Polyimide binder for a high-energy-density composite anode electrode with graphite and silicon

Abstract

Different types of binders, including polyimide(PI), polyvinylidene difluoride (PVdF), and Styrenebutadiene rubber/carboxymethylcellulose (SBR/CMC) are used to produce high-energy-density anode electrodes with various combinations of graphite and silicon active materials, and these anodes are investigated to improve electrochemical performance in lithium-ion batteries. The PI binder efficiently provides good electrochemical performance by holding Si as well as graphite, whereas SBR/CMC and PVdF present reasonable performance with a pure graphite electrode. FT-IR results confirm that PI forms an effective chemical interaction on the Si powder, maintaining the electrochemical performance of the graphite in the composite electrode. Because of these effective characteristics, the electrochemical performance of a cell with 30 wt% Si and 70 wt% graphite and a PI binder is greatly enhanced, showing 84% cycle retention and 75% rate capability under a 10C rate (49% and 68%, respectively, for the same combination with the SBR/CMC binder). In particular, systematic electrochemical analyses with AC impedance and galvanostatic intermittent titration techniques are performed to understand the different binder behavior in the different electrodes. Semi-in-situ FE-SEM results on the same position of the electrode support the concept that the PI binder is effective in holding the active materials during repeated charge and discharge cycles that cause large volume changes.