Dependence of Linker Length and Composition on Ionic Conductivity and Lithium Deposition in Single-Ion Conducting Network Polymers

• Published in: Macromolecules Vol. 54; no. 16; pp. 7582 - 7589
• Main Authors: Aubrey, Michael L, Axelson, Jordan C, Engler, Kaitlyn E, Long, Jeffrey R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.08.2021
• Subjects: electrical conductivity; electrolytes; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; lithium; materials; polymers
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.1c00911

Single-ion conducting electrolytes stand as promising alternatives to state-of-the-art electrolytes in lithium batteries, although a single-ion conducting material with high Li+ conductivity, stability in contact with lithium, and suitable mechanical properties has been slow to emerge. Here, we describe the synthesis of a series of single-ion conducting network polymers from the reaction of tetrakis­(4-(chloromethyl)-2,3,5,6-tetrafluoro­phenyl)­borate with oligoethylene glycoxide linkers Li2O­[(CH2CH2)­O] n (n = 1, 2, 3, 9, and 22). Polymers with the longest linkers (n = 9 and 22; ANP-9 and ANP-10, respectively) form materials with conductivities of ∼10–6 S cm–1 at 100 °C. With the addition of 65 wt % propylene carbonate (PC), all the network polymers in the series exhibit high conductivities at ambient temperatures, with the n = 1 material (ANP-6) achieving a bulk ionic conductivity of 2.5 × 10–4 S cm–1 at 25 °C. More conductive single-ion conducting gels could be prepared by using the less coordinating pentanediol dilithium salt as a linker (ANP-11; σ = 3.5 × 10–4 S cm–1 at 25 °C), although this material exhibited a surprisingly high interfacial resistance in contact with a lithium electrode. In contrast, the gel formed with ANP-6 is notably stable in contact with metallic lithium electrodes, displays a lithium-ion transference number of unity, and boasts a wide electrochemical stability window of greater than 4.5 V. Temperature-dependent ac impedance analysis reveals that the ionic conductivity of this materialand likely the other gels in the seriesmatches closely to a Vogel–Tamman–Fulcher temperature model.