Zinc bis(2–ethylhexanoate), a homogeneous and bifunctional additive, to improve conductivity and lithium deposition for poly (ethylene oxide) based all-solid-state lithium metal battery

Abstract Poly (ethylene oxide) based solid polymer electrolytes are suitable candidates for constructing all-solid-state lithium metal batteries. However, the low ionic conductivities, poor mechanical strength and incompetence to suppress the penetration of Li dendrites hinder their practical application. Herein, we introduce Zinc bis(2-ethylhexanoate) (Zn (BEH)2) as a homogeneous and bifunctional additive into PEO network by a simple solution casting method to achieve improvements of ionic conductivity and uniformity of lithium deposition. It is shown that the Lewis acid–base interactions between Zn (BEH)2 and PEO chains suppress the polymer crystallization and weaken the O–Li+ interaction, resulting in a good ionic conductivity of 1.1 × 10−5 S cm−1 at 30 °C, 2.7 × 10−4 S cm−1 at 60 °C and an improved lithium ion transfer number of 0.5 at 60 °C. Furthermore, a LiZn alloy layer is formed in-situ on lithium metal anode via the reaction between Zn (BEH)2 and Li, which effectively prevents dendrite growth. Based on PEO–Zn (BEH)2 polymer electrolyte, a Li/Li symmetric cell exhibits a steady cycling over 500 h with a low polarization potential of 150 mV. This strategy will illuminate new design strategy to advance polymer electrolytes towards high performance solid-state lithium batteries.