Demystifying the Asymmetry in Lithiation/Delithiation Behaviors of Silicon Anodes for Lithium-Ion Batteries

Abstract

One critical factor that impedes the wide adoption of electric vehicles is the charging time, which is considerably longer when compared to the refuel time of internal combustion vehicles. To shorten the charging time to less than 6 minutes, extremely fast charging (XFC) of more than 10C is required. In recent years, silicon was regarded as a promising candidate for fast charging because it has a high energy density and is less prone to lithium dendrite growth. However, existing Silicon technologies have not surpassed the 6-minute charging goal. Here, we discuss the possibility for XFC of a three-dimensionally engineered electrically conductive porous Ni/Si composite anode. This anode structure can effectively alleviate the huge volume change upon cycling and provide a pathway for fast electron and ion conduction. Although it shows excellent delithiation (discharging) rate capabilities when coupled with an optimized electrolyte, the lithiation capacity is severely limited at higher C-rates. To study the asymmetry in lithiation/delithiation and the mechanism of relatively sluggish lithiation, we performed rate performance test, Galvanostatic Intermittent Titration Technique (GITT) and Direct Current Electrochemical Impedance Spectroscopy (DCEIS). Based on our findings, we propose the potential rate limiting step for lithiation, which is believed to improve the charging rates substantially when overcome.