Solid state electrolytes

The electrochemical storage and conversion of energy comprises broad fields related to fuel cells, photoelectrochemical processes in phosphors, lasers and solar cells, as well as the mechanism used in ion batteries used to power a huge range of mobile devices and, more recently, vehicles. While mobile battery applications impose quite severe restrictions on the volume and weight of the device material (currently dominated by Li-ion batteries), these are far less important in large-scale stationary applications, such as remote area power-grid systems which are capable of storing energy transmitted from thermal power plants, hydroelectric power stations or solar/wind mills, for instance. Large scale applications are hence predicted to be dominated by Na-based battery grids.
In the Laboratory of Crystallography we are searching for novel complex hydride materials which show enhanced mobility of the Na+ and Li+ ion in the solid state. These materials are named solid state electrolytes or superionics.

Scheme_AllSolidBattery_web

Superionic complex hydrides

In this context, complex hydrides, in particular metal borohydrides can be promising candidates, owed to the structural dynamics of anion groups (paddle wheel effect) and their reducing nature which could minimize electrode reactions (formation of oxide layers..). Numerous projects of our lab deal with the design of novel material and their implementation into batteries, in particular exploiting structural analogies to reconstruct oxide-electrolytes. Larger molecules such as the dodeca-hydroborate anion B12H122- are also being considered in anion-mixed compounds to open up the structural topology and maximize both dynamics as well as migration pathways available to the mobile species. Some of the recently discovered and characterized materials are capable of conducting both Li+ and Na+ in the same network.

Ionic conductivity of different B12H12 – BH4 based materials

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