Bimetal Fluorides with Adjustable Vacancy Concentration Reinforcing Ion Transport in Poly(ethylene oxide) Electrolyte
Ming‐Xia Zhou, Kai Cui, Tianshuai Wang, Zhihong Luo, Li Chen, Yun Zheng, Bin Li, Bin Shi, Jiangtao Liu, Jiao‐Jing Shao, Guangmin Zhou, Shubin Yang, Yan‐Bing He
Abstract
The poor ambient ionic transport properties of poly(ethylene oxide) (PEO)-based SPEs can be greatly improved through filler introduction. Metal fluorides are effective in promoting the dissociation of lithium salts via the establishment of the Li–F bond. However, too strong Li–F interaction would impair the fast migration of lithium ions. Herein, magnesium aluminum fluoride (MAF) fillers are developed. Experimental and simulation results reveal that the Li–F bond strength could be readily altered by changing fluorine vacancy (V F ) concentration in the MAF, and lithium salt anions can also be well immobilized, which realizes a balance between the dissociation degree of lithium salts and fast transport of lithium ions. Consequently, the Li symmetric cells cycle stably for more than 1400 h at 0.1 mA cm –2 with a LiF/Li 3 N-rich solid electrolyte interphase (SEI). The SPE exhibits a high ionic conductivity (0.5 mS cm –1 ) and large lithium-ion transference number (0.4), as well as high mechanical strength owing to the hydrogen bonding between MAF and PEO. The corresponding Li//LiFePO 4 cells deliver a high discharge capacity of 160.1 mAh g –1 at 1 C and excellent cycling stability with 100.2 mAh g –1 retaining after 1000 cycles. The as-assembled pouch cells show excellent electrochemical stability even at rigorous conditions, demonstrating high safety and practicability.