Facile hydrogel-derived sub-10 nm tin–iron alloy embedded in 3D carbon nanocorals with improved cycle life and rate capability

Tin-based alloys have been regarded as promising anodes to replace commercial carbon materials for Li-ion batteries, but their Li-storage performance, especially cycle life, still fails to meet the requirements for electric vehicles and large-scale electricity storages. Herein, we propose a facile and scalable hydrogel-derived route for uniformly immobilizing sub-10 nm Sn-based alloys within three-dimensional (3D) carbon nanocorals, using polymer-hybridized cyano-bridged coordination polymer hydrogels (cyanogels) as precursors. As a representative example, 3D Sn–Fe@C nanocorals have been constructed through freeze-drying and thermal-autoreduction processes using polyethylene glycol (PEG) hybridized Sn(IV)–Fe(II) cyanogels as precursors. PEG plays critical roles in structural tailoring of hybrid cyanogels and size control of Sn–Fe alloys, and as a result, the average alloy size in optimized Sn–Fe@C nanocoral is only 5.9 nm. The ultrasmall alloy size, uniform dispersity of alloy, as well as coral-like framework structure, enable the Sn–Fe@C nanocorals to exhibit long-term cyclic life and high-rate performance.