Improved Electrochemical Performances of Li/CF_x-MnO₂ Primary Batteries Via the Optimization of Electrolytes

Abstract

The lithium(Li) primary batteries have been widely used in power sources for military applications. According to the military standards, the design temperatures for the basic climate category including the mid-altitude areas will include the ambient air temperature range of -32 o C through +60 o C, considering the operational, storage, and transit conditions of materiel systems. Among a variety of Li primary batteries, lithium/thionyl chloride (Li/SOCl 2 ) primary batteries have been commonly utilized in military applications due to their high energy density, high operating voltage, and competitive cost. However, Li/SOCl 2 batteries have serious challenges due to initial voltage delay by lithium chloride passivation layer and possible safety issues by a formation of toxic sulfur-dioxide (SO 2 ) gas and solid sulfur during discharge. To overcome the intrinsic disadvantages of Li/SOCl 2 batteries, research into lithium/carbon fluoride-manganese dioxide (Li/CFx-MnO 2 ) batteries has been ramped up for military applications due to their high energy density and good rate capability. In this study, we have focused on an optimization of solvents and Li salts to improve the electrochemical performances of Li/CFx-MnO 2 batteries in a wide operating temperature ranges. We have investigated candidate solvents for Li/CFx-MnO 2 batteries with different compositions of methyl butyrate (MB) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as well as conventional solvents including propylene carbonate (PC), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), ethyl acetate (EA), and 1,2-dioxolane (DOL). Moreover, we have investigated the effects of Li salts, lithium perchlorate (LiClO 4 ) and lithium bis(trifluoromethanesulfonyl)imide (LiFSI), on the electrochemical performances in the low and high operating temperatures. Ionic conductivity measurements and differential scanning calorimetry (DSC) analysis were also carried out to investigate the physical properties and stability of electrolyte. This study will provide an opportunity to develop the new electrolyte systems for Li/CFx-MnO 2 batteries in a wide operating temperature window.