## 6 Functional Properties and Applications of Nanocomposites
### Lithium-ion batteries
#### 6.5.1 Polymer-nanocomposite electrolytes applying passive ceramic nanofillers
Unfortunately, only a correlation between TG and melting temperature could be verified. [PERSON] and coworkers measured the impact of passive (TiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\)) and active fillers (LiAlO\({}_{2}\)) on the conductivity and the lithium interface resistance [205]. In both cases the passive nanofillers delivered better values due to their small particle size and large surface area in comparison to the micron-sized active filler. Similar results were described by [PERSON] _et al._[206]. A solvent-free preparation of the composite electrolyte using hot-pressing as a membrane shaping method and nanosized fumed SiO\({}_{2}\) or alumina as plasticizers were developed, enabling a simpler cell preparation [207, 208]. The longtime research on PEO-based systems showed, that due to the semicrystalline properties a good ionic conductivity under ambient conditions cannot be achieved. Hence, alternative polymer systems, polymer blends and composites have been investigated for the last years. [PERSON] and coworkers developed polymer gels consisting of PVDF as matrix, the polar organic solvents ethylenecarbonate and propylenecarbonate as plasticizers and nanosized hydrophilic fumed SiO\({}_{2}\) (7 nm) as mechanical stabilizer [209]. They found, that the addition of the nanosized filler did not affect the electrochemical properties, but a strong influence of the mechanical strength as function of the SiO\({}_{2}\) load could be detected. A polymer gel, consisting of a poly(acrylnitril-methacrylate) copolymer and LiClO\({}_{4}\), solved in an ethylenecarbonate/propylencarbonate-mixture, was placed as electrolyte on a polyethylene separator in a cell with a lithium metal anode [210]. All\({}_{3}\) was added for the suppression of dendritic deposition of lithium during cycling. In addition to the enhanced cycling behavior the authors measured a good ionic conductivity under ambient conditions of 7.6 \(\times\) 10\({}^{-4}\) S/cm and an electrochemical stability window around 5 V [210]. A comprehensive review on separators used in electrolytes for lithium-ion batteries is given in [211]. A completely different electrolyte system used the amorphous copolymer poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP), a room temperature ionic liquid (RTIL) and nanosized TiO\({}_{2}\)[212]. Ionic liquids consist of an organic cation, combined with an inorganic anion like Cl' or large, asymmetric organic anions like [(CF\({}_{3}\)SO\({}_{2}\))\({}_{2}\)N]', forming stable, low viscous salts under ambient conditions with a negligible vapor pressure and flammability as well as high thermal and electrochemical stability [192, 213]. Suitable ionic liquids show an intrinsic ionic conductivity around 10\({}^{-3}\)-10\({}^{-4}\) S/cm. The authors found, that at concentration of 18 wt % of the nanosized TiO\({}_{2}\) a maximum ionic conductance of 3.1 \(\times\) 10\({}^{-3}\) S/cm could be achieved [212]. A further concentration increase caused a decay of the conductivity due to a stiffening effect, which improves the mechanical stability. PEG based gel electrolytes, containing either hydrophilic or hydrophobic Aerosils(r) (A200 and R805 from Evonik) and Li[(CF\({}_{3}\)SO\({}_{2}\))\({}_{2}\)N] as conducting salt, were been investigated with respect to the corrosion behavior of the electrolyte to the aluminum foils, which are used as current collectors in lithium-ion-batteries [214]. It was demonstrated earlier, that the applied lithium salt caused pronounced aluminum corrosion [215]. The authors found, that the addition of fumed silica hindered aluminum corrosion, especially in case of the hydrophilic Aerosil(r) A200. In addition of aluminum surface coating, which protects the metal, a moisture scavenging behavior at the hydrophilic surface explained the corrosion protecting effect [214].