Pulse Electrodeposition of Amorphous Si Film Anodes for Li-Ion Battery

Abstract

INTRODUCTIONOver the past two decades, lithium ion batteries have carved a significant market for use in consumer and portable electrical and electronic devices. However, in recent years, the quest for environmentally clean technology in the automotive industry has resulted in a greater demand for increased energy storage capacity and improved performance of Li ion batteries. Silicon shows a high theoretical capacity of ~4212 mAh/g, corresponding to Li22Si5 phase and was identified as promising material to replace graphite (~372 mAh/g) anode which is currently used in the Li-ion batteries. However, during alloying and de-alloying of lithium with the Si anode there is a very large well known volumetric change (~400% volume) leading to colossal mechanical stresses in the electrode causing cracking and consequently loss of inter – particle contact. Hence, there is delamination of the electrode layer leading to rapid capacity fade of battery (1).Nanostructured and amorphous Si synthesized by physical (2,3) and chemical vapor deposition (4) show improved performance but are not economically viable for secondary batteries. Electrodeposition is a very inexpensive process which has been widely studied and used in many industrial applications for plating metals and alloys. Electrodeposition of silicon from organic solvents and ionic liquids on metallic and graphite substrates has previously been reported in the literature (5). Additionally, the electrodeposition technique provides the opportunity to generate films with different morphologies and functional properties by controlling the parameters such as electrolyte composition, applied voltage/current density and time of deposition.In the current study, Si thin films were electrodeposited on copper substrate using galvanostatic and pulse current conditions in an argon environment. Electrochemical investigations were performed on the electrodeposited Si thin films on copper foil which served as the working electrode. A 2016/2025 coin cell assembly in a half cell configuration was used by employing lithium (Li) foil as counter electrode and 1 M LiPF6 in ethylene carbonate and di-ethyl carbonate (EC:DEC = 1:2, by volume) as the electrolyte. The assembled cells were tested by cycling between 0.02 and 1.2 V vs. Li+/Li employing a constant current density. Scanning Electron Microscopy (SEM) studies were performed to study the effect of deposition on the morphology of the Si films before (Fig. 1) and after electrochemical cycling. The electrochemical testing of these films as Li-ion anodes showed stable cycling data with an improvement in the stability of the films. The SEM analysis of the films showed that the films were stable even after running over 100 cycles.