Influence of Dimensionality of Carbon-based Additives on Thermoelectric Transport Parameters in Polymer Electrolytes

This paper investigates the thermoelectric properties of solid polymer electrolytes (SPE) containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) salts, along with carbon-based additives of various dimensionalities. Increasing salt concentration leads to higher Seebeck coefficients as a result of the increasing number of free charge carriers and additional, superimposed effects by ion-ion and ion-polymer interactions. NaTFSI-based electrolytes exhibit negative Seebeck coefficients (up to $S = -1.5\,\mathrm{mV\,K^{-1}}$), indicating dominant mobility of $\mathrm{TFSI^-}$ ions. Quasi-one-dimensional carbon nanotubes (CNTs) increase the Seebeck coefficient by a factor of 3. Planar, two-dimensional graphite flakes (GF) moderately enhance it, affecting $\mathrm{Na^+}$ and $\mathrm{TFSI^-}$ ion mobilities and electronic conductivity. Bulky, three-dimensional carbon black (CB) additives induce a unique behavior where the sign of the Seebeck coefficient changes with temperature, presumably due to interaction with $\mathrm{TFSI^-}$ ions within the CB structure. Changes in activation energy and Vogel temperature with salt concentration suggest structural and mechanical modifications in the polymer matrix. The choice of carbon-based additives and salt concentration significantly influences the thermoelectric properties of SPEs thermoelectric properties, providing insights into their potential for thermoelectric applications. Sodium-based electrolytes emerge as promising, sustainable alternatives to lithium-based systems, aligning with sustainable energy research demands.