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.
Selenium-sulfur(SexSy) composites can be used as energy storage materials for lithium batteries benefit from their integration of the high capacity of sulfur and the high conductivity of selenium. Herein, we prepared amorphous three dimensional reduced graphene oxide/selenium sulfide(a-3DG/Se4.7S3.3) composites and crystalline 3DG/Se4.7S3.3(c-3DG/Se4.7S3.3) composites by in situ synthesis and hydrothermal methods, respectively, in order to research the effect of different morphologies of 3DG/Se4.7S3.3 composites on the electrochemical properties of all-solid-state lithium batteries. Our study found that the a-3DG/Se4.7S3.3 cathodes displayed greater capacity and outstanding rate performance, with an initial discharge capacity of 926 mAh g-1 and utilization rate of 103% at 1/2C. And a first discharge capacity of up to 706 mAh g-1 at 7C. Although the first discharge capacity of c-3DG/Se4.7S3.3 was 523 mAh g-1, its cycling stability was significantly improved compared with that of a-3DG/Se4.7S3.3 cathodes, and the Coulombic efficiency remained above 97% after 60 cycles at 1/2C. In this work, we investigate the performance of solid-state batteries by preparing new SexSy composites with different morphologies and rational design of electrodes in terms of structure and morphology, which provides ideas for the preparation of electrodes in the future.
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