Silicon-based
materials are the desirable anodes for next-generation
lithium-ion batteries; however, the large volume change of Si during
the charging/discharging process causes electrode fracture and an
unstable solid–electrolyte interphase (SEI) layer, which severely
impair their stability and Coulombic efficiency. Herein, a bundle
of silicon nanoparticles is encapsulated in robust micrometer-sized
MXene frameworks, in which the MXene nanosheets are precrumpled by
capillary compression force to effectively buffer the stress induced
by the volume change, and the abundant covalent bonds (Ti–O–Ti)
between adjacent nanosheets formed through a facile thermal self-cross-linking
reaction further guarantee the robustness of the MXene architecture.
Both factors stabilize the electrode structure. Moreover, the abundant
fluorine terminations on MXene nanosheets contribute to an in situ formation of a highly compact, durable, and mechanically
robust LiF-rich SEI layer outside the frameworks upon cycling, which
not only shuts down the parasitic reaction between Si and an organic
electrolyte but also enhances the structural stability of MXene frameworks.
Benefiting from these merits, the as-prepared anodes deliver a high
specific capacity of 1797 mA h g–1 at 0.2 A g–1 and a high capacity retention of 86.7% after 500
cycles at 2 A g–1 with an average Coulombic efficiency
of 99.6%. Significantly, this work paves the way for other high-capacity
electrode materials with a strong volume effect.
The high-capacity
silicon anode is regarded as a promising electrode material for next-generation
lithium-ion batteries. Unfortunately, its practical application is
still severely hindered by electrode fracture and unstable solid electrolyte
interphase during cycling. Herein, we design a structure of encapsulating
silicon in a robust “janus shell”, in which an internal
graphene shell with sufficient void space is used to absorb the mechanical
stress induced by volume expansion, and the conformal carbon outer
shell is introduced to strongly bond the loosely stacked graphene
shell and simultaneously seal the nanopores on the surface. With the
ultrastable janus carbon shell, the excellent structural integrity
of the electrode and stable solid electrolyte interphase layer could
be effectively preserved, resulting in an impressive cycling behavior.
Indeed, the as-synthesized anodes demonstrate superior cycle stability
and excellent rate performance, delivering a high reversible capacity
of 1416 mA h g–1 at a current density of 0.2 A g–1 and 852 mA h g–1 at a high current
density of 5 A g–1. Remarkably, the superior capacity
retention of 88.5% could be achieved even after 400 cycles at a high
current density of 2 A g–1. More importantly, this
work opens up a novel avenue to address high-capacity anodes with
a large volume change.
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