Fundamentals of Charge Transport in Single Ion Conducting Polymers

Polymer electrolytes will provide good solution for solid state batteries and other energy storage and conversion technologies due to their mechanical flexibility, good adhesion to electrodes and ease of large scale production. However, traditional poly(ethylene oxide) (PEO) based electrolytes suffer from low conductivity and low cation transport number t+. The latter is critical for efficient battery performance, and can be resolved using single ion conducting polymers (SICP). However, conductivity remains low also in SICP. In this talk we present an overview of fundamental mechanisms of ion transport, and discuss how chemical structure and ion size control dynamics and ionic conductivity in polymers. We emphasize the importance of decoupling of ion transport from polymer segmental dynamics for achieving the required level of conductivity ~1 mS/cm. We demonstrate that the decoupled ionic conductivity is controlled by the energy barrier for ion hopping E_σ in essentially frozen (on time scale of ion jumps) matrix. Our analysis [1,2] reveals two critical mechanisms controlling E_σ: coulombic interactions that dominates the energy barrier for small ions, and elastic forces that dominate for larger ions. Our studies also revealed [3] that traditional approach using apparent Arrhenius law strongly overestimates the ion hopping energy barrier E_σ, and we suggest alternative more accurate way to estimate E_σ. Next, we discuss the role of polymer structure and charge delocalization on segmental dynamics and ion conductivity in SICPs. Analysis of the data also reveals significant ion-ion correlations that strongly reduce ionic conductivity in polymer electrolytes [1,2]. We discuss possible mechanisms of these correlations, and propose morphology that might significantly enhance ionic conductivity in polymer electrolytes [2]. At the end, we summarize the perspectives of use of polymer electrolytes in solid state batteries.



References

[1] E. W. Stacy, et al., Macromolecules 51 (2018) 8637-8645.

[2] V. Bocharova, A.P. Sokolov, Macromolecules 53 (2020) 4141-4157.

[3] C. Gainaru, et al., Macromolecules 56 (2023) 6051-6059.