Mechanism Study of Li/Se Rechargeable Batteries in Different Electrolytes

Lithium-seleniume battery has been reported as one of the promising new high energy density energy storage systems considering its high theoretical gravimetric capacity of 678 mAh/g and volumetric capacity density of 3268 mAh/cm³, which is comparable to that of S (3467 mAh/cm³). It has been reported that Se cathode could be cycled versus both Li and Na at room temperature. Moreover, a long cycle life up to 1000 cycles with high efficiency have been reported by Wang et al recently. We have proved that Se is reduced into Li₂Se through the formation of intermediate polyselenide in the ether-based electrolyte by in-situ synchrotron techniques. However, a different mechanism is expected in the carbonate-based electrolyte based on the different voltage profiles. Then we experimentally demonstrated that the Se is directly transformed into Li₂Se without any intermediate phase formation. These results further proved that the electrolytes have a significant effect on this battery system. This mechanism study provides essential information on strategy selection for furhter performance improvement of Li-Se baterry.