Ionic conductivity is a very important research area for solid state materials chemistry. The opportunities that solid conductivity presents for the advancement of battery technologies – making less inflammable and safer batteries – is of great interest to the energy industry. As a society we are attempting to move away from fossil fuel sources and more towards renewable sources of energy. This means that energy storage is becoming a bigger issue and improvements in our current technology is necessary.
Ionic conductivity can arise due to point defects within an ionic material. The two main types are Schottky and Frenkel defects. Schottky defects occur when a pair of ions leave the structure and vacant sites remain. This allows conductivity to occur in sodium chloride as well as in lead(IV) oxide in fluorite structures. Vacancy defects can also occur in lead(IV) oxide rutile structures which allow them to be used in lead acid batteries. Frenkel defects occur when an ion moves into an interstitial site it would not normally occupy. Conductivity can occur in a concerted motion, for example in alpha silver iodide. Alpha silver iodide has an interesting structure that leads to this phenomenon.
These types of conductivity are both used in solid electrolytes for sodium ion batteries. Sodium ion batteries work on the same basis as lithium ion batteries but have many advantages over lithium ion batteries. Sodium ion batteries use less toxic material than lead acid batteries and the core material – sodium – is far more abundant and cheaper than lithium with better cycling ability. NASICONs are a solid electrolyte (below) that is being developed that uses both Frenkel and Schottky mechanisms of conduction.
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