Dynamics computational analysis of PEO/PVDF/SN composite solid-state electrolyte for lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are widely employed in electric tools, electric cars, and mobile gadgets because of their high energy density, great power capability, and reasonable lifespan. However, conventional organic liquid electrolytes may be flammable and lead to danger of explosion at high temperatures. The demand for all-solid-state Li-ion batteries (ASSLIBs) is high because it can address the abovementioned safety concerns, and also increase energy density by using lithium metal as anode. However, ASSLIBs have several inherent issues that have to be addressed before their practical deployment, such as limited room temperature (RT) ionic conductivity (σ), and low lithium ion transference number (t+). For polymer-based solid electrolytes, modifying the polymer host or adding some inorganic fillers or plasticizers into the polymer is shown to be effective in addressing the issues. In the present study, polyethylene oxide (PEO), the well-known lithium ion conductive polymer is chosen as a host polymer, polyvinylidene fluoride (PVDF) as a blended polymer or binder, succinonitrile (SN) as a plasticizer to create a new plasticized blended solid polymer electrolyte (PBSPE), and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) as salt for lithium-ion sources. Before experimentally testing the new material, its properties are desired to be predicted theoretically. In this regard, the classical molecular dynamics (CMD) simulation method was employed to design and study the dynamics of ions in the proposed PEO/PVDF/SN/LiTFSI PBSPE. The concentrations of LiTFSI salt and PEO [Li: EO] varied from 0.02 to 0.20. The mass percentages of PVDF and SN changed from 0 to 40 wt.% and 0 to 25 wt.% under operating temperatures varying from 298.15 K to 363.15 K. The g(r) obtained from the CMD simulation in this work is per the investigation in neutron diffraction experiments. The Nernst-Einstein equation was employed to measure the Li-ion and TFSI-ion diffusion coefficients. In all cases, the first peak of radial distribution function g(r) was observed at r ≅0.210 Å, indicating the strong interaction between Li-ion and OPEO. The Li-OPEO coordination number (CN) of 4.9-6 has been observed. The trend for diffusion coefficients of both Li+ and TFSI- ions are in good agreement with the literature with the highest values of 2.1 × 10-8 cm2 s-1 and 4.73 × 10-8 cm2 s-1, respectively at room temperature (RT = 298.15 K). The highest ionic conductivity at RT was 1.45 × 10-4 S cm-1 achieved at 25 mass% of SN, which increases to 1.37 × 10-3 S cm-1 as the temperature reaches 363.15 K. High Li-ion transference number of 0.45 at RT has also been obtained at 10 mass % of SN. This study shows that the new composite solid-state electrolytes can be experimentally investigated for potential utilization in ASSLIBs with high performances.