Fabrication of Single-Ion Conductors Based on Liquid Crystal Polymer Network for Quasi-Solid-State Lithium Ion Batteries.

Abstract

Single-ion conductive polymer electrolytes can improve the safety of lithium ion batteries (LIBs) by increasing the lithium transference number (tLi+) and avoiding the growth of lithium dendrites. Meanwhile, the self-assembled ordered structure of liquid crystal polymer networks (LCNs) can provide specific channels for the ordered transport of Li ions. Herein, single-ion conductive nematic and cholesteric LCN electrolyte membranes (denoted as NLCN-Li and CLCN-Li) were successfully prepared. NLCN-Li was then coated on commercial Celgard 2325 while CLCN-Li was coated on poly(vinylidene fluoride-hexafluoropropylene) film, coupled with plasticizer, to make NLCN-Li/Cel and CLCN-Li/Pv quasi-solid-state electrolyte membranes, respectively. Their electrochemical properties were evaluated, and it was found that they possessed benign thermal stability and electrolyte/electrode compatibility, high tLi+ up to 0.98 and high electrochemical stability window up to 5.2 V. A small amount (0.5M) of extra Li salt added to the plasticizer could improve the ion conductivity from 1.79 × 10-5 to 5.04 × 10-4 S cm-1, while the tLi+ remained 0.85. The assembled LFP|Li batteries also exhibited excellent cycling and rate performances. The orderliness of the LCN layer played an important role in the distribution and movement of Li ions, thereby affecting the Li deposition and growth of Li dendrites. As the first report of nematic and cholesteric LCN single-ion conductors, this work sheds light on the design and fabrication of ordered quasi-solid-state electrolytes for high-performance and safe LIBs.