Polymer Templating Method for the Formation of Hierarchically Porous Nitrogen-Rich Tin-Carbon Composite Anodes

Abstract

This study aims to provide a new platform for the fabrication of metal-carbon composites. Herein we show that the high density crosslinking of a polymer can be used to homogenously trap metal nanoparticles and other components. In this setting, we utilized the cross-linking of poly(maleic anhydride-at 1-octadecene) [PMAO] with ethylene glycol to trap metal nanoparticles and carbon nitride (C3N4) within the polymeric structure. During inert, high-temperature pyrolysis, the polymer acts as a soft-template and prevents agglomeration of metallic tin during the synthesis. Inspired by the work of Tang et al. the carbon nitride is employed to act as a nitrogen dopant source and textural template for the final product. Through an analysis variable experimental parameter, we have shown that this method provides an avenue for the tunable fabrication of nitrogen-rich porous composites. To demonstrate the practicality of this synthetic method, composites with a variety of different nitrogen moieties and textural compositions were electrochemically analyzed. The resulting composites were then used as a platform to demonstrate not only the tunability of the synthetic method but also an example of how much these effects drastically dictate the electrochemistry of the system. Of the samples analyzed it was shown that a urea based composite demonstrated the best electrochemistry touting high rate capability, stable cycling, and high coulombic efficiency (CE).The results of long-term performance testing reveal the excellent electrochemical properties of the U-Sn-CN composite, supplying an initial capacity of ~ 600 mAh g–1 and 82.0 % capacity retention over 400 cycles at a high current density of 1 A g–1 (1C) with an average CE of 99.8 %. Lower current density studies [500 mA g-1 (C/2)] have shown the material to have an initial capacity of ~ 640 mAh g–1 with 86.0 % capacity retention over 400 cycles. Electrochemical and post-mortem analysis of this composite material suggest the performance properties can be attributed to the unique nitrogen-doped carbon framework, which is able to buffer the large volumetric expansion of the tin due to its disordered flexible nature whilst contributing to the overall capacity of the composite from its high degree of nitrogen doping (~11.9 at %). Figure 1