Dependence Of Linker Length And Composition On Ionic Conductivity And Lithium Deposition In Single-Ion Conducting Network Polymers

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 similar to 10(-6) S cm(-1) at 100 degrees 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 x 10(-4) S cm(-1) at 25 degrees C. More conductive single-ion conducting gels could be prepared by using the less coordinating pentanediol dilithium salt as a linker (ANP-11; sigma = 3.5 x 10(-4) S cm(-1) at 25 degrees 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.