Improving the Cycling Performance of Lithium Ion Batteries Silicon/Graphite Anodes Using PI Binder

Abstract

As the market for Electric Vehicles (EV) and Energy Storage System (ESS) grows, there is a growing demand for Lithium secondary batteries with high energy density. However, graphite (372 mAh g-1 for LiC6), a commercially available anode active material, is not suitable for large scale battery system such as EV or ESS due to its low theoretical capacity. Although, Silicon (Si, 4200 mAh g-1 for Li22Si5 or Li4.4Si) has a higher theoretical capacity than graphite, it has not been successfully implemented in commercialized LIBs due to suffering from large volume changes (> 300 %) during alloying and dealloying. Moreover, the stresses accompanying these changes cause mechanical failure and result in severely degraded electrochemical performances of Si electrodes. Consequently, Si/C composite anodes (Si/C anodes), wherein Si constitutes only a portion of the active material, have been proposed as an alternative to pure Si anodes. This approach exhibits certain advantages, since even if the theoretical anode capacity increases infinitely, the total theoretical capacity of the battery soon reaches saturation due to the limited theoretical capacity of the cathode. Herein, we used PVdF and P84 binder in high-loading Si/C anodes (~4.0 mg cm-2) and investigated their electrochemical and mechanical properties. Specifically, mechanical properties such as electrochemical stability, cycling performance and rate capability were evaluated using cyclic voltammetry, with the corresponding data recorded using a battery cycler. The mechanical properties of the above anodes were evaluated using Surface And Interfacial Cutting Analysis System (SAICAS).