Pyrolysis of cyano-bridged hetero-metallic aerogels: a general route to immobilize Sn-M (M = Fe, Ni) alloys within a carbon matrix for stable and fast lithium storage.

The practical application of Sn-M (M = Fe, Ni, Co, and Cu) alloys, a promising anodic category for lithium-ion batteries, is hindered primarily by their huge volume change upon cycling. Immobilization of Sn-M alloys within carbon matrices has proven to be effective to improve their cycling stability, but the traditional pyrolysis of separate Sn, M, and C precursors often leads to uneven distribution of the three components in Sn-M-C ternary anodes. Herein, we report a facile and general aerogel-derived pyrolysis route to realize homogeneous embedding of uniformly-sized Sn-M alloy nanocrystals, within a nanoporous carbon matrix, using cyano-bridged hetero-metallic (Sn-M) aerogels hybridized with carbon sources as precursors. Using the optimized citric acid (CA) as a carbon source, the formations of nanoporous Sn-Fe@C and Sn-Ni@C networks have been illustrated as examples through pyrolyzing CA/Sn-Fe and CA/Sn-Ni aerogels, respectively. By virtue of their compositional/structural superiorities toward lithium storage, the as-prepared Sn-Fe@C and Sn-Ni@C networks manifest higher capacities, enhanced cycling stability, and improved rate capability compared to the Sn-M-C composites and carbon samples derived from bare aerogels and CA precursors, respectively. Specifically, the Sn-Fe@C network manifests a high reversible capacity of 441.6 mA h g-1 after 100 cycles at 100 mA g-1 and an average capacity of 438.6 mA h g-1 at 1 A g-1. This work shows a new guideline for designing highly-uniform Sn-M-C, Sb-M-C, and Bi-M-C ternary anodes for boosting energy storage.