The Effect of Grain Size on the Ionic Conductivity. of a Block Copolymer Electrolyte

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1 SUPPORTING INFORMATION FOR: The Effect of Grain Size on the Ionic Conductivity of a Block Copolymer Electrolyte Mahati Chintapalli, # X. Chelsea Chen, # Jacob L. Thelen, ǁ Alexander A. Teran, ǁ Xin Wang, Bruce A. Garetz, Nitash P. Balsara ǁ# * Department of Materials Science and Engineering, University of California, Berkeley, California 94720, United States Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States ǁ Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States # Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States Department of Chemical and Biomolecular Engineering, NYU Polytechnic School of Engineering, Brooklyn, NY 11201, United States Corresponding Author * nbalsara@berkeley.edu

2 Electrolyte Characterization Figure S1. Proton nuclear magnetic resonance spectroscopy ( 1 H NMR) of polymer electrolyte. The 1 H NMR spectrum for the electrolyte is shown. The spectrum was taken in CDCl 3 solvent with tetramethylsilane as a reference compound. The spectrum was acquired using a 400 MHz Bruker Avance instrument. A schematic of the polymer is shown and regions giving rise to spectral features are indicated. Shifts of major peaks (in ppm) are shown at the top. Electrolyte purity and thermal properties were assessed by nuclear magnetic resonance spectroscopy (NMR) and differential scanning calorimetry (DSC), respectively. To confirm that the freeze-dried electrolyte was free of water and solvent, 1 H NMR was performed on a Bruker AVB400 instrument (400 MHz) using dry CDCl 3 solvent. The electrolyte was transferred to a

3 sealed NMR tube without exposure to air. The resulting spectrum is shown in Figure S1. Features from CHCl 3, PS, and PEO can be seen. Two small peaks appearing at shifts of 3.37 and 3.08 ppm arise from the isopropyl alcohol-terminated PEO chain ends. No trace of water, which would appear as a sharp peak near 1.56 ppm, is observed. The glass transition temperature, T g, of PS and the melting point of PEO were determined by DSC. Electrolyte was transferred to an aluminum pan and hermetically sealed in an Ar glovebox. The data shown in Figure S2 were obtained on the second heating run at a heating rate of 10 o C min -1. The range of temperatures scanned was -40 to 140 o C. The T g,ps was found to be 71 o C, and a weak melting peak was observed for PEO around 36 o C. The T g of PEO was outside the range of the scan. Interestingly, the melting of PEO apparently did not affect the observed ionic conductivity; however, a strong conclusion cannot be drawn because in the vicinity of 36 o C, conductivity and SAXS measurements were made with large temperature steps

4 Figure S2. DSC data. Heat flow is plotted as a function of temperature for the second heating of the electrolyte sample. Endothermic heat flow is up. Two features are clear, a melting peak from PEO and a glass transition due to PS. Temperature Calibration The samples were heated on a home-built temperature-controlled heating stage. The stage temperature was measured and used to control the temperature setpoint, T Setpoint ; however the actual sample temperature, T Sample, was slightly offset from the setpoint due to the design of the stage. A separate calibration experiment was performed to correlate the sample temperature to the temperature setpoint. The sample temperature is given by: T Sample = 0.96 T Setpoint The sample temperature is reported throughout the paper. Figure S3. Sample temperature calibration. Sample temperature, measured by a wire thermocouple, is plotted as a function of controller setpoint temperature.

5 Additional Results In SAXS experiments, the main change in scattering profiles that was observed for temperatures between 63 and 116 o C was the narrowing of the FWHM. In this temperature regime, q* also shifted irreversibly with time and temperature. The domain spacing, d, of the polymer is related to q* as follows: d = 2π / q*. Figure S4 shows the dependence of d on temperature and time during heating. During cooling, d, did not change significantly from its value at 116 o C. Overall, the domain spacing changed by about 1 nm during annealing. It is possible that changes in d could affect the ionic conductivity; however, we do not believe that a 1 nm (or six percent) change can entirely account for a five-fold change in ionic conductivity, as we have observed. Figure S4. Domain spacing as a function of temperature during heating. Domain spacing, determined from the q* position in SAXS data, is plotted against temperature for the heating run. The color scale represents the amount of time spent at each temperature.

6 In Figure 7b, we presented conductivity as a function of grain size, L, with the conductivity normalized by the VTF fit to the stable cooling data. Alternatively, one could normalize the conductivity by a VTF fit to the stable heating data collected in the temperature range 29 to 63 o C (Figure S5). As in Figure 7b, the data in Figure S5 collapse onto a single line as with values approximately five times smaller than those in Figure 7b. The factor of five comes from the difference in the values of the prefactor, A, in the two VTF fits. The five-fold change in conductivity is commensurate with the approximately five-fold change in L over the course of annealing. Figure S5. Normalization of conductivity data by Vogel-Tammann-Fulcher fit to stable heating data. Conductivity during heating is normalized by the VTF fit to the initial heating data and plotted against L. Color indicates the temperature at which the data point was collected.