Ion Speciation and Mobility in Solid Polymer Electrolytes: Insights from Molecular Dynamics Simulations
Abstract
As demand for high energy density and safety in rechargeable batteries intensifies, lithium metal batteries based on solid polymer electrolytes have emerged as promising alternatives. However, challenges such as low Li-ion mobility and limited cation transference numbers restrict their wider application. This study uses molecular dynamics simulations to investigate the effects of various salts (LiTFSI, LiPF6, and LiClO4) in PEO systems on ion speciation (solvent-separated ion pairs, contact ion pairs, and aggregates) and their impacts on ion mobility and transference numbers under varying field strengths. Notably, even ions that exhibit similar speciation distributions can demonstrate distinct mobility and transference behaviors, suggesting the influence of additional factors. We assess quantitatively the ion mobility contributions from each speciation type, clarifying how each influences the overall mobility. Despite similar ion speciation distributions in systems with LiTFSI and LiPF6, the primary contributors to ion mobility differ significantly. Moreover, cation transference numbers correlate strongly with the solvation radius ratio of cations to anions, emphasizing its pivotal role in ion transport. These findings offer critical insights for designing advanced solid polymer electrolytes to enhance the efficiency of lithium metal batteries.
Copyright and License
Supplemental Material
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpclett.5c01336.
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Simulation cell compositions and sizes, standard deviation from fitted Gaussian distribution from EMD simulations, cation and anion mobility of SSIP, CIP, and AGG forms from NEMD simulations, simulation procedure using TSP method, RDFs between Li ions and anions, and the average radius of AGG; Additionally, the fitted Gaussian distributions from EMD, the probability density distribution of displacement from NEMD simulations, the comparison between approximated and total mobility, the RDFs between Li ions and PEO atoms, and anions and PEO atoms are presented (PDF)
Funding
This work was supported by the National Research Foundation of Korea (NRF), grants funded by the Korean government (MSIT) (Nos. RS-2024–00405261, RS-2024–00435493, and 2021R1A2C2009643). W.A.G. was supported by the US National Science Foundation (CBET 2311117).
Conflict of Interest
The authors declare no competing financial interest.
Additional details
- National Research Foundation of Korea
- RS-2024-00405261
- National Research Foundation of Korea
- RS-2024–00435493
- Division of Chemical, Bioengineering, Environmental, and Transport Systems
- 2311117
- National Research Foundation of Korea
- 2021R1A2C2009643
- Available
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2025-07-07
- Caltech groups
- Division of Chemistry and Chemical Engineering (CCE), Materials and Process Simulation Center
- Publication Status
- Published