Electrochemical Properties of LLTO/Fluoropolymer-Shell Cellulose-Core Fibrous Membrane for Separator of High Performance Lithium-Ion Battery
A superfine Li0.33La0.557TiO3 (LLTO, 69.4 nm) was successfully synthesized by a facile solvent-thermal method to enhance the electrochemical properties of the lithium-ion battery separator. Co-axial nanofiber of cellulose and Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was prepared by a co-axial electrospinning technique, in which the shell material was PVDF-HFP and the core was cellulose. LLTO superfine nanoparticles were incorporated into the shell of the PVDF-HFP. The core–shell composite nanofibrous membrane showed good wettability (16.5°, contact angle), high porosity (69.77%), and super electrolyte compatibility (497%, electrolyte uptake). It had a higher ionic conductivity (13.897 mS·cm−1) than those of pure polymer fibrous membrane and commercial separator. In addition, the rate capability (155.56 mAh·g−1) was also superior to the compared separator. These excellent performances endowed LLTO composite nanofibrous membrane as a promising separator for high-performance lithium-ion batteries.
Peculiarities of Li0.5La0.5TiO3 Formation during the Synthesis by Solid-State Reaction or Precipitation from Solutions
It is shown that whatever the technique used, conventional solid-state reaction or precipitation from solutions, the formation of lithium lanthanum titanate, Li0.5La0.5TiO3, is a multistage process, which occurs in a wide temperature range. Thermal analyses, X-ray powder diffraction (XRPD), and infrared (IR) spectroscopy are used to investigate the phase transformations that occur during the preparation of these ceramics. The different steps involved in the mechanism of formation of this titanate are described as temperature is increased. Both techniques lead to a pure perovskite phase. However, synthesis from solutions allows one to produce nanosized powders of titanate phase and to carry out synthesis under milder conditions as compared with solid state reaction synthesis. Furthermore, it has been observed that, independently of the method used, a considerable loss of lithium occurs during the synthesis of the ceramic samples and that the real composition is Li0.41La0.5TiO2.955 for both ceramics. The co...
Hydrophilicity/porous structure-tuned, SiO2/polyetherimide-coated polyimide nonwoven porous substrates for reinforced composite proton exchange membranes.
Porous substrate-reinforced composite proton exchange membranes have drawn considerable attention due to their promising application to polymer electrolyte membrane fuel cells (PEMFCs). In the present study, we develop silica (SiO(2)) nanoparticles/polyetherimide (PEI) binders-coated polyimide (PI) nonwoven porous substrates (referred to as "S-PI substrates") for reinforced composite membranes. The properties of S-PI substrates, which crucially affect the performance of resulting reinforced composite membranes, are significantly improved by controlling the hygroscopic SiO(2) particle size. The 40 nm S-PI substrate (herein, 40 nm SiO(2) particles are employed) shows the stronger hydrophilicity and highly porous structure than the 530 nm S-PI substrate due to the larger specific surface area of 40 nm SiO(2) particles. Based on the comprehensive understanding of the S-PI substrates, the structures and performances of the S-PI substrates-reinforced composite membranes are elucidated. In comparison with the 530 nm S-PI substrate, the hydrophilicity/porous structure-tuned 40 nm S-PI substrate enables the impregnation of a large amount of a perfluorosulfonic acid ionomer (Nafion), which thus contributes to the improved proton conductivity of the reinforced Nafion composite membrane. Meanwhile, the reinforced Nafion composite membranes effectively mitigate the steep decline of proton conductivity with time at low humidity conditions, as compared to the pristine Nafion membrane. This intriguing finding is further discussed by considering the unusual features of the S-PI substrates and the state of water in the reinforced Nafion composite membranes.