Abstract
In this study, graphene–selenium hybrid microballs (G–SeHMs) are prepared in one step by aerosol microdroplet drying using a commercial spray dryer, which represents a simple, scalable continuous process, and the potential of the G–SeHMs thus prepared is investigated for use as cathode material in applications of lithium–selenium secondary batteries. These morphologically unique graphene microballs filled with Se particles exhibited good electrochemical properties, such as high initial specific capacity (642 mA h g−1 at 0.1 C, corresponding to Se electrochemical utilisation as high as 95.1%), good cycling stability (544 mA h g−1 after 100 cycles at 0.1 C; 84.5% retention) and high rate capability (specific capacity of 301 mA h g−1 at 5 C). These electrochemical properties are attributed to the fact that the G–SeHM structure acts as a confinement matrix for suppressing the dissolution of polyselenides in the organic electrolyte, as well as an electron conduction path for increasing the transport rate of electrons for electrochemical reactions. Notably, based on the weight of hybrid materials, electrochemical performance is considerably better than that of previously reported Se-based cathode materials, attributed to the high Se loading content (80 wt%) in hybrid materials.
Highlights
Rapid development in electric vehicles as well as large-scale renewable energy storage devices has resulted in an urgent need for lithium secondary batteries with high energy densities, power densities, long cycling lives and low cost
Se particles with an average size of 1 μm, same as that of the commercial Se particles used in this study, were observed within the graphene–selenium hybrid microballs (G–SeHMs); this observation was confirmed by point- and line-scanning spectroscopy and elemental scanning electron microscopy (SEM) mapping (Fig. S2 in Supporting Information)
(Supporting Information), after the cycling test, the morphology of G–SeHMs was well retained. This result suggested that G–SeHMs exhibit good structural stability during electrochemical reactions. These results directly indicate that the dissolution of polyselenide species into the ether-based organic electrolyte is suppressed by the unique-structured reduced GO (RGO) microball and that shuttling during charging/discharging is prevented, resulting in a better cycling stability and high CE for the Li–Se cell
Summary
Were sprayed downwards towards a heated zone at 200 °C, which is considerably greater than the boiling point of water. Two binding energy peaks were observed at 55.1 and 56.2 eV, respectively, in the deconvoluted Se 3d XPS profiles, attributed to the Se−Se chemical bonds in a cyclo-octa-structured Se particles encapsulated in graphene microballs. The results obtained from comparative TGA performed with/ without hydrazine hydrate (Fig. S4 in Supporting Information) confirmed that the chemical reduction of the GO sheets occurs during spray-drying. This result suggested that G–SeHMs exhibit good structural stability during electrochemical reactions. These results directly indicate that the dissolution of polyselenide species into the ether-based organic electrolyte is suppressed by the unique-structured RGO microball and that shuttling during charging/discharging is prevented, resulting in a better cycling stability and high CE for the Li–Se cell
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