Surface-Modified Tin Nanoparticles and Their Electrochemical Performance in Lithium Ion Battery Cells

Abstract

Due to its relatively high availability, low cost, high volumetric delithiation capacity, and high electronic conductivity, tin (Sn) is frequently considered as anode material for lithium ion batteries (LIBs) to replace state-of-the-art graphitic carbons or to be part of anode composites. However, Sn materials suffer from their low capacity retention due to the large volume changes upon lithiation/delithiation. In particular, the influence of the surface chemistry of Sn particles on the electrochemical performance is not well-understood so far. In this work, we present a comprehensive study on the synthesis and characterization of hydroxide- (OH–), polyvinylpyrrolidone- (PVP), sulfide- (Sx–), and mercaptopropionic acid (MPA)-capped core/shell Sn/SnOx nanoparticles with two different particle size distributions (≈20 nm and ≈20–200 nm) and the influence of the different surface modifications and sizes on their electrochemical performance as negative electrodes for LIBs. The Sn nanomaterials are comprehensively studied in terms of particle and surface characteristics, i.e., their particle size, surface morphology, crystallinity, thermal stability, and surface chemistry. Further, the influence of these different ligands in combination with the particle size effect on the overall electrochemical performance is thoroughly studied. Small-sized OH–-modified Sn nanoparticles show the most outstanding performance in terms of cycling stability, rate performance, and reduced irreversible side reactions. We suggest that the OH–-modification improves not only the particle–binder interactions but also exhibits a thin surface layer, resulting in an effective solid electrolyte interphase (SEI) formation, as indicated by thermogravimetric analysis and electrochemical results. Overall, we can show significant differences between the different ligands, thus providing a suitable strategy on how to design thin and effective surface coatings for improved electrochemical performance of Sn composite anodes.