EB (Ethyl Butyrate) as a Cosolvent of Electrolyte Tuning an Ultrathin CEI Membrane for Improving the Ultralow-Temperature Behaviors of LiNi_0.8Co_0.1Mn_0.1O₂ Batteries

Abstract

Adding lithium difluorophosphate into the original electrolyte results in outstanding eletrochemical performances among low temperatures, as documented in our earlier published work; therefore, to be able to gain more stability in lowtemperature performances, in this work, a kind of linear carboxylate cosolvent, EB (ethyl butyrate), is introduced, which has low viscosity (0.639 mPa s), high ion conductivity (5.18 mS cm −1 ), and ultralow melting point (−93 °C). The study's results show that the basic electrolyte's conductivity and viscosity are correspondingly 2.9 mS cm −1 and 3.34 mPa s at −40 °C; however, comparing under the same condition, after adding 16% EB into the baseline, the conductivity and viscosity are 3.37 mS cm −1 and 3.07 mPa s, whose amplitude changes show that the conductivity has increased by 16.2% and the viscosity has dropped by 8% in the interim. Therefore, the addition of EB can clearly boost conductivity, also drastically decreasing the electrolyte's viscosity, further to signify that the addition of EB can contribute to the decrease in the resistance during lithium-ion transport in cold conditions. Besides, the electrochemical properties of the batteries during cold conditions can be obviously improved by adding EB. In addition, after 50 cycles of −40 °C, the basic electrolyte has a discharge capacity of 81.94 mAh g −1 ; on the contrary, the cells using the 16 EB-modified coreagent maintains a discharge capacity of 112.3 mAh g −1 under the same conditions. Overall, the cells containing EB perform exceptionally well at low temperatures and are capable of meeting the appliance of Li-ion batteries in a cool environment.