Available on-demand - F.EN07.06.18
Late News: Mixed-Anion Na-Hydroborates as New Class of Solid Electrolytes
Matteo Brighi1,Fabrizio Murgia1,Radovan Cerny1
University of Geneva1
Li- and Na-based hydroborates are known for their high ion dynamic, leading to liquid-like cation mobility after an order-disorder phase transition, suggesting their use as solid electrolytes for all-solid batteries.[1,2] However this transition takes place at elevate temperature, outside the typical operation range of a conventional battery .[3–5]
A systematic study on Na-based closoborates and carba-closoborates has been conducted by means of anion mixing, in order to stabilize room temperature Na-conducting phases, relying on increased structural disorder. The effect of such mixing is the suppression of any phase transition, leading to six novel Na-conductors with a Na-conductivity close to 1 mS cm-1 at room temperature.
Due to the three-dimensional aromatic nature of the boron cage, closoborates are among the more robust available polyanions;[6,7] the six presented phases are indeed thermodynamically stable in the investigated temperature range 100 < T < 700 K, while depending from the mixture the electrochemical stability window varies from 3 to 4.1 V versus Na+/Na, allowing their implementation in high -voltage next generation solid-state batteries.
The physical/electrochemical properties of this family will be presented, with particular remark to the non-Arrhenius conductivity behavior, arising from the ion-ion interaction. Their flexibility, in terms of operating voltage window, allowed also to check their compatibility towards different class of cathode materials such as NaCrO2[9,10], Na2Fe2(SO4)3 and Na3V2(PO4)2F3.
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