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Ø Current technological advancements create a much larger role for batteries in everyday life

Ø Portable and sustainable batteries are required to advance renewable energy technologies, as well as electric vehicles and home energy storage

INTRODUCTION

MATERIALS AND METHODS

CONCLUSIONS

Ø Conductivity increases as a function of salt concentration due to increase in ion concentration. But then it drops at higher concentration due to increase in TG and slowing down of polymer dynamics.

Ø Though it is evident that conductivity generally increases as a function of salt concentration, further work is needed to define the optimal ion concentration and polymer structure.

Ø Electron Polarization and Random Barrier models examine separate regions of BDS measurement to find ion diffusivity

Ø These models have several assumptions which require farther verification. As a result, they provide contradictory results.

REFERENCES1. Y. Wang et al., Polymer 55, 4067 (2014).2. J. C. Dyre, J. Appl. Phys. 64, 2456 (1988).3. Y. Want et al., Phys. Rev. E 87, 042308 (2013).4. Kremer F, Scho ̈nhals A (Eds) (2003) Broadband dielectric

spectroscopy. Springer-Verlag Berlin Heidelberg GmbH, ISBN 978-3-642- 62809-2, DOI 10.1007/978-3-642-56120-7

5. H. Wagner, R. Richert, J. Phys. Chem. B 103 (1999) 4071

ACKNOWLEDGEMENTS

1Department of Chemistry, University of Tennessee, Knoxville, Tennessee, 37996, United States2Department of Physics and Astronomy, University of Tennessee, Knoxville, 37996, United States

3Fakultät für Physik, Technische Universität Dortmund, 44221 Dortmund, Germany4Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States

Presented by Weston Bell1, Eric W. Stacy,2 Fei Fan,1 Catalin Gainaru,1,3 Tomonori Saito4 and Alexei Sokolov1,4

Investigation of Carbonate-Based Copolymer Electrolytes for Decoupled Li-Ion Conductivity

Broadband Dielectric Spectroscopy

VC-co-DEGMEMEA Copolymer

Fig. 4. The dielectric spectra versus frequency at different temperatures for TS1-198 (Li-TFSi) at few selected temperatures. There are four different spectra of this sample: (a) real part of permittivity, (b) imaginary part of permittivity, (c) real part of conductivity, and (d) imaginary part of conductivity.

CONTACTSWeston BellDr. Sokolov's Group, Department of Chemistry,The University of Tennesse, Knoxville, TN, 37996, United StatesEmail: jbell54@vols.utk.edu

Proposed Approach

Motivation

Fig.1. General representation of Dielectric spectra versus frequency.

RESULTS

Ø Low Li conductivity in polymers hinders their broad adoption in current technologies

Ø Based on previous research [1], present work analyzes the relationship between ionic transport and the concentration of LiTFSi in a copolymer matrix

Ø Previous research [1] indicates a limit to the increase in conductivity based on salt concentration

Ø The Random Barrier Model [2] and Electrode Polarization models [3] reveal strong deviation of Li ion transport from ideal behavior.

Ø The dielectric spectra was collected in the frequency range of 10-1 – 107

Hz using Novocontrol system which includes an Alpha-A Impedance Analyzer and Quantro Cryosystem temperature control unit.

Ø These samples were measured using a parallel-plate configuration dielectric cell made of invar and sapphire which is describe with ref [5]. Separation between the electrodes is 47 micrometers which yielded a geometrical capacitance of 21 pF

Above: Fig. 2. Polymer TSI-198

Right: Fig. 3. Salt LiTFSi

Ø Sample 11% wt. VC and 89% wt. DEGMEMEA with glass transition temperature of 243 K

Fig. 7. Diffusivity spectra versus 1000/T of sample according two our two models; Electrode Polarization [3] and Random Barrier [2]

Ion Diffusivity

Ø Dyre’s Random Barrier Model – describes ion hopping within randomly varying energy barriers. It relates the ion diffusion D to the ion jump length λ and characteristic time of a jump τmax that can be defined from the conductivity spectra σ(ω), and shown with ref [4].

!!σ *(ω )=σ 0

iωτmaxln(1+ iωτmax )⎡

⎣⎢

⎤

⎦⎥

ε *(ω ) = εB +ΔεEP

1+ iωτ EP

Ø Electrode Polarization Model – as ions accumulate near electrodes, an additional polarization process appears in the dielectric spectra as an Electrode Polarization effect. It can be analyzed as tan(δ), and D can be estimated from the amplitude and frequency of tan(δ), and the sample thickness L, all shown with ref [3].

AssumptionsØ Cations and anions carry the

same amount of chargeØ Ions have equal diffusivityØ Sample thickness is much

larger than the Debye length

!!D= < λ2 >

2τmax

!!D=

2π fmaxL232(tanδ )max3

Ø The necessity of alternative energy in the face of climate change creates an opportunity to develop batteries to store excess energy for later use

Ø Use of Solid Polymer Electrolytes (SPE) instead of traditional liquid electrolytes can substantially improve safety and performance of batteries, including increase in the energy density

Ø Conductivity of 10-3 S/cm2 at room temperature is required for many batteries applications. Current SPEs cannot provide so high conductivity, and fundamental understanding of ionic conductivity in polymers is required for development of advanced SPE.

Name VC(mol%)

DEGMEMEA(mol%)

VC(wt%)

DEGMEMEA(Wt%)

TG(˚C)

σ(S/cm2)

TW1-55D 48 52 30 70TW1-56F 38 62 22 78TW1-56G 76 24 59 41TS1-198 21 79 11 89 -30.6TS2-118 53 47 34 66 -21

Table 1. Future work based on varying concentrations of VC and DEGMEMEA

Diffusivity

Fig. 6. Conductivity spectra versus Tg/T of each sample.

Conductivity for TG/T

Fig. 5. The conductivity spectra versus 1000/T of each sample. The ion transport of 10% ion concentration is conducting faster compared to the other concentrations.

Conductivity for 1000/T