PEO基聚合物电解质及其锂硫电池性能研究

Poly(ethylene oxide) Based Polymer Electrolytes for All-Solid-State Li-S Batteries

锂硫电池由于具有高的理论比能量引起了广泛关注,然而传统液态锂硫电池由于多硫化物的"穿梭效应"以及安全问题而限制了其应用,全固态锂硫电池可显著提高电池安全性能并有望解决多硫化物的穿梭问题.本文采用传统的溶液浇铸法制备了具有不同的[EO]/[Li+]的PEO-Li TFSI聚合物电解质,并将其应用于锂硫电池.研究发现,虽然[EO]/[Li+]=8的聚合物电解质具有更高的离子电导率,但是[EO]/[Li+]=20的电解质与金属锂负极间的界面阻抗更低,界面稳定性更好. Li|PEO-Li TFSI([EO]/[Li+]=20)|Li对称电池在60℃,电流密度为0.1 m A·cm-2时可稳定循环超过300 h,而Li|PEO-Li TFSI ([EO]/[Li+]=8)|Li对称电池循环75 h就出现了短路现象.基于PEO-Li TFSI([EO]/[Li+]=20)电解质的锂硫电池首圈放电比容量为934 m Ah·g^-1,循环16圈后放电比容量为917 m Ah·g^-1以上.而基于PEO-Li TFSI ([EO]/[Li+]=8)电解质的锂硫电池,由于与锂负极较低的界面稳定性不能够正常循环,首圈就出现了严重过充现象.

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 m Ah·g^-1, sulfur ~ 1675 m Ah·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/Li TFSI polymer electrolytes with different [EO]/[Li+] ratios were prepared and applied to Li-S batteries. It is found that although the PEO/Li TFSI([EO]/[Li+] = 8) electrolyte had higher ionic conductivity, the PEO/Li TFSI([EO]/[Li+] = 20) electrolyte resulted in lower interfacial resistance and higher interfacial stability with lithium anode. The Li|PEO/Li TFSI([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 ℃ and current density of 0.1 m A·cm-2. However, the PEO/Li TFSI([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/Li TFSI([EO]/[Li+] =20) electrolyte delivered a high first discharge capacity of 934 m Ah·g^-1 and good cycling stability with a capacity retention of 917 m Ah·g^-1 after 16 cycles at 60 ℃. In contrast, the PEO/Li TFSI([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/Li TFSI([EO]/[Li+] =8) electrolyte with lithium anode.