.