Investigation the effect of a Linear carboxylic ester in EC-based electrolyte as a co-solvent for improving low-temperature performance of lithium-ion battery

The importance of lithium-ion battery (LIB) as electric energy storage has been increased. Additionally, LIBs have been widely used as power sources in portable devices such as cell phones, lap top computers, and digital cameras due to their high energy density, cycle stability, and high voltage. Some applications of LIBs such as aerospace require good low-temperature performance of LIB.The deterioration performance of LIB at low temperatures can be investigated in three aspects of anode, cathode, and electrolyte. To improve the low-temperature performance of LIB, some procedures are proposed. For anode and cathode, surface coating and doping are adopted. For the electrolyte, modifying the solvent and salt of electrolyte as well as the addition of functional electrolyte additives can improve the low-temperature performance of LIB. The high melting points of widely used carbonate based solvents such as ethylene carbonate (EC) and dimethyl carbonate (DMC), is responsible for severe fading of the LIB capacity and power at low temperatures.For the electrolyte, modifying the solvent and salt of electrolyte as well as the addition of functional electrolyte additives can improve the low-temperature performance of LIB. A common approach for improving the low-temperature performance of LIB is using the low melting point solvents like propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Additionally, utilization of fluorinated carbonate solvents like ethyl ۲,۲,۲-trifluoroethyl carbonate and propyl ۲,۲,۲-trifluoroethyl carbonate is another proposed manner to improve the low-temperature property of electrolyte. These solvents can form a more conductive SEI layer on the electrode which decreases the charge transfer resistance of LIB. Linear carboxylic esters like methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), and ethyl butyrate (EB) with lower melting point and viscosity than that of the carbonate solvents are modifying agents of electrolyte for low-temperature applications. In this regard, Smart et al. illustrated that the use of organic esters in EC-based electrolyte greatly improves the electrolyte conductivity especially at low temperatures.In this work, the effect of ethyl acetate as a co-solvent is investigated on the low-temperature performance of the lithium-ion battery.The addition of EA with low melting point and viscosity as a co-solvent to electrolyte can solve this problem. The electrolyte with EA showed higher conductivities compared to the electrolyte without EA at both ۲۵ and − ۴۰ °C. Addition of EA shifted the reduction potential of the blank electrolyte to the higher potential and also decreased the charge transfer resistance and the total resistance of the cell. Remarkably, the cell without EA cannot operate at − ۴۰ °C due to the freezing of electrolyte while the cell with EA showed the ۵۹% capacity retention compared to its discharge capacity at room temperature.