Electrochemical Properties of Electrodeposited Sn Anodes for Na-Ion Batteries

Introduction Over the past few decades, Li-ion batteries (LIBs) have been widely used as power sources for mobile electronic products and power tools, and nowadays a much effort has been focused on the use of these batteries in large-scale applications such as electric vehicles, hybrid electric vehicles and electrical energy storage (EES) devices. However, because the amount of the Li resources would not be sufficient to meet industrial needs in the long term, the expansion of the LIBs market takes concern on the sustainable supply of Li and the raising of the Li prices. Accordingly, in recent years, rechargeable Na-ion batteries (SIBs) have received great attention as a possible alternative to replace LIBs. Owing to the abundant resource, low cost and a relatively low redox potential (0.3 V above that of Li/Li + ), NIBs are expected to be a near-term alternative for large-scale systems such as grid storages [1]. Despite the high specific capacity, pure Na metal is inappropriate as an anode material for practical applications of NIBs because the dendiritc deposition of sodium during charging can cause the severe safety problems as well as the reduced capacity and increasing electrode impedance. To overcome these problems, the research for finding suitable electrode materials which have high specific capacity, low irreversible loss, high coulombic efficiency and long cycle life for SIBs have been extensively conducted. Among the various candidate materials, Sn is one of the most attractive anode materials because of its high theoretical capacity and low reaction potential. When assuming complete sodiation of Sn into Na 15 Sn 4 , the capacity of Sn is approximately 847 mAh g -1 [1], which is substantially higher than the reversible capacity of carbonaceous materials (approximately 250 mAh g -1 ) [2]. In this study, the electrochemical performance and the sodiation/desodiation mechanisms of electrodeposited Sn were investigated based on previous studies. Herein, two Sn electrodes that have completely different morphologies and crystal structures were prepared by electrodeposition, and their electrochemical properties for Na-ion battery applications were examined, with an emphasis on the effects of the morphology and the phase structure of Sn on the cyclability of the electrodes. Experimental. Two different Sn electrodes were prepared by electrodeposition from different electrolytes. The electrodeposition of Sn was performed in a two-electrode cell that consis