关键词: 锂硫电池, 聚合物固体电解质, 聚氧化乙烯, 界面稳定性

Abstract:

In recent years, research on lithium-sulfur (Li-S) batteries has received much attention because the sulfur positive electrode and the lithium metal negative electrode produce a high theoretical specific capacity (lithium metal ~ 3800 mAh·g^-1, sulfur ~ 1675 mAh·g^-1). In addition, sulfur is considered to be the most promising cathode material for secondary lithium batteries, due to its advantages of low price and environmental friendly. However, the practical application of conventional liquid Li-S batteries is still obstructed by several critical issues, such as lithium ploysulfides shuttle effect, long-term stability of lithium metal anode with organic liquid electrolytes, and the safety concerns related to the lithium anode and liquid electrolyte. All-solid-state Li-S batteries using solid state electrolytes are considered as one of the most promising techniques to address the safety challenges of lithium ion batteries. Herein poly(ethylene oxide) (PEO)-based solid polymer electrolytes were prepared and investigated as electrolyte membranes for all-solid-state Li-S batteries. PEO/LiTFSI polymer electrolytes with different [EO]/[Li⁺] ratios were prepared and applied to Li-S batteries. It is found that although the PEO/LiTFSI ([EO]/[Li⁺] = 8) electrolyte had higher ionic conductivity, the PEO/LiTFSI ([EO]/[Li⁺] = 20) electrolyte resulted in lower interfacial resistance and higher interfacial stability with lithium anode. The Li|PEO/LiTFSI ([EO]/[Li⁺] = 20) |Li symmetric cell exhibited very stable voltage evolution without obvious erratic values or Li infiltration even being cycled for over 300 h at 60 °C and current density of 0.1 mA·cm^-2. However, the PEO/LiTFSI ([EO]/[Li⁺] = 8) based one failed due to intern short circuit after being cycled for less than 75 h. The polymer Li-S cells comprising PEO/LiTFSI ([EO]/[Li⁺] = 20) electrolyte delivered a high first discharge capacity of 934 mAh·g^-1 and good cycling stability with a capacity retention of 917 mAh·g^-1 after 16 cycles at 60 ^oC. In contrast, the PEO/LiTFSI ([EO]/[Li⁺] = 8) electrolyte based cell was not able to be charged normally and severe overcharge occurred even at the first cycle due to the poor interfacial stability of PEO/LiTFSI ([EO]/[Li⁺] = 8) electrolyte with lithium anode.

Key words: Li-S batteries, solid polymer electrolyte, polyethylene oxide, interfacial stability