Influence of Surface Structure on the Capacity and Irreversible Capacity Loss of Sn-Based Anodes for Lithium Ion Batteries

The lithium ion battery is viewed as one of the most important energy storage devices for sustainable transport of power, and it is now attracting tremendous attention. In the present work, dense Sn films were pulse electrodeposited on a Cu substrate and then post-treated at 200 degrees C under different conditions, including electroplating a Cu coating film and heat treatment in different atmospheres. Surface morphology and composition of the films were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy. These films were then assembled as anodes for Li ion batteries with their electrochemical properties investigated. The Sn-based anode with a Cu coating post-heated in argon for 12 h forms a surface with Cu6Sn5/Sn as the primary phase. It showed the largest first cycle charge/discharge capacity and highest irreversible capacity loss (IRC). The Sn-based anode sintered in air for 48 h was surface modified by SnO and showed the smallest IRC. Change in charge/discharge capacities as well as IRC at different cycles was also analyzed with the architecture of multi-layered anodes. Defects in the Cu6Sn5/Sn surface phase lead to an increase in both the first cycle capacity and IRC of the anode, while the existence of SnO is beneficial to the decrease in the first cycle IRC of the anode. This work provides a fundamental understanding for the influence of the surface morphology, composition, and microstructure of Sn-based anodes on their electrochemical performances.