Influence of Fluoroethylene Carbonate Additive Concentration on Silicon/Graphene Composite Anode

Abstract

Silicon has been promising anode material in lithium ion battery due to higher theoretical capacity of 4200 mAh/g and abundance (1, 2). However, volume expansion and contraction of silicon particle over cycling lead to electrode deformation and poor cyclic performance. Irreversible capacity loss from solid electrolyte interface (SEI) film formation is also major factor to degrade cyclic performance (3). Generally SEI film is getting thicker due to continuous consumption of Li salt and reduction of carbonate electrolyte. Previous studies has demonstrated the effect of additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and other additives. FEC is found to be effective additive to improve the performance of silicon electrode (1, 4-6). In this study, we focused on influence of FEC additive concentration in carbonate electrolyte on electrochemical performance. Electrode morphology and surface chemistry of SEI was investigated with various FEC concentrations (3, 5, 10, 20 wt%) in 1.2M LiPF6 at EC/EMC (3/7, by wt) electrolyte. Electrodes were prepared by blending Si/graphene active material (XG sciences), graphene and poly acrylic acid (PAA) and casting the slurry on copper foil. In the presence of FEC additive, the better capacity retention with cycling, as shown in Figure 1, was obtained, which is consistent to previous report because of thinner and stable SEI film formation (5). FEC concentration effect on cycle performance of silicon electrodes can also be observed from Figure 1. Initially, cell containing 3wt% FEC has higher reversible capacity only until 20th cycle. The cells with other FEC concentration (5-20% FEC) have better capacity retention up to 69thcycles. Lower FEC concentration in Si/graphene electrode may not lead to enough SEI layer formation due to lack of the additive for longer cyclic life. In order to find out the FEC concentration related SEI properties, we conducted electrochemical impedance spectroscopy (EIS). Other surface analysis, such as SEM, EDX and Raman, will be reported. Optimum amount of FEC additive concentration will be discussed. Acknowledgement The silicon material is provided by XG sciences. The validation was conducted under Cell Analysis, Modeling, and Prototyping (CAMP) Facility at ANL. Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged.