Double-Network Nanostructured Hydrogel-Derived Ultrafine Sn-Fe Alloy in Three-Dimensional Carbon Framework for Enhanced Lithium Storage.

Tin-based alloys (Sn-M, M = Fe, Co, Ni, and Cu) have been considered as promising alternatives for graphite anode in advanced Li-ion batteries, but their practical application is hindered by huge volume change-induced poor cycle life. We propose here a facile inorganic-organic double-network nanostructured hydrogel-enabled methodology for uniformly immobilizing ultrafine Sn-M alloys in hierarchical carbon frameworks. The double-network nanostructured gel, consisting of three-dimensional (3D) intertwined cyano-bridged Sn(IV)-Fe(II) inorganic gel and chitosan-glutaraldehyde organic polymer gel, can realize 3D space confinement in molecular scale and thus obtain ultrafine Sn-Fe alloy particles (average size ∼2.7 nm) uniformly embedded in hierarchical 1D to 3D carbon framework. These unique structural features enable the Sn-Fe@C framework electrodes to exhibit long cycle life (516 mA h g-1 after 500 cycles at 0.1 A g-1) and high rate capability (491 and 270 mA h g-1 at 1 and 10 A g-1, respectively). This work provides new insight into controlled synthesis of ultrafine alloys in hierarchical 3D carbon frameworks for improving energy storage properties.