silicon (c-Si) possesses extremely finite sodium storage capability based on firstprinciple calculations due to the large energy consumption of sodium insertion into c-Si. [6,7] On the contrary, amorphous silicon (a-Si) is capable of holding 0.76 Na atom each Si, the capacity is highly 725 mAh g -1 correspondingly. [7] Till now, there is only a little literature dedicated to the study of a-Si as an anode material for SIBs. [8][9][10][11][12] One reason for this is the preparation difficultly of a-Si. Expensive and unstable raw materials such as silicon tetrachloride and complicated devices are usually involved. Moreover, most of these a-Si have no special structures, leading to unsatisfactory Na-storage performance. Silica with a non-toxic, easy to use, and stable chemical property, is abundant in nature. Carbothermic reduction is a common industrial procedure to manufacture solar energy c-Si from quartz sand (natural mineral) in an electric arc furnace described in Equation (1). [13] Since Nature published the first report in 2007 on using magnesiothermic reduction to prepare c-Si from diatom frustules (marine plant) according to Equation (2), [14] the method has been extensively applied in the field of LIBs. [4,5,15] Therefore, it will be of great significance to develop a low-temperature facile approach to produce carefully crafted a-Si structures from silica for SIBs.
Amorphous silicon (a-Si), due to its satisfactory theoretical
capacity,
moderate discharge potential, and abundant reserves, is treated as
one of the most prospective materials for the anode of sodium-ion
batteries (SIBs). However, the slow Na
+
diffusion kinetics,
poor electrical conductivity, and rupture-prone structures of a-Si
restrict its further development. In this work, a composite (a-Si@rGO)
consisting of porous amorphous silicon hollow nanoboxes (a-Si HNBs)
and reduced graphene oxide (rGO) is prepared. The a-Si HNBs are synthesized
through “sodiothermic reduction” of silica hollow nanoboxes
at a relatively low temperature, and the rGO is covered on the surface
of the a-Si HNBs by electrostatic interaction. The as-synthesized
composite anode applying in SIBs exhibits a high initial discharge
capacity of 681.6 mAh g
–1
at 100 mA g
–1
, great stability over 2000 cycles at 800 mA g
–1
, and superior rate performance (261.2, 176.8, 130.3, 98.4, and 73.3
mAh g
–1
at 100, 400, 800, 1500, and 3000 mA g
–1
, respectively). The excellent electrochemical properties
are ascribed to synergistic action of the porous hollow nanostructure
of a-Si and the rGO coating. This research not only offers an innovative
synthetic means for the development of a-Si in various fields but
also provides a practicable idea for the design of other alloy-type
anodes.
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