TEM Investigations on FeF2 based Nanocomposite Battery Materials

The application of conversion materials in electrochemical storage devices is one of the few options to build batteries with considerably increased energy density, e.g. based on metal fluorides, which react reversibly with lithium. However, as metal fluorides are electrical insulators and show large volume changes during cycling, batteries based on micron-sized particles rapidly lose capacity. In contrast, with nanocrystalline electrode materials high cycling stability and a fast charging and discharging can be achieved. In particular, iron fluorides are an important class due to their low cost and low toxicity. FeF2 is an interesting cathode material which has a thermodynamic reduction potential of 2.66 V versus lithium and a theoretical specific capacity of 571 mAh g-1, which leads to a theoretical gravimetric energy density of 1519 Wh kg-1[1]. FeF2 is an electrical insulator and needs to be in intimate contact with electronic conductors at the nanoscale in order to become electrochemically active. A good choic