## 6 Functional Properties and Applications of Nanocomposites
### Lithium-ion batteries  
In the last years the development of electrical storage systems like primary and secondary batteries has gained a worldwide significance for portable electronic devices as well as for hybrid or full-electric driven vehicles [189]. Especially the future development of large-scale lithium-ion-batteries towards a powerful and safe storage system with huge energy density and specific power will enable a sustainable individual mobility [190]. With respect to application as rechargeable battery (secondary battery) the following criteria have to be fulfilled [191,192]:  
* mechanical and chemical stability of the used electrode and electrolyte materials
* huge energy storage capability
* wide temperature range of operation (-40-85 \({}^{\circ}\)C)
* negligible self-discharge
* flat shape of the discharge curve
* short charge time
* long cycle life time with almost unchanged capacity
* low costs
* enhanced safety especially inflammability.  
Following the current technical setup of lithium-ion-batteries the basic functional elements are:  
* anode: pure lithium metal or more common graphite
* cathode: spinel-type lithium-metal oxides like LiCoO\({}_{2}\) or LiMn\({}_{2}\)O\({}_{4}\)
* electrolyte: highly polar, aprotic low-viscous organic solvents mixtures containing a conducting salt like LiClO\({}_{4}\), LiPF\({}_{6}\) or LiBF\({}_{4}\)
* separator: physical barrier between the electrodes avoiding short-circuit and supporting a mechanical stability, consisting of a porous inert material filled with e.g., a polymer-gel.  
Besides the mentioned low viscous, organic solvent based electrolytes, which suffer from pronounced flammability, which is inacceptable in automotive usage, polymer-gels, solid polymers as well as polymer composites can be found as electrolytes in lithium-ion-batteries; mostly in small-sized devices like mobile phones or in niche applications as in model airplanes. These electrolytes possess an enhanced safety due to an improved protection against leakage, no internal shorting, reduced combustibility and better freedom of design [192]. The basic requirements for the use of polymer-based electrolytes in modern lithium-ion-batteries are a high ionic conductivity in a wide temperature range, an acceptable mechanical stability, a huge lithium ion transference number, improved thermal stability in the aspired operation range, formation of a porous solid-electrolyte-interface (SEI), which is permeable for lithium ions and guarantees a reproducible charging-discharging cycling behavior and finally a good wetting of the electrodes [193,194]. Three different types of polymer-based electrolytes have been developed: solvent-free polymer electrolytes, gel polymer electrolytes and polymer composite electrolytes. In the latter case ceramic nanoparticles, dispersed in the polymer matrix, have been widely under investigation for their use as additives enabling an ionic conductivity increase especially under ambient conditions [194,195].  
In the following the impact of nanosized ceramics on the development of lithium-ion-batteries will be discussed in more detail.