Study on the electrochemical characteristics of the lithium/sulfur rechargeable batteries with plasticized polymer electrolytes and protected lithium anodes

Abstract

In this study, lithium/sulfur rechargeable batteries based on the plasticized polymer electrolytes and the protected Li anodes were prepared and their electrochemical characteristics were investigated. Lithium/sulfur rechargeable batteries consist of sulfur cathode, electrolyte, and lithium anode. The sulfur cathode with a new polymer binder, P(VdF-co-HFP), was prepared by newly proposed method. The morphological and electrochemical characteristics of the cathodes were investigated with the composition of the sulfur/carbon black/ P(VdF-co-HFP). The plasticized polymer electrolytes based on P(VdF-co-HFP), tetra(ethylene glycol) dimethyl ether (TEGDME), and lithium perchlorate $(LiClO_4)$ with a different salt concentration were prepared for the lithium/sulfur batteries by solution casting with a doctor-blade. The polymer electrolyte with EO:Li ratio of 16:1 showed the maximum ionic conductivity, $6.5\times10^{-4}$ S/cm at room temperature. To understand the effect of the salt concentration in the polymer electrolyte and the cathode on the electrochemical performance, the polymer electrolytes were characterized using FRA, FT-IR, viscometer, and DSC. The higher concentration and mobility of the charge carriers could lead to enhance the utilization of sulfur active materials and the cyclability of the Li/S unit cell. The protection layer on the Li anode was introduced to enhance the charge/discharge performance of lithium sulfur batteries. The protection layer reduced the growth of SEI layer and suppressed the reaction between Li and soluble polysulfide to prevent overcharge phenomena. The charge/discharge performance of the unit cells with the protected Li anodes was investigated with different electrolytes, liquid electrolyte and plasticized polymer electrolyte. The unit cells with liquid electrolytes showed the averaged discharge capacity, 270 mAh/g-cathode, which was twice as high as that of lithium ion battery within 100 cycles. Therefore, the cell with pr...