Quantitative Determination of Carbon Dioxide Content in Organic Electrolytes by Infrared Spectroscopy

Abstract

CO2 has been shown to be an effective additive to improve the cycling characteristics of silicon negative electrodes for Li-ion batteries. However, a quantitative technique for measuring the CO2 content in electrolyte is not readily available. Here, FTIR was used to accurately determine the CO2 content of various carbonate-based Li-ion battery electrolytes. The accuracy of this method was validated with the weight variation method. Using this method, it was found that in EC/DEC electrolytes with 1M LiPF6 and LiTFSI salts, CO2 was found to have a maximum solubility of 0.37 wt% when the LiPF6:LiTFSI molar ratio is 3:1. In 1M LiPF6 solutions, CO2 solubility is in the order of PC ≈ EMC > DEC for the pure solvents. Mixed non-polar solvents are also favorable for CO2 dissolution. When used in silicon alloy cells, electrolytes saturated with CO2 (0.33% CO2 in EC/DEC) resulted in the best cycling stability.