We report foamed Si particles as a high-performance lithium storage material prepared by a milling-assisted alkaline etching process. The resulting foamed Si electrode showed excellent cycling performance of over 300 cycles with an initial discharge capacity of about 2750 mA h g.
Carbon nanofiber (CNF)/3D nanoporous (3DNP) Si hybrid materials were prepared by chemical etching of melt-spun Si/Al-Cu-Fe alloy nanocomposites, followed by carbonization using a pitch. CNFs were successfully grown on the surface of 3DNP Si particles using residual Fe impurities after acidic etching, which acted as a catalyst for the growth of CNFs. The resulting CNF/3DNP Si hybrid materials showed an enhanced cycle performance up to 100 cycles compared to that of the pristine Si/Al-Cu-Fe alloy nanocomposite as well as that of bare 3DNP Si particles. These results indicate that CNFs and the carbon coating layer have a beneficial effect on the capacity retention characteristics of 3DNP Si particles by providing continuous electron-conduction pathways in the electrode during cycling. The approach presented here provides another way to improve the electrochemical performances of porous Si-based high capacity anode materials for lithium-ion batteries.
Huge
volume changes of silicon particles upon alloying and dealloying
reactions with lithium are a major reason for the poor cycle performance
of silicon-based anodes for lithium-ion batteries. To suppress dimensional
changes of silicon is a key strategy in attempts to improve the electrochemical
performance of silicon-based anodes. Here, we demonstrate that a conductive
agent can be exploited to offset the mechanical strain imposed on
silicon electrodes caused by volume expansion of silicon associated
with lithiation. Hollow graphene particles as a conductive agent inhibit
volume expansion by absorbing the swelling of silicon upon lithiation
through flattening the free voids surrounded by the graphene shell.
As a result, silicon electrodes with hollow graphene showed a height
expansion of 20.4% after full lithiation with a capacity retention
of 69% after 200 cycles, while the silicon electrode with conventional
carbon black showed an expansion of 76.8% under the same conditions
with a capacity retention of 38%. Some of the deflated hollow graphene
returns to its initial shape on delithiation due to the mechanical
flexibility of the graphene shell layer. Such a robust microstructure
of a silicon electrode incorporating hollow graphene that serves as
both an expansion inhibitor and a conductive agent greatly improves
capacity retention compared with silicon electrodes with the conventionally
used carbon black.
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