Amorphous Selenium and Crystalline Selenium Nanorods Graphene Composites as Cathode Materials for All-Solid-State Lithium Selenium Batteries

Selenium (Se) is an element in the same main group as sulfur and is characterized by high electrical conductivity and large capacity (675 mAh g^-1 ). Herein, a novel ultra-high dispersion amorphous selenium graphene composite (a-Se/rGO) was synthesized and a selenium nanorods graphene composite (b-Se/rGO) was prepared by hydrothermal method as the cathode material for all solid-state lithium-selenium (Li-Se) batteries, hoping to improve the efficiency and utilization rate of active substances in all solid-state batteries. The all-solid-state batteries were assembled using a heated thawing electrolyte (2LiIHPN-LiI; HPN=3-hydroxypropionitrile). The utilization rate of a-Se/rGO was 103 % and the capacity was 697 mAh g^-1 , which remained at 281 mAh g^-1 (41.6 % of the 675 mAh g^-1 ) after 30 cycles under 0.5 C. Notably, a-Se/rGO showed excellent performance concerning its utilization rate, with a capacity of up to 610 mAh g^-1 at 2 C, due to the high availability of amorphous Se and the special properties of the electrolytes. However, in the charge and discharge cycles, the second discharge capacity of a-Se/rGO was more significantly attenuated than that of the first discharge due to the formation of larger crystals of selenium during the charging process. The battery assembled using b-Se/rGO maintained a capacity of 270.58 mAh g^-1 after 30 cycles (the retention rate of discharge capacity was 66.13 % compared with that in the first cycle). Through TEM and other relevant tests, it is speculated that amorphous selenium is conducive to capacity release, which, however, is affected by the formation of crystalline selenium after the first charge process.