Lithiated Nanoparticles Doped with Ionic Liquids as Quasi-Solid Electrolytes for Lithium Batteries

Highlights: • Two composite electrolytes are obtained, appearing as powder-like solids. • Li⁺BF₄⁻ and [Li(TFSI)₂]^- are formed owing to the dissociation of Li⁺ from LiFT component. • At 30 °C a conductivity of 1.36 × 10⁻² S cm⁻¹ is achieved by LiFT/(EMImTFSI)_0.087. • Li⁺ are exchanged between LiFT nanoparticles and among adjacent ionic aggregates. • Battery cycling is achieved using a quasi-solid composite electrolyte. -- Abstract: This work reports two quasi-solid composite electrolytes based on LiFT (Lithiated Fluorinated Titania) nanopowder and either 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) ionic liquid (IL). In details, LiFT nanopowder is doped with ca. 30 wt% of IL, giving rise to materials with formula LiFT/(EMImBF₄)_0.183 and LiFT/(EMImTFSI)_0.087. The resulting composite electrolytes appear as powder-like solids as the IL is completely absorbed by LiFT. The correlation between structure, thermal properties and long-range charge migration processes of the here proposed electrolytes is investigated by several characterization techniques, as follows: i) differential scanning calorimetry (DSC) and high-resolution thermogravimetry (HR-TGA); ii) Fourier-transform infrared spectroscopy in both the medium and the far infrared (FT-MIR and FT-FIR); and iii) broadband electrical spectroscopy (BES). The conductivity of the here proposed composite electrolytes is promising. Indeed, at 30 and 100 °C it corresponds respectively to 1.75 × 10⁻³ S cm⁻¹ and 1.05 × 10⁻² S cm⁻¹ for LiFT/(EMImBF₄)_0.183, and 1.36 × 10⁻² S cm⁻¹ and 4.42 × 10⁻² S cm⁻¹ for LiFT/(EMImTFSI)_0.087. Finally, LiFT/(EMImTFSI)_0.087 is used to fabricate a coin cell prototype, that is tested by galvanostatic cycling for performance and durability.